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An indium tin oxide electrode modified with gold nanorods for use in potential-controlled surface plasmon resonance studies
Analytical ChemistryBiosensorsMicrochimica ActaMicrochimica Acta, Volume 180, June 2013, Pages 1013-1020
The modification of electrodes with gold nanoparticles results in an increased electrode surface area, enhanced mass transport, and improved catalytic properties. We have extended this approach to indium tin oxide (ITO) electrodes to obtain optically transparent gold nanorod-modified electrodes which display enhanced electrochemical capabilities and have the additional advantage of showing a tunable surface plasmon resonance. The procedures for attaining high surface coverage (15 gold nanorods per square µm) of such electrodes were optimized, and the potential-dependent surface plasmon resonance was studied under controlled electrical potential. In an exemplary sensor application, we demonstrate the detection of mercury via potential-dependent formation of an Au-Hg amalgam.
Rapid detection of different DNA analytes using a single electrochemical sensor
Journal ArticleSensors and Actuators B: ChemicalDawn M. Mills, Marcos V. Foguel, Christopher P. Martin, Tiffany T. Trieu, Ola Kamar, Percy Calvo-Marzal, Dmitry M. Kolpashchikov, Karin Y. Chumbimuni-Torres, Rapid detection of different DNA analytes using a single electrochemical sensor, Sensors and Actuators B: Chemical, Volume 293, 2019, Pages 11-15, ISSN 0925-4005, https://doi.org/10.1016/j.snb.2019.04.149.
A unique platform for the detection of two distinct DNA sequences by using one single electrochemical sensor was developed. The sensor consists of a universal stem loop probe attached to a solid surface, and two analyte-specific adaptor strands. These adaptor strands hybridize to a nucleic acid analyte and provide both highly specific recognition and high binding affinity. The universal probe can be regenerated by a simple and quick rinse with urea and water. As a proof of concept, we differentiated long target sequences of Zika (141 nt.) and Dengue (114 nt.) viruses that contain secondary structures. The proposed sensor provides a platform for rapid and cost-efficient detection of potentially any DNA or RNA sequence using a single electrochemical sensor.
A universal and label-free impedimetric biosensing platform for discrimination of single nucleotide substitutions in long nucleic acid strands
BiosensorsJournal ArticleJournal of Biosensors and BioelectronicsDawn M. Mills, Christopher P. Martin, Stephanie M. Armas, Percy Calvo-Marzal, Dmitry M. Kolpashchikov, Karin Y. Chumbimuni-Torres, A universal and label-free impedimetric biosensing platform for discrimination of single nucleotide substitutions in long nucleic acid strands, Biosensors and Bioelectronics, Volume 109, 2018, Pages 35-42, ISSN 0956-5663, https://doi.org/10.1016/j.bios.2018.02.059.
We report a label-free universal biosensing platform for highly selective detection of long nucleic acid strands. The sensor consists of an electrode-immobilized universal stem-loop (USL) probe and two adaptor strands that form a 4J structure in the presence of a specific DNA/RNA analyte. The sensor was characterized by electrochemical impedance spectroscopy (EIS) using K3[Fe(CN)6]/K4[Fe(CN)6] redox couple in solution. An increase in charge transfer resistance (RCT) was observed upon 4J structure formation, the value of which depends on the analyte length. Cyclic voltammetry (CV) was used to further characterize the sensor and monitor the electrochemical reaction in conjunction with thickness measurements of the mixed DNA monolayer obtained using spectroscopic ellipsometry. In addition, the electron transfer was calculated at the electrode/electrolyte interface using a rotating disk electrode. Limits of detection in the femtomolar range were achieved for nucleic acid targets of different lengths (22 nt, 60 nt, 200 nt). The sensor produced only a background signal in the presence of single base mismatched analytes, even in hundred times excess in concentration. This label-free and highly selective biosensing platform is versatile and can be used for universal detection of nucleic acids of varied lengths which could revolutionize point of care diagnostics for applications such as bacterial or cancer screening.
An electrochemical biosensor based on Hairpin-DNA modified gold electrode for detection of DNA damage by a hybrid cancer drug intercalation
BiosensorsJournal ArticleJournal of Biosensors and BioelectronicsLozano Untiveros, K., da Silva, E. G., de Abreu, F. C., da Silva-Júnior, E. F., de Araújo-Junior, J. X., Mendoça de Aquino, T., Armas, S. M., de Moura, R. O., Mendonça-Junior, F. J. B., Serafim, V. L., & Chumbimuni-Torres, K. (2019). An electrochemical biosensor based on Hairpin-DNA modified gold electrode for detection of DNA damage by a hybrid cancer drug intercalation. Biosensors and Bioelectronics, 133, 160-168. https://doi.org/https://doi.org/10.1016/j.bios.2019.02.071
We studied an efficient and new electrochemical biosensor for detection of DNA damage, induced by the interaction of the hybrid anti-cancer compound (7ESTAC01) with DNA by using differential pulse voltammetry (DPV). The biosensor consists of a Stem-Loop DNA (SL-DNA) probe covalently attached to the gold electrode (GE) surface that hybridizes to a complementary DNA strand (cDNA) to form a double-stranded DNA (dsDNA). The interaction and DNA damage induced by 7ESTAC01 was electrochemically studied based on the oxidation signals of the electroactive nucleic acids on the surface of the GE by DPV. As a result, the SL-DNA/GE and dsDNA/GE were tested with the reduced 7ESTAC01, showing the voltammetric signal of guanine and adenine, increase in the presence of 7ESTAC01. Under optimum conditions, the dsDNA/GE biosensor exhibited excellent DPV response in the presence of 7ESTAC01. The bonding interaction between 7ESTAC01 and calf thymus DNA (ctDNA) was confirmed by UV–Vis absorption spectroscopy, dynamic simulations (performed to investigate the DNA structure under physiological conditions), and molecular docking. Theoretical results showed the presence of hydrogen bonding and intercalation in the minor groove of DNA, involving hydrophobic interactions.
Cost-Effective Modular Biosensor for SARS-CoV-2 and Influenza A Detection
BiosensorsJournal ArticleMurray, A., Ojeda, J., El Merhebi, O., Calvo-Marzal, P., Gerasimova, Y., & Chumbimuni-Torres, K. (2023). Cost-Effective Modular Biosensor for SARS-CoV-2 and Influenza A Detection. Biosensors, 13(9), 874. https://www.mdpi.com/2079-6374/13/9/874
We developed a modular, multi-purpose, and cost-effective electrochemical biosensor based on a five-stranded four-way junction (5S-4WJ) system for SARS-CoV-2 (genes S and N) and Influenza A virus (gene M) detection. The 5S-4WJ structure consists of an electrode-immobilized universal stem-loop (USL) strand, two auxiliary DNA strands, and a universal methylene blue redox strand (UMeB). This design allows for the detection of specific nucleic acid sequences using square wave voltammetry (SWV). The sequence-specific auxiliary DNA strands (m and f) ensure selectivity of the biosensor for target recognition utilizing the same USL and UMeB components. An important feature of this biosensor is the ability to reuse the USL-modified electrodes to detect the same or alternative targets in new samples. This is accomplished by a simple procedure involving rinsing the electrodes with water to disrupt the 5S-4WJ structure and subsequent re-hybridization of the USL strand with the appropriate set of strands for a new analysis. The biosensor exhibited minimal loss in signal after rehybridization, demonstrating its potential as a viable multiplex assay for both current and future pathogens, with a low limit of quantification (LOQ) of as low as 17 pM.
Dna nanotechnology for nucleic acid analysis: sensing of nucleic acids with DNA junction-probes
AnalystJournal ArticleFoguel, M. V., Zamora, V., Ojeda, J., Reed, M., Bennett, A., Calvo-Marzal, P., Gerasimova, Y. V., Kolpashchikov, D., & Chumbimuni-Torres, K. Y. (2024). DNA nanotechnology for nucleic acid analysis: sensing of nucleic acids with DNA junction-probes [10.1039/D3AN01707A]. Analyst, 149(3), 968-974. https://doi.org/10.1039/D3AN01707A
In this study, we introduced a nucleic acid five-way junction (5WJ) structure for direct electrochemical analysis of full-length biological RNAs. To the best of our knowledge, this is the first report on the interrogation of such long nucleic acid sequences by hybridization probes attached to a solid support. A hairpin-shaped electrode-bound oligonucleotide hybridizes with three adaptor strands, one of which is labeled with methylene blue (MB). The four strands are combined into a 5WJ structure only in the presence of specific DNA or RNA analytes. Upon interrogation of a full-size 16S rRNA in the total RNA sample, the electrode-bound MB-labeled 5WJ association produces a higher signal-to-noise ratio than electrochemical nucleic acid biosensors of alternative design. This advantage was attributed to the favorable geometry on the 5WJ nanostructure formed on the electrode’s surface. The 5WJ biosensor is a cost-efficient alternative to the traditional electrochemical biosensors for the analysis of nucleic acids due to the universal nature of both the electrode-bound and MB-labeled DNA components.
Highly reproducible electrochemical biosensors for Influenza A virus towards low-resource settings
Journal ArticleJournal of Analytical MethodsOjeda, J., Torres-Salvador, F., Bruno, N., Eastwood, H., Gerasimova, Y., & Chumbimuni-Torres, K. (2024). Highly reproducible electrochemical biosensor for Influenza A virus towards low-resource settings [10.1039/D3AY01825C]. Analytical Methods, 16(5), 772-779. https://doi.org/10.1039/D3AY01825C
We have validated a highly reproducible electrochemical biosensor, employing a five-stranded four-way junction (5S-4WJ) system through square wave voltammetry, for the detection of Influenza A virus (InfA). We completed a comprehensive assessment of its linearity, precision, accuracy, and robustness which has demonstrated its compliance with FDA standards. Integration with Nucleic Acid-Based Amplification (NASBA) has showcased its selectivity for InfA, enabling the detection of InfA RNA with a standard heater set at 41 °C. This platform offers a straightforward setup well-suited for use at low-resource facilities.
A Single Electrochemical Biosensor Designed to Detect Any Virus
Analytical ChemistryAnalytical ChemistryJournal ArticleJournal of Analytical ChemistryTorres-Salvador, F., Ojeda, J., Castro, C., Gerasimova, Y., & Chumbimuni-Torres, K. (2024). A Single Electrochemical Biosensor Designed to Detect Any Virus. Analytical Chemistry, 96(15), 5752-5756. https://doi.org/10.1021/acs.analchem.3c05962
We combine an innovative virus detection method with a single electrochemical biosensor with a modified nucleic acid sequence-based amplification (NASBA) protocol, incorporating a 22-nucleotide tag for specific identification of three different viruses. This cost-effective approach presents a significant advancement for efficient and accessible diagnostic tools that can be used in resource-limited settings.
n Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water
Environmental Science and TechnologyJournal ArticleA novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water–metal interface of a brass-leaded solder galvanic joint in a prepared chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diameter) showed excellent performance toward soluble lead (Pb2+) with sensitivity of 22.2 ± 0.5 mV decade–1 and limit of detection (LOD) of 1.22 × 10–6 M (0.25 mg L–1). The response time was less than 10 s with a working pH range of 2.0–7.0. Using the lead micro-ISE, lead concentration microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb2+ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were observed above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concentrations (42.9 vs 11.6 mg L–1) and 5 times higher fluxes (18.5 × 10–6 vs 3.5 × 10–6 mg cm–2 s–1). Continuous surface lead leaching monitoring was also conducted for 16 h.
Ready to use single-strip paper based sensor for multiplex ion detection
Journal ArticleSensors and Actuators B: ChemicalIon-selective electrodes (ISEs) are an efficient and versatile tool for ion detection. However, portability and applicability for field applications are often limited by the need of a conditioning step, and high cost of the needed bulky reference electrode. Herein, the traditional conditioning protocol of ISEs has been eliminated and a paper-based solid-contact ISE (PBSC-ISE) has been integrated with a paper-based solidcontact reference electrode (PBSC-RE) in a single strip format for on-site analysis. The PBSC-RE is based on the copolymer methyl methacrylate-co-decyl methacrylate (MMA-DMA) (support matrix), combined with ionic liquids (ILs) to create and maintain a stable potential that is un affected by a change in ionic activity. This single-strip ready-to-use sensor yields a Nernstian response towards Na+, K+, and I− ions with submicromolar limits of detection, and is able to be used for multiplex analysis.
Development and Characterization of Needle-Type Ion-Selective Microsensors for in situ Determination of Foliar Uptake of Zn2+ in Citrus Plants
ElectroanalysisJournal ArticleFor over a decade, the incidence of Huanglongbing (HLB) has grown at an alarming rate, affecting citrus crops worldwide. Current methods of nutrient therapy have little to no effect in alleviating symptoms of HLB, and scarce research has been put forth towards non-destructive tools for monitoring zinc transport in citrus plants. Here, we have developed and characterized a solid contact micro-ion-selective electrode (SC-μ-ISE) for the determination of zinc transport in sour orange seedlings using a non-invasive microelectrode ion flux estimation (MIFE) technique. The SC-μ-ISE displayed a 26.05±0.13 mV decade−1 Nernstian response and a LOD of (3.96±2.09)×10−7 M. Results showed a significant Zn2+ uptake in the leaves and roots of sour orange seedlings when bulk concentrations were higher than 5.99 mM. Above this concentration, a linear relationship between flux and bulk Zn2+ concentration was observed. This relationship suggests passive diffusion may be a key mechanism for Zn transport into plants. Overall, this study is the first to use a Zn2+ SC-μ-ISE for the determination of ion transport processes in plants. This novel tool can be used to further knowledge the effect of nutrient therapy and disease progression on HLB infected citrus plants.
The safer and scalable mechanochemical synthesis of edge-chlorinated and fluorinated few-layer graphenes
Journal ArticleMaterials ScienceHalogen functionalization of the edges of the graphene sheets can improve processability, add new properties, and enhance its interactions with other materials. Through functionalization, improved materials can be realized. Typically, halogenated graphenes are produced from pure or reactive halogen sources. Current approaches present significant safety challenges. By generating reactive dichlorine monoxide (Cl2O) in situ, a chlorinated graphene with the nominal composition C17Cl2OH can be realized safely and scalably. Chlorinated graphene can be used as a precursor for an array of functionalized materials by mechanically driven solid-state metathesis reactions. For example, nearly 75% of the chlorine in chlorinated graphene can be exchanged with fluorine by using the safer fluorine-containing compound ammonium fluoride (NH4F) as a reagent. A material with the composition C34Cl3F(OH)2 is realized. Preliminary work shows that F–graphene has oxygen reduction properties and Cl–graphene can improve existing zinc–air fuel cells. A scalable production of chlorinated and fluorinated graphenes and graphites will accelerate their adoption in fuel cells, batteries, polymer composites, and catalysts.
A Single Electrochemical Probe Used for Analysis of Multiple Nucleic Acid Sequences
ElectroanalysisJournal ArticleMills, D. M., Calvo-Marzal, P., Pinzon, J. M., Armas, S., Kolpashchikov, D. M., & Chumbimuni-Torres, K. Y. (2016). A Single Electrochemical Probe Used for Analysis of Multiple Nucleic Acid Sequences. Electroanalysis An International Journal Devoted to Electroanalysis, Sensors and Bioelectronic Devices, 29(3), 837-879. https://doi.org/10.1002/elan.201600548
Electrochemical hybridization sensors have been explored extensively for analysis of specific nucleic acids. However, commercialization of the platform is hindered by the need for attachment of separate oligonucleotide probes complementary to a RNA or DNA target to an electrode’s surface. Here we demonstrate that a single probe can be used to analyze several nucleic acid targets with high selectivity and low cost. The universal electrochemical four-way junction (4J)-forming (UE4J) sensor consists of a universal DNA stem-loop (USL) probe attached to the electrode’s surface and two adaptor strands (m and f) which hybridize to the USL probe and the analyte to form a 4J associate. The m adaptor strand was conjugated with a methylene blue redox marker for signal ON sensing and monitored using square wave voltammetry. We demonstrated that a single sensor can be used for detection of several different DNA/RNA sequences and can be regenerated in 30 seconds by a simple water rinse. The UE4J sensor enables a high selectivity by recognition of a single base substitution, even at room temperature. The UE4J sensor opens a venue for a re-useable universal platform that can be adopted at low cost for the analysis of DNA or RNA targets.
MVF Sensor Enables Analysis of Nucleic Acids with Stable Secondary Structures
ElectroanalysisJournal ArticleFoguel, M. V., Balcarcel, A. M., Reed, M. A., Calvo‐Marzal, P., Gerasimova, Y. V., Kolpashchikov, D. M., & Chumbimuni‐Torres, K. Y. (2020). MVF Sensor Enables Analysis of Nucleic Acids with Stable Secondary Structures. Electroanalysis, 32(4), 835–841. https://doi.org/10.1002/elan.201900690
One major challenge in nucleic acids analysis by hybridization probes is a compromise between the probe’s tight binding and sequence-selective recognition of nucleic acid targets folded into stable secondary structures. We have been developing a four-way junction (4WJ)-based sensor that consists of a universal stem-loop (USL) probe immobilized on an electrode surface and two adaptor strands (M and F). The sensor was shown to be highly selective towards single base mismatches at room temperature, able to detect multiple targets using the same USL probe, and have improved ability to detect folded nucleic acids. However, some nucleic acid targets, including natural RNA, are folded into very stable secondary and tertiary structures, which may represent a challenge even for the 4WJ sensors. This work describes a new sensor, named MVF since it uses three probe stands M, V and F, which further improves the performance of 4WJ sensors with folded targets. The MVF sensor interrogating a 16S rRNA NASBA amplicon with calculated folding energy of −32.82 kcal/mol has demonstrated 2.5-fold improvement in a signal-to-background ratio in comparison with a 4WJ sensor lacking strand V. The proposed design can be used as a general strategy in the analysis of folded nucleic acids including natural RNA.
Single-Step Integration of Poly(3-Octylthiophene) and Single-Walled Carbon Nanotubes for Highly Reproducible Paper-Based Ion-Selective Electrodes
Analytical ChemistryBiosensorsAnalytical Chemistry 2021 93 (3), 1271-1276
Calibration of ion-selective electrodes (ISEs) is cumbersome, time-consuming, and constitutes a significant limitation for the development of single-use and wearable disposable sensors. To address this problem, we have studied the effect of ion-selective membrane solvent on ISE reproducibility by comparing tetrahydrofuran (THF) (a typical solvent for membrane preparation) and cyclohexanone. In addition, a single-step integration of semiconducting/transducer polymer poly(3-octylthiophene) (POT) with single-walled carbon nanotubes (SWCNTs) into the paper-based ISEs (PBISEs) substrate was introduced. PBISEs for potassium and sodium ions were developed, and these ISEs present outstanding sensor performance and high potential reproducibility, as low as ±1.0 mV (n = 3).
Development and Characterization of Needle-type Ion-selective Microsensors for in situ Determination of Foliar Uptake of Zn2+ in Citrus Plants
Analytical ChemistryBiosensorsElectroanalysis, Volume 30, Issue 4, Special Issue: Mátrafüred 2017 – International Conference on Electrochemical Sensors, April 2018, Pages 626-632
For over a decade, the incidence of Huanglongbing (HLB) has grown at an alarming rate, affecting citrus crops worldwide. Current methods of nutrient therapy have little to no effect in alleviating symptoms of HLB, and scarce research has been put forth towards non-destructive tools for monitoring zinc transport in citrus plants. Here, we have developed and characterized a solid contact micro-ion-selective electrode (SC-μ-ISE) for the determination of zinc transport in sour orange seedlings using a non-invasive microelectrode ion flux estimation (MIFE) technique. The SC-μ-ISE displayed a 26.05±0.13 mV decade−1 Nernstian response and a LOD of (3.96±2.09)×10−7 M. Results showed a significant Zn2+ uptake in the leaves and roots of sour orange seedlings when bulk concentrations were higher than 5.99 mM. Above this concentration, a linear relationship between flux and bulk Zn2+ concentration was observed. This relationship suggests passive diffusion may be a key mechanism for Zn transport into plants. Overall, this study is the first to use a Zn2+ SC-μ-ISE for the determination of ion transport processes in plants. This novel tool can be used to further knowledge the effect of nutrient therapy and disease progression on HLB infected citrus plants.
Ready-to-use single-strip paper based sensor for multiplex ion detection
Analytical ChemistryBiosensorsSensors and Actuators B: ChemicalSensors and Actuators B: Chemical, Volume 255, Part 2, 2018, Pages 1781-1787
Ion-selective electrodes (ISEs) are an efficient and versatile tool for ion detection. However, portability and applicability for field applications are often limited by the need of a conditioning step, and high cost of the needed bulky reference electrode. Herein, the traditional conditioning protocol of ISEs has been eliminated and a paper-based solid-contact ISE (PBSC-ISE) has been integrated with a paper-based solid-contact reference electrode (PBSC-RE) in a single strip format for on-site analysis. The PBSC-RE is based on the copolymer methyl methacrylate-co-decyl methacrylate (MMA-DMA) (support matrix), combined with ionic liquids (ILs) to create and maintain a stable potential that is un-affected by a change in ionic activity. This single-strip ready-to-use sensor yields a Nernstian response towards Na+, K+, and I− ions with submicromolar limits of detection, and is able to be used for multiplex analysis.
Reversible Photovoltage Generation Using Metastable-State Photoacids in the Solid State with Visible Light
The Journal of Physical ChemistryThe Journal of Physical Chemistry C 2021 125 (46), 25879-25885
Herein, for the first time, we demonstrate a reversible photovoltage generation using metastable-state photoacids (mPAH) in the solid state upon visible light irradiation. To accomplish this, a solid-state cell was fabricated, where the mPAH was modified with a thiol moiety to allow for covalent linkage to a gold surface. Proton released from the mPAH upon light irradiation (470 nm) was transported through a solid electrolyte support to quickly generate a photovoltage of ∼200 mV. This gain is ∼30 times greater than that of the control solid-state cell under the same conditions. The novel solid-state cell proposed here displays good reversibility with reproducible photovoltage changes, opening new avenues for lower power electronic applications.
Highly Reproducible Flexible Ion-selective Electrodes for the Detection of Sodium and Potassium in Artificial Sweat
Analytical ChemistryElectroanalysisElectroanalysis, Volume 35, Issue 3, March 2023
It is well known that potentiometric sensors provide a versatile, cost-effective, and efficient platform for wearable applications. Unfortunately, mass production and commercialization of such devices is often constrained by the requirement of a calibration step, which is due to the poor sensor-to-sensor reproducibility and the need of conditioning the electrodes in the analyte before use. Herein, we fabricated calibration-free flexible sensors including ion-selective electrode and reference electrode by integrating single-walled carbon nanotubes (SWCNTs) with poly(3-octylthiophene) (POT) and applying on polyethylene terephthalate (PET) substrate. The developed sodium and potassium ion-selective electrodes (ISEs) display excellent repeatability, selectivity, stability as well as high sensor-to-sensor reproducibility, with a standard deviation of as low as 1.0 mV in artificial sweat microliter samples volume.
In Situ Monitoring of Pb2+ Leaching from the Galvanic Joint Surface in a Prepared Chlorinated Drinking Water
Analytical ChemistryEnvironmental Science and TechnologyEnvironmental Science & Technology 2018 52 (4), 2126-2133
A novel method using a micro-ion-selective electrode (micro-ISE) technique was developed for in situ lead monitoring at the water–metal interface of a brass-leaded solder galvanic joint in a prepared chlorinated drinking water environment. The developed lead micro-ISE (100 μm tip diameter) showed excellent performance toward soluble lead (Pb2+) with sensitivity of 22.2 ± 0.5 mV decade–1 and limit of detection (LOD) of 1.22 × 10–6 M (0.25 mg L–1). The response time was less than 10 s with a working pH range of 2.0–7.0. Using the lead micro-ISE, lead concentration microprofiles were measured from the bulk to the metal surface (within 50 μm) over time. Combined with two-dimensional (2D) pH mapping, this work clearly demonstrated that Pb2+ ions build-up across the lead anode surface was substantial, nonuniform, and dependent on local surface pH. A large pH gradient (ΔpH = 6.0) developed across the brass and leaded-tin solder joint coupon. Local pH decreases were observed above the leaded solder to a pH as low as 4.0, indicating it was anodic relative to the brass. The low pH above the leaded solder supported elevated lead levels where even small local pH differences of 0.6 units (ΔpH = 0.6) resulted in about four times higher surface lead concentrations (42.9 vs 11.6 mg L–1) and 5 times higher fluxes (18.5 × 10–6 vs 3.5 × 10–6 mg cm–2 s–1). Continuous surface lead leaching monitoring was also conducted for 16 h.
Visible Light Activated Ion Sensing Using a Photoacid Polymer for Calcium Detection
Analytical ChemistryAnalytical ChemistryBiosensorsAnalytical Chemistry 2014 86 (13), 6184-6187
Presented here is a sensing membrane consisting of a modified merocyanine photoacid polymer and a calcium ionophore in plasticized poly(vinyl chloride). This membrane is shown to actively exchange protons with calcium ions when switched ON after illumination at 470 nm, and the exchange can be followed by UV–vis spectroscopy. The sensing membrane shows no response in the ON state when calcium ions are absent. The limit of detection of the sensor is 5.0 × 10–4 M with an upper detection limit of 1.0 M. Thus, we demonstrate for the first time the use of a visible light activated, lipophilic photoacid polymer in an ion-sensing membrane for calcium ions, which highly discriminates potassium, sodium, and magnesium ions.
Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes
Analytical Chemistry 2016 88 (17), 8404-8408
Preparation of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, we eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion solution. This proof of concept experiment was performed with iodide, silver, and sodium selective electrodes. The proposed methodology significantly shortened the preparation time of ISEs, yielding functional electrodes with submicromolar detection limits. Moreover, it is anticipated that this approach may form the basis for the development of miniaturized all-solid-state ion-selective electrodes for in situ measurements.
Tuning the Equilibrium Response Time of Meta-Stable Photoacids in Ion-Sensors by Appropriate Functionalization
ElectroanalysisJournal ArticlePatel, P. K., Johns, V. K., Mills, D. M., Boone, J. E., Calvo-Marzal, P., & Chumbimuni-Torres, K. Y. (2015). Tuning the Equilibrium Response Time of Meta‐Stable Photoacids in Ion‐Sensors by Appropriate Functionalization. Electroanalysis, 27(3), 677–683. https://doi.org/10.1002/elan.201400601
We present different functionalized meta-stable photoacids in ion-sensors to tune the equilibrium response time. As a proof of concept, two new meta-stable photoacids were synthesized, one contains an ether group and the other has an ester functional group. These functionalized meta-stable photoacids were elucidated in solution of ethanol and in ion-sensing films via pH and kinetic studies. In comparison from our previous work, the response time was reduced from hours to minutes by utilizing an ether functional group in the meta-stable photoacid.
Editorial: Chemical Sensors for Biomedical Use
Journal ArticleXie, X., Citterio, D., Chumbimuni-Torres, K., Xue, M., & Wang, X. (2021). Editorial: Chemical Sensors for Biomedical Use [Editorial]. Frontiers in Chemistry, 9. https://doi.org/10.3389/fchem.2021.685563
Dr. Torres worked with other researchers around the world to create an editorial on the research topic: Chemical Sensors for Biomedical Use.
Nanomolar Detection Limits of Cd2+, Ag+, and K+ Using Paper-Strip Ion-Selective Electrodes
Analytical ChemistryJournal ArticleMensah, S. T., Gonzalez, Y., Calvo-Marzal, P., & Chumbimuni-Torres, K. Y. (2014). Nanomolar Detection Limits of Cd2+, Ag+, and K+ Using Paper-Strip Ion-Selective Electrodes. Analytical Chemistry, 86(15), 7269-7273. https://doi.org/10.1021/ac501470p
Paper-based ion-selective electrodes (ISEs) are simple, flexible, and cost-efficient in comparison to conventional solid-contact ISEs. Yet, paper-based ISEs have poor limits of detection (in the micromolar range) relative to conventional solid-contact ISEs. Here we describe the construction and optimization of ISEs based on commercially available filter paper modified with single-walled carbon nanotubes (SWCNTs), sputtered gold, and conductive polymer poly(3-octylthiophene) to support an ion-selective membrane. The ion-selective membrane presented here is based on the copolymer methyl methacrylate-decyl methacrylate (MMA-DMA). The copolymer MMA-DMA is highly water-repellent and has a low coefficient of diffusion, which makes it particularly suitable for the creation of sensors with high performance in reaching low limits of detection. Three different configurations of the electrodes have been characterized by using contact angle surface analysis, oxygen influence, and testing for the presence of a water layer. Paper-strip ISEs for cadmium, silver, and potassium ions were developed with groundbreaking limits of detection of 1.2, 25.1, and 11.0 nM, respectively. In addition to such low limits of detection, paper-strip ISEs display high selectivity for their ion of interest and high reproducibility.
Circumventing Traditional Conditioning Protocols in Polymer Membrane-Based Ion-Selective Electrodes
Analytical ChemistryJournal ArticlePreparation of ion-selective electrodes (ISEs) often requires long and complicated conditioning protocols limiting their application as tools for in-field measurements. Herein, we eliminated the need for electrode conditioning by loading the membrane cocktail directly with primary ion solution. This proof of concept experiment was performed with iodide, silver, and sodium selective electrodes. The proposed methodology significantly shortened the preparation time of ISEs, yielding functional electrodes with submicromolar detection limits. Moreover, it is anticipated that this approach may form the basis for the development of miniaturized all-solid-state ion-selective electrodes for in situ measurements.
Visible Light-Induced Ion-Selective Optodes based on a Metastable Photoacid for Cation Detection
AnalystJournal ArticleA new platform of ion-selective optode is presented here to detect cations under thermodynamic equilibrium via ratiometric analysis. This novel platform utilizes a ‘one of a kind’ visibile light-induced metastable photoacid as a reference ion indicator to achieve activatable and controllable sensors. These ion-selective optodes were studied in terms of its stability, sensitivity, selectivity, and theoretical aspects.
Potentiometric biosensing of proteins with ultrasensitive ion-selective microelectrodes and nanoparticles labels
Journal ArticleJournal of the American Chemical SocietyJ. Am. Chem. Soc. 2006, 128, pp13676-13677
We report here for the first time on the use of potentiometry for ultrasensitive nanoparticle-based detection of protein interactions. A silver ion-selective microelectrode is used to detect silver ions oxidatively released from silver enlarged gold nanoparticle labels in a sandwich immunoassay. Since potentiometry is expected to largely maintain its analytical characteristics upon reducing the sample volume, it is anticipated that this approach may form the basis for bioassays with attractive detection limits.
Determination of glutathione in hemolysed erythrocyte with amperometric sensor based on TTF-TCNQ
Clinica Chimica ActaJournal ArticleClin Chim Acta., 2006, 371(1-2), pp152-158
BACKGROUND:
GSH has a relevant role in human metabolism as an indicator of disease risks. An amperometric sensor for glutathione (GSH) determination is described as an alternative method featuring simple construction procedure and short time analysis.
METHOD:
The developed sensor was used to determine glutathione at low potential using a TTF-TCNQ complex.
RESULTS:
The sensor exhibits a linear response range from 5 to 340 micromol/l under applied potential of 200 mV vs. SCE. The sensitivity and detection limit were 90.1 microA l/mmol cm(2) and 0.3 micromol/l, respectively.
CONCLUSION:
When the sensor was tested in hemolysed erythrocyte samples for GSH determination, a good correlation in results was observed between the sensor and the spectrophotometric method. The sensor showed recovery values between 98% and 102%.
Application of Blind Source Separation Methods to Ion-Selective Electrode Arrays in Flow-Injection Analysis
IEEE Sensors JournalJournal ArticleIEEE Sensors J, 2014, 14(7), 2228-2229
As shown recently, the interference problem typical of ion-selective electrodes can be dealt with via smart arrays adjusted by blind source separation methods. In this letter, we resume this study and show that such an approach can be applied even when faced with a limited number of samples acquired through flow-injection analysis.
Adsorption of Proteins to thin-films of PDMS and its effect on the adhesion of human endothelial cells
Journal ArticleRSC AdvancesRSC Advances,2011, 1, pp 706-714
This paper describes a simple and inexpensive procedure to produce thin-films of poly(dimethylsiloxane). Such films were characterized by a variety of techniques (ellipsometry, nuclear magnetic resonance, atomic force microscopy, and goniometry) and used to investigate the adsorption kinetics of three model proteins (fibrinogen, collagen type-I, and bovine serum albumin) under different conditions. The information collected from the protein adsorption studies was then used to investigate the adhesion of human dermal microvascular endothelial cells. The results of these studies suggest that these films can be used to model the surface properties of microdevices fabricated with commercial PDMS. Moreover, the paper provides guidelines to efficiently attach cells in BioMEMS devices.
Modern directions for potentiometric sensors.
Journal ArticleJournal of the Brazilian Chemical SocietyJ. Braz. Chem. Soc. 2008 19(4), pp 612-629
This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the basic membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications.
Simultaneous determination of calcium and potassium in coconut water by a flow-injection method with tubular potentiometric sensors
Journal ArticleJournal of Food Composition and AnalysisJ. Food Comp. Anal.,2006, 19(2-3), pp 225-230
In the present work, a simultaneous determination of calcium and potassium in coconut water samples using a flow-injection system with tubular ion-selective electrodes (ISEs) in series is described. The samples were injected into a 0.1 mol L−1 HEPES (pH=6.0) carrier solution, using an injection volume of 100 μL and a flow of 2.0 mL min−1 in the FIA system. The electrodes developed exhibited nernstian response for calcium and potassium in the concentration range between 1.0×10−5 and 1.0×10−1 mol L−1 with detection limits of 5.6×10−6 mol L−1 for calcium and 9.5×10−6 mol L−1 for potassium. And no significant interference between both ions was observed. The flow-injection analysis (FIA) system with tubular ISEs was suitable for the simultaneous calcium and potassium on-line monitoring. The determination of potassium presented good results when compared to the reference method. And the recovery results were 95±1% for calcium and 102±2% for potassium, showing a good evidence of the accuracy of the method.
Determination of reduced glutathione using an amperometric carbon paste electrode chemically modified with TTF–TCNQ
Journal ArticleSensors and Actuators B: ChemicalSens. Actuators, B, 2004,100(3), pp 333-340
The development of an amperometric sensor for the determination of reduced glutathione (GSH) is described. The sensor is based on tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) incorporated into the graphite powder/Nujol oil matrix. The electrooxidation of GSH was monitored amperometrically at 200 mV versus SCE (saturated calomel electrode). The amperometric response of the sensor was linearly proportional to the GSH concentration between 20 and 300 μmol l−1, in 0.1 mol l−1phosphate buffer (pH 8.0), containing 0.1 mol l−1 KCl and 0.5 mmol l−1 Na2H2EDTA, as supporting electrolyte.
The detection limit, considering signal/noise ratio equal three, was 4.2 μmol l−1 for GSH and the repeatability obtained as relative standard deviation was of 5.1% for a series of 10 successive measurements.
Use of self-plasticizing EVA membrane for potentiometric anion detection
Journal ArticleTalantaTalanta, 2001,53(4), pp 807-814
In this work, five different types of membranes were developed responsible to anion-selective electrodes. The membranes were based on tri-caprylyl-trimethyl-ammonium chloride (Aliquat-336S) supported on poly(ethylene-co-vinyl-acetate) copolymer (EVA). The sensors were prepared by solubilizing the copolymer with the appropriate exchanger in chloroform, without using of any plasticizers. The ion-selective electrodes prepared using these membranes show the utility for anions determinations in the concentration range between 10−5 and 10−1 mol l−1 in the steady-state. The membrane performance was also evaluated in FIA system using tubular electrode for salicylate and iodide. In FIA system, the electrode exhibited nernstian response for salicylate in the concentration range of 2.5×10−3 and 1.0×10−1, while for iodide from 5.0×10−4 up to 1.0×10−1 mol l−1. The systems were employed for the salicylate and iodide determination in pharmaceutical samples obtaining a relative deviation of 1.6%, when compared to the reference method.
Tuning the Equilibrium Response Time of Meta-Stable Photoacids in Ion-Sensors by Appropriate Functionalization
ElectroanalysisJournal ArticleElectroanalysis,2015, 27(3), pp 677-683
Herein, we present different functionalized meta-stable photoacids in ion-sensors to tune the equilibrium response time. As a proof of concept, two new meta-stable photoacids were synthesized, one contains an ether group and the other has an ester functional group. These functionalized meta-stable photoacids were elucidated in solution of ethanol and in ion-sensing films via pH and kinetic studies. In comparison from our previous work, the response time was reduced from hours to minutes by utilizing an ether functional group in the meta-stable photoacid.
An indium tin oxide electrode modified with gold nanorods for use in potential-controlled surface plasmon resonance studies
Journal ArticleMicrochimica ActaMicrochimica Acta.,2013, 180(11-12), pp1013-1020
The modification of electrodes with gold nanoparticles results in an increased electrode surface area, enhanced mass transport, and improved catalytic properties. We have extended this approach to indium tin oxide (ITO) electrodes to obtain optically transparent gold nanorod-modified electrodes which display enhanced electrochemical capabilities and have the additional advantage of showing a tunable surface plasmon resonance. The procedures for attaining high surface coverage (15 gold nanorods per square µm) of such electrodes were optimized, and the potential-dependent surface plasmon resonance was studied under controlled electrical potential. In an exemplary sensor application, we demonstrate the detection of mercury via potential-dependent formation of an Au-Hg amalgam
Visible Light Activated Ion Sensing Using a Photoacid Polymer for Calcium Detection
Journal ArticleJournal of Analytical ChemistryAnal. Chem., 2014, 86 (13), pp 6184–6187
Presented here is a sensing membrane consisting of a modified merocyanine photoacid polymer and a calcium ionophore in plasticized poly(vinyl chloride). This membrane is shown to actively exchange protons with calcium ions when switched ON after illumination at 470 nm, and the exchange can be followed by UV–vis spectroscopy. The sensing membrane shows no response in the ON state when calcium ions are absent. The limit of detection of the sensor is 5.0 × 10–4 M with an upper detection limit of 1.0 M. Thus, we demonstrate for the first time the use of a visible light activated, lipophilic photoacid polymer in an ion-sensing membrane for calcium ions, which highly discriminates potassium, sodium, and magnesium ions.
Solid contact potentiometric sensors for trace level measurements
Journal ArticleJournal of Analytical ChemistryAnal. Chem. 78, 2006, pp1318-1322.
A simple procedure for the development of a range of polymeric ion-selective electrodes (ISEs) with low detection limits is presented. The electrodes were prepared by using a plasticizer-free methyl methacrylate−decyl methacrylate copolymer as membrane matrix and poly(3-octylthiophene) as intermediate layer deposited by solvent casting on gold sputtered copper electrodes as a solid inner contact. Five different electrodes were developed for Ag+, Pb2+, Ca2+, K+, and I-, with detection limits mostly in the nanomolar range. In this work, the lowest detection limits reported thus far with solid contact ISEs for the detection of silver (2.0 × 10-9M), potassium (10-7 M), and iodide (10-8 M) are presented. The developed electrodes exhibited a good response time and excellent reproducibility.
Solid-contact potentiometric polymer membrane microelectrodes for the detection of silver ions at the femtomole level
Journal ArticleSensors and Actuators B: ChemicalSensor and Actuators B 121, pp135-141
In recent years, ion-selective electrodes based on polymer membranes have been shown to exhibit detection limits that are often in the nanomolar concentration range, and thus drastically lower than traditionally accepted. Since potentiometry is less dependent on scaling laws that other established analytical techniques, their performance in confined sample volumes is explored here. Solid-contact silver-selective microelectrodes, with a sodium-selective microelectrode as a reference, were inserted into a micropipette tip used as a 50-μl sample. The observed potential stabilities, reproducibilities and detection limits were attractive and largely matched that for large 100-ml samples. This should pave the way for further experiments to detecting ultra-small total ion concentrations by potentiometry, especially when used as a transducer after an amplification step in bioanalysis.
Potentiometric Detection of DNA Hybridization using Enzyme-Induced Metallization and a Silver Ion Selective Electrode
Journal ArticleJournal of Analytical ChemistryAnal. Chem.,2009, 81, 10007-10012
Here, we report on a highly sensitive potentiometric detection of DNA hybridization. The new assay uses a low-volume solid-contact silver ion-selective electrode (Ag+-ISE) to monitor the depletion of silver ions induced by the biocatalytic reaction of the alkaline-phosphatase enzyme tag. The resultant potential change of the Ag+-ISE, thus, serves as the hybridization signal. Factors affecting the potentiometric hybridization response have been optimized to offer a detection limit of 50 fM (0.2 amol) DNA target. The new potentiometric assay was applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria to achieve a low detection limit of 10 CFU in the 4 μL sample. Such potentiometric transduction of biocatalytically induced metallization processess holds great promise for monitoring various bioaffinity assays involving common enzyme tags.
High-Temperature Potentiometry: Modulated Response of Ion-Selective Electrodes during Heat Pulses
Journal ArticleJournal of Analytical ChemistryAnal. Chem., 2009, 81, 10290-10294
The concept of locally heated polymeric membrane potentiometric sensors is introduced here for the first time. This is accomplished in an all solid state sensor configuration, utilizing poly(3-octylthiophene) as the intermediate layer between the ion-selective membrane and underlying substrate that integrates the heating circuitry. Temperature pulse potentiometry (TPP) gives convenient peak-shaped analytical signals and affords an additional dimension with these sensors. Numerous advances are envisioned that will benefit the field. The heating step is shown to give an increase in the slope of the copper-selective electrode from 31 to 43 mV per 10-fold activity change, with a reproducibility of the heated potential pulses of 1% at 10 μM copper levels and a potential drift of 0.2 mV/h. Importantly, the magnitude of the potential pulse upon heating the electrode changes as a function of the copper activity, suggesting an attractive way for differential measurement of these devices. The heat pulse is also shown to decrease the detection limit by half an order of magnitude.
Amplified potentiometric transduction of DNA hybridization using ion-loaded liposomes
AnalystJournal ArticleAnalyst, 2010, 135, 1618-1623
Amplified potentiometric transduction of DNA hybridization based on using liposome ‘nanocarriers’ loaded with the signaling ions is reported. The liposome-amplified potentiometric bioassay involved the duplex formation, followed by the capture of calcium-loaded liposomes, asurfactant-induced release and highly-sensitive measurements of the calcium signaling ions using a Ca2+ ion-selective electrode (ISE). The high loading yield of nearly one million signaling ions per liposome leads to sub-fmol DNA detection limits. Factors affecting the ion encapsulation efficiency and signal amplification are evaluated and discussed. The influence of the surfactant lysing agent is also examined. Such use of ‘green’ calcium signaling ions addresses the inherent toxicity of Agand CdS nanoparticle tags used in previous potentiometric bioassays. The new strategy was applied for the detection of low levels of E. coli bacteria. It could be readily extended to trace measurements of other important biomolecules in connection to different biorecognition events. The attractive analytical performance makes liposomes a useful addition to the armory of potentiometric bioassays.
Real-time probing of the growth dynamics of nanoparticles using potentiometric ion-selective electrodes
Electrochemistry CommunicationsJournal ArticleElectrochem. Commun., 11, pp1964-1967
This Communication demonstrates the ability of potentiometric ion-selective electrodes (ISE) to probe the growth dynamics of metal nanoparticles in real-time. The new monitoring capability is illustrated using a solid-contact silver ISE for monitoring the hydroquinone-induced precipitation of silver on gold nanoparticle seeds. Potential-time recordings obtained under different conditions are used to monitor the depletion of the silver ion during the nanoparticle formation and shed useful insights into the growth dynamics of the nanoparticles. Such potentiometric profiles correlate well with the analogous optical measurements. The new real-time electrochemical probing of the particle growth process reflects the direct, rapid and sensitive response of modern ISE to changes in the level of the precipitated metal ion from the bulk solution and holds considerable promise for probing the preparation of different nanoscale materials.
Comparison Between Potentiometric and Stripping Voltammetric Detection of Trace Metals: Measurements of Cadmium and Lead in the Presence of Thalium, Indium and Tin
ElectroanalysisJournal ArticleElectroanalysis, 21, pp1939-1943.
Recent advances in ion-selective electrodes have pushed the detection limits of direct potentiometry to the nanomolar concentration range. Here we present a direct comparison of the sensitivity and selectivity of potentiometric and stripping-voltammetric measurements of cadmium and lead. While both techniques offer a similar sensitivity, the potentiometric method offers higher selectivity in the presence of excess of metal ions (e.g., thallium, tin) that commonly interfere in the stripping-voltammetric operation. Because of the complementary nature of the potentiometric and stripping-voltammetric methods, it is recommended that these techniques will be selected based on the specific analytical problem or used in parallel to provide additional analytical information.
Real-time electrochemical monitoring of drug release from therapeutic nanoparticles
Journal ArticleJournal of Controlled ReleaseJ. Control. Release, 140(1), pp69-73
An electrochemical protocol for real-time monitoring of drug release kinetics from therapeutic nanoparticles (NPs) is described. The method is illustrated for repetitive square-wave voltammetric measurements of the reduction of doxorubicin released from liposomes at a glassy-carbon electrode. Such operation couples high sensitivity down to 20 nM doxorubicin with high speed and stability. It can thus monitor in real time the drug release from NP carriers, including continuous measurements in diluted serum. Such direct and continuous monitoring of the drug release kinetics from therapeutic NPs holds great promise for designing new drug delivery NPs with optimal drug release properties. These NPs can potentially be used to deliver many novel compounds such as marine-life derived drugs and hydrophobic drugs with limited water solubility that are usually difficult to be characterized by traditional analytical tools.
Nanoparticle-induced potentiometric biosensing of NADH at copper ion-selective electrodes
AnalystJournal ArticleAnalyst. 2009, 134(8), pp1614-7
We demonstrate the first example of using potentiometry at ion-selective electrodes (ISEs) for probing in real-time monitoring of biometallization processes. A copper ISE is used for real-time monitoring of the NADH-mediated reduction of copper in the presence of gold nanoparticle seeds. Such potentiometric detection of NADH is not susceptible to surface fouling common with analogous amperometric measurements of this co-factor. Biosensing of ethanol is illustrated in the presence of alcohol dehydrogenase and NAD(+), along with potentiometric detection of the NADH product at the copper ISE. The concept can be readily expanded to the monitoring of various biometallization processes in connection to different enzymatic transformations and ISE, and used for ultrasensitive detection of bioaffinity interactions in connection to common enzyme tags.
Electrochemical sample matrix elimination for trace level potentiometric detection with polymeric membrane ion-selective electrodes
Journal ArticleJournal of Analytical ChemistryAnal. Chem., 2008, 80 (15), pp 6114–6118
Potentiometric sensors are today sufficiently well understood and optimized to reach ultratrace level (subnanomolar) detection limits for numerous ions. In many cases of practical relevance, however, a high electrolyte background hampers the attainable detection limits. A particularly difficult sample matrix for potentiometric detection is seawater, where the high saline concentration forms a major interfering background and reduces the activity of most trace metals by complexation. This paper describes for the first time a hyphenated system for the online electrochemically modulated preconcentration and matrix elimination of trace metals, combined with a downstream potentiometric detection with solid contact polymeric membrane ion-selective microelectrodes. Following the preconcentration at the bismuth-coated electrode, the deposited metals are oxidized and released to a medium favorable to potentiometric detection, in this case calcium nitrate. Matrix interferences arising from the saline sample medium are thus circumvented. This concept is successfully evaluated with cadmium as a model trace element and offers potentiometric detection down to low parts per billion levels in samples containing 0.5 M NaCl background electrolyte.
Potentiometric detection of DNA hybridization
Journal ArticleJournal of the American Chemical SocietyJ. Am. Chem. Soc., 2008, 130 (2), pp 410–411
The use of potentiometric microsensors is demonstrated here for the first time to detect DNA hybridization. Cadmium sulfide nanocrystal labels bound on a secondary oligonucleotide are dissolved and detected with cadmium-selective microelectrodes exhibiting DNA detectionlimits of ca. 2 fmol in a 200 μL sample.
Aptamer-based potentiometric measurements of proteins using ion-selective microelectrodes
Journal ArticleJournal of Analytical ChemistryAnal. Chem., 2008, 80 (3), pp 707–712
We here report on the first example of an aptamer-based potentiometric sandwich assay of proteins. The measurements are based on CdS quantum dot labels of the secondary aptamer, which were determined with a novel solid-contact Cd2+-selective polymer membrane electrode after dissolution with hydrogen peroxide. The electrode exhibited cadmium ion detection limits of 100 pM in 100 mL samples and of 1 nM in 200 μL microwells, using a calcium-selective electrode as a pseudoreference electrode. As a prototype example, thrombin was measured in 200 μL samples with a lower detection limit of 0.14 nM corresponding to 28 fmol of analyte. The results show great promise for the potentiometric determination of proteins at very low concentrations in microliter samples.
Recent advances and new perspectives of ion-selective electrodes
Journal ArticleQuímica NovaQuim. Nova, 2006, 29(5), pp1094-1100
This paper describes the recent progress in the development of polymeric membranes for ion-selective electrodes. The importance of knowing the mechanism of potential development in membranes for ion-selective electrodes to reach lower detection limits and improve selectivity are discussed. Recent advances and future trends of research on ion-selective electrodes are also reported.
Nanomolar Detection Limits of Cd2+, Ag+, and K+ Using Paper-Strip Ion-Selective Electrodes
Journal ArticleJournal of Analytical ChemistryAnal. Chem., 2014, 86 (15), pp 7269–7273
Paper-based ion-selective electrodes (ISEs) are simple, flexible, and cost-efficient in comparison to conventional solid-contact ISEs. Yet, paper-based ISEs have poor limits of detection (in the micromolar range) relative to conventional solid-contact ISEs. Here we describe the construction and optimization of ISEs based on commercially available filter paper modified with single-walled carbon nanotubes (SWCNTs), sputtered gold, and conductive polymer poly(3-octylthiophene) to support an ion-selective membrane. The ion-selective membrane presented here is based on the copolymer methyl methacrylate-decyl methacrylate (MMA-DMA). The copolymer MMA-DMA is highly water-repellent and has a low coefficient of diffusion, which makes it particularly suitable for the creation of sensors with high performance in reaching low limits of detection. Three different configurations of the electrodes have been characterized by using contact angle surface analysis, oxygen influence, and testing for the presence of a water layer. Paper-strip ISEs for cadmium, silver, and potassium ions were developed with groundbreaking limits of detection of 1.2, 25.1, and 11.0 nM, respectively. In addition to such low limits of detection, paper-strip ISEs display high selectivity for their ion of interest and high reproducibility.