Disposable Electrodes for Capacitive Immunosensor

A Fabrication of Multichannel Graphite Electrode Using Low-Cost Stencil-Printing Technique

Multichannel graphite electrodes (MGrEs) have been designed and fabricated in this study. A template was cut from an adhesive plastic sheet using a desktop cutting device. The template was placed on a polypropylene substrate, and carbon graphite ink was applied with a squeegee to the template. The size of the auxiliary electrode (AE) as well as the location of the reference electrode (RE) of MGrEs design were investigated. Scanning electron microscopy was used to determine the thickness of the ink on the four working electrodes (WEs), which was 21.9 ± 1.8 µm. Cyclic voltammetry with a redox probe solution was used to assess the precision of the four WEs. The intra-electrode repeatability and inter-electrode reproducibility of the MGrEs production were satisfied by low RSD (<6%). Therefore, the MGrEs is reliable and capable of detecting four replicates of the target analyte in a single analysis. The electrochemical performance of four WEs was investigated and compared to one WE. The sensitivity of the MGrEs was comparable to the sensitivity of a single WE. The MGrEs’ potential applications were investigated by analyzing the nitrite in milk and tap water samples (recoveries values of 97.6 ± 0.4 to 110 ± 2%).

Subnanomolar detection of promethazine abuse using a gold nanoparticle-graphene nanoplatelet-modified electrode

A simple, sensitive, and effective adsorptive stripping voltammetric sensor for the detection of trace-level promethazine was created based on a gold nanoparticle-graphene nanoplatelet-modified glassy carbon electrode (AuNP-GrNP/GCE). AuNP-GrNP nanocomposites were synthesized using an electroless deposition process, and the morphology was characterized using UV-vis spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrochemical behavior and detection of promethazine at the AuNP-GrNP/GCE were investigated utilizing cyclic voltammetry and adsorptive stripping voltammetry. The AuNP-GrNP/GCE showed outstanding synergistic electrochemical activity for promethazine oxidation, a highly active surface area, great adsorptivity, and outstanding catalytic properties. The electrolyte pH, amount of AuNP-GrNP nanocomposite, preconcentration potential (vs. Ag/AgCl), and time were optimized to obtain a high performance electrochemical sensor. Under optimal conditions, the proposed sensor displayed two linear concentration ranges from 1.0 nmol L^-1 to 1.0 μmol L^-1 and from 1.0 to 10 μmol L^-1. The limits of detection and quantitation were 0.40 and 1.4 nmol L^-1, respectively. This sensor displayed high sensitivity, a capability for rapid analysis, and excellent repeatability and reproducibility. The developed sensor was effective and practical for promethazine detection in biological fluids and forensic samples, and the obtained results exhibited excellent agreement with the results obtained using the method described in the British Pharmacopoeia. Graphical abstract.

Electrochemical sensor for the quantification of iodide in urine of pregnant women

An electrochemical method has been developed to determine iodide in urine using an electrode modified with silver oxide microparticles-poly acrylic acid/poly vinyl alcohol (Ag₂OMPs-PAA/PVA). Silver oxide particles were formed by electrochemical oxidation via cyclic voltammetry. The modified electrode exhibited an excellent response to iodide detection by cathodic stripping voltammetry. The fabrication and operation conditions were optimized in terms of PVA concentration, K₂HPO₄ concentration, amount of AgMPs-PAA/PVA, number of cycles for oxide formation, electrolyte, applied potential (vs. Ag/AgCl), and time. Under the optimum conditions, iodide determination produced a linear range from 1 to 40 μM. The limit of detection was 0.3 μM. Precision was found to be within 7.4% RSD. The developed method was applied to the determination of iodide in urine samples of pregnant women with satisfying recoveries (86 ± 1 to 108 ± 1%). Graphical abstract.

Bioimprinting as a tool for the detection of aflatoxin B1 using a capacitive biosensor

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Bioimprinting of proteins is used for production of selective binding sites for aflatoxin.

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An inert protein, ovalbumin was used for the bioimpriting.

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When stabilizing the imprinted molecule by internal cross-linking, it was possible to use the same imprint more than 25 times.

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A limit of detection of 6 × 10⁻¹² M was observed.

A strategy for the detection of aflatoxin B1 using a capacitive biosensor has been studied. The use of proteins for the generation of sites with high specificity against aflatoxin B1 are produced via bioimprinting. This technique has become a tool for the detection of aflatoxin B1 using a capacitive biosensor. The results demonstrate the ability to generate specific interactions with aflatoxin B1 with a linear relation between signals registered and log concentration of the target aflatoxin in the concentration range of 3.2 × 10⁻⁶ to 3.2 × 10⁻⁹ M when using ovalbumin as framework for the bioimprinting.

Screening of self-assembled monolayer for aflatoxin B1 detection using immune-capacitive sensor

A capacitive biosensor was used for detection of aflatoxin B1. Two different methods for cleaning gold electrodes were evaluated using cyclic voltammetry in the presence of ferricyanide as redox couple. The methods involve use of a sequence of cleaning steps avoiding the use of Piranha solution and plasma cleaner. Anti-aflatoxin B1 was immobilized on self-assembled monolayers (SAM). The immune-capacitive biosensor is able to detect aflatoxin B1 concentrations in a linear range of 3.2 × 10⁻¹² M to 3.2 × 10⁻⁹ M when thiourea was used to form the SAM; 3.2 × 10⁻⁹ M to 3.2 × 10⁻⁷ M when thioctic acid was used. When the gold surface was isolated with tyramine-electropolymerization linear ranges of 3.2 × 10⁻¹³ M to 3.2 × 10⁻⁷ M and 3.2 × 10⁻⁹ M to 3.2 × 10⁻⁷ M where obtained, respectively. The results obtained show the difference in linear range, limit of detection, and limit of quantification when different self-assembled monolayers are used for aflatoxin B1 detection.

Affinity sensor based on immobilized molecular imprinted synthetic recognition elements

An affinity sensor based on capacitive transduction was developed to detect a model compound, metergoline, in a continuous flow system. This system simulates the monitoring of low-molecular weight organic compounds in natural flowing waters, i.e. rivers and streams. During operation in such scenarios, control of the experimental parameters is not possible, which poses a true analytical challenge. A two-step approach was used to produce a sensor for metergoline. Submicron spherical molecularly imprinted polymers, used as recognition elements, were obtained through emulsion polymerization and subsequently coupled to the sensor surface by electropolymerization. This way, a robust and reusable sensor was obtained that regenerated spontaneously under the natural conditions in a river. Small organic compounds could be analyzed in water without manipulating the binding or regeneration conditions, thereby offering a viable tool for on-site application.

Development of a real-time capacitive biosensor for cyclic cyanotoxic peptides based on Adda-specific antibodies

The harmful effects of cyanotoxins in surface waters have led to increasing demands for accurate early warning methods. This study proposes a capacitive immunosensor for broad-spectrum detection of the group of toxic cyclic peptides called microcystins (∼80 congeners) at very low concentration levels. The novel analytical platform offers significant advances compared to the existing methods. Monoclonal antibodies (mAbs, clone AD4G2) that recognize a common element of microcystins were used to construct the biosensing layer. Initially, a stable insulating anchor layer for the mAbs was made by electropolymerization of tyramine onto a gold electrode surface, with subsequent incorporation of gold nanoparticles (AuNPs) on the glutaraldehyde (5%) activated polytyramine surface. The biosensor responded linearly to microcystin concentrations from 1×10(-13)M to 1×10(-10)M MC-LR standard with a limit of detection of 2.1×10(-14)M. The stability of the biosensor was evaluated by repeated measurements of the antigen and by determining the capacitance change relative to the original response, which decreased below 90% after the 30th cycle.