Employment of electrostriction phenomenon for label-free electrochemical immunosensing of tetracycline.

The presented work describes a simple label-free electrochemical immunosensor for the determination of tetracycline (TC). The functioning of the sensor was based on the electrostriction of a antibody-terminated thiol layer self-assembled on a gold electrode surface, serving as a dielectric membrane. The intensity of electrostriction was correlated with the amount of TC captured through an affinity reaction with its specific antibody, and was followed in the form of capacitance-potential curves. The process of the immunosensor construction was optimized using electrochemical impedance spectroscopy (EIS). The chemisorption time of the thiol, the duration of the TCAb immobilization and its concentration were optimized. The developed immunosensor exhibited a linear response in two concentration ranges: from 0.95 to 10 µmol L-1 and from 10 to 140 µmol L-1, with the mean sensitivity of 6.27 nF µmol-1 L (88.67 nF µmol-1 L cm-2) and 0.56 nF µmol-1 L (7.84 nF µmol-1 L cm-2), respectively. The limit of detection was evaluated as 28 nmol L-1. The specificity of the proposed sensor toward other antibiotics, amoxicillin and ciprofloxacin, was examined. The immunosensor was successfully employed to quantify TC in a tablet form and in a matrix of river water.

Bioelectrocatalytic and electrochemical cascade for phosphate sensing with up to 6 electrons per analyte molecule.

Despite the availability of numerous electroanalytical methods for phosphate quantification, practical implementation in point-of-use sensing remains virtually nonexistent because of interferences from sample matrices or from atmospheric O2. In this work, phosphate determination is achieved by the purine nucleoside phosphorylase (PNP) catalyzed reaction of inosine and phosphate to produce hypoxanthine which is subsequently oxidized by xanthine oxidase (XOx), first to xanthine and then to uric acid. Both PNP and XOx are integrated in a redox active Os-complex modified polymer, which not only acts as supporting matrix for the bienzymatic system but also shuttles electrons from the hypoxanthine oxidation reaction to the electrode. The bienzymatic cascade in this second generation phosphate biosensor selectively delivers four electrons for each phosphate molecule present. We introduced an additional electrochemical process involving uric acid oxidation at the underlying electrode. This further enhances the anodic current (signal amplification) by two additional electrons per analyte molecule which mitigates the influence of electrochemical interferences from the sample matrix. Moreover, while the XOx catalyzed reaction is sensitive to O2, the uric acid production and therefore the delivery of electrons through the subsequent electrochemical process are independent of the presence of O2. Consequently, the electrochemical process counterbalances the O2 interferences, especially at low phosphate concentrations. Importantly, the electrochemical uric acid oxidation specifically reports on phosphate concentration since it originates from the product of the bienzymatic reactions. These advantageous properties make this bioelectrochemical-electrochemical cascade particularly promising for point-of-use phosphate measurements.

Flow manifold for chemical H-point standard addition method implemented to electrochemical analysis based on the capacitance measurements.

The paper presents a novel analytical method for electrochemical potassium determination using gold electrodes with self-assembled thiol monolayers (SATMs) deposited on its surface. The whole analytical procedure was carried out in a dedicated flow manifold using capacitance detection mode. The terminal functional groups on the surface of the dielectric monolayer interacts selectively with the analyte, changing the thickness of the layer depending on the amount of the analyte and the applied voltage, resulting in a change in the registered dielectric capacitance. New calibration approach based on the Chemical H-point Standard Addition Method (C-HPSAM), allowing both specific (proportional) and unspecific (constant) interference effects caused by sodium ions to be corrected, was applied. The calibration method is based on the registration of the calibration graphs by the standard addition method (SAM) three times in such different chemical conditions, which are able to differentiate the slope of each graph. The C-HPSAM was applied for the first time in electrochemical analysis. As a chemical parameter differentiating the sensitivity of the calibration graphs, the concentration of ionic strength stabilizer (ethylenediamine) was used. In order to improve the analytical procedure, to make it faster and automated, the dedicated flow system was applied. The constructed flow system was composed of several modules individually dedicated to the appropriate step of the whole analytical procedure: electrochemical cleaning of work electrode surface, adsorption of SATMs and analytical calibration. The calibration curves were obtained in the range of 0.1-0.9 mmol L-1 with good linearity (R2 = 0.996 ±â€¯0.001) and the LOD and LOQ of 28.6 and 85.8 µmol L-1, respectively. The proposed method was employed for potassium determination in highly mineralized water, juice and pharmaceutical samples without any special pretreatment.