Andrei V. Okhokhonin.

This work presents a voltammetric immunosensor based on a screen‑printed carbon electrode modified with a composite layer of multi‑walled carbon nanotubes and polydopamine, which serves as a platform for covalent antibody immobilization. The sensor employs an immobilized redox label, an original bipyridinium derivative (MFB), which exhibits a pronounced electrochemical response in the cathodic potential region in aqueous media. Using a cathodic redox label in the negative potential region avoids interference from biological oxidants that usually complicate anodic detection. MFB immobilized in the polydopamine film provides stable signals without external redox mediators, enabling reagent-free analysis. The electrochemical behavior of MFB in aqueous buffer solution and within the modifier layer on the surface of a glassy carbon electrode was studied in detail. The kinetic parameters of electron transfer, calculated from the experimental data, together with the analytical and operational characteristics, enabled the use of MFB as a redox probe in the immunorecognition layer for the sensitive voltammetric determination of carcinoembryonic antigen (CEA) and Escherichia coli bacteria. Under the selected operating conditions, the linear range for CEA was 1–20 ng/mL with a detection limit of 0.086 ng/mL (R² = 0.995, n = 10, P = 0.95). For E. coli, the linear range was 10–10⁵ CFU/mL with a detection limit of 1 CFU/mL (R² = 0.997, n = 10, P = 0.95). The proposed approach is promising for the development of portable point‑of‑care diagnostic systems in clinical oncology, infectious disease diagnostics, and environmental monitoring.

Infectious diseases pose a serious threat to global public health, and the COVID-19 pandemic has clearly demonstrated the critical need for rapid, accurate, and accessible diagnostic tools. Portable point-of-care analytical systems provide an alternative to conventional laboratory methods such as ELISA and PCR, enabling rapid pathogen identification outside centralized facilities, which is essential for timely diagnosis and treatment decisions. Beyond initial detection, such systems also hold potential for quantitative monitoring of viral or bacterial load, relevant for assessing disease stage and therapy effectiveness. Electrochemical biosensing platforms most favorably combine the required analytical performance with broad possibilities for miniaturization, automation, and scaling. However, despite the exponential growth in publications, clinical translation and commercialization of such devices remain limited by insufficient stability and reproducibility of the bioreceptor layer, uncontrolled interfacial orientation, and matrix effects in complex biological samples. This review provides a critical analysis of current approaches to the directed structuring of the bioreceptor layer in electrochemical sensors, comparing biological recognition elements (antibodies, DNA/RNA probes) with synthetic and biomimetic alternatives (aptamers, engineered peptides, and molecularly imprinted polymers). Particular attention is given to the multifaceted roles of small organic molecules as structural elements — cross-linkers for oriented immobilization, redox mediators and electrocatalysts for signal transduction, and independent low-molecular-weight recognition ligands — for the design of next-generation electrochemical test platforms with operational characteristics tunable at the molecular level.

Several new derivatives of 2,2′‐bipyridines with a spacer group separated from the 2,2‐bipyridine fragment, namely, an ethynyl fragment, were obtained using the Sonagashira cross‐coupling reaction. The resulting derivatives were physically adsorbed on platinum electrode and were then used as activators of the catalytic activity of a platinum electrode in the reaction of cholesterol electrooxidation in an acetonitrile medium. Sensitivity, limit of detection and detectable concentration range were calculated, and the best results was established as 6.2±0.6 μA/mM, 0.08 mM and 0–0.3 mM, respectively. These results show that the prepared compounds adsorbed on platinum electrode are perspective systems for developing of new enzymeless cholesterol sensor based on them.

Fast and accurate determination of creatinine is critical in kidney function diagnostics. This paper discusses the usage of the metal-organic framework based on copper(II) and acetylenedicarboxylic acid (CuADCA) as a catalyst of electrochemical oxidation of creatinine, glucose and urea. CuADCA was synthesized by deprotonation with triethylamine for the first time. Successful synthesis was confirmed by FTIR and EDS. The material was characterized by SEM, EIS, and CV. CuADCA forms laminated-like flakes with diameter from 1 µm to 20 µm, which is consistent with the polymer-like structure. CV and EIS analyses showed that CuADCA immobilized on GCE acts as a catalyst in electrooxidation reaction of glucose, urea, and creatinine. The sensitivity of creatinine detection, 1057±99 µA/mM, was higher than the detection sensitivity of glucose and urea by more than 100 times with the limit of detection of 2 µM, so CuADCA is a promising material for further development of enzymeless sensors for creatinine.

In this paper a new enzymeless electrochemical glucose sensor based on carboxylated multiwalled carbon nanotubes (cMWCNT) with immobilized nickel (II) acetylacetonate (NiL) as electrocatalyst and molecularly imprinted polymer fabricated through electrostatic self‐assembling of polyethyleneimine (PEI) crosslinked with glutaric dialdehyde (GDA). The electrocatalytic properties of NiL and PEI‐cMWCNT, PEI‐GDA and PEI‐glucose interactions is studied for the first time. Developed sensor demonstrates excellent electrocatalytic activity towards glucose oxidation and possessing high stability, sensitivity of 5897.42±161.00 μA ⋅ mM⁻¹ cm⁻², LOD of 0.138 mM and high selectivity in the presence of creatinine, L‐alanine, glycine, D‐glutamine, uric acid, L‐ascorbic acid, urea and BSA.

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors’ application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the “test-tube to the smartphone”.

We present the results of synthesis and study of the electrocatalytic activity of gold and silver nanoparticles of different composition (individual metals, core–shell particles, nanoalloys, and particles synthesized electrochemically), immobilized on the surface of a glassy carbon electrode, with respect to cholesterol. A surfactant (cetyltrimethylammonium bromide) is selected to create an aqueous–organic emulsion of cholesterol. It is demonstrated that nanoparticles with a gold core and a silver shell with the regression equation of I = 1.4 × 10^–5c_chol + 5.8 × 10^–5 (R² = 0.97) and silver nanoparticles synthesized electrochemically with the regression equation of I = 1.0 × 10^–5c_chol + 3.0 × 10^–4 (R² = 0.95) possess optimal electrocatalytic characteristics.

Methods are developed for the non-enzymatic chronoamperometric determination of urea in blood serum and creatinine in model solutions imitating the composition of blood serum. The selectivity of...