Simple and Economical Analytical Voltammetry in 15 μL Volumes: Paracetamol Voltammetry in Blood Serum as a Working Example

Innovative localized surface plasmon resonance sensing technique for a green spectrofluorimetric assay of ketoprofen, paracetamol and chlorzoxazone in pharmaceutical preparations and biological fluids

A green, quick and sensitive spectrofluorimetric technique was investigated and validated for the assay of three different drugs namely, ketoprofen (KPN), paracetamol (PAR), and chlorzoxazone (CLX). The method is based on fluorescence quenching of the fluorescence probe, silver nanoparticles (SNPs). The fluorescence quenching of SNPs may be attributed to the complexation between each of the studied drugs with SNPs. The fluorescence of SNPs alone or after complexation with the studied drugs were measured at 485 nm (λ _ex 242 nm) without the need to extract the formed complex. Chemical reduction was employed for preparing SNPs, where silver nitrate was reduced by sodium borohydride in deionized water without adding organic stabilizer. SNPs were found soluble in water, had high stability and had a narrow emission band. The studied drugs were found to decrease the fluorescence of SNPs significantly through static quenching according to Stern-Volmer equation. Factors affecting the reaction between the drugs and NPs were carefully examined and optimized. Using the optimum conditions, the difference in the fluorescence intensity of SNPs before and after complexation with the studied drugs was in a good linear relationship with the concentration of the studied drugs, where (R ² = 0.9998, 0.9998 and 0.9991) in the ranges of 0.5-5.0, 0.15-3.0 and 0.5-9.0 μg mL^-1 for KPN, PAR and CLX, respectively. Validity of the proposed method was investigated according to ICH recommendations. The proposed technique was also employed for the analysis of each of the three drugs in commercial or laboratory prepared tablets and in spiked human plasma with very good recoveries as well as high level of accuracy and precision. This method was intended to the analysis of the proposed drugs in their single formulation and single drug administration. The suggested technique is considered an eco-friendly method, as it uses water as the safest and least expensive solvent. Moreover, the recommended technique does not involve solvent extraction of the formed complexes. Greenness assessment of the suggested procedure was accomplished by applying the four standard assessment tools. Consequently, the recommended method can be used in the routine quality control analysis of the cited drugs with minimum harmful effect on the environment as well as the individuals.

An electrochemical method for detecting the biomarker 4-HPA by allosteric activation of Acinetobacterbaumannii reductase C1 subunit

The C1 (reductase) subunit of 4-hydroxy-phenylacetate (4-HPA) 3-hydroxylase (HPAH) from the soil-based bacterium Acinetobacterbaumannii catalyzes NADH oxidation by molecular oxygen, with hydrogen peroxide as a by-product. 4-HPA is a potent allosteric modulator of C1, but also a known urinary biomarker for intestinal bacterial imbalance and for some cancers and brain defects. We thus envisioned that C1 could be used to facilitate 4-HPA detection. The proposed test protocol is simple and in situ and involves addition of NADH to C1 in solution, with or without 4-HPA, and direct acquisition of the H₂O₂ current with an immersed Prussian Blue–coated screen-printed electrode (PB-SPE) assembly. We confirmed that cathodic H₂O₂ amperometry at PB-SPEs is a reliable electrochemical assay for intrinsic and allosterically modulated redox enzyme activity. We further validated this approach for quantitative NADH electroanalysis and used it to evaluate the activation of NADH oxidation of C1 by 4-HPA and four other phenols. Using 4-HPA, the most potent effector, allosteric activation of C1 was related to effector concentration by a simple saturation function. The use of C1 for cathodic biosensor analysis of 4-HPA is the basis of the development of a simple and affordable clinical routine for assaying 4-HPA in the urine of patients with a related disease risk. Extension of this principle to work with other allosteric redox enzymes and their effectors is feasible.

Rapid sub-micromolar amperometric enzyme biosensing with free substrate access but without nanomaterial signalling support: oxidase-based glucose detection as a proof-of-principle example

High-sensitivity electrochemical glucose biosensing has so far been possible only through incorporation of nanomaterials into the glucose oxidase-(GOx) containing polymer layer on the detector surface. Here, as a conceptionally novel simplified option, pure gelatin thin films with covalently attached GOx were used to convert platinum (Pt) disk electrodes into rapidly responding amperometric glucose probes with a sub-micromolar limit of detection. The advanced enzymatic tools are easy to make and, as is crucial for a focus on waste minimization, green and sustainable, through restriction of sensor modification to readily available economical materials.