All-solid-state paper-based potentiometric combined sensor modified with reduced graphene oxide (rGO) and molecularly imprinted polymer for monitoring losartan drug in pharmaceuticals and biological samples

A cost-effective, highly selective and sensitive paper-based potentiometric combined sensor for losartan potassium drug (LOS) is fabricated, characterized and used for the drug monitoring. The sensor consists of 2 strips of filter paper (20 × 5 mm each) as platform, each imprinted with 4 mm diameter circular spot of carbon. One carbon spot is covered by a reduced graphene oxide (rGO) for use as a substrate for the recognition sensor and the other without rGO is used for the reference electrode. LOS molecularly imprinted drug polymer (MIP) is applied onto the graphene oxide containing strip to act as a drug recognition sensing material and a solid-state polyvinyl butyral (PVB) is applied onto the second carbon spot to act as a reference electrode. Performance characteristics of the combined sensor are examined with chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). Increase effect of rGO on the interfacial double-layer capacitance of the sensing membrane and consequently on the potential stability is confirmed. The developed combined sensor (strip cell) displays a Nernstian slope of −58.2 ± 0.3 mV/decade (R² = 0.9994) over the linear range 8.5 × 10⁻⁷ - 6.9 × 10⁻² M with a detection limit of 2.7 ± 0.3 × 10⁻⁷ M. The sensor shows remarkable selectivity toward various related compounds especially those commonly used by the COVID-19 patients such as paracetamol, ascorbic acid and dextromethorphan. The assay method is validated and proved to be satisfactory for direct potentiometric determination of LOS-K in some pharmaceutical formulations and in spiked human urine samples. An average recovery of 96.3 ± 0.3–98.7 ± 0.6% of the nominal or spiked concentration and a mean relative standard deviation of ±0.6% are obtained. The use of an indicating and a reference electrodes combined into a single flexible disposable paper platform enables applications to a minimum sample volume due to the close proximity of the responsive membrane and the liquid junction. The efficiency of the proposed sensor in complex urine matrix suggests its application in hospitals for rapid diagnosis of overdose patients and for quality control/quality assurance tests in pharmaceutical industry.