Nitrite (NO2-) is widely used as an additive to extend the shelf life of food products. Excessive nitrite intake not only causes blood-related diseases but also has the potential risk of causing cancers. A disposable screen-printed electrode was modified with nano‑palladium decorated bismuth sulfide microspheres (nanoPd@Bi2S3MS/SPE), and integrated with a smartphone-interfaced potentiostat to develop a portable, electrochemical nitrite sensor. NanoPd@Bi2S3MS was prepared by the hydrothermal reduction of a Bi2S3MS and Pd2+ dispersion and drop cast on the SPE. The nanoPd@Bi2S3MS/SPE was coupled with a smartphone-controlled portable potentiostat and applied to determine nitrite in food samples. The linear range of the sensor was 0.01-500 μM and the limit of detection was 0.0033 μM. The proposed system showed good repeatability, reproducibility, catalytic stability, and immunity to interferences. The proposed electrode material and a smartphone-based small potentiostat created a simple, portable, fast electrochemical sensing system that accurately measured nitrite in food samples.
Xylazine and ketamine are psychoactive substances that may be encountered in drug-facilitated crimes, including their presence in beverages. Rapid and portable screening methods are therefore desirable for preliminary forensic analysis, particularly at the scene of investigation. This study developed a portable voltammetric sensor based on a screen-printed electrode modified with carbon graphite paste ink (CGP-ink/SPE) for the presumptive detection of xylazine and ketamine in spiked beverage samples using differential pulse voltammetry (DPV). Electrochemical characterization showed that the oxidation of both xylazine and ketamine was diffusion-controlled and irreversible. Key experimental parameters, including the volume of CGP-ink, pH of buffer, and DPV conditions, were systematically optimized to improve electrochemical response. Under optimized conditions, the CGP-ink/SPE exhibited linear response ranges of 2.0 to 50 μg mL-1 for xylazine and 2.0 to 70 μg mL-1 for ketamine, with a detection limit of 0.62 μg mL-1 and 0.60 μg mL-1, respectively. The sensor demonstrated excellent repeatability and reproducibility, as well as good recoveries of 98 ± 3% to 103 ± 1% for xylazine and 98 ± 1% to 104 ± 1% for ketamine in drug-spiked beverage samples. The developed CGP-ink/SPE provides a simple, rapid, and portable approach for the dual presumptive screening of xylazine and ketamine in beverages and highlights its potential for supporting forensic investigations of drug-facilitated crimes.