Development of portable electrochemical sensor in detecting xylazine for forensic investigation

Xylazine is a non-narcotic medication and its misuses have been reported in facilitating robbery and rape cases due to its colourless, scentless, and tasteless nature. It potentially poses severe threat to the society and communities, especially when dealing with borders of countries having different legal status. Therefore, this study was aimed to develop simple, low cost, portable, sensitive, fast response and without pre-treatment electrochemical sensor to facilitate forensic investigation. Firstly, an electrochemical sensor was fabricated and developed based on graphene nanoplatelets (GNPs) modified screen-printed carbon electrode (SPCE), and subsequently determined by adsorptive stripping voltammetry (AdSV). Scanning electron microscope and cyclic voltammetry were used to characterise the surface morphology and electrochemical behaviour of xylazine on GNPs/SPCE. The loading of GNPs for modification, pH of electrolyte, accumulation potential and accumulation time of AdSV were also optimised. Under the optimal conditions, the sensor provided linear readings at the concentration range of 0.4 – 6.0 μg mL-1 and 6.0 – 80.0 μg mL-1 . The limit of detection (LOD) and the limit of quantitation (LOQ) were determined as 0.1 μg mL-1 and 0.4 μg mL-1 , respectively. Good reproducibility (3.57 - 6.85%) was also reported. Application of GNPs/SPCE on xylazine-spiked drinks also demonstrated good recoveries between 80.8 ± 0.2 and 108.1 ± 0.3%. GNPs/SPCE was further improved with development of an electrochemical paper-based analytical device (ePAD). The ePAD was fabricated using a craft cutter printer and low-tack transfer tape to create the three-electrode template mask. Graphene ink was then coated on the paper by screen-printed technique and further improved with nano coral-like polyaniline (PANI). The PANI/ePAD sensor was tested by analysing xylazine through AdSV. The fabrication and operating conditions for PANI/ePAD were optimised, where PANI was found to have provided a larger effective surface area, promoting the charge transfer between xylazine and electrode surface. Linearity was obtained in the ranges of 0.2 - 5.0 μg mL-1 and 5 - 100 μg mL-1, with LOD and LOQ of 0.06 μg mL-1 and 0.22 μg mL-1, respectively. PANI/ePAD sensor also showed good reproducibility (1.52 – 4.79%) and good recoveries between 85.0 ± 3.0% and 105.0 ± 2.0% for the determination of xylazine in beverage samples. The portable electrochemical sensors for the detection of xylazine were successfully developed for the first time to test for the presence of xylazine. They could serve to support the forensic analysis, aiding the screening and monitoring procedures