Saisahas, Kasrin
(2022)
Development of portable electrochemical sensor in detecting xylazine for forensic investigation.
Masters thesis, Universiti Sains Malaysia.
Abstract
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.
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