Paithoon Prasertying,^a,b,c Nanthatchaphon Jantawong,^a,b Thitaporn Sonsa-ard^,a,b Thinnapong
Wongpakdee,^a,b Nuttamon Khoonrueng,^a,b Supatana Buking^d and Duangjai Nacapricha ^*a,b
a Flow Innovation-Research for Science and Technology Laboratories (Firstlabs), Thailand. E-mail: dnacapricha@gmail.com ^b
Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok, 10400 Thailand c Center of Excellence on Agricultural Biotechnology (AG-BIO/PERDO-CHE), Bangkok, 10900 Thailand ^d Office of Police Forensic Science, Royal Thai Police, Bangkok, 10330 Thailand

This work presents the first planar three-electrode electrochemical sensor comprising local gold
leaf as the working electrode and printed, or hand-drawn, counter and reference electrodes, respectively.
The gold leaf was mounted on a polyvinyl chloride (PVC) adhesive sheet (15 mm × 30 mm) and covered
with a second PVC sheet printed with the counter and reference electrodes. This sheet has a 3 mm circle
and a 2 mm × 3 mm rectangle removed to expose the gold electrode area and electrical contacts,
respectively. A third shorter insulating layer with a 10 mm circular hole was placed on top to delineate
the sensing area of all electrodes. The sensor displayed expected performances in various modes of
operation, such as cyclic voltammetry, square wave voltammetry and anodic stripping voltammetry. For
the latter mode, the limit of detection of Pb(II) was 3.2 μg L−1, compliant with regulation for drinking
water (10 μg L−1 Pb(II)). Although designed as a disposable unit, the electrode is effective for up to 200
cycles and applicable for multiple use. The gold leaf was modified by electrodeposition of the gold
network and large nano-size gold particles which significantly enhanced the sensitivity of all
voltammetric sensing, giving lower limits of detection. For stripping voltammetry, the electroplating
structure modification improved the simultaneous detection of lead and copper, with the copper response
increasing 6-fold. The device has the capability of on-site identification of copper/lead bullets from
gunshot residues within 6 min.