*3.4. Square Wave Voltammogram (SWV)*

Meanwhile, SWV is the fastest and the most sensitive pulse voltammetry technique. The detection limits can be compared with those of chromatographic and spectroscopic techniques. In addition, the analysis of the characteristic parameters of this technique also enables the evaluation of the kinetics and mechanism of the electrode process under study [71,73]. According to Marie et al., the lower limit of detection value means the lowest concentration of glucose (analyte) that can be detected by the device [74].

Zhang et al. constructed an aqueous ammonia sensor using a low cost, high sensitivity, and great stability construct based on Ni foam-supported silver/polypyrrole and platinum nanoparticles electrode (Pt-Ag/PPy-NiF). They found that the ammonia sensor showed a sensitivity of 0.089 mA μM−<sup>1</sup> with a detection limit of 37 nM and a wide linear range, as well as possessing a good anti-interference capability against many common ions found in water. The Pt-Ag/PPy-NiF electrode possessed a lower detection limit and higher sensitivity compared to most electrochemical aqueous ammonia sensors. Its excellent performance can be mainly attributed to the large specific surface area of the electrode and great electrocatalytic ability of Pt nanoparticles [59].

Salunke et al. prepared a sensor device by electrodepositing gold nanoparticles onto a single PPy nanowire for arsenic detection. They found that the sensitivity of Au-NPs decorated Ppy-NW towards arsenic (for two set of as conc. range) was 0.22 and 4.38 μM−<sup>1</sup> with a good detection limit of 0.32 μM. Their result was better in respect of sensitivity and LOD, and this could be due to the change in sensor dimensions where they used nanowire as a base material and the gold nanoparticles as the sensing material. This led to the finding of a high surface area as being a dimension factor for the enhancement of sensor sensitivity with rapid detection and accuracy [75].

In other work done by Zaabal et al., they studied a polypyrrole modified glassy carbon electrode (PPy/GCE) for the electrochemical sensing of adefovir (ADV). ADV is a broad-spectrum antiviral agent whose action is as a DNA polymerase inhibitor. The detection limit of ADV obtained was 3.10 nM. Moreover, they also determined ADV in human serum and urine and found that the detection limit was 0.06 μM and 0.04 μM, respectively. Their detection limit value was much lower compared to the findings in other research works [76,77]. This showed that PPy/GCE can be an effective alternative sensor for the electrochemical determination of ADV in commercial pharmaceutical dosage forms and biological fluids.
