*3.2. Limit of Detection (LOD)*

Voltammetry can be used to obtain quantitative information which is deduced from peak current intensity [48]. Usually, it is used to determine the sensitivity value of the sensor.

Sensitivity, analytical sensitivity, functional sensitivity, lower limit of detection (LOD), etc., are terms used to describe the smallest concentration of a measure that can be measured (detected) with statistical significance employing a given analytical procedure [67]. It is also defined as the minimum input quantity that can be distinguished with more than 99% reliability [68]. *LOD* is also a valuable quantitative measurement usually in the healthcare industry where it can be used as a biomarker in the detection of disease, environmental pollutants such as heavy metals, and other chemical contaminants that are part of the environmental liability in contemporary societies [69]. The value of the *LOD* can be determined through calculation using Equation (5).

The equation to calculate the *LOD* is:

$$LOD = \frac{\mathfrak{Z} \times SD}{\mathfrak{m}} \tag{5}$$

where *SD* is the magnitude of the error bar at blank while *m* is the slope of the calibration curve of the blank [69]. Before it can be calculated, a graph of current or current density with different concentrations of the sensing material needs to be plotted (Figure 9a).

**Figure 9.** Example graphs of current response with different concentrations of pyocyanin biomarker using a DPV analyzer where the calibration curve for the three different mediums (0.5 M PBS at pH 7.4 (blue), human urine (grey) and human saliva (red)) at the potential range of −0.8 V to 0 V (**a**) and DPV current response of pyocyanin (5–100 μM) in 0.5 M PBS (**b**) [70]. Reproduced with permission from [J.I.A.Rashid], [An electrochemical sensor based on gold nanoparticles-functionalized reduced graphene oxide screen printed electrode for the detection of pyocyanin biomarker in Pseudomonas aeruginosa infection]; published by [Elsevier], [2020].

The current peak (*i*p) value can be obtained either from the peak of a cyclic voltammogram (CV), differential pulse voltammogram (DPV), or square wave voltammogram (SWV). Most researchers use DPV and SWV to determine the current peak (Figure 9b). This is because of the high sensitivity of the technique compared to CV. In general, CV can provide essential information, such as the reversibility process and types of redox processes present in an analysis (matrix, analyte, and electrode); however, DPV and SWV are used for quantitative determinations [71].
