## 4 Nanocomposite as Sensors
### QD-GO Composites/Hybrids  
Graphene and its derivatives have attracted much attention in different areas of research because of their good physical and chemical properties [82]. Graphene oxide (GO) can be best described as a single-layer planar hexagonal array of carbon atoms to which different functional groups such as carboxylic acid, hydroxyl and epoxy are attached [83]. These carbon-based materials are emerging as the most promising platform for the preparation of nanocomposites for different sensing of NACs and PAHs [84].  
Graphene, graphene oxide (GO) and reduced graphene oxide (rGO) can be easily combined with semiconductor QDs to form composites with enhanced sensitivity and selectivity towards the detection of organic pollutants [85]. Graphene, GO and their composites have been widely used for wastewater treatment because of their high adsorption capacity. The \(\pi\)-electron system of graphene and its derivative make them suitable modifiers of QDs for the fluorescence detection of \(\pi\)-electron-rich organic pollutants. [PERSON] et al. (2016) explored rGO-based sensors for the fluorescence detection of both PAH analytes and NACs. The results of their study showed an enhancement of PL intensity of the sensor by the pollutants (Figure 6) [67]. In 2016 and 2017 [PERSON] et al. investigated the selectivity and sensitivity of a QD-GO composite for the detection of PAHs [4; 60]. Their study showed that PAHs could be detected by a QD-GO composite through an enhancement mechanism. Recently, [PERSON] et al. synthesized CuInS2 quantum dot (QD) and graphene oxide (GO) nanocomposites as a fluorescent sensor for the detection of kanamycin [82].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Semiconductor Sensor** & **Modifier** & **Detection Technique** & **LOD** & **Detection Range** & **Pollutant/Analve** & **References** \\ \hline GO-CdSeTe/ZnS & L-cysteine & Fluorescence & \(2.26\times 10^{-9}\)\(\mu\)M & \(0.1\)–\(0.5\times 10^{-6}\) & PAHs & [4] \\ GO-CdSeTe/ZnS/ZnS & L-cysteine & Fluorescence & \(0.19\) mg/L & \(0.1\)–\(0.5\times 10^{-6}\) & PAHs & [60] \\ CuInS2 & BSA & Fluorescence & \(28\) nmol/L & \(5.0\times 10^{-8}\)-\(3\times 10^{-6}\) & Nitro-aromatics & [61] \\ CdTe & L-cysteine & & & & & [41] \\ Fluorescence & \(1.1\) nM & Nitroamatics & & & [73] \\ CdS & lysozyme & Fluorescence & & \(0.1\) & \(5\times 10^{-7}\)-\(1.5\times 10^{-5}\) & Nitro-aromatics & [48] \\ CdTe(S) & polyacrylamide & Fluorescence & \(2.1\) nmol/L & \(0\)–\(7.0\times 10^{-9}\) & Nitro-aromatics & [74] \\ CdTe & (TGA)/CD & Fluorescence & \(0.085\)\(\mu\)M & \(5\times 10^{-7}\)-\(7.5\times 10^{-5}\) & PAHs & [40] \\ CdSe & \(1\),4-dihydroxy-oncotinamide & Fluorescence & \(21\times 10^{-8}\) mol/L & & Nitro-aromatics & [75] \\ CdSe/ZnS & \(1\),4-dihydroxy-oncotinamide & Fluorescence & \(0.1\) nM & & & RDX & [76] \\  & adenine dinucleotide (NADH) & & \(0.4\) nM & \(1.0\times 10^{-7}\)-\(1.58\times 10^{-5}\) & & [75] \\ CQDs & -NH\({}_{2}\) & & \(27\) nM & \(5.5\times 10^{-8}\)-\(5.5\times 10^{-7}\) & & [76] \\ CdSe & PAMAM-Cd dendrimer & & \(5.5\times 10^{-8}\)-\(5.5\times 10^{-7}\) & & [77] \\ CQDs & -NH\({}_{2}\) & & \(2.13\times 10^{-7}\) & \(0\)–\(1.0\times 10^{-6}\) & & [77] \\ CQDs & Sulfur & & \(9.3\times 10^{-8}\) & \(1.0\times 10^{-9}\)-\(9.9\times 10^{-5}\) & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Effect of different materials on the limit of detection of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.