# Advances in Graphene Field Effect Transistors (FETs) for Annine Neurotransmitter Sensing
## 3 Amine Neurotransmitter Detection via GFETs
### Dopamine
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Neurotransmitter/Targeted** & **FET Technology** & **Gate Material** & \begin{tabular}{c} **Functionalisation** \\ **Approach** \\ \end{tabular} & **LOD** & **Ref.** \\ \hline \multirow{3}{*}{\begin{tabular}{c} SER \\ **(C\({}_{10}\)H\({}_{12}\)N\({}_{2}\)O)** \\ \end{tabular} } & \multirow{3}{*}{FET} & \multirow{3}{*}{\
\begin{tabular}{c} APDAPmer \\ \end{tabular} } & CVD graphene &
\begin{tabular}{c} electrode/fing \\ \end{tabular} & 10 pM & [163] \\ \cline{2-5}  & & & & & \\ \cline{1-1} \cline{3-5}  & & & & & \\ \cline{1-1} \cline{3-5}  & & & & & \\ \cline{1-1} \cline{3-5}  & & & & & \\ \cline{1-1} \cline{3-5}  & & & & & \\ \hline \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \multicolumn{5}{c}{} \\ \hline \hline
**Histamine (C\({}_{5}\)H\({}_{9}\)N\({}_{3}\))** & FET & CVD graphene/CNTs & Gold nanoparticles & 100 nM & [180] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._Nafion exchange membranes can be dissolved in ethanol, their sensors allowed for reusability. Further work involved using pyrene-1-boronic acid (PBA) and 11-mercaptoethanolenoic acid-gold nanoclusters (MUA-AuNCs) [159] to bind the thiol groups on the linker surface with the carboxyl groups on 11-MUA and the \(\pi\)-\(\pi\) stacking between graphene's surface and the aromatic rings of the linker. As a result, the sensor's selectivity was enhanced while its LOD decreased to 0.01 uM. Organic electrochemical transistors (OECTs) have emerged as robust alternatives to traditional sensors [191] due to their intrinsic amplifying characteristics [192], their biocompatibility, their ease of fabrication, their fast switching speed [193], and their operation in aqueous solutions as an ion-to-electron converter [194]. [PERSON] et al. [160] demonstrated OECT sensors with a coplanar GFET configuration for selective and sensitive DA detection. The platinum (Pt) electrode surface was modified with chitosan and Nafion, similar to previously disclosed OECT-based enzymatic sensors [183; 195]. The study revealed that Pt devices' effect on V\({}_{\text{G}}\) changed due to DA's reactivity. The LOD for Pt electrodes modified with chitosan and Nafion were 100 nM and 50 nM, respectively. When the Pt electrodes were coated with graphene and rGO, the LOD decreased to 5 nM for graphene-based electrodes and 50 nM for rGO-based electrodes when functionalised with Nafion. The stability of a liquid-ion solution is important in FET biosensing. [PERSON] et al. [161] developed a non-enzymatic DA sensor based on organic FET (OFET) technology with top-gated configuration and Pt nanoparticle-decorated rGO (Pt_rGO). The solution was spin-coated and secured on a large-area chemical vapour deposition (CVD)-grown graphene sheet, creating a stable and uniform receptor layer. DA molecules adhered to Pt_rGO's surface through \(\pi\)-\(\pi\) interactions with rGO's benzene ring [196; 197; 198; 199; 200]. Pt nanoparticles catalysed DA molecules into DA-O-quinone molecules, reducing the number of holes in the rGO structure and I\({}_{\text{SD}}\). The FET sensor demonstrated a concentration-dependent decrease in I\({}_{\text{SD}}\) and a quick real-time response (<1 s) and was on par with DA in the presence of interferements, with a LOD of 10 nM. The sensor monitored minimal signal variations in sensitivity over 4 weeks of testing. Wafer-scale graphene synthesis and biosensor fabrication can enhance device uniformity and enable integrated designs for high-throughput measurements in real-world NT biosensing [201; 202; 203; 204; 205]. An aptamer is an approach considered in developing GFET biosensors, offering high affinity, selectivity, flexibility, affordability, and ease of manufacturing [206; 207].