## 4 Conclusions  
A novel and highly sensitive sensor based on \(\text{ERGO}/\text{NiNP}\) nanocomposite material-modified electrodes was developed for SY determination. The method, using cyclic voltammetry techniques, is a particularly robust process. Starting from low-cost graphene oxide and nickel salt materials, a repetitive cyclic potential scan rapidly leads to the deposition of ERGO/NiNP nanocomposites onto the GCE surface, ready to use for sensing applications. The FE-SEM images confirm a homogeneous deposition of nickel and ERGO nanostructured materials, in which nickel nanoparticles present a very uniform distribution with an average size of 20-30 nm into the ERGO matrix. The ERGO-NiNP-modified surfaces exhibit remarkably high performance for SY detection with a low detection limit of 3.7 nM and high sensitivity of 7 uA/uM, which matched the HPLC probed value with low relative error. The prepared GCE/ERGO-NiNP sensor could be cleaned and reused for multi-measurements even in real samples. This work demonstrated that electrochemical techniques present an efficient route for the fabrication of graphene/metal nanocomposite materials. This ERGO-NiNP nanocomposite presents great potential for developing reliable and portable sensors for on-site monitoring of toxics in food and the environment. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **Added (nM)** & **Expected (nM)** & **Found (nM)** & **RSD (\%) (\(n\) = 3)** & **Recovery (\%)** & **By HPLC (nM)** & **Relative Error (\%)** \\ \hline \multirow{2}{*}{Mirinda} & & & 127.8 & 2.50 & & 127.6 & 0.2 \\ \cline{2-7}  & & & 235.4 & 3.85 & 103.3 & & \\ \hline \multirow{2}{*}{Samurai} & & & 120.5 & 4.45 & & 128.8 & \(-\)6.4 \\ \cline{2-7}  & 100 & 228.8 & 229.3 & 4.03 & 100.2 & & \\ \hline \multirow{2}{*}{Number 1} & & & 111.2 & 5.84 & & 109.40 & 1.6 \\ \cline{2-7}  & 100 & 211.2 & 228.9 & 6.48 & 108.4 & & \\ \hline \multirow{2}{*}{Sting} & & & 86.4 & 3.93 & & 90.00 & \(-\)6.1 \\ \cline{2-7}  & 100 & 186.4 & 171.1 & 4.10 & 91.8 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: SY detection in soft drink samples using the electrochemical sensor and HPLC methods. Figure 8: Typical DPV responses of the GCE/ERGO-NiNPs for SY detection in Mirinda: acetate buffer pH 4 (black), addition of 7 uL Mirinda sample (red), addition of 100 nM SY (green). **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12052614/s1](https://www.mdpi.com/article/10.3390/app12052614/s1)]([https://www.mdpi.com/article/10.3390/app12052614/s1](https://www.mdpi.com/article/10.3390/app12052614/s1)), Figure S1. First and second CVs (scan rate = 50 mV s\({}^{-1}\)) of GCE in 0.1 M LiClO4 containing 1 mg ml\({}^{-1}\) GO + 0.5 mM NiCl\({}_{2}\). Figure S2. EDX of ERGO-NiNPs deposited onto ITO substrate using 10 CV scans between +0.6 \(\div\) -1.5V/ SCE in 0.1 M LiClO4 electrolyte solution containing 1 (mg mL\({}^{-1}\)) GO + 0.5 mM NiCl\({}_{2}\). Figure S3. XRD pattern of ERGO-NiNPs deposited onto ITO substrate using 10 CV scans between +0.6 \(\div\) -1.5V/ SCE in 0.1 M LiClO4 electrolyte solution containing 1 (mg mL\({}^{-1}\)) GO + 0.5 mM NiCl\({}_{2}\). Figure S4. Cyclic voltammograms of GCE, GCE/ERGO and GCE/ERGO-NiNPs in 0.1 mM KCl + 1 mM K3 Fe(CN)/6/K4 Fe(CN)6 with the scan rate varying from 20 to 400 mV s\({}^{-1}\) namely, 20 (black), 50 (red), 100 (green), 200 (blue), 300 (cyan), 400 (magenta) mV s\({}^{-1}\). And (B) Variation of the peak currents towards square root of the scan rate. Figure S5. DPV of GCE/ERGO-NiNPs surface in acetate buffer pH 4 + 0.5 uM SY at different scan rates from v = 10-35 mVs\({}^{-1}\) (Es varying from 5 to 17.5 mV; ts = 500 ms; EP = 50 mV; tp = 200 ms, Idt = 100 ms). Accumulation time of 2 minutes at 0 V/SCE. Figure S6. DPV of GCE/ERGO-NiNPs surface in acetate buffer pH 4 + 0.5 uM SY at scan rate v = 20 mV s\({}^{-1}\) with different step potentials from Es = 4-12 mV, ts/tp/Lgt = 10/4/1/2. Accumulation time of 2 minutes at 0 V/ECS. Figure S7.