## 4 Conclusions  
This paper has shown proof-of-principle studies to demonstrate the feasibility of fabricating a functioning amperometric glycerol biosensor based on an MB-SPCE with immobilised GLDH and NAD\({}^{+}\). This device is convenient to use due to its planar geometry, which permits a microlitre volume of liquid sample or standard solution to be deposited on the biosensor's surface and interrogated using a chronoamperometric procedure. Such chronoamperometric methods can nowadays be performed with small, commercial hand-held potentiostats, which allow samples to be analysed outside of the laboratory. Our approach utilises the most popular industrial method for fabricating biosensors, screen printing with low-cost carbon materials. It should be noted that the one-shot glucose biosensors for diabetes monitoring are fabricated using screen-printing technology, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \multicolumn{3}{c}{**Recovery (gL\({}^{-1}\))**} \\ \cline{2-4}  & \multicolumn{2}{c}{**Biosensor**} & \multicolumn{2}{c}{**Spectrophotometry**} \\ \hline
1 & 12.58 & 11.70 \\
2 & 12.46 & 11.94 \\
3 & 11.74 & 11.94 \\
4 & 10.06 & 12.01 \\
5 & 12.58 & 11.94 \\ Mean & 11.88 1  & 11.91  \\ SD & 0.964 & 0.097 \\ CV (\%) & 8.08 & 0.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Recovery of glycerol content (in gL\({}^{-1}\)) from red wine using a glycerol biosensor and Spectrophotometry. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Biosensor Fabrication** & **Technique** & **LOD** & **Linear Range** & \begin{tabular}{c} **Potential for Commercialisation** \\ \end{tabular} & **References** \\ \hline GLDH/NAD\({}^{+}\) on a meldolas blue-screen-printed carbon electrode & Chronoamperometry Applied potential 0.87 mM & 1.0 to 7.5 mM & Yes & \begin{tabular}{c} Our approach approach \\ Appl. Sci. \\ 2024 \\ \end{tabular} \\ GLDH/NAD\({}^{+}\)/Fe-S on a gold electrode & \begin{tabular}{c} Ampperometry in a \\ stirred solution \\ Applied potential \\ +0.6 V vs. Ag/AgCl \\ \end{tabular} & 0.43 \(\mu\)M & 1 \(\mu\)M to 0.1 mM & No & [25] \\ Alcohol dehydrogenase from Pseudomonas putida immobilised on graphite rod electrode modified with carbon nanotubes and a redox mediator tetrathiafulvalene. & \begin{tabular}{c} Ampperometry in a \\ stirred solution Applied \\ potential +0.05 V vs. \\ SCE \\ \end{tabular} & 18 \(\mu\)M & 0.05 to 10 mM & No & [27] \\ GLDH/NAD\({}^{+}\)/poly(o-phenylenediamine/carbon paste tube electrode & \
\begin{tabular}{c} Ampperometry in a \\ stirred solution Applied \\ potential 0.0 V vs. \\ Ag/AgCl \\ \end{tabular} & 0.43 \(\mu\)M & 1 \(\mu\)M to 100 mM & No & [26] \\ Glycerol kinase/glycerol-3-phosphate nanoparticles (NPs) onto graphene oxide nanoparticles (GrONPs) modified pencil graphite (PG) electrode. &
\begin{tabular}{c} Ampperometry \\ Applied potential +0.6 V \\ vs. Ag/AgCl \\ \end{tabular} & 0.002 \(\mu\)M & 1\(\mu\)M to 60 mM & No & [24] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Brief fabrication details, operating technique, and performance of glycerol biosensors. and nowadays, these biosensors have the greatest market share. A simple, single-step enzyme deposition method readily converts the resulting planar transducers into biosensors. In conclusion, our developed MB-SPCE glycerol biosensors can be used as a rapid and efficient analytical method for determining glycerol in wines. This makes the current method suitable for commercialisation and applicable for the large-scale control of alcoholic beverages. In the future, we will investigate approaches to extend the linear range beyond the limits (1-7.5 mM) described in this paper. This should be readily feasible by adjusting the enzyme and co-factor loadings as well as the biosensor operation. This can help form a platform for developing a novel rapid technology for point-of-test evaluation of glycerol and to assess the practical applicability of the MB-SPCE glycerol biosensors in real-world wine production and quality.