# Trends in Quantification of HbA1c Using Electrochemical and Point-of-Care Analyzers
## 4 Non-Enzymatic HbA1c Sensors Based on FV Detection Principle  
Several non-enzymatic superometric sensors have also been developed for FV-based HbA1c detection. FcBA-based quantification of FV was attempted using a glassy carbon \begin{table}
\begin{tabular}{c c c c c c} \hline
**Biosensors** & **Transducers** & **Type** & **Detection Range (HbA1c)** & **Sensitivity** & **LoD** & **Ref.** \\ \hline \multirow{8}{*}{**Immunousensors**} & Anti-HbA1c/MPA/Au & \multirow{2}{*}{DPV} & 7.5–20 ug/mL (0.1 M PBS) & \multirow{2}{*}{NA} & \multirow{2}{*}{NA} & \multirow{2}{*}{[49]} \\  & Anti-HbA1c/MPA/Au & & 0.10–2.5 mg/mL & & & \\  & & & (undiluted human serum) & & & \\ \cline{2-5}  & GPP/PhA/Au/Pu-NH\({}_{2}\)/GC & \multirow{2}{*}{Impedimetric} & \multirow{2}{*}{0–23.3\%} & \multirow{2}{*}{NA} & \multirow{2}{*}{NA} & \multirow{2}{*}{[51]} \\  & (Competitive inhibition assay) & & & & & \\ \cline{2-5}  & GPP/PohmA/ABA/Au/Pu-NH\({}_{2}\)/GC & \multirow{2}{*}{Amperometric} & \multirow{2}{*}{4.6–15.1\%} & \multirow{2}{*}{NA} & \multirow{2}{*}{NA} & \multirow{2}{*}{[52]} \\  & (Competitive inhibition assay) & & & & & \\ \cline{2-5}  & Anti-HbA1c/Au/Piry/Au & \multirow{2}{*}{Potentiometric} & \multirow{2}{*}{4–18 ug/mL} & \multirow{2}{*}{1.5087 Mv ug\({}^{-1}\) mL} & \multirow{2}{*}{NA} & \multirow{2}{*}{[53]} \\ \cline{2-5}  & Anti-HbA1c/Mixed SAM-wrapped & \multirow{2}{*}{Potentiometric} & \multirow{2}{*}{50–170.5 ng/mL} & \multirow{2}{*}{94.73 uV ng\({}^{-1}\) mL} & \multirow{2}{*}{NA} & \multirow{2}{*}{[54]} \\  & Au spheres/Au & & & & & \\ \cline{2-5}  & Anti-HbA1c/AuNP/SAM/Au & \multirow{2}{*}{Potentiometric} & \multirow{2}{*}{4–24 ug/mL} & \multirow{2}{*}{\(-\)90.6 mV/[log(ug/mL)]} & \multirow{2}{*}{NA} & \multirow{2}{*}{[55]} \\ \cline{2-5}  & Anti-HbA1c/Mixed & \multirow{2}{*}{Potentiometric} & \multirow{2}{*}{1.67–72.14 ng/mL} & \multirow{2}{*}{165.2 uV ng\({}^{-1}\) mL} & \multirow{2}{*}{NA} & \multirow{2}{*}{[56]} \\ \cline{2-5}  & SA/ANN/Au & & & & \\ \cline{2-5}  & CdIe & \multirow{2}{*}{Anodic stripping} & \multirow{2}{*}{4–16\%} & \multirow{2}{*}{NA} & \multirow{2}{*}{NA} & \multirow{2}{*}{[58]} \\ \cline{2-5}  & Anti-HbA1c/BSA/MWCNTs/GA/SFCE & \multirow{2}{*}{Volumetric} & \multirow{2}{*}{2–15\%} & \multirow{2}{*}{NA} & \multirow{2}{*}{0.4\%} & \multirow{2}{*}{[46]} \\ \hline \end{tabular}  
NA: Not applicable.  
\end{table} 
Table 2: _Cont._paste electrode (GCPE) as well as with a glassy carbon electrode (GCE) as the working electrode. It was reported that 3 mM of FcBA added to phosphate buffer solution successfully detected the varying concentrations of FV with a LoD below 0.05 mM at a low oxidation potential of +0.1 V [64]. In a novel strategy, the catalytic property of polyvinyl-dazole (PVI) was employed as an artificial dehydrogenase sensor to detect FV. The PVI was immobilized in the carbon paste electrode and used for amperometric detection studies, where a linear range of 20 to 700 \(\upmu\)M was achieved. Colorimetric detection of FV was also demonstrated by mixing PVI, meta-phenazinemethosulphate (m-PMS), dichloromethane indophenol (DCIP), and Triton X-100 in phosphate buffer of pH 7.0. The reduction in absorption intensity of DCIP upon FV addition was quantified at 600 nm. The linear range of detection by this method was wider, between 50 \(\upmu\)M and 10 mM [65]. The sensitivity of detection of the electrochemical approach was better but the range of detection was limited, which was attributed to the poor performance of the redox mediator employed in the study, namely m-PMS. Molecular imprinting techniques that create a recognition site for a specific analyte on a substrate, that is usually a polymeric matrix, have been employed for development of molecularly imprinted polymeric (MIP) sensors. In electrochemical MIP sensors, specific capture and subsequent quantification of the captured analyte are achieved through monitoring the changes in the electrochemical properties. The MIP sensors are a cost-effective method for quantification with high specificity of the molecule of interest.