# Highly Sensitive Non-Enzymatic Detection of Glucose at MWCNT-CuBTC Composite Electrode
## 3 Results
### Linear Sweep Voltammetry (LSV)  
Based on the presented results, the electrochemical performance of the MWCNT-CuBTC composite electrode's ability to detect glucose was assessed by linear sweep voltammetry (LSV). Figure 3 shows a series of LSVs recorded at the MWCNT-CuBTC composite electrode within a glucose concentration range similar to that of the CV runs. In addition, the linear dependence of the anodic current recorded at +0.6 V/SCE versus the glucose concentration was achieved with a lower sensitivity of 0.12 (inset of Figure 3) versus the 0.62 mA\(\cdot\)mM\({}^{-1}\) achieved by CV within a similar glucose concentration range, which means that the electrode fouling was stronger in its manifestation using LSV. It can also be noticed that a high response was recorded at 1 mM of glucose, with the possibility to obtain a response for lower glucose concentrations, particularly in a range below 1 mM.  
Figure 2: Cyclic voltammetry (CV) recordings at the MWCNT-CuBTC composite electrode in 0.1 M of NaOH supporting electrolyte (curve 1) and in the presence of various glucose concentrations: 0.1–0.9 mM (curves 2–10) and 1–5 mM (curves 11–15). The inset is the calibration plots of the current, recorded at +0.5 V/SCE versus the glucose concentration.  
To propose a preconcentration/voltammetric detection scheme for glucose determination at the MWCNT-CuBTC composite electrode, the accumulation time represented an important parameter because it could influence the degree of adsorption on the electrode surface. An important role that may be played by MOFs is their ability to concentrate species within their nanoporous structures. To determine the enhancement factor as the ratio of the peak current before and after the sorption process, the effect of the accumulation time on the anodic peak current was investigated using LSV. Figure 4 shows the LSV recordings at the MWCNT-CuBTC composite electrode after different accumulation times, which represent the time for maintaining the electrode at its open-circuit potential (OCP) to concentrate glucose at the electrode surface. The useful oxidation peak current and the enhancement factor, determined for 1 mM of glucose using a preconcentration/voltammetric detection procedure at different accumulation times, are shown in the inset of Figure 4. The oxidation peak currents for this compound increased with the accumulation time up to 30 min, which was selected as the optimum accumulation time due to a maximum enhancement factor of 2.5 being reached. Meanwhile, at longer accumulation times, the peak currents remained constant, and a plateau was reached. The enhancement factor of about 2.5 at the oxidation potential of +0.6 V/SCE revealed an effective concentration effect of the MWCNT-CuBTC composite electrode on glucose, regarding the improvement of its oxidation signal. As a consequence, the accumulation time of 30 min was chosen as an optimum time for further preconcentration and linear sweep voltammetric detection experiments.  
An LSV series was recorded under the optimum conditions of the preconcentration scheme, which assumed an accumulation time of 30 min within a glucose concentration ranging from 0.2 mM to 1 mM (the results are not shown here). Under these working conditions, a significant enhancement of the electroanalytical parameters of glucose detection was achieved, with a sensitivity which was about five times better and a detection limit that was five times lower (see Table 2).  
Figure 3: Linear scan voltammetry (LSV) recordings at the MWCNT-CuBTC composite electrode in 0.1 M of NaOH supporting electrolyte (curve 1) and in the presence of various glucose concentrations, ranging from 1 mM to 10 mM (curves 2–11). The inset contains calibration plots of the current recorded at +0.6 V/SCE versus the glucose concentration.