Using the above equation Eq the

Using the above equation (Eq. (2)), the surface concentration in our case was found to be 0.23×10−8mol/cm2. The diffusion coefficient (D) value of the redox species from the electrolyte to L/IL/ITO electrode was calculated using the Randles–Sevcik equation given by [33]where Ip is the peak current of the electrode (Ia anodic and Ic cathodic), n is the number of electrons involved or electron stoichiometry equal to 1, A is the surface area of the L/IL/ITO electrode equal to 0.25 cm2, D is the diffusion co-efficient, C is the concentration of redox species (3.3mM [Fe(CN)6]3/4), and V is the scan rate which is 20mV/s. The value of the heterogeneous electron transfer rate constant (Ks) for L/IL/ITO was calculated by Eq. (4) based on the model of Laviron [33] given bywhere m is the peak-to-peak separation, F is the Faraday constant, V is the scan rate given as 20mV/s, n is the number of transferred electrons, R is the gas constant and T is the temperature (room temperature in our case). The values of all these parameters for L/IL/ITO are listed in Table 1, and for comparison the same for L/ITO is provided. The electrochemical response of L/IL/ITO electrode was investigated as a function of concentration in range 1–20mM of different analytes such as glucose, citric acid, urea, ascorbic acid, cholesterol and oxalic cholinesterase inhibitor using CV technique at 20mV/s scan rate. The calibration curve for L/IL/ITO as a function of different analyte concentration obtained through cyclic voltammetric is shown in Fig. 4. Upon addition of analytes (oxalic acid, ascorbic acid and cholesterol), distinct change in CV profile was observed (Fig. 2b) which indicated increase in oxidation (Ia) and reduction current (Ic). The anodic (Ia) peak current increased linearly in range 1–20mM for oxalic acid, cholesterol and ascorbic acid. This increase in current with addition of analytes led us to conclude that electro catalytic reaction was due to the presence of analytes. We did not find any redox response for urea and citric acid, and it was poor for glucose (data not presented). The sensitivity of the L/IL/ITO electrode calculated from slope of the curve in the range 1–20mM from Fig. 4 was found to be 8.01μAmM−1cm−2 for oxalic acid, 4.16μAmM−1cm−2 cholesterol and 2.47μAmM−1cm−2 for ascorbic acid with linear regression coefficient (R2) of 0.92, 0.88 and 0.85, respectively. On comparing the behavior of anodic peak current of L/IL/ITO as a function of concentration (Fig. 4a) of analytes, we observed that the best sensing behavior was for oxalic acid. Thus, the ionogel film allowed the sensing of the three analytes discussed above. However, when we examined the sensitivity for these analytes towards L/ITO, we found that the detection range was limited to 1–8mM (Fig. S2 Supplementary Information), and the sensitivity was 2.08, 3.94 and 2.72μAmM−1cm−2 with regression coefficient R2=0.93, 0.96 and 0.86 for oxalic acid, cholesterol and ascorbic acid, respectively. The stability of L/IL/ITO electrode was established by measuring its cyclic voltammetric profile obtained over a period of 3days. The stability of ionogel films may be ascribed to interaction between positive edges of laponite platelets with negatively charged face of other platelets where formation of IL double layer inhibit electrostatic interactions [11]. The selectivity of L/IL/ITO electrode towards oxalic acid was monitored using potential interferents such as ascorbic acid and cholesterol. The interferents (analytes) solution at normal concentration of oxalic acid (6mM) was taken and the redox behavior was monitored with other two analytes. The change in the anodic current peak (Ia) was measured using equal amount of oxalic acid and the other analytes. From the Fig. 5, we found that the electrode was specific to oxalic acid as it did not shows interference effects (Fig. 5). For other cases i.e. with cholesterol and ascorbic acid, the change in peak current was observed (not shown).