Electronic Supplementary Material

Highly sensitive and wide range nonenzymatic disposable glucose sensor based on a screen printed carbon electrodes modified with reduced graphene oxide and Pd-CuO nanoparticles

Keerthy Dharaa, Thyagarajan Ramachandrana, Bipin G. Nairb, Thekkedath Gopalakrishnan Satheesh Babua*

aDepartment of Sciences, Amrita Vishwa Vidyapeetham, Amritanagar P.O., Coimbatore – 641112, India

bAmrita School of Biotechnology, Amrita Vishwa Vidyapeetham, Clappana P.O., Kollam – 690525, India

*Corresponding Author, e-mail address: (T. G. Satheesh Babu), Tel.: +91 9442368632, Fax: +91 422 2656274

Fig. S1 shows the X-ray diffraction patterns of the graphite powder and nanocomposites. A peak at 2θ = 26.5o with a d-spacing value of 0.33 nm corresponding to the characteristic peak of hexagonal graphite (Fig. S1a). After oxidation, the peak shifted from 26.5o to 9.65o with a d-spacing value of 0.92 nm indicating that the graphite powder is converted to graphite oxide (Fig. S1b). The three fold increase in d-spacing due to the intercalation of carboxy, hydroxy and epoxy functional groups between the carbon layers. Fig. S1c shows the XRD pattern of reduced graphene oxide. After reduction, the peak shifted to 25.6o with a d spacing of 0.69 nm.

Fig. S1: XRD patterns of (a) graphite, (b) graphene oxide and (c) reduced graphene oxide


Fig. S2 shows the high resolution transmission electron microscopic images of CuO/rGO (Fig. S2a and b) and Pd/rGO (Fig.S2c and d) nanocomposites. The images clearly illustrate that the CuO and Pd nanoparticles are dispersed on the reduced graphene oxide sheet.

Fig. S2: HRTEM images of CuO/rGO (a and b) and Pd/rGO (c and d) nanocomposites

Fig. S3 shows the Bode plot for Pd/rGO/SPE, CuO/rGO/SPE and Pd-CuO/rGO/SPE. It is well known that the capacitance is directly related to the surface area, and the surface area in turn increases with the surface roughness [25]. Hence the electrode with greater surface roughness will have more capacitance. This is evident from our study also, that the Pd-CuO/rGO/SPE exhibited greater capacitance value when compared to Pd/rGO/SPE and CuO/rGO/SPE. The charge transfer resistance (R1), capacitance and Warburg impedance of the modified electrodes is mentioned in the Table S1.

Fig.S3: Bode plots of Pd/rGO/SPE, CuO/rGO/SPE and Pd-CuO/rGO/SPE

Table S1: Rct and capacitance values obtained for modified electrodes

Electrode / Rct value (R1) (ohms) / Capacitance (Farad) / Warburg (siemens.sec^(1/2)) / Error
Pd/rGO/SPE / 74.23 / 0.000128287 / 0.00025763 / 0.196
CuO/rGO/SPE / 177.11 / 0.000236246 / 9.29E-05 / 0.1574
Pd-CuO/rGO/SPE / 102.95 / 0.000427048 / 0.000139278 / 0.168

Effect of electrolyte concentration

The mechanism of oxidation of glucose involves hydroxide anion (OH-) and it is well known that the concentration of OH- greatly influences the rate of oxidation. Hence the effect of NaOH concentration on the voltammetric response on Pd-CuO/rGO/SPE towards glucose is studied and given in Fig.S1. It can be seen that the oxidation peak currents increases with increase in concentration of NaOH from 0.1 M to 0.2 M (Fig.S4a) with a decrease in peak potential (Fig.S4b). However further increase in NaOH concentration gives rise to decrease in peak current. Hence 0.2 M NaOH was selected as the optimum electrolyte concentration for the oxidation of glucose in this work.

Fig. S4: Variation of response current (a) and applied potential (b) with concentration of NaOH solution

Fig. S5 displays LSVs on the Pd-CuO/rGO/SPE in 0.2 M NaOH containing 3 mM glucose at various scan rates ranging from 0.01 to 0.13 V s-1. On increasing the scan rate, anodic peak current increases with a slight shift in peak potential [46]. The oxidation peak current was proportional to the scan rate with a linear regression equation of Ip (µA) = 125.32 + (5.09) ʋ (mV s-1) and a correlation coefficient of r = 0.999, n = 13 (Inset of Fig. S5). This indicates that the oxidation of glucose on Pd-CuO/rGO/SPE was surface controlled electrochemical process and it obeys Nernstian condition for adsorption controlled reactions, iP = (n2F2 υ AГ*O/4RT) where iP is the peak current, F is Faradays constant (in coulombs), n is the number of electrons involved, R is gas constant (J mol-1 K-1), A is the area (in cm2), υ is the scan rate (in V s-1).

The amperometric response of the Pd-CuO/rGO/SPE in NaOH solution with three different concentrations of glucose was given Fig. S6. The sensor is linearly responding to glucose concentration. The calibration graph is given in the inset of Fig. S6.

Fig.S5: LSVs on Pd-CuO/rGO/SPE with 3 mM glucose at different scan rate from 0.01 V s-1 to 0.13 V s-1 (Inset: peak current vs scan rate).

Fig. S6: Amperometric response on Pd-CuO/rGO in 0.2 M NaOH solution under various concentrations of glucose at +0.6 V.