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*
a
Department of Sciences, Amrita Vishwa Vidyapeetham, Amritanagar P.O., Coimbatore – 641112,
India
b
Amrita School of Biotechnology, Amrita Vishwa Vidyapeetham, Clappana P.O., Kollam – 690525,
India
*Corresponding Author, e-mail address: tgsatheesh@gmail.com (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.
Pd/rGO/SPE
CuO/rGO/SPE
Pd-CuO/rGO/SPE
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
Capacitance
Warburg
Error
(R1) (ohms)
(Farad)
(siemens.sec^(1/2))
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 PdCuO/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.