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Synthesis and characterization of rGO + SnO 2 composite for bio sensor
application
Article · May 2019
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Medha Gijare
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Suyog Danane
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Manisha Modak
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© 2019 JETIR May 2019, Volume 6, Issue 5 www.jetir.org (ISSN-2349-5162)
JETIRCP06003 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 17
Synthesis and characterization of rGO + SnO2
composite for bio sensor application
Medha Gijare1
Suyog Danane2
, Manisha Modak3
, Anil Garje4#
1
PDEA’s Baburaoji Gholap College, sangvi, Pune 27, Maharashtra, India
234
S.P. College, Pune, Maharashtra, India
Abstract: In the present work, Graphene oxide (GO) was prepared using improved modified Hummer’s method. Reduced
Graphene oxide (rGO) is synthesized by cow urine extract using sonication and refluxing process. Tin Oxide quantum dots were
synthesized using wet chemical method. RGO/SnO2 based pellets were prepared using hydraulic press. These pellets were
characterized for glucose. Structural and optical characterization of GO, rGO and SnO2 quantum dots was performed using XRD,
UV-visible and FTIR. The sensors show good response towards glucose.
Keywords: graphene oxide, reduced graphene oxide, quantum dot, glucose sensor
Introduction
Nanotechnology and nanostructured materials provide new and exhilarating opportunities for exploring
biosensing applications [1–3]. In recent years, an increasing number of researchers have explored the
production of novel nano-scale metal oxides, noble metal-doped metal oxides, metal oxide-CNTs
nanocomposites, and metal oxide-polymer composites. . It is reported that during the last two decades
tremendous efforts have been made for the detection of glucose based on nanostructured metal oxides and
their composites Graphene, graphene oxide (GO) and reduced graphene oxide (rGO) composites with metal
oxide quantum dots and nanoparticles are very useful for large scale production of selective chemical and
biosensors. Numerous processes and methodologies have been developed for creating new glucose
biosensors such as electrochemical methods [4], colorimetry [5], conductometry [6], optical methods [7],
and fluorescent spectroscopy [8]. Among them, the electrochemical glucose sensors have attracted the most
attention over the last 40 years because of their unbeaten sensitivity and selectivity. Additionally,
electrochemical techniques show lower detection limit, faster response time, better long term stability and
inexpensiveness. The catalytic ability of metal oxides as candidate electrode materials has been extensively
investigated to develop biosensors with high sensitivity, fast response and stability for glucose determination
through electrochemical oxidation.[9-11]. Graphene has extraordinary potential as a bio sensing material
due to good electrical conductivity, biocompatibility, flexibility and ease of functionalization. Sensors based
on graphene do not require high impedance circuit [12]. Recent progress shows that graphene based bio
sensing materials can have profound impact on applications such as real time health monitoring ,early
diagnosis of life threatening diseases like cancer and biosensors namely pH sensor, DNA sensor, glucose
sensors etc.[13 ]. Given the good electron transfer ability and unsaturated dangling bonds of rGO, as well as
the ample electro catalytic active sites of quantum-sized SnO2 NPs on unfolded rGO sheets, the fabricated
SnO2–rGO nanocomposite exhibited excellent performance in the non-enzymatic electrochemical detection
of glucose molecules.

EXPERIMENTATION
Preparation of Grapheme Oxide:
In the present work, improved modified Hummer’s method was used for the preparation of graphene
oxide (GO) [14 ]. It has two phases the solid phase is a mixture of 10 g of graphite powder and 5 g NaNO3.
The liquid phase contains 216 ml of concentrated H2SO4 mixed with 24 ml concentrated H3PO4. The liquid
phase ratio was maintained as 9:1 (wt %). After addition of 30 g of potassium permanganate, the mixture
was stirred for 1 hour at temperature of 100o
C. Addition of 30 ml of H2O2 into the mixture resulting in
yellow color represents great level of oxidation. For the complete removal of SO4
2-
, solution was
repeatedly washed with 5% HCl and DI followed by centrifuge (4000 rpm). Finally the material was air
dried for nearly 24 h and a brown black sample was collected.
Preparation of rGO using cow urine extract.
The prepared graphene oxide solution was mixed with 10 ml concentration of cow urine extract. The
solution was heated to 95°C using water bath to get homogeneous heating under reflux condition for 15 hrs.
.The solution was centrifuged at 4000 rpm for 20 min. The precipitate collected was washed repeatedly
using DI water and re-centrifuged to obtain reduced graphene oxide.
Synthesis of SnO2 quantum dots.
0.4 g of tin chloride was dissolved in 80 ml of methanol under magnetic stirring for 3 h. After complete
dissolution of the SnCl2 source, NH3 solution was added drop wise and the pH of the solution was
maintained as 9. The prepared solution was heated at 80 °C for 2 hours till the tin hydroxide precipitate was
formed. The precipitate was separated by centrifugation and washed repeatedly with DI water and ethanol
for the removal of by-products. The calcination of the precipitate was carried out at 400˚C for 2 hours to
obtain tin (di) oxide quantum dots.
Preparation of rGO/SnO2 composite
SnO2 and rGO at a ratio of 1:2 by weight were mixed with HPMC and PVA at a ratio of 3:2 by weight to
form nanocomposites. Few drops of DI water were added to prepare pellet using hydraulic press. The pellet
was annealed at 100°C for 1 hour. The diameter of the pellet was 9 mm with thickness of about 2mm.
Pellets were prepared by considering the proportions of SnO2, rGO, HPMC and PVA to form
nanocomposites as shown in table 1. Few drops of DI water were added to prepare pellet using hydraulic
press.
Table 1: composition of Pellet
Pellet No rGO
(wt %)
SnO2
(wt %)
HPMC
(wt %)
PVA
(wt %)
1 50 - 25 25
2 - 50 25 25
3 50 25 15 10

Structural characterization
X-ray diffraction (XRD) patterns of the samples were recorded using Phillip, Holland instrument with
CuKα_ radiation (0.1541 nm) in the range of 5° to 85° with scanning rate 2° per minute.
Optical characterization
Fourier Transform Infrared (FTIR) and UV-visible spectra of the samples were recorded on Perkin-Elmer
FTIR Spectrometer RXI and Shimadzu UV-2450 UV visible spectrophotometer respectively.
Results and discussion:
XRD analysis
Figure 1 depicts XRD pattern of graphite powder, prepared GO, rGO and rGO+SnO2 nanocomposites.
Fig. 1: XRD patteren of (a) graphite ( b) GO (c) rGo ( d) SnO2 and ( e) rGO + SnO2
The characteristic peak (002) at 2θ = ~ 26.8° with interlayer distance of 0.39 nm represents few un-
oxidized graphite. It can be seen that after oxidation of graphite into GO, the sharp peak of graphite
disappears and new peak appears at 2θ ~9.18° corresponding to (001) plane. Due to formation of functional
groups on both sides of loosely arranged graphite sheets interlayer distance increases to 0.54 nm. The broad
peak to 2θ ~ 27° observed in figure 1(c) depicts layered formation of rGO sheets corresponding to (002)
plane. XRD pattern of SnO2 nanoparticles (Figure 1d) shows the diffraction peaks of (110), (101), (211) and
(301) planes at various values of 2θ 26.2°, 33.4°, 51.7° and 66.4° respectively which magnificently matches
with JCPDS card # 77-0452. The average crystallite size was estimated according to the Scherer equation



Cos
D
9
.
0


The average crystallite size was ∿2 nm.The XRD pattern of rGO-SnO2 nanocomposites (Fig. 1e) shows
SnO2 peaks but the intensity of the peaks are reduced and broaden when compared with XRD pattern of
individual rGO and SnO2.
Optical characterization
UV-visible analysis
Figure 3 shows UV visible spectra of prepared GO, rGO and rGO+SnO2 pellets
The absorption peak for GO was observed at 228 nm depicts π→π*transition of C=C bonds [15]. The red
shift in absorption peak from 228 to 272 nm is after the reduction of GO by reflux method using cow urine
extract. The shift signifies deoxygenation of the GO sheets and the rebuilding of the sp2
bonded hybridized
carbon structure. This phenomenon shift has been used as a monitoring tool for the reduction of GO. During
the reduction of GO, the colour of GO solution changes from yellow brown to black. This is in agreement
with the work reported by few researchers [16]. The absorption band at 219 nm originates from the band gap
transitions and leads to the existence of highly crystalline SnO2. The absorption band at 205 nm shows low
absorbance of rGO/SnO2 nanocomposites.
FTIR analysis:
Figure 4 indicates FTIR spectra of prepared Graphite powder, GO, rGO and rGO+SnO2
nanocomposites.
The FTIR of graphite powder shows various characteristic absorption hydroxyl, epoxy functional groups and
bands of oxygen-containing groups. Analysis of Go shows broad absorption spectrum at 3457 cm-1
equivalent to O-H stretching vibrations. This represents existence of water molecules and structural O-H
groups in GO. The broad peak in GO indicates stretching in O-H and C-H bands. The band at 1734 cm-1
can
be related to C=O stretching of –COOH groups at the edges and defects in GO. The peak near 1750-1552
cm-1
becomes wide and shifts to 1475 cm-1
. This depicts presence of un-oxidized aromatic regions. The
FTIR spectrum of Tin Oxide shows broad absorption band ~3457 cm-1
equivalent to O-H stretching
vibration due to absorbed water molecules. A band at ~614 cm-1
relates to O-Sn-O stretching. Broad and

sharp absorption spectrum can be observed at ~3457 cm-1
corresponding O-H stretching vibration in rGO-
SnO2. Peak at 1640cm-1
corresponding O-H bending vibration indicating existence of absorbed water
molecules and structural O-H groups in rGO-SnO2. Similarly, a sharp band at ~614 cm-1
related to O-Sn-O
stretching in rGO-SnO2 refers to the integration of SnO2 quantum dots.
Resistance measurement for the glucose sensor
As prepared pellets were used to sense starch followed by amylase using drop casting method. Original
resistance of pallet was measured with well calibrated 6 1/2 digit resistance meter. A drop of starch was
placed on a pallet followed by diluted amylase. Change in resistance was measured at every stage. It was
observed that the resistance of pellet decreases successively. This can be considered as one of the parameter
for the capability of as prepared pellets towards glucose sensor. The change in resistance of pellets was as
shown in Table 2.
Table 2: Resistance measurements
Pellet No Original resistance After placing a drop
of Starch
After placing a drop of
Amylase
1 45-50 KΩ 11.5 KΩ 10 KΩ
2 1-2 MΩ 90 KΩ 23 KΩ
3 700 KΩ 7.5 KΩ 10 KΩ
In this class of biosensors, the enzyme is immobilized on a transducer surface and its capability to transform
a substrate in an electroactive, measurable byproduct is exploited. Such biosensors rely on enzymes that
belong to oxidases type. [17]
Conclusions
The cow urine extract was successfully used as green reducing agent for reduction of graphene oxide (GO)
into reduced graphene oxide (rGO). Tin Oxide quantum dots were synthesized using wet chemical method.
Average crystallite size of SnO2 quantum dots was ∿ 2 nm. rGO/SnO2 based pellets were characterized for
starch and amylase and hence for glucose. Change in resistance was measured at every stage and it was
observed that the resistance of pellet decreases consecutively. For rGO/SnO2 based pellet the resistance
decreases up to 10 KΩ from 700 KΩ. This proves that rGO/SnO2 based pellets are capable of sensing
glucose. The method reported in this work is sustainable, cost effective, bio safe and more ecofriendly. The
sensors show good response towards glucose.
References
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[17] Liang, Y.T.; Vijayan, B.K.; Gray, K.A.; Hersam, M.C., Nano Lett., 11, 2011, 2865–2870.
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