Electronic Supplementary Material
A glassy carbon electrode modified with a nanocomposite consisting of MoS2 and
reduced graphene oxide for electrochemical simultaneous determination of ascorbic
acid, dopamine, and uric acid
Liwen Xing, Zhanfang Ma*
Department of Chemistry, Capital Normal University, Beijing 100048, China
*Corresponding author, E-mail: mazhanfang@cnu.edu.cn
Fig. S1 XPS spectra of MoS2 and MoS2/rGO nanocomposite, respectively.
Fig. S2 FTIR spectra of GO and MoS2/rGO nanocomposite.
1
The broad peak at around 3390 cm-1 of GO was attributed to the stretching vibration of
-COOH and -OH groups. The peaks at around 1732 and 1228 cm-1 were related to the
presence of abundant C=O and C-O functional groups on the surface of graphene oxide
nanosheets. After the one-pot hydrothermal process, these peaks were largely weakened in
the MoS2/rGO nanocomposite, indicating the reduction of GO.
Fig. S3 XPS spectra of S 2p (A) and Mo 3d (B) for MoS2 and MoS2/rGO nanocomposite,
respectively.
Fig. S4 CVs of MoS2/rGO/GCE, MoS2/GCE and bare GCE in 0.1 M PB (pH 7.0) containing
(A) 1 mM AA, (B) 100 M DA, (C) 200 M UA and (D) the mixture of 1 mM AA, 100 M
DA and 200 M UA. CV scan rate: 100 mV s-1 (data recorded from -0.2 V to 0.6 V, vs.
Ag/AgCl).
2
Fig. S5 Baseline-corrected DPVs of MoS2/rGO/GCE in 0.1M PB (pH 7.0) containing 1mM
AA, 100 M DA and 200 M UA (data recorded from -0.2 V to 0.6 V, vs. Ag/AgCl).
Fig. S6 Effect of pH (from 4 to 9) on DPV peak potential (A) and peak current (B) for the
oxidation of 1 mM AA, 100 M DA and 200 M UA in 0.1 M PB.
3
Fig. S7 Effect of scan rate on CVs of 1 mM AA (A), 100 M DA (B) and 200 M UA (C) on
MoS2/rGO/GCE at 25, 75, 100, 200, 300, 400 and 500 mV s-1. Inset: plots of peak current Ip
vs scan rate for AA, DA, and UA, respectively (data recorded from -0.2 V to 0.6 V, vs.
Ag/AgCl).
As pH value increased in the range from 4 to 9, the oxidation peak potentials of AA, DA,
and UA shifted negatively (Fig. S6A), demonstrating that protons directly participated in the
overall electrode reaction processes. The linear slopes value of DA and UA were 56.7 and
53.6 mV/pH, respectively, close to the theory value of 59 mV/pH (298 K), which indirectly
proved equal numbers of proton and electron transfer during the electrooxidation reactions
[1]. The slope value of 34.3 for AA was slightly lower than the theory value, implying that
the electrooxidation of AA at the MoS2/rGO/GCE occurred with less than one proton
involved [2]. As shown in Fig. S6B, the oxidation peak current of DA decreased with a
higher pH value and that of AA had no sharp change in the pH range of 4 to 9; the maximum
oxidation peak current was obtained at pH 7.0 for UA. Considering the separation effect and
detection sensitivity, an eclectic pH value of 7.0 was thus chosen in the following
measurements. Under the pH value of 7.0, the effect of scan rate on CV response of the three
biomolecules was investigated. The oxidation peak currents of the three biomolecules were
all linear with the scan rate in the range from 25 mVs-1 to 500 mVs-1 (inset plot of Fig. S7),
clearly indicating a surface-controlled process [3].
4
Fig. S8 CVs of bare GCE, MoS2/GCE and MoS2/rGO/GCE in 5 mM [Fe(CN)6]3-/4- aqueous
solution containing 0.1 M KCl. CV scan rate: 50 mV s-1 (data recorded from -0.2 V to 0.6 V,
vs. Ag/AgCl).
The electroactive surface area (ECSA) of bare GCE, MoS2/GCE and MoS2/rGO/GCE
were measured based on the Randles-Sevcik equation [3] as follows:
I p  2.69 105 AD1 2 n3 2 1 2C
where Ip was the peak current, A was the ECSA (cm2), D was the diffusion coefficient of
K3[Fe(CN)6] ((6.70 ± 0.02) × 10-6 cm2s-1), n was the number of transferred electrons for
[Fe(CN)6]3-/4- redox couple (n = 1), was the scan rate (V s-1) and C was the bulk
concentration of the K3[Fe(CN)6] (mol L-1). Accordingly, the ECSA were calculated in the
trend of bare GCE (0.0707 cm2) < MoS2/GCE (0.0723 cm2) < MoS2/rGO/GCE (0.0885 cm2),
suggesting that MoS2/rGO nanocomposite enlarges the apparent surface area of the electrode
because of its porous nanostructure which contributed to the quick mass transfer of target
molecules [4].
5
Table S1 Comparison of the analytical performance of MoS2/rGO nanocomposite with other
modified electrode based on rGO and/or noble metal materials in electrochemical detection of
AA, DA and/or UA.
Sensitivity
Peak separation
Linear range (M)
(mV)
Electrode
LOD (M )
(A M-1 cm-2)
Ref.
AA-DA
DA-UA
AA
DA
UA
AA
DA
UA
AA
DA
UA
Pd3Pt1/PDDA-RGO/GCE
184
116
40-1200
4-200
4-400
0.61
0.04
0.10
0.077
0.64
0.49
5
PdNPs-GO/GCE
-
-
20-2280
-
-
-
-
-
0.087
-
-
6
(P2W16V2-AuPd/PEI)8/ITO
-
-
1.2-1610
2.1-2060
-
0.43
0.83
-
-
-
-
7
PdNPs/GR/CS/GCE
252
144
100-4000
0.5-200
20
0.1
0.17
0.19
1.05
8
Au/RGO/GCE
200
110
240-1500
6.8-410
8.8-530
51
1.4
1.8
0.002
0.31
0.15
3
Ag-Pt/pCNFs/GCE
-
-
-
10-500
-
-
0.11
-
-
2.24
-
9
MoS2/rGO/GCE
232
152
12-5402
5-545
25-2745
0.72
0.05
0.46
0.12
4.11
1.59
0.5-15
20-200
3.16
0.88
Fig. S9 Peak current ratio of the MoS2/rGO/GCE to 1 mM AA (A), 100 M DA (B) and 200
M UA in the presence of 1mM of various interfering substances (from left to right: glucose,
citric acid, cysteine, Ca(NO3)2, Mg(NO3)2, ZnCl2 and Na2SO4, respectively.)
6
this
work
Fig. S10 CV of MoS2/rGO/GCE with 50 circles of continuous scan in 5 mM [Fe(CN)6]3-/4aqueous solution containing 0.1 M KCl. CV scan rate: 50 mV s-1 (data recorded from -0.2 V
to 0.6 V, vs. Ag/AgCl).
Table S2 Simultaneous detection of AA, DA, and UA in human serum samplesa
AA
Sample
DA
UA
Added
Found
Recovery
Added
Found
Recovery
Added
Found
Recovery
(M)
(M)
(%)
(M)
(M)
(%)
(M)
(M)
(%)
1
0.00
-
-
0.00
-
-
0.00
-
-
2
500.0
502.80
104.16
100.0
102.3
102.30
200.0
197.8
98.90
3
1000.0
998.76
99.88
200.0
198.5
99.25
400.0
402.3
100.58
No.
a Three replicate measurements were made on each sample
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