Electronic Supplementary Material
Electrochemical determination of dopamine using octahedral SnO2 nanocrystals
bound to reduced graphene oxide nanosheets
Hong-Fei Maa, Ting-Ting Chena,b, Yu Luob, Fen-Ying Kongb*, Da-He Fanb, Hai-lin
Fangb, Wei Wangb*
a
College of Sciences, Nanjing Technology University, Nanjing 211816, China
b
School of Chemistry and Chemical Engineering, Yancheng Institute of Technology,
Yancheng 224051, China
*Corresponding authors, Tel: +86-515-88298186; Fax: +86-515-88298186. E-mail address:
kongfy@ycit.edu.cn; wangw@ycit.edu.cn
Effect of solution pH
The pH of the solution considerably influences the redox peak potential and peak
current of DA. With the increase of pH value, redox peak potentials of DA shifted to
the negative potential (as shown in Fig. S1A). The formal peak potential Ep [Ep = (Epa
+ Epc)/2] are linearly proportional in the pH range of 4.0 to 9.0 with a linear equation
of Ep = 0.711 − 0.051 pH, r = 0.9958m (Fig. S1B). The slope of −51 mV/pH was
close to the theoretical value of −59 mV/pH, which indicated that the same amounts
of protons and electrons were involved in the redox reaction of DA. Besides, the Ipa vs.
pH plot (inset of Fig. S1A) revealed that the peak current displayed a maximum at pH
7.0 and decreased sharply in both directions. Therefore, the optimum pH for DA
determination was 7.0.
Effect of fraction of SnO2 in the nanocomposites
The amount of SnO2 plays an important role in the determination of DA. As
shown in Fig. S1C, the oxidation peak currents of DA increased with increasing SnO2
content in the nanocomposites. It reached a maximum value at the mass ratio of 1:1
(r-GO/SnO2) and decreased at 1:5, which is probably attributed to the smaller
conductivity of SnO2. So, the fraction was fixed at 1 for further investigation in this
work.
Effect of scan rate
The influence of scan rate on the cyclic voltammetric response of 50 μM DA on
r-GO-SnO2/GCE was recorded with the results shown in Fig. S1D. With the increase
of scan rate, the redox peak currents increased gradually. A good liner relationship
between the redox peak currents (Ip) and the scan rates (v) was plotted in the range
from 10 to 200 mV s-1 with the results shown as the inset of Fig. S1D. Two linear
equations were calculated as Ipc (μA) = −1.201 − 0.035v (mV s-1), r = 0.9903 and Ipa
(μA) = 2.821 + 0.042v (mV s-1), r = 0.9952. This suggests that the reaction is
adsorption-controlled electrode reaction. At higher scan rate, the redox peak potential
(Ep) and ln v also exhibited a good liner relationship with the liner equations
calculated as Epa (V) = 0.076 + 0.066 ln v, r = 0.9945 and Epc (V) = 0.379 − 0.04 ln v, r
= 0.9946. According to the related equations [1,2], the electron number (n) was
calculated as 2, which is consistent with that reported in literature [3,4].
Fig. S1 CVs of 50 μM DA at the r-GO-SnO2/GCE (A) in the different pHs of 0.1 M phosphate
buffer media (a→f: 4.0, 5.0, 6.0, 7.0, 8.0, 9.0). Scan rate, 100 mV s-1. Inset: Plot of Ipa vs. pH; (B)
Plot of pH versus the formal potential of the DA redox peak; (C) with different fraction
(r-GO/SnO2): (a) 10:1, (b) 2:1, (c)1:1, (d) 1:5 in 0.1 M phosphate buffer (pH 7.0), Scan rate, 100
mV s-1; (D) with different scan rate (a→g: 10, 30, 50, 80,100, 150, 200 mv s-1) in 0.1 M phosphate
buffer (pH 7.0). Inset: plots of anodic and cathodic peak currents versus scan rates.
Table S1 Results for determination of DA with some potentially interfering ions. a
a
Coexisting Substance
Concentration
I S/I O (%)
L-Cysteine
50 mg/L
96.6
L-Glutamine
50 mg/L
96.7
Glucose
5 μM/L
93.5
NaCl
5 μM/L
98.8
KCl
5 μM/L
96.1
Citric acid
5 μM/L
101
Number of samples assayed: 3.
References
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