Electronic Supplementary Material
Electrochemical aptasensor for tetracycline using a screen-printed carbon electrode
modified with an alginate film containing reduced graphene oxide and magnetite (Fe 3O4)
nanoparticles
Xuejia Zhan, A Guangzhi Hu, B,C Thomas Wagberg, C Shenshan Zhan, A Hanchu Xu, A Pei
Zhou A
A
School of Agriculture and Biology & Bor S. Luh Food Safety Research Center, Shanghai
Jiaotong University, Shanghai 200240, PR China; Key Laboratory of Urban Agriculture
(South), Ministry of Agriculture, Shanghai 200240, PR China
B
Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of
Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, PR China
C
Department of Physics, Umea University, Umea 901 87, Sweden
Optimization the performance of aptasensor
To achieve optimal sensing performance, different experimental parameters including the
loading amount of rGO-Fe3O4, the concentration of TET aptamer, the pH of the test solution
and the incubation time were investigated, respectively.
Influence of the loading amount of rGO-Fe3O4
To achieve an optimal electrochemical signaling, the loading concentration of rGO-Fe3O4 on
the response of the aptasensor was investigated. As shown in Fig. S1A, the peak current rose
with increasing concentration of rGO-Fe3O4 immobilized on the electrode and reached the
maximum at 0.375 mg mL-1, then tend to decreased. This is attributed to the increase of film
 Corresponding author. 800, Dongchuan road, Shanhai Jiaotong University, Shanghai 200240, PR China.
Tel.: +86-21-34205762. Email: peizhousjtu@163.com (Pro. P. Zhou)
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thickness, which led to an increase of interface electron transfer resistance, making the
electron transfer more difficult [1]. Therefore, 0.375 mg mL-1 was selected as the optimum
concentration of rGO-Fe3O4 in the subsequent work.
Fig. S1 Effect of (A) loading amount of reduced graphene oxide- Fe3O4 (rGO-Fe3O4), (B) the
concentration of tetracycline (TET) aptamer, (C) pH, (D) incubation time on the
electrochemical response
Optimization of the concentration of TET aptamer
Generally, the density of the aptamer immobilized on the electrode surface is another
important parameter to affect the sensing response [2]. As shown in Fig. S1B, the response
increased along with the increasing concentration of the aptamer and reached the maximum
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value at 5.0 µM, whereas the further increase of aptamer concentration led to the decrease of
peak current. That is, a low density leads to a low response, while the dense immobilization of
aptamer may mask the electrode surface and decrease the response [3]. Therefore, 5.0 µM
was used as the optimized concentration of the aptamer.
Effect of pH on aptasensor response
The pH of the test solution was investigated as it may influence the sensitivity of the
aptasensor. As shown in Fig. S1C, the maximum reduction peak current was obtained at pH
6.0, and hence a pH value of 6.0 was selected for determination of TET.
Effect of incubation time
The effect of incubation time is vital to the aptasensor. In order to enhance detection
sensitivity, the incubating time was also optimized. With the increasing incubation time, the
obtained peak current increased and tended to a steady value after 50 min, indicating a
tendency to thoroughly capture target on the aptasensor surface (Fig. S1D). Therefore, 50 min
was chosen as the optimal incubation time.
References
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2. Rant U, Arinaga K, Fujita S, Yokoyama N, Abstreiter G, Tornow M (2004) Structural
properties of oligonucleotide monolayers on gold surfaces probed by fluorescence
investigations. Langmuir 20 (23):10086-10092
3. Kim YJ, Kim YS, Niazi JH, Gu MB (2010) Electrochemical aptasensor for tetracycline
detection. Bioprocess Biosyst Eng 33:31-37
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