Electronic Supplementary Material
Electrochemical aptasensor for tetracycline using a screen-printed carbon electrode modified with an alginate film containing reduced graphene oxide and magnetite (Fe3O4) 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 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 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
1. Xin X, Sun S, Li H, Wang M, Jia R (2015) Electrochemical bisphenol A sensor based on core–shell multiwalled carbon nanotubes/graphene oxide nanoribbons. Sens Actuators B Chem 209:275-280
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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[(]* Corresponding author. 800, Dongchuan road, Shanhai Jiaotong University, Shanghai 200240, PR China. Tel.: +86-21-34205762. Email: (Pro. P. Zhou)