Electronic Supplementary Material s7

Electronic Supplementary Material

Electrochemical immunoassay for the cancer marker LMP-1 (Epstein-Barr virus- derived latent membrane protein 1) using a glassy carbon electrode modified with Pd@Pt nanoparticles and a nanocomposite consisting of graphene sheets and MWCNTs

Xing Zhanga, Dandan Zhoub, Shangchun Shengc, Juan Yanga, Xueping Chena, Guoming Xiea*, Hua Xianga* a Key Laboratory of Laboratory Medical Diagnostics, Chinese Ministry of Education, Department of Laboratory Medicine, Chongqing Medical University, Chongqing 400016, P R China b Clinical Laboratories, The First Affiliated Hospital of Chongqing Medical University, Chongqing 400016, P R China c Center Laboratory for Point of Care Testing and Translational Medicine, Center Laboratory for Tuberculosis Prevention and Control, The Second People's Hospital of Yibin city, Sichuan, China

*Correspondence authors: Guoming Xie, E-mail address: [email protected] Hua Xiang, E-mail address: [email protected] Fig.S1. Photographs of colloidal suspensions taken at different reaction times of reduction of

Na2PdCl4 and K2PtCl4 during ultrasonic irradiation and SEM of prepared Pd@Pt nanoparticles.

Pd3d Scan 6.10E+04

6.00E+04

5.90E+04

5.80E+04

5.70E+04

5.60E+04 s

5.50E+04 s t n u

o 5.40E+04 Pd3d C 5.30E+04

5.20E+04

5.10E+04

5.00E+04

4.90E+04

4.80E+04 350 349 348 347 346 345 344 343 342 341 340 339 338 337 336 335 Binding Energy (eV) Pt4f Scan 1.80E+05

1.60E+05

1.40E+05

1.20E+05 s

/ 1.00E+05

s t n u o

C 8.00E+04

6.00E+04

4.00E+04

2.00E+04

0.00E+00 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70 69 68 Binding Energy (eV)

Fig. S2. XPS spectra of Pd3d and Pt4f in the Pd@Pt nanoparticles.

Fig.S3. The following parameters were optimized: the ratio of GS-MWCNTs (a), the reaction time of Ab-Ag (b), the pH value of sample (c) and the concentration of H2O2 (d). The RSD were 4.8%, 3.2%, 3.9% and 4.1%, respectively. Error bar = RSD (n = 5). Fig. S4. The CVs experiments response of different modified (a) GS/GCE; (b) MWCNTs/GCE; (c) GS-MWCNTs/GCE.

Fig. S5. TEM of Pd@Pt nanoparticles after store 3 months.

Signal-to-noise ratio (S/N) analysis

We used horseradish peroxidase (HRP) catalyzes the hydrogen peroxide (H2O2) under the action of electron media thionine. After combination of Pd@Pt NPs, synergistic effect between the Pd@Pt NPs and HRP happened in the presence of H2O2. Experiments of Fig. S6 is conducted to detect LMP-1 to demonstrate that the proposed method of nanomaterials combination really could improve the S/N of the immunosensor. As shown in Fig. S6, the S/N of this three strategies are 1.08, 1.96, 4.18, respectively, exhibits low background. These results clearly indicate that synergistic effect between the Pd@Pt NPs and HRP significantly improves the sensitivity since they reduce the background noise.

Fig. S6. The DPV response of different probes (A) Ab2/Thi/MWCNTs; (B)

Ab2/Thi/HRP/MWCNTs; (C) Ab2/Thi/HRP/Pd@Pt-MWCNTs . Without (a) and with (b) LMP-1 antigen (20 ng mL-1). Error bar = RSD (n = 5).

Table S1 Values of the equivalent circuit parameters of the fitting curves for the stepwise fabrication of the immunosensor by Zview 2 software. layer-by-layer assembly process Ret (Ω) Rs (Ω) CPE (F) Zw (Ω)

bare GCE 179.1±2.7 214.8 -43.0 184.2

GS-MWCNTs/GCE 70.2±2.8 3910.0 -5.3 70.4

Ab1/GS-MWCNTs/GCE 368.7±2.6 68.1 -73.3 375.9

BSA/Ab1/GS-MWCNTs/GCE 497.7±1.9 38.3 -96.7 507.0

Ag/BSA/Ab1/GS-MWCNTs/GCE 832.4±2.1 21.5 -129.9 842.5

EIS data were fitted to a Randles equivalent circuit (inset of Fig. 3B). Containing charge transfer resistance (Ret), electrolyte resistance (Rs), constant phase element (CPE) and Warburg element (Zw) [1, 2]. For the Faradic impedance measurement, Rs and Zw were almost not influenced by the electrode surface modification, whereas the variation in CPE was unnoticeable compared with the change in Ret. Thus, Ret is the most sensitive and straightforward parameter that can be used to characterize the events occurring on the surface of the work electrode (Table S1). Its value varies when different substances are adsorbed onto the electrode surface.

Table S2 Comparison of different immunoassay for determination of Epstein-Barr virus Method Analyte Line arrange Detection limit Reference

Immunoassay Epstein-Barr virus- 0.001 to 10 ng mL-1 0.001 ng mL-1 [3] (Quantum dots) derived latent membrane protein 1

Quartz crystal Epstein-Barr 0.5 to 10 ng mL-1 0.5 ng mL-1 [4] microbalance nuclear antigen 1

Immunosensor Epstein-Barr virus- 0.01 to 40 ng mL-1 0.62 pg mL-1 This work derived latent membrane protein 1

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