SCIENCE CHINA Chemistry, Volume 61, Issue 4: 476-482(2018) https://doi.org/10.1007/s11426-017-9204-8

C-dots assisted synthesis of gold nanoparticles as labels to catalyze copper deposition for ultrasensitive electrochemical sensing of proteins

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  • ReceivedOct 19, 2017
  • AcceptedJan 2, 2018
  • PublishedJan 25, 2018


We report an ultrasensitive protocol for electrochemical sensing using the hydroxyl-rich C-dots assisted synthesis of gold nanoparticles (C-dots@AuNP) as labels with copper depositon reaction. The C-dots catalyzing copper deposition reaction was implemented for the first time. We constructed a sandwich-type immunosensor on the chitosan modified glassy carbon electrode (GCE) by glutaraldehyde (GA) crosslinking, with C-dots@AuNP as biolabels. Copper was deposited on the catalytic surfaces of second antibody-conjugated C-dots@AuNP nanoparticles through CuSO4-ascorbic acid reduction, because both C-dots and AuNPs could strongly catalyze the CuSO4 and ascorbic acid to form Cu particles, which amplified the detection signal. Then the corresponding antigen was quantified based on simultaneous chemical-dissolution/cathodic-preconcentration of copper for in-situ analysis using anodic stripping square wave voltammetry (ASSWV) directly on the modified electrode. Under optimized conditions, these electrodes were employed for sandwich-type immunoanalysis, pushing the lower limits of detection (LODs) down to the fg mL−1 level for human immunoglobulin G (IgG) and cardiac troponin I (cTnI), a cardiac biomarker. These novel sensors have good stability and acceptable accuracy and reproducibility, suggesting potential applications in clinical diagnostics.

Funded by

the National Key Research and Development Program of China(2016YFA0201300)

the National Natural Science Foundation of China(21335001,21575006)

China Postdoctoral Science Foundation(2016M600846)


This work was supported by the National Key Research and Development Program of China (2016YFA0201300), the National Natural Science Foundation of China (21335001, 21575006) and China Postdoctoral Science Foundation (2016M600846).

Interest statement

The authors declare that they have no conflict of interest.


The supporting information is available online at http://chem.scichina.com and http://link.springer.com/journal/11426. The supporting materials are published as submitted, without typesetting or editing. The responsibility for scientific accuracy and content remains entirely with the authors.


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  • Figure 1

    (a) TEM images of C-dots. (b) UV-Vis spectra and photo pictures (inset) of the suspensions of 0.50 mL C-dots (1), C-dots@AuNP (2), copper deposition solution (3, 0.09 M CuSO4+0.05 M AA), the C-dots and C-dots@AuNP after treated by copper deposition solution for 1 min (4 and 5). (c, d) SEM images of C-dots after treated by copper deposition solution (c) and corresponding EDX spectra (d) (color online).

  • Scheme 1

    Schematic diagram of the preparation of Ab2-C-dots@AuNP (a) and construction of immune-electrodes and key electrochemical steps for determination (b) (color online).

  • Figure 2

    CV (A) and EIS (B) at bare GCE (a), GA-CS/GCE (b), Ab1/GA-CS/GCE (c), BSA/Ab1/GA-CS/GCE (d), antigen/BSA/Ab1/GA-CS/GCE (e), Ab2-C-dots@AuNP/antigen/BSA/Ab1/GA-CS/GCE (f), and copper/Ab2-C-dots@AuNP/antigen/BSA/Ab1/GA-CS/GCE (g) in 0.1 M PBS containing 2.0 mM K4Fe(CN)6. Scan rate: 50 mV s−1. EIS: 100 kHz–1 Hz,5 mV rms, 0.21 V vs. SCE. Here, the working electrode potential was fixed at the formal potential of the Fe(CN)63−/4− redox couple (0.21 V vs. SCE) after being pre-conditioned at this potential for 100 s. Here, Ab1, antigen, and Ab2 refer to anti-IgG, IgG and anti-IgG, respectively (color online).

  • Figure 3

    SEM images of Ab2-C-dots/antigen/BSA/Ab1/GA-CS/GCE (a, e), copper/Ab2-C-dots/antigen/BSA/Ab1/GA-CS/GCE (b, f), Ab2-C-dots @AuNP/antigen/BSA/Ab1/GA-CS/GCE (c, g), and copper/Ab2-C-dots @AuNP/antigen/BSA/Ab1/GA-CS/GCE (d, h). The 200 nm scale bar in panel (c) also applies for other SEM pictures. Panels (e–h) show corresponding EDX spectra. Concentration of IgG: 500 ng mL−1 (color online).

  • Figure 4

    The ASSWV curves (a) and corresponding curves for optimization the time of the copper deposition on the immunoelectrode (b) (n=3). Concentration of IgG: 5 pg mL−1 (color online).

  • Figure 5

    The ASSWV curves for cTnI (a) and IgG (c) immunoassay using our protocol and standard curves (b, d) (n=3) (color online).

  • Table 1   Immunoassay of cTnI in clinical serum samples using our method and the reference method




    method a)

    Our method b)

    (pg mL−1)

    RSD (%)

























    The reference method was qualitatively testing conducted on an Myocardial troponin I test kit in the hospital (the positive “+”/negative “−” usually means that the concentration of cTnI is higher than/lower than 400 pg mL−1 respectively; b) given as the average value of three repeated assays.

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