Electronic Supplementary Material
Sensitive electrochemical determination of α-fetoprotein using a glassy carbon electrode
modified with in-situ grown gold nanoparticles, graphene oxide and MWCNTs acting as
signal amplifiers
Yan-Sha Gao,a,b Xiao-Fei Zhu,a Tao-Tao Yang,a Jing-Kun Xu,a* Li-Min Lu,b* Kai-Xin Zhang a
a
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal
University, Nanchang 330013, PR China
b
College of Science, Jiangxi Agricultural University, Nanchang 330045, PR China
Characterization of UV–vis spectrum
Fig. S1 shows the UV–vis spectrum of MWCNTs (a), GO (b) and AuNPs/GO-MWCNTs (c).
As shown, the absorption peak at about 270 nm is attributed to the characteristic absorption of
MWCNTs [1]. While GO exhibited two characteristic peaks, a maximum at 230 nm, which
corresponds to π–π* transitions of aromatic C–C bonds, and a shoulder at 300 nm, which is
attributed to n→π* transitions of C=O bonds (curve b) [2]. In the UV–vis spectrum of
AuNPs/GO-MWCNTs (c), besides the same absorption peak derived from GO centered at 300
nm, the absorption peak centered at 230 nm was shifted to higher wavelength (253 nm),
which was indicative of strong π–π interaction between GO and MWCNTs. A peak at 523 nm
was also observed (curve c), which was attributed to the formation of AuNPs [3].
Fig. S1. UV–vis absorption spectra of the MWCNTs (a), GO (b), AuNPs/GO-MWCNTs (c).
Optimization of the method
The goal of this study was to control the optimal experimental conditions to obtain the
excellent performance of the proposed immunosensors for α-FP detection. The factors
influencing the performance of the immunosensor included the concentration of HAuCl4 in
the dispersion of GO, the buffer pH, the incubation temperature, and the incubation time.
Fig. S2. Effect of the concentration of HAuCl4 on the response of the immunosensor to 100
ng mL-1 α-FP. The concentrations of GO was 0.5 mg mL-1.
The effect of the concentration of HAuCl4 in the dispersion of GO was optimized. As
shown in Fig. S2, the current responses of the immunosensor increased with the increment of
HAuCl4 concentration, and then reached the highest at 5 mM. The current signal gradually
decreased at higher concentration. Thus, 5 mM HAuCl4 was adopted in the following
experiments.
The effect of pH on the detection solution on the immunosensor behavior was investigated
over a pH range from 5.5 to 8.0 with 100 ng mL-1 α-FP. As shown in Fig. S3a, the current
responses increased from pH 5.5 to 7.4 to reach the maximum value and decreased from pH
7.4 to 8.0. Hence, pH 7.4 was chosen as the optimum pH of the detection solution throughout
this study to obtain a high sensitivity. Temperature was an important factor for the activity of
the antibody and antigen. The effect of temperature on the immunosensor response was also
studied in the temperature range from 5 to 45 °C. As shown in Fig. S3b, maximum response
was achieved at a temperature around 35 °C. However, temperature above 40 °C might cause
irreversible denaturation of α-FP and anti-α-FP. As is well known, long-time use in high
temperature may damage the modifier and affect the lifetime of the immunosensor. Taking
into account the activity, lifetime, and response characteristics of biomolecules, we chose the
normal room temperature of 25 °C as the measure temperature in our study. The
immunosensor was incubated in a constant concentration of α-FP for different times. ∆ I
rapidly increased within the first 40 min and then tended to level off. Therefore, 40 min was
chosen as the optimal incubation time (shown in Fig. S3c).
Fig. S3. Influence of the pH of the PBS (a), incubation temperature (b) and incubation time (c)
on the current responses of the developed immunosensor.
Fig. S4. (A) Plot of Q-t curves of GO-MWCNTs/GCE (a), AuNPs/GO-MWCNTs/GCE (b),
in 1 mM K3[Fe(CN)6] containing 0.1 M KCl. The inset shows the Plot of Q-t1/2 curves on
GO-MWCNTs/GCE (a’), AuNPs/GO-MWCNTs/GCE (b’) (B) Cyclic voltammograms of the
GO-MWCNTs/GCE (a), AuNPs/GO-MWCNTs/GCE (b) in pH 7.4 phosphate buffer
containing 0.1 M KCl and 5.0 mM Fe(CN)63-/4- at the scan rate of 50 mV-1.
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