Electronic Supplementary Material
Electrochemical immunosensor for the prostate specific antigen detection based on
carbon nanotube and gold nanoparticle amplification strategy
Jing Yang, Wei Wen, Xiuhua Zhang, Shengfu Wang*
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry
of Education Key Laboratory for the Synthesis and Application of Organic Functional
Molecules & College of Chemistry and Chemical Engineering, Hubei University, Wuhan
430062, PR China
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*Corresponding author, Fax: +86-27-88663043; Telephone: +86-27-50865309; E-mail
address: wangsf@hubu.edu.cn (S. Wang)
Characterization of gold nanoparticles
The gold nanoparticle was characterization by UV–vis spectrum and Transmission
Electron Microscopy (TEM). As shown in Fig. S1, an absorption peak at 520 nm was
observed in the UV–vis spectrum of AuNPs in water and an average diameter of
approximately 13 nm as measured by TEM.
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Fig. S1 UV-vis characterization of the gold nanoparticle, insert is the TEM image of AuNPs.
Grafting 1, 7-diaminoheptane on glassy carbon electrode
The electrochemical modification of the GCE surface with a monolayer of 1,
7-diaminoheptane was carried out by applying a potential to the electrode between 0.2 V and
1.6 V for three cycles at a scan rate of 20 mV﹒s−1 in an absolute ethanol solution containing
2 mM 1, 7-diaminoheptane and 0.1 M NaClO4. A broad and irreversible oxidation peak was
observed at 1.30 V, shown in Fig. S2.
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Current / mA
20
1
15
2
10
3
5
0
-5
0.0
0.3
0.6
0.9
1.2
1.5
1.8
Potenvial / V
Fig. S2 Cyclic voltammograms of a freshly polished GCE upon scanning in 2 mM DAH and
0.1 M NaClO4 ethanol solution. (1) First, (2) second and (3) third cycles.
2
Optimization of experimental conditions
In order to provide the immunosenor with a better performance, the volume ratio of Ab2
to Fc, the volume of Ab2 when prepare the Ab2-Fc-AuNPs conjugates, and the incubation time
of Ab1 and Ab2-Fc-AuNPs with PSA were investigated.
The process for preparation of the Ab2-Fc-AuNPs conjugates was optimized to achieve
the best DPV performance. The volume ratio of Ab2 (0.1 mg﹒mL−1) to Fc (5mM) was
studied from 4:1 to 2:3 as shown in Fig.S3A. We found that a volume of 4:1 gave the highest
DPV signal response, which indicated the linking efficiency of Ab2 to Fc at the certain ratio is
relatively the highest. When the volume ratio is higher than 4:1, less Ab2 molecules were
linked to the AuNPs. In this regard, less amount of Ab2-Fc-AuNPs conjugates combined with
the PSA resulted in a decrease in the electrochemical signal. So the volume ratio of 4:1 was
chosen for the subsequent assays.
Under the optimized volume ratio of Ab2 to Fc, the dosage of the Ab2 also affected the
efficiency of the Ab2-Fc-AuNPs conjugates binds to PSA, which would influence the DPV
signal. As shown in Fig. S3B, with an increase in the amount of Ab2, the current value
gradually increased and then became nearly balanced when the volume of Ab2 was 250 μL.
Therefore, the optimum dosage of the Ab2 was chosen as 250 μL.
Fig. S3 (A) Optimization of the experimental condition for DPV response to the different
volume ratio of AuNPs modified Ab2 (0.1 mg﹒mL−1) and Fc (5mM). (B) Optimization of the
experimental condition for DPV response to different volume of Ab2.
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The effect of incubation time between Ab1 and PSA (Fig.S4A), Ab2-Fc-AuNPs and PSA
(Fig.S4B) of the immunosensor were examined from 15 to 120 min, respectively. It is found
that the peak current response of the immunosensor to 100 ng﹒mL−1 PSA increases with
increasing incubation time, and reached a platform till 75 min (Fig.S4A) and 90 min
(Fig.S4B). This result suggests that the immunoreaction of the antibodies and PSA have
entirely completed in certain time. Thus, 75 min and 90 min were adopted in this work for the
incubation time of Ab1 and PSA, Ab2-Fc-AuNPs and PSA, respectively.
Fig. S4 DPV peak currents plotted against incubation time of the Ab1 modified electrode (A)
and Ab2-Fc-AuNPs conjugates (B) with PSA (100 ng﹒mL−1) solution at 37 °C.
Controlled experiments
In order to confirm the amplification strategy, we compare the results of the controlled
experiments without multi-walled carbon nanotubes (MWNTs) to the immunosensor shown
in Fig. S5.
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Fig. S5 (A) DPV responses of the immunosensor without MWNTs incubated with different
concentrations of PSA (From a → i: 0, 1, 10, 20, 30, 40, 60, 80, 100 ng﹒mL−1). (B) Linear
relationship between the current response and PSA concentration. The error bars indicated the
standard deviation of three measurements.
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