Supporting Section
Label-free electrochemical immunoassay of carcinoembryonic antigen in human serum using magnetic nanorods as sensing probes
Xiaohong Fu[*]· Jinyue Wang · Na Li · Li Wang · Lan Pu
Results and discussion
Optimization of experimental conditions
The effect of pH of the detection solution (PBS) on the potentiometric response of the developed immunosensor was studied between 4.0 and 8.5 (Fig.s1a). The potentiometric response initially increased with increasing pH value from 4.0 to 7.4, and then decreased at high pH. The optimal response for the antigen-antibody interaction takes place at pH 7.4, which was in accordance with the optimal binding for most immunoreactions. It is well known that at relatively high pH, the bioactivity of the antigen-antibody complex will be inhibited. So, pH 7.4 of PBS was used as the supporting electrolyte for the detection of CEA.
Another factor influencing the performance of the developed immunosensor is the magnetic density of the external magnet. The higher the magnetic density is, the more magnetic bionanorods will accumulate the surface of the magnetic electrode, which might inhibit the antigen-antibody reaction. If the magnetic density of the external magnet is too lower, the amount of the magnetic bionanorods on the electrode surface will be reduced, which might decrease the sensitivity of the immunoassay. Seen from Fig. s1b, theoptimal response wasobtained at 0.3 T. When the magnetic intensitywas larger than 0.3 T, a higher signal was achieved, but the background signal also increased. Thus, 0.3 T of the external magnet was selected for the immobilization of the antibodies.
Additionally, the incubation time and incubation temperature for the antigen-antibody reaction in the incubation solution greatly affected the potentiometric response of the developed immunosensor. As shown in Fig. s1c, the potentiometric change of the developed immunosensor toward 50 ng·mL-1 CEA exhibits optimal response at 37 ºC.At this temperature, the potentiometric response of the immunosensor to50 ng·mL-1 CEA increased with the increment of incubation time and leveled off after 30 min (Fig. s1d). Longer incubation time did not improve the response. Therefore, 37 ºC and 30 min were chosen for the antigen-antibody reaction in the incubation solution.
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Supporting Section
Fig. s1 The effects of (a) pH of PBS, (b) magnetic density of the external magnet, (c) incubation temperature, and (d) incubation time on the potentiometric response of the developed immunosensor toward 50 ng·mL-1 CEA
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[*]X. Fu · J. Wang · N. Li · L. Wang · L. Pu
School of Chemistry and Chemical Engineering,
Yibin University,Yibin 644000,
People’s Republic of China
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