Ternary Pt-Co-Cu nanodendrites for ultrasensitive voltammetric determination of insulin at very low working potential

Fengying Shao1, Lei Jiao1, Qin Wei1, He Li1*

1 School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China

* Corresponding author: Dr. He Li (Email: )

Electrochemical impedance spectroscopy (EIS)

The A.C. impedance spectroscopy of the GCE (curve a) appears to be a smaller diameter, whichattributed to a free electron-transfer process. The electrodeposited Au NP (curve b) possessed excellent property of enhancing electron transfer in the sensing. Accordingly, the spectroscopy exhibits almost a linear. After modification of the electrode with Ab1 (curve c), the semicircular obviously increases than Au NP(curve b) because the Ab1 is non-conductive bioactive substances. After coating BSA (curve d), the semicircle was increased which demonstrated that BSA as non-conductive protein closed nonspecific sites. After incubation with antigen (curve e), the resistance further increased than BSA, which indicated that antigen was bound on the modified electrode and prevent electron transfer successfully. Furthermore, the resistance of the immunosensor increased significantly after the Pt-Co-Cu-Ab2 (curvef) was added onto the electrode.

The electrochemical surface area(ESA)

Here, 6 μL 2.0 mg/mL Co-Cu nanoalloy, Pt nanoparticles, Pt-Co nanodendrites, Pt-Cu nanoalloy and Pt-Co-Cu nanoalloy were modified on the electrode, respectively. Ternary Pt-Co-Cu nanoalloywas used as an example. The ESA was detected by chronoamperometry method and the step potential was from 0.5 V to -0.5 V, number of steps was 1, pulse width was 0.25 s, sample interval was 0.002 s, and the quiet time was 2 s. According to the Cottrell equation as following:

Where the n is the number of electron transfer (n=1), F is the Faraday constant (F=96485 C·mol-1), A is the electrochemical surface area, is the concentration of the electrolyte solution (), and the is the apparentdiffusioncoefficient of the potassium ferricyanide (K3Fe(CN)6) in 0.1 mol·L-1 KCl solution (). The detection result was shown in Fig. S1 (A), and the red line in Fig. S1 (B) was the fitting a straight line. The line was choice the as independent variable and the lineslope was 6.83. According to theCottrell equation, the calculated result of A was 0.353 cm2. The ESA of Co-Cu nanoalloy (0.241 cm2), Pt nanoparticles (0.289 cm2), Pt-Co nanodendrites (0.236 cm2), Pt-Cu nanoalloy (0.272 cm2) were obtained by thesimilar with Pt-Co-Cu nanoalloy.

Fig.S1Thelimited currentrelationships with time (A) and-0.5 power of time (B).

FigureS2Nyquist plots of the AC impedance for each immobilized step recorded in 0.1 M KCl solution containing 2.5mM Fe(CN)63-/ Fe(CN)64-from 1 to 105 Hz of bare GCE (a), Au NP/GCE (b), Ab1/Au NP/GCE (c), BSA/Ab1/Au NP/GCE (d), Insulin /BSA/Ab1/Au NP/GCE (e) and Pt-Co-Cu-Ab2/Insulin /BSA/Ab1/Au NP/GCE (f).

Table S1Simulation parameters of the equivalent circuit components

Electrode / Rs (Ω) / Ret (Ω) / Cdl (F) / Zw
GCE / 137.7 / 41.45 / 3.917×10-6 / 0.003564
GCE/Au NPs / 128.9 / 23.84 / 7.681×10-6 / 0.001068
GCE/Au NPs/Ab1 / 122.9 / 86.8 / 3.071×10-6 / 0.002152
GCE/Au NPs/Ab1/BSA / 129.5 / 152.9 / 7.616×10-7 / 0.001469
GCE/Au NPs/Ab1/BSA/insulin / 122.1 / 188.6 / 1.539×10-7 / 0.003338
GCE/Au NPs/Ab1/BSA/ insulin/ Pt-Co-Cu-Ab2 / 132.2 / 220.7 / 6.531×10-7 / 0.004676

Figure S3Effect of pH (A) and the different concentration of Pt-Co-Cu-Ab2 (B) in the response of the immunosensor for the detection of 200 pM insulin.(Amperometryat -0.015 V) Error bar=RSD (n=5).