In-Situ Fabrication of Electroactive Cu2+-Trithiocyanate Complex and Its Application for Label-Free Electrochemical Aptasensing of Thrombin

Abstract

The preparation of an electroactive matrix for the immobilization of the bioprobe shows great promise to construct the label-free biosensors. Herein, the electroactive metal-organic coordination polymer has been in-situ prepared by pre-assembly of a layer of trithiocynate (TCY) on a gold electrode (AuE) through Au-S bond, followed by repetitive soaking in Cu(NO₃)₂ solution and TCY solutions. Then the gold nanoparticles (AuNPs) and the thiolated thrombin aptamers were successively assembled on the electrode surface, and thus the electrochemical electroactive aptasensing layer for thrombin was achieved. The preparation process of the biosensor was characterized by an atomic force microscope (AFM), attenuated total reflection-Fourier transform infrared (ATR-FTIR), and electrochemical methods. Electrochemical sensing assays showed that the formation of the aptamer-thrombin complex changed the microenvironment and the electro-conductivity of the electrode interface, causing the electrochemical signal suppression of the TCY-Cu²⁺ polymer. Additionally, the target thrombin can be label-free analyzed. Under optimal conditions, the aptasensor can detect thrombin in the concentration range from 1.0 fM to 1.0 μM, with a detection limit of 0.26 fM. The spiked recovery assay showed that the recovery of the thrombin in human serum samples was 97.2-103%, showing that the biosensor is feasible for biomolecule analysis in a complex sample.

Keywords: Cu2+; aptasensor; electrochemical; thrombin; trithiocynate.

Scheme 1

Schematic illustration for the preparation of AuNPs/Cu²⁺-TCY polymer-based aptasensing film on a gold electrode and its analytical application.

Figure 1

Topographic (a), three-dimensional (b) and cross-sectional (c) AFM images of AuE upon stepwise assembly of p(Cu²⁺-TCY) (A), AuNPs (B), and MCH/TBA (C). The triangle symbols in the c represents the lowest and the highest points in the cross-sectional line.

Figure 2

CV (A) and EIS (B) plots of 0.1 M KCl containing 1.0 mM [Fe(CN)₆]^3−/4− at AuE (a), p(Cu²⁺-TCY)/AuE (b), AuNPs/p(Cu²⁺-TCY)/AuE (c), and MCH/TBA/AuNPs/p(Cu²⁺-TCY)/AuE (d).

Figure 3

CVs (A) of p(Cu²⁺-TCY)/AuE (a) upon successive assembly of AuNPs (b), MCH/TBA (c) and binding with thrombin (d) and the corresponding histogram of oxidation peak currents (I_p) of each electrode (B). (C) CVs of p(Cu²⁺-TCY)/AuE at different scan rates ranging from 0.01 V s⁻¹ to 0.5 V s⁻¹ in 0.01 M PBS (pH = 6.80) and (D) the corresponding relationships of peak currents (I_p) versus scan rate (ν).

Figure 4

(A) DPVs of the aptasensor in PBS buffer after incubation in thrombin solution with concentrations ranging from 0 to 1 nM, and (B) the linear relationship between the peak current (I_p) versus the negative logarithm of thrombin concentration (−lgC). (C) Histogram of the peak current difference (ΔI_p) of the aptasensor after incubation in blank buffer, BSA, Hb, thrombin, and their mixture. The concentration of thrombin is 1.0 fM, and the two control proteins are 10 pM. (D) Histogram of the peak current retained after storage of the prepared aptasensor for one week.