Construction of self-signal DNA electrochemical biosensor employing WS2 nanosheets combined with PIn6COOH

Abstract

In this work, a novel self-signal DNA electrochemical biosensor was constructed based on tungsten disulfide (WS₂) nanosheets combined with poly(indole-6-carboxylic acid) (PIn6COOH) as the sensing interface. The WS₂ nanosheets were synthesized via a simple solvent exfoliation method from bulk WS₂, and then PIn6COOH was electropolymerized on the WS₂ nanosheet-modified carbon paste electrode to obtain a unique nanocomposite. The electropolymerization efficiency was remarkably improved, ascribed to the physical adsorption between WS₂ nanosheets and aromatic In6COOH monomers, resulting in an increase of the electrochemical response of PIn6COOH. Owing to the presence of π-π interactions between the conjugated PIn6COOH/WS₂ nanocomposite and DNA bases, the probe ssDNA was noncovalently assembled on the nanocomposite substrate. After the hybridization of the probe ssDNA with the target DNA, the formation of the double-helix structure induced the resulting dsDNA to be released from the surface of the conjugated nanocomposite, accompanied with the self-signal regeneration of the nanocomposite ("signal-on"). The constructed PIn6COOH/WS₂ nanocomposite was not only employed as an interface for DNA immobilization but also reflected the signal transduction stemming from DNA immobilization and hybridization without any external indicators or complex labeling processes. A detection limit of 2.3 × 10^-18 mol L^-1 has been estimated and a dynamic range of 1.0 × 10^-17 mol L^-1 to 1.0 × 10^-11 mol L^-1 has been shown for the detection of a PIK3CA gene related to lung cancer. Selectivity of the biosensor has been researched in the presence of noncomplementary and base mismatched DNA sequences.

Scheme 1. The schematic illustration of the construction process of the self-signal electrochemical sensing platform.

Fig. 1. TEM images of WS₂ (A), PIn6COOH/WS₂ (B) and PIn6COOH (C).

Fig. 2. Representative cyclic voltammograms of the bare CPE (a), PIn6COOH/CPE (b) and PIn6COOH/WS₂/CPE (c) in 0.3 mol L⁻¹ PBS (pH 7.0).

Fig. 3. Representative cyclic voltammograms of the PIn6COOH/WS₂/CPE (a), ssDNA/PIn6COOH/WS₂/CPE (b) and dsDNA/PIn6COOH/WS₂/CPE (c) in 0.3 mol L⁻¹ PBS (pH 7.0).

Fig. 4. Representative Bode plots of the PIn6COOH/WS₂/CPE (a), dsDNA/PIn6COOH/WS₂/CPE (hybridized with cDNA), (b), hybridized with single-base mismatched DNA (c), hybridized with three-base mismatched DNA (d), hybridized with ncDNA (e), and ssDNA/PIn6COOH/WS₂/CPE (f) in 0.3 mol L⁻¹ PBS (pH 7.0).

Fig. 5. (A) Representative Bode plots of the ssDNA/PIn6COOH/WS₂/CPE (a) and after hybridization reaction with different concentrations of PIK3CA gene target sequences: (b) 1.0 × 10⁻¹⁷, (c) 1.0 × 10⁻¹⁶, (d) 1.0 × 10⁻¹⁵, (e) 1.0 × 10⁻¹⁴, (f) 1.0 × 10⁻¹³, (g) 1.0 × 10⁻¹² and (h) 1.0 × 10⁻¹¹ mol L⁻¹ in 0.3 mol L⁻¹ PBS (pH 7.0). (B) The plot of Δlog Z versus the logarithm of the PIK3CA gene target sequence concentrations.