Thiolated poly(aspartic acid)-functionalized two-dimensional MoS2, chitosan and bismuth film as a sensor platform for cadmium ion detection

Abstract

In this work, a sensitive electrochemical platform for determination of cadmium ions (Cd²⁺) is obtained using thiolated poly(aspartic acid) (TPA)-functionalized MoS₂ as a sensor platform by differential pulse anodic stripping voltammetry (DPASV). The performance of the TPA-MoS₂-modified sensor is systemically studied. It demonstrates that the TPA-MoS₂ nanocomposite modified sensor exhibits superior analytical performance for Cd²⁺ over a linear range from 0.5 μg L^-1 to 50 μg L^-1, with a detection limit of 0.17 μg L^-1. Chitosan is able to form a continuous coating film on the surface of the GC electrode. The good sensing performance of the TPA-MoS₂-modified sensor may be attributed to the following factors: the large surface area of MoS₂ (603 m² g^-1), and the abundant thiol groups of TPA. Thus, the TPA-MoS₂-modified sensor proves to be a reliable and environmentally friendly tool for the effective monitoring of Cd²⁺ existing in aquacultural environments.

Fig. 1. TEM image of MoS₂ nanosheets (A), the TPA functionalized MoS₂ (B), and the TPA–MoS₂ with bismuth and cadmium (C).

Fig. 2. FTIR image of TPA and TPA–MoS₂.

Fig. 3. Cyclic voltammograms of bare GC, MoS₂/GC and TPA–MoS₂/GC electrodes in 2 mmol L⁻¹ [Fe(CN)₆]^3−/4− at a scan rate of 100 mV s⁻¹.

Fig. 4. (A) DPASVs obtained for different concentrations of Cd²⁺ using a bismuth-coated TPA–MoS₂/GC electrode; from bottom to top, 0.5, 10, 25, 50, 75, 100 μg L⁻¹ with 10 mg L⁻¹ Bi³⁺ electrodeposited for 210 s under stirring in 100 mmol L⁻¹ acetate buffer (pH 5.0). (B) Calibration curves of MoS₂/GC (red color) and TPA–MoS₂/GC (black color) electrodes for Cd²⁺.

Fig. 5. The stability of 10 repetitive measurements of 50 μg L⁻¹ Cd²⁺ in 0.1 mol L⁻¹ acetate buffer (pH 5.0) containing 3 mg L⁻¹ Bi³⁺.

Scheme 1. Schematic diagram of Cd²⁺ absorption on TPA–MoS₂ nanocomposites.