Non-aqueous Molecularly Imprinted Polymer/Polyoxometalate Nanocomposite Film With Enhanced Sensitivity for Ampicillin Detection

Abstract

Electrostatic layer-by-layer (LbL) self-assembly for preparing composite films electrode has shown great potential in high-performance electrochemical sensors owing to its precise nanoscale control over film construction and enhanced long-term stability of the films. However, most multifunctional materials that can be incorporated into composite films through electrostatic LbL self-assembly are water-soluble, which poses a major barrier to the widespread application of high-performance nonaqueous solvent materials as modification materials in electrochemical sensors. Herein, the solubility of molecularly imprinted polymer (MIP) synthesized via bulk polymerization was constantly enhanced by optimizing the molar ratio of functional monomer to cross-linker and replacing the reaction solvent, which enabled their more stable immobilization onto films. Consequently, the novel nanocomposite films containing nonaqueous MIP and Dawson-type phosphotungstic polyoxometalate (P₂W₁₈) were successfully fabricated using the electrostatic LbL self-assembly method. The MIPs, P₂W₁₈ and nanocomposite films were characterized using Fourier transform infrared (FT-IR), thermogravimetric analysis (TG), ultraviolet-visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Electrochemical sensing performance of the composite film electrode for ampicillin was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). The MIP-P₂W₁₈ nanocomposite film electrode exhibited superior selectivity and sensitivity over P₂W₁₈-only film electrode, which is attributable to the high recognition capability of MIPs via their specific recognition cavities. Electrochemical results showed that the nanocomposite film electrode had excellent electrochemical activity for ampicillin detection, including a broad linear concentration range (1.0 × 10⁻¹²–1.0 × 10⁻⁷ M) and a low limit of detection (1.5 × 10⁻¹² M). This is a significant improvement over our earlier work (1.0 × 10⁻¹⁰ M) and successfully achieved picomolar-level detection. Moreover, the MIP-P₂W₁₈ nanocomposite film electrode exhibited outstanding signal discrimination ability against potential interfering species, reliable current retention capability during 50 continuous use and robust current responses after 5 weeks. The nanocomposite film electrode could also detect ampicillin in river water and milk samples with high recovery, making it a promising sensing tool for the analysis of trace substances.