Electrochemical molecularly imprinted sensor for hippuric acid detection based on bifunctional monomers

Hippuric acid (HA), a primary metabolite of toluene, is commonly found in urine. Its concentration in the human body correlates with the duration of toluene exposure. This study presents a molecularly imprinted polymers (MIPs) electrochemical sensor utilizing bifunctional monomers for the detection of HA, a biomarker of toluene exposure. In this design, aniline (ANI) and o-phenylenediamine (o-PD) serve as bifunctional monomers, with HA as the template molecule. A polymer film was fabricated via electropolymerization on a screen-printed electrode modified with gold nanoparticles. The electron-donating properties of ANI, combined with the superior electron transport capabilities of gold nanoparticles, significantly enhance the sensor's sensitivity. Furthermore, the two functional monomers provide abundant functional groups that interact with HA to form imprinted cavities, thereby broadening the sensor's detection range. We characterized the surface morphology of the electrode using scanning electron microscopy, atomic force microscopy and fourier transform infrared spectroscopy. Experimental conditions were optimized by investigating factors including the molar ratio of monomers to template, pH of the electropolymerization solution, scan rates, number of scan cycles, and the elution and adsorption times of HA. Under optimized conditions, the sensor was tested for HA concentrations ranging from 0 to 10,000 nM. It exhibited excellent linearity (R² = 0.983) and a low detection limit of 0.64 nM, demonstrating a broad dynamic range. The sensor also exhibited excellent specificity, repeatability, and stability. Its detection performance showed strong agreement with the gold-standard method of high-performance liquid chromatography, highlighting its significant potential for practical applications in HA detection.