Single drop detection of furfural in wine by an SPR sensor based on molecularly imprinted polymer as biomimetic receptor

A surface plasmon resonance (SPR) platform, based on a D-shaped plastic optical fiber (POF), combined with a biomimetic receptor, i.e. a molecularly imprinted polymer (MIP), has been proposed by our research group. It is an easy to use and cheap device for chemical sensing of substances of interest in different fields, as health, environment and industry. The possibility of performing single drop measurements is a further favourable aspect for practical applications. We proposed the use of the SPR-MIP sensor for food industry controls, i.e. the analysis of 2-furaldheide (2-FAL) in fermented beverages as wine. The platform is based on a multimode POF with a characteristic D-shaped sensing region, which makes it possible to perform the measurement in a drop simply deposited over the flat surface. It presents, on the exposed POF core, a multilayer configuration with a buffer layer (a photoresist of high refractive index, 1.5 μm thick), a thin metal film (gold, 60 nm thick) and a MIP layer as a specific chemical receptor. The MIP was built up in situ, dropping over the gold layer the prepolymeric mixture and allowing polymerization. In the SPR here described the resonance wavelength is determined exploiting a white light source and a spectrometer. The sorption curve in aqueous solution, at constant pH, was modelled by the Langmuir equation, with a constant response for concentrations higher than 1 mg/L, corresponding to the saturation of the receptor. The affinity constant, K_aff, in water is 4.8 L/mg. The LOD in water was 0.03 mg/L, but a somewhat higher value was determined in a white wine, due to the effect of the complex matrix on K_aff. Despite the slightly higher LOD, the sensor is suitable for 2-FAL analysis in wines.