# A Molecularly Imprinted Polymer Based SPR Sensor for 2-Furaldehyde Determination in Oil Matrices
###### Abstract  
Optical chemosensors with surface plasmon resonance (SPR) transduction are widely employed, even in complex environments, such as those outside the laboratory. In this context, not only the chemical nature but also the physical form of the receptor layer is particularly relevant. Synthetic receptors as molecularly imprinted polymers (MIPs) are well suited. This is demonstrated here in the case of an SPR sensor platform based on a multimode plastic optical fiber, which is very promising for on site application due to the low dimensions and low cost. A specific MIP was used as the receptor, with high affinity for the substance to be determined, 2-furaldehyde, in water. Here, a medium of high refractive index, i.e., vegetable oil, was considered because of the high interest for its determination in industrial diagnostics. The effects of the MIP layer thickness and the washing extent on the quality of the analytical signal were investigated. Better spectra were generated at the thinner MIP layer, while a lower detection limit is reached with extended washing. molecularly imprinted polymer; optical sensor; plastic optical fiber; surface plasmon resonance; 2-furaldehyde; vegetable oil +
Footnote †: journal: Medical Imaging  
considerable time, effort and expense, and can produce some changes in the sample composition before analysis. An alternative approach consists of portable monitoring systems relying on sensing methods. They appear to be well suited to complement standard analytical methods and, also, can be permanently installed at monitoring sites and can transmit data remotely. Considering the wide range of application areas, a huge number of bio- and chemo-receptor-based sensors have been described in the last twenty years, among which those based on optical transduction, and in particular on optical fibers, have been shown as well suited for numerous applications [6; 7; 8; 9; 10; 11]. The sensing platform used here for the determination of 2-FAL in vegetable oil is based on an optical transduction method, surface plasmon resonance (SPR), on optical fiber, and based on a synthetic chemical receptor, a molecularly imprinted polymer (MIP). It has been previously used for a number of applications in aqueous matrices [12; 13; 14], but a different matrix was also considered, i.e., a mineral oil of the isolated transformers [15]. The optical fiber sensing platforms based on SPR allow marker-free detection, and plastic optical fibers (POFs) are especially advantageous for low-cost sensing systems due to their excellent flexibility, easy manipulation, great numerical aperture, large diameter and the fact that plastic can withstand smaller bend radii than glass [16]. The platform proposed here consists of a planar surface of an exposed POF core, embedded in a resin block (D-shaped POF platform), covered with a dielectric layer of photoresist with high RI and a thin gold layer [17]. The receptor layer is deposited on the gold surface. The flat shape of the sensing part is particularly suitable for measurements in a drop, for which no expensive and bulky flow-through cell is required. MIPs are a class of artificial solid receptors [18; 19; 20] containing sites functionally and dimensionally complementary to the target molecular structure, similar to the receptor sites in bioreceptors. The process of MIP preparation is based on a template-assisted synthesis [19]. MIPs often possess recognition properties analogous to natural receptors but have the stability, ease of preparation, micromachining, integrability and low cost of production typical of synthetic materials. Moreover, MIPs can be easily produced as layers in tight contact with the transducing surfaces [12; 14]. In this form, MIPs are different from the usual bioreceptors, for example, antibodies or aptamers, since the thickness of the layer, while being not larger than a few hundred nanometers, is certainly much higher than that of the bioreceptors layers, usually constituted by only one or a few molecular layers.