Optical fiber sensor for the detection of tetracycline using surface plasmon resonance and molecular imprinting

We present a simple and highly selective optical fiber sensor for the detection of tetracycline in foodstuffs by using the combination of surface plasmon resonance (SPR) and a molecular imprinted polymer (MIP) matrix. The sensor is fabricated first by coating a thin film of silver metal over the unclad portion of an optical fiber, and then preparing a molecular imprinting of the target molecules over the metal coated region. The MIP creates several binding sites/nano-cavities which have the complementary shape and functional groups of the target molecules on its surface. The sensor works on the wavelength modulation scheme in which the shift in resonance wavelength is measured with respect to the change in tetracycline concentration. Two kinds of tetracycline, tetracycline hydrochloride (TC) and oxytetracycline hydrochloride (OTC) have been selected as the imprinting molecules because these possess similar structures. The presence of tetracycline samples in the vicinity of the sensing region causes the interaction between binding sites and target molecules which results in the change in the dielectric properties of the sensing surface, causing the shift in the SPR spectrum towards the red region. The selectivity of the sensor for dissimilar compounds, and cross-selectivity between TC and OTC, has been tested. The reusability of the sensor has also been checked. The present sensor is suitable for commercialization for the detection of tetracycline in food as it has several advantageous features such as low cost, ease of handling, a miniaturized probe, fast response, high selectivity, reusability and the possibility of online monitoring and remote sensing.