Full-field photonic biosensors based on tunable bio-doped sol–gel glasses

Abstract

A full-field generic photonic biosensor approach, which relies on a bio-doped polymeric strip waveguide configuration, is described. We show the potential of tailor-made hybrid polymeric materials prepared by sol–gel technology for the fabrication of ultra-compact biosensor devices, where both the transducer and the recognition elements are merged into one single microstructure. Such devices were fabricated by micromolding in capillaries (MIMIC) soft lithographic technique. In contrast to evanescent field sensors, the sensor response does not only rely on the interaction of the evanescent wave with the recognition element, but on the interaction of the whole field, thus enabling a reduction of the sensor dimensions and/or a decrease of its limit of detection (LOD). The potential of this generic approach was demonstrated by developing a biosensor for the detection of H₂O₂ using horseradish peroxidase (HRP) as the doping agent. Solutions containing 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic) acid (ABTS) and different concentrations of H₂O₂ were dispensed over the waveguide and the green-coloured cation radical ABTS˙⁺ product was mainly obtained inside the photonic structure, resulting in a maximum absorption increase of 2.5 a.u. at a set working wavelength of 670 nm over the H₂O₂ concentration range studied. The sensor exhibited a sensitivity of (3.1 ± 0.2) × 10³ a.u./mol L⁻¹ and a limit of detection (LOD) of 4.4 × 10⁻⁵ mol L⁻¹ H₂O₂. These results anticipate that full-field waveguide microstructures based on bio-doped sol–gel polymers will enable the fabrication of cost-effective photonic biosensors. Moreover, the ease of fabrication by a soft lithography technique and the use of such polymeric materials are fully compatible with their integration in compact automatic analysis systems.