Surface chemical functionalisation of epoxy photoresist-based microcantilevers with organic-coated TiO2 nanocrystals

In this Letter, a solution-based approach has been used for chemically immobilising oleic acid (OLEA)-capped TiO₂ nanocrystals (NCs) on the surface of microcantilevers formed of SU-8, a negative tone epoxy photoresist. The immobilisation has been carried out at room temperature, under visible light, in ambient atmosphere and without applying any external driving force or chemical activation of the epoxy photoresist surface. Atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy investigation demonstrate the spontaneous chemical anchoring of the organic-coated TiO₂ NCs on the microcantilevers, which resulted in a highly interconnected nanoporous multilayer structure. The chemical and morphological characterisation shows that the immobilised NCs do not change either their pristine morphology or the chemical structure after binding. Spectroscopic investigation infers that the TiO₂ NCs chemically bind through the free and highly reactive epoxy groups located on the epoxy photoresist surface by means of the OLEA capping molecules. Finally, the results show that the fabrication procedure of the microcantilevers has not been affected by the immobilisation protocol. The capability of the immobilised TiO₂ NCs to generate surface-reactive hydroxyl radicals under UV-light irradiation has a good potential for detecting families of organic compounds when integrating the modified microcantilevers in electronic noses.