Fluorescence based low-cost microbiosensors using simultaneously microfabrication process and enzyme immobilisation

A novel one-step microfabrication process of SU-8 films is proposed for developing inexpensive, small size and light-weight optical glucose micro-biosensors. Experimental work was performed in order to investigate whether the widely used in MEMS applications SU-8 photoresists polymers, can be utilised as immobilisation matrices for the simultaneous encapsulation of an oxygen-sensitive fluorescent indicator and glucose oxidase. The enzyme immobilisation, the encapsulation of the indicator and the patterning of the SU-8 take place simultaneously, thus offering a significant simplification of the microfabrication process. Despite the process involved contact with organic solvents, UV-light exposure and heating for pre- and post-bake, and the embedding of the enzyme in a hard and rigid epoxy resin matrix, it was observed that the enzyme demonstrated activity after encapsulation in SU-8. Testing of the immobilised enzyme´s activity inside the SU-8 matrix, was carried out with the measurement of oxygen consumption using an oxygen-sensitive indicator during the enzymatic oxidation of glucose. Negligible variation in fluorescence intensity upon the addition of glucose was observed in films without enzyme, whereas films with encapsulated enzyme and oxygen-sensitive fluorescent indicator showed a very clear increase in fluorescence intensity upon addition of glucose. A high transparency and negligible fluorescence of the SU-8 films were observed. The presented work opens up new possibilities for combining BioMEMS, advanced optoelectronic components with smart biosensor technology for personalised medicine diagnostic applications.