Simulteanous enzyme immobilisation and micro-nanofabrication process for low-cost biosensor applications

Biosensors which are based on BioMEMS combine developments in micro-nanotechnology and biological recognition elements, in order to enable the measurement of low level analyte concentrations with portable detection-systems. A major challenge of such small biochips is the accuracy of the sensing process. The main aim of the present research project was the investigation and development of novel low cost matrices based on custom-made SU-8 polymer for simultaneous microfabrication and immobilisation of enzymes in order to form the basis for the development of novel low-cost micro-nano-biosensors. The negative photoresist SU-8 was utilised because of its attractive characterestics such as stability under environmental conditions, biocompatibility and low cost. The entrapment of biological molecules into the SU-8 structures was experimentally assessed using the enzyme glucose oxidase; and, electrochemical and optical sensing techniques were employed. The major emphasis of the experimental studies was on selectivity, sensitivity and stability improvements as well as on the optimum design, and microfabrication process. A detailed investigation of the optimum microfabrication process and composition of biocompatible SU-8 matrices with encapsulated enzyme such as glucose oxidase was carried out. The conditions of the various steps of the SU-8 processing are hostile to the enzymes’ survival. Improving the process conditions and encapsulation matrices were primordial for the success of this work. This study implied variation in enzyme concentration matrices in order to improve the activity of the encapsulated enzyme inside the matrix. Different sacrificial materials for SU-8 and their influence on the used enzyme and on the products of enzymatic reactions were investigated.