Picodroplet-deposition of enzymes on functionalized self-assembled monolayers as a basis for miniaturized multi-sensor structures

We are reporting on a novel approach for structured immobilisation of enzym es on gold surfaces modified with monolayers of functionalised alkylthiols. The formation of enzyme spots is achieved by shooting very small volumes o f an appropriate enzyme solution (down to 100 pl) onto a thiol-monolayer mo dified gold surface using a micro-dispenser. Formation of enzyme patterns i s obtained by moving the micro-dispenser relative to the modified gold surf ace using a micro-positioning device. Enzyme spots with typical lateral dim ensions of 100 ml are obtained, but also, more complex structures, e.g. lin es or meander structures, can be achieved by multiple droplets dispensed du ring the concomitant movement of the micro-dispenser. The first enzyme laye r on top of the functionalised thiol-monolayer is subsequently covalently i mmobilised using either carbodiimide activation of carboxilic headgroups at the enzyme or via already introduced activated ester functions at the mono layer. Immobilised enzyme activities of glucose oxidase and lactate oxidase patterns have been characterised by means of scanning electrochemical micr oscopy. The product of the enzyme-catalysed reaction, H2O2, is detected wit h an micro-electrode in the presence of either or both substrates, glucose and lactate, leading to a visualisation of the corresponding enzyme pattern and the lateral enzymatic activity. (C) 2001 Elsevier Science B.V. All rig hts reserved.