Advanced immobilization and protein techniques on thin film biosensors

Abstract Thin film technology providing the high purity and reproducibility required of an electrode surface for structures making use of monomolecular layers requires the adaptation of surface and protein chemistry to the necessities of molecular monolayers. Stepwise chemical modification of the metal electrode surface turned out to be most practical for these biosensors. Glass and polyimide sheets as well as aluminium oxide ceramics were used as electrode carriers. An electron gun was used to coat the substrates with a platinum layer (as electrochemical electrode) up to a thickness of 60 nm. To increase the peel strength of the sensors an adhesion layer of titanium up to a thickness of 80 nm was applied underneath. Structuring of these thin films was performed by a lift off technique. Metal layers were isolated by silicon nitride or polyimide layers which were structured by plasma etching. Different chemical oxidation techniques were applied to activate the highly purified platinum for further derivatization. The platinum oxide sites were silanized in order to obtain amino or mercapto coupling groups. To activate the electrodes for protein coupling six different coupling procedures were tested to immobiize different preparations of glucose oxidase from Aspergillus niger and l -lactate oxidase from Pediococcus species. To obtain a quantitative suppression of interfering substances differential measurement employing photochemical inactivation of enzymes was the most effective method.