ABSTRACT Monolayers of genetically modified proteins with an hexahistidine tag, (His)6, were obtained by using a Ni -NTA chelator synthesized on gold sputtered surfaces (via sulphide bonds), or on gold and graphite (via sililating agents) working electrodes of screen-printed devices. Two kinds of proteins were produced and purified for this study: a) a recombinant antibody, derived from the 'single chain Fv' ( scFv) format; b) a photosystem II (PSII) core complex isolated from the mutant strain CP43-H of the thermophilic cyanobacterium Synechococcus elongatus. An scFv, previously isolated from a synthetic 'phage display' library, was further engineered with an alkaline phosphatase activity genetically added between the carbossi-terminal of the scFvs and the (His)6 to allow direct measurement of immobilisation. Renewable specific binding of (His)6-proteins to gold and graphite surfaces and fast and sensitive electrochemical or optical detection of analytes were obtained. Additionally, "on chip" protein preconcentration was conveniently achieved for biosensing purposes, starting from crude unpurified extracts and avoiding protein purification steps
