A new immobilization procedure based on gelling oligopeptides for biosensors development

One of the most important aspects that have to be taken into account in the development of electrochemical biosensors is represented by the redox proteins immobilization on the electrode surface. An ideal immobilization procedure should ensure the stable presence of the proteins, maintaining their electrocatalytic properties and allowing a good accessibility to the target analyte and an efficient communication with the electrode surface. In this work, we studied different oligopeptides for the immobilization of redox proteins. The first molecule tested was a Fluorenylmethyloxycarbonyl-triphenylalanine (Fmoc-Phe3), a gelling tripeptide synthesized in our laboratories by a lipase-catalyzed reaction between Phe2 and Fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-Phe) in phosphate buffer solution [1]. The Fmoc moiety caused the formation of a hydrogel based on 3-dimensional nanofibers that could efficiently entrap the proteins. To increase the adhesion of the hydrogel to the electrode surface we also modified the active molecule by adding a terminal cysteine methyl ester unit. This latter moiety ensuring a stable covalent bond S-Au on a gold electrode surface. The Fmoc-triphenylalanine-cysteine methyl ester tetrapeptides (Fmoc-Phe3-Cys(OMe)) was prepared, according to the above mentioned procedure, starting from a diphenylalanine-cysteine methyl ester tripeptides (Phe2-Cys(OMe)) previously synthesized. Lastly, the same Phe2-Cys was employed in the formation of a self-assembled monolayer (SAM) on a gold surface as an alternative chemical immobilization method. The enzymatic biosensors were characterized by surface spectroscopy and electrochemical techniques resulting in a simplified and cost-effective immobilization procedure that also ensured a good stability and reproducibility of the enzymatic-polymeric film. [1] L. Chronopoulou et al. Soft Matter, 2014, 10, 1944