Manipulation of electrical charge of proteins for sensitive biosensing using field-effect transistors

To gain better signals in potentiometric biosensing of protein, site-selective chemical modification of amino acid residues was employed by exogenous acylation and glycation reactions of primary amines and the guanidinium group, converting them from cationic into anionic or neutral. The site-selectivity of the charge-conversions resulted in maintained structural integrity and bioactivity of the proteins. The estimated negative charge density of bovine serum albumin (BSA) under physiological pH increased by 5-fold. The potential shifts by the adsorption was 3-fold higher in succinylated BSA than original BSA, whereas more significant amplification of the signal (11-fold) was observed by the modifications of lysozyme using a field-effect transistor (FET) biosensor.