Direct electrochemical addressing of immunoglobulins: immuno-chip on screen-printed microarray

An original immobilisation technology is presented for the development of chemiluminescent protein biochips, suitable for measurement in complex matrices. The immobilisation strategy involved is based on diazotated aniline derivatives, which could be electro-addressed, thus creating a covalent linkage with a conducting material surface. The present electrochemical system is a cost effective and mass-produced carbon paste screen-printed (SP) microarray composed of eight 0.2 mm2 working electrodes, one carbon pseudo-reference electrode and one auxiliary electrode. Rabbit immunoglobulins (IgG) were chemically modified with an aniline derivative (4-carboxymethylaniline) in order to be easily electro-grafted to the SP microarray surface. The possibility of successively electro-address the eight sensing layers of a particular array, with a good reproducibility (more than 80%) and without loss of reactivity was demonstrated. Moreover, these immobilised proteins were subsequently used as a capture agent for the determination of rheumatoid factor (RF) in human sera. The absence of non-specific signal or interference problem enabled the detection of RF values in complex samples in the 5.3-485 IU/ml range with a good correlation with the standard Auraflex ELISA test method.