Surface activation and functionalization with aryl-diazonium chemistry enable biomolecules grafting on 3D printed carbon-based electrodes

Carbon-based electrodes printed using fused deposition modelling (FDM) technology constitute appealing platforms for electrochemical biosensors. However, immobilizing bioreceptors that retain their stability and recognition properties at the electrode surface is quite challenging. So far, only few successful biosensors based on covalently binding antibodies, DNA strands or aptamers have been reported on FDM printed electrodes, most relying on complex and costly fabrication protocols. In this study, an electrografting technique using aryl diazonium chemistry is implemented to modify the surface of 3D-printed electrodes produced using a filament composed of polylactic acid (PLA) and carbon black (CB). The effect of electrochemical cycling in NaOH or oxygen-plasma pre-treatment on the physical, chemical and surface reactivity of the electrodes is assessed. Successful functionalization with carboxyl groups by electrografting of 4-carboxyphenyl diazonium cations generated in situ from 4-aminobenzoic acid is demonstrated. Using the (aminomethyl)ferrocene redox probe reveals superior grafting on plasma treated surfaces. Covalent binding of an aptamer targeting Bacillus cereus bacteria on the -COOH modified surfaces through carbodiimide chemistry is subsequently demonstrated using electrochemical impedance spectroscopy and fluorescence microscopy. This approach paves the way for the development of a new generation of aptasensors based on thermoplastic modified electrodes.