Functional polymer brushes for on-chip electrochemical sensors

Functional polymer brushes have a tremendous interest for surface engineering, thanks to their stimuli-responsive behaviour, allowing applications in the fields of the development of switchable wettability/adhesion devices, controlled release devices and especially sensors. In this context, standard characterization techniques (GPC and NMR) are not able to provide a deep insight in their structure due to the very small amount of polymer grafted (~0.01 mg cm-2). In this work [1], functional, hydrophilic polymer brushes were grown using Surface-Initiated Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (SI-ARGET ATRP) from silicon substrates which were previously functionalized with a suitable alkoxysilane-type initiator (BIB-APTES). Using different feed ratios of the two monomers employed (2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate hydrochloride (AMA), both homopolymer (PHEMA, PAMA) and copolymer (PHEMA-co-PAMA 80:20, PHEMA-co-PAMA 50:50) brushes were obtained. Micropatterned polymer brushes were obtained using remote photocatalytic lithography [2] on the initiator monolayer. Every step of the grafting procedure (Figure 1) was studied using electrochemical techniques, in particular electrochemical impedance spectroscopy (EIS) (Figure 2), demonstrating the power and simplicity of these techniques in investigating such systems. The homogeneity and density of the initiator layer and of the resulting brushes, their composition and thickness and also the post-functionalization reactions have been easily investigated. Brushes with different loading of cationic groups could be differentiated through their marked reactions to an anionic redox probe. Noteworthy, the brushes were grown on silicon substrate which is an atypical electrode material due to its very poor electrochemical response. Grafted-from brushes allowed the reaction of ferrocyanide at the silicon surface, behaving as «tentacles» to capture the redox probe and keep it in proximity of the silicon surface. Micropatterning was found to improve the electrochemical behaviour of the system. The obtained results pave the way to the development of on-chip electrochemical devices and microsensors. Applications for drug-delivery and microfluidics can be envisaged as well. References [1] G. Panzarasa, G. Soliveri, V. Pifferi, J. Mater. Chem. C 4, 2016, pp 340-347. [2] G. Panzarasa, G. Soliveri, K. Sparnacci, S. Ardizzone, Chem. Commun. 51, 2015, pp 7313–7316.