Marzia Iarossi4,Angela De Fazio1,Pascal Welzen2,Jan Van Hest2,Elisabetta Colombo1,3,Fabio Benfenati1,3,Francesco De Angelis1
Istituto Italiano di Tecnologia1,Eindhoven University of Technology2,IRCCS Ospedale Policlinico San Martino3,Italian Institute of Technology4
Marzia Iarossi4,Angela De Fazio1,Pascal Welzen2,Jan Van Hest2,Elisabetta Colombo1,3,Fabio Benfenati1,3,Francesco De Angelis1
Istituto Italiano di Tecnologia1,Eindhoven University of Technology2,IRCCS Ospedale Policlinico San Martino3,Italian Institute of Technology4
Achieving precise control on the regulation of a flow is of outmost importance to obtain a reliable valve for the selective delivery of material from one side to the other of the valve itself, in the attempt to mimic the selectivity and properties of cell membranes. In the literature numerous efforts of externally controlled gating have been reported; however, many of these strategies lack of scalability, fast responsiveness of the gating, efficient external control.<br/>In this work, we aim to achieve controllable delivery of a neurotransmitter, glutamate, using light-gated solid-state channels. The channels were obtained by milling conical nanopores in a 500 nm thick Si<sub>3</sub>N<sub>4</sub> membrane; then they were functionalized with an azobenzene-based polymer. The presence of numerous azobenzene molecules generates a polymeric structure able to switch between an expanded <i>trans</i> structure and a collapsed <i>cis</i> configuration. This conformational switch results into a gating behaviour inside the channels, between a closed (<i>trans</i> isomer) and an open (<i>cis</i> isomer) configuration. The polymer functionalisation was examined by AFM, while the amount of loaded polymer was quantified using a quartz microbalance. The <i>cis-trans</i> isomerisation within the channels was monitored by ellipsometry.<br/>To test the light responsiveness and the gating efficiency, the nanopatterned membrane was encased in a home-made microfluidic device consisting of a chamber on top of the membrane and a bottom reservoir, located underneath the membrane. This was used to flow glutamate molecules through the channels. The gating capability was monitored by Current-Voltage (IV) measurements, while the amount of translocated neurotransmitter was quantified by fluorescence spectroscopy.<br/>This light-gated microfluidic device may represent a viable option for any application requiring precise and controlled delivery of specific molecules in specific locations. For example, we envision the use of this technology in the field of retinal prosthetics, where it could be employed to restore the light-evoked glutamate outflow on the denervated inner retinal neurons upon photoreceptors degeneration.