Spatially selective biomolecules immobilization on silicon nitride waveguides through contact printing onto plasma treated photolithographic micropattern: Step-by-step analysis with TOF-SIMS chemical imaging

Abstract Time-of-flight secondary ion mass spectrometry has been employed to characterize micropatterning of aminosilane layer by photolithography and oxygen plasma treatment to achieve spatially selective biofunctionalization of Si3N4 waveguides surface corresponding to the sensing arm area of Mach-Zehnder interferometric biosensors integrated on silicon-chip. Si3N4 surface with (3-aminopropyl)triethoxysilane (APTES) layer was examined after photolithography, plasma treatment, photoresist removal, and after robotic spotting with biotinylated bovine serum albumin (BSA), blocking with BSA and specific binding of streptavidin. TOF-SIMS chemical imaging and microanalysis provided an inside view regarding the resolution and selectivity of surface modification after each step of both the APTES layer patterning and biofunctionalization procedures. More particular, the effective APTES removal and surface oxidization to create 20-µm wide APTES stripes through photolithography and oxygen plasma treatment was demonstrated. Exclusive adsorption of biotinylated-BSA on the APTES stripes through spotting of the patterned surface is then revealed, followed by a preferential but not exclusive BSA adsorption during the blocking step. The pattern was clearly developed through exclusive streptavidin binding to biotinylated-BSA only onto the APTES regions. The proposed spatially-selective biofunctionalization, performed with biotinylated-BSA, was demonstrated for the Si3N4 waveguide surface of an integrated on chip interferometric biosensor sensing arm for the detection of streptavidin.