Figure 1.

Main steps in microsensor chip fabrication. (a) Microfluidic master mold preparation: i. cleaning the glass substrate for the microfluidic mold blank; ii. spin-coating the blank with photoresist and prebaking; iii. exposing the photoresist through a mask to UV light and postbaking; iv. removing any unexposed photoresist from the blank with SU-8 developer and drying. (b) Microfluidic housing preparation: v. cleaning the microfluidic mold under N₂; vi. casting the microchannels in the housing in PDMS; vii. removing the PDMS housing from the mold; viii. cutting access holes in the microfluidic housing to allow connections to external fluid sources. (c) Microsensor substrate preparation: ix. cleaning the cover-glass; x. dispensing the nanosphere solution onto the coverglass; xi. drying the coverglass under low vacuum to attach the nanospheres to the coverglass; xii. sputtering gold over the nanospheres and glass surface to make a microsensor substrate. (d) Microsensor chip preparation: xiii. plasma cleaning the PDMS housing and microsensor substrate; xiv. joining the coverglass microsensor substrate and PDMS housing to make a microsensor chip; xv. connecting the fluid access lines to the microsensor chip. (e) Scanning electron micrograph (75° tilt) showing two microsensors ≈5 μm apart on a microsensor substrate. Each microsensor consists of a 780-nm polystyrene nanosphere attached to a flat glass surface, then uniformly sputtered with a 170-nm-thick Au film over Cr. (f) Schematic of a microsensor chip assembly with fluid supply attached via inlet tubes. The microfluidic channels cover a gold stripe with ≈5,000 randomly distributed microsensors. Two 4-mm-long input channels bring buffer and reagent to the microsensors. We have backfilled one inlet tube so that an air bubble separates its reagent from the remaining buffer. We control flow hydrostatically using the valves indicated. Arrows show flow direction. Not to scale.