Microfabricated pressure sensing particles with integrated retroreflectors

We report the microfabrication of engineered colorimetric pressure-sensing particles (PSPs) suitable for pressure measurements within microfluidic environments. Each 18-µm diameter particle consists of a semi-transparent elastic shell enclosing a compressible reference vacuum cavity. The flexible shell and compressible cavity form an optical resonator that determines its color. The particle color and corresponding pressure are interrogated optically using conventional white light microscopy. The particle shell includes a molded retroreflector that improves the angular readout efficiency. The particles exhibit a spectral shift pressure sensitivity of −19 nm/MPa with angular interrogation range >15 deg.