Optical and photothermal properties of CsWO3 nanoparticles endow poly(dimethylsiloxane) fluidic lenses with non-invasive thermo-optic and thermo-expansion effects for fluorescence imaging

Abstract

The capabilities of CsWO₃ nanoparticles to transmit in the visible range from 400 nm to 650 nm and undergo strong near-infrared photothermal conversion from 750 nm to 2400 nm may make them functional materials in the fabrication of focus-tunable optical lenses. In this research, the noninvasive focal length tuning of a poly(dimethylsiloxane) (PDMS)-structured fluidic lens by near-infrared irradiated cesium tungsten oxide nanoparticles (CsWO₃ NPs), which generates heat and induces photothermal and thermo-optic effects on PDMS, was explored. The temperature-dependent mechanical property of PDMS and the stoichiometric, structural and photothermal properties of CsWO₃ NPs were characterized. Young's modulus ranged from 4.5 MPa to 3.7 MPa as the temperature of the PDMS sample increased from 25 °C to 48 °C and allowed a delicate tuning of the fluidic lens’ front focal length from 21.02 mm to 20.89 mm when the near-infrared (NIR) optical power density increased from 0 mW cm⁻² to 226 mW cm⁻² while retaining the concentric shape of the focused beam spot. The fluidic lens was then incorporated into the detection arm of a light sheet fluorescence microscope, and it successfully captured the contrast-enhanced images of the fluorescein-coated CsWO₃ NPs.