Responsive etalon based on PNIPAM@SiO₂ composite spacer with rapid response rate and excellent repeatability for sensing application.

In this paper, we demonstrate a responsive etalon fabricated through combining colloidal lithography and surface-initiated atom-transfer radical polymerization (SI-ATRP). The responsive etalon is simply constructed with one responsive spacer sandwiched by two reflective layers, and the middle responsive spacer is constructed by grafting thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes on a SiO2 nanosphere array. The etalon possesses one single interference peak in the visible region, and the interference peak changes sensitively against the concentration of the external stimulant (water vapor) or the temperature of the system, owing to the responsiveness of the PNIPAM brush. Importantly, the as-prepared etalon shows a rapid response rate and excellent stability, and it is also handy to realize the miniaturization and integration of the responsive etalon based on a conventional micro-fabrication method. These features all make the as-prepared responsive etalon an attractive candidate for future sensing applications. We believe such responsive etalons are promising for the fabrication of smart photonic materials and optical sensors that may be useful in tissue engineering, medical diagnosis, public security, and biochip areas.