Metamaterial grating for colorimetric chemical sensing applications

We propose and demonstrate a metamaterial grating sensor (MGS) composed of gold (Au) nanograting on a silver (Ag) thin-film and then encapsulated with a polydimethylsiloxane (PDMS) microfluidic chip for colorimetric chemical sensing applications. MGS is sensitive to the wavevector of incident light owing to the surface plasmonic resonance of metamaterial grating results in specific reflected colors of MGS affected by background refractive index (n) and incident angle (theta). The measured reflection spectra of MGS exhibit angle-dependence characteristic by changing theta value from 10 degrees to 45 degrees, whose resonances are blue-shifted 80 nm from the wavelength of 691 nm-611 nm and 88 nm from the wavelength of 671 nm-583 nm by injecting isopropyl alcohol (IPA) and deionized (DI) water solutions into MGS, respectively. This angle-dependence characteristic of MGS is visual in ambient light. Moreover, by injecting IPA solution with different concentrations, the maximum sensitivity of reflected resonance to n value is 1474 nm/RIU at theta = 45 degrees. Similarly, the reflected color shows green, yellow, dark yellow, and cyan colors for MGS covering with DI water, acetone, 1 ppm lapatinib in acetone, and IPA solutions, respectively in the ambient light environment. The proposed MGS proves the potential applications in portable and convenient biochemical sensing without spectrometers.