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In this paper, we describe a high-reflectance liquid mirror prepared from densely packed silver nanoparticles (AgNPs) of two different sizes. We controlled the particle size during the synthetic process by controlling the temperature. Varying the concentration of the ligand also allowed us to optimize the arrangement of the AgNPs to achieve liquid mirrors exhibiting high specular reflectance. Scanning electron microscopy and atomic force microscopy confirmed that the particles of the liquid mirror were well-packed with an interparticle distance of merely 2 nm; thus, the interstices and surface roughness of the NPs were effectively minimized. As a result of decreased scattering loss, the reflectance in the shorter wavelength regime was increased effectively. The AgNP film was also sufficiently thick to reflect the light in the longer wavelength regime. In addition, we used three-dimensional finite-difference time domain simulations and experimental measurements to investigate the relationship between the localized surface plasmon resonance (LSPR) and the specular reflection of the liquid mirrors. By changing the packing density of the AgNPs, we found that the LSPR effect could yield either a specular reflection peak or dip at the LSPR wavelengths in the reflection spectra of the liquid mirrors. Relative to previously reported liquid mirrors, the reflectance of our system is obviously much greater, especially in the shorter wavelength regime. The average reflectance in the range from 400 to 1000 nm could reach 77%, comparable with that of mercury-based liquid mirrors.

SU-8 resist was used as a coreicladding waveguide material to fabricate a Mach-Zehnder interferometer (MZI) for biochemical sensing. The refractive index and the W lithography processes of the SU-8 resist were optimized to give a SU-8 MZI chip with single-mode and high-efficiency transmission. Optical measurements reveal that the SU-8 MZI chip can transmit the NIR laser (h=1310 nm) with a total loss less than 6 dB. The bio-probes (rabbit IgG) were then immobilized on the surface of the SU-8 waveguide. When one branch of the MZI is in contact with the analyte (sheep anti-lgG), the interfered intensity changes accordingly and then stabilizes when the soaking time extended. The MZI chip is very sensitive and a dilute anti-IgG solution with a concentration as low as g/ml can be detected. The polymer MZI chip will be fabricated by molding (or LIGA) process. The low-cost, label-free, real-time and high-sensitivity MZ1 chip will benefit many applications related to biological, environmental and industrial detection.

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