Nanoimprint Lithography with UV-Curable Hyperbranched Polymer Nanocomposites for Optical Biosensing Applications

Abstract

AbstractPolymer nanocomposite gratings with a 363 nm period and a 12 nm step height were replicated using a glass master in a rapid, low-pressure imprint process. The composite materials were based on a UV-curable acrylated hyperbranched polymer and nanosized SiO2 particles. The influence of particle fraction up to 25 vol%, process pressure and UV intensity on the grating geometry was analyzed using atomic force microscopy. The period of the grating was found to be identical to that of the glass master for all investigated conditions. It was shown that the gel point of the nanocomposite was an important factor that determined the stability as well as the dimensions of the imprinted structure. However, a distortion of the grating was observed with increasing fraction of SiO2, which was correlated to the increased internal stress of the composite. Wavelength interrogated optical sensors were produced by depositing a high refractive index TiO2 layer on the composite gratings. The laser signal strength of the polymer sensors was equal to that of the reference high precision glass sensor with 10-12 g/mm2 sensitivity. The strength was lower for the nanocomposites due to propagation losses argued to result from residual porosity.