Metal-enhanced bright-field microscopy

Transparent samples pose serious challenges in bright-field microscopic imaging due to their low optical contrast, which also affects the imaging speed. While the role of the substrate in enhancing optical contrast has been investigated for imaging modalities such as fluorescence, a similar analysis for bright-field imaging has not been conducted. Here, we explore the effect of the substrate on the optical contrast and imaging speed in bright-field microscopic imaging. We develop a simulation model to explain the significant improvement in these imaging parameters by the introduction of reflective back substrates. We explain the effects using energy density distribution plots, power coupling, and scattering. Further, we explore the notion of optical contrast in the case of microfeatures and a procedure for selecting an appropriate metric to quantify the same. This work concludes with experimental results showing a twofold improvement in contrast and a fivefold improvement in imaging rate by an appropriate choice of back substrate. (C) 2020 Optical Society of America