LSPR Substrate‐Enhanced Label‐Free Dark‐Field Optical Microscopy

ABSTRACT Label‐free optical imaging of tiny biological samples is quite challenging due to the weak scattered signals of the samples. This work proposes a localized surface plasmon resonance (LSPR) substrate to hold low‐refractive‐index biological samples and realize high‐contrast label‐free imaging using a dark‐field illumination optical microscope. The LSPR substrate can increase the scattering signal of a sample on the substrate and adjust the scattering angle to a more acceptable angle. The scattering intensity of the sample on the LSPR substrate is 1.86 and 7.12 times that on the Ag‐coated substrate and the glass slide, respectively. The contrast of the sample on the LSPR substrate is 1.55 and 3.64 times that on the Ag‐coated substrate and the glass slide, respectively. This work can inspire the development of high‐contrast, label‐free imaging of biological samples under optical microscopy.