Nonlinear Label-Free Super-Resolution Microscopy Using Structured Illumination

Abstract

Optical microscopy is a standard tool to study biological objects. Diffrac-tion limits the achievable lateral resolution of an optical microscope to around 200 nm restricting its applicability. However, recent advances in optical super-resolution techniques have shown that the diffraction does not impose a fundamental limit to resolution and can be circumvented. These super-resolution techniques can provide resolution approaching the nanometer scale and are enabling studies of biological objects with unprecedented capabilities. However, most of the super-resolution techniques are based on using fluorescent dyes, complicating their use in medical research and applications. Therefore, a need exists for label-free super-resolution techniques, which could be especially valuable for clinical applications. To answer this need, several such techniques have been recently developed. In this chapter, we introduce the reader to some of these techniques, discuss their applications, and of the possible future directions. In order to limit the scope of this vastly expanding topic, we focus on techniques based on structured illumination and intrinsic nonlinear responses of materials.