This Spotlight reviews the development of label-free, nanoparticle-based nanoscopy concepts, including (1) multiwavelength time-modulation illumination to enhance the signal-to-noise ratio (SNR) and reduce the overall time to map the full field of view; (2) time-dependent polarization modulation to enhance the resolution and SNR; (3) free versus controlled nanoparticle movement; (4) image-processing concepts to improve localization capabilities; and (5) realization of 3-D nanoscopy.
Many microscopy imaging methods have been developed over the years. The invention of the phase microscope, confocal microscopy, light-sheet microscopy, and more have made it possible to investigate a variety of samples. But in order to respond to the needs of current research, imaging systems must reach higher resolutions, along with different types of requirements. In the last decade, an increasing number of super-resolution imaging methods have been proposed that enable high spatial resolution along with other considerations, such as large fields of view, faster acquisition, and compatibility with various types of sensors. Most of the influential methods in the field require some sort of sample labeling. Fluorescent labeling is the most common, especially with biological samples, due to the vast amount of knowledge on specific functional labeling. On the other hand, labeling the sample with a fluorescent dye also poses significant limitations. The labeling process is a complex task that may ruin the sample, the process is expensive, and specialized labels are usually needed. The markers or fluorescence process may also cause phototoxicity in living organisms. To overcome these limitations, nonlabeled approaches have emerged and are rapidly maturing. This Spotlight will discuss recent microscopy methods that use nanoparticles to assist in realizing super-resolved imaging of the inspected sample. While the sample itself is not labeled, its optical properties, form, and other characteristics are revealed from the agent’s location and movement.