The Nobel Prize-winning innovation of super-resolution microscopy, which allows imaging below the diffraction limit of light, has enabled some breathtakingly sharp views of tiny biological structures. However, it is not something you would find in a typical biology lab; instead, it necessitates sometimes using complex and expensive tools and extensive image post-processing. Researchers have developed a method to bring 3D sub-diffraction imaging capability to standard confocal microscopes in bio labs. The technique, dubbed upconversion super-linear excitation-emission (uSEE) microscopy by the researchers, is based on the clever use of so-called upconversion nanoparticles (UCNPs) as fluorescent markers, which provide sharp, tunable narrow emissions when excited by low-power, near-infrared light.
Achieving super-resolution microscopy on confocal microscopes using “super-linear” emitters dates back several decades. In essence, these luminescent markers belong to a class of materials whose fluorescent emission is super-linearly proportional to the power of the exciting laser.
In practice, this means that when a low-power laser beam strikes the super-linear emitter, only the center of the beam profile, where the beam intensity is greatest, will cause significant emissions. This implies that the size of the emitting region will be smaller than the size of the beam profile itself, resulting in sharper resolution. The higher the resolution, the more super-linear the material.