Excitation polarization provides structural resolution of individual non-blinking nano-objects

Parallel Polarization Illumination with a Multifocal Axicon Metalens for Improved Polarization Imaging

Polarization imaging is an important branch of the microscopy technique that can provide additional information and enhanced contrast. The illumination system of a polarization microscope enables many different polarizations but makes the setup bulky, complicated, and slow. Here, we design and fabricate an ultrathin planar axicon metalens that also enables parallel illumination with different polarizations. Our results reveal a diffraction-limited size and high degree of linear polarization. To verify our approach, we accurately map the polarization angle of an aluminum grating, which is used as a polarizer. Furthermore, we demonstrate that elliptical polarization can be generated without additional design. A single metalens has the same capabilities as a conventional illumination module containing a polarizer, compensator, and rotation-stage/optical modulator. In addition, our device has the potential to enable rapid super-resolution polarization imaging. The new method could be useful in many applications and areas, including, e.g., materials research and biomedicine.

Fluorescence Anisotropy Reloaded-Emerging Polarization Microscopy Methods for Assessing Chromophores' Organization and Excitation Energy Transfer in Single Molecules, Particles, Films, and Beyond

Fluorescence polarization is widely used to assess the orientation/rotation of molecules, and the excitation energy transfer between closely located chromophores. Emerging since the 1990s, single molecule fluorescence spectroscopy and imaging stimulate the application of light polarization for studying molecular organization and energy transfer beyond ensemble averaging. Here, traditional fluorescence polarization and linear dichroism methods used for bulk samples are compared with techniques specially developed for, or inspired by, single molecule fluorescence spectroscopy. Techniques for assessing energy transfer in anisotropic samples, where the traditional fluorescence anisotropy framework is not readily applicable, are discussed in depth. It is shown that the concept of a polarization portrait and the single funnel approximation can lay the foundation for alternative energy transfer metrics. Examples ranging from fundamental studies of photoactive materials (conjugated polymers, light-harvesting aggregates, and perovskite semiconductors) to Förster resonant energy transfer (FRET)-based biomedical imaging are presented. Furthermore, novel uses of light polarization for super-resolution optical imaging are mentioned as well as strategies for avoiding artifacts in polarization microscopy.

Giant photoluminescence blinking of perovskite nanocrystals reveals single-trap control of luminescence

Fluorescence super-resolution microscopy showed correlated fluctuations of photoluminescence intensity and spatial localization of individual perovskite (CH3NH3PbI3) nanocrystals of size ∼200 × 30 × 30 nm(3). The photoluminescence blinking amplitude caused by a single quencher was a hundred thousand times larger than that of a typical dye molecule at the same excitation power density. The quencher is proposed to be a chemical or structural defect that traps free charges leading to nonradiative recombination. These trapping sites can be activated and deactivated by light.