Elliptical mirror-based TIRF microscopy with shadowless illumination and adjustable penetration depth

Chip-based wide field-of-view total internal reflection fluorescence microscopy

Conventional total internal reflection fluorescence (TIRF) microscopy requires either an oil-immersed objective with high numerical aperture or a bulky prism with high refractive index to generate the evanescent waves that work as the illumination source for fluorophores. Precise alignment of the optical path is necessary for optimizing the imaging performance of TIRF microscopy, which increases the operation complexity. In this Letter, a planar photonic chip composed of a dielectric multilayer and a scattering layer is proposed to replace the TIRF objective or the prism. The uniform evanescent waves can be excited under uncollimated incidence through this chip, which simplifies the alignment of the optical configurations and provides shadowless illumination. Due to the separation of the illumination and detection light paths, TIRF microscopy can have a large field-of-view (FOV).

High-performance imaging of cell-substrate contacts using refractive index quantification microscopy

Non-invasive imaging of living cells is an advanced technique that is widely used in the life sciences and medical research. We demonstrate a refractive index quantification microscopy (RIQM) that enables label-free studies of glioma cell-substrate contacts involving cell adhesion molecules and the extracellular matrix. This microscopy takes advantage of the smallest available spot created when an azimuthally polarized perfect optical vortex beam (POV) is tightly focused with a first-order spiral phase, which results in a relatively high imaging resolution among biosensors. A high refractive index (RI) resolution enables the RI distribution within neuronal cells to be monitored. The microscopy shows excellent capability for recognizing cellular structures and activities, demonstrating great potential in biological sensing and live-cell kinetic imaging.

Quantitative objective-based ring TIRFM system calibration through back focal plane imaging

Being the established imaging tool for cell membrane-associated studies, total internal reflection fluorescence microscopy (TIRFM) still has some limitations. The most important one is the inhomogeneous evanescent excitation field mainly caused by the large-angle and fixed-azimuth illumination scheme, which can be eliminated by using ring-shaped illumination (ring TIRFM). However, it is challenging in assembling a ring TIRFM system with precise parameter control that works well. Here we emphasize the quantification of the ring TIRFM system and introduce a robust calibration routine to simultaneously rectify the asymmetry of the spinning light beam and determine the crucial experimental parameter, i.e., the incident angle. The calibration routine requires no specific sample preparation and is entirely based on the automatic back focal plane manipulation, avoiding possible errors caused by the sample difference and manual measurement. Its effectiveness is experimentally demonstrated by both the qualitative and quantitative comparisons of the images acquired using different samples, illumination schemes, and calibration approaches. These characteristics should enable our approach to greatly improve the practicability of TIRFM in life sciences.

Artifact-free, penetration-adjustable elliptical-mirror-based TIRF microscopy

Evanescent field distribution in the focal region of the elliptical-mirror-based total-internal-reflection fluorescence (e-TIRF) microscopy is analyzed based on vectorial diffraction theory. The simulation demonstrates that the intensity of an evanescent field generated by elliptical mirror decreases exponentially with the penetration depth, and the polarization characteristic of the evanescent wave in various directions is given. We build up an e-TIRF microscope utilizing a focused hollow-cone illumination with all-direction and large range of incidence. The experiment shows the artifact effect can be well suppressed by using the azimuthal-direction illumination method. In addition, the penetration depth of the evanescent field can be controlled by adjusting the sizes of the aperture and obstruction with a large range.