Fluorescence imaging with tailored light

Highly sensitive volumetric single-molecule imaging

Volumetric subcellular imaging has long been essential for studying structures and dynamics in cells and tissues. However, due to limited imaging speed and depth of field, it has been challenging to perform live-cell imaging and single-particle tracking. Here we report a 2.5D fluorescence microscopy combined with highly inclined illumination beams, which significantly reduce not only the image acquisition time but also the out-of-focus background by ∼2-fold compared to epi-illumination. Instead of sequential z-scanning, our method projects a certain depth of volumetric information onto a 2D plane in a single shot using multi-layered glass for incoherent wavefront splitting, enabling high photon detection efficiency. We apply our method to multi-color immunofluorescence imaging and volumetric super-resolution imaging, covering ∼3-4 µm thickness of samples without z-scanning. Additionally, we demonstrate that our approach can substantially extend the observation time of single-particle tracking in living cells.

A near-infrared fluorescent probe for viscosity: Differentiating cancer cells from normal cells and dual-modal imaging in tumor mice

As a basic parameter of the intracellular microenvironment, viscosity is closely related to the development of cancer. Thus, it is necessary to utilize a sensitive tool to visualize the viscosity in tumor cells and mice, which is helpful for the diagnosis of cancer. Herein, a novel dual-modal probe (IX-V) that has a near-infrared fluorescence (NIRF) and photoacoustic (PA) response to viscosity is synthesized. In low viscosity media, the probe has no fluorescence. With the increase of viscosity, the fluorescence is produced in the near-infrared region due to the inhibition of the TICT process. At the same time, the probe shows different photoacoustic (PA) signals in different viscosity media. Most notably, the viscosity in tumor cells has been imaged successfully by the application of IX-V, and the probe can effectively distinguish cancer cells from normal cells co-cultured in one dish by the difference of fluorescence intensity. In addition, the probe has been used for dual-modal imaging (NIRF and PA) of viscosity in tumor mice, which provides a tool for exploring the relationship between viscosity and diseases. That is to say, IX-V can achieve complementary imaging effects and has great application prospects in the tumor diagnosis.

Optimization of highly inclined illumination for diffraction-limited and super-resolution microscopy

In HILO microscopy, a highly inclined and laminated light sheet is used to illuminate the sample, thus drastically reducing background fluorescence in wide-field microscopy, but maintaining the simplicity of the use of a single objective for both illumination and detection. Although the technique has become widely popular, particularly in single molecule and super-resolution microscopy, a limited understanding of how to finely shape the illumination beam and of how this impacts on the image quality complicates the setting of HILO to fit the experimental needs. In this work, we build up a simple and comprehensive guide to optimize the beam shape and alignment in HILO and to predict its performance in conventional fluorescence and super-resolution microscopy. We model the beam propagation through Gaussian optics and validate the model through far- and near-field experiments, thus characterizing the main geometrical features of the beam. Further, we fully quantify the effects of a progressive reduction of the inclined beam thickness on the image quality of both diffraction-limited and super-resolution images and we show that the most relevant impact is obtained by reducing the beam thickness to sub-cellular dimensions (< 3 µm). Based on this, we present a simple optical solution that exploits a rectangular slit to reduce the inclined beam thickness down to 2.6 µm while keeping a field-of-view dimension suited for cell imaging and allowing an increase in the number of localizations in super-resolution imaging of up to 2.6 folds.

AIEgens-Doped Photonic Crystals for High Sensitivity Fluorescence Detection of Tumor Markers

Detection of tumor markers is of great significance to preliminarily judge whether patients have malignant tumors. Fluorescence detection (FD) is an effective means to achieve sensitive detection of tumor markers. Currently, the increased sensitivity of FD has attracted research interest worldwide. Here, we have proposed a method of doping luminogens with aggregation-induced emission (AIEgens) into photonic crystals (PCs), which can significantly enhance the fluorescence intensity to achieve high sensitivity in the detection of tumor markers. PCs are made by scraping and self-assembling, which has the special effect of fluorescence enhancement. The combination of AIEgens and PCs can enhance the fluorescence intensity 4-7 times. These characteristics make it extremely sensitive. The limit of detection (LOD) for the detection of alpha-fetoprotein (AFP) in the AIE10 (Tetraphenyl ethylene-Br) doped PCs with a reflection peak of 520 nm is 0.0377 ng/mL. LOD for the detection of carcinoembryonic antigen (CEA) in the AIE25 (Tetraphenyl ethylene-NH₂) doped PCs with a reflection peak of 590 nm is 0.0337 ng/mL. Our concept offers a good solution for highly sensitive detection of tumor markers.

Incoherent superposition of polychromatic light enables single-shot nondiffracting light-sheet microscopy

We demonstrate single-shot nondiffracting light-sheet microscopy by the incoherent superposition of dispersed polychromatic light sources. We characterized our technique by generating a Bessel light-sheet with a supercontinuum light-source and a C-light-sheet using a diode laser, and demonstrated its applicability to fluorescence microscopy. We emphasize that our method is easily implementable and compatible with the requirements of high-resolution microscopy.

2.5D microscopy with polarization independent SLM for enhanced detection efficiency and aberration correction

Fast, volumetric imaging by fluorescence microscopy is essential in studying biological phenomena and cellular functions. Recently, single-shot 2.5D microscopy showed promising results for high-throughput quantitative subcellular analysis via extended depth of field imaging without sequential z-scanning; however, the detection efficiency was limited and it lacked depth-induced aberration correction. Here we report that a spatial light modulator (SLM) in a polarization insensitive configuration can significantly improve the detection efficiency of 2.5D microscopy, while also compensating for aberrations at large imaging depths caused by the refractive index mismatch between the sample and the immersion medium. We highlight the improved efficiency via quantitative single-molecule RNA imaging of mammalian cells with a 2-fold improvement in the fluorescence intensity compared to a conventional SLM-based microscopy. We demonstrate the aberration correction capabilities and extended depth of field by imaging thick specimens with fewer z-scanning steps.

2.5D microscopy: Fast, high-throughput imaging via volumetric projection for quantitative subcellular analysis

Imaging-based single-cell analysis is essential to study the expression level and functions of biomolecules at subcellular resolution. However, its low throughput has prevented the measurement of numerous cellular features from multiples cells in a rapid and efficient manner. Here we report 2.5D microscopy that significantly improves the throughput of fluorescence imaging systems while maintaining high-resolution and single-molecule sensitivity. Instead of sequential z-scanning, volumetric information is projected onto a 2D image plane in a single shot by engineering the emitted fluorescence light. Our approach provides an improved imaging speed and uniform focal response within a specific imaging depth, which enabled us to perform quantitative single-molecule RNA measurements over a 2×2 mm2 region within an imaging depth of ~5 μm for mammalian cells in <10 min and immunofluorescence imaging at a >30 Hz volumetric frame rate with reduced photobleaching. Our microscope also offers the ability of multi-color imaging, depth control and super-resolution imaging.

Single-shot, shadowless total internal reflection fluorescence microscopy via annular fiber bundle

We demonstrate a method of generating instantaneous and uniform total internal reflection fluorescence (TIRF) excitation by using an annular fiber bundle and spatially incoherent light sources. We show the flexibility of our method in that it can generate TIRF excitation with either a laser light source or an LED of different wavelengths, and facilitate switching between TIRF and epi illumination. In this report we detail the design of the fiber bundle, then demonstrate the performance via single-molecule imaging in the presence of high background and high throughput, and uniform TIRF imaging of cells over a large field of view. Our versatile method will enable quantitative shadowless TIRF imaging.

Instantaneous non-diffracting light-sheet generation by controlling spatial coherence

We demonstrate single-shot non-diffracting light-sheet generation by controlling the spatial coherence of light. A one-dimensional coherent beam, created by either increasing the spatial coherence of an LED or decreasing the spatial coherence of a laser, makes it unnecessary to scan non-diffracting beams to generate light-sheets. We theoretically and experimentally demonstrate the equivalence between our method and a scanned light-sheet, and investigate the characteristics of the light-sheet in detail. Our method is easily implementable and universally applicable for high-resolution multicolor light-sheet fluorescence imaging.

Optimizing the performance of multiline-scanning confocal microscopy

Line-scanning confocal microscopy provides high imaging speed and moderate optical sectioning strength, which makes it a useful tool for imaging various biospecimens ranging from living cells to fixed tissues. Conventional line-scanning systems have only used a single excitation line and slit, and thus have not fully exploited benefits of parallelization. Here we investigate the optical performance of multi-line scanning confocal microscopy (mLS) by employing a digital micro-mirror that provides programmable patterns of the illumination beam and the detection slit. Through experimental results and optical simulations, we assess the depth discrimination of mLS under different optical parameters and compare it with multi-point systems such as scanning disk confocal microscopy (SDCM). Under the same illumination duty cycle, we find that mLS has better optical sectioning than SDCM at a high degree of parallelization. The optimized mLS provides a low photobleaching rate and video-rate imaging while its optical sectioning is similar to single line-scanning confocal microscopy.