Mirrored pyramidal wells for simultaneous multiple vantage point microscopy

Reflective imaging improves spatiotemporal resolution and collection efficiency in light sheet microscopy

Light-sheet fluorescence microscopy (LSFM) enables high-speed, high-resolution, and gentle imaging of live specimens over extended periods. Here we describe a technique that improves the spatiotemporal resolution and collection efficiency of LSFM without modifying the underlying microscope. By imaging samples on reflective coverslips, we enable simultaneous collection of four complementary views in 250 ms, doubling speed and improving information content relative to symmetric dual-view LSFM. We also report a modified deconvolution algorithm that removes associated epifluorescence contamination and fuses all views for resolution recovery. Furthermore, we enhance spatial resolution (to <300 nm in all three dimensions) by applying our method to single-view LSFM, permitting simultaneous acquisition of two high-resolution views otherwise difficult to obtain due to steric constraints at high numerical aperture. We demonstrate the broad applicability of our method in a variety of samples, studying mitochondrial, membrane, Golgi, and microtubule dynamics in cells and calcium activity in nematode embryos.

High-resolution real-time dual-view imaging with multiple point of view microscopy

Most methods to observe three-dimensional processes in living samples are based on imaging a single plane that is sequentially scanned through the sample. Sequential scanning is inherently slow, which can make it difficult to capture objects moving quickly in three dimensions. Here we present a novel method, multiple point-of-view microscopy (MPoVM), that allows simultaneous capturing of the front and side views of a sample with high resolution. MPoVM can be implemented in most fluorescence microscopes, offering new opportunities in the study of dynamic biological processes in three dimensions.

Single objective light-sheet microscopy for high-speed whole-cell 3D super-resolution

We have developed a method for performing light-sheet microscopy with a single high numerical aperture lens by integrating reflective side walls into a microfluidic chip. These 45° side walls generate light-sheet illumination by reflecting a vertical light-sheet into the focal plane of the objective. Light-sheet illumination of cells loaded in the channels increases image quality in diffraction limited imaging via reduction of out-of-focus background light. Single molecule super-resolution is also improved by the decreased background resulting in better localization precision and decreased photo-bleaching, leading to more accepted localizations overall and higher quality images. Moreover, 2D and 3D single molecule super-resolution data can be acquired faster by taking advantage of the increased illumination intensities as compared to wide field, in the focused light-sheet.

Multi-view second-harmonic generation imaging of mouse tail tendon via reflective micro-prisms

Here we experimentally show that second-harmonic generation (SHG) imaging is not sensitive to collagen fibers oriented parallel to the direction of laser propagation and, as a consequence, can potentially miss important structural information. As an alternative approach, we demonstrate the use of reflective micro-prisms to enable multi-view SHG imaging of mouse tail tendon by redirecting the focused excitation and collection of subsequent emission. Our approach data corroborates the theoretical treatment on vanishing and nonvanishing orientations, where fibers along the laser direction are largely transparent by SHG. In strong contrast, the two-photon excited fluorescence of dye-labeled collagen fibers is isotropic and is not subject to this constraint. We utilized Pearson correlation to quantify differences in fluorescent and backward detected SHG images of the tendon fiber structure, where the SHG and TPEF were highly statistically correlated (0.6-0.8) for perpendicular excitation but were uncorrelated for excitation parallel to the fiber axis. The results suggest that improved imaging of 3D collagen structure is possible with multi-view SHG microscopy.

A simple low-cost method to enhance luminescence and fluorescence signals in PDMS-based microfluidic devices

The addition of titanium dioxide particles to PDMS is a simple low-cost method to enhance fluorescence and luminescence signals in microfluidic devices.

A microfluidic-enabled mechanical microcompressor for the immobilization of live single- and multi-cellular specimens

A microcompressor is a precision mechanical device that flattens and immobilizes living cells and small organisms for optical microscopy, allowing enhanced visualization of sub-cellular structures and organelles. We have developed an easily fabricated device, which can be equipped with microfluidics, permitting the addition of media or chemicals during observation. This device can be used on both upright and inverted microscopes. The apparatus permits micrometer precision flattening for nondestructive immobilization of specimens as small as a bacterium, while also accommodating larger specimens, such as Caenorhabditis elegans, for long-term observations. The compressor mount is removable and allows easy specimen addition and recovery for later observation. Several customized specimen beds can be incorporated into the base. To demonstrate the capabilities of the device, we have imaged numerous cellular events in several protozoan species, in yeast cells, and in Drosophila melanogaster embryos. We have been able to document previously unreported events, and also perform photobleaching experiments, in conjugating Tetrahymena thermophila.

Theoretical model of errors in micromirror-based three-dimensional particle tracking

Several recently developed particle-tracking and imaging methods have achieved three-dimensional sensitivity through the introduction of angled micromirrors into the observation volume of an optical microscope. We model the imaging response of such devices and show how the direct and reflected images of a fluorescent particle are affected. In particle-tracking applications, asymmetric image degradation manifests itself as systematic tracking errors. Based on our results, we identify strategies for reducing systematic errors to the 10nm level in practical applications.

Near-isotropic 3D optical nanoscopy with photon-limited chromophores

Imaging approaches based on single molecule localization break the diffraction barrier of conventional fluorescence microscopy, allowing for bioimaging with nanometer resolution. It remains a challenge, however, to precisely localize photon-limited single molecules in 3D. We have developed a new localization-based imaging technique achieving almost isotropic subdiffraction resolution in 3D. A tilted mirror is used to generate a side view in addition to the front view of activated single emitters, allowing their 3D localization to be precisely determined for superresolution imaging. Because both front and side views are in focus, this method is able to efficiently collect emitted photons. The technique is simple to implement on a commercial fluorescence microscope, and especially suitable for biological samples with photon-limited chromophores such as endogenously expressed photoactivatable fluorescent proteins. Moreover, this method is relatively resistant to optical aberration, as it requires only centroid determination for localization analysis. Here we demonstrate the application of this method to 3D imaging of bacterial protein distribution and neuron dendritic morphology with subdiffraction resolution.

Lab-on-Chip for fast 3D particle tracking in living cells

We present a novel Lab-on-Chip technology for 3D particle tracking in living cells based on V-shaped micro-mirrors, which are used to observe fluorescent specimens from multiple vantage points, providing simultaneous stereo-images that can be recombined for 3D reconstruction. Our technology can be readily used with standard fluorescence microscopes, and we apply it to study chromatin dynamics using yeast strains with one or two GFP-tagged gene loci. Using an Andor EMCCD camera, loci are followed in 3D with inter-frame intervals of up to 10 ms and with an error of 27 nm per axis, yielding quantitative information on their dynamics with exquisite temporal spatial resolution.

Micro-mirrors for nanoscale three-dimensional microscopy

A research-grade optical microscope is capable of resolving fine structures in two-dimensional images. However, three-dimensional resolution, or the ability of the microscope to distinguish between objects lying above or below the focal plane from in-focus objects, is not nearly as good as in-plane resolution. In this issue of ACS Nano, McMahon et al. report the use of mirrored pyramidal wells with a conventional microscope for rapid, 3D localization and tracking of nanoparticles. Mirrors have been used in microscopy before, but recent work with MPWs is unique because it enables the rapid determination of the x-, y-, and z-position of freely diffusing nanoparticles and cellular nanostructures with unprecedented speed and spatial accuracy. As inexpensive tools for 3D visualization, mirrored pyramidal wells may prove to be invaluable aids in nanotechnology and engineering of nanomaterials.

3D particle trajectories observed by orthogonal tracking microscopy

We demonstrate high-resolution, high-speed 3D nanoparticle tracking using angled micromirrors. When angled micromirrors are introduced into the field of view of an optical microscope, reflected side-on views of a diffusing nanoparticle are projected alongside the usual direct image. The experimental design allows us to find the 3D particle trajectory using fast, centroid-based image processing, with no nonlinear computing operations. We have tracked polystyrene particles of 190 nm diameter with position measurement precision <20 nm in 3D with 3 ms frame duration (i.e., at an imaging rate >330 frames per second). Because the image processing requires only approximately 1 ms per frame, this technique could enable real-time feedback-controlled nanoparticle assembly applications with nanometer precision.

FRAP analysis of chemosensory components of Dictyostelium

Dictyostelium discoideum is a useful cell model for studying protein-protein interactions and deciphering complex signaling pathways similar to those found in mammalian systems. Many of these interactions were analyzed using classical in vitro biochemical techniques. However, with the accessibility of fluorescently tagged proteins, extensive protein networks are now being mapped out in living cells using a variety of microscopic techniques. One such technique, fluorescent recovery after photobleaching (FRAP), has been used in Dictyostelium to investigate a number of cellular processes including actin and cytoskeleton dynamics during chemotaxis and cytokinesis (J. Muscle Res. Cell Motil. 23:639-649, 2002; Biophys. J. 81:2010-2019, 2001; Mol. Biol. Cell 16:4256-4266, 2005), to follow trafficking of proteins to organelles such as the membrane, nucleus, and endoplasmic reticulum (Development 130:797-804, 2003; J. Cell Biol. 154:137-146, 2001), and to understand the role of proteins in cell adhesion during motility and division (Mol. Biol. Cell 18:4074-4084, 2007; J. Cell Sci. 120:4302-4309, 2007). FRAP is a powerful tool that should provide a vast amount of information on the mobility of a number of proteins, not only in Dictyostelium, but in many organisms. This study will lay out the methods of conducting FRAP experiments in Dictyostelium and discuss the large amount of knowledge which can be gained by adopting this as a common technique.