1,720,972 research outputs found
Simultaneous imaging of different focal planes in fluorescence microscopy for the study of cellular dynamics in three dimensions
No full textThe imaging of cellular dynamics in three dimensions using a standard microscope is severely limited due to the fact that only one focal plane can be imaged at a given point in time. Here we present a modification of the classical microscope design with which two or more focal planes can be imaged simultaneously. This is achieved by a modification of the emission pathway of a standard microscope. The efficacy of the design is shown by imaging bead samples and an FcRn-green fluorescent protein expressing tubule that leaves a sorting endosome and subsequently exocytoses at the plasma membrane.</p
Simultaneous imaging of several focal planes in fluorescence microscopy for the study of cellular dynamics in 3D
No full textFluorescence microscopy of live cells is an important tool to investigate cellular trafficking pathways. The existing microscope design is very well suited to image fast moving vesicles, tubules and organelles in one focal plane. More problematic is the imaging of cellular components that move between different focal planes. This is due to the fact that tracking of such cellular components requires that the focal plane of the microscope be changed. This has to be done with a focusing device, which is relatively slow. More importantly, only one focal plane can be imaged at a time. Therefore, while the cell is imaged at one focal plane, important events could be missed at other focal planes. To overcome these shortcomings, we present a modification of the classical microscope design with which two or more focal planes can be imaged simultaneously. In this design, the emission light collected by a single stationary objective lens is split into multiple channels. Light in each channel is focused on a CCD camera by a tube lens. By ensuring that the camera position with respect to the tube lens focal plane position is not the same in any two channels, distinct planes within the specimen can be simultaneously imaged. Here we discuss the implementation of a configuration with which four focal planes can be imaged simultaneously.</p
Dual objective fluorescence microscopy for single molecule imaging applications
No full textFluorescence microscopy is an invaluable tool for studying biological processes in cells. In the recent past there has been significant interest in imaging cellular processes at the single molecule level. Single molecule experiments remove ensemble averaging effects and provide information that is typically not accessible through bulk experiments. One of the major requirements in single molecule imaging applications is that a sufficient number of photons be detected from the single molecule. This is not only important for the visual identification of single molecules, but also plays a crucial role in the quantitative analysis of the acquired data. Here, we demonstrate the use of a dual objective imaging configuration for single molecule studies. The configuration uses two opposing objective lenses, where one of the objectives is in an inverted position and the other objective is in an upright position. The use of opposing objective lenses has been previously demonstrated in 4pi confocal microscopy and I5M to achieve high axial resolution when compared to confocal/widefield microscopes. Here we emonstrate that the dual objective imaging configuration provides higher photon collection efficiency when compared to a regular microscope for a given illumination condition. As a result, single molecules can be localized with better accuracy when imaged through opposing objective lenses than when imaged through a regular optical microscope. Analytical tools are introduced to estimate the 2D location of single molecules and to characterize the accuracy with which they can be determined.</p
Improved single particle localization accuracy with dual objective multifocal plane microscopy
No full textIn single particle imaging applications, the number of photons detected from the fluorescent label plays a crucial role in the quantitative analysis of the acquired data. For example, in tracking experiments the localization accuracy of the labeled entity can be improved by collecting more photons from the labeled entity. Here, we report the development of dual objective multifocal plane microscopy (dMUM) for single particle studies. The new microscope configuration uses two opposing objective lenses, where one of the objectives is in an inverted position and the other objective is in an upright position. We show that dMUM has a higher photon collection efficiency when compared to standard microscopes. We demonstrate that fluorescent labels can be localized with better accuracy in 2D and 3D when imaged through dMUM than when imaged through a standard microscope. Analytical tools are introduced to estimate the nanoprobe location from dMUM images and to characterize the accuracy with which they can be determined.</p
High Accuracy 3D Quantum Dot Tracking with Multifocal Plane Microscopy for the Study of Fast Intracellular Dynamics in Live Cells
No full textAbstractSingle particle tracking in three dimensions in a live cell environment holds the promise of revealing important new biological insights. However, conventional microscopy-based imaging techniques are not well suited for fast three-dimensional (3D) tracking of single particles in cells. Previously we developed an imaging modality multifocal plane microscopy (MUM) to image fast intracellular dynamics in three dimensions in live cells. Here, we introduce an algorithm, the MUM localization algorithm (MUMLA), to determine the 3D position of a point source that is imaged using MUM. We validate MUMLA through simulated and experimental data and show that the 3D position of quantum dots can be determined over a wide spatial range. We demonstrate that MUMLA indeed provides the best possible accuracy with which the 3D position can be determined. Our analysis shows that MUM overcomes the poor depth discrimination of the conventional microscope, and thereby paves the way for high accuracy tracking of nanoparticles in a live cell environment. Here, using MUM and MUMLA we report for the first time the full 3D trajectories of QD-labeled antibody molecules undergoing endocytosis in live cells from the plasma membrane to the sorting endosome deep inside the cell
Three-dimensional single molecule tracking of quantum-dot labeled antibody molecules using multifocal plane microscopy
No full textSingle molecule tracking in three dimensions (3D) in a live cell environment promises to reveal important new insights into cell biological mechanisms. However, classical microscopy techniques suffer from poor depth discrimination which severely limits single molecule tracking in 3D with high temporal and spatial resolution. We introduced a novel imaging modality, multifocal plane microscopy (MUM) for the study of subcellular dynamics in 3D. We have shown that MUM provides a powerful approach with which single molecules can be tracked in 3D in live cells. MUM allows for the simultaneous imaging at different focal planes, thereby ensuring that trajectories can be imaged continuously at high temporal resolution. A critical requirement for 3D single molecule tracking as well as localization based 3D super-resolution imaging is high 3D localization accuracy. MUM overcomes the depth discrimination problem of classical microscopy based approaches and supports high accuracy 3D localization of singe molecule/particles. In this way, MUM opens the way for high precision 3D single molecule tracking and 3D super-resolution imaging within a live cell environment. We have used MUM to reveal complex intracellular pathways that could not be imaged with classical approaches. In particular we have tracked quantum dot labeled antibody molecules in the exo/endocytic pathway from the cell interior to the plasma membrane at the single molecule level. Here, we present a brief review of these results.</p
A novel approach to determining the three-dimensional location of microscopic objects with applications to 3D particle tracking
No full textRecent technological advances have rendered widefield fluorescence microscopy as an invaluable tool to image fast dynamics of trafficking events in two dimensions (i.e., in the plane of focus). Three-dimensional trafficking events are studied by sequentially imaging different planes within the specimen by moving the plane of focus with a focusing device. However, these devices are typically slow and hence when the cell is being imaged at one focal plane, important events could be missed at other focal planes. To overcome this limitation, we recently developed a novel imaging technique called multifocal plane microscopy that enables the simultaneous imaging of multiple focal planes within the sample. Here, by using tools of information theory, we present a quantitative evaluation of this technique in the context of 3D particle tracking. We calculate the Fisher information matrix for the problem of determining the 3D location of an object that is imaged on a multifocal plane setup. In this way, we derive a lower bound on the accuracy with which the object can be localized in 3D. We illustrate our results by considering the object of interest to be a single molecule. It is well known that a conventional widefield microscope has poor depth discrimination capability and therefore there exists significant uncertainty in determining the axial location of the object, especially when it is close to the plane of focus. Our results predict that the multifocal plane microscope setup offers improved accuracy in determining the axial location of objects than a conventional widefield microscope.</p
Overcoming the depth discrimination barrier in widefield microscopes: 3D single molecule tracking with high axial accuracy
No full textCurrent widefield microscopy techniques are well suited for imaging fast moving single molecules in two dimensions even within cells. However, the 3D imaging of single molecules poses several technical challenges. Foremost being that in the current microscope design only one focal plane can be imaged at any given point in time. Hence single molecule tracking in a 3D environment such as a cell is problematic since the molecule can easily move out of the focal plane that is currently being imaged. Focusing devices such as piezo nano-positioners could be used to overcome this shortcoming by sequentially scanning the sample at different planes. However, these devices are typically slow and therefore may not be suitable for 3D tracking of fast moving single molecules. Aside from this, widefield microscopes suffer from poor depth discrimination capability. Therefore, there exists significant uncertainty in determining the axial location of the single molecule, especially when the molecule is close to the plane of focus. To overcome the above limitations, we have developed a new microscopy technique called multifocal plane microscopy (MUM) that can simultaneously image distinct planes within the specimen. In contrast to standard microscopes, a MUM setup exhibits significantly improved depth discrimination capability, especially close to focus, which markedly improves the accuracy with which the axial position of the single molecule can be determined. Results are presented to illustrate the applicability of MUM for 3D single molecule tracking.</p
Resolution beyond Rayleigh's criterion: A modern resolution measure with applications to single molecule imaging
No full textRayleigh's criterion, although extensively used, is well known to be based on heuristic notions that are inadequate for modern optical microscopy applications. This inadequacy has necessitated a reassessment of the resolution limits of optical microscopes. By adopting a stochastic framework and using the statistical theory concerning the Fisher information matrix, we have derived a new resolution measure that overcomes the limitations of Rayleigh's criterion. Here, we provide a brief overview of this and other related results published by our group. The new resolution measure predicts that there is no resolution limit, but that the resolvability depends on the number of detected photons. It has been experimentally verified that distances well below Rayleigh's limit can be measured from images of closely spaced single molecules with an accuracy as predicted by the new resolution measure. The stochastic framework used to obtain the new resolution measure is applicable to a wide variety of estimation problems encountered in optical microscopy. As an application, we have investigated the localization accuracy problem, which is concerned with how accurately the 2D/3D location of a microscopic object can determined from its image. One of the shortcomings of current microscopy techniques is that they suffer from poor depth discrimination and as a result they are not well adapted for 3D tracking of single molecules/particles. We have recently developed a novel imaging modality called multifocal plane microscopy (MUM) to overcome this limitation. Using the stochastic framework, we have shown that MUM has significantly improved depth discrimination, which in turn enables 3D single particle tracking at high axial localization accuracy.</p
Elucidation of intracellular recycling pathways leading to exocytosis of the Fc receptor, FcRn, by using multifocal plane microscopy
No full textThe intracellular events on the recycling pathway that lead from sorting endosomes to exocytosis at the plasma membrane are central to cellular function. However, despite intensive study, these processes are poorly characterized in spatial and dynamic terms. The primary reason for this is that, to date, it has not been possible to visualize rapidly moving intracellular compartments in three dimensions in cells. Here, we use a recently developed imaging setup in which multiple planes can be simultaneously imaged within the cell in conjunction with visualization of the plasma membrane plane by using total internal reflection fluorescence microscopy. This has allowed us to track and characterize intracellular events on the recycling pathway that lead to exocytosis of the MHC Class I-related receptor, FcRn. We observe both direct delivery of tubular and vesicular transport containers (TCs) from sorting endosomes to exocytic sites at the plasma membrane, and indirect pathways in which TCs that are not in proximity to sorting endosomes undergo exocytosis. TCs can also interact with different sorting endosomes before exocytosis. Our data provide insight into the intracellular events that precede exocytic fusion.</p
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