Optimal integration of wide field illumination and holographic optical tweezers for multimodal microscopy with ultimate flexibility and versatility

We introduce one-of-a-kind optical microscope that we have developed through optimized integration of wide-field and focused-light microscopies. This new instrument has accomplished operation of the same laser for both wide field illumination and holographic focused beam illumination interchangeably or simultaneously in a way scalable to multiple lasers. We have demonstrated its powerful capability by simultaneously carrying out Epi-fluorescence, total internal reflection fluorescence microscopy, selective plane illumination microscopy, and holographic optical tweezers with five lasers. Our instrument and the optical design will provide researchers across diverse fields, cell-biology and biophysics in particular, with a practical guidance to build an all-around multimodal microscope that will further inspire the development of novel hybrid microscopy experiments.

The α-β circular scanning with large range and low noise

A circular-route scanning method called α-β circular scanning is proposed and realized using sinusoidal signals with a constant phase difference of π/2. Experiments show that the circular scanning range of α-β circular scanning is 57% greater than the rectangular scanning range of raster scanning within an effective optical field of view. Moreover, the scanning speed is improved by 7.8% over raster scanning because the whole sine signal is utilized in α-β circular scanning whereas the flyback area of the saw-tooth signal needs to be discarded in raster scanning. The maximum scanning acceleration decreases by a factor of 44, drastically decreasing the high noise, which should considerably elongate the lifetime of the galvanometers while inhibiting internal vibration. The proposed α-β circular scanning technique could be used in scanning imaging, optical tweezers and laser-beam fabrication.

A hyphenated optical trap capillary electrophoresis laser induced native fluorescence system for single-cell chemical analysis

Single-cell measurements allow a unique glimpse into cell-to-cell heterogeneity; even small changes in selected cells can have a profound impact on an organism's physiology. Here an integrated approach to single-cell chemical sampling and assay are described. Capillary electrophoresis (CE) with laser-induced native fluorescence (LINF) has the sensitivity to characterize natively fluorescent indoles and catechols within individual cells. While the separation and detection approaches are well established, the sampling and injection of individually selected cells requires new approaches. We describe an optimized system that interfaces a single-beam optical trap with CE and multichannel LINF detection. A cell is localized within the trap and then the capillary inlet is positioned near the cell using a computer-controlled micromanipulator. Hydrodynamic injection allows cell lysis to occur within the capillary inlet, followed by the CE separation and LINF detection. The use of multiple emission wavelengths allows improved analyte identification based on differences in analyte fluorescence emission profiles and migration time. The system enables injections of individual rat pinealocytes and quantification of their endogenous indoles, including serotonin, N-acetyl-serotonin, 5-hydroxyindole-3-acetic acid, tryptophol and others. The amounts detected in individual cells incubated in 5-hydroxytryptophan ranged from 10(-14) mol to 10(-16) mol, an order of magnitude higher than observed in untreated pinealocytes.

Optics clustered to output unique solutions: a multi-laser facility for combined single molecule and ensemble microscopy

Optics clustered to output unique solutions (OCTOPUS) is a microscopy platform that combines single molecule and ensemble imaging methodologies. A novel aspect of OCTOPUS is its laser excitation system, which consists of a central core of interlocked continuous wave and pulsed laser sources, launched into optical fibres and linked via laser combiners. Fibres are plugged into wall-mounted patch panels that reach microscopy end-stations in adjacent rooms. This allows multiple tailor-made combinations of laser colours and time characteristics to be shared by different end-stations minimising the need for laser duplications. This setup brings significant benefits in terms of cost effectiveness, ease of operation, and user safety. The modular nature of OCTOPUS also facilitates the addition of new techniques as required, allowing the use of existing lasers in new microscopes while retaining the ability to run the established parts of the facility. To date, techniques interlinked are multi-photon/multicolour confocal fluorescence lifetime imaging for several modalities of fluorescence resonance energy transfer (FRET) and time-resolved anisotropy, total internal reflection fluorescence, single molecule imaging of single pair FRET, single molecule fluorescence polarisation, particle tracking, and optical tweezers. Here, we use a well-studied system, the epidermal growth factor receptor network, to illustrate how OCTOPUS can aid in the investigation of complex biological phenomena.

Analysis of single quantum-dot mobility inside 1D nanochannel devices

We visualized individual quantum dots using a combination of a confining nanochannel and an ultra-sensitive microscope system, equipped with a high numerical aperture lens and a highly sensitive camera. The diffusion coefficients of the confined quantum dots were determined from the experimentally recorded trajectories according to the classical diffusion theory for Brownian motion in two dimensions. The calculated diffusion coefficients were three times smaller than those in bulk solution. These observations confirm and extend the results of Eichmann et al (2008 Langmuir 24 714-21) to smaller particle diameters and more narrow confinement. A detailed analysis shows that the observed reduction in mobility cannot be explained by conventional hydrodynamic theory.

Distribution and dynamics of rat basophilic leukemia immunoglobulin E receptors (FcepsilonRI) on planar ligand-presenting surfaces

There is considerable interest in the signaling mechanisms of immunoreceptors, especially when triggered with membrane-bound ligands. We have quantified the spatiotemporal dynamics of the redistribution of immunoglobulin E-loaded receptors (IgE-FcepsilonRI) on rat basophilic leukemia-2H3 mast cells in contact with fluid and gel-phase membranes displaying ligands for immunoglobulin E, using total internal reflection fluorescence microscopy. To clearly separate the kinetics of receptor redistribution from cell spreading, and to precisely define the initial contact time (+/-50 ms), micropipette cell manipulation was used to bring individual cells into contact with surfaces. On ligand-free surfaces, there are micron-scale heterogeneities in fluorescence that likely reflect regions of the cell that are more closely apposed to the substrate. When ligands are present, receptor clusters form with this same size scale. The initial rate of accumulation of receptors into the clusters is consistent with diffusion-limited trapping with D approximately 10(-1) microm2/s. These results support the hypothesis that clusters form by diffusion to cell-surface contact regions. Over longer timescales (>10 s), individual clusters moved with both diffusive and directed motion components. The dynamics of the cluster motion is similar to the dynamics of membrane fluctuations of cells on ligand-free fluid membranes. Thus, the same cellular machinery may be responsible for both processes.

Optical manipulation for single-cell studies

In the last decade optical manipulation has evolved from a field of interest for physicists to a versatile tool widely used within life sciences. This has been made possible in particular due to the development of a large variety of imaging techniques that allow detailed information to be gained from investigations of single cells. The use of multiple optical traps has high potential within single-cell analysis since parallel measurements provide good statistics. Multifunctional optical tweezers are, for instance, used to study cell heterogeneity in an ensemble, and force measurements are used to investigate the mechanical properties of individual cells. Investigations of molecular motors and forces on the single-molecule level have led to discoveries that would have been difficult to make with other techniques. Optical manipulation has prospects within the field of cell signalling and tissue engineering. When combined with microfluidic systems the chemical environment of cells can be precisely controlled. Hence the influence of pH, salt concentration, drugs and temperature can be investigated in real time. Fast advancing technical developments of automated and user-friendly optical manipulation tools and cross-disciplinary collaboration will contribute to the routinely use of optical manipulation techniques within the life sciences.