Research

Our research spans optics, fluidics, and biology with the goal of developing and using cutting edge imaging techniques to learn more about nano-scale biological and physical phenomena. Below are some research projects we are currently working on.

3D Single-Acquisition Super-Resolution Imaging

Even with the utmost care and effort, the resolution of an optical imaging system is fundementally limited by diffraction. When the light passes through an aperture, be it the primary mirror on a telescope, the lens on your phone’s camera, or the front of a microscope objective diffraction causes the light to spread out. The larger the aperture the less the light spreads out, part of the reason for ever larger telescopes and microscope objectives with increasingly large numerical objectives.

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Image of 500 nm beads imaged with a 40x 0.6 NA microscope objective. The individual beads are below the diffraction limit of the system as can be seen in (a). Adding the Bessel Beam Microscopy system improves the diffraction limited system, permitting viewing of the individual beads (b).

With the Bessel Beam Microscopy system we have discovered a way to improve the diffraction limited resolution of an imaging system with little cost to image contrast. An example of this is shown above. This is a fundementally different approach to super-resolution imaging providing several orders of magnitude increase in temporal resolution. In plain words you can see much faster things in higher detail.

Our current work is in developing image analysis algorithms to extract more information from these images as well as applying this tool towards imaging fast nano-scale biological phenomena. If you are interested in this work or in collaborating please feel free to contact Dr. Snoeyink.

Ultra-high Resolution 3D Particle Locating

Often times when we are trying to measure something that is not directly visible we will use a fluorescent bead as a proxy for that object. In fluid mechanics we will often “seed” the flow with these beads and then track their movement. The distance the beads have moved between frames gives an approximation for the fluid velocity near the bead. In biology we will often attach a fluorescent molecule or “label” to a protein or enzyme that we are particularly interested in. By tracking the location of the label we can infer the position and motion of the protein we want to watch. In both of these cases, the quality of your data depends heavily on the resolution with which you can locate the fluorescent bead or molecule.

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Simulated image of a particle as imaged by the BBM system.

When we image these beads or labels with the Bessel Beam Microscopy system you get an image like that shown to the right. By correctly designing the Bessel Beam Microscopy system we have shown that you can achieve very high resolution measurements of the particle location. With a 20x 0.4 NA microscope objective we have been able to locate 1 micron particles with a resolution in all directions of better than 50 nm. With higher magnification lenses dramatically higher resolution on the order of 10 nm is possible. Furthermore, our technique has several advantages:

  • No calibration is required. As long as you know the physical dimensions and properties of the optical imaging system it is possible to calculate the absolute location of the particles. This is a tremendous advantage when one wants to perform measurements that are at a higher resolution then the available Z stage.
  • Highly customizable resolution and depth of field. One can easily achieve high depth resolution or large depth of field with simple alterations to the optical design.
  • No single particle feature is important. Unlike related techniques the BBM system doesn’t rely on a single feature of a particle image like width or intensity. As a result the technique is insensitive to particle size or variations in illumination intensity.
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Position of a 1 micron particle as it is carried along in bulk flow. Green trace is line fit to particle path, red traces are deviations from that path. Estimated resolution is better than 50 nm in all directions.