Optical microscopy is an excellent Advanced Laboratory tool: it offers students the chance to immediately see diffusion in action, while also offering quantitative analysis and an opportunity for extensions to more complex fluid dynamics such as boundary-particle hydrodynamic coupling.  And an open-source optical microscope offers the chance for student modifications for even more experiments.

Figure 1.  Picture of the microscope.  The sample sits on the aluminum holder in the middle of the picture and is imaged from below.

At this immersion, participants will:

(1)    Build a research-grade fluorescence microscope (four-color fluorescence, single molecule imaging, diffraction limited resolution of ~250 nm);

(2)    Use their microscope to explore diffusion of microscopic objects, extracting the diffusion coefficients, Boltzmann’s constant, and solution viscosity with ~2% precision and 1% accuracy. 

Day 1:  Participants will begin by building, aligning, and characterizing this open-source-design microscope, comprising a mix of machined, 3D-printed, and off-the-shelf optical components. 

Day 2: Participants will then learn to operate the microscope while imaging microspheres (100-1000 nm dia.) and using open-source tracking software to extract diffusion coefficients.  Additionally, participants will learn to use 3D imaging to examine hindered diffusion when these microspheres are within a few diameters of a planar boundary.  Time will be available to re-design and print custom parts as desired. 

Day 3 (morning only): Participants will explore other uses of this microscope.  Possibilities include imaging fluorescently labeled biological cells, imaging molecular motors in action, imaging swimming micro-organisms.

All equipment will be provided; participants may also collect data on their own laptops. 

If participants wish to take home their newly-built apparatus at the end of the immersion, arrangements should be made ahead of time to handle lead-time for ordering parts.

References to the relevant physics:

Einstein: “On the Motion of Small Particles Suspended in Liquids at Rest Required by the Molecular-Kinetic Theory of Heat”, (1905). 

Koo, H. P., and Verkman, A. S., “Tracking of single fluorescent particles in three dimensions: use of cylindrical optics to encode particle position” (1994). 

Banerjee, A., and Khim, K. D., “Experimental verification of near-wall hindered diffusion for the Brownian motion of nanoparticles using evanescent wave microscopy”, (2005).

Approximate cost to implement:

$8500                Microscope (including illumination, optics, electronics, machined and 3D printed parts)

$1500                Alignment optics, tools for assembly, carrying case, samples for imaging

$500                   Computer to control the microscope