Articles by Laurence G. Wilson in JoVE
Digital Inline Holographic Microscopy (DIHM) of Weakly-scattering Subjects Camila B. Giuliano1,2, Rongjing Zhang1, Laurence G. Wilson1 1The Rowland Institute, Harvard University, 2Faculdade de Ciências e Letras de Assis, Universidade Estadual Paulista The three-dimensional locations of weakly-scattering objects can be uniquely identified using digital inline holographic microscopy (DIHM), which involves a minor modification to a standard microscope. Our software uses a simple imaging heuristic coupled with Rayleigh-Sommerfeld back-propagation to yield the three-dimensional position and geometry of a microscopic phase object.
Other articles by Laurence G. Wilson on PubMed
Small-world Rheology: an Introduction to Probe-based Active Microrheology Physical Chemistry Chemical Physics : PCCP. Jun, 2011 | Pubmed ID: 21556428 We introduce active, probe-based microrheological techniques for measuring the flow and deformation of complex fluids. These techniques are ideal for mechanical characterization either when little sample is available, or when samples show significant spatial heterogeneity. We review recent results, paying particular attention to comparing and contrasting rheological parameters obtained from micro- and macro-rheological techniques.
Differential Dynamic Microscopy: a High-throughput Method for Characterizing the Motility of Microorganisms Biophysical Journal. Oct, 2012 | Pubmed ID: 23083706 We present a fast, high-throughput method for characterizing the motility of microorganisms in three dimensions based on standard imaging microscopy. Instead of tracking individual cells, we analyze the spatiotemporal fluctuations of the intensity in the sample from time-lapse images and obtain the intermediate scattering function of the system. We demonstrate our method on two different types of microorganisms: the bacterium Escherichia coli (both smooth swimming and wild type) and the biflagellate alga Chlamydomonas reinhardtii. We validate the methodology using computer simulations and particle tracking. From the intermediate scattering function, we are able to extract the swimming speed distribution, fraction of motile cells, and diffusivity for E. coli, and the swimming speed distribution, and amplitude and frequency of the oscillatory dynamics for C. reinhardtii. In both cases, the motility parameters were averaged over ∼10(4) cells and obtained in a few minutes.
High-speed Holographic Microscopy of Malaria Parasites Reveals Ambidextrous Flagellar Waveforms Proceedings of the National Academy of Sciences of the United States of America. Nov, 2013 | Pubmed ID: 24194551 Axonemes form the core of eukaryotic flagella and cilia, performing tasks ranging from transporting fluid in developing embryos to the propulsion of sperm. Despite their abundance across the eukaryotic domain, the mechanisms that regulate the beating action of axonemes remain unknown. The flagellar waveforms are 3D in general, but current understanding of how axoneme components interact stems from 2D data; comprehensive measurements of flagellar shape are beyond conventional microscopy. Moreover, current flagellar model systems (e.g., sea urchin, human sperm) contain accessory structures that impose mechanical constraints on movement, obscuring the "native" axoneme behavior. We address both problems by developing a high-speed holographic imaging scheme and applying it to the (male) microgametes of malaria (Plasmodium) parasites. These isolated flagella are a unique, mathematically tractable model system for the physics of microswimmers. We reveal the 3D flagellar waveforms of these microorganisms and map the differential shear between microtubules in their axonemes. Furthermore, we overturn claims that chirality in the structure of the axoneme governs the beat pattern [Hirokawa N, et al. (2009) Ann Rev Fluid Mech 41:53-72], because microgametes display a left- or right-handed character on alternate beats. This breaks the link between structural chirality in the axoneme and larger scale symmetry breaking (e.g., in developing embryos), leading us to conclude that accessory structures play a critical role in shaping the flagellar beat.