Browsing by Author "Wang, Wenxiao"

Now showing 1 - 6 of 6
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    Enhanced super-resolution microscopy by phase modulation
    (2016-08-12) Wang, Wenxiao; Landes, Christy F; Kelly, Kevin F
    Super-resolution microscopy typically achieves high 2D spatial resolution but the detection of depth is always difficult. At the same time the temporal resolution remains low and obstructs most biological and chemical researches. In this thesis, I firstly introduced the depth detection method via phase modulation with a 4f system. In the Fourier domain, a phase mask encodes the depth information with a specific phase pattern, double helix phase mask. The final point spread functions deviates from the standard Gaussian point spread functions and the depth information can be measured with high precision by fitting the corresponding double helix point spread functions. Based on the 4f system, I modified the instrument and propose a novel technique Super Temporal-Resolved Microscopy (STReM) to improve the temporal resolution of 2D super-resolution microscopy. The fundamental basis for STReM is the utilization of a double helix phase mask which is rotated at fast speeds to encode temporal information in Fourier domain. The signal can be analyzed either by single emitter fitting or a l_1norm constrained optimization process, which is based on dynamic properties of emitter movement. STReM has been verified using both simulated and experimental 2D data for adsorption/desorption and 2D transport. The temporal resolution has been improved roughly 20 times when comparing traditional methods to that of the novel method of STReM presented in this thesis.
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    Fast Step Transition and State Identification (STaSI) for Discrete Single-Molecule Data Analysis
    (American Chemical Society, 2014) Shuang, Bo; Cooper, David; Taylor, J. Nick; Kisley, Lydia; Chen, Jixin; Wang, Wenxiao; Li, Chun Biu; Komatsuzaki, Tamiki; Landes, Christy F.; Rice Quantum Institute
    We introduce a step transition and state identification (STaSI) method for piecewise constant single-molecule data with a newly derived minimum description length equation as the objective function. We detect the step transitions using the Student’s t test and group the segments into states by hierarchical clustering. The optimum number of states is determined based on the minimum description length equation. This method provides comprehensive, objective analysis of multiple traces requiring few user inputs about the underlying physical models and is faster and more precise in determining the number of states than established and cutting-edge methods for single-molecule data analysis. Perhaps most importantly, the method does not require either time-tagged photon counting or photon counting in general and thus can be applied to a broad range of experimental setups and analytes.
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    Generalized method to design phase masks for 3D super-resolution microscopy
    (Optical Society of America, 2019) Wang, Wenxiao; Ye, Fan; Shen, Hao; Moringo, Nicholas A.; Dutta, Chayan; Robinson, Jacob T.; Landes, Christy F.
    Point spread function (PSF) engineering by phase modulation is a novel approach to three-dimensional (3D) super-resolution microscopy, with different point spread functions being proposed for specific applications. It is often not easy to achieve the desired shape of engineered point spread functions because it is challenging to determine the correct phase mask. Additionally, a phase mask can either encode 3D space information or additional time information, but not both simultaneously. A robust algorithm for recovering a phase mask to generate arbitrary point spread functions is needed. In this work, a generalized phase mask design method is introduced by performing an optimization. A stochastic gradient descent algorithm and a Gauss-Newton algorithm are developed and compared for their ability to recover the phase masks for previously reported point spread functions. The new Gauss-Newton algorithm converges to a minimum at much higher speeds. This algorithm is used to design a novel stretching-lobe phase mask to encode temporal and 3D spatial information simultaneously. The stretching-lobe phase mask and other masks are fabricated in-house for proof-of-concept using multi-level light lithography and an optimized commercially sourced stretching-lobe phase mask (PM) is validated experimentally to encode 3D spatial and temporal information. The algorithms’ generalizability is further demonstrated by generating a phase mask that comprises four different letters at different depths.
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    Generalized recovery algorithm for 3D super-resolution microscopy using rotating point spread functions
    (Springer Nature, 2016) Shuang, Bo; Wang, Wenxiao; Shen, Hao; Tauzin, Lawrence J.; Flatebo, Charlotte; Chen, Jianbo; Moringo, Nicholas A.; Bishop, Logan D.C.; Kelly, Kevin F.; Landes, Christy F.
    Super-resolution microscopy with phase masks is a promising technique for 3D imaging and tracking. Due to the complexity of the resultant point spread functions, generalized recovery algorithms are still missing. We introduce a 3D super-resolution recovery algorithm that works for a variety of phase masks generating 3D point spread functions. A fast deconvolution process generates initial guesses, which are further refined by least squares fitting. Overfitting is suppressed using a machine learning determined threshold. Preliminary results on experimental data show that our algorithm can be used to super-localize 3D adsorption events within a porous polymer film and is useful for evaluating potential phase masks. Finally, we demonstrate that parallel computation on graphics processing units can reduce the processing time required for 3D recovery. Simulations reveal that, through desktop parallelization, the ultimate limit of real-time processing is possible. Our program is the first open source recovery program for generalized 3D recovery using rotating point spread functions.
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    Phase modulation in super-resolution microscopy
    (2018-12-18) Wang, Wenxiao; Landes, Christy F
    Phase modulation attracts arising attention in super-resolution studies because of the convenience and efficiency in encoding the information. Current super-resolution microscopy typically achieves high spatial resolution, but the temporal resolution remains low and obstructs most physical and chemical studies. Based on phase modulation, the novel technique Super Temporal-Resolved Microscopy is proposed to compress time information and thus improve the temporal resolution of 2D super-resolution microscopy. The fundamental basis for STReM is the utilization of a double helix phase mask that is rotated at fast speed to encode temporal information in the Fourier domain. Complicated movement can be also dissolved and reconstructed through an L1 norm constrained optimization process. STReM has been verified using both simulated and experimental 2D data and the temporal resolution is improved 20 times when comparing traditional methods to that of the novel method of STReM presented in this thesis. Besides the application to boost the temporal resolution, phase modulation is also applied to extract depth information in super-resolution microscopy. Most physical and chemical processes occur in 3D space and the underlying mechanism is usually unavailable or misleading due to the poor depth detection ability. Recently, phase modulation is reported as a promising solution to 3D imaging in super-resolution microscopy. Various functions have been achieved through phase modulation such as improving the axial spatial localization precision and expanding the axial detection range. However, a current challenge is the lack of a robust and efficient algorithm to design a phase mask for arbitrary desired point spread function patterns in 3D continuous space. In this thesis the phase mask design algorithm is proposed using a phase retrieval scheme. Multiple algorithms were studied and compared for solving the phase retrieval, including Gerchberg Saxton, stochastic gradient decent, and Gauss-Newton methods. The Gauss-Newton method is proved to be the best by reaching the minima of the phase retrieval optimization. Several phase mask patterns for 3D super-resolution microscopy are proposed, and their corresponding PM patterns are successfully designed and experimentally fabricated with light lithography. Finally, by combining both depth and time modulations, phase modulation is proposed to encode the information simultaneously in 4D space, which will definitely benefit super-resolution studies in the future.
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    Snapshot Hyperspectral Imaging (SHI) for Revealing Irreversible and Heterogeneous Plasmonic Processes
    (American Chemical Society, 2018) Kirchner, Silke R.; Smith, Kyle W.; Hoener, Benjamin S.; Collins, Sean S.E.; Wang, Wenxiao; Cai, Yi-Yu; Kinnear, Calum; Zhang, Heyou; Chang, Wei-Shun; Mulvaney, Paul; Landes, Christy F.; Link, Stephan
    Plasmon-mediated processes provide unique opportunities for selective photocatalysis, photovoltaics, and electrochemistry. Determining the influence of particle heterogeneity is an unsolved problem because often such processes introduce irreversible changes to the nanocatalysts and/or their surroundings. The challenge lies in monitoring heterogeneous nonequilibrium dynamics via the slow, serial methods that are intrinsic to almost all spectral acquisition methods with suitable spatial and/or spectral resolution. Here, we present a new metrology, snapshot hyperspectral imaging (SHI), that facilitates in situ readout of the tube lens image and first-order diffraction image of the dark-field scattering from many individual plasmonic nanoparticles to extract their respective spectra simultaneously. Evanescent wave excitation with a supercontinuum laser enabled signal-to-noise ratios greater than 100 with a time resolution of only 1 ms. Throughput of ∼100 simultaneous spectra was achieved with a highly ordered nanoparticle array, yielding a spectral resolution of 0.21 nm/pixel. Additionally, an alternative dark-field excitation geometry utilized a combination of a supercontinuum laser and a reflecting objective for polarization-controlled SHI. Using a simplified version of SHI, we temporally resolve on the millisecond time scale the heterogeneous kinetics of an electrochemical surface redox reaction for many individual gold nanoparticles simultaneously.