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Stollmann A, Garcia-Guirado J, Hong JS, Rüedi P, Im H, Lee H, Ortega Arroyo J, Quidant R. Molecular fingerprinting of biological nanoparticles with a label-free optofluidic platform. Nat Commun 2024; 15:4109. [PMID: 38750038 PMCID: PMC11096335 DOI: 10.1038/s41467-024-48132-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 04/22/2024] [Indexed: 05/18/2024] Open
Abstract
Label-free detection of multiple analytes in a high-throughput fashion has been one of the long-sought goals in biosensing applications. Yet, for all-optical approaches, interfacing state-of-the-art label-free techniques with microfluidics tools that can process small volumes of sample with high throughput, and with surface chemistry that grants analyte specificity, poses a critical challenge to date. Here, we introduce an optofluidic platform that brings together state-of-the-art digital holography with PDMS microfluidics by using supported lipid bilayers as a surface chemistry building block to integrate both technologies. Specifically, this platform fingerprints heterogeneous biological nanoparticle populations via a multiplexed label-free immunoaffinity assay with single particle sensitivity. First, we characterise the robustness and performance of the platform, and then apply it to profile four distinct ovarian cell-derived extracellular vesicle populations over a panel of surface protein biomarkers, thus developing a unique biomarker fingerprint for each cell line. We foresee that our approach will find many applications where routine and multiplexed characterisation of biological nanoparticles are required.
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Affiliation(s)
- Alexia Stollmann
- Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092, Zurich, Switzerland
| | - Jose Garcia-Guirado
- Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092, Zurich, Switzerland
| | - Jae-Sang Hong
- Center for Systems Biology, Massachusetts General Hospital, Boston, MA, 02114, USA
| | - Pascal Rüedi
- Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092, Zurich, Switzerland
| | - Hyungsoon Im
- Center for Systems Biology, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 02114, USA
| | - Hakho Lee
- Center for Systems Biology, Massachusetts General Hospital, Boston, MA, 02114, USA
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 02114, USA
| | - Jaime Ortega Arroyo
- Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092, Zurich, Switzerland.
| | - Romain Quidant
- Nanophotonic Systems Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, 8092, Zurich, Switzerland.
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2
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Oh C, Ma HJ, Lee K, Kim DK, Park Y. Non-resonant lasing in a deep-hole scattering cavity. OPTICS EXPRESS 2022; 30:47816-47825. [PMID: 36558700 DOI: 10.1364/oe.475610] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 11/15/2022] [Indexed: 06/17/2023]
Abstract
Random lasers are promising in the spectral regime, wherein conventional lasers are unavailable, with advantages of low fabrication costs and applicability of diverse gain materials. However, their practical application is hindered by high threshold powers, low power efficiency, and difficulties in light collection. Here, we demonstrate a power-efficient easy-to-fabricate non-resonant laser using a deep hole on a porous gain material. The laser action in this counterintuitive cavity was enabled by non-resonant feedback from strong diffuse reflections on the inner surface. Additionally, significant enhancements in slope efficiency, threshold power, and directionality were obtained from cavities fabricated on a porous Nd:YAG ceramic.
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3
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Arcab P, Mirecki B, Stefaniuk M, Pawłowska M, Trusiak M. Experimental optimization of lensless digital holographic microscopy with rotating diffuser-based coherent noise reduction. OPTICS EXPRESS 2022; 30:42810-42828. [PMID: 36522993 DOI: 10.1364/oe.470860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 09/23/2022] [Indexed: 06/17/2023]
Abstract
Laser-based lensless digital holographic microscopy (LDHM) is often spoiled by considerable coherent noise factor. We propose a novel LDHM method with significantly limited coherent artifacts, e.g., speckle noise and parasitic interference fringes. It is achieved by incorporating a rotating diffuser, which introduces partial spatial coherence and preserves high temporal coherence of laser light, crucial for credible in-line hologram reconstruction. We present the first implementation of the classical rotating diffuser concept in LDHM, significantly increasing the signal-to-noise ratio while preserving the straightforwardness and compactness of the LDHM imaging device. Prior to the introduction of the rotating diffusor, we performed LDHM experimental hardware optimization employing 4 light sources, 4 cameras, and 3 different optical magnifications (camera-sample distances). It was guided by the quantitative assessment of numerical amplitude/phase reconstruction of test targets, conducted upon standard deviation calculation (noise factor quantification), and resolution evaluation (information throughput quantification). Optimized rotating diffuser LDHM (RD-LDHM) method was successfully corroborated in technical test target imaging and examination of challenging biomedical sample (60 µm thick mouse brain tissue slice). Physical minimization of coherent noise (up to 50%) was positively verified, while preserving optimal spatial resolution of phase and amplitude imaging. Coherent noise removal, ensured by proposed RD-LDHM method, is especially important in biomedical inference, as speckles can falsely imitate valid biological features. Combining this favorable outcome with large field-of-view imaging can promote the use of reported RD-LDHM technique in high-throughput stain-free biomedical screening.
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4
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Rogalski M, Cywińska M, Ahmad A, Patorski K, Micó V, Ahluwalia BS, Trusiak M. Hilbert phase microscopy based on pseudo thermal illumination in the Linnik configuration. OPTICS LETTERS 2022; 47:5793-5796. [PMID: 37219105 DOI: 10.1364/ol.471858] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 09/18/2022] [Indexed: 05/24/2023]
Abstract
Quantitative phase microscopy (QPM) is often based on recording an object-reference interference pattern and its further phase demodulation. We propose pseudo Hilbert phase microscopy (PHPM) where we combine pseudo thermal light source illumination and Hilbert spiral transform (HST) phase demodulation to achieve hybrid hardware-software-driven noise robustness and an increase in resolution of single-shot coherent QPM. Those advantageous features stem from physically altering the laser spatial coherence and numerically restoring spectrally overlapped object spatial frequencies. The capabilities of PHPM are demonstrated by analyzing calibrated phase targets and live HeLa cells in comparison with laser illumination and phase demodulation via temporal phase shifting (TPS) and Fourier transform (FT) techniques. The performed studies verified the unique ability of PHPM to combine single-shot imaging, noise minimization, and preservation of phase details.
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Lipke W, Winnik J, Trusiak M. Numerical analysis of the effect of reduced temporal coherence in quantitative phase microscopy and tomography. OPTICS EXPRESS 2022; 30:21241-21257. [PMID: 36224847 DOI: 10.1364/oe.458167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2022] [Accepted: 04/20/2022] [Indexed: 06/16/2023]
Abstract
We present the numerical analysis of the effect of the temporarily partially coherent illumination on the phase measurement accuracy in digital holography microscopy (DHM) and optical diffraction tomography (ODT), as reconstruction algorithms tend to assume purely monochromatic conditions. In the regime of reduced temporal coherence, we simulate the hologram formation in two different optical setups, representing classical off-axis two-beam and grating common-path configurations. We consider two ODT variants: with sample rotation and angle-scanning of illumination. Besides the coherence degree of illumination, our simulation considers the influence of the sample normal dispersion, shape of the light spectrum, and optical parameters of the imaging setup. As reconstruction algorithms we employ Fourier hologram method and first-order Rytov approximation with direct inversion and nonnegativity constraints. Quantitative evaluation of the measurement results deviations introduced by the mentioned error sources is comprehensively analyzed, for the first time to the best of our knowledge. Obtained outcomes indicate low final DHM/ODT reconstruction errors for the grating-assisted common-path configuration. Nevertheless, dispersion and asymmetric spectrum introduce non-negligible overestimated refractive index values and noise, and should be thus carefully considered within experimental frameworks.
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6
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Hugonnet H, Lee MJ, Park YK. Quantitative phase and refractive index imaging of 3D objects via optical transfer function reshaping. OPTICS EXPRESS 2022; 30:13802-13809. [PMID: 35472985 DOI: 10.1364/oe.454533] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 03/19/2022] [Indexed: 06/14/2023]
Abstract
Deconvolution phase microscopy enables high-contrast visualization of transparent samples through reconstructions of their transmitted phases or refractive indexes. Herein, we propose a method to extend 2D deconvolution phase microscopy to thick 3D samples. The refractive index distribution of a sample can be obtained at a specific axial plane by measuring only four intensity images obtained under optimized illumination patterns. Also, the optical phase delay of a sample can be measured using different illumination patterns.
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Lee C, Baek Y, Hugonnet H, Park Y. Single-shot wide-field topography measurement using spectrally multiplexed reflection intensity holography via space-domain Kramers-Kronig relations. OPTICS LETTERS 2022; 47:1025-1028. [PMID: 35230281 DOI: 10.1364/ol.446159] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 01/04/2022] [Indexed: 06/14/2023]
Abstract
Surface topology measurements of micro- or nanostructures are essential for both scientific and industrial applications. However, high-throughput measurements remain challenging in surface metrology. We present single-shot full-field surface topography measurement using Kramers-Kronig holographic imaging and spectral multiplexing. Three different intensity images at different incident angles were simultaneously measured with three different colors, from which a quantitative phase image was retrieved using spatial Kramers-Kronig relations. A high-resolution topographic image of the sample was then reconstructed using synthetic aperture holography. Various patterned structures at the nanometer scale were measured and cross-validated using atomic force microscopy.
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Park C, Lee K, Baek Y, Park Y. Low-coherence optical diffraction tomography using a ferroelectric liquid crystal spatial light modulator. OPTICS EXPRESS 2020; 28:39649-39659. [PMID: 33379510 DOI: 10.1364/oe.405418] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 11/12/2020] [Indexed: 06/12/2023]
Abstract
Optical diffraction tomography (ODT) is a three-dimensional (3D) label-free imaging technique. The 3D refractive index distribution of a sample can be reconstructed from multiple two-dimensional optical field images via ODT. Herein, we introduce a temporally low-coherence ODT technique using a ferroelectric liquid crystal spatial light modulator (FLC SLM). The fast binary-phase modulation provided by the FLC SLM ensures the high spatiotemporal resolution. To reduce coherent noise, a superluminescent light-emitting diode is used as an economic low-coherence light source. We demonstrate the performance of the proposed system using various samples, including colloidal microspheres and live epithelial cells.
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Chang T, Ryu D, Jo Y, Choi G, Min HS, Park Y. Calibration-free quantitative phase imaging using data-driven aberration modeling. OPTICS EXPRESS 2020; 28:34835-34847. [PMID: 33182943 DOI: 10.1364/oe.412009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 10/09/2020] [Indexed: 06/11/2023]
Abstract
We present a data-driven approach to compensate for optical aberrations in calibration-free quantitative phase imaging (QPI). Unlike existing methods that require additional measurements or a background region to correct aberrations, we exploit deep learning techniques to model the physics of aberration in an imaging system. We demonstrate the generation of a single-shot aberration-corrected field image by using a U-net-based deep neural network that learns a translation between an optical field with aberrations and an aberration-corrected field. The high fidelity and stability of our method is demonstrated on 2D and 3D QPI measurements of various confluent eukaryotic cells and microbeads, benchmarking against the conventional method using background subtractions.
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Trusiak M, Cywińska M, Micó V, Picazo-Bueno JÁ, Zuo C, Zdańkowski P, Patorski K. Variational Hilbert Quantitative Phase Imaging. Sci Rep 2020; 10:13955. [PMID: 32811839 PMCID: PMC7435195 DOI: 10.1038/s41598-020-69717-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Accepted: 07/15/2020] [Indexed: 11/09/2022] Open
Abstract
Utilizing the refractive index as the endogenous contrast agent to noninvasively study transparent cells is a working principle of emerging quantitative phase imaging (QPI). In this contribution, we propose the Variational Hilbert Quantitative Phase Imaging (VHQPI)-end-to-end purely computational add-on module able to improve performance of a QPI-unit without hardware modifications. The VHQPI, deploying unique merger of tailored variational image decomposition and enhanced Hilbert spiral transform, adaptively provides high quality map of sample-induced phase delay, accepting particularly wide range of input single-shot interferograms (from off-axis to quasi on-axis configurations). It especially promotes high space-bandwidth-product QPI configurations alleviating the spectral overlapping problem. The VHQPI is tailored to deal with cumbersome interference patterns related to detailed locally varying biological objects with possibly high dynamic range of phase and relatively low carrier. In post-processing, the slowly varying phase-term associated with the instrumental optical aberrations is eliminated upon variational analysis to further boost the phase-imaging capabilities. The VHQPI is thoroughly studied employing numerical simulations and successfully validated using static and dynamic cells phase-analysis. It compares favorably with other single-shot phase reconstruction techniques based on the Fourier and Hilbert-Huang transforms, both in terms of visual inspection and quantitative evaluation, potentially opening up new possibilities in QPI.
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Affiliation(s)
- Maciej Trusiak
- Institute of Micromechanics and Photonics, Warsaw University of Technology, 8 Sw. A. Boboli St., 02-525, Warsaw, Poland.
| | - Maria Cywińska
- Institute of Micromechanics and Photonics, Warsaw University of Technology, 8 Sw. A. Boboli St., 02-525, Warsaw, Poland.
| | - Vicente Micó
- Departamento de Óptica y de Optometría y Ciencias de la Visión, Facultad de Física, Universitat de Valencia, C/Doctor Moliner 50, 46100, Burjassot, Spain
| | - José Ángel Picazo-Bueno
- Departamento de Óptica y de Optometría y Ciencias de la Visión, Facultad de Física, Universitat de Valencia, C/Doctor Moliner 50, 46100, Burjassot, Spain
| | - Chao Zuo
- Jiangsu Key Laboratory of Spectral Imaging and Intelligence Sense, Nanjing University of Science and Technology, Nanjing, 210094, Jiangsu, China
| | - Piotr Zdańkowski
- Institute of Micromechanics and Photonics, Warsaw University of Technology, 8 Sw. A. Boboli St., 02-525, Warsaw, Poland
| | - Krzysztof Patorski
- Institute of Micromechanics and Photonics, Warsaw University of Technology, 8 Sw. A. Boboli St., 02-525, Warsaw, Poland
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11
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Wang Y, Xu G, Xiong S, Wu G. Large-field step-structure surface measurement using a femtosecond laser. OPTICS EXPRESS 2020; 28:22946-22961. [PMID: 32752547 DOI: 10.1364/oe.398400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 07/11/2020] [Indexed: 06/11/2023]
Abstract
We present a femtosecond laser-based interferometry for step-structure surface measurement with a large field of view. A height axial scanning range of 348 µm is achieved by using the method of repetition frequency scanning with reference to the Rb atomic clock and the optical path length difference design for 21 times of the pulse interval. A combined method, which includes the envelope peak positioning method for rough measurement, synthetic-wavelength interferometry for connection, and carrier wave interferometry for fine measurement, is proposed to reconstruct the surface. A three-step specimen with heights of approximately 20, 50, and 70 µm was successfully measured with a height precision of 7 nm, and the accuracy was verified by a commercial white light interferometer. The diameter of the field of view that was demonstrated was 17.3 mm, which could be much larger owing to the high spatial coherence of the femtosecond laser. The results show that the femtosecond laser system combines the step-structure measurement performance of white light interferometry and the high-precision large-field performance of phase shifting interferometry, indicating its potential for widespread use in ultra-precision manufacturing of micro/nano-devices, such as semiconductor chips, integrated circuits, and micro-electro-mechanical systems.
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Choi G, Ryu D, Jo Y, Kim YS, Park W, Min HS, Park Y. Cycle-consistent deep learning approach to coherent noise reduction in optical diffraction tomography. OPTICS EXPRESS 2019; 27:4927-4943. [PMID: 30876102 DOI: 10.1364/oe.27.004927] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
We present a deep neural network to reduce coherent noise in three-dimensional quantitative phase imaging. Inspired by the cycle generative adversarial network, the denoising network was trained to learn a transform between two image domains: clean and noisy refractive index tomograms. The unique feature of this network, distinct from previous machine learning approaches employed in the optical imaging problem, is that it uses unpaired images. The learned network quantitatively demonstrated its performance and generalization capability through denoising experiments of various samples. We concluded by applying our technique to reduce the temporally changing noise emerging from focal drift in time-lapse imaging of biological cells. This reduction cannot be performed using other optical methods for denoising.
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Wu Y, Cheng H, Wen Y, Chen X, Wang Y. Coherent noise reduction of phase images in digital holographic microscopy based on the adaptive anisotropic diffusion. APPLIED OPTICS 2018; 57:5364-5370. [PMID: 30117828 DOI: 10.1364/ao.57.005364] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Accepted: 05/29/2018] [Indexed: 06/08/2023]
Abstract
The suppression of coherent noise can produce higher-quality reconstructed images in digital holographic microscopy. A robust and effective phase coherent noise denoising algorithm is proposed in this paper that combines the anisotropic diffusion equation and the phase quality map. In order to accurately identify the noise and signal pixels, we introduce the phase quality map and edge detection to quantify the quality of the pixel information. In addition, a synthetic diffusion function is established to control the speed of the anisotropic diffusion process based on the quality coefficient. Several experiments have been carried out to validate the effectiveness of the proposed algorithm for coherent noise reduction. The results demonstrate that the proposed algorithm can reduce coherent noise and preserve edge details well.
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Choi I, Lee K, Park Y. Compensation of aberration in quantitative phase imaging using lateral shifting and spiral phase integration. OPTICS EXPRESS 2017; 25:30771-30779. [PMID: 29221103 DOI: 10.1364/oe.25.030771] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 11/09/2017] [Indexed: 06/07/2023]
Abstract
We present a simple and effective method to eliminate system aberrations in quantitative phase imaging. Using spiral phase integration, complete information about system aberration is calculated from three laterally shifted phase images. The present method is especially useful when measuring confluent samples in which acquisition of background area is challenging. To demonstrate validity and applicability, we present measurements of various types of samples including microspheres, HeLa cells, and mouse brain tissue. Working conditions and limitations are systematically analyzed and discussed.
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Lee M, Shin S, Park Y. Reconstructions of refractive index tomograms via a discrete algebraic reconstruction technique. OPTICS EXPRESS 2017; 25:27415-27430. [PMID: 29092215 DOI: 10.1364/oe.25.027415] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 10/20/2017] [Indexed: 05/27/2023]
Abstract
Optical diffraction tomography (ODT) provides three-dimensional refractive index (RI) tomograms of a transparent microscopic object. However, because of the finite numerical aperture of objective lenses, ODT has a limited access to diffracted light and suffers from poor spatial resolution, particularly along the axial direction. To overcome the limitation of the quality of RI tomography, we present an algorithm that accurately reconstructs RI tomography of a specimen with discrete and uniform RI, using prior information about the RI levels. Through simulations and experiments on various samples, including microspheres, red blood cells, and water droplets, we show that the proposed method can precisely reconstruct RI tomograms of samples which have discrete and homogenous RI distributions in the presence of the missing information and noise.
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Pan F, Yang L, Xiao W. Coherent noise reduction in digital holographic microscopy by averaging multiple holograms recorded with a multimode laser. OPTICS EXPRESS 2017; 25:21815-21825. [PMID: 29041474 DOI: 10.1364/oe.25.021815] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
In digital holographic microscopy (DHM), it is undesirable to observe coherent noise in the reconstructed images. The sources of the noise are mainly the parasitic interference fringes caused by multiple reflections and the speckle pattern caused by the optical scattering on the object surface. Here we propose a noise reduction approach in DHM by averaging multiple holograms recorded with a multimode laser. Based on the periodicity of the temporal coherence of a multimode semiconductor laser, we acquire a series of holograms by changing the optical path length difference between the reference beam and object beam. Because of the use of low coherence light, we can remove the parasitic interference fringes caused by multiple reflections in the holograms. In addition, the coherent noise patterns change in this process due to the different optical paths. Therefore, the coherent noise can be reduced by averaging the multiple reconstructions with uncorrelated noise patterns. Several experiments have been carried out to validate the effectiveness of the proposed approach for coherent noise reduction in DHM. It is shown a remarkable improvement both in amplitude imaging quality and phase measurement accuracy.
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Park G, Han D, Kim G, Shin S, Kim K, Park JK, Park Y. Visualization and label-free quantification of microfluidic mixing using quantitative phase imaging. APPLIED OPTICS 2017; 56:6341-6347. [PMID: 29047833 DOI: 10.1364/ao.56.006341] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Microfluidic mixing plays a key role in various fields, including biomedicine and chemical engineering. To date, although various approaches for imaging microfluidic mixing have been proposed, they provide only quantitative imaging capability and require exogenous labeling agents. Quantitative phase imaging techniques, however, circumvent these problems and offer label-free quantitative information about concentration maps of microfluidic mixing. We present the quantitative phase imaging of microfluidic mixing in various types of polydimethylsiloxane microfluidic channels with different geometries; the feasibility of the present method was validated by comparing it with the results obtained by theoretical calculation based on Fick's law.
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