Fast label-free microscopy technique for 3D dynamic quantitative imaging of living cells

Ultra-high spatio-temporal resolution imaging with parallel acquisition-readout structured illumination microscopy (PAR-SIM)

Structured illumination microscopy (SIM) has emerged as a promising super-resolution fluorescence imaging technique, offering diverse configurations and computational strategies to mitigate phototoxicity during real-time imaging of biological specimens. Traditional efforts to enhance system frame rates have concentrated on processing algorithms, like rolling reconstruction or reduced frame reconstruction, or on investments in costly sCMOS cameras with accelerated row readout rates. In this article, we introduce an approach to elevate SIM frame rates and region of interest (ROI) coverage at the hardware level, without necessitating an upsurge in camera expenses or intricate algorithms. Here, parallel acquisition-readout SIM (PAR-SIM) achieves the highest imaging speed for fluorescence imaging at currently available detector sensitivity. By using the full frame-width of the detector through synchronizing the pattern generation and image exposure-readout process, we have achieved a fundamentally stupendous information spatial-temporal flux of 132.9 MPixels · s-1, 9.6-fold that of the latest techniques, with the lowest SNR of -2.11 dB and 100 nm resolution. PAR-SIM demonstrates its proficiency in successfully reconstructing diverse cellular organelles in dual excitations, even under conditions of low signal due to ultra-short exposure times. Notably, mitochondrial dynamic tubulation and ongoing membrane fusion processes have been captured in live COS-7 cell, recorded with PAR-SIM at an impressive 408 Hz. We posit that this novel parallel exposure-readout mode not only augments SIM pattern modulation for superior frame rates but also holds the potential to benefit other complex imaging systems with a strategic controlling approach.

Intuitive Cell Manipulation Microscope System with Haptic Device for Intracytoplasmic Sperm Injection Simplification

In recent years, the demand for effective intracytoplasmic sperm injection (ICSI) for the treatment of male infertility has increased. The ICSI operation is complicated as it involves delicate organs and requires a high level of skill. Several cell manipulation systems that do not require such skills have been proposed; notably, several automated methods are available for cell rotation. However, these methods are unfeasible for the delicate ICSI medical procedure because of safety issues. Thus, this study proposes a microscopic system that enables intuitive micropipette manipulation using a haptic device that safely and efficiently performs the entire ICSI procedure. The proposed system switches between field-of-view expansion and three-dimensional image presentation to present images according to the operational stage. In addition, the system enables intuitive pipette manipulation using a haptic device. Experiments were conducted on microbeads instead of oocytes. The results confirmed that the time required for the experimental task was improved by 52.6%, and the injection error was improved by 75.3% compared to those observed in the conventional system.

Quantitative real-time phase microscopy for extended depth-of-field imaging based on the 3D single-shot differential phase contrast (ssDPC) imaging method

Optical diffraction tomography (ODT) is a promising label-free imaging method capable of quantitatively measuring the three-dimensional (3D) refractive index distribution of transparent samples. In recent years, partially coherent ODT (PC-ODT) has attracted increasing attention due to its system simplicity and absence of laser speckle noise. Quantitative phase imaging (QPI) technologies represented by Fourier ptychographic microscopy (FPM), differential phase contrast (DPC) imaging and intensity diffraction tomography (IDT) need to collect several or hundreds of intensity images, which usually introduce motion artifacts when shooting fast-moving targets, leading to a decrease in image quality. Hence, a quantitative real-time phase microscopy (qRPM) for extended depth of field (DOF) imaging based on 3D single-shot differential phase contrast (ssDPC) imaging method is proposed in this research study. qRPM incorporates a microlens array (MLA) to simultaneously collect spatial information and angular information. In subsequent optical information processing, a deconvolution method is used to obtain intensity stacks under different illumination angles in a raw light field image. Importing the obtained intensity stack into the 3D DPC imaging model is able to finally obtain the 3D refractive index distribution. The captured four-dimensional light field information enables the reconstruction of 3D information in a single snapshot and extending the DOF of qRPM. The imaging capability of the proposed qRPM system is experimental verified on different samples, achieve single-exposure 3D label-free imaging with an extended DOF for 160 µm which is nearly 30 times higher than the traditional microscope system.

Multiple-scattering simulator-trained neural network for intensity diffraction tomography

Recovering 3D phase features of complex biological samples traditionally sacrifices computational efficiency and processing time for physical model accuracy and reconstruction quality. Here, we overcome this challenge using an approximant-guided deep learning framework in a high-speed intensity diffraction tomography system. Applying a physics model simulator-based learning strategy trained entirely on natural image datasets, we show our network can robustly reconstruct complex 3D biological samples. To achieve highly efficient training and prediction, we implement a lightweight 2D network structure that utilizes a multi-channel input for encoding the axial information. We demonstrate this framework on experimental measurements of weakly scattering epithelial buccal cells and strongly scattering C. elegans worms. We benchmark the network's performance against a state-of-the-art multiple-scattering model-based iterative reconstruction algorithm. We highlight the network's robustness by reconstructing dynamic samples from a living worm video. We further emphasize the network's generalization capabilities by recovering algae samples imaged from different experimental setups. To assess the prediction quality, we develop a quantitative evaluation metric to show that our predictions are consistent with both multiple-scattering physics and experimental measurements.

Optical diffraction tomography of 3D microstructures using a low coherence source

Optical diffraction tomography (ODT) is a label-free technique for three dimensional imaging of micron-sized objects. Coherence and limited sampling of 3D Fourier space are often responsible for the appearance of artifacts. Here we present an ODT microscope that uses low temporal coherence light and spatial light modulators to retrieve reliable 3D maps of the refractive index. A common-path interferometer, based on a spatial light modulator, measures the complex fields transmitted by a sample. Measured fields, acquired while scanning the illumination direction using a digital micro-mirror device, are fed into a Rytov reconstruction algorithm to obtain refractive index maps whose accuracy is directly evaluated on microfabricated 3D test objects. Even for challenging shapes such as pyramids, bridges, and dumbbells, we obtain volumetric reconstructions that compare very well with electron microscopy images.

Multi-slice ptychographic imaging with multistage coarse-to-fine reconstruction

The ability to image 3D samples with optical sectioning is essential for the study of tomographic morphology in material and biological sciences. However, it is often hampered by limitations of acquisition speed and equipment complexity when performing 3D volumetric imaging. Here, we propose, to the best of our knowledge, a new method for 3D reconstruction from a minimum of four intensity-only measurements. The complementary structured patterns provided by the digital micromirror device (DMD) irradiate the outermost layer of the sample to generate the corresponding diffraction intensities for recording, which enables rapid scanning of loaded patterns for fast acquisition. Our multistage reconstruction algorithm first extracts the overall coarse-grained information, and then iteratively optimizes the information of different layers to obtain fine features, thereby achieving high-resolution 3D tomography. The high-fidelity reconstruction in experiments on two-slice resolution targets, unstained Polyrhachis vicina Roger and freely moving C. elegans proves the robustness of the method. Compared with traditional 3D reconstruction methods such as interferometry-based methods or Fourier ptychographic tomography (FPT), our method increases the reconstruction speed by at least 10 times and is suitable for label-free dynamic imaging in multiple-scattering samples. Such 3D reconstruction suggests potential applications in a wide range of fields.

Transport of intensity diffraction tomography with non-interferometric synthetic aperture for three-dimensional label-free microscopy

We present a new label-free three-dimensional (3D) microscopy technique, termed transport of intensity diffraction tomography with non-interferometric synthetic aperture (TIDT-NSA). Without resorting to interferometric detection, TIDT-NSA retrieves the 3D refractive index (RI) distribution of biological specimens from 3D intensity-only measurements at various illumination angles, allowing incoherent-diffraction-limited quantitative 3D phase-contrast imaging. The unique combination of z-scanning the sample with illumination angle diversity in TIDT-NSA provides strong defocus phase contrast and better optical sectioning capabilities suitable for high-resolution tomography of thick biological samples. Based on an off-the-shelf bright-field microscope with a programmable light-emitting-diode (LED) illumination source, TIDT-NSA achieves an imaging resolution of 206 nm laterally and 520 nm axially with a high-NA oil immersion objective. We validate the 3D RI tomographic imaging performance on various unlabeled fixed and live samples, including human breast cancer cell lines MCF-7, human hepatocyte carcinoma cell lines HepG2, mouse macrophage cell lines RAW 264.7, Caenorhabditis elegans (C. elegans), and live Henrietta Lacks (HeLa) cells. These results establish TIDT-NSA as a new non-interferometric approach to optical diffraction tomography and 3D label-free microscopy, permitting quantitative characterization of cell morphology and time-dependent subcellular changes for widespread biological and medical applications.

Nonparaxial optical transfer function for arbitrary illumination in partially coherent imaging systems and the oblique source application

Recent research in quantitative phase and refractive index microscopy showed promising results with methods using a partially coherent imaging setup, such as partially coherent optical diffraction tomography. For these methods, the phase optical transfer function (POTF), which describes the transmission of spatial frequencies by the imaging system, is crucial. Here, a one-dimensional integral representation of the POTF for imaging systems with arbitrary illumination is derived. It generalizes the existing expression, which is limited to axially symmetric setups. From the general integral form, an analytical solution is derived for the case of oblique homogeneous disk-shaped illumination. This demonstrates the potential of the general representation by offering an additional approach for illumination design in quantitative phase and refractive index microscopy.

Accelerated Fourier ptychographic diffraction tomography with sparse annular LED illuminations

Fourier ptychographic diffraction tomography (FPDT) is a recently developed label-free computational microscopy technique that retrieves high-resolution and large-field three-dimensional (3D) tomograms by synthesizing a set of low-resolution intensity images obtained with a low numerical aperture (NA) objective. However, in order to ensure sufficient overlap of Ewald spheres in 3D Fourier space, conventional FPDT requires thousands of intensity measurements and consumes a significant amount of time for stable convergence of the iterative algorithm. Herein, we present accelerated Fourier ptychographic diffraction tomography (aFPDT), which combines sparse annular light-emitting diode (LED) illuminations and multiplexing illumination to significantly decrease data amount and achieve computational acceleration of 3D refractive index (RI) tomography. Compared with existing FPDT technique, the equivalent high-resolution 3D RI results are obtained using aFPDT with reducing data requirement by more than 40 times. The validity of the proposed method is experimentally demonstrated on control samples and various biological cells, including polystyrene beads, unicellular algae and clustered HeLa cells in a large field of view. With the capability of high-resolution and high-throughput 3D imaging using small amounts of data, aFPDT has the potential to further advance its widespread applications in biomedicine.

Analytical phase optical transfer function for Gaussian illumination and the optimized illumination profiles

The imaging performance of tomographic deconvolution phase microscopy can be described in terms of the phase optical transfer function (POTF) which, in turn, depends on the illumination profile. To facilitate the optimization of the illumination profile, an analytical calculation method based on polynomial fitting is developed to describe the POTF for general nonuniform axially symmetric illumination. This is then applied to Gaussian and related profiles. Compared to numerical integration methods that integrate over a series of annuli, the present analytical method is much faster and is equally accurate. Further, a "balanced distribution" criterion for the POTF and a least-squares minimization are presented to optimize the uniformity of the POTF. An optimum general profile is found analytically by relaxed optimal search, and an optimum Gaussian profile is found through a tree search. Numerical simulations confirm the performance of these optimum profiles and support the balanced distribution criterion introduced.

Quantitative 3D refractive index tomography of opaque samples in epi-mode

Three-dimensional (3D) refractive index (RI) tomography has recently become an exciting new tool for biological studies. However, its limitation to (1) thin samples resulting from a need of transmissive illumination and (2) small fields of view (typically ~50 μm × 50 μm) has hindered its utility in broader biomedical applications. In this work, we demonstrate 3D RI tomography with a large field of view in opaque, arbitrarily thick scattering samples (unsuitable for imaging with conventional transmissive tomographic techniques) with a penetration depth of ca. one mean free scattering path length (~100 μm in tissue) using a simple, low-cost microscope system with epi-illumination. This approach leverages a solution to the inverse scattering problem via the general non-paraxial 3D optical transfer function of our quantitative oblique back-illumination microscopy (qOBM) optical system. A theoretical analysis is presented along with simulations and experimental validations using polystyrene beads, and rat and human thick brain tissues. This work has significant implications for the investigation of optically thick, semi-infinite samples in a non-invasive and label-free manner. This unique 3D qOBM approach can extend the utility of 3D RI tomography for translational and clinical medicine.

Modularized microscope based on parallel phase-shifting digital holography for imaging of living biospecimens

SIGNIFICANCE

Parallel phase-shifting digital holographic microscope (PPSDHM) is powerful for three-dimensional (3D) measurements of dynamic specimens. However, the PPSDHM reported previously was directly fixed on the optical bench and imposed difficulties case, thus it is required to modify the specification of the microscope or transport the microscope to another location.

AIM

We present a modularized PPSDHM. We construct the proposed PPSDHM and demonstrate the 3D measurement capability of the PPSDHM.

APPROACH

The PPSDHM was designed as an inverted microscope to record transparent objects and modularized by integrating the optical elements of the PPSDHM on an optical breadboard. To demonstrate the effectiveness of the PPSDHM, we recorded a 3D motion-picture of moving Volvoxes at 1000  frames  /  s and carried out 3D tracking of the Volvoxes.

RESULTS

The PPSDHM was practically realized and 3D images of objects were successfully reconstructed from holograms recorded with a single-shot exposure. The 3D trajectories of Volvoxes were obtained from the reconstructed images.

CONCLUSIONS

We established a modularized PPSDHM that is capable of 3D image acquisition by integrating the optical elements of the PPSDHM on an optical breadboard. The recording capability of 3D motion-pictures of dynamic specimens was experimentally demonstrated by the PPSDHM.

Three-dimensional phase optical transfer function in axially symmetric microscopic quantitative phase imaging

Three-dimensional quantitative phase imaging (3D QPI) is widely recognized as a potentially high-impact microscopic modality. Central to determining the resolution capability of 3D QPI is the phase optical transfer function (POTF). The magnitude of the POTF over its spatial frequency coverage (SFC) specifies the intensity of the response for each allowed spatial frequency. In this paper, a detailed analysis of the POTF for an axially symmetric optical configuration is presented. First, a useful geometric interpretation of the SFC, which enables its visualization, is presented. Second, a closed-form 1D integral expression is derived for the POTF in the general nonparaxial case, which enables rapid calculation of the POTF. Third, this formulation is applied to disk, annular, multi-annuli, and Gaussian illuminations as well as to an annular objective. Taken together, these contributions enable the visualization and simplified calculation of the 3D axially symmetric POTF and provide a basis for optimizing QPI in a wide range of applications.

Label-free bioanalysis of Leishmania infantum using refractive index tomography with partially coherent illumination

In this work, we report the use of refractive index (RI) tomography for quantitative analysis of unstained DH82 cell line infected with Leishmania infantum. The cell RI is reconstructed by using a modality of optical diffraction tomography technique that employs partially coherent illumination, thus enabling inherent compatibility with conventional wide-field microscopes. The experimental results demonstrate that the cell dry mass concentration (DMC) obtained from the RI allows for reliable detection and quantitative characterization of the infection and its temporal evolution. The RI provides important insight for studying morphological changes, particularly membrane blebbing linked to an apoptosis (cell death) process induced by the disease. Moreover, the results evidence that infected DH82 cells exhibit a higher DMC than healthy samples. These findings open up promising perspectives for clinical diagnosis of Leishmania.

Partially coherent illumination engineering for enhanced refractive index tomography

Optical diffraction tomography based on partially coherent illumination (PC-ODT) is a quantitative label-free imaging technique that allows reconstructing of the object's 3D refractive index from measured through-focus intensity images. PC illumination provides advantages such as speckle noise-free imaging and inherent compatibility with conventional wide-field microscopes. Here we experimentally demonstrate that a proper design of the PC illumination, different from the familiar bright-field one, and the use of more realistic optical transfer functions (OTFs) have crucial importance in PC-ODT to significantly increase the accuracy in 3D refractive index reconstruction. While realistic OTFs properly account for the real experimental illumination conditions, the proposed PC illumination design allows for gathering the object spatial-frequency content attenuated when bright-field illumination is used.

Programmable optical transport of particles in knot circuits and networks

A freestyle single-beam laser trap allows for multi-particle optical transport along arbitrary open or closed trajectories with independent control of the all-optical confinement and propulsion forces exerted over the particles. Here, exploiting this manipulation tool, we propose and experimentally demonstrate an optical dynamic routing technique to assist multi-particle transport in knot circuits and networks exhibiting multiple crossing paths. This new functionality for optical transport enables the particle circulation in such complex systems handling traffic jams and making possible particle separation/mixing in them. It is important for the development of programmable particle delivery and other automated optical transport operations of interest in colloidal physics, optofluidics, biophysics, etc.

Dynamic morphing of 3D curved laser traps for all-optical manipulation of particles

The development of optical manipulation techniques focused on the confinement and transport of micro/nano-particles has attracted increased interest in the last decades. In particular the combination of all-optical confinement and propelling forces, respectively arising from high intensity and phase gradients of a strongly focused laser beam, is promising for optical transport. The recently developed freestyle laser trap exploits this manipulation mechanism to achieve optical transport along arbitrary 3D curves. In practice, reconfigurable 3D optical transport of numerous particles is a challenging problem because it requires the ability to easily adapt the trajectory in real time. In this work, we introduce and experimentally demonstrate a strategy for on-task adaptive design of freestyle laser traps based on a dynamic morphing technique. This provides programmable smooth transformation of the 3D shape of the curved laser trap with independent control of the propelling forces along it, that can be configured according to the considered application. Dynamic morphing, proven here on the example of colloidal dielectric micro-particles, significantly simplifies the important problem of real-time reconfigurable 3D optical transport and opens up routes for other sophisticated optical manipulation tasks.

Three-dimensional tomographic microscopy technique with multi-frequency combination with partially coherent illuminations

We demonstrate a three-dimensional (3D) optical diffraction tomographic technique with multi-frequency combination (MFC-ODT) for the 3D quantitative phase imaging of unlabeled specimens. Three sets of through-focus intensity images are captured under an annular aperture and two circular apertures with different coherence parameters. The 3D phase optical transfer functions (POTF) corresponding to different illumination apertures are combined to obtain a synthesized frequency response, achieving high-quality, low-noise 3D reconstructions with imaging resolution up to the incoherent diffraction limit. Besides, the expression of 3D POTF for arbitrary illumination pupils is derived and analyzed, and the 3D imaging performance of annular illumination is explored. It is shown that the phase-contrast washout effect in high-NA circular apertures can be effectively addressed by introducing a complementary annular aperture, which strongly boosts the phase contrast and improves the imaging resolution. By incorporating high-NA illumination as well as high-NA detection, MFC-ODT can achieve a theoretical transverse resolution up to 200 nm and an axial resolution of 645 nm. To test the feasibility of the proposed MFC-ODT technique, the 3D refractive index reconstruction results are based on a simulated 3D resolution target and experimental investigations of micro polystyrene bead and unstained biological samples are presented. Due to its capability for high-resolution 3D phase imaging as well as the compatibility with a widely available commercial microscope, the MFC-ODT is expected to find versatile applications in biological and biomedical research.

High-throughput intensity diffraction tomography with a computational microscope

We demonstrate a motion-free intensity diffraction tomography technique that enables the direct inversion of 3D phase and absorption from intensity-only measurements for weakly scattering samples. We derive a novel linear forward model featuring slice-wise phase and absorption transfer functions using angled illumination. This new framework facilitates flexible and efficient data acquisition, enabling arbitrary sampling of the illumination angles. The reconstruction algorithm performs 3D synthetic aperture using a robust computation and memory efficient slice-wise deconvolution to achieve resolution up to the incoherent limit. We demonstrate our technique with thick biological samples having both sparse 3D structures and dense cell clusters. We further investigate the limitation of our technique when imaging strongly scattering samples. Imaging performance and the influence of multiple scattering is evaluated using a 3D sample consisting of stacked phase and absorption resolution targets. This computational microscopy system is directly built on a standard commercial microscope with a simple LED array source add-on, and promises broad applications by leveraging the ubiquitous microscopy platforms with minimal hardware modifications.

Iterative optimization in tomographic deconvolution phase microscopy

Tomographic deconvolution phase microscopy (TDPM) is a three-dimensional (3D) quantitative phase imaging (QPI) method using partially coherent light that can be implemented on a commercial microscope platform. However, the measurement procedure is relatively time-consuming because it requires many illumination angles. In the present work, an edge-preserving iterative optimization algorithm is presented and applied to TDPM, so that the required number of illumination angles is reduced from 15 to 3, while the measurement accuracy remains high. In addition, the iterative algorithm does not require matrix representation of operators, so the memory requirement is correspondingly reduced.

Optical diffraction tomography with fully and partially coherent illumination in high numerical aperture label-free microscopy [Invited]

Quantitative label-free imaging is an important tool for the study of living microorganisms that, during the last decade, has attracted wide attention from the optical community. Optical diffraction tomography (ODT) is probably the most relevant technique for quantitative label-free 3D imaging applied in wide-field microscopy in the visible range. The ODT is usually performed using spatially coherent light illumination and specially designed holographic microscopes. Nevertheless, the ODT is also compatible with partially coherent illumination and can be realized in conventional wide-field microscopes by applying refocusing techniques, as it has been recently demonstrated. Here, we compare these two ODT modalities, underlining their pros and cons and discussing the optical setups for their implementation. In particular, we pay special attention to a system that is compatible with a conventional wide-field microscope that can be used for both ODT modalities. It consists of two easily attachable modules: the first for sample illumination engineering based on digital light processing technology; the other for focus scanning by using an electrically driven tunable lens. This hardware allows for a programmable selection of the wavelength and the illumination design, and provides fast data acquisition as well. Its performance is experimentally demonstrated in the case of ODT with partially coherent illumination providing speckle-free 3D quantitative imaging.