Viewing early life without labels: optical approaches for imaging the early embryo

Embryo quality is an important determinant of successful implantation and a resultant live birth. Current clinical approaches for evaluating embryo quality rely on subjective morphology assessments or an invasive biopsy for genetic testing. However, both approaches can be inherently inaccurate and crucially, fail to improve the live birth rate following the transfer of in vitro produced embryos. Optical imaging offers a potential non-invasive and accurate avenue for assessing embryo viability. Recent advances in various label-free optical imaging approaches have garnered increased interest in the field of reproductive biology due to their ability to rapidly capture images at high-resolution, delivering both morphological and molecular information. This burgeoning field holds immense potential for further development, with profound implications for clinical translation. Here, our review aims to: 1) describe the principles of various imaging systems, distinguishing between approaches that capture morphological and molecular information, 2) highlight the recent application of these technologies in the field of reproductive biology, and 3) assess their respective merits and limitations concerning the capacity to evaluate embryo quality. Additionally, the review summarizes challenges in the translation of optical imaging systems into routine clinical practice, providing recommendations for their future development. Finally, we identify suitable imaging approaches for interrogating the mechanisms underpinning successful embryo development.

Learning algorithms for identification of whisky using portable Raman spectroscopy

Reliable identification of high-value products such as whisky is vital due to rising issues of brand substitution and quality control in the industry. We have developed a novel framework that can perform whisky analysis directly from raw spectral data with no human intervention by integrating machine learning models with a portable Raman device. We demonstrate that machine learning models can achieve over 99% accuracy in brand or product identification across twenty-eight commercial samples. To demonstrate the flexibility of this approach, we utilized the same algorithms to quantify ethanol concentrations, as well as measuring methanol levels in spiked whisky samples. To demonstrate the potential use of these algorithms in a real-world environment we tested our algorithms on spectral measurements performed through the original whisky bottle. Through the bottle measurements are facilitated by a beam geometry hitherto not applied to whisky brand identification in conjunction with machine learning. Removing the need for decanting greatly enhances the practicality and commercial potential of this technique, enabling its use in detecting counterfeit or adulterated spirits and other high-value liquids. The techniques established in this paper aim to function as a rapid and non-destructive initial screening mechanism for detecting falsified and tampered spirits, complementing more comprehensive and stringent analytical methods.

UVA Hyperspectral Light-Sheet Microscopy for Volumetric Metabolic Imaging: Application to Preimplantation Embryo Development

Cellular metabolism is a key regulator of energetics, cell growth, regeneration, and homeostasis. Spatially mapping the heterogeneity of cellular metabolic activity is of great importance for unraveling the overall cell and tissue health. In this regard, imaging the endogenous metabolic cofactors, nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD), with subcellular resolution and in a noninvasive manner would be useful to determine tissue and cell viability in a clinical environment, but practical use is limited by current imaging techniques. In this paper, we demonstrate the use of phasor-based hyperspectral light-sheet (HS-LS) microscopy using a single UVA excitation wavelength as a route to mapping metabolism in three dimensions. We show that excitation solely at a UVA wavelength of 375 nm can simultaneously excite NAD(P)H and FAD autofluorescence, while their relative contributions can be readily quantified using a hardware-based spectral phasor analysis. We demonstrate the potential of our HS-LS system by capturing dynamic changes in metabolic activity during preimplantation embryo development. To validate our approach, we delineate metabolic changes during preimplantation embryo development from volumetric maps of metabolic activity. Importantly, our approach overcomes the need for multiple excitation wavelengths, two-photon imaging, or significant postprocessing of data, paving the way toward clinical translation, such as in situ, noninvasive assessment of embryo viability.

Fano Resonance-Assisted All-Dielectric Array for Enhanced Near-Field Optical Trapping of Nanoparticles

Near-field optics can overcome the diffraction limit by creating strong optical gradients to enable the trapping of nanoparticles. However, it remains challenging to achieve efficient, stable trapping without heating and thermal effects. Dielectric structures have been used to address this issue but usually offer weak trap stiffness. In this work, we exploit the Fano resonance effect in an all-dielectric quadrupole nanostructure to realize a 20-fold enhancement of trap stiffness, compared to the off-resonance case. This enables a high effective trap stiffness of 1.19 fN/nm for 100 nm diameter polystyrene nanoparticles with 4.2 mW/μm2 illumination. Furthermore, we demonstrate the capability of the structure to simultaneously trap two particles at distinct locations within the nanostructure array.

Snapshot hyperspectral imaging of intracellular lasers

Intracellular lasers are emerging as powerful biosensors for multiplexed tracking and precision sensing of cells and their microenvironment. This sensing capacity is enabled by quantifying their narrow-linewidth emission spectra, which is presently challenging to do at high speeds. In this work, we demonstrate rapid snapshot hyperspectral imaging of intracellular lasers. Using integral field mapping with a microlens array and a diffraction grating, we obtain images of the spatial and spectral intensity distribution from a single camera acquisition. We demonstrate widefield hyperspectral imaging over a 3 × 3 mm2 field of view and volumetric imaging over 250 × 250 × 800 µm3 (XYZ) volumes with a lateral (XY) resolution of 5 µm, axial (Z) resolution of 10 µm, and a spectral resolution of less than 0.8 nm. We evaluate the performance and outline the challenges and strengths of snapshot methods in the context of characterizing the emission from intracellular lasers. This method offers new opportunities for a diverse range of applications, including high-throughput and long-term biosensing with intracellular lasers.

Measuring picometre-level displacements using speckle patterns produced by an integrating sphere

As the fields of optical microscopy, semiconductor technology and fundamental science increasingly aim for precision at or below the nanoscale, there is a burgeoning demand for sub-nanometric displacement and position sensing. We show that the speckle patterns produced by multiple reflections of light inside an integrating sphere provide an exceptionally sensitive probe of displacement. We use an integrating sphere split into two independent hemispheres, one of which is free to move in any given direction. The relative motion of the two hemispheres produces a change in the speckle pattern from which we can analytically infer the amplitude of the displacement. The method allows a noise floor of 5 pm/[Formula: see text] ([Formula: see text]) above 30 Hz in a facile implementation, which we use to measure oscillations of 17 pm amplitude ([Formula: see text]) with a signal to noise ratio of 3.

An Exploratory Study of Physical Therapists From High-Income Countries Practising Outside of Their Scope in Low and Middle-Income Countries

PURPOSE

To quantify how often physical therapists from high-income countries (HIC) travelling to low- and middle-income countries (LMIC) practise outside their scope of practice, in what circumstances, and their likelihood of doing the same in the future.

METHODS

An exploratory descriptive study using a survey.

RESULTS

One hundred and twenty-six licensed physical therapists from around the world participated. Physical therapists typically spent less than a month (73.8 per cent) in LMIC; 67.5 per cent believed that physical therapists practise outside of their scope, and 31.7 per cent reported doing so. Reasons were believing that something is better than nothing (47.5 per cent ), a mismatch between the physical therapist's and host's expectations (40.0 per cent ), and preserving their relationship with the host (25.0 per cent ). It was deemed appropriate by 64.5 per cent to practise outside of their scope in some situations and 53.8% considered repeating the activity in the future. Half of the respondent's first experience in LMIC occurred as a student or in their first decade of practice.

CONCLUSIONS

Working in LMIC requires a keen understanding of the risks and challenges associated with such experiences. To ensure best practice, a skill set that consists of critical self-reflection, systems thinking, and structural competency combined with clinical competency and accountability is imperative.

Spatially offset optical coherence tomography: Leveraging multiple scattering for high-contrast imaging at depth in turbid media

The penetration depth of optical coherence tomography (OCT) reaches well beyond conventional microscopy; however, signal reduction with depth leads to rapid degradation of the signal below the noise level. The pursuit of imaging at depth has been largely approached by extinguishing multiple scattering. However, in OCT, multiple scattering substantially contributes to image formation at depth. Here, we investigate the role of multiple scattering in OCT image contrast and postulate that, in OCT, multiple scattering can enhance image contrast at depth. We introduce an original geometry that completely decouples the incident and collection fields by introducing a spatial offset between them, leading to preferential collection of multiply scattered light. A wave optics-based theoretical framework supports our experimentally demonstrated improvement in contrast. The effective signal attenuation can be reduced by more than 24 decibels. Notably, a ninefold enhancement in image contrast at depth is observed in scattering biological samples. This geometry enables a powerful capacity to dynamically tune for contrast at depth.

Investigation of refractive index dynamics during in vitro embryo development using off-axis digital holographic microscopy

Embryo quality is a crucial factor affecting live birth outcomes. However, an accurate diagnostic for embryo quality remains elusive in the in vitro fertilization clinic. Determining physical parameters of the embryo may offer key information for this purpose. Here, we demonstrate that digital holographic microscopy (DHM) can rapidly and non-invasively assess the refractive index of mouse embryos. Murine embryos were cultured in either low- or high-lipid containing media and digital holograms recorded at various stages of development. The phase of the recorded hologram was numerically retrieved, from which the refractive index of the embryo was calculated. We showed that DHM can detect spatio-temporal changes in refractive index during embryo development that are reflective of its lipid content. As accumulation of intracellular lipid is known to compromise embryo health, DHM may prove beneficial in developing an accurate, non-invasive, multimodal diagnostic.

Experimentally unsupervised deconvolution for light-sheet microscopy with propagation-invariant beams

Deconvolution is a challenging inverse problem, particularly in techniques that employ complex engineered point-spread functions, such as microscopy with propagation-invariant beams. Here, we present a deep-learning method for deconvolution that, in lieu of end-to-end training with ground truths, is trained using known physics of the imaging system. Specifically, we train a generative adversarial network with images generated with the known point-spread function of the system, and combine this with unpaired experimental data that preserve perceptual content. Our method rapidly and robustly deconvolves and super-resolves microscopy images, demonstrating a two-fold improvement in image contrast to conventional deconvolution methods. In contrast to common end-to-end networks that often require 1000-10,000s paired images, our method is experimentally unsupervised and can be trained solely on a few hundred regions of interest. We demonstrate its performance on light-sheet microscopy with propagation-invariant Airy beams in oocytes, preimplantation embryos and excised brain tissue, as well as illustrate its utility for Bessel-beam LSM. This method aims to democratise learned methods for deconvolution, as it does not require data acquisition outwith the conventional imaging protocol.

Vitrification within a nanoliter volume: oocyte and embryo cryopreservation within a 3D photopolymerized device

Purpose

Vitrification permits long-term banking of oocytes and embryos. It is a technically challenging procedure requiring direct handling and movement of cells between potentially cytotoxic cryoprotectant solutions. Variation in adherence to timing, and ability to trace cells during the procedure, affects survival post-warming. We hypothesized that minimizing direct handling will simplify the procedure and improve traceability. To address this, we present a novel photopolymerized device that houses the sample during vitrification.

Methods

The fabricated device consisted of two components: the Pod and Garage. Single mouse oocytes or embryos were housed in a Pod, with multiple Pods docked into a Garage. The suitability of the device for cryogenic application was assessed by repeated vitrification and warming cycles. Oocytes or early blastocyst-stage embryos were vitrified either using standard practice or within Pods and a Garage and compared to non-vitrified control groups. Post-warming, we assessed survival rate, oocyte developmental potential (fertilization and subsequent development) and metabolism (autofluorescence).

Results

Vitrification within the device occurred within ~ 3 nL of cryoprotectant: this volume being ~ 1000-fold lower than standard vitrification. Compared to standard practice, vitrification and warming within our device showed no differences in viability, developmental competency, or metabolism for oocytes and embryos. The device housed the sample during processing, which improved traceability and minimized handling. Interestingly, vitrification-warming itself, altered oocyte and embryo metabolism.

Conclusion

The Pod and Garage system minimized the volume of cryoprotectant at vitrification—by ~ 1000-fold—improved traceability and reduced direct handling of the sample. This is a major step in simplifying the procedure.

Supplementary information

The online version contains supplementary material available at 10.1007/s10815-022-02589-8.

Meshless Monte Carlo radiation transfer method for curved geometries using signed distance functions

SIGNIFICANCE

Monte Carlo radiation transfer (MCRT) is the gold standard for modeling light transport in turbid media. Typical MCRT models use voxels or meshes to approximate experimental geometry. A voxel-based geometry does not allow for the precise modeling of smooth curved surfaces, such as may be found in biological systems or food and drink packaging. Mesh-based geometry allows arbitrary complex shapes with smooth curved surfaces to be modeled. However, mesh-based models also suffer from issues such as the computational cost of generating meshes and inaccuracies in how meshes handle reflections and refractions.

AIM

We present our algorithm, which we term signedMCRT (sMCRT), a geometry-based method that uses signed distance functions (SDF) to represent the geometry of the model. SDFs are capable of modeling smooth curved surfaces precisely while also modeling complex geometries.

APPROACH

We show that using SDFs to represent the problem's geometry is more precise than voxel and mesh-based methods.

RESULTS

sMCRT is validated against theoretical expressions, and voxel and mesh-based MCRT codes. We show that sMCRT can precisely model arbitrary complex geometries such as microvascular vessel network using SDFs. In comparison with the current state-of-the-art in MCRT methods specifically for curved surfaces, sMCRT is more precise for cases where the geometry can be defined using combinations of shapes.

CONCLUSIONS

We believe that SDF-based MCRT models are a complementary method to voxel and mesh models in terms of being able to model complex geometries and accurately treat curved surfaces, with a focus on precise simulation of reflections and refractions. sMCRT is publicly available at https://github.com/lewisfish/signedMCRT.

A laser-driven optical atomizer: photothermal generation and transport of zeptoliter-droplets along a carbon nanotube deposited hollow optical fiber

From mechanical syringes to electric field-assisted injection devices, precise control of liquid droplet generation has been sought after, and the present state-of-the-art technologies have provided droplets ranging from nanoliter to subpicoliter volume sizes. In this study, we present a new laser-driven method to generate liquid droplets with a zeptoliter volume, breaking the fundamental limits of previous studies. We guided an infrared laser beam through a hollow optical fiber (HOF) with a ring core whose end facet was coated with single-walled carbon nanotubes. The laser light was absorbed by this nanotube film and efficiently generated a highly localized microring heat source. This evaporated the liquid inside the HOF, which rapidly recondensed into zeptoliter droplets in the surrounding air at room temperature. We spectroscopically confirmed the chemical structures of the liquid precursor maintained in the droplets by atomizing dye-dissolved glycerol. Moreover, we explain the fundamental physical principles as well as functionalities of the optical atomizer and perform a detailed characterization of the droplets. Our approach has strong prospects for nanoscale delivery of biochemical substances in minuscule zeptoliter volumes.

Measurement of Variations in Gas Refractive Index with 10-9 Resolution Using Laser Speckle

Highly resolved determination of refractive index is vital in fields ranging from biosensing through to laser range finding. Laser speckle is known to be a sensitive probe of the properties of the light and the environment, but to date speckle-based refractive index measurements have been restricted to 10^-6 resolution. In this work we identify a strategy to optimize the sensitivity of speckle to refractive index changes, namely, by maximizing the width of the distribution of optical path lengths in the medium. We show that this can be realized experimentally by encapsulating the medium of interest within an integrating sphere. While mitigating against laser-induced heating effects, we demonstrate that variations of the refractive index of air as small as 4.5 × 10^-9 can be resolved with an uncertainty of 7 × 10^-10. This is an improvement of 3 orders of magnitude when compared to previous speckle-based methods.

To focus-match or not to focus-match inverse spatially offset Raman spectroscopy: a question of light penetration

The ability to identify the contents of a sealed container, without the need to extract a sample, is desirable in applications ranging from forensics to product quality control. One technique suited to this is inverse spatially offset Raman spectroscopy (ISORS) which illuminates a sample of interest with an annular beam of light and collects Raman scattering from the center of the ring, thereby retrieving the chemical signature of the contents while suppressing signal from the container. Here we explore in detail the relative benefits of a recently developed variant of ISORS, called focus-matched ISORS. In this variant, the Fourier relationship between the annular beam and a tightly focused Bessel beam is exploited to focus the excitation light inside the sample and to match the focal point of excitation and collection optics to increase the signal from the contents without compromising the suppression of the container signal. Using a flexible experimental setup which can realize both traditional and focus-matched ISORS, and Monte-Carlo simulations, we elucidate the relative advantages of the two techniques for a range of optical properties of sample and container.

Does artificial intelligence have a role in the IVF clinic?

The success of IVF has remained stagnant for a decade. The focus of a great deal of research is to improve on the current ~30% success rate of IVF. Artificial intelligence (AI), or machines that mimic human intelligence, has been gaining traction for its potential to improve outcomes in medicine, such as cancer diagnosis from medical images. In this commentary, we discuss whether AI has the potential to improve fertility outcomes in the IVF clinic. Based on existing research, we examine the potential of adopting AI within multiple facets of an IVF cycle, including egg/sperm and embryo selection, as well as formulation of an IVF treatment regimen. We discuss both the potential benefits and concerns of the patient and clinician in adopting AI in the clinic. We outline hurdles that need to be overcome prior to implementation. We conclude that AI has an important future in improving IVF success.

Polarization and Orbital Angular Momentum of Light in Biomedical Applications: feature issue introduction

In the last decade, consistent and successful innovations have been achieved in the field of lasers and optics, collectively known as 'photonics', founding new applications in biomedicine, including clinical biopsy. Non-invasive photonics-based diagnostic modalities are rapidly expanding, and with their exponential improvement, there is a great potential to develop practical instrumentation for automatic detection and identification of different types and/or sub-types of diseases at a very early stage. While using conventional light for the studies of different properties of objects in materials science, astrophysics and biomedicine already has a long history, the interaction of polarized light and optical angular momentum with turbid tissue-like scattering media has not yet been ultimately explored. Since recently this research area became a hot topic. This feature issue is a first attempt to summarize the recognitions achieved in this emerging research field of polarized light and optical angular momentum for practical biomedical applications during the last years.

Optical manipulation: advances for biophotonics in the 21st century

SIGNIFICANCE

Optical trapping is a technique capable of applying minute forces that has been applied to studies spanning single molecules up to microorganisms.

AIM

The goal of this perspective is to highlight some of the main advances in the last decade in this field that are pertinent for a biomedical audience.

APPROACH

First, the direct determination of forces in optical tweezers and the combination of optical and acoustic traps, which allows studies across different length scales, are discussed. Then, a review of the progress made in the direct trapping of both single-molecules, and even single-viruses, and single cells with optical forces is outlined. Lastly, future directions for this methodology in biophotonics are discussed.

RESULTS

In the 21st century, optical manipulation has expanded its unique capabilities, enabling not only a more detailed study of single molecules and single cells but also of more complex living systems, giving us further insights into important biological activities.

CONCLUSIONS

Optical forces have played a large role in the biomedical landscape leading to exceptional new biological breakthroughs. The continuous advances in the world of optical trapping will certainly lead to further exploitation, including exciting in-vivo experiments.

BPM-Matlab: an open-source optical propagation simulation tool in MATLAB

We present the use of the Douglas-Gunn Alternating Direction Implicit finite difference method for computationally efficient simulation of the electric field propagation through a wide variety of optical fiber geometries. The method can accommodate refractive index profiles of arbitrary shape and is implemented in a tool called BPM-Matlab. We validate BPM-Matlab by comparing it to published experimental, numerical, and theoretical data and to commercially available state-of-the-art software. It is user-friendly, fast, and is available open-source. BPM-Matlab has a broad scope of applications in modeling a variety of optical fibers for diverse fields such as imaging, communication, material processing, and remote sensing.

Extended Kalman Filtering Projection Method to Reduce the 3σ Noise Value of Optical Biosensors

Optical biosensors have experienced a rapid growth over the past decade because of their high sensitivity and the fact that they are label-free. Many optical biosensors rely on tracking the change in a resonance signal or an interference pattern caused by the change in refractive index that occurs upon binding to a target biomarker. The most commonly used method for tracking such a signal is based on fitting the data with an appropriate mathematical function, such as a harmonic function or a Fano, Gaussian, or Lorentz function. However, these functions have limited fitting efficiency because of the deformation of data from noise. Here, we introduce an extended Kalman filter projection (EKFP) method to address the problem of resonance tracking and demonstrate that it improves the tolerance to noise, reduces the 3σ noise value, and lowers the limit of detection (LOD). We utilize the method to process the data of experiments for detecting the binding of C-reactive protein in a urine matrix with a chirped guided mode resonance sensor and are able to improve the LOD from 10 to 1 pg/mL. Our method reduces the 3σ noise value of this measurement compared to a simple Fano fit from 1.303 to 0.015 pixels. These results demonstrate the significant advantage of the EKFP method to resolving noisy data of optical biosensors.

Through-bottle whisky sensing and classification using Raman spectroscopy in an axicon-based backscattering configuration

Non-intrusive detection systems have the potential to characterise materials through various transparent glass and plastic containers. Food and drink adulteration is increasingly problematic, representing a serious health risk as well as an economic issue. This is of particular concern for alcoholic spirits such as Scotch whisky which are often targeted for fraudulent activity. We have developed a Raman system with a novel geometry of excitation and collection, exploiting the beam propagation from an axicon lens, which results in an annular beam at the bottle surface before focusing within the sample. This facilitates the efficient acquisition of Raman signals from the alcoholic spirit contained inside the bottle, while avoiding the collection of auto-fluorescence signals generated by the bottle wall. Therefore, this technique provides a way of non-destructive and non-contact detection to precisely analyse the contents without the requirement to open the bottle.

Willin/FRMD6 Influences Mechanical Phenotype and Neuronal Differentiation in Mammalian Cells by Regulating ERK1/2 Activity

Willin/FRMD6 is part of a family of proteins with a 4.1 ezrin-radixin-moesin (FERM) domain. It has been identified as an upstream activator of the Hippo pathway and, when aberrant in its expression, is associated with human diseases and disorders. Even though Willin/FRMD6 was originally discovered in the rat sciatic nerve, most studies have focused on its functional roles in cells outside of the nervous system, where Willin/FRMD6 is involved in the formation of apical junctional cell-cell complexes and in regulating cell migration. Here, we investigate the biochemical and biophysical role of Willin/FRMD6 in neuronal cells, employing the commonly used SH-SY5Y neuronal model cell system and combining biochemical measurements with Elastic Resonator Interference Stress Micropscopy (ERISM). We present the first direct evidence that Willin/FRMD6 expression influences both the cell mechanical phenotype and neuronal differentiation. By investigating cells with increased and decreased Willin/FRMD6 expression levels, we show that Willin/FRMD6 not only affects proliferation and migration capacity of cells but also leads to changes in cell morphology and an enhanced formation of neurite-like membrane extensions. These changes were accompanied by alterations of biophysical parameters such as cell force, the organization of actin stress fibers and the formation of focal adhesions. At the biochemical level, changes in Willin/FRMD6 expression inversely affected the activity of the extracellular signal-regulated kinases (ERK) pathway and downstream transcriptional factor NeuroD1, which seems to prime SH-SY5Y cells for retinoic acid (RA)-induced neuronal differentiation.

Photopolymerization with high-order Bessel light beams

We study photopolymerization with high-order Bessel light beams with phase singularities on-axis. Self-trapping and self-focusing of propagation-invariant light beams in a photopolymer allow the fabrication of extended helical microfibers with a length scale of a centimeter, which is more than an order of magnitude larger than the propagation distance of the Bessel light beams. We show the evolution of microfibers rotating at a rate proportional to the incident optical power, while the periodicity of the helical structures remains constant, irrespective of the laser power. This suggests that optical momentum transfer plays a predominant role in the growth and rotation of such fiber structures.

Reducing data acquisition for light-sheet microscopy by extrapolation between imaged planes

Light-sheet fluorescence microscopy (LSFM) is a powerful technique that can provide high-resolution images of biological samples. Therefore, this technique offers significant improvement for three-dimensional (3D) imaging of living cells. However, producing high-resolution 3D images of a single cell or biological tissues, normally requires high acquisition rate of focal planes, which means a large amount of sample sections. Consequently, it consumes a vast amount of processing time and memory, especially when studying real-time processes inside living cells. We describe an approach to minimize data acquisition by interpolation between planes using a phase retrieval algorithm. We demonstrate this approach on LSFM data sets and show reconstruction of intermediate sections of the sparse samples. Since this method diminishes the required amount of acquisition focal planes, it also reduces acquisition time of samples as well. Our suggested method has proven to reconstruct unacquired intermediate planes from diluted data sets up to 10× fold. The reconstructed planes were found correlated to the original preacquired samples (control group) with correlation coefficient of up to 90%. Given the findings, this procedure appears to be a powerful method for inquiring and analyzing biological samples.

Coherent oscillations of a levitated birefringent microsphere in vacuum driven by nonconservative rotation-translation coupling

We demonstrate an effect whereby stochastic, thermal fluctuations combine with nonconservative optical forces to break detailed balance and produce increasingly coherent, apparently deterministic motion for a vacuum-trapped particle. The particle is birefringent and held in a linearly polarized Gaussian optical trap. It undergoes oscillations that grow rapidly in amplitude as the air pressure is reduced, seemingly in contradiction to the equipartition of energy. This behavior is reproduced in direct simulations and captured in a simplified analytical model, showing that the underlying mechanism involves nonsymmetric coupling between rotational and translational degrees of freedom. When parametrically driven, these self-sustained oscillators exhibit an ultranarrow linewidth of 2.2 μHz and an ultrahigh mechanical quality factor in excess of 2 × 10⁸ at room temperature. Last, nonequilibrium motion is seen to be a generic feature of optical vacuum traps, arising for any system with symmetry lower than that of a perfect isotropic microsphere in a Gaussian trap.

Multi-photon attenuation-compensated light-sheet fluorescence microscopy

Attenuation of optical fields owing to scattering and absorption limits the penetration depth for imaging. Whilst aberration correction may be used, this is difficult to implement over a large field-of-view in heterogeneous tissue. Attenuation-compensation allows tailoring of the maximum lobe of a propagation-invariant light field and promises an increase in depth penetration for imaging. Here we show this promising approach may be implemented in multi-photon (two-photon) light-sheet fluorescence microscopy and, furthermore, can be achieved in a facile manner utilizing a graded neutral density filter, circumventing the need for complex beam shaping apparatus. A "gold standard" system utilizing a spatial light modulator for beam shaping is used to benchmark our implementation. The approach will open up enhanced depth penetration in light-sheet imaging to a wide range of end users.

Femtometer-resolved simultaneous measurement of multiple laser wavelengths in a speckle wavemeter

Many areas of optical science require an accurate measurement of optical spectra. Devices based on laser speckle promise compact wavelength measurement, with attometer-level sensitivity demonstrated for single wavelength laser fields. The measurement of multimode spectra using this approach would be attractive, yet this is currently limited to picometer resolution. Here, we present a method to improve the resolution and precision of speckle-based multi-wavelength measurements. We measure multiple wavelengths simultaneously, in a device comprising a single 1-m-long step-index multimode fiber and a fast camera. Independent wavelengths separated by as little as 1 fm are retrieved with 0.2 fm precision using principal component analysis. The method offers a viable way to measure sparse spectra containing multiple individual lines and may find application in the tracking of multiple lasers in fields such as quantum technologies and optical telecommunications.

Optimal compressive multiphoton imaging at depth using single-pixel detection

Compressive sensing can overcome the Nyquist criterion and record images with a fraction of the usual number of measurements required. However, conventional measurement bases are susceptible to diffraction and scattering, prevalent in high-resolution microscopy. In this Letter, we explore the random Morlet basis as an optimal set for compressive multiphoton imaging, based on its ability to minimize the space-frequency uncertainty. We implement this approach for wide-field multiphoton microscopy with single-pixel detection, which allows imaging through turbid media without correction. The Morlet basis promises a route for rapid acquisition with lower photodamage.

Label-free optical hemogram of granulocytes enhanced by artificial neural networks

An outstanding challenge for immunology is the classification of immune cells in a label-free fashion with high speed. For this purpose, optical techniques such as Raman spectroscopy or digital holographic microscopy have been used successfully to identify immune cell subsets. To achieve high accuracy, these techniques require a post-processing step using linear methods of multivariate processing, such as principal component analysis. Here we demonstrate for the first time a comparison between artificial neural networks and principal component analysis (PCA) to classify the key granulocyte cell lineages of neutrophils and eosinophils using both digital holographic microscopy and Raman spectroscopy. Artificial neural networks can offer advantages in terms of classification accuracy and speed over a PCA approach. We conclude that digital holographic microscopy with convolutional neural networks based analysis provides a route to a robust, stand-alone and high-throughput hemogram with a classification accuracy of 91.3 % at a throughput rate of greater than 100 cells per second.

The dyslexia susceptibility KIAA0319 gene shows a specific expression pattern during zebrafish development supporting a role beyond neuronal migration

Dyslexia is a common neurodevelopmental disorder caused by a significant genetic component. The KIAA0319 gene is one of the most robust dyslexia susceptibility factors but its function remains poorly understood. Initial RNA-interference studies in rats suggested a role in neuronal migration whereas subsequent work with double knock-out mouse models for both Kiaa0319 and its paralogue Kiaa0319-like reported effects in the auditory system but not in neuronal migration. To further understand the role of KIAA0319 during neurodevelopment, we carried out an expression study of its zebrafish orthologue at different embryonic stages. We used different approaches including RNAscope in situ hybridization combined with light-sheet microscopy. The results show particularly high expression during the first few hours of development. Later, expression becomes localized in well-defined structures. In addition to high expression in the brain, we report for the first time expression in the eyes and the notochord. Surprisingly, kiaa0319-like, which generally shows a similar expression pattern to kiaa0319, was not expressed in the notochord suggesting a distinct role for kiaa0319 in this structure. This observation was supported by the identification of notochord enhancers enriched upstream of the KIAA0319 transcription start site, in both zebrafish and humans. This study supports a developmental role for KIAA0319 in the brain as well as in other developing structures, particularly in the notochord which, is key for establishing body patterning in vertebrates.

Overcoming the speckle correlation limit to achieve a fiber wavemeter with attometer resolution

The measurement of the wavelength of light using speckle is a promising tool for the realization of compact and precise wavemeters and spectrometers. However, the resolution of these devices is limited by strong correlations between the speckle patterns produced by closely spaced wavelengths. Here, we show how principal component analysis of speckle images provides a route to overcome this limit. Using this, we demonstrate a compact wavemeter that measures attometer-scale wavelength changes of a stabilized diode laser, eight orders of magnitude below the speckle correlation limit.

Light sheet microscopy with acoustic sample confinement

Contactless sample confinement would enable a whole host of new studies in developmental biology and neuroscience, in particular, when combined with long-term, wide-field optical imaging. To achieve this goal, we demonstrate a contactless acoustic gradient force trap for sample confinement in light sheet microscopy. Our approach allows the integration of real-time environmentally controlled experiments with wide-field low photo-toxic imaging, which we demonstrate on a variety of marine animal embryos and larvae. To illustrate the key advantages of our approach, we provide quantitative data for the dynamic response of the heartbeat of zebrafish larvae to verapamil and norepinephrine, which are known to affect cardiovascular function. Optical flow analysis allows us to explore the cardiac cycle of the zebrafish and determine the changes in contractile volume within the heart. Overcoming the restrictions of sample immobilisation and mounting can open up a broad range of studies, with real-time drug-based assays and biomechanical analyses.

Three-photon light-sheet fluorescence microscopy

We present the first demonstration of three-photon excitation light-sheet fluorescence microscopy. Light-sheet fluorescence microscopy in single- and two-photon modes has emerged as a powerful wide-field, low-photodamage technique for fast volumetric imaging of biological samples. We extend this imaging modality to the three-photon regime, enhancing its penetration depth. Our present study uses a conventional femtosecond pulsed laser at 1000 nm wavelength for the imaging of 450 μm diameter cellular spheroids. In addition, we show, experimentally and through numerical simulations, the potential advantages in three-photon light-sheet microscopy of using propagation-invariant Bessel beams in preference to Gaussian beams.

Wide-field multiphoton imaging through scattering media without correction

Optical approaches to fluorescent, spectroscopic, and morphological imaging have made exceptional advances in the last decade. Super-resolution imaging and wide-field multiphoton imaging are now underpinning major advances across the biomedical sciences. While the advances have been startling, the key unmet challenge to date in all forms of optical imaging is to penetrate deeper. A number of schemes implement aberration correction or the use of complex photonics to address this need. In contrast, we approach this challenge by implementing a scheme that requires no a priori information about the medium nor its properties. Exploiting temporal focusing and single-pixel detection in our innovative scheme, we obtain wide-field two-photon images through various turbid media including a scattering phantom and tissue reaching a depth of up to seven scattering mean free path lengths. Our results show that it competes favorably with standard point-scanning two-photon imaging, with up to a fivefold improvement in signal-to-background ratio while showing significantly lower photobleaching.

Optical trapping with planar silicon metalenses

Contactless manipulation of micron-scale objects in a microfluidic environment is a key ingredient for a range of applications in the biosciences, including sorting, guiding, and analysis of cells and bacteria. Optical forces are powerful for this purpose but, typically, require bulky focusing elements to achieve the appropriate optical field gradients. To this end, realizing the focusing optics in a planar format would be very attractive and conducive to the integration of such microscale devices, either individually or as arrays. Here we report on, to the best of our knowledge, the first experimental demonstration of optical trapping using planar silicon metalenses illuminated with a collimated laser beam. The structures consist of high-contrast gratings with a locally varying period and duty cycle. They are designed to mimic parabolic reflectors with a numerical aperture of 0.56 at a vacuum wavelength of 1064 nm. We achieve both two- and three-dimensional trapping in water, with the latter realized by omitting the central Fresnel zones. This Letter highlights the versatility of such lithographically defined metastructures for exerting optical forces without the need for traditional optical elements.

Fast volume-scanning light sheet microscopy reveals transient neuronal events

Light sheet fluorescence microscopy offers considerable potential to the cellular neuroscience community as it makes it possible to image extensive areas of neuronal structures, such as axons or dendrites, with a low light budget, thereby minimizing phototoxicity. However, the shallow depth of a light sheet, which is critical for achieving high contrast, well resolved images, adds a significant challenge if fast functional imaging is also required, as multiple images need to be collected across several image planes. Consequently, fast functional imaging of neurons is typically restricted to a small tissue volume where part of the neuronal structure lies within the plane of a single image. Here we describe a method by which fast functional imaging can be achieved across a much larger tissue volume; a custom-built light sheet microscope is presented that includes a synchronized galvo mirror and electrically tunable lens, enabling high speed acquisition of images across a configurable depth. We assess the utility of this technique by acquiring fast functional Ca²⁺ imaging data across a neuron's dendritic arbour in mammalian brain tissue.

Light-sheet microscopy with attenuation-compensated propagation-invariant beams

Scattering and absorption limit the penetration of optical fields into tissue. We demonstrate a new approach for increased depth penetration in light-sheet microscopy: attenuation-compensation of the light field. This tailors an exponential intensity increase along the illuminating propagation-invariant field, enabling the redistribution of intensity strategically within a sample to maximize signal and minimize irradiation. A key attribute of this method is that only minimal knowledge of the specimen transmission properties is required. We numerically quantify the imaging capabilities of attenuation-compensated Airy and Bessel light sheets, showing that increased depth penetration is gained without compromising any other beam attributes. This powerful yet straightforward concept, combined with the self-healing properties of the propagation-invariant field, improves the contrast-to-noise ratio of light-sheet microscopy up to eightfold across the entire field of view in thick biological specimens. This improvement can significantly increase the imaging capabilities of light-sheet microscopy techniques using Airy, Bessel, and other propagation-invariant beam types, paving the way for widespread uptake by the biomedical community.

Towards automated cancer screening: Label-free classification of fixed cell samples using wavelength modulated Raman spectroscopy

The ability to provide quantitative, objective and automated pathological analysis would provide enormous benefits for national cancer screening programmes, in terms of both resource reduction and improved patient wellbeing. The move towards molecular pathology through spectroscopic methods shows great promise, but has been restricted by spectral quality, acquisition times and lack of direct clinical application. In this paper, we present the application of wavelength modulated Raman spectroscopy for the automated label- and fluorescence-free classification of fixed squamous epithelial cells in suspension, such as those produced during a cervical smear test. Direct comparison with standard Raman spectroscopy shows marked improvement of sensitivity and specificity when considering both human papillomavirus (sensitivity +12.0%, specificity +5.3%) and transformation status (sensitivity +10.3%, specificity +11.1%). Studies on the impact of intracellular sampling location and storage effects suggest that wavelength modulated Raman spectroscopy is sufficiently robust to be used in fixed cell classification, but requires further investigations of potential sources of molecular variation in order to improve current clinical tools.

An Organic Vortex Laser

Optical vortex beams are at the heart of a number of novel research directions, both as carriers of information and for the investigation of optical activity and chiral molecules. Optical vortex beams are beams of light with a helical wavefront and associated orbital angular momentum. They are typically generated using bulk optics methods or by a passive element such as a forked grating or a metasurface to imprint the required phase distribution onto an incident beam. Since many applications benefit from further miniaturization, a more integrated yet scalable method is highly desirable. Here, we demonstrate the generation of an azimuthally polarized vortex beam directly by an organic semiconductor laser that meets these requirements. The organic vortex laser uses a spiral grating as a feedback element that gives control over phase, handedness, and degree of helicity of the emitted beam. We demonstrate vortex beams up to an azimuthal index l = 3 that can be readily multiplexed into an array configuration.

Depth-resolved multimodal imaging: Wavelength modulated spatially offset Raman spectroscopy with optical coherence tomography

A major challenge in biophotonics is multimodal imaging to obtain both morphological and molecular information at depth. We demonstrate a hybrid approach integrating optical coherence tomography (OCT) with wavelength modulated spatially offset Raman spectroscopy (WM-SORS). With depth colocalization obtained from the OCT, we can penetrate 1.2-mm deep into strong scattering media (lard) to acquire up to a 14-fold enhancement of a Raman signal from a hidden target (polystyrene) with a spatial offset. Our approach is capable of detecting both Raman and OCT signals for pharmaceutical particles embedded in turbid media and revealing the white matter at depth within a 0.6-mm thick brain tissue layer. This depth resolved label-free multimodal approach is a powerful route to analyze complex biomedical samples.

Detecting Phenotypically Resistant Mycobacterium tuberculosis Using Wavelength Modulated Raman Spectroscopy

Raman spectroscopy is a non-destructive and label-free technique. Wavelength modulated Raman (WMR) spectroscopy was applied to investigate Mycobacterium tuberculosis cell state, lipid rich (LR) and lipid poor (LP). Compared to LP cells, LR cells can be up to 40 times more resistant to key antibiotic regimens. Using this methodology single lipid rich (LR) from lipid poor (LP) bacteria can be differentiated with both high sensitivity and specificity. It can also be used to investigate experimentally infected frozen tissue sections where both cell types can be differentiated. This methodology could be utilized to study the phenotype of mycobacterial cells in other tissues.

Multimode fibre based imaging for optically cleared samples

Optical clearing is emerging as a popular approach particularly for studies in neuroscience. However the use of corrosive clearing solutions typically requires sophisticated objectives or extreme care with optical components chosen for single- or multi-photon imaging. In contrast to the use of complex, custom-made microscope objectives, we show that the use of a corrected multimode fibre (MMF) offers a route that is resistant to corrosion, can be used in clearing media, is not constrained by the refractive index of the immersion medium and offers flexible working distances. Using a corrected MMF, we demonstrate fluorescence imaging of beads and stained neuroblastoma cells through optically cleared mouse brain tissue, as well as imaging in an extreme oxidative environment to show the versatility of our approach. Additionally, we perform Raman imaging of polystyrene beads in clearing media to demonstrate that this approach may be used for vibrational spectroscopy of optically cleared samples.

Label-free optical vibrational spectroscopy to detect the metabolic state of M. tuberculosis cells at the site of disease

Tuberculosis relapse is a barrier to shorter treatment. It is thought that lipid rich cells, phenotypically resistant to antibiotics, may play a major role. Most studies investigating relapse use sputum samples although tissue bacteria may play an important role. We developed a non-destructive, label-free technique combining wavelength modulated Raman (WMR) spectroscopy and fluorescence detection (Nile Red staining) to interrogate Mycobacterium tuberculosis cell state. This approach could differentiate single "dormant" (lipid rich, LR) and "non-dormant" (lipid poor, LP) cells with high sensitivity and specificity. We applied this to experimentally infected guinea pig lung sections and were able to distinguish both cell types showing that the LR phenotype dominates in infected tissue. Both in-vitro and ex-vivo spectra correlated well, showing for the first time that Mycobacterium tuberculosis, likely to be phenotypically resistant to antibiotics, are present in large numbers in tissue. This is an important step in understanding the pathology of relapse supporting the idea that they may be caused by M. tuberculosis cells with lipid inclusions.

Modal beam splitter: determination of the transversal components of an electromagnetic light field

The transversal profile of beams can always be defined as a superposition of orthogonal fields, such as optical eigenmodes. Here, we describe a generic method to separate the individual components in a laser beam and map each mode onto its designated detector with low crosstalk. We demonstrate this with the decomposition into Laguerre-Gaussian beams and introduce a distribution over the integer numbers corresponding to the discrete orbital and radial momentum components of the light field. The method is based on determining an eigenmask filter transforming the incident optical eigenmodes to position eigenmodes enabling the detection of the state of the light field using single detectors while minimizing cross talk with respect to the set of filter masks considered.

Raman imaging through a single multimode fibre

Vibrational spectroscopy is a widespread, powerful method of recording the molecular spectra of constituent molecules within a sample in a label-free manner. As an example, Raman spectroscopy has major applications in materials science, biomedical analysis and clinical studies. The need to access deep tissues and organs in vivo has triggered major advances in fibre Raman probes that are compatible with endoscopic settings. However, imaging in confined geometries still remains out of reach for the current state of art fibre Raman systems without compromising the compactness and flexibility. Here we demonstrate Raman spectroscopic imaging via complex correction in single multimode fibre without using any additional optics and filters in the probe design. Our approach retains the information content typical to traditional fibre bundle imaging, yet within an ultra-thin footprint of diameter 125 μm which is the thinnest Raman imaging probe realised to date. We are able to acquire Raman images, including for bacteria samples, with fields of view exceeding 200 μm in diameter.

Harnessing speckle for a sub-femtometre resolved broadband wavemeter and laser stabilization

The accurate determination and control of the wavelength of light is fundamental to many fields of science. Speckle patterns resulting from the interference of multiple reflections in disordered media are well-known to scramble the information content of light by complex but linear processes. However, these patterns are, in fact, exceptionally rich in information about the illuminating source. We use a fibre-coupled integrating sphere to generate wavelength-dependent speckle patterns, in combination with algorithms based on the transmission matrix method and principal component analysis, to realize a broadband and sensitive wavemeter. We demonstrate sub-femtometre wavelength resolution at a centre wavelength of 780 nm, and a broad calibrated measurement range from 488 to 1,064 nm. This compares favourably to the performance of conventional wavemeters. Using this speckle wavemeter as part of a feedback loop, we stabilize a 780 nm diode laser to achieve a linewidth better than 1 MHz.

Multimodal discrimination of immune cells using a combination of Raman spectroscopy and digital holographic microscopy

The ability to identify and characterise individual cells of the immune system under label-free conditions would be a significant advantage in biomedical and clinical studies where untouched and unmodified cells are required. We present a multi-modal system capable of simultaneously acquiring both single point Raman spectra and digital holographic images of single cells. We use this combined approach to identify and discriminate between immune cell populations CD4+ T cells, B cells and monocytes. We investigate several approaches to interpret the phase images including signal intensity histograms and texture analysis. Both modalities are independently able to discriminate between cell subsets and dual-modality may therefore be used a means for validation. We demonstrate here sensitivities achieved in the range of 86.8% to 100%, and specificities in the range of 85.4% to 100%. Additionally each modality provides information not available from the other providing both a molecular and a morphological signature of each cell.