Biomaterial microlasers implantable in the cornea, skin, and blood

Antigen-independent single-cell circulating tumor cell detection using deep-learning-assisted biolasers

Circulating tumor cells (CTCs) in the bloodstream are important biomarkers for clinical prognosis of cancers. Current CTC identification methods are based on immuno-labeling, which depends on the differential expression of specific antigens between the cancer cells and white blood cells. Here we present an antigen-independent CTC detection method utilizing a deep-learning-assisted single-cell biolaser. Single-cell lasers were measured from nucleic-acid-stained cells inside optical cavities. A Deep Cell-Laser Classifier (DCLC) was developed to detect tumor cells from a patient CTC-derived pancreatic cell line using their unique single-cell lasing mode patterns. We further showed that the knowledge learned from one type of pancreatic cancer cell line can be transferred to detect other pancreatic cancer cell lines by the DCLC in zero-shot. A sensitivity of 94.3% and a specificity of 99.9% were achieved. Finally, enumeration was performed on CTCs obtained from pancreatic cancer patients. We further demonstrated the DCLC's ability in zero-shot generalization of enumeration on lung cancer patients' CTCs. The counting trends were consistent with those observed using conventional immunofluorescence imaging techniques. Employing our DCLC model, single-cell lasers open new avenues for both future biological studies and clinical applications, including classification of cell types and identification of rare cells.

Whispering Gallery Mode Micro/Nanolasers for Intracellular Probing at Single Cell Resolution

Intracellular probing at single cell resolution is key to revealing the heterogeneity of cells, learning new cell subtypes and functions, understanding the pathophysiology of disease, and ensuring precise diagnosis and treatment. Despite the best efforts, an enormous challenge remains due to the very small size, extremely low content, and dynamic microenvironment of a single cell. Whispering gallery mode (WGM) micro/nanolasers (active WGM) offer unique advantages of small mode volume, high quality factors, bright and low threshold laser emission, and narrow line width, particularly suitable for integration within a single cell. In this review, we provide a focused overview of WGM micro/nanolasers for intracellular probing. We deliver information on WGM micro/nanolaser concepts, sensing mechanism, and biocompatibility, as well as recent progress in intracellular probing applications mainly covering cellular-level sensing, molecular-level detection, and feasibility for cellular imaging. At the end, challenges and prospects of WGM micro/nanolasers for intracellular applications are discussed.

High quality factor, monodisperse micron-sized random lasers based on porous PLGA spheres

Miniature random lasers with high quality factor are crucial for applications in barcoding, bioimaging, and on-chip technologies. However, achieving monodisperse and size-tunable biocompatible random lasers has been a significant challenge. In this study, we employed poly(lactic-co-glycolic) acid (PLGA), a biocompatible material approved for medical use, as the base material for random lasers. By integrating a dye-doped PLGA solution with a microfluidic system, we successfully fabricated monodisperse and miniature dye-doped PLGA spheres with tunable sizes ranging from 25 to 52 µm. Upon optical pulse excitation, these spheres exhibited strong random lasing emission at 610-640 nm with a threshold of approximately 22 µJ·mm-2. The lasing modes demonstrated a spectral linewidth of 0.2 nm, corresponding to a quality factor of 3100. Fourier transform analysis of the lasing emission revealed fundamental cavity lengths, providing insights into the properties of the random lasers.

High-Sensitivity Detection of Changes in Local Refractive Index and Absorption by Analyzing WGM Microlaser Emission via a 2D Dispersion Spectrometer

Microlasers have been widely used in biosensing applications because of their high sensitivity to changes in local conditions. However, in most applications, the sensitivity limit is not dictated by the microlaser line width but rather by the much worse spectral resolution of the detection system, typically a grating spectrometer. To address this issue, we built and characterized a two-dimensional (2D) dispersion spectrometer with a virtually imaged phase array etalon and a diffraction grating. The spectrometer can analyze microlaser emission with a spectral resolution of better than 0.300 pm, which enables high-precision measurements of spectral shifts in laser peak emission wavelength and sufficient resolution to detect changes in peak line width. Using commercial fluorescent microspheres as the microlasers, the 2D dispersion spectrometer demonstrated a detection limit for the refractive index change of a liquid medium of 1.37 × 10-5 RIU and a detection limit for absorption changes of less than 0.02 cm-1.

Aggregation-Induced Stimulated Emission of 100% Dye Microspheres

Dyes with aggregation-induced emission (AIE) properties have gained interests due to their bright luminescence in solid-state aggregates. While fluorescence from AIE dyes have been widely exploited, relatively little is known about aggregation-induced stimulated emission. Here, we investigated stimulated emission of tetraphenylethene (TPE)-based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers. Using femtosecond pump-probe spectroscopy, gain coefficients up to 230 cm-1 at 500 nm were measured. Using rate equations, we analyzed concentration- and pump-dependent gain dynamics as well as laser build up dynamics. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. We fabricated solid-state microspheres made of 100% AIE dyes via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 μm in diameter showed lasing by nanosecond pumping with a threshold of ~10 pJ μm-2. Polymer coated, but not bare, microspheres were internalized by live cells and generated narrowband cavity mode emission from within the cytoplasm. Our work shows the potential of AIE dyes as laser materials.

Phase-Transition Microcavity Laser

Liquid-crystal microcavity lasers have attracted considerable attention because of their extraordinary tunability and sensitive response to external stimuli, and because they operate generally within a specific phase. Here, we demonstrate a liquid-crystal microcavity laser operated in the phase transition in which the reorientation of liquid-crystal molecules occurs from aligned to disordered states. A significant wavelength shift of the microlaser is observed, resulting from the dramatic changes in the refractive index of liquid-crystal microdroplets during the phase transition. This phase-transition microcavity laser is then exploited for sensitive thermal sensing, enabling a two-order-of-magnitude enhancement in sensitivity compared with the nematic-phase microlaser operated far from the transition point. Experimentally, we demonstrate an exceptional sensitivity of -40 nm/K and an ultrahigh resolution of 320 μK. The phase-transition microcavity laser features compactness, softness, and tunability, showing great potential for high-performance sensors, optical modulators, and soft matter photonics.

Autonomous Microlasers for Profiling Extracellular Vesicles from Cancer Spheroids

Self-propelled micro/nanomotors are emergent intelligent sensors for analyzing extracellular biomarkers in circulating biological fluids. Conventional luminescent motors are often masked by a highly dynamic and scattered environment, creating challenges to characterize biomarkers or subtle binding dynamics. Here we introduce a strategy to amplify subtle signals by coupling strong light-matter interactions on micromotors. A smart whispering-gallery-mode microlaser that can self-propel and analyze extracellular biomarkers is demonstrated through a liquid crystal microdroplet. Lasing spectral responses induced by cavity energy transfer were employed to reflect the abundance of protein biomarkers, generating exclusive molecular labels for cellular profiling of exosomes derived from 3D multicellular cancer spheroids. Finally, a microfluidic biosystem with different tumor-derived exosomes was employed to elaborate its sensing capability in complex environments. The proposed autonomous microlaser exhibits a promising method for both fundamental biological science and applications in drug screening, phenotyping, and organ-on-chip applications.

Paradigm shift in future biophotonics for imaging and therapy: Miniature living lasers to cellular scale optoelectronics

Advancements in light technology, devices and its applications have tremendously changed the facets of biomedical science and engineering to provide powerful diagnostic and therapeutic capabilities ranging from basic research to clinics. Recent novel innovations and concepts in the field of material science, biomedical optics, processing technology and nanotechnology have enabled increasingly sophisticated technologies such as cellular scale, wireless, remotely controlled micro device for in vivo integrations. This review deals with such futuristic applications of biophotonics like miniature living lasers, wireless remotely controlled implantable and cellular optoelectronics for novel imaging, diagnostic and therapeutic applications. We begin with an overview of the competency and progress in biophotonics as one of the most active frontiers in advanced analytical, diagnostic and therapeutic modalities. This is further followed by comprehensive discussion on recent advances, importance and applications, towards miniaturization size of laser to integrate into live cells as biological lasers, and wearable and implantable optoelectronic devices. Such applications form a novel biocompatible platform for intracellular sensing, cytometry and imaging devices. Further, the opportunities and possible challenges for future research directions to transform this basic research to clinical applications are also discussed.

In vivo tracking of individual stem cells labeled with nanowire lasers using multimodality imaging

Emerging cell-based regenerative medicine and stem cell therapies have drawn wide attention in medical research and clinical practice to treat tissue damage and numerous incurable diseases. In vivo observation of the distribution, migration, and development of the transplanted cells is important for both understanding the mechanism and evaluating the treatment efficacy and safety. However, tracking the 3D migration trajectories for individual therapeutic cells in clinically relevant pathological environments remains technically challenging. Using a laser photocoagulation model in living rabbit eyes, this study demonstrates a multimodality imaging technology integrating optical coherence tomography (OCT), fluorescence microscopy (FM), and lasing emission for in vivo longitudinal tracking of the 3D migration trajectories of individual human retinal pigment epithelium cells (ARPE-19) labeled with CdS nanowires. With unique lasing spectra generated from the subtle microcavity differences, the surface-modified nanowires perform as distinct spectral identifiers for labeling individual ARPE-19 cells. Meanwhile, with strong optical scattering and natural fluorescence emission, CdS nanowires also served as OCT and FM contrast agents to indicate the spatial locations of the transplanted ARPE-19 cells. A longitudinal study of tracking individual ARPE-19 cells in rabbit eyes over a duration of 28 days was accomplished. This method could potentially promote an understanding of the pharmacodynamics and pharmacokinetics of implanted cells in the development of cell-based therapies.

Ultralow-threshold green fluorescent protein laser based on high Q microbubble resonators

Biological lasers have attracted vast attention because of their potential medical application prospects, especially the low threshold biological laser that can be used for ultrasensitive biological detection while leaving the luminous gain medium undamaged by the pump light. By coupling the low concentration green fluorescent protein (GFP) solution with a high Q whispering gallery mode microbubble resonator, we managed to fabricate a miniature GFP laser with the lowest threshold and highest Q value compared to any known type of the GFP laser. The threshold energy is as low as 380 fJ, two orders of magnitude lower than any type of GFP laser at present. The Q value of the optical cavity in this biological laser is 5.3 × 10⁷, two orders higher than the highest Q value of GFP lasers. We further confirmed the long-term stability of the working characteristics of GFP laser. It can work well nearly a month in temperature 3-4°C. Finally, we measured the effects of different concentrations of fluorescent protein on laser threshold. The data show that this biological laser can be used for highly sensitive detection of GFP concentration, which is particularly useful when the GFP is used as tracers.

Monitoring Various Bioactivities at the Molecular, Cellular, Tissue, and Organism Levels via Biological Lasers

The laser is considered one of the greatest inventions of the 20th century. Biolasers employ high signal-to-noise ratio lasing emission rather than regular fluorescence as the sensing signal, directional out-coupling of lasing and excellent biocompatibility. Meanwhile, biolasers can also be micro-sized or smaller lasers with embedded/integrated biological materials. This article presents the progress in biolasers, focusing on the work done over the past years, including the molecular, cellular, tissue, and organism levels. Furthermore, biolasers have been utilized and explored for broad applications in biosensing, labeling, tracking, bioimaging, and biomedical development due to a number of unique advantages. Finally, we provide the possible directions of biolasers and their applications in the future.

Cellular lasers for cell imaging and biosensing

The possibility to produce laser action involving biomaterials, in particular (single) biological cells, has fostered the development of cellular lasers as a novel approach in biophotonics. In this respect, cells that are engineered to carry gain medium (e.g., fluorescent dyes or proteins) are placed inside an optical cavity (i.e., typically a sandwich of highly reflective mirrors), allowing the generation of stimulated emission upon sufficient optical pumping. In another scenario, micron-sized optical resonators supporting whispering-gallery mode (WGM) or semiconductor-based laser probes can be internalized by the cells and support light amplification. This review summarizes the recent advances in the fields of biolasers and cellular lasers, and most importantly, highlights their potential applications in the fields of in vitro and in vivo cell imaging and analysis. They include biosensing (e.g., in vitro detection of sodium chloride (NaCl) concentration), cancer cell imaging, laser-emission-based microscope, cell tracking, cell distinction study, and tissue contraction monitoring in zebrafish. Lastly, several fundamental issues in developing cellular lasers including laser probe fabrication, biocompatibility of the system, and alteration of local refractive index of optical cavities due to protein absorption or probe aggregation are described. Cellular lasers are foreseen as a promising tool to study numerous biological and biophysical phenomena. STATEMENT OF SIGNIFICANCE: Biolasers are generation of laser involving biological materials. Biomaterials, including single cells, can be engineered to incorporate laser probes or fluorescent proteins or fluorophores, and the resulting light emission can be coupled to optical resonator, allowing generation of cellular laser emission upon optical pumping. Unlike fluorescence, this stimulated emission is very sensitive and is capable of detecting small alterations in the optical property of the cells and their environment. In this review, recent development and applications of cellular lasers in the fields of in vitro and in vivo cell imaging, cell tracking, biosensing, and cell/tissue analysis are highlighted. Several challenges in developing cellular lasers including probe fabrication and biocompatibility as well as alteration of cellular environment are explained.

Deep tissue localization and sensing using optical microcavity probes

Optical microcavities and microlasers were recently introduced as probes inside living cells and tissues. Their main advantages are spectrally narrow emission lines and high sensitivity to the environment. Despite numerous novel methods for optical imaging in strongly scattering biological tissues, imaging at single-cell resolution beyond the ballistic light transport regime remains very challenging. Here, we show that optical microcavity probes embedded inside cells enable three-dimensional localization and tracking of individual cells over extended time periods, as well as sensing of their environment, at depths well beyond the light transport length. This is achieved by utilizing unique spectral features of the whispering-gallery modes, which are unaffected by tissue scattering, absorption, and autofluorescence. In addition, microcavities can be functionalized for simultaneous sensing of various parameters, such as temperature or pH value, which extends their versatility beyond the capabilities of standard fluorescent labels.

Immuno-modulatory Effects of Microparticles Formulated from Degradable Polystyrene Analogue

Environmental accumulation of non-degradable polystyrene (PS) microparticles from plastic waste poses potential adverse impact on marine life and human health. Herein, we formulate microparticles from a degradable polystyrene analogue (dePS) and comprehensively evaluate their immuno-modulatory characteristics. Both dePS copolymer and microparticles are chemically degradable under accelerated hydrolytic condition. In vitro studies show that dePS microparticles are non-toxic to three immortalized cell lines. While dePS microparticles do not induce macrophage polarization in vitro, dePS microparticles induce in vivo upregulation of both pro-inflammatory and anti-inflammatory biomarkers in immuno-competent mice, suggesting the coexistence of mixed phenotypes of macrophages in the host immune response to these microparticles. Interestingly, on day 7 post-injection, dePS microparticles induce a lower level of several immuno-modulatory biomarkers (MMPs activity, TNF-α, and arginase activity) compared to that of reference poly(lactic-co-glycolic acid) PLGA microparticles. Remarkably, compared to PS microparticles, dePS microparticles exhibit similar in vitro and in vivo bioactivity while acquiring additional chemical degradability. Overall, our research gains new insights into the host immune response to dePS microparticles and suggests that this degradable polystyrene analogue might be explored as an alternative material choice for biomedical and consumer care applications. This article is protected by copyright. All rights reserved.

Microdroplet lasers and their applications

Bio-integrated lasers, that are lasers made of biological and biocompatible materials and implanted into cells and tissues, are gaining interest from the research community. Here we show how whispering gallery mode microlasers and microcavities made of solid beads or droplets can be used for sensing different processes in biological materials including inside cells. By making microcavities of a predefined size they can also be used to encode some information and for cell tracking. Sensing and tracking can be applied to highly scattering tissues.

Compact Quantum-Dot Microbeads with Sub-Nanometer Emission Linewidth

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, we demonstrate microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 μm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi-color imaging in vivo is demonstrated.

Bioresorbable Photonics: Materials, Devices and Applications

Bio-photonic devices that utilize the interaction between light and biological substances have been emerging as an important tool for clinical diagnosis and/or therapy. At the same time, implanted biodegradable photonic devices can be disintegrated and resorbed after a predefined operational period, thus avoiding the risk and cost associated with the secondary surgical extraction. In this paper, the recent progress on biodegradable photonics is reviewed, with a focus on material strategies, device architectures and their biomedical applications. We begin with a brief introduction of biodegradable photonics, followed by the material strategies for constructing biodegradable photonic devices. Then, various types of biodegradable photonic devices with different functionalities are described. After that, several demonstration examples for applications in intracranial pressure monitoring, biochemical sensing and drug delivery are presented, revealing the great potential of biodegradable photonics in the monitoring of human health status and the treatment of human diseases. We then conclude with the summary of this field, as well as current challenges and possible future directions.

Biophotonic probes for bio-detection and imaging

The rapid development of biophotonics and biomedical sciences makes a high demand on photonic structures to be interfaced with biological systems that are capable of manipulating light at small scales for sensitive detection of biological signals and precise imaging of cellular structures. However, conventional photonic structures based on artificial materials (either inorganic or toxic organic) inevitably show incompatibility and invasiveness when interfacing with biological systems. The design of biophotonic probes from the abundant natural materials, particularly biological entities such as virus, cells and tissues, with the capability of multifunctional light manipulation at target sites greatly increases the biocompatibility and minimizes the invasiveness to biological microenvironment. In this review, advances in biophotonic probes for bio-detection and imaging are reviewed. We emphatically and systematically describe biological entities-based photonic probes that offer appropriate optical properties, biocompatibility, and biodegradability with different optical functions from light generation, to light transportation and light modulation. Three representative biophotonic probes, i.e., biological lasers, cell-based biophotonic waveguides and bio-microlenses, are reviewed with applications for bio-detection and imaging. Finally, perspectives on future opportunities and potential improvements of biophotonic probes are also provided.

Elastomeric nematic colloids, colloidal crystals and microstructures with complex topology

Control of physical behaviors of nematic colloids and colloidal crystals has been demonstrated by tuning particle shape, topology, chirality and surface charging. However, the capability of altering physical behaviors of such soft matter systems by changing particle shape and the ensuing responses to external stimuli has remained elusive. We fabricated genus-one nematic elastomeric colloidal ring-shaped particles and various microstructures using two-photon photopolymerization. Nematic ordering within both the nano-printed particle and the surrounding medium leads to anisotropic responses and actuation when heated. With the thermal control, elastomeric microstructures are capable of changing from genus-one to genus-zero surface topology. Using these particles as building blocks, we investigated elastomeric colloidal crystals immersed within a liquid crystal fluid, which exhibit crystallographic symmetry transformations. Our findings may lead to colloidal crystals responsive to a large variety of external stimuli, including electric fields and light. Pre-designed response of elastomeric nematic colloids, including changes of colloidal surface topology and lattice symmetry, are of interest for both fundamental research and applications.

Review of biosensing with whispering-gallery mode lasers

Lasers are the pillars of modern optics and sensing. Microlasers based on whispering-gallery modes (WGMs) are miniature in size and have excellent lasing characteristics suitable for biosensing. WGM lasers have been used for label-free detection of single virus particles, detection of molecular electrostatic changes at biointerfaces, and barcode-type live-cell tagging and tracking. The most recent advances in biosensing with WGM microlasers are described in this review. We cover the basic concepts of WGM resonators, the integration of gain media into various active WGM sensors and devices, and the cutting-edge advances in photonic devices for micro- and nanoprobing of biological samples that can be integrated with WGM lasers.

Bioresorbable Microdroplet Lasers as Injectable Systems for Transient Thermal Sensing and Modulation

Minimally invasive methods for temperature sensing and thermal modulation in living tissues have extensive applications in biological research and clinical care. As alternatives to bioelectronic devices for this purpose, functional nanomaterials that self-assemble into optically active microstructures offer important features in remote sensing, injectability, and compact size. This paper introduces a transient, or bioresorbable, system based on injectable slurries of well-defined microparticles that serve as photopumped lasers with temperature-sensitive emission wavelengths (>4-300 nm °C^-1). The resulting platforms can act as tissue-embedded thermal sensors and, simultaneously, as distributed vehicles for thermal modulation. Each particle consists of a spherical resonator formed by self-organized cholesteric liquid crystal molecules doped with fluorophores as gain media, encapsulated in thin shells of soft hydrogels that offer adjustable rates of bioresorption through chemical modification. Detailed studies highlight fundamental aspects of these systems including particle sensitivity, lasing threshold, and size. Additional experiments explore functionality as photothermal agents with active temperature feedback (ΔT = 1 °C) and potential routes in remote evaluation of thermal transport properties. Cytotoxicity evaluations support their biocompatibility, and ex vivo demonstrations in Casper fish illustrate their ability to measure temperature within biological tissues with resolution of 0.01 °C. This collective set of results demonstrates a range of multifunctional capabilities in thermal sensing and modulation.

Bioresponsive microlasers with tunable lasing wavelength

Lasing particles are emerging tools for amplifying light-matter interactions at the biointerface by exploiting its strong intensity and miniaturized size. Recent advances in implementing laser particles into living cells and tissues have opened a new frontier in biological imaging, monitoring, and tracking. Despite remarkable progress in micro- and nanolasers, lasing particles with surface functionality remain challenging due to the low mode-volume while maintaining a high Q-factor. Herein, we report the novel concept of bioresponsive microlasers by exploiting interfacial energy transfer based on whispering-gallery-mode (WGM) microdroplet cavities. Lasing wavelengths were manipulated by energy transfer-induced changes of a gain spectrum resulting from the binding molecular concentrations at the cavity surface. Both protein-based and enzymatic-based interactions were demonstrated, shedding light on the development of functional microlasers. Finally, tunable lasing wavelengths over a broad spectral range were achieved by selecting different donor/acceptor pairs. This study not only opens new avenues for biodetection, but also provides deep insights into how molecules modulate laser light at the biointerface, laying the foundation for the development of smart bio-photonic devices at the molecular level.

Chicken albumen-based whispering gallery mode microlasers

Microlasers based on biomaterials have attracted enormous interest because of their promising potential for future applications in medical treatments, bio-tracking, and biosensing. In this work, we demonstrate chicken albumen as a novel and excellent low-cost biomaterial for a laser cavity. By using a simple but effective emulsion process, rhodamine B-doped chicken albumen microspheres with various diameters ranging from 20 μm to 100 μm can be fabricated. Under optical pulse excitation, these microspheres emit lasing emission. The lasing mechanism is investigated and ascribed to the whispering gallery mode (WGM). A threshold of 23.2 μJ mm-2 and a high Q-factor of approximately 2400 are obtained from an 82 μm-diameter microsphere. Size-dependent lasing characteristics are also examined, and the result shows good agreement with the WGM theory. Interestingly, these microsphere biolasers can operate in aqueous and biological environments such as water and human blood serum, which makes them a promising candidate for laser-based biosensing and biological applications.

Optical Waveguides and Integrated Optical Devices for Medical Diagnosis, Health Monitoring and Light Therapies

Optical waveguides and integrated optical devices are promising solutions for many applications, such as medical diagnosis, health monitoring and light therapies. Despite the many existing reviews focusing on the materials that these devices are made from, a systematic review that relates these devices to the various materials, fabrication processes, sensing methods and medical applications is still seldom seen. This work is intended to link these multidisciplinary fields, and to provide a comprehensive review of the recent advances of these devices. Firstly, the optical and mechanical properties of optical waveguides based on glass, polymers and heterogeneous materials and fabricated via various processes are thoroughly discussed, together with their applications for medical purposes. Then, the fabrication processes and medical implementations of integrated passive and active optical devices with sensing modules are introduced, which can be used in many medical fields such as drug delivery and cardiovascular healthcare. Thirdly, wearable optical sensing devices based on light sensing methods such as colorimetry, fluorescence and luminescence are discussed. Additionally, the wearable optical devices for light therapies are introduced. The review concludes with a comprehensive summary of these optical devices, in terms of their forms, materials, light sources and applications.

Mass production of thin-walled hollow optical fibers enables disposable optofluidic laser immunosensors

Disposable biosensors are of great importance in disease diagnosis due to their inherent merits of no cross-contamination and ease of use. Optofluidic laser (OFL) sensors are a new category of sensitive biosensors; however, it is challenging to cost-effectively mass-produce them to achieve disposability. Here, we report a disposable optofluidic laser immunosensor based on thin-walled hollow optical fibers (HOFs). Using a fiber draw tower, the fabrication parameters, including drawing speed and gas flow rate, are explored, and the HOF geometry is precisely controlled, which allows identical laser microring resonators to be distributed along the fibers. The disposable OFL immunosensor detects the protein concentration in the HOF through a wash-free immunoassay. Enabled by the disposable sensors, the statistical characteristics of 80 tests for each concentration greatly reduces the bioassay uncertainty. A low coefficient of variation (CV) of 3.3% confirms the high reproducibility of the disposable HOF-OFL sensors, and the mean of the normal distribution of the logarithmic OFL intensity serves as the sensing output. A limit of detection of 11 nM within a short assay time of 15 min is achieved. These disposable immunosensors possess the advantages of low cost, high reproducibility, fast assay, and low-volume consumption of sample and reagents. We believe that this work will inspire disposable optofluidics through the mass production of multifunctional microstructured optical fibers.

Optical-resonance-assisted generation of super monodisperse microdroplets and microbeads with nanometer precision

Droplets with predefined sizes have been controllably produced at the tip of a micro-capillary immersed in an external fluid while tracking the high Q-factor whispering gallery modes (WGM). The modes were fitted to a model to give precise real-time size measurement, which was used as a feedback to control the pressure in the capillary and the release of the droplet from the capillary when it reached the target size. In this way a dispersion of highly monodisperse droplets anywhere in the size range from 5 μm to 50 μm were produced. To fabricate solid beads, the droplets were made from a liquid photopolymer and were later polymerized with UV light. The polymerized beads showed long term stability. The diameter of the generated oil droplets and polymerized microbeads could be reproduced with a standard deviation of 1.1 nm and 20 nm, respectively. Overall, the demonstrated method improves the size precision by three and two orders of magnitude for microdroplets and microbeads, respectively, compared to standard production methods such as reported in microfluidics. Encoding of short words and numbers has been demonstrated by producing three beads with predefined sizes. The stored information has been read from the emitted spectrum.

Waterproof Cesium Lead Bromide Perovskite Lasers and Their Applications in Solution

The many advantageous optoelectronic properties of lead halide perovskites have made them promising materials in both solar cells and light source applications. However, lead halide perovskites are soluble in polar solvents, which hinders their practical applications. Thus, the effective protection of perovskite against polar solvents is of great significance. Herein, we report a waterproof CsPbBr₃ nanoplate (NP) laser protected by large-scale on-chip microprocess-compatible atomic layer deposition (ALD) Al₂O₃. The 50 nm Al₂O₃ coated CsPbBr₃ NPs can continuously lase in water for over an hour and can still lase after being immersed in water for a month. Moreover, the lasing behaviors of the 20 nm Al₂O₃ coated CsPbBr₃ NP, in the mixed solution of water and glycerine with the refractive index ranging from 1.33 to 1.47, are also studied. As the environmental refractive index increases, the NP laser goes through a mode selection process, showing single-mode (540.3 nm) to dual-mode and to single-mode (533.9 nm) lasing behavior, which is caused by mode competition resulting from the decrease of quality factor (Q factor) and the blue-shift of the material's gain spectra. Besides, lasing thresholds of the CsPbBr₃ NP increase with the environmental refractive index, which can be utilized for sensing with a measured sensitivity of 129.7 μJ cm^-2 RIU^-1 (per refractive index unit) (388.2 μJ cm^-2 RIU^-1) for the long (short)-wavelength lasing mode. Our work demonstrates that the ALD Al₂O₃ protection method can effectively protect CsPbBr₃ against polar solvents, enhance the material's stability, and enable perovskite's practical applications in both on-chip integration and solvent systems.

Protein-based microsphere biolasers fabricated by dehydration

Biolasers made of biological materials have attracted considerable research attention due to their biocompatibility and biodegradability, and have the potential for biosensing and biointegration. However, the current fabrication methods of biolasers suffer from several limitations, such as complicated processing, time-consuming and environmentally unfriendly nature. In this study, a novel approach with green processes for fabricating solid-state microsphere biolasers has been demonstrated. By dehydration via a modified Microglassification™ technology, dye-doped bovine serum albumin (BSA) droplets could be quickly (less than 10 minutes) and easily changed into solid microspheres with diameters ranging from 10 μm to 150 μm. The size of the microspheres could be effectively controlled by changing either the concentration of the BSA solution or the diameter of the initial droplets. The fabricated microspheres could act as efficient microlasers under an optical pulse excitation. A lasing threshold of 7.8 μJ mm-2 and a quality (Q) factor of about 1700 to 3100 were obtained. The size dependence of lasing characteristics was investigated, and the results showed a good agreement with whispering gallery mode (WGM) theory. Our findings contribute an effective technique for the fabrication of high-Q factor microlasers that may be potential for applications in biological and chemical sensors.

An invisible private 2D barcode design and implementation with tunable fluorescent nanoparticles

The popularity of 2D barcodes is playing a key role in simplifying people's daily life activities, such as identification, quick payment, checking in and checking out, etc. However, relevant issues have emerged as their popularity has soared. The most urgent and representative problem is decryption, which may lead to serious information leakage and substantial damage to organizations, such as governments and international enterprises. This issue is mainly due to the visibility of 2D barcodes. In order to prevent potential privacy violation and sensitive information leakage through easy access of those visible 2D barcodes, we have designed and fabricated invisible 2D barcodes that will only be visible under UV illumination. This approach provides a promising solution to address the previous problem by transferring 2D barcodes into an invisible state. We have employed a typical micro-emulsion method to fabricate polystyrene (PS) fluorescent nanoparticles due to its simplicity. The invisible patterns can and will only be accessed and recognized under UV light illumination to protect personal private information. These invisible 2D barcodes provide a feasible solution for personal information protection and fit with a patient's privacy protection scenario very well, as we have demonstrated.

Chromatin laser imaging reveals abnormal nuclear changes for early cancer detection

We developed and applied rapid scanning laser-emission microscopy (LEM) to detect abnormal changes in cell nuclei for early diagnosis of cancer and cancer precursors. Regulation of chromatins is essential for genetic development and normal cell functions, while abnormal nuclear changes may lead to many diseases, in particular, cancer. The capability to detect abnormal changes in "apparently normal" tissues at a stage earlier than tumor development is critical for cancer prevention. Here we report using LEM to analyze colonic tissues from mice at-risk for colon cancer (induced by a high-fat diet) by detecting pre-polyp nuclear abnormality. By imaging the lasing emissions from chromatins, we discovered that, despite the absence of observable lesions, polyps, or tumors under stereoscope, high-fat mice exhibited significantly lower lasing thresholds than low-fat mice. The low lasing threshold is, in fact, very similar to that of adenomas and is caused by abnormal cell proliferation and chromatin deregulation that can potentially lead to cancer. Our findings suggest that conventional detection methods, such as colonoscopy followed by histopathology, by itself, may be insufficient to reveal hidden or early tumors under development. We envision that this innovative work will provide new insights into LEM and support existing tools for early tumor detection in clinical diagnosis, and fundamental biological and biomedical research of chromatin changes at the biomolecular level of cancer development.

Polymeric biomaterials for biophotonic applications

With the growing importance of optical techniques in medical diagnosis and treatment, there exists a pressing need to develop and optimize materials platform for biophotonic applications. Particularly, the design of biocompatible and biodegradable materials with desired optical, mechanical, chemical, and biological properties is required to enable clinically relevant biophotonic devices for translating in vitro optical techniques into in situ and in vivo use. This technological trend propels the development of natural and synthetic polymeric biomaterials to replace traditional brittle, nondegradable silica glass based optical materials. In this review, we present an overview of the advances in polymeric optical material development, optical device design and fabrication techniques, and the accompanying applications to imaging, sensing and phototherapy.

Non-obstructive intracellular nanolasers

Molecular dyes, plasmonic nanoparticles and colloidal quantum dots are widely used in biomedical optics. Their operation is usually governed by spontaneous processes, which results in broad spectral features and limited signal-to-noise ratio, thus restricting opportunities for spectral multiplexing and sensing. Lasers provide the ultimate spectral definition and background suppression, and their integration with cells has recently been demonstrated. However, laser size and threshold remain problematic. Here, we report on the design, high-throughput fabrication and intracellular integration of semiconductor nanodisk lasers. By exploiting the large optical gain and high refractive index of GaInP/AlGaInP quantum wells, we obtain lasers with volumes 1000-fold smaller than the eukaryotic nucleus (V_laser < 0.1 µm³), lasing thresholds 500-fold below the pulse energies typically used in two-photon microscopy (E_th ≈ 0.13 pJ), and excellent spectral stability (<50 pm wavelength shift). Multiplexed labeling with these lasers allows cell-tracking through micro-pores, thus providing a powerful tool to study cell migration and cancer invasion.

Distributed fibre optofluidic laser for chip-scale arrayed biochemical sensing

Optofluidic lasers (OFLs) are an emerging technological platform for biochemical sensing, and their good performance especially high sensitivity has been demonstrated. However, high-throughput detection with an OFL remains a major challenge due to the lack of reproducible optical microcavities. Here, we introduce the concept of a distributed fibre optofluidic laser (DFOFL) and demonstrate its potential for high-throughput sensing applications. Due to the precise fibre geometry control via fibre drawing, a series of identical optical microcavities uniformly distributed along a hollow optical fibre (HOF) can be achieved to obtain a one-dimensional (1D) DFOFL. An enzymatic reaction catalysed by horseradish peroxidase (HRP) can be monitored over time, and the HRP concentration is detected by DFOFL-based arrayed colorimetric detection. Experimentally, five-channel detection in parallel with imaging has been demonstrated. Theoretically, spatial multiplexing of hundreds of channels is achievable with DFOFL-based detection. The DFOFL wavelength is tuned over hundreds of nanometers by optimizing the dye concentration or reconfiguring the liquid gain materials. Extending this concept to a two-dimensional (2D) chip through wavelength multiplexing can further enhance its multi-functionality, including multi-sample detection and spectral analysis. This work opens the door to high-throughput biochemical sensing.

Remote and autonomous temperature measurement based on 3D liquid crystal microlasers

We demonstrate non-contact temperature measurement with one tenth of a kelvin precision at distances of several meters using omnidirectional laser emission from dye-doped cholesteric liquid crystal droplets freely floating in a fluid medium. Upon the excitation with a pulsed laser the liquid crystal droplet emits laser light due to 3D Bragg lasing in all directions. The spectral position of the lasing is highly dependent on temperature, which enables remote and contact-less temperature measurement with high precision. Both laser excitation and collection of light emitted by microlasers is performed through a wide telescope aperture optics at a distance of up to several meters. The optical excitation volume, where the droplets are excited and emitting the laser light is of the order of ten cubic millimeters. The measurement is performed with ten second accumulation time, when several droplets pass through the excitation volume due to their motion. The time of measurement could easily be shortened to less than a second by increasing the rate of the excitation laser. Since the method is based solely on measuring the spectral position of a single and strong laser line, it is quite insensitive to scattering, absorption and background signals, such as autofluorescence. This enables a wide use in science and industry, with a detection range exceeding tens of meters.

Nanowire lasers as intracellular probes

We investigate a cadmium sulfide (CdS) nanowire (NW) laser that is spontaneously internalized into a single cell to serve as a stand-alone intracellular probe. By pumping with nano-joule light pulses, green laser emission (500-520 nm) can be observed inside cells with a peak linewidth as narrow as 0.5 nm. Due to the sub-micron diameter (∼200 nm), the NW has an appreciable fraction of the evanescent field outside, facilitating a sensitive detection of cellular environmental changes. By monitoring the lasing peak wavelength shift in response to the intracellular refractive index change, our NW laser probe shows a sensitivity of 55 nm per RIU (refractive index units) and a figure of merit of approximately 98.

Flying particle microlaser and temperature sensor in hollow-core photonic crystal fiber

Whispering-gallery mode (WGM) resonators combine small optical mode volumes with narrow resonance linewidths, making them exciting platforms for a variety of applications. Here we report a flying WGM microlaser, realized by optically trapping a dye-doped microparticle within a liquid-filled hollow-core photonic crystal fiber (HC-PCF) using a CW laser and then pumping it with a pulsed excitation laser whose wavelength matches the absorption band of the dye. The laser emits into core-guided modes that can be detected at the endfaces of the HC-PCF. Using radiation forces, the microlaser can be freely propelled along the HC-PCF over multi-centimeter distances-orders of magnitude farther than in previous experiments where tweezers and fiber traps were used. The system can be used to measure temperature with high spatial resolution, by exploiting the temperature-dependent frequency shift of the lasing modes, and may also permit precise delivery of light to remote locations.

A robust tissue laser platform for analysis of formalin-fixed paraffin-embedded biopsies

Laser emission-based detection and imaging technology has attracted significant interest in biomedical research due to its high sensitivity, narrow linewidth, and superior spectral and spatial resolution. Recent advances have further revealed the potential to use laser emission to investigate chromatin dynamics, as well as to diagnose cancer tissues based on nuclear biomarkers. To move the laser emission based detection technology a step further towards practical use, in this work, we developed a highly robust tissue laser platform by microfabricating an SU8 spacer with a fixed height on the top mirror of the Fabry-Pérot (FP) cavity, which allows generation of reproducible and stable lasing results regardless of tissue thickness. Then we applied this platform to achieve lasing emission from formalin-fixed, paraffin-embedded (FFPE) lung tissues, which account for an overwhelming fraction of tissues collected for research and clinical use worldwide. We further showed that the cancer and normal FFPE lung tissues can be distinguished by their respective lasing thresholds. Two different tissue thicknesses (10 μm and 5 μm) commonly used in pathological labs were explored. Finally, we tested three additional types of tissues (colon, stomach, and breast) that were prepared independently by lab technicians in a pathology lab in China and shipped to the US in order to validate the general applicability and practicality of the laser emission-based technology as well as the corresponding sample preparation protocol and the tissue laser platform. Our work will not only vastly broaden the applications of laser emission-based detection/imaging technology but also help translate it from the laboratory to an automated system for clinical practice that may eventually benefit biomedicine and biological research.