Search

Advances in switchable microlasers have emerged as a building block with immense potential in controlling light-matter interactions and integrated photonics. Compared to artificially designed interfaces, a stimuli-responsive biointerface enables a higher level of functionalities and versatile ways of tailoring optical responses at the nanoscale. However, switching laser emission with biological recognition has yet to be addressed, particularly with reversibility and wavelength tunability over a broad spectral range. Here we demonstrate a self-switchable laser exploiting the biointerface between label-free DNA molecules and dye-doped liquid crystal matrix in a Fabry-Perot microcavity. Laser emission switching among different wavelengths was achieved by utilizing DNA conformation changes as the switching power, which alters the orientation of the liquid crystals. Our findings demonstrate that different concentrations of single-stranded DNA lead to different temporal switching of lasing wavelengths and intensities. The lasing wavelength could be reverted upon binding with the complementary sequence through DNA hybridization process. Both experimental and theoretical studies revealed that absorption strength is the key mechanism accounting for the laser shifting behavior. This study represents a milestone in achieving a biologically controlled laser, shedding light on the development of programmable photonic devices at the sub-nanoscale by exploiting the complexity and self-recognition of biomolecules.

We conduct DNA high-resolution melting (HRM) analysis using optofluidic lasers based on a Fabry-Pérot microcavity. Compared to the fluorescence-based HRM, the laser-based HRM has advantages of higher emission intensity for better signal-to-noise ratio and sharper transition for better temperature resolution. In addition, the melting temperature can be lowered by optimizing the laser conditions such as external pump and cavity Q-factor. In this work, we first theoretically analyze the laser-based HRM. Then experiments are performed on three long DNA sequences as model systems, one being 99 bases and the other two being 130 bases long but with different GC contents. We show that the laser-based HRM is able to distinguish the target and the single-base mismatched DNA as long as 130 bases and with nearly 50% GC content. The dependence of laser threshold on the temperature for each DNA sample is first experimentally investigated and by optimizing the external pump, the melting temperature is reduced by more than 10 °C, compared to the fluorescence-based HRM for long DNA sequences up to 130 bases. Finally, we demonstrate an alternative method of using the laser-based HRM for rapid DNA screening that does not exist for the fluorescence-based HRM, in which laser excitation is scanned at a fixed temperature to distinguish the target and the base-mismatched DNA sequences. It is shown that the 130-bases-long DNA with nearly 50% GC content can have as much as 20% difference in the laser threshold and 40% difference in the laser output slope between the target and the single-base mismatched sequences, despite only 0.5 °C difference in their melting temperature, indicating that the laser-excitation-scanning method can also be suitable for long DNA sequences with higher GC content.

Biolasers are an emerging technology for next generation biochemical detection and clinical applications. Progress has recently been made to achieve lasing from biomolecules and single living cells. Tissues, which consist of cells embedded in an extracellular matrix, mimic more closely the actual complex biological environment in a living body and therefore are of more practical significance. Here, we developed a highly versatile tissue laser platform, in which tissues stained with fluorophores are sandwiched in a high-Q Fabry-Pérot microcavity. Distinct lasing emissions from muscle and adipose tissues stained respectively with fluorescein isothiocyanate (FITC) and boron-dipyrromethene (BODIPY), and hybrid muscle/adipose tissue with dual staining were achieved with a threshold of only ∼10 μJ mm -2 . Additionally, we investigated how the tissue structure/geometry, tissue thickness, and staining dye concentration affect the tissue laser. Lasing emission from FITC conjugates (FITC-phalloidin) that specifically target F-actin in muscle tissues was also realized. It is further found that, despite the large fluorescence spectral overlap between FITC and BODIPY in tissues, their lasing emissions could be clearly distinguished and controlled due to their narrow lasing bands and different lasing thresholds, thus enabling highly multiplexed detection. Our tissue laser platform can be broadly applicable to various types of tissues/diseases. It provides a new tool for a wide range of biological and biomedical applications, such as diagnostics/screening of tissues and identification/monitoring of biological transformations in tissue engineering.

We report the development of an optofluidic laser array fabricated on a chip using stable plano-concave Fabry-Pérot (FP) microcavities, which are far less susceptible to optical misalignment during device assembly than the commonly used plano-plano FP microcavities. The concave mirrors in our FP microcavities were created by first generating an array of microwells of a few micrometers in depth and a few tens of micrometers in diameter on a fused silica chip using a CO2 laser, followed by coating of distributed Bragg reflection (DBR) layers. The plano-concave FP microcavity had a Q-factor of 5.6 × 10(5) and finesse of 4 × 10(3), over 100 times higher than those for the FP microcavities in existing optofluidic lasers. 1 mM R6G dye in ethanol was used to test the plano-concave FP microcavities, showing an ultralow lasing threshold of only 90 nJ mm(-2), over 10 times lower than that in the corresponding unstable plano-plano FP microcavities formed by the same DBR coatings on the same chip. Simultaneous laser emission from the optofluidic laser array on the chip and single-mode lasing operation were also demonstrated. Our work will lead to the development of optofluidic laser-based biochemical sensors and novel on-chip photonic devices with extremely low lasing thresholds (nJ mm(-2)) and mode volumes (fL).

• An improved model capable of analyzing the effects of ambient gas on laser polishing is proposed. • Mass transfer, solutocapillary force, and chemical reaction are added to the model. • Convection is the main mass transfer mechanism in the molten pool, not diffusion. • The solutocapillary force always acts in the opposite direction to the melt flows. • The dissolved oxygen enhances the thermocapillary force driving the melt to flow inward. Laser polishing, as an effective surface finishing process, is significantly affected by ambient gas. Previous studies on the contribution of ambient gas to laser polishing mostly focused on experiments, but rarely on numerical simulations. Given this, this paper proposes an improved model capable of analyzing the effects of ambient gas on the laser-polished surface's morphology evolution mechanisms, by expanding an existing laser polishing model with the influences of mass transfer, solutocapillary forces, and chemical reactions. Argon and air were used as ambient gasses for comparison. Through this model, the surface morphology evolution of laser polishing in air was compared with that in argon in terms of the velocity field, temperature field, concentration field, melt surface velocity, molten pool surface profile, and surface forces. The respective contributions of chemical reaction heat, oxygen mass flux, mass transfer, and surface forces were also presented. Furthermore, the numerical model was verified on 304 stainless steel from the perspectives of polished surface roughness, molten pool depth, and oxygen element distribution. [Display omitted] [ABSTRACT FROM AUTHOR]

• Melting analysis of DNA methylation based on laser-emission in a Fabry-Pérot microcavity was proposed. • DNA molecules were distinguished by the melting temperature from the laser-based melting curves. • The method of laser slope was proposed to discriminate DNA molecules at a constant temperature. • Five mixes of methylated and non-methylated DNA samples were discriminated by the laser slope. In this paper, we first analyzed the DNA methylation by using the method of laser-based melting in a Fabry-Pérot (FP) microcavity. Pumped with an external intensity, four types of artificially synthesized DNA sequences with/without cytosine methylation in each strand were first analyzed and distinguished by the melting temperatures of the laser-based high-resolution melting (HRM) curves. Meanwhile the dependance of the laser threshold on the melting temperature for each sample was investigated; the experimental result indicates that, by optimizing the pump intensity, a lower melting temperature can be obtained for each sample. On the other hand, by setting the melting temperature at an optimized value, the samples can be distinguished by the laser behaviors above the threshold; this provides a new way for DNA analysis, and cannot be realized in the fluorescence-based melting analysis. For example, the four types of DNA samples were distinguished with an obvious difference in the laser slope coefficients when the melting temperature was set at 60 °C. Finally, five mixes of methylated and non-methylated DNAs with different mole percentages were analyzed by the laser slope coefficients. [ABSTRACT FROM AUTHOR]

Keywords: biological lasers; cell phenotyping; deep learning; laser modes; microcavities; single cells EN biological lasers cell phenotyping deep learning laser modes microcavities single cells 1 1 1 11/23/21 20211118 NES 211118 In article number 2101421, Zhen Qiao, Yu-Cheng Chen and co-workers demonstrate the biological function of complex laser modes by exploiting deep learning technology. Biological lasers, cell phenotyping, deep learning, laser modes, microcavities, single cells Brain cells extracted from rat were classified through hyperspectral imaging of cell laser modes, offering new prospects for single cell analysis and biophotonic applications. [Extracted from the article]

In article number 2100096, Pin Chieh Wu, Yu-Cheng Chen, and co-workers report a novel concept to study tiny structural molecular interactions through the dynamic changes of vector laser beams. The complex topology of laser modes is discovered and developed into laser barcode to monitor peptide-lipid membrane interactions for a wide range of biomedical applications. Laser Modes: Topological Encoded Vector Beams for Monitoring Amyloid-Lipid Interactions in Microcavity (Adv. Sci. 12/2021). [Extracted from the article]

• Simulation and modeling on laser polishing in melting and transition regimes. • Mechanism of surface topography evolution in laser polishing is revealed. • Contributions of surface forces and material removal in laser polishing are analyzed. • Thermocapillary force affected by surface-active component results in a bulge structure on the polished surface. • Surface roughness prediction is tried through the established model with a maximum error of 14.9%. Previous studies on the mechanism of laser polishing were limited to the melting regime, this paper proposed a numerical model for the melting and transition regimes of laser polishing, which coupled heat transfer, fluid flow, and material vaporization. Based on the model, the evolution of the temperature and velocity fields of the molten pool in laser polishing was presented. And the mechanism of surface topography evolution was revealed from the perspective of surface forces (capillary force, thermocapillary force, and recoil pressure), fluid velocity, and material removal. Furthermore, the corresponding relationships between surface forces, fluid velocity, and surface topography were determined. The contributions of surface forces and vaporization front velocity in laser polishing were investigated, and the reason for the formation of the bulge structure and the influence of laser power on it were analyzed. And the velocity direction change points which have a great influence on the surface evolution were found, and the method to determine the positions of these points was proposed. Besides, the surface roughness prediction after laser polishing was tried through the numerical model, and the maximum error between the predicted results and the experimental results is 14.9%. Therefore, this model can be used to optimize process parameters. [ABSTRACT FROM AUTHOR]

A new method of surface structuring by laser remelting with the help of surface tension (mainly thermocapillary force and solutocapillary force) and volume expansion was proposed. A multiphysics coupled numerical model was proposed for this surface structuring method, in which the calculation of surface tension and solutocapillary force is improved. Using the established numerical model, the formation mechanism of the surface structure was explored from the aspects of surface tension, fluid flow, volume expansion, and surface profile evolution. The reason why the surface structure changes from a "W" shape to an "A" shape was explained, and the contributions of thermocapillary force, solutocapillary force, and volume expansion to the surface structure were investigated. The effects of laser power, scanning speed, and beam diameter on the surface profile of the surface structure were studied by experiments, which indicates that the desired surface structure can be obtained by adjusting the process parameters. All the experimental results were simulated by the established numerical model, and the simulation results are in good agreement with the experimental results, indicating that the numerical model is effective and available. • A new surface structuring by laser remelting was proposed. • The function between main chemical elements and the surface tension was established. • A multiphysics coupled model for the surface structuring was established and verified. • The contributions of thermocapillary force, solutocapillary, and volume expansion was investigated. • The formation mechanism of the surface structure was revealed. [ABSTRACT FROM AUTHOR]

We demonstrate a concatenated fuzzy matching algorithm to restrain local strong regions for the spatial beam shaping of a focused laser with quasi-near-field characteristics on the cross section in the focusing light path. Considering that the light field is redistributed according to the spatial angular spectrum after the laser beam is converged, modulations increasing with the propagation distance will decrease the smoothness of the beam. An effective algorithm for the spatial beam shaping of such focused laser is discussed by establishing the cascaded correspondence between the light field in the front stage and the later stage. The results show that the fluence contrast reduces from 37.2% to 21.4%, and the intensity modulation from 3.33:1–1.86:1. Meanwhile, the low-frequency components corresponding to local large-scale strong regions of the light field in the PSD distribution are effectively suppressed. A more regular spatial intensity profile of the focused laser is finally obtained. [ABSTRACT FROM AUTHOR]

In the study, we investigate the generation of optofluidic laser in stable planar-concave Fabry–Pérot (FP) microcavities. The concave mirror is created on the end-facet of a fiber using the method of CO 2 laser ablation and subsequent coating with dielectric layers. Coumarin 6 in ethanol is used as the gain solution to test the FP microcavities. For comparison, we first test the laser generation in a stable FP microcavity formed by a concave mirror on a fiber and a planar mirror on the substrate of a fused silica without cavity assembly. In this configuration, we can obtain the laser emission with an ultralow pumping energy of 25.5 μ J/ mm2 at the gain concentration of 10 μ M and a detection limit of gain solution as low as 2 μ M. Then, the generation of optofluidic laser is explored in a polymeric optofluidic chip integrated with a stable fiber FP microcavity in the format of planar-concave mirrors and a microfluidic channel. Laser results in this configuration show a laser threshold of 36.9 μ J/mm2 at the gain concentration of 10 μ M and a deduced Q-factor of 7.8 × 105 of the FP microcavity. • We investigate the generation of optofluidic laser in a stable planar-concave fiber Fabry–Pérot microcavity. • Optofluidic laser with low laser threshold of 36.9 μ J/mm2 at the gain concentration of 10 μ M is obtained. • Calculation shows a deduced Q-factor of 7. 8 × 1 0 5 of the FP microcavity. [ABSTRACT FROM AUTHOR]

Enzyme-linked immunosorbent assay (ELISA) is a powerful analytical method for biomolecular analysis due to high sensitivity and specificity. The large background fluorescence can be eliminated by using optofluidic laser-based ELISA. However, the detection time is too long, especially for the detection of low concentration of analyte. Such a drawback can potentially be overcome by using particle with high surface-to-volume ratio. The effect of particle on the lasing threshold of optofluidic laser based on Fabry–Pérot microcavity was demonstrated, which is a fundamental issue on magnetic particle-based optofluidic laser ELISA. The 1 mM R6G ethanol solution and different concentrations of magnetic particles (Fe 3 O 4) solution (5, 10, 20, 40 and 80 μ g/ml) with the diameter 30 or 100 nm was be tested the effect of particle on optofluidic laser. The results show that the lasing threshold increases with the concentration and diameter of particles increasing, but the adverse effect is very small for the detection of low concentration of analyte. Our work will lead to the development of magnetic particle-based optofluidic laser ELISA, which can shorten the detection time and push the detection limit. [ABSTRACT FROM AUTHOR]