Biofluidic Random Laser Cytometer for Biophysical Phenotyping of Cell Suspensions

Broad-band-enhanced plasmonic random laser in silver nanostar arrays

As a novel optical device, the plasmonic random laser has unique working principle and emission characteristics. However, the simultaneous enhancement of absorption and emission by plasmons is still a problem. In this paper, we propose a broad-band-enhanced plasmonic random laser. Two-dimensional silver (Ag) nanostar arrays were prepared using a bottom-up method with the assistance of self-assembled nanosphere templates. The plasmon resonance of Ag nanostars contributes to the pump light absorption and photoluminescence (PL) of RhB. Coherent random lasing was achieved in RhB@PVA film based on localized surface plasmon resonance (SPR) dual enhancement and scattering feedback of Ag nanostars. Ag nanostars prepared with different nanosphere diameters affect the laser emission wavelength. In addition, the random laser device achieves wavelength tunability on a flexible substrate under mechanical external force.

Direct generation of a 635 nm red random laser based on praseodymium (Pr)-doped ZBLAN fiber

Visible random fiber lasers have garnered significant attention due to their unique emission properties and potential applications in various fields. We first, to the best of our knowledge, demonstrated a compact all-fiber structure, red wavelength, and random fiber laser (RFL) based on a double-clad Pr-doped ZBLAN fiber. The simple half-open cavity consists of a high-reflectivity fiber pigtail mirror and the Pr-doped ZBLAN fiber. The Pr-doped ZBLAN fiber not only served as a gain medium but also offered random backward scattering. We investigated the effects of different lengths on output power and slope efficiency of the RFL. For 21 m Pr-doped fiber, the RFL emitted a maximum output power of 208.50 mW with a slope efficiency of 11.09%. For 15 m Pr-doped fiber, the maximum power decreased to 120.18 mW with the slope efficiency of 7.27%. We are also numerically simulating the output power versus the pump power at different fiber lengths based on power steady-state light propagation equations. This novel RFL has the potential for broad applications in fields such as display technology, spectroscopy, biomedical imaging, and optical sensing due to its unique properties and simple all-fiber structure.

Tunable and switchable multi-wavelength actively Q-switched random fiber laser based on an electro-optic modulator and Sagnac loop filter

In this article, an actively Q-switched multi-wavelength random fiber laser based on a Sagnac loop filter and electro-optic modulator is proposed and demonstrated experimentally. The random distributed feedback media is a section of a 25 km long single-mode fiber. When the pump power is 350 mW, the polarization angle of the Sagnac loop filter can be adjusted by polarization controller to achieve the switching of a single, double, triple, and quadruple channels laser output. In the case of a single laser channel, dual laser channels, and three laser channels output, multiple laser channels can be tuned simultaneously with a fixed wavelength interval. In addition, by changing the waveform of the external signal source, the light and dark pulses can be switched. Owing to the half-open cavity structure and the high gain of the erbium-doped fiber, the laser threshold was reduced to 25 mW, and the light conversion efficiency was 0.67%. The laser is an ideal light source for medical imaging and long-distance sensing.

Properties and Applications of Random Lasers as Emerging Light Sources and Optical Sensors: A Review

In a random laser (RL), optical feedback arises from multiple scattering instead of conventional mirrors. RLs generate a laser-like emission, and meanwhile take advantage of a simpler and more flexible laser configuration. The applicability of RLs as light sources and optical sensors has been proved. These applications have been extended to the biological field, with tissues as natural scattering materials. Herein, the current state of the RL properties and applications was reviewed.

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.

Direct Measurement of the Reduced Scattering Coefficient by a Calibrated Random Laser Sensor

The research in optical sensors has been largely encouraged by the demand for low-cost and less or non-invasive new detection strategies. The invention of the random laser has opened a new frontier in optics, providing also the opportunity to explore new possibilities in the field of sensing, besides several different and peculiar phenomena. The main advantage in exploiting the physical principle of the random laser in optical sensors is due to the presence of the stimulated emission mechanism, which allows amplification and spectral modification of the signal. Here, we present a step forward in the exploitation of this optical phenomenon by a revisitation of a previous experimental setup, as well as the measurement method, in particular to mitigate the instability of the results due to shot-to-shot pump energy fluctuations. In particular, the main novelties of the setup are the use of optical fibers, a reference sensor, and a peristaltic pump. These improvements are devoted to: eliminating optical beam alignment issues; improving portability; mitigating the variation in pump energy and gain medium performances over time; realizing an easy and rapid change of the sensed medium. The results showed that such a setup can be considered a prototype for a portable device for directly measuring the scattering of liquid samples, without resorting to complicated numerical or analytic inversion procedures of the measured data, once the suitable calibration of the system is performed.

Random Lasing from Label-Free Living Cells for Rapid Cytometry of Apoptosis

A random laser carrying the scattering information on a biological host is a promising tool for the characterization of biophysical properties. In this work, random lasing from label-free living cells is proposed to achieve rapid cytometry of apoptosis. Random lasing is achieved by adding biocompatible gain medium to a confocal dish containing cells under optically pumped conditions. The random lasing characteristics are distinct at different stages of cell apoptosis after drug treatment. By analyzing the power Fourier transform results of the random lasing spectra, the percentage of apoptotic cells could be distinguished within two seconds, which is more than an order of magnitude faster than traditional flow cytometry. These results provide a label-free approach for rapid cytometry of apoptosis, which is advantageous for further research of random lasers in the biological field.

Identification of Thioflavin T Binding Modes to DNA: A Structure-Specific Molecular Probe for Lasing Applications

The binding mechanism of thioflavin T (ThT) to DNA was studied using polarized light spectroscopy and fluorescence-based techniques in solutions and in solid films. Linear dichroism measurements showed that ThT binds to DNA duplex by intercalation. Time-resolved fluorescence studies revealed a second binding mode which is the external binding to the DNA phosphate groups. Both binding modes represent the nonspecific type of interactions. The studies were complemented with the analysis of short oligonucleotides having DNA cavities. The results indicate that the interplay between three binding modes-intercalation, external binding, and binding inside DNA cavities-determines the effective fluorescence quantum yield of the dye in the DNA structures. External binding was found to be responsible for fluorescence quenching because of energy transfer between intercalated and externally bound molecules. Finally, amplified spontaneous emission (ASE) was successfully generated in the ThT-stained films and used for detecting different DNA structures. ASE measurements show that ThT-stained DNA structures can be used for designing bioderived microlasers.

Random Lasing Detection of Mutant Huntingtin Expression in Cells

Huntington's disease (HD) is an autosomal dominant, incurable neurodegenerative disease caused by mutation in the huntingtin gene (HTT). HTT mutation leads to protein misfolding and aggregation, which affect cells' functions and structural features. Because these changes might modify the scattering strength of affected cells, we propose that random lasing (RL) is an appropriate technique for detecting cells that express mutated HTT. To explore this hypothesis, we used a cell model of HD based on the expression of two different forms-pathogenic and non-pathogenic-of HTT. The RL signals from both cell profiles were compared. A multivariate statistical analysis of the RL signals based on the principal component analysis (PCA) and linear discriminant analysis (LDA) techniques revealed substantial differences between cells that expressed the pathogenic and the non-pathogenic forms of HTT.

The up-to-date strategies for the isolation and manipulation of single cells

Due to the large cellular heterogeneity, the strategies for the isolation and manipulation of single cells have been pronounced indispensable in the fields of disease diagnostics, drug delivery, and cancer biology at the single-cell resolution. Herein, an overview of the up-to-date techniques for precise manipulation/separation and analysis of single-cell is accomplished, these include the various approaches for the isolation and detection of individual cells in flow cytometry, microfluidic systems, micromodule systems, and others. In addition, the advanced application of these protocols is discussed. In particular, a few designs are highlighted for visualization, non-invasion, and intelligentization in single cell analysis, i.e., imaging flow cytometry, label-free microfluidic platform, single-cell capillary probe, and other related techniques. At the present, the main barriers in the various schemes for single cell manipulation which limited their practical applications are their cumbersome construction and single-functionality. The future opportunities and outstanding challenges in the isolation/manipulation of single cells are depicted.

A ring-shaped random laser in momentum space

A ring-shaped random laser in momentum space is designed by directly coupling a random laser with a commercial optical fiber. By using a simple approach of selectively coating the random gain layer on the surface of the fiber, red and yellow random lasers are respectively achieved with low threshold values and a good emission direction due to the guiding role of optical fibers. The unique coupling mechanism leads to a random laser with a ring shape in momentum space, which is an excellent illuminating source for high-quality imaging with an extremely low speckle noise. More importantly, a triple-state color-switchable random laser with yellow, red and yellow-red dual-colors can be flexible, and is obtained by simply moving the pump position. The results may promote the practical applications of random lasers in the fields of sensing, in vivo biological imaging, and high brightness full-field illumination.