Time and power dependence of laser-induced photodamage on human sperm revealed by longitudinal rolling measurement using optical tweezers.

Lasers are widely applied in assisted reproductive technologies, including sperm fixation, sperm selection and intracytoplasmic sperm injections, to reduce procedure time and improve consistency and reproducibility. However, quantitative studies on laser-induced photodamage of sperm are lacking. In this study, we demonstrated that, by using optical tweezers, the kinematic parameters of freely swimming sperm are correlated with the frequency as well as the percentage of pausing duration of longitudinal rolling of the same sperm head in the optical trap. Furthermore, by trapping individual sperm cells using 1064-nm optical tweezers, we quantitatively characterized the time-dependence of longitudinal rolling frequency and percentage of pausing duration of sperm under different laser powers. Our study revealed that, as trapping time and the laser power time increase, the longitudinal rolling frequency of the optically trapped sperm decreases with an increasing percentage of pausing duration, which characterizes the effect of laser power and duration on the photodamage of individual sperm cells. Our study provides experimental basis for the optimization of laser application in assisted reproductive technology, which may reduce the photodamage-induced biosafety risk in the future.

Laser-induced microbubble as an in vivo valve for optofluidic manipulation in living Mice's microvessels.

Optofluidic regulation of blood microflow in vivo represents a significant method for investigating illnesses linked to abnormal changes in blood circulation. Currently, non-invasive strategies are limited to regulation within capillaries of approximately 10 µm in diameter because the adaption to blood pressure levels in the order of several hundred pascals poses a significant challenge in larger microvessels. In this study, using laser-induced microbubble formation within microvessels of the mouse auricle, we regulate blood microflow in small vessels with diameters in the tens of micrometers. By controlling the laser power, we can control the growth and stability of microbubbles in vivo. This controlled approach enables the achievement of prolonged ischemia and subsequent reperfusion of blood flow, and it can also regulate the microbubbles to function as micro-pumps for reverse blood pumping. Furthermore, by controlling the microbubble, narrow microflow channels can be formed between the microbubbles and microvessels for assessing the apparent viscosity of leukocytes, which is 76.9 ± 11.8 Pa·s in the in vivo blood environment. The proposed design of in vivo microbubble valves opens new avenues for constructing real-time blood regulation and exploring cellular mechanics within living organisms.

Optothermal Microparticle Oscillator Induced by Marangoni and Thermal Convection.

The light-fueled microparticle oscillator, exemplifying sustained driving in a static light source, potentially holds applications in fundamental physics, cellular manipulation, fluid dynamics, and various other soft-matter systems. The challenges of photodamage due to laser focusing on particles and the control of the oscillation direction have always been two major issues for microparticle oscillators. Here, we present an optical-thermal method for achieving a 3D microparticle oscillator with a fixed direction by employing laser heating of the gold film surface. First, the microparticle oscillation without direction limitation is studied. The photothermal conversion originates from the laser heating of a gold film. The oscillation mechanism is the coordination of the forces exerted on the particles, including the thermal convective force, thermophoresis force, and gravity. Subsequently, the additional Marangoni convection force, generated by the temperature gradient on the surface of a microbubble, is utilized to control the oscillation direction of the microparticle. Finally, a dual-channel oscillation mode is achieved by utilizing two microbubbles. During the oscillation process, the microparticle is influenced by flow field forces and temperature gradient force, completely avoiding optical damage to the oscillating microparticle.

Plug-and-play DPC-based quantitative phase microscope.

Point-of-care testing (POCT) plays an increasingly important role in biomedical research and health care. Quantitative phase microscopes (QPMs) with good contrast, no invasion, no labeling, high speed and automation could be effectively applied for POCT. However, most QPMs are fixed on the optical platform with bulky size, lack of timeliness, which remained challenging in POCT solutions. In this paper, we proposed a plug-and-play QPM with multimode imaging based on the quantitative differential phase contrast (qDPC) method. The system employs a programmable LED array as the light source and uses the GPU to accelerate the calculation, which can realize multi-contrast imaging with six modes. Accurate phase measurement and real-time phase imaging are implemented by the proposed qDPC algorithms for quantitative phase targets and biomedical samples. A 3D electric control platform is designed for mechanical control of field of view and focusing without manual operations. The experimental results verify the robustness and high performance of the setup. Even a rookie could finish the POCT scheme for biomedical applications at the scene using the QPM with a compact size of 140 × 165 × 250 mm3.

Measurement of red blood cell deformability during morphological changes using rotating-glass-plate-based scanning optical tweezers.

It is important to measure the deformability of red blood cells (RBCs) before transfusion, which is a key factor in the gas transport ability of RBCs and changes during storage of RBCs in vitro. Moreover, the morphology of RBCs also changes during storage. It is proposed that the change in morphology is related to the change in deformability. However, the efficiency of typical methods that use particles as handles is low, especially in the deformability measurement of echinocyte and spherocytes. Therefore, the deformability of RBCs with different morphologies is hard to be measured and compared in the same experiment. In this study, we developed a cost-effective and efficient rotating-glass-plate-based scanning optical tweezers device for the measurement of deformability of RBCs. The performance of this device was evaluated, and the deformability of three types of RBCs was measured using this device. Our results clearly show that the change of erythrocyte morphology from discocyte to echinocyte and spherocyte during storage in vitro is accompanied by a decrease in deformability.

Deformability of mouse erythrocytes in different diluents measured using optical tweezers.

Optical tweezers are widely used to measure the mechanical properties of erythrocytes, which is crucial to the study of pathology and clinical diagnosis of disease. During the measurement, the blood sample is diluted and suspended in an exogenous physiological fluid, which may affect the elastic properties of the cells in vitro. Here, we investigate the effect of different diluents on the elastic properties of mouse erythrocytes by quantitatively evaluating their elastic constants using optical tweezers. The diluents are plasma extracted from mouse blood, veterinary blood diluent (V-52D), Dulbecco's modified Eagle's medium (DMEM), phosphate-buffered saline (PBS), and normal saline (NS). To create an environment that closely resembles in vivo conditions, the experiment is performed at 36.5 °C. The results show that the spring constant of mouse erythrocytes in plasma is 6.23 ± 0.41 µN m-1. The elasticity of mouse erythrocytes in V-52D and DMEM is 8.21 ± 0.91 and 6.95 ± 0.85 µN m-1, which are higher than that in plasma extracted from blood, whereas, the elasticity in PBS and NS is 4.23 ± 0.85 and 4.68 ± 0.79 µN m-1, which are less than that in plasma extracted from blood. At last, we observe the size and circularity of erythrocytes in different diluents, and consider that the erythrocyte diameter and circularity may affect cell deformability. Our results provide a reference of the diluent choice for measuring the mechanical properties of erythrocytes in vitro.

Effects of the cone angle on the SERS detection sensitivity of tapered fiber probes.

In this paper, we investigate the effects of taper angle on the SERS detection sensitivity using tapered fiber probes with single-layer uniform gold spherical nanoparticles (GSNs). We show that the photothermal damage caused by excessive excitation laser power is the main factor that restricts the improvement of detection sensitivity of tapered fiber probes. Only when the cone angle is appropriate can a balance be achieved between increasing the excitation laser power and suppression of the transmission and scattering losses of the nanoparticles on the tapered fiber surface, thereby obtaining the best SERS detection sensitivity. Furthermore, the optimal cone angle depends on the complex refractive index of the equivalent composite dielectric (ECD) layer containing GSNs. For three SERS fiber probes with different ECD layers, the optimal cone angles measured are between 11-13°.

Efficient Frequency Mixing of Guided Surface Waves by Atomically Thin Nonlinear Crystals.

Monolayer transition metal dichalcogenides possess considerable second-order nonlinear coefficients but a limited efficiency of frequency conversion due to the short interaction length with light under the typical direct illumination. Here, we demonstrate an efficient frequency mixing of the guided surface waves on a monolayer tungsten disulfide (WS2) by simultaneously lifting the temporal and spatial overlap of the guided wave and the nonlinear crystal. Three orders-of-magnitude enhancement of the conversion efficiency was achieved in the counter-propagating excitation configuration. Also, the frequency-mixing signals are highly collimated, with the emission direction and polarization controlled, respectively, by the pump frequencies and the rotation angle of WS2 relative to the propagation direction of the guided waves. These results indicate that the rules of nonlinear frequency conversion are applicable even when the crystal is scaled down to the ultimate single-layer limit. This study provides a versatile platform to enhance the nonlinear optical response of 2D materials and favor the scalable generation of a coherent light source and entangled photon pairs.

Optical Trapping with Focused Surface Waves.

Near-field optical trapping can be realized with focused evanescent waves that are excited at the water-glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water-gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film.

Switchable Assembly and Guidance of Colloidal Particles on an All-Dielectric One-Dimensional Photonic Crystal.

Dielectric multilayer photonic-band-gap structures, called one-dimensional photonic crystals (1DPCs), have drawn considerable attention in the fields of physics, chemistry, and biophotonics. Here, experimental results verify the feasibility of a 1DPC working as a substrate for switchable manipulations of colloidal microparticles. The optically induced thermal convective force on a 1DPC can assemble colloidal particles that are dispersed in a water solution, while the photonic scattering force on the same 1DPC caused by propagating evanescent waves can guide these particles. Additionally, in the 1DPC, one internal mode can be excited that has seldom been noticed previously. This mode shows an ability to assemble particles over large areas even when the incident power is low. The assembly and guidance of colloidal particles on the 1DPC are switchable just through tuning the polarization and angle of the incident laser beam. Numerical simulations are carried out, which are consistent with these experimental observations.

Label-free surface-sensitive photonic microscopy with high spatial resolution using azimuthal rotation illumination.

Surface plasmon resonance microscopy (SPRM) with single-direction illumination is a powerful platform for biomedical imaging because of its wide-field, label-free, and high-surface-sensitivity imaging capabilities. However, two disadvantages prevent wider use of SPRM. The first is its poor spatial resolution that can be as large as several micrometers. The second is that SPRM requires use of metal films as sample substrates; this introduces working wavelength limitations. In addition, cell culture growth on metal films is not as universally available as growth on dielectric substrates. Here we show that use of azimuthal rotation illumination allows SPRM spatial resolution to be enhanced by up to an order of magnitude. The metal film can also be replaced by a dielectric multilayer and then a different label-free surface-sensitive photonic microscopy is developed, which has more choices in terms of the working wavelength, polarization, and imaging section, and will bring opportunities for applications in biology.

Manipulating Propagation Constants of Silver Nanowire Plasmonic Waveguide Modes Using a Dielectric Multilayer Substrate.

Experiments and numerical simulations demonstrate that when a silver nanowire is placed on a dielectric multilayer, but not the commonly used bare glass slide, the effective refractive index of the propagating surface plasmons along the silver nanowire can be controlled. Furthermore, by increasing the thickness of the top dielectric layer, longer wavelength light can also propagate along a very thin silver nanowire. In the experiment, the diameter of the silver nanowire can be as thin as 70 nm, with the incident wavelength as long as 640 nm. The principle of this control is analysed from the existence of a photonic band gap and the Bloch surface wave with this dielectric multilayer substrate.

The effects of Shuxuetong on the pathology of cerebral ischemia-reperfusion injury and GABA and TNF-alpha expression in gerbil models.

Objective To study the protective effect and mechanism of Shuxuetong on gerbil brain tissue from the area of ischemia-reperfusion. Methods Cerebral ischemia-reperfusion animal model has made by transient clipping bilateral common carotid arteries in gerbils. Pathological changes in the hippocampal tissue were observed at different reperfusion time (12h, 3 d, 7 d). The expression levels of GABA and TNF-alpha in the hippocampal CA1 subfield were observed using immunohistochemitry at 12 h, 3 d after reperfusion. The difference of above indices among false operation group, ischemia-reperfusion group and treatment group were compared. Results The injuries of pathology to hippocampal area in ischemia reperfusion group were more serious than treatment group. The expression levels of GABA in treatment group were significantly increased compared with ischemia-reperfusion group, but the expression levels of TNF-alpha between the two groups have no difference. Conclusion Shuxuetong has protective effect on brain tissue of ischemia-reperfusion by enhancing the expression of GABA in the hippocampal tissue.