Laser Tweezers Research Articles

Trans-cinnamaldehyde fumigation inhibits Escherichia coli by affecting the mechanism of intracellular biological macromolecules

This study aimed to determine the antibacterial mechanism of cinnamaldehyde fumigation in Escherichia coli (E. coli). Through vapour fumigation, cinnamaldehyde was confirmed to exhibit effective antibacterial activity against E. coli. The minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC) were 0.25 μL/mL and 0.5 μL/mL, respectively. Based on transmission electron microscopy, the wrinkled bacterial cells observed after fumigation could be related to the leakage of intracellular substances. Laser tweezers Raman spectroscopy revealed changes in the main chain of proteins, the hydrogen bond system and spatial structure, and single- and double-stranded DNA breaks. In addition, breakage of the fatty acyl chain backbone was found to affect the vertical order degree of the lipid bilayer and cell membrane fluidity, thereby inhibiting the growth of E. coli. Overall, our findings indicate that cinnamaldehyde fumigation inhibits E. coli growth by inducing changes in intracellular biological macromolecules.

Assessing Radiation Effects on Chemo-Treated BT20 and 4T1 Breast Cancer, and Neuroblastoma Cell Lines: A Study of Single and Multiple-Cell Ionization via Infrared Laser Trapping

Background: Our study aimed to assess the radiation sensitivity of BT20, a human breast tumor cell line, using the laser-trapping technique and compare it with N2a and 4T1 cells. Additionally, we investigated the impact of the antitumor compound 2-Dodecyl-6-methoxycyclohexa-2,5-diene-1,4-dione (DMDD) on radiation sensitivity. Methods and Materials: We employed laser trapping to calculate both the threshold ionization energy (TIE) and threshold radiation dose (TRD) for BT20, N2a, and 4T1 cells. We assessed the effect of DMDD on BT20 cells’ radiosensitivity and conducted comparisons across these cell lines. Results: Our findings reveal that DMDD significantly enhances the radiosensitivity of BT20 breast carcinoma cells. Moreover, we observed distinct trends in TIE and TRD across the three cell lines, with differences attributed to variations in cell size and composition. When multiple cell ionizations were considered, a notable reduction in TRD was observed, implicating factors such as the chain effect of ionizing radiation and the influence of DMDD. The study found that TIE increased with the number of cells in the trap while TRD consistently decreased across all three cell lines, suggesting comparable radiation sensitivity, and oligostilbene treatment further reduced TRD, presenting the potential for enhancing therapeutic ratios in cancer treatment. Conclusion: The antitumor compound DMDD enhances the radiosensitivity of BT20 breast carcinoma cells, highlighting its potential in cancer treatment. Furthermore, our study underscores the impact of cell size and multiple-cell ionizations on TRD. Leveraging laser trapping techniques, biocompatible nanoparticles, and advanced optical tweezers opens promising avenues for personalized and effective cancer therapy approaches.

Observation of magnet-induced star-like radiation of a plasma created from cancer cells in a laser trap.

We present a new phenomenon resulting from the interaction of magnetic beads with cancer cells in a laser trap formed on a slide containing a depression 16.5mm in diameter and 0.78mm of maximum depth. This phenomenon includes the apparent formation and expansion of a dark bubble that attracts and incinerates surrounding matter when it explodes, which leads to a plasma emitting intense radiation that has the appearance of a star on a microscopic scale. We have observed the star-like phenomenon for more than 4years, and the intensity depends on the laser's power. Measuring the laser power of the dark bubble shows the entrapment of electromagnetic energy as it expands.

Measurement report: Water diffusion in single suspended phase-separated aerosols

Abstract. Water diffusion is a typical thermodynamic process in ambient aerosols that plays pivotal roles in their physicochemical properties and atmospheric lifetime and influences the climate and human health. A fair amount of aerosols become phase-separated after experiencing atmospheric aging processes such as efflorescence, amorphization, and liquid–liquid phase separation. However, detecting the hygroscopicity of heterogeneous aerosols is quite intractable. Here, for the first time, we directly characterized the water diffusion in single suspended phase-separated aerosols via a self-constructed laser tweezer Raman spectroscopy (LTRS) system. The H2O–D2O isotope exchange was harnessed to trace the water diffusion in single laser-levitated homogenous/heterogeneous microdroplets. The time-resolved cavity-enhanced Raman spectra of the microdroplets were used to detect the diffusion process in real time. Two archetypes of phase-separated aerosols, i.e., partially engulfed and core–shell, were studied. Moreover, we quantified the dynamic water diffusion process by experimentally measuring the diffusion coefficients. The results showed that compared with the homogenous aerosols, water diffusion limitations existed in the phase-separated aerosols. The incomplete diffusion may stem from the formation of certain hydrated molecule clusters. This work provides possible implications for the evolutions, especially the gas–particle partition, of the actual phase-separated atmospheric aerosols.

Steady motional entanglement between two distant levitated nanoparticles

Quantum entanglement in macroscopic systems is not only essential for practical quantum information processing, but also valuable for the study of the boundary between quantum and the classical world. However, it is very challenging to achieve the steady remote entanglement between distant macroscopic systems. We consider two distant nanoparticles, both of which are optically trapped in two cavities. Based on the coherent scattering mechanism, we find that the ultrastrong optomechanical coupling between the cavity modes and the motion of the levitated nanoparticles could be achieved. The large and steady entanglement between the filtered output cavity modes and the motion of nanoparticles can be generated if the trapping laser is under the red sideband. Then through entanglement swapping, the steady motional entanglement between the distant nanoparticles can be realized. We numerically simulate and find that the two nanoparticles with 10 km distance can be entangled for the experimentally feasible parameters, even in room temperature environments. The generated continuous variable multipartite entanglement is the key to realizing the quantum enhanced sensor network and the sensitivity beyond the standard quantum limit.

Laser frequency stabilization by modulation transfer spectroscopy and balanced detection of molecular iodine for laser cooling of 174Yb.

We report laser frequency stabilization by the combination of modulation transfer spectroscopy and balanced detection of a relatively weak hyperfine transition of the R(158)25-0 line of molecular iodine (127I2), which is used as a new frequency reference for laser trapping and cooling of 174Yb on the 1S0 - 3P1 transition. The atomic cloud is characterized by time-of-flight measurements, and an on-resonance optical depth of up to 47 is obtained. We show laser noise reduction and characterize the short-term laser frequency instability by the Allan deviation of the laser fractional frequency. The minimum measured value is 3.9 ×10-13 at 0.17 s of averaging time.

Revealing force- and orientation-dependence of F-actin interaction with mechanotrasductor proteins by ultra-fast laser tweezers

Revealing force- and orientation-dependence of F-actin interaction with mechanotrasductor proteins by ultra-fast laser tweezers

Rapid and accurate identification of marine bacteria spores at a single-cell resolution by laser tweezers Raman spectroscopy and deep learning.

Marine bacteria have been considered as important participants in revealing various carbon/sulfur/nitrogen cycles of marine ecosystem. Thus, how to accurately identify rare marine bacteria without a culture process is significant and valuable. In this work, we constructed a single-cell Raman spectra dataset from five living bacteria spores and utilized convolutional neural network to rapidly, accurately, nondestructively identify bacteria spores. The optimal CNN architecture can provide a prediction accuracy of five bacteria spore as high as 94.93% ± 1.78%. To evaluate the classification weight of extracted spectra features, we proposed a novel algorithm by occluding fingerprint Raman bands. Based on the relative classification weight arranged from large to small, four Raman bands located at 1518, 1397, 1666, and 1017 cm-1 mostly contribute to producing such high prediction accuracy. It can be foreseen that, LTRS combined with CNN approach have great potential for identifying marine bacteria, which cannot be cultured under normal condition.

Magnetic moments of thallium isotopes in the vicinity of magic N = 126

The magnetic dipole moments (μ) of 209Tlg (N=128) and 207Tlm (N=126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ(Tlg, Iπ=1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with Iπ=1/2+.

Tunable growth of a single high-density ZIF nanoshell on a gold nanoparticle isolated in an optical trap.

Here, we demonstrate an all-optical method using an optical tweezer to controllably grow high quality zeolitic imidazolate framework (ZIF) nanoshells on the surface of gold nanoparticles (AuNPs) and monitor the growth via darkfield spectroscopy. Our single particle approach allows us to localize an individual NP within a microscope slide chamber containing ZIF precursors at the focus of an optical microscope and initiate growth through localized heating without affecting the bulk system. Darkfield spectroscopy is used to characterize changes to the localized surface plasmon resonance (LSPR) of the AuNP resulting from refractive index changes as the ZIF crystal grows on the surface. We show that the procedure can be generalized to grow various types of ZIF crystals, such as ZIF-8, ZIF-11, and a previously undocumented ZIF variety. Utilizing both computational models and experimental methods, we identify the thickness of ZIF layers to be self-limiting to ∼50 nm or less, depending on the trapping laser power. Critically, the refractive index of the shells here was found to be above 1.6, indicating the formation of high-density crystals, previously accessible only through slow atomic layer deposition and not through a bulk heating process. The single particle method developed here opens the door for bottom-up controllable growth of custom nanostructures with tunable optical properties.

Self-oscillation of 3D trapped bubbles

In this study, we focus on the trapping and self-oscillation of microbubbles in ethanol using a low-power continuous-wave laser. The microbubble formation is achieved by heating of ethanol by light absorption (λ = 658 nm) at silver nanoparticles deposited on the distal end of a multi-mode optical fiber. Subsequently, a second low-power continuous-wave laser (λ = 1,550 nm) coupled to a single-mode optical fiber is used to trap the microbubble. To trap the microbubble, the red laser is turned off after its generation, and immediately the trapping laser is activated. The bulk light absorption at λ = 1,550 nm in ethanol modulates the surface tension of the bubble wall, creating a 3D potential well that effectively traps the bubble. Once the bubble is trapped, random variations in the bubble's radius led to instabilities in the trap, triggering the microbubble oscillation. The trapped bubble tends to oscillate along the light propagation between two points of quasi-steady-state equilibrium. These bubble oscillations result from the opposing competing forces: a changing-direction Marangoni force and drag forces and the upward buoyancy force. To explain the self-oscillation, we present a simple model that qualitatively describes the main features observed in the experimental data.

Mechanical coupling coordinates microtubule growth

During mitosis, kinetochore-attached microtubules form bundles (k-fibers) in which many filaments grow and shorten in near-perfect unison to align and segregate each chromosome. However, individual microtubules grow at intrinsically variable rates, which must be tightly regulated for a k-fiber to behave as a single unit. This exquisite coordination might be achieved biochemically, via selective binding of polymerases and depolymerases, or mechanically, because k-fiber microtubules are coupled through a shared load that influences their growth. Here, we use a novel dual laser trap assay to show that microtubule pairs growing in vitro are coordinated by mechanical coupling. Kinetic analyses show that microtubule growth is interrupted by stochastic, force-dependent pauses and indicate persistent heterogeneity in growth speed during non-pauses. A simple model incorporating both force-dependent pausing and persistent growth speed heterogeneity explains the measured coordination of microtubule pairs without any free fit parameters. Our findings illustrate how microtubule growth may be synchronized during mitosis and provide a basis for modeling k-fiber bundles with three or more microtubules, as found in many eukaryotes.

Mechanical coupling coordinates microtubule growth.

During mitosis, kinetochore-attached microtubules form bundles (k-fibers) in which many filaments grow and shorten in near-perfect unison to align and segregate each chromosome. However, individual microtubules grow at intrinsically variable rates, which must be tightly regulated for a k-fiber to behave as a single unit. This exquisite coordination might be achieved biochemically, via selective binding of polymerases and depolymerases, or mechanically, because k-fiber microtubules are coupled through a shared load that influences their growth. Here, we use a novel dual laser trap assay to show that microtubule pairs growing in vitro are coordinated by mechanical coupling. Kinetic analyses show that microtubule growth is interrupted by stochastic, force-dependent pauses and indicate persistent heterogeneity in growth speed during non-pauses. A simple model incorporating both force-dependent pausing and persistent growth speed heterogeneity explains the measured coordination of microtubule pairs without any free fit parameters. Our findings illustrate how microtubule growth may be synchronized during mitosis and provide a basis for modeling k-fiber bundles with three or more microtubules, as found in many eukaryotes.

Femtosecond pulsed laser technology and applications

This paper describes femtosecond pulsed laser technology and related applications. The focus is on two core femtosecond pulsed laser technologies: femtosecond pulsed laser generation and amplification. In the generation of femtosecond pulsed lasers, mode-locking techniques, Kerr-lens mode-locking, and semiconductor saturable absorber mirrors are presented; in the amplification of femtosecond pulsed lasers, chirped-pulse amplification and coherent synthesis techniques are presented. This paper analyses the applications of femtosecond pulsed lasers in both the biomedical and manufacturing sectors and gives the development trends as well as the challenges of femtosecond laser technology. Femtosecond lasers are now used in a wide range of applications. Femtosecond pulsed lasers will develop in the directions of high power, miniaturisation, intelligence and precision. Laser tweezers will become the new direction of development in the future.

Characterization of the field ionization extension for the laser ion source and trap: Measurement of the ionization potential of ytterbium

We report on the development and application of the Field Ionization Laser Ion Source and Trap (FI-LIST) at the RISIKO mass separator at Mainz University. The FI-LIST is an adaptation of the well-established LIST unit developed at Mainz and successfully adapted to CERN-ISOLDE. It is specifically designed for field ionization of highly excited atoms in a homogeneous electric field. To assess the performance of the device for future use on radioactive species of e.g. actinides, we conducted ionization potential (IP) measurements on ytterbium, for which the IP is precisely known. The IP value was derived by applying the saddle-point model with a relative precision of 3⋅10−6 and in very good agreement with the literature value.

Threshold bandgap of lead halide hybrid perovskites for making stable single crystal by NIR laser trapping

The remarkable optoelectronic properties of hybrid halide perovskites position them as pivotal materials for the next generation of electronic devices, LEDs, lasers, and solar cells, potentially revolutionizing these technological domains. In this study, we harness the capabilities of contemporary laser trapping technology—a non-contact method for manipulating particles—to elucidate the conditions necessary for stable perovskite crystal formation. Using a 1064 nm near-infrared (NIR) continuous-wave (CW) laser, commonly selected for trapping experiments, we establish the threshold bandgap essential for the stable crystallization of MAPbX3 perovskite crystals. Our research reveals that MAPbI3, with a bandgap of 1.59 eV, undergoes rapid explosive crystallization when subjected to the 1064 nm laser, making it unsuitable for stable crystal growth. In contrast, MAPbBr3 with a bandgap of 2.26 eV forms stable single crystals within 6 min at the air-solution interface, when exposed to the same 1064 nm NIR laser at 1.0 W output power. Notably, a minor reduction in bandgap to 2.23 eV in the mixed halide MAPbBr2.75I0.25 results in an abrupt transition to explosive crystallization. These findings introduce a novel insight into the bandgap dependency for the crystallization process, delineating a threshold bandgap of 2.26 eV for MAPbBr3, below which the crystal growth becomes unstable under a 1064 nm laser. The study provides a significant advancement in the field by defining the precise bandgap necessary for the formation of robust, stable perovskite crystals using laser trapping techniques. This threshold bandgap knowledge is crucial for developing controlled synthesis protocols for perovskites, optimizing their optoelectronic properties for application in modern technologies. Moreover, the investigation suggests that to achieve stable crystallization of perovskites with a bandgap below 2.26 eV, laser trapping with wavelengths longer than 1064 nm may be required, opening new avenues for material processing and device fabrication.

Analysis of the Principle and State-of-art Applications for Laser Cooling and Trapping

As a matter of fact, the laser cooling and trapping has already been widely used in various fields in advanced atoms controlling. With this in mind, this study gives a systematical analysis of the principle of laser cooling and trapping, and the development of them in the recent years. To be specific, this study will discuss the applications that has invented in the recent year based on the laser colling and trapping (especially for the state-of-art facilities), and makes a comparison between the concepts of laser cooling and laser trapping accordingly. Then, based on the analysis and evaluations, the limitations of laser cooling and laser trapping have been shown, and the future outlooks are also claimed and demonstrated as well. To sum up, the study concludes by discussing the limitations of these techniques, and gives some methods to solve these issues. Overall, these results shed light on guiding further exploration of laser cooling and trapping.

Significantly enhanced laser trapping and heating of carbon nanotube/carbon fibre hierarchical composites for efficient laser-assisted automated fibre placement

Laser-assisted automated fibre placement (LAFP) process is promising for manufacturing large-scale thermoplastic composite parts. However, its laydown speed suffers from the near-infrared (NIR) laser reflection from carbon fibres (CFs) and the high specific heat capacity of prepregs. Herein, the light-trapping carbon nanotube (CNT) forest was grown on CFs using a low-cost flame synthesis process, followed by its embedding in the poly-ether-ether-ketone (PEEK) matrix to produce CF/PEEK/CNTs prepregs with simultaneously enhanced laser absorption and reduced specific heat capacity. Spectroscopic analysis shows that CNTs reduce the NIR reflectance of prepregs due to enhanced light-trapping efficiency with hierarchical CNT/CF structures, further evidenced by a transition from diffuse reflection to specular reflection. Additionally, CNTs reduce 19 % of the specific heat capacity by restricting polymer chain movement. Therefore, the hierarchical structure increases the heating rate and maximum temperature of CF/PEEK prepregs by 18.5 % and 16.0 %, respectively, under 1080 nm laser radiation during the LAFP process.

Laser trapping of cavitation bubbles in liquids

Cavitation has a significant impact on pulsed laser ablation of liquids. At high repetition rates of laser pulses, it tends to hinder laser breakdown and associated processes. Here, we report on the particular case of the cavitation process occurring only at the elevated pulse repetition rate — the formation of a laser trapped bubble. The effect was observed in liquid hydrocarbons (n-hexane and ethanol) and water. The cavitation bubbles generated by picosecond pulses were captured in the caustic beam in front of the laser focus and stay there for a long time (several seconds). After growing up to ∼100μm in size, such a bubble completely blocks the laser radiation and stops all processes in the laser waist. The scenario of laser trapped bubble formation is investigated, the effects of pulse energy and pulse repetition rate are analyzed, and a possible mechanism for the observed effect is proposed. The special importance of laser trapped bubbles for the optimization of laser synthesis of new materials, particularly the linear carbon chains in hydrocarbons, is demonstrated.

The 5P3/2→6PJ(J=1/2,3/2) Electric Dipole Forbidden Transitions in Rubidium

This paper presents a general review of the results of the experimental and theoretical work carried out by our research group to study the 5P3/2→6PJ electric quadrupole transition in atomic rubidium. The experiments were carried out with room-temperature atoms in an absorption cell. A steady-state population of atoms in the 5P3/2 excited state is produced by a a narrow-bandwidth preparation laser locked to the D2 transition. A second CW laser is used to produce the forbidden transition with resolution of the 6PJ hyperfine states of both rubidium isotopes. The process is detected by recording the 420(422) nm fluorescence that occurs when the atoms in the 6PJ state decay directly into the 5S ground state. The fluorescence spectra show a strong dependence on the relative polarization directions of the preparation laser and the beam producing the forbidden transition. This dependence is directly related to a strong anisotropy in the populations of the 5P3/2 intermediate magnetic substates, and also to the electric quadrupole selection rules over magnetic quantum numbers. A calculation based on the rate equations that includes velocity and detuning dependent transition rates is adequate to reproduce these results. The forbidden transition is also shown to be an ideal probe to measure the Autler–Townes splitting generated in the preparation of the 5P3/2 state. Examples of spectra obtained with cold atoms in a magneto-optical trap (MOT) are also presented. These spectra show the expected Autler–Townes doublet structure with asymmetric line profiles that result as a consequence of the red-detuning of the trapping laser in the MOT.