Low Laser Power Density Research Articles

Ferroelectric BaTiO3 Freestanding Sheets for an Ultra-High-Speed Light-Driven Actuator.

Light-driven actuators convert optical energy into physical motion. Organic materials, commonly used in light-driven actuators thus far, suffer from two limitations: slow repetitive operation and the requirement of two different light sources. Herein, we report a high-speed, light-driven actuator that can be operated by a single light source with low-energy density. We achieved this breakthrough by utilizing a freestanding epitaxial sheet of ferroelectric BaTiO3. One repetitive operation takes only 120 μs, which is 104 times faster than that of organic-based counterparts. The high-speed operation is derived from the light-induced nonthermal deformation provided by the excellent ferroelectricity (remnant polarization of 23 μC/cm2) and piezoelectricity (d33 of 600 pm/V) of the sheet. The displacement-to-length ratio is achieved to be 3.7% with a relatively low laser power density (10-200 mW/cm2) compared to previously reports (150-109 mW/cm2). Furthermore, the actuator was operable even in water, demonstrating its potential in various applications.

Positron Emission Tomography‐Assisted Photothermal Therapy with Gold Nanorods

AbstractPhotothermal anticancer therapy based on plasmonic nanoparticles is proposed to enhance treatment efficacy while mitigating unintended side effects. However, most studies blindly rely on the accumulation of nanoparticles at the tumor site, which may result in inefficient treatment. In this study, the aim is to evaluate relevant parameters to improve plasmonic photothermal therapy. Gold nanorods (AuNRs) with an optimized aspect ratio and either amino or carboxylic acid surface functionalization are selected as photothermal agents. AuNR biocompatibility and photothermal activity in 2D and 3D human MDA‐MB‐231 triple‐negative breast cancer cell models, evaluating localized hyperthermal cell death upon irradiation with resonant near‐infrared (NIR) light, are analyzed first. To ensure reliable tracking of biodistribution in vivo, AuNRs are labeled with the positron emitter copper‐64 (64Cu), and their distribution in a murine MDA‐MB‐231 tumor model is studied via positron emission tomography (PET) imaging. PET images reveal enhanced tumor accumulation of carboxylic acid‐functionalized AuNRs compared to amino‐functionalized AuNRs post‐intravenous administration. Relatively low NIR laser power densities (0.5 W cm−2) are used for controlled heating – keeping local temperature below 50 °C – upon irradiation of intravenously and intratumorally administered AuNRs. As a result, tumor growth is significantly decelerated, even 9 days after application of photothermal therapy.

Unveiling the effect of Ce3+ doping concentration in YAG:Ce single crystals towards high luminance laser lighting

Doping concentration of a phosphor is key parameter, affecting multiple properties such as light absorption, quantum yield, luminescence decay, thermal conductivity, and thermal quenching, etc. These properties could directly influence the luminous efficacy, the saturation threshold, and the emitting area of the phosphor when irradiated by laser, thus determining the peak luminance of a phosphor-converted laser lighting device. But surprisingly no systematic investigation has been done to research the effect of phosphor doping concentration on the luminance performance of laser lighting. Here we report the YAG:Ce single crystal phosphors with different Ce3+-doping concentrations (between 0.05 at% and 0.30 at%) and thicknesses (0.15 mm–0.45 mm). The relationship between Ce3+ concentration, phosphor thickness, and the colorimetric/photometric parameters (luminous efficacy, luminous flux, luminance) are built and elucidated. It is found that the thinner sample with higher doping density tends to be saturated at lower laser power density (314.1 W/mm2) and the device shows lower luminance. This result is also verified by thermal simulation that the corresponding sample shows highest working temperature. Remarkably, the optimal sample with thickness of 0.45 mm and Ce3+ density of 0.30 at% presents a record high luminous exitance of 33414 lm/mm2 and a record high luminance of 10636 Mcd/m2, indicating potential for use in special lighting, projector, and optical communication fields.

A BRD4‐Targeting Photothermal Agent for Controlled Protein Degradation

AbstractBRD4 protein plays a pivotal role in cell cycle regulation and differentiation. Disrupting the activity of BRD4 has emerged as a promising strategy for inhibiting the growth and proliferation of cancer cells. Herein, we introduced a BRD4‐targeting photothermal agent for controlled protein degradation, aiming to enhance low‐temperature photothermal therapy (PTT) for cancer treatment. By incorporating a BRD4 protein inhibitor into a cyanine dye scaffold, the photothermal agent specifically bond to the bromodomain of BRD4. Upon low power density laser irradiation, the agent induced protein degradation, directly destroying the BRD4 structure and inhibiting its transcriptional regulatory function. This strategy not only prolonged the retention time of the photothermal agent in cancer cells but also confined the targeted protein degradation process solely to the tumor tissue, minimizing side effects on normal tissues through the aid of exogenous signals. This work established a simple and feasible platform for future PTT agent design in clinical cancer treatment.

A BRD4-Targeting Photothermal Agent for Controlled Protein Degradation.

BRD4 protein plays a pivotal role in cell cycle regulation and differentiation. Disrupting the activity of BRD4 has emerged as a promising strategy for inhibiting the growth and proliferation of cancer cells. Herein, we introduced a BRD4-targeting photothermal agent for controlled protein degradation, aiming to enhance low-temperature photothermal therapy (PTT) for cancer treatment. By incorporating a BRD4 protein inhibitor into a cyanine dye scaffold, the photothermal agent specifically bond to the bromodomain of BRD4. Upon low power density laser irradiation, the agent induced protein degradation, directly destroying the BRD4 structure and inhibiting its transcriptional regulatory function. This strategy not only prolonged the retention time of the photothermal agent in cancer cells but also confined the targeted protein degradation process solely to the tumor tissue, minimizing side effects on normal tissues through the aid of exogenous signals. This work established a simple and feasible platform for future PTT agent design in clinical cancer treatment.

Harnessing Croconaine Organic Photosensitizers for a Milder Surface‐Mediated Transfection

AbstractPolydopamine‐based materials, notably Polydopamine‐polyethyleneimine (PDA‐PEI), have gained considerable interest for surface‐mediated transfection. However, the high laser power density required to achieve high transfection efficiency poses a significant challenge in preserving cell viability. An organic photosensitizer CRO32TMI was developed to improve the photothermal conversion capability of PDA‐PEI. The modified PDA‐PEI‐CRO32TMI exhibited remarkable photothermal and photostability properties upon NIR irradiation, enabling it to achieve better transfection efficiency at lower laser power density as compared to the traditional solution or lipid‐based transfection methods.

J-aggregates of multi-groups cyanine dye for NIR-IIa fluorescence-guided mild photothermal therapy under 1064 nm irradiation

NIR-IIa fluorescence imaging (FI) and NIR-II photothermal therapy (PTT) have gained popularity due to the advantages of high temporal and spatial resolution and deep penetration. However, the hyperthermia (>48 °C) of conventional PTT with nonspecific warming and thermal diffusion may inevitably cause damage to healthy tissues or organs surrounding the tumor. Therefore, it is highly desirable to provide effective cancer treatment by implementing mild photothermal therapy (mPTT) at mild temperatures with lower laser power density. Here, the nanotheranostic platform FN@P-GA NPs with NIR-II absorption and NIR-IIa emission was developed by constructing J-aggregates. FN@P-GA possesses good biocompatibility, favorable NIR-IIa FI performance, decent stability, and high photothermal conversion efficiency (57.6 %), which lays a solid foundation for FI-guided mPTT. Due to its ability to effectively down-regulate the expression of HSP90 and reduce cellular thermoresistance to kill cancer cells, FN@P-GA successfully achieved NIR-IIa FI-guided mPTT and demonstrated its potent anti-tumor effect under 1064 nm laser irradiation at mild temperature and low power density (0.3 W/cm2).

Simulation and experimental study on laser cleaning of paint-rust mixed layer on a Q235 surface

In this paper, the theoretical model of laser cleaning of paint-rust mixed layer on the surface of a Q235 steel plate is established from the perspective of the laser ablation effect and the thermal vibration effect. The study simulates the temperature and stress field variations of the mixed layer under different laser power densities. The experiment recorded ablative fumes and vibrational spattering generated during the cleaning process and measured the micro-morphology and surface roughness of the cleaned specimens. The results show that the cleaning mechanism of the paint-rust mixed layer is dominated by the ablation effect at low laser power densities, while the combined effects of ablation and thermal vibration dominate at high laser power densities. However, excessive laser energy can damage the substrate. At a laser power density of 12.37×106W/cm2, the substrate surface is free from contamination residues and exhibits a bright, white, metallic gloss, which can be determined as the cleaning threshold for laser cleaning of paint-rust mixed layers. This study provides a valuable reference for the laser cleaning of mixed pollutants of paint and rust on metal surfaces.

Hydrophilic properties of the aluminum alloy induced by femtosecond laser structuring

This study explored the changes in wetting property and surface morphology in aluminum alloy plates due to femtosecond laser structuring. The laser scanning produced a hierarchical micro- and nano-scale structure consisting of microchannels decorated by irregular shape particles. The surface morphology was controlled by laser power and scanning line density. The surface wettability gradually changed from hydrophilic to hydrophobic one due to various chemical reactions for low laser power and scanning line density. However, femtosecond laser structuring with appropriate laser power and scanning line density was demonstrated to maintain strong and stable hydrophilic properties of aluminum alloy surfaces.

NIR-Active Gold Dogbone Nanorattles Impregnated in Cationic Dextrin Nanoparticles for Cancer Nanotheranostics.

Theranostic systems, which integrate therapy and diagnosis into a single platform, have gained significant attention as a promising approach for noninvasive cancer treatment. The field of image-guided therapy has revolutionized real-time tumor detection, and within this domain, plasmonic nanostructures have garnered significant attention. These structures possess unique localized surface plasmon resonance (LSPR), allowing for enhanced absorption in the near-infrared (NIR) range. By leveraging the heat generated from plasmonic nanoparticles upon NIR irradiation, target cancer cells can be effectively eradicated. This study introduces a plasmonic gold dogbone-nanorattle (AuDB NRT) structure that exhibits broad absorption in the NIR region and demonstrates a photothermal conversion efficiency of 35.29%. When exposed to an NIR laser, the AuDB NRTs generate heat, achieving a maximum temperature rise of 38 °C at a concentration of 200 μg/mL and a laser power density of 3 W/cm2. Additionally, the AuDB NRTs possess intrinsic electromagnetic hotspots that amplify the signal of a Raman reporter molecule, making them an excellent probe for surface-enhanced Raman scattering-based bioimaging of cancer cells. To improve the biocompatibility of the nanorattles, the AuDB NRTs were conjugated with mPEG-thiol and successfully encapsulated into cationic dextrin nanoparticles (CD NPs). Biocompatibility tests were performed on HEK 293 A and MCF-7 cell lines, revealing high cell viability when exposed to AuDB NRT-CD NPs. Remarkably, even at a low laser power density of 1 W/cm2, the application of the NIR laser resulted in a remarkable 80% cell death in cells treated with a nanocomposite concentration of 100 μg/mL. Further investigation elucidated that the cell death induced by photothermal heat followed an apoptotic mechanism. Overall, our findings highlight the significant potential of the prepared nanocomposite for cancer theranostics, combining effective photothermal therapy along with the ability to image cancer cells.

Study of spatially confined copper plasma by probe beam deflection technique

In the last decade, laser induced plasma (LIP) has emerged as one of the most promising techniques for various applications. It is now commonly investigated using various expensive techniques. Probe beam deflection (PBD) is an inexpensive technique generally utilized to characterize the shock wave. In this work, the copper laser-induced plasma plume and shock wave are both investigated using PBD technique. The plasma is generated at atmospheric pressure using Nd:YAG laser at a low laser power density (0.8 GW/cm2). The contribution of the plasma plume components to the PBD signal is clarified in space and time. The spatial confinement effect by a metallic disk is also investigated. It approves the physical mechanisms responsible for the deflection signal. As well, the spatial distribution of the weak shock wave velocity is considered.

Influence of NIR-laser radiation on the underwater arc welding process with flux-cored wire

The combination of laser radiation and electric arc as hybrid welding is used successfully in industry. In the underwater area, this technology is currently being researched but is not yet part of the industry. This paper demonstrates laser-stabilized arc welding with flux-cored electrode for underwater applications where the laser power density of the laser radiation does not result in a deep penetration welding effect. Steel samples (S235-JR) with a thickness of 10 mm were examined as bead-on-plate welds with a laser power density of 0.7-2.8 x 104 W/cm² at a wavelength of 1030 nm. The addition of laser radiation at low laser power density stabilizes the arc and produces a homogeneous weld seam. The process behavior and stability are characterized by measuring the current and voltage signals and analyzed regarding the laser beam and current source parameters. The metallographic analyses are used to compare the weld seam geometry and the microstructure properties.

Graphene-wrapped petal-like gap-enhanced Raman tags for enhancing photothermal conversion and Raman imaging

Multifunctional nanoplatform that combine imaging, diagnostic, and therapeutic functions into a single agent have great significance for the early diagnosis and efficient treatment of diseases, particularly tumors. In this study, we report on a novel graphene-wrapped petal-like gap-enhanced Raman tags with mesoporous silica shells (MS-GP-GERTs). These MS-GP-GERTs have 4-NBT Raman reporters embedded in the gap between the gold nanocore and the petal-shaped shell and are wrapped in graphene and mesoporous silica. The results of photothermal measurement experiments show that graphene layers significantly enhanced the photothermal effect of gap-enhanced Raman tags (GERTs). The photothermal conversion efficiency of MS-GP-GERTs reaches 40.8%, comparable to pure graphene. Moreover, MS-GP-GERTs show good photothermal performance in agarose phantoms, heating the phantom to 47 °C within 5 min under a low power density laser (0.5 W/cm2). MS-GP-GERTs also exhibit excellent photothermal stability and physiological environment stability, making them a promising candidate for repeated photothermal therapy. Raman spectra and mapping imaging experiments demonstrate MS-GP-GERTs' low detection limit (100 fM), large imaging depth (2.74 mm), and excellent ability to image simulated biological tissue and cells. This novel Raman tag has the potential to become a multifunctional nano platform for integrating Raman imaging diagnosis and photothermal therapy.

Palladium Nanocapsules for Photothermal Therapy in the Near-Infrared II Biological Window.

Recent developments in nanomaterials with programmable optical responses and their capacity to modulate the photothermal effect induced by an extrinsic source of light have elevated plasmonic photothermal therapy (PPTT) to the status of a favored treatment for a variety of malignancies. However, the low penetration depth of near-infrared-I (NIR-I) lights and the need to expose the human body to a high laser power density in PPTT have restricted its clinical translation for cancer therapy. Most nanostructures reported to date exhibit limited performance due to (i) activity only in the NIR-I region, (ii) the use of intense laser, (iii) need of large concentration of nanomaterials, or (iv) prolonged exposure times to achieve the optimal hyperthermia state for cancer phototherapy. To overcome these shortcomings in plasmonic nanomaterials, we report a bimetallic palladium nanocapsule (Pd Ncap)─with a solid gold bead as its core and a thin, perforated palladium shell─with extinction both in the NIR-I as well as the NIR-II region for PPTT applications toward cancer therapy. The Pd Ncap demonstrated exceptional photothermal stability with a photothermal conversion efficiency of ∼49% at the NIR-II (1064 nm) wavelength region at a very low laser power density of 0.5 W/cm2. The nanocapsules were further surface-functionalized with Herceptin (Pd Ncap-Her) to target the breast cancer cell line SK-BR-3 and exploited for in vitro PPTT applications using NIR-II light. Pd Ncap-Her caused more than 98% cell death at a concentration of just 50 μg/mL and a laser power density of 0.5 W/cm2 with an output power of only 100 mW. Flow cytometric and microscopic analyses revealed that Pd Ncap-Her-induced apoptosis in the treated cancer cells during PPTT. Additionally, Pd Ncaps were found to have reactive oxygen species (ROS) scavenging ability, which can potentially reduce the damage to cells or tissues from ROS produced during PPTT. Also, Pd Ncap demonstrated excellent in vivo biocompatibility and was highly efficient in photothermally ablating tumors in mice. With a high photothermal conversion and killing efficiency at very low nanoparticle concentrations and laser power densities, the current nanostructure can operate as an effective phototherapeutic agent for the treatment of different cancers with ROS-protecting ability.

Effects of nanosecond laser shock peening on residual stress, corrosion and tribocorrosion behavior of WE43 magnesium alloys

Biodegradable magnesium (Mg) alloys are promising candidates for use as next-generation implants due to their similar mechanical properties to natural bones, excellent biocompatibility, and the ability to completely degrade in vivo. However, a great challenge of Mg alloys in physiological environments is their fast corrosion rate and low tribocorrosion resistance, which makes it difficult to ensure adequate structural integrity over the required time for complete tissue and bone healing. In this work, the effects of nanosecond laser shock peening (ns-LSP) processing parameters on the surface tribocorrosion resistance of WE43 Mg alloys was investigated. The laser power densities and overlapping ratios were tuned to control the magnitude and depth of residual stresses and the amount of cold work. The tribocorrosion behaviors of WE43 Mg after the ns-LSP treatment were measured in stagnant blood bank buffered saline (pH of 7.0–7.2) under ∼ 37 °C. The tribocorroded surfaces were characterized via X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy. It was found that the optimum peening effect was achieved at lower laser power density and overlapping ratio, where the corrosion cathodic reaction rate was decreased and tribocorrosion rate was reduced by 47.8%, compared to those of the untreated samples. The established processing-performance (i.e., surface hardness, corrosion and tribocorrosion) relationship in this study could shed light on the future LSP process optimization for enhancing surface properties of Mg alloys.

Continuous-wave terahertz quantum cascade laser based on a hybrid bound to bound quantum design

We report a low threshold power density and high power output terahertz quantum cascade laser emitting at ∼3.9 THz operating in continuous-wave mode. The high output power and wall-plug efficiency are achieved based on a hybrid bound-to-bound quantum active design. A record output power of 312 mW and a low threshold power density of 0.8 kW/mm3 (threshold current density of 109 A/cm2) in continuous-wave mode at 20 K is demonstrated for a 300-μm-wide and 2-mm-long single-ridge device. The highest wall-plug efficiency is 1.38% and the slope efficiency is 684 mW/A with an internal quantum efficiency of ∼120 photons per injected electron. The demonstration of this low-threshold and high-power THz laser will promote THz-based remote sensing and standoff detection for pharmaceutical and health industry applications.

A hybrid graphene-PbS quantum dots photodetector with positive and negative photocurrents

Different graphene photodetectors may have different light response mechanisms, and in general, most graphene photodetectors tend to generate only positive or negative photocurrents. Here, we demonstrate a photodetector based on graphene grown by Chemical Vapor Deposition (CVD) and PbS quantum dots (QDs) with both positive and negative photocurrents. Under the irradiation of a 635 nm laser, the device generated positive photocurrents of 9 μA at a low laser power density (0.17 μW), the responsivity of which was up to 39.58 A/W due to the high gain mechanism. However, at high laser power density (9.59 μW), the device exhibits completely opposite characteristics due to thermal scattering. The negative photocurrents of 20 μA were generated and the responsivity of the device was 10.29 A/W. The device exhibits the coexistence of two response mechanisms. It is necessary to explore the mechanism of positive and negative photocurrent in graphene, which is helpful to investigate the regulation of graphene carriers, and can also provide a possible research direction for graphene-based memristor devices.

Collagen-induced assembly of adenosine monophosphate-modified gold nanoparticles for photothermal cancer therapy

BackgroundPhotothermal therapy (PTT) has become an attractive approach for cancer treatment due to its merits of minimal invasiveness, location selectivity, and suitability for various cancer types. In PTT, photosensitizers are usually adopted to convert light to heat at tumor site, thereby generating heat-induced necroptosis or apoptosis. Therefore, the performance of photosensitizer (e.g., photothermal conversion efficiency (PCE), surface property, tumor accumulation and retention, etc.) determines the clinical manifestation of PTT. Currently, the poor tumor retention and potential long-term toxicity are two main obstacles for developing efficient photosensitizers. To address these issues, we have developed an in vivo tumor microenvironment stimuli-responsive self-assembled photosensitizer, which consists of a biomolecule, adenosine monophosphate (AMP) modified gold nanoparticles (AAu NPs), to enhance the accumulation and retention within tumor tissue for efficient PTT.ResultsThe obtained AAu NPs with a hydrodynamic diameter of 9.12 ± 0.82 nm have excellent colloidal stability in aqueous solution. No sediments can be observed in the AAu NPs aqueous phase even after several months. The temperature of AAu aqueous suspension is elevated to 53.0 ℃ within 8 min at a low particle concentration of 80 μg/mL. A high PCE of 62.8% is obtained for AAu NPs based on the temperature change curves. The near-infrared (NIR) absorption and PCE of AAu NPs are enhanced compared to the surfactant-free Au NPs, enabling excellent photothermal cell-killing in vitro. When the AAu NPs arrive at the tumor tissue, they quickly form large aggregates via a collagen-induced assembly, leading to enhanced NIR absorption and improved tumor accumulation and retention, which enables a high PTT efficacy in vivo at a low photosensitizer dose of 40 μg and a low laser power density of 1.91 W/cm2.ConclusionsA collagen-induced self-assembled gold photosensitizer for efficient PTT has been synthesized based on a biomolecule, AMP modification method. The synthesized AAu NPs with high PTT efficacy, superior biosafety and fast excretion from the body is an effective therapeutic agent in photothermal cancer therapy.

Modulated plasmonic nanofibrous scaffold reinforced breast cancer photo-ablation and breast neurotization with resensation

Herein, we report the bioactivity of the hybrid plasmonic aligned nanofibrous scaffolds composed of reduced graphene oxide (rGO, 209 nm) nanosheets enfolded gold nanorods (AuNR) with polycaprolactone (PCL) for breast cancer photo-therapy and subsequent nerve regeneration. The strategic inclusion of 0.00068 wt% (OD = 4.0) of monodispersed AuNR-rGO in PCL (AuNR-rGO@PCL (4.0)) leads to significant higher physicochemical and optical properties such as higher mechanical strength (7-fold increase), electrical conductivity (∼6-times enhancement), larger surface area (6.4 times), and more NIR light absorbance. Hence, the AuNR-rGO@PCL (4.0) was found to be an excellent photo agent for breast tumor ablation with more than 90% cancer cell (MCF-7) death under 808 nm NIR irradiation at low laser power density (0.72 W/cm2). Also, the nanofibrous scaffold was observed to have a substantial effect on adhesion, proliferation, growth, and differentiation of PC12 and high affinity to S42 cell proliferation and migration which led to an exceptional nerve growth with a 2.5-fold (with NIR light after 3 days) and 2-fold (without NIR light after 7 days) increase in neurite length in comparison to PCL. The present study provides a new bioactive, biocompatible, non-toxic, and bifunctional aligned plasmonic scaffolds as an excellent single platform for breast cancer treatment and potential bioimplant to regain sensation loss after breast surgery and reconstruction.

Self-assembled Cu2−xS nanochains network with tunable diameters for efficient photothermal conversion

Cu 2−x S nanochains network (NCNW) with tunable diameter in the range of 5–9 nm is prepared by a self-assembly strategy. Control experiments reveal that poly (sodium 4-styrenesulfonate) plays a key role in guiding the assembly of the nanochains. The Cu 2−x S NCNW demonstrates a broad localized surface plasmon resonance (LSPR) band in the near-infrared-Ⅱ region, which matches the optical window of biological tissues. The LSPR band of the Cu 2−x S NCNW red-shifts and intensifies with the increase of diameter. The Cu 2−x S NCNW with an average diameter of 8.7 nm exhibits a high photothermal conversion efficiency of 80.7% under 808 nm laser (0.75 W cm −2 ). Furthermore, the thermal effect stability of the Cu 2−x S NCNW is also good. In vitro experiments demonstrate that all the nanochains possess low cell cytotoxicity. The 8.7 nm Cu 2−x S NCNW own the maximum cellular uptake, and can cause> 90% apoptosis rate of Hela cells under low power density laser (808 nm, 0.75 W cm −2 ), demonstrating its promising application in photothermal therapy. • Cu 2−x S nanochains network with tunable diameter is synthesized. • The Cu 2−x S NCNW exhibits strong LSPR in the Near-Infrared region. • The 8.7 nm Cu 2−x S NCNW exhibits high PCE of 80.7% under 808 nm laser. • The 8.7 nm NCNW has highest cellular uptake and photothermal cell ablation ability.