Laser- synthesized TiN nanoparticles as promising plasmonic alternative for biomedical applications

Laser-synthesized plasmonic HfN-based nanoparticles as a novel multifunctional agent for photothermal therapy

Hafnium nitride nanoparticles (HfN NPs) can offer appealing plasmonic properties at the nanoscale, but the fabrication of stable water-dispersible solutions of non-toxic HfN NPs exhibiting plasmonic features in the window of relative biological transparency presents a great challenge. Here, we demonstrate a solution to this problem by employing ultrashort (femtosecond) laser ablation from a HfN target in organic solutions, followed by a coating of the formed NPs with polyethylene glycol (PEG) and subsequent dispersion in water. We show that the fabricated NPs exhibit plasmonic absorption bands with maxima around 590 nm, 620 nm, and 650 nm, depending on the synthesis environment (ethanol, acetone, and acetonitrile, respectively), which are largely red-shifted compared to what is expected from pure HfN NPs. The observed shift is explained by including nitrogen-deficient hafnium nitride and hafnium oxynitride phases inside the core and oxynitride coating of NPs, as follows from a series of structural characterization studies. We then show that the NPs can provide a strong photothermal effect under 808 nm excitation with a photothermal conversion coefficient of about 62%, which is comparable to the best values reported for plasmonic NPs. MTT and clonogenic assays evidenced very low cytotoxicity of PEG-coated HfN NPs to cancer cells from different tissues up to 100 μg mL-1 concentrations. We finally report a strong photothermal therapeutic effect of HfN NPs, as shown by 100% cell death under 808 nm light irradiation at NP concentrations lower than 25 μg mL-1. Combined with additional X-ray theranostic functionalities (CT scan and photon capture therapy) profiting from the high atomic number (Z = 72) of Hf, plasmonic HfN NPs promise the development of synergetically enhanced modalities for cancer treatment.

Colloidal Titanium Nitride Nanoparticles by Laser Ablation in Solvents for Plasmonic Applications

Titanium nitride (TiN) is a candidate material for several plasmonic applications, and pulsed laser ablation in liquids (PLAL) represents a rapid, scalable, and environmentally friendly approach for the large-scale production of nanomaterials with customized properties. In this work, the nanosecond PLAL process is developed, and we provide a concise understanding of the process parameters, such as the solvent and the laser fluence and pulse wavelength, to the size and structure of the produced TiN nanoparticles (NPs). TiN films of a 0.6 μm thickness developed by direct-current (DC) magnetron sputtering were used as the ablation targets. All laser process parameters lead to the fabrication of spherical NPs, while the laser pulse fluence was used to control the NPs' size. High laser pulse fluence values result in larger TiN NPs (diameter around 42 nm for 5 mJ and 25 nm for 1 mJ), as measured from scanning electron microscopy (SEM). On the other hand, the wavelength of the laser pulse does not affect the mean size of the TiN NPs (24, 26, and 25 nm for 355, 532, and 1064 nm wavelengths, respectively). However, the wavelength plays a vital role in the quality of the produced TiN NPs. Shorter wavelengths result in NPs with fewer defects, as indicated by Raman spectra and XPS analysis. The solvent type also significantly affects the size of the NPs. In aqueous solutions, strong oxidation of the NPs is evident, while organic solvents such as acetone, carbides, and oxides cover the TiN NPs.

Lateral Flow Assay Biotesting by Utilizing Plasmonic Nanoparticles Made of Inexpensive Metals─Replacing Colloidal Gold

Nanoparticles (NPs) can be conjugated with diverse biomolecules and employed in biosensing to detect target analytes in biological samples. This proven concept was primarily used during the COVID-19 pandemic with gold-NP-based lateral flow assays (LFAs). Considering the gold price and its worldwide depletion, here we show that novel plasmonic NPs based on inexpensive metals, titanium nitride (TiN) and copper covered with a gold shell (Cu@Au), perform comparable to or even better than gold nanoparticles. After conjugation, these novel nanoparticles provided high figures of merit for LFA testing, such as high signals and specificity and robust naked-eye signal recognition. Since the main cost of Au NPs in commercial testing kits is the colloidal synthesis, our development with the Cu@Au and the laser-ablation-fabricated TiN NPs is exciting, offering potentially inexpensive plasmonic nanomaterials for various bioapplications. Moreover, our machine learning study showed that biodetection with TiN is more accurate than that with Au.

Lateral Flow Assays Biotesting by Utilizing Plasmonic Nanoparticles Made of Inexpensive Metals - Replacing Colloidal Gold

Nanoparticles (NPs) can be conjugated with diverse biomolecules and employed in biosensing to detect target analytes in biological samples. This proven concept was primarily used during the COVID-19 pandemic with gold NPs-based lateral flow assays (LFAs). Considering the gold price and its worldwide depletion, here we show that novel plasmonic nanoparticles (NPs) based on inexpensive metals, titanium nitride (TiN) and copper covered with a gold shell (Cu@Au), perform comparable or even better than gold nanoparticles. After conjugation, these novel nanoparticles provided high figures of merit for LFA testing, such as high signals and specificity and robust naked-eye signal recognition. To the best of our knowledge, our study represents the 1st application of laser-ablation-fabricated nanoparticles (TiN) in the LFA and dot-blot biotesting. Since the main cost of the Au NPs in commercial testing kits is in the colloidal synthesis, our development with TiN is very exciting, offering potentially very inexpensive plasmonic nanomaterials for various bio-testing applications. Moreover, our machine learning study showed that the bio-detection with TiN is more accurate than that with Au.

Cytotoxicity of Laser-Synthesized Nanoparticles of Elemental Bismuth

High X-ray absorption combined with photothermal properties make bismuth nanoparticles (Bi NP) a promising agent for multimodal cancer theranostics. However, the synthesis of Bi NP by the "classical" chemical methods has numerous limitations, including potential toxicity of the produced nanomaterials. Here we studied in vitro toxicity of laser-synthesized Bi NP coated with Pluronic F-127 on mouse fibroblast cell line L929. The survival of L929 cells decreased linearly with increasing the concentration of Bi NP in a concentration range of 3-500 μg/ml; the LC50 value was 57 μg/ml. The unique combination of functional properties and moderate toxicity of the laser-synthesized Bi NP makes them a new promising platform for sensitization of multimodal cancer theranostics.

Broadband optical properties of Ti3C2 MXene revisited

The exceptional optical, electrical, and mechanical capabilities of layered transition metal carbides, nitrides, and carbonitrides, called MXenes, revolutionized materials science. Among them, Ti3C2 received the most attention owing to the developed synthesis and processing methods, high conductivity, and pronounced plasmonic response. The latter, however, remains controversial with the open question of whether the peak around 800 nm has plasmonic or interband transition origin. To address this issue, we combine spectroscopic ellipsometry and transmittance results with first-principle computations. Their combination reveals that although Ti3C2 is a metal, its optical response becomes plasmonic (Re ε < 0) above 1415 nm, in contrast to the previous understanding. In addition to fundamental significance, this dual dielectric/plasmonic optical response opens a path for theranostic applications, as we demonstrated on the example of Ti3C2 nanospheres. Thus, our study revisits broadband (300-3300 nm) optical constants of Ti3C2 and broadens its application scope in photonics.

Enhancing in vitro photothermal therapy using plasmonic gold nanorod decorated multiwalled carbon nanotubes

Photothermal therapy (PTT) is a promising approach for cancer treatment that selectively heats malignant cells while sparing healthy cells. Here, the light-to-heat conversion efficiency of multiwalled carbon nanotubes (MWCNTs) within the near-infrared biological transmission window is enhanced by decorating them with plasmonic gold nanorods (GNRs). The results reveal a significant photothermal enhancement of hybrid MWCNTs-GNRs compared to bare MWCNTs, displaying a 4.9 enhancement factor per unit mass. The enhanced plasmonic PTT properties of MWCNTs-GNRs are also investigated in vitro using PC3 prostate cancer cell lines, demonstrating a potent ablation efficiency. These findings advance innovative hybrid plasmonic nanostructures for clinical applications.

Laser-Ablative Synthesis of Silicon-Iron Composite Nanoparticles for Theranostic Applications

The combination of photothermal and magnetic functionalities in one biocompatible nanoformulation forms an attractive basis for developing multifunctional agents for biomedical theranostics. Here, we report the fabrication of silicon-iron (Si-Fe) composite nanoparticles (NPs) for theranostic applications by using a method of femtosecond laser ablation in acetone from a mixed target combining silicon and iron. The NPs were then transferred to water for subsequent biological use. From structural analyses, it was shown that the formed Si-Fe NPs have a spherical shape and sizes ranging from 5 to 150 nm, with the presence of two characteristic maxima around 20 nm and 90 nm in the size distribution. They are mostly composed of silicon with the presence of a significant iron silicide content and iron oxide inclusions. Our studies also show that the NPs exhibit magnetic properties due to the presence of iron ions in their composition, which makes the formation of contrast in magnetic resonance imaging (MRI) possible, as it is verified by magnetic resonance relaxometry at the proton resonance frequency. In addition, the Si-Fe NPs are characterized by strong optical absorption in the window of relative transparency of bio-tissue (650-950 nm). Benefiting from such absorption, the Si-Fe NPs provide strong photoheating in their aqueous suspensions under continuous wave laser excitation at 808 nm. The NP-induced photoheating is described by a photothermal conversion efficiency of 33-42%, which is approximately 3.0-3.3 times larger than that for pure laser-synthesized Si NPs, and it is explained by the presence of iron silicide in the NP composition. Combining the strong photothermal effect and MRI functionality, the synthesized Si-Fe NPs promise a major advancement of modalities for cancer theranostics, including MRI-guided photothermal therapy and surgery.

Boron Nanoparticle-Enhanced Proton Therapy for Cancer Treatment

Proton therapy is one of the promising radiotherapy modalities for the treatment of deep-seated and unresectable tumors, and its efficiency can further be enhanced by using boron-containing substances. Here, we explore the use of elemental boron (B) nanoparticles (NPs) as sensitizers for proton therapy enhancement. Prepared by methods of pulsed laser ablation in water, the used B NPs had a mean size of 50 nm, while a subsequent functionalization of the NPs by polyethylene glycol improved their colloidal stability in buffers. Laser-synthesized B NPs were efficiently absorbed by MNNG/Hos human osteosarcoma cells and did not demonstrate any remarkable toxicity effects up to concentrations of 100 ppm, as followed from the results of the MTT and clonogenic assay tests. Then, we assessed the efficiency of B NPs as sensitizers of cancer cell death under irradiation by a 160.5 MeV proton beam. The irradiation of MNNG/Hos cells at a dose of 3 Gy in the presence of 80 and 100 ppm of B NPs led to a 2- and 2.7-fold decrease in the number of formed cell colonies compared to control samples irradiated in the absence of NPs. The obtained data unambiguously evidenced the effect of a strong proton therapy enhancement mediated by B NPs. We also found that the proton beam irradiation of B NPs leads to the generation of reactive oxygen species (ROS), which evidences a possible involvement of the non-nuclear mechanism of cancer cell death related to oxidative stress. Offering a series of advantages, including a passive targeting option and the possibility of additional theranostic functionalities based on the intrinsic properties of B NPs (e.g., photothermal therapy or neutron boron capture therapy), the proposed concept promises a major advancement in proton beam-based cancer treatment.

Impact of Plasmonic Nanoparticles on Poikilocytosis and Microrheological Properties of Erythrocytes

Plasmonic nanoparticles (NP) possess great potential in photothermal therapy and diagnostics. However, novel NP require a detailed examination for potential toxicity and peculiarities of interaction with cells. Red blood cells (RBC) are important for NP distribution and the development of hybrid RBC-NP delivery systems. This research explored RBC alterations induced by noble (Au and Ag) and nitride-based (TiN and ZrN) laser-synthesized plasmonic NP. Optical tweezers and conventional microscopy modalities indicated the effects arising at non-hemolytic levels, such as RBC poikilocytosis, and alterations in RBC microrheological parameters, elasticity and intercellular interactions. Aggregation and deformability significantly decreased for echinocytes independently of NP type, while for intact RBC, all NP except Ag NP increased the interaction forces but had no effect on RBC deformability. RBC poikilocytosis promoted by NP at concentration 50 μg mL-1 was more pronounced for Au and Ag NP, compared to TiN and ZrN NP. Nitride-based NP demonstrated better biocompatibility towards RBC and higher photothermal efficiency than their noble metal counterparts.

Materials Perspectives of Integrated Plasmonic Biosensors

With the growing need for portable, compact, low-cost, and efficient biosensors, plasmonic materials hold the promise to meet this need owing to their label-free sensitivity and deep light-matter interaction that can go beyond the diffraction limit of light. In this review, we shed light on the main physical aspects of plasmonic interactions, highlight mainstream and future plasmonic materials including their merits and shortcomings, describe the backbone substrates for building plasmonic biosensors, and conclude with a brief discussion of the factors affecting plasmonic biosensing mechanisms. To do so, we first observe that 2D materials such as graphene and transition metal dichalcogenides play a major role in enhancing the sensitivity of nanoparticle-based plasmonic biosensors. Then, we identify that titanium nitride is a promising candidate for integrated applications with performance comparable to that of gold. Our study highlights the emerging role of polymer substrates in the design of future wearable and point-of-care devices. Finally, we summarize some technical and economic challenges that should be addressed for the mass adoption of plasmonic biosensors. We believe this review will be a guide in advancing the implementation of plasmonics-based integrated biosensors.

Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics

Recent developments in the area of resonant dielectric nanostructures have created attractive opportunities for concentrating and manipulating light at the nanoscale and the establishment of the new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS₂ and WS₂) nanoparticles (NPs) of variable size (5 to 250 nm). Such NPs demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the NPs. Furthermore, such NPs offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the NPs exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC NPs offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging.

Photothermal heating of titanium nitride nanomaterials for fast and uniform laser warming of cryopreserved biomaterials

Titanium nitride (TiN) is presented as an alternative plasmonic nanomaterial to the commonly used gold (Au) for its potential use in laser rewarming of cryopreserved biomaterials. The rewarming of vitrified, glass like state, cryopreserved biomaterials is a delicate process as potential ice formation leads to mechanical stress and cracking on a macroscale, and damage to cell walls and DNA on a microscale, ultimately leading to the destruction of the biomaterial. The use of plasmonic nanomaterials dispersed in cryoprotective agent solutions to rapidly convert optical radiation into heat, generally supplied by a focused laser beam, proposes a novel approach to overcome this difficulty. This study focuses on the performance of TiN nanoparticles (NPs), since they present high thermal stability and are inexpensive compared to Au. To uniformly warm up the nanomaterial solutions, a beam splitting laser system was developed to heat samples from multiple sides with equal beam energy distribution. In addition, uniform laser warming requires equal distribution of absorption and scattering properties in the nanomaterials. Preliminary results demonstrated higher absorption but less scattering in TiN NPs than Au nanorods (GNRs). This led to the development of TiN clusters, synthetized by nanoparticle agglomeration, to increase the scattering cross-section of the material. Overall, this study analyzed the heating rate, thermal efficiency, and heating uniformity of TiN NPs and clusters in comparison to GNRs at different solution concentrations. TiN NPs and clusters demonstrated higher heating rates and solution temperatures, while only clusters led to a significantly improved uniformity in heating. These results highlight a promising alternative plasmonic nanomaterial to rewarm cryopreserved biological systems in the future.

Nanotechnology-Based Combinatorial Anti-Glioblastoma Therapies: Moving from Terminal to Treatable

Aggressive glioblastoma (GBM) has no known treatment as a primary brain tumor. Since the cancer is so heterogeneous, an immunosuppressive tumor microenvironment (TME) exists, and the blood–brain barrier (BBB) prevents chemotherapeutic chemicals from reaching the central nervous system (CNS), therapeutic success for GBM has been restricted. Drug delivery based on nanocarriers and nanotechnology has the potential to be a handy tool in the continuing effort to combat the challenges of treating GBM. There are various new therapies being tested to extend survival time. Maximizing therapeutic effectiveness necessitates using many treatment modalities at once. In the fight against GBM, combination treatments outperform individual ones. Combination therapies may be enhanced by using nanotechnology-based delivery techniques. Nano-chemotherapy, nano-chemotherapy–radiation, nano-chemotherapy–phototherapy, and nano-chemotherapy–immunotherapy for GBM are the focus of the current review to shed light on the current status of innovative designs.

Laser-ablative aqueous synthesis and characterization of elemental boron nanoparticles for biomedical applications

Boron-based nano-formulations look very promising for biomedical applications, including photo- and boron neutron capture therapies, but the fabrication of non-toxic water-dispersible boron nanoparticles (NPs), which contain the highest boron atom concentration, is difficult using currently available chemical and plasma synthesis methods. Here, we demonstrate purely aqueous synthesis of clean boron NPs by methods of femtosecond laser ablation from a solid boron target in water, thus free of any toxic organic solvents, and characterize their properties. We show that despite highly oxidizing water ambience, the laser-ablative synthesis process follows an unusual scenario leading to the formation of boron NPs together with boric acid (H₃BO₃) as an oxidation by-product coating the nanoparticles, which acts to stabilize the elemental boron NPs dispersion. We then demonstrate the purification of boron NPs from residual boric acid in deionized water, followed by their coating with polyethylene glycol to improve colloidal stability and biocompatibility. It was found that the formed NPs have a spherical shape with averaged size of about 37 nm, and are composed of elemental boron in mostly amorphous phase with the presence of certain crystalline fraction. The synthesized NPs demonstrate low toxicity and exhibit strong absorption in the NIR window of relative tissue transparency, promising their use in photoacoustic imaging and phototherapy, in addition to their promise for neutron capture therapy. This combined potential ability of generating imaging and therapy functionalities makes laser-synthesized B NPs a very promising multifunctional agent for biomedical applications.

Advances in Electrospun Hybrid Nanofibers for Biomedical Applications

Electrospun hybrid nanofibers, based on functional agents immobilized in polymeric matrix, possess a unique combination of collective properties. These are beneficial for a wide range of applications, which include theranostics, filtration, catalysis, and tissue engineering, among others. The combination of functional agents in a nanofiber matrix offer accessibility to multifunctional nanocompartments with significantly improved mechanical, electrical, and chemical properties, along with better biocompatibility and biodegradability. This review summarizes recent work performed for the fabrication, characterization, and optimization of different hybrid nanofibers containing varieties of functional agents, such as laser ablated inorganic nanoparticles (NPs), which include, for instance, gold nanoparticles (Au NPs) and titanium nitride nanoparticles (TiNPs), perovskites, drugs, growth factors, and smart, inorganic polymers. Biocompatible and biodegradable polymers such as chitosan, cellulose, and polycaprolactone are very promising macromolecules as a nanofiber matrix for immobilizing such functional agents. The assimilation of such polymeric matrices with functional agents that possess wide varieties of characteristics require a modified approach towards electrospinning techniques such as coelectrospinning and template spinning. Additional focus within this review is devoted to the state of the art for the implementations of these approaches as viable options for the achievement of multifunctional hybrid nanofibers. Finally, recent advances and challenges, in particular, mass fabrication and prospects of hybrid nanofibers for tissue engineering and biomedical applications have been summarized.

Synthesis of Titanium Nitride Nanoparticles by Pulsed Laser Ablation in Different Aqueous and Organic Solutions

Owing to a strong photothermal response in the near-IR spectral range and very low toxicity, titanium nitride (TiN) nanoparticles (NPs) synthesized by pulsed laser ablation in liquids (PLAL) present a novel appealing object for photo-induced therapy of cancer, but the properties of these NPs still require detailed investigation. Here, we have elaborated methods of femtosecond laser ablation from the TiN target in a variety of liquid solutions, including acetonitrile, dimethylformamide, acetone, water, and H₂O₂, to synthesize TiN NPs and clarify the effect of liquid type on the composition and properties of the formed NPs. The ablation in all solvents led to the formation of spherical NPs with a mean size depending on the liquid type, while the composition of the NPs ranged from partly oxidized TiN to almost pure TiO₂, which conditioned variations of plasmonic peak in the region of relative tissue transparency (670–700 nm). The degree of NP oxidation depended on the solvent, with much stronger oxidation for NPs prepared in aqueous solutions (especially in H₂O₂), while the ablation in organic solvents resulted in a partial formation of titanium carbides as by-products. The obtained results contribute to better understanding of the processes in reactive PLAL and can be used to design TiN NPs with desired properties for biomedical applications.

Multiphysical numerical study of photothermal therapy of glioblastoma with photoacoustic temperature monitoring in a mouse head

This paper presents a multiphysical numerical study of a photothermal therapy performed on a numerical phantom of a mouse head containing a glioblastoma. The study has been designed to be as realistic as possible. Heat diffusion simulations were performed on the phantom to understand the temperature evolution in the mouse head and therefore in the glioblastoma. The thermal dose has been calculated and lesions caused by heat are shown. The thermal damage on the tumor has also been quantified. To improve the effectiveness of the therapy, the photoabsorber's concentration was increased locally, at the tumor site, to mimic the effect of using absorbing contrast agents such as nanoparticles. Photoacoustic simulations were performed in order to monitor temperature in the phantom: as the Grüneisen parameter changes with the temperature, the photoacoustic signal undergoes changes that can be linked to temperature evolution. These photoacoustic simulations were performed at different instants during the therapy and the evolution of the photoacoustic signal as a function of the spatio-temporal distribution of the temperature in the phantom was observed and quantified. We have developed in this paper a numerical tool that can be used to help defining key parameters of a photothermal therapy.

Laser-Ablative Synthesis of Ultrapure Magneto-Plasmonic Core-Satellite Nanocomposites for Biomedical Applications

The combination of magnetic and plasmonic properties at the nanoscale promises the development of novel synergetic image-guided therapy strategies for the treatment of cancer and other diseases, but the fabrication of non-contaminated magneto-plasmonic nanocomposites suitable for biological applications is difficult within traditional chemical methods. Here, we describe a methodology based on laser ablation from Fe target in the presence of preliminarily ablated water-dispersed Au nanoparticles (NPs) to synthesize ultrapure bare (ligand-free) core-satellite nanostructures, consisting of large (several tens of nm) Fe-based core decorated by small (mean size 7.5 nm) Au NPs. The presence of the Fe-based core conditions a relatively strong magnetic response of the nanostructures (magnetization of >12.6 emu/g), while the Au NPs-based satellite shell provides a broad extinction peak centered at 550 nm with a long tale in the near-infrared to overlap with the region of relative tissue transparency (650-950 nm). We also discuss possible mechanisms responsible for the formation of the magnetic-plasmonic nanocomposites. We finally demonstrate a protocol to enhance colloidal stability of the core-satellites in biological environment by their coating with different polymers. Exempt of toxic impurities and combining strong magnetic and plasmonic responses, the formed core-satellite nanocomposites can be used in biomedical applications, including photo- and magneto-induced therapies, magnetic resonance imaging or photoacoustic imaging.

Exploiting Nanomaterials for Optical Coherence Tomography and Photoacoustic Imaging in Nanodentistry

There is already a societal awareness of the growing impact of nanoscience and nanotechnology, with nanomaterials (with at least one dimension less than 100 nm) now incorporated in items as diverse as mobile phones, clothes or dentifrices. In the healthcare area, nanoparticles of biocompatible materials have already been used for cancer treatment or bioimaging enhancement. Nanotechnology in dentistry, or nanodentistry, has already found some developments in dental nanomaterials for caries management, restorative dentistry and orthodontic adhesives. In this review, we present state-of-the-art scientific development in nanodentistry with an emphasis on two imaging techniques exploiting nanomaterials: optical coherence tomography (OCT) and photoacoustic imaging (PAI). Examples will be given using OCT with nanomaterials to enhance the acquired imaging, acting as optical clearing agents for OCT. A novel application of gold nanoparticles and nanorods for imaging enhancement of incipient occlusal caries using OCT will be described. Additionally, we will highlight how the OCT technique can be properly managed to provide imaging with spatial resolution down to 10's-100's nm resolution. For PAI, we will describe how new nanoparticles, namely TiN, prepared by femtosecond laser ablation, can be used in nanodentistry and will show photoacoustic microscopy and tomography images for such exogenous agents.

Nanoparticle Fragmentation Below the Melting Point Under Single Picosecond Laser Pulse Stimulation

Understanding the laser-nanomaterials interaction including nanomaterial fragmentation has important implications in nanoparticle manufacturing, energy, and biomedical sciences. So far, three mechanisms of laser-induced fragmentation have been recognized including non-thermal processes and thermomechanical force under femtosecond pulses, and the phase transitions under nanosecond pulses. Here we show that single picosecond (ps) laser pulse stimulation leads to anomalous fragmentation of gold nanoparticles that deviates from these three mechanisms. The ps laser fragmentation was weakly dependent on particle size, and it resulted in a bimodal size distribution. Importantly, ps laser stimulation fragmented particles below the whole particle melting point and below the threshold for non-thermal mechanism. We propose a framework based on near-field enhancement and nanoparticle surface melting to account for the ps laser-induced fragmentation observed here. This study reveals a new form of surface ablation that occurs under picosecond laser stimulation at low fluence.

Surface-Enhanced Raman scattering of methylene blue on titanium nitride nanoparticles synthesized by laser ablation in organic solvents

Suspensions of titanium nitride (TiN) nanoparticles (NPs) were prepared using nanosecond Ce:Nd:YAG pulsed laser ablation (λ = 1064 nm) of a TiN target immersed in various solvents such as Toluene (C₆H₅CH₃), Acetonitrile (CH₃CN), and N, N-dimethylformamide (C₃H₇NO). The synthesized NPs were characterized by applying a range of spectroscopic, structural, and compositional analysis techniques. The obtained TiN NPs in N, N-dimethylformamide (DMF-TiN NPs) solvent showed strong optical absorption in the near-infrared (NIR) range; Whereas, the obtained TiN NPs in toluene (T-TiN NPs) and acetonitrile (AN-TiN NPs) solvents were covered with a carbon matrix layer that quenched their surface plasmon resonance (SPR). The carbon matrix on the NPs was removed by thermal oxidation to obtain carbon-free TiN NPs. All the prepared carbon-free TiN NPs were employed as substrates for the surface-enhanced Raman scattering (SERS) spectroscopy of methylene blue (MB) molecules as a probe molecule adsorbed on the surface. All substrates indicated nearly the same order of enhancement factors (EFs) (~10³) for MB.

Development of a multi-functional preclinical device for the treatment of glioblastoma

Glioblastoma multiforme (GBM) is one of the most common and aggressive malignant primary brain tumors in adults. The treatment of GBM is limited by the blood-brain barrier (BBB), which limits the diffusion of appropriate concentrations of therapeutic agents at the tumor site. Among experimental therapies, photo-thermal therapy (PTT) mediated by nanoparticles is a promising strategy. To propose a preclinical versatile research instrument for the development of new PTT for GBM, a multipurpose integrated preclinical device was developed. The setup is able to perform: i) BBB permeabilization by focused ultrasound sonication (FUS); ii) PTT with continuous wave laser; iii) in situ temperature monitoring with photo-acoustic (PA) measurements. In vivo preliminary subcutaneous and transcranial experiments were conducted on healthy or tumor-bearing mice. Transcranial FUS-induced BBB permeabilization was validated using single photon emission computed tomography (SPECT) imaging. PTT capacities were monitored by PA thermometry, and are illustrated through subcutaneous and transcranial in vivo experiments. The results show the therapeutic possibilities and ergonomy of such integrated device as a tool for the validation of future treatments.

Short-Pulse Lasers: A Versatile Tool in Creating Novel Nano-/Micro-Structures and Compositional Analysis for Healthcare and Wellbeing Challenges

Driven by flexibility, precision, repeatability and eco-friendliness, laser-based technologies have attracted great interest to engineer or to analyze materials in various fields including energy, environment, biology and medicine. A major advantage of laser processing relies on the ability to directly structure matter at different scales and to prepare novel materials with unique physical and chemical properties. It is also a contact-free approach that makes it possible to work in inert or reactive liquid or gaseous environment. This leads today to a unique opportunity for designing, fabricating and even analyzing novel complex bio-systems. To illustrate this potential, in this paper, we gather our recent research on four types of laser-based methods relevant for nano-/micro-scale applications. First, we present and discuss pulsed laser ablation in liquid, exploited today for synthetizing ultraclean "bare" nanoparticles attractive for medicine and tissue engineering applications. Second, we discuss robust methods for rapid surface and bulk machining (subtractive manufacturing) at different scales by laser ablation. Among them, the microsphere-assisted laser surface engineering is detailed for its appropriateness to design structured substrates with hierarchically periodic patterns at nano-/micro-scale without chemical treatments. Third, we address the laser-induced forward transfer, a technology based on direct laser printing, to transfer and assemble a multitude of materials (additive structuring), including biological moiety without alteration of functionality. Finally, the fourth method is about chemical analysis: we present the potential of laser-induced breakdown spectroscopy, providing a unique tool for contact-free and space-resolved elemental analysis of organic materials. Overall, we present and discuss the prospect and complementarity of emerging reliable laser technologies, to address challenges in materials' preparation relevant for the development of innovative multi-scale and multi-material platforms for bio-applications.

Laser Ablation-Assisted Synthesis of Plasmonic Si@Au Core-Satellite Nanocomposites for Biomedical Applications

Owing to strong plasmonic absorption and excellent biocompatibility, gold nanostructures are among best candidates for photoacoustic bioimaging and photothermal therapy, but such applications require ultrapure Au-based nanoformulations of complex geometry (core-shells, nanorods) in order to shift the absorption band toward the region of relative tissue transparency (650-1000 nm). Here, we present a methodology for the fabrication of Si@Au core-satellite nanostructures, comprising of a Si core covered with small Au nanoparticles (NP), based on laser ablative synthesis of Si and Au NPs in water/ethanol solutions, followed by a chemical modification of the Si NPs by 3-aminopropyltrimethoxysilane (APTMS) and their subsequent decoration by the Au NPs. We show that the formed core-satellites have a red-shifted plasmonic absorption feature compared to that of pure Au NPs (520 nm), with the position of the peak depending on APTMS amount, water-ethanol solvent percentage and Si-Au volume ratio. As an example, even relatively small 40-nm core-satellites (34 nm Si core + 4 nm Au shell) provided a much red shifted peak centered around 610 nm and having a large tail over 700 nm. The generation of the plasmonic peak is confirmed by modeling of Si@Au core-shells of relevant parameters via Mie theory. Being relatively small and exempt of any toxic impurity due to ultraclean laser synthesis, the Si@Au core-satellites promise a major advancement of imaging and phototherapy modalities based on plasmonic properties of nanomaterials.

Smart Electrospun Hybrid Nanofibers Functionalized with Ligand-Free Titanium Nitride (TiN) Nanoparticles for Tissue Engineering

Herein, we report the fabrication and characterization of novel polycaprolactone (PCL)-based nanofibers functionalized with bare (ligand-free) titanium nitride (TiN) nanoparticles (NPs) for tissue engineering applications. Nanofibers were prepared by a newly developed protocol based on the electrospinning of PCL solutions together with TiN NPs synthesized by femtosecond laser ablation in acetone. The generated hybrid nanofibers were characterised using spectroscopy, microscopy, and thermal analysis techniques. As shown by scanning electron microscopy measurements, the fabricated electrospun nanofibers had uniform morphology, while their diameter varied between 0.403 ± 0.230 µm and 1.1 ± 0.15 µm by optimising electrospinning solutions and parameters. Thermal analysis measurements demonstrated that the inclusion of TiN NPs in nanofibers led to slight variation in mass degradation initiation and phase change behaviour (T_m). In vitro viability tests using the incubation of 3T3 fibroblast cells in a nanofiber-based matrix did not reveal any adverse effects, confirming the biocompatibility of hybrid nanofiber structures. The generated hybrid nanofibers functionalized with plasmonic TiN NPs are promising for the development of smart scaffold for tissue engineering platforms and open up new avenues for theranostic applications.

Computational investigation of the plasmonic properties of TiN, ZrN, and HfN nanoparticles: the role of particle size, medium, and surface oxidation

Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong plasmonic responses in the visible and near-infrared regimes, exhibit high melting points and significant chemical stability, and thus are potential earth-abundant alternatives to Au and Ag based plasmonic applications. However, a detailed understanding of the relationship between TMN NP physical properties and plasmonic response is required to maximize their utility. In this study, the localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) NPs were examined as a function of the particle size, surface oxidation, and refractive index of the surrounding medium using finite element method (FEM). A linear redshift in the LSPR frequency and a linear increase in the associated full width at half maximum (FWHM) was observed with increasing the particle size, oxidation layer thickness, and medium refractive index. We show that the effect of surface oxidation on plasmonic properties of TMN NPs is strongly size-dependent with a significant LSPR redshift, intensity reduction, and broadening in small NPs compared with larger NPs. Furthermore, the performance and efficiency of HfN, ZrN, and TiN, as well as Au NPs for narrowband (photothermal therapy, PTT) and broadband (solar energy conversion) applications, was investigated in detail. The results indicate that narrowband and broadband photothermal performance of NPs strongly depend on the particle size, surface properties, and in case of narrowband absorption, excitation wavelength.

Photothermal Therapy for the Treatment of Glioblastoma: Potential and Preclinical Challenges

Glioblastoma (GBM) is a very aggressive primary malignant brain tumor and finding effective therapies is a pharmaceutical challenge and an unmet medical need. Photothermal therapy may be a promising strategy for the treatment of GBM, as it allows the destruction of the tumor using heat as a non-chemical treatment for disease bypassing the GBM heterogeneity limitations, conventional drug resistance mechanisms and side effects on peripheral healthy tissues. However, its development is hampered by the distinctive features of this tumor. Photoabsorbing agents such as nanoparticles need to reach the tumor site at therapeutic concentrations, crossing the blood-brain barrier upon systemic administration. Subsequently, a near infrared light irradiating the head must cross multiple barriers to reach the tumor site without causing any local damage. Its power intensity needs to be within the safety limit and its penetration depth should be sufficient to induce deep and localized hyperthermia and achieve tumor destruction. To properly monitor the therapy, imaging techniques that can accurately measure the increase in temperature within the brain must be used. In this review, we report and discuss recent advances in nanoparticle-mediated plasmonic photothermal therapy for GBM treatment and discuss the preclinical challenges commonly faced by researchers to develop and test such systems.

Nonlinear photoacoustic response of suspensions of laser-synthesized plasmonic titanium nitride nanoparticles

A nonlinear photoacoustic (PA) response from solutions of 40 nm plasmonic titanium nitride nanoparticles (NPs) synthesized by laser ablation in a liquid environment (acetone) is reported. Using a photoacoustic Z-scan with 5 ns pumping pulses, values of effective nonlinear absorption (NLA) coefficients β_PA,eff were measured and found to be 3.27±0.17 × 10^-8, 6.41±0.32 × 10^-8, and 3.22±0.16 × 10^-8 for 600, 700, and 800 nm pumping wavelengths, respectively. To take into account the influence of nonlinear scattering, absorption-dependent PA measurements were carried out together with the optical Z-scan, and the obtained data were compared. The origin of the effective absorptive nonlinearity is discussed based on combined NLA in NPs, nonlinear scattering, and bubble generation triggered by NP-mediated light absorption. Potential applications include biomedical diagnostics and therapy.

Laser-synthesized TiN nanoparticles for biomedical applications: Evaluation of safety, biodistribution and pharmacokinetics

Having plasmonic absorption within the biological transparency window, titanium nitride (TiN) nanoparticles (NPs) can potentially outperform gold counterparts in phototheranostic applications, but characteristics of available TiN NPs are still far from required parameters. Recently emerged laser-ablative synthesis opens up opportunities to match these parameters as it makes possible the production of ultrapure low size-dispersed spherical TiN NPs, capable of generating a strong phototherapy effect under 750-800 nm excitation. This study presents the first assessment of toxicity, biodistribution and pharmacokinetics of laser-synthesized TiN NPs. Tests in vitro using 8 cell lines from different tissues evidenced safety of both as-synthesized and PEG-coated NPs (TiN-PEG NPs). After systemic administration in mice, they mainly accumulated in liver and spleen, but did not cause any sign of toxicity or organ damage up to concentration of 6 mg kg^-1, which was confirmed by the invariability of blood biochemical parameters, weight and hemotoxicity examination. The NPs demonstrated efficient passive accumulation in EMT6/P mammary tumor, while concentration of TiN-PEG NPs was 2.2-fold higher due to "stealth" effect yielding 7-times longer circulation in blood. The obtained results evidence high safety of laser-synthesized TiN NPs for biological systems, which promises a major advancement of phototheranostic modalities on their basis.

Laser-Ablative Synthesis of Stable Aqueous Solutions of Elemental Bismuth Nanoparticles for Multimodal Theranostic Applications

Elemental bismuth (Bi) nanoparticles (NPs), with the high atomic density of the Bi nuclei, could serve as efficient targeted agents for cancer treatment, with applications such as contrast agents for computed tomography (CT) imaging, sensitizers for image-guided X-ray radiotherapy, and photothermal therapy. However, the synthesis of elemental Bi NPs suitable for biological applications is difficult using conventional chemical routes. Here, we explore the fabrication of ultrapure Bi-based nanomaterials by femtosecond laser ablation from a solid Bi target in ambient liquids and characterize them by a variety of techniques, including TEM, SEM, XRD, FTIR, Raman, and optical spectroscopy. We found that laser-ablative synthesis using an elemental Bi solid target leads to the formation of spherical Bi NPs having the mean size of 20–50 nm and a low size-dispersion. The NPs prepared in water experience a fast (within a few minutes) conversion into 400–500 nm flake-like nanosheets, composed of bismuth subcarbonates, (BiO)₂CO₃ and (BiO)₄CO₃(OH)₂, while the NPs prepared in acetone demonstrate high elemental stability. We introduce a procedure to obtain a stable aqueous solution of elemental Bi NPs suitable for biological applications, based on the coating of Bi NPs prepared in acetone with Pluronic^® F68 and their subsequent transfer to water. We also show that the laser-synthesized elemental Bi NPs, due to their vanishing band gap, exhibit remarkable absorption in the infrared range, which can be used for the activation of photothermal therapy in the near IR-to-IR window with maximum optical transparency in biological media. Exempt of any toxic synthetic by-products, laser-ablated elemental Bi NPs present a novel appealing nanoplatform for combination image-guided photoradiotherapies.

Overview of Synthetic Methods to Prepare Plasmonic Transition-Metal Nitride Nanoparticles

The search for new plasmonic materials that are low-cost, chemically and thermally stable, and exhibit low optical losses has garnered significant attention among researchers. Recently, metal nitrides have emerged as promising alternatives to conventional, noble-metal-based plasmonic materials, such as silver and gold. Many of the initial studies on metal nitrides have focused on computational prediction of the plasmonic properties of these materials. In recent years, several synthetic methods have been developed to enable empirical analysis. This review highlights synthetic techniques for the preparation of plasmonic metal nitride nanoparticles, which are predominantly free-standing, by using solid-state and solid-gas phase reactions, nonthermal and arc plasma methods, and laser ablation. The physical properties of the nanoparticles, such as shape, size, crystallinity, and optical response, obtained with such synthetic methods are also summarized.

Photothermal Transduction Efficiencies of Plasmonic Group 4 Metal Nitride Nanocrystals

The photothermal transduction efficiencies of group 4 metal nitrides, TiN, ZrN, and HfN, at λ = 850 nm are reported, and the performance of these materials is compared to an Au nanorod benchmark. Transition metal nitride nanocrystals with an average diameter of ∼15 nm were prepared using a solid-state metathesis reaction. HfN exhibited the highest photothermal transduction efficiency of 65%, followed by ZrN (58%) and TiN (49%), which were all higher than those of the commercially purchased Au nanorods (43%). Computational studies performed using a finite element method showed HfN and Au to have the lowest and highest scattering cross section, respectively, which could be a contributing factor to the efficiency trends observed. Furthermore, the changes in temperature as a function of illumination intensity and solution concentration, as well as the cycling stability of the metal nitride solutions, were studied in detail.

Numerical investigation of plasmon sensitivity and surface-enhanced Raman scattering enhancement of individual TiN nanosphere multimers

Titanium nitride (TiN) nanoparticles have recently been considered as potential candidate plasmonic materials; such materials support localized surface plasmon resonances (LSPRs) and show excellent thermal stability with a high melting point. The electromagnetic (EM) field coupling and gap distance between components of individual TiN nanosphere multimers are critical parameters affecting their plasmonic sensitivity and surface-enhanced Raman scattering (SERS) performance, both of which are numerically investigated by the finite element method. It is demonstrated that the fractional shifts of both the dipolar LSPR wavelength [Formula: see text] and the refractive index sensitivity factor S follow the universal 'plasmon ruler' behavior, which is explained well in terms of EM field distribution. The response of the obtained S to [Formula: see text] is also presented and elucidated in terms of the optical response of the dielectric constants of TiN. The maximum S and SERS enhancement (excited by three normally available lasers in experiments) are also predicted; both are comparable to the values for Au dimeric nanoparticles. The present work holds great promise for the development of non-noble metal plasmonic materials in both SERS and plasmonic sensing applications.

Bare laser-synthesized palladium–gold alloy nanoparticles as efficient electrocatalysts for glucose oxidation for energy conversion applications

Laser-synthesized PdAu nanoparticles demonstrate a strong synergetic effect on glucose oxidation combining high catalytic activity with ultrafast kinetics at low potentials.

Laser-Ablative Synthesis of Isotope-Enriched Samarium Oxide Nanoparticles for Nuclear Nanomedicine

Nuclear nanomedicine is an emerging field, which utilizes nanoformulations of nuclear agents to increase their local concentration at targeted sites for a more effective nuclear therapy at a considerably reduced radiation dosage. This field needs the development of methods for controlled fabrication of nuclear agents carrying nanoparticles with low polydispersity and with high colloidal stability in aqueous dispersions. In this paper, we apply methods of femtosecond (fs) laser ablation in deionized water to fabricate stable aqueous dispersion of 152Sm-enriched samarium oxide nanoparticles (NPs), which can capture neutrons to become 153Sm beta-emitters for nuclear therapy. We show that direct ablation of a 152Sm-enriched samarium oxide target leads to widely size- and shape-dispersed populations of NPs with low colloidal stability. However, by applying a second fs laser fragmentation step to the dispersion of initially formed colloids, we achieve full homogenization of NPs size characteristics, while keeping the same composition. We also demonstrate the possibility for wide-range tuning of the mean size of Sm-based NPs by varying laser energy during the ablation or fragmentation step. The final product presents dispersed solutions of samarium oxide NPs with relatively narrow size distribution, having spherical shape, a controlled mean size between 7 and 70 nm and high colloidal stability. The formed NPs can also be of importance for catalytic and biomedical applications.

Texture and Stress Evolution in HfN Films Sputter-Deposited at Oblique Angles

In this study, polycrystalline hafnium nitride (HfN) thin films were grown by oblique angle deposition (OAD) technique to investigate the relationship between column tilt angle, texture development and residual stress evolution with varying inclination angle α of the substrate. The films (~1 μm thickness) were grown at various angles (α = 5°, 25°, 35°, 65°, 75°, and 85°) with respect to the substrate normal by reactive magnetron sputtering at 0.3 Pa and 300 °C. The film morphology, crystal structure and residual stress state were characterized by scanning electron microscopy and X-ray diffraction (XRD), including pole figure and sin2ψ measurements. All HfN films had a cubic, NaCl-type crystal structure with an [111] out-of-plane orientation and exhibited a biaxial texture for α ≥ 35°. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids, with a side and a corner facing the projection of the incoming particle flux (indicative of a double in-plane alignment). A columnar microstructure was formed for α ≥ 35°, with typical column widths of 100 nm. It is observed that the column tilt angle β increases monotonously for α ≥ 35°, reaching β = 34° at α = 85°. This variation at microscopic scale is correlated with the tilt angle of the (111) crystallographic planes, changing from −24.8 to 11.3° with respect to the substrate surface. The residual stress changes from strongly compressive (~−5 GPa at α = 5°) to negligible or slightly tensile for α ≥ 35°. The observed trends are compared to previous works of the literature and discussed based on existing crystal growth and stress models, as well as in light of energy and angular distribution of the incident particle flux calculated by Monte Carlo. Importantly, a decrease of the average kinetic energy of Hf particles from 22.4 to 17.7 eV is found with increasing α due to an increase number of collisions.