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Owing to a red-shifted absorption/scattering feature compared to conventional plasmonic metals, titanium nitride nanoparticles (TiN NPs) constitute a promising candidate for nanomedicine. However, their potential is still underexplored due to difficulties of synthesis of stable biocompatible colloids of TiN NPs. Here, we provide results of elaboration of laser-ablative synthesis of TiN NPs in liquids which can solve the problem. Laser-ablated TiN NPs have strong plasmonic peak in near-IR. We also present their first comprehensive biocompatibility assessment. 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.

Radiation nanomedicine is an emerging field, which utilizes nanoformulations of high-Z elements and nuclear agents to improve therapeutic outcome and to reduce radiation dosage. This field lacks methods for controlled fabrication of biocompatible nanoformulations. Here, we present application of femtosecond laser ablation in liquids to fabricate stable colloidal solutions of ultrapure elemental Bi and isotope-enriched samarium oxide nanoparticles (NPs). The obtained spherical Bi and Sm oxide NPs have controllable size, while Bi NPs have remarkable absorption in the near-IR region. Exempt of any toxic by-products, laser-ablated Bi and Sm oxide NPs present a novel appealing nanoplatform for nuclear and radiotherapies.

Welcome and Introduction to SPIE Photonics West LASE conference 11675: Synthesis and Photonics of Nanoscale Materials XVIII

The presentation will overview our on-going activities on laser ablative synthesis of novel biocompatible colloidal nanomaterials (TiN, Si, Sm2O3, Bi, Au-Fe3O4 core-shells,) and their testing in tasks of bioimaging (optical non-linear imaging) and therapies (photo-hyperthermia, nuclear therapy)

Nanotechnology promises a major improvement of efficacy of nuclear medicine by targeted delivery of radioactive agents to tumors, but this approach still needs novel efficient nanoformulations to maximize diagnostic and therapeutic functions. Here, we present a two-step method of laser ablation and fragmentation in water to produce non-radioactive 152Sm-enriched samarium oxide nanoparticles (Sm NPs), which can be converted to radioactive form of 153Sm beta-emitters by neutron capture reaction. We found that laser ablation in deionized water leads to the formation of NPs having diverse morphology and broad size dispersion. To improve size characteristics of formed NPs, we applied additional femtosecond laser fragmentation step, which made possible a good control of mean NPs size under a drastic narrowing of size dispersion, and the spherical shape of formed NPs. Obtained colloidal solutions of Sm NPs were stable for several weeks after the synthesis. The formed NPs present a very promising object for nuclear nanomedicine.

In food industry, detection of spoilage yeasts such as W. anomalus and B. bruxellensis and pathogens such as certain Listeria and E. coli species can be laborious and time-consuming. In the present study, a simple and repeatable technique was developed for rapid yeast detection using a combination of patterned gold coated polymer SERS substrates and gold nanoparticles [1−4]. For the first time, a state-of-the-art time-gated Raman detection approach was used as a complementary technique to show the possibility of using 532-nm pulsed laser excitation and avoid the destructive influence of induced fluorescence [3]. Conventional nanoparticles synthesized by colloidal chemistry are typically contaminated by non-biocompatible by-products (surfactants, anions), which can have negative impacts on many live objects under examination (cells, bacteria) and thus decrease the precision of bioidentification. Here, we explore novel ultrapure laser-synthesized Au-based nanomaterials, including Au NPs and Au Si hybrid nanostructures, as mobile SERS probes in tasks of bacteria detection [3]. We demonstrate successful identification of two types of bacteria (L. innocua and E. coli) and yeast (W. anomalus and B. bruxellensis). They showed several differing characteristic peaks making the discrimination of these yeasts possible without the need for chemometric analysis [2]. The use of composite gold-silicon laser-ablated nanoparticles in combination with the SERS substrate gave distinctive spectra for all the detected species. The detection limit of the studied species varied within 104-107 CFU/ml. The obtained results open up opportunities for non-disturbing investigation of biological systems by profiting from excellent non-disturbing nature of laser-synthesized nanomaterials in combination with outstanding optical detection technologies [2, 3]. [1] Uusitalo et al. 2016, http://pubs.rsc.org/en/content/articlehtml/2016/ra/c6ra08313g [2] Uusitalo et al. 2017a, https://www.sciencedirect.com/science/article/pii/S0260877417302054 [3] Kogler et al. 2018, https://onlinelibrary.wiley.com/doi/abs/10.1002/jbio.201700225 [4] Uusitalo et al. 2017b, https://www.spiedigitallibrary.org/journalArticle/Download?fullDOI=10.1117/1.OE.56.3.037102

Methods of femtosecond laser ablation were used to fabricate bare (ligand-free) silicon (Si) nanoparticles in deionized water. The nanoparticles were round in shape, crystalline, free of any impurities, and water-dissolvable, while the dissolution rate depended on the concentration of oxygen defects in their composition. The nanoparticles were then eletrospun with chitosan to form nanoparticle decorated nanofibrous matrices. We found that the functionalization of nanofibers by the nanoparticles can affect the morphology and physico-chemical characteristics of resulting nanostructures. In particular, the presence of Si nanoparticles led to the reduction of fibers thickness, suggesting a potential improvement of fiber’s surface reactivity. We also observed the improvement of thermal stability of hybrid nanofibers. We believe that the incorporated Si nanoparticles can serve as functional elements to improve characteristics of chitosan-based matrices for cellular growth, as well as to enable novel imaging or therapeutic functionalities for tissue engineering applications.

Nanostructured silicon can exhibit visible photoluminescence (PL) with quantum efficiency of up to few percent, although bulk silicon has a small (1.11 eV) and indirect band gap. This luminescent property gives a promise fo the creation of Si-based optoelectronics devices and their potential integration in standard Si-based microelectronics chips. The search of methods for the production of visible light-emission from Si-based materials becomes currently a great task and a subject of numerous studies, while "dry" fabrication techniques are of particular interest due to a much better compatibility with silicon processing technology.

Femtosecond laser fragmentation from preliminarily prepared water-dispersed Si microcolloids was used to synthesize bare (ligand-free) spherical silicon nanoparticles (Si-NPs) with low size dispersion and controllable mean size from a few nm to several tens of nm. In order to control the oxidation state of Si-NPs, the fragmentation was performed in normal oxygen-saturated water (oxygen-rich conditions) or in water disoxygenated by pumping with noble gases (Ag, He) before and during the experiment (oxygen-free conditions). XPS and TEM studies revealed that Si-NPs were composed of Si nanocrystals with inclusions of silicon oxide species, covered by SiOx (1 < x < 2) shell, while the total oxide content depended whether Si-NPs were prepared in oxygen-rich or oxygen-free conditions. When placed into a dialysis box, waterdispersed Si-NPs rapidly dissolved, which was evidenced by TEM data. In this case, NPs prepared under oxygen-rich conditions demonstrated much faster dissolution kinetics and their complete disappearance after 7-10 days, while the dissolution process of less oxidized counterparts could last much longer (25-30 days). Much fast dissolution kinetics of more oxidized Si-NPs was attributed to more friable structure of nanoparticle core due to the presence of numerous oxidation-induced defects. Laser-synthesized Si-NPs are of paramount importance for biomedical applications.

Plasmonic biosensors form the core label-free technology for studies of biomolecular interactions, but they still need a drastic improvement of sensitivity and novel nano-architectural implementations to match modern trends of nanobiotechnology. Here, we consider the generation of resonances in light reflected from 3D woodpile plasmonic crystal metamaterials fabricated by Direct Laser Writing by Multi-Photon Polymerization, followed by silver electroless plating. We show that the generation of these resonances is accompanied by the appearance of singularities of phase of reflected light and examine the response of phase characteristics to refractive index variations inside the metamaterial matrix. The recorded phase sensitivity (3*104 deg. of phase shift per RIU change) outperforms most plasmonic counterparts and is attributed to particular conditions of plasmon excitation in 3D plasmonic crystal geometry. Combined with a large surface for biomolecular immobilizations offered by the 3D woodpile matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.

Conference on Synthesis and Photonics of Nanoscale Materials XIII, San Francisco, CA, FEB 15-17, 2016; International audience; We examine absorption of electromagnetic radio-frequency (RF) radiation in aqueous suspensions of semiconductor (silicon) and metal (gold) nanoparticles (NPs) and theoretically investigate the heat release in these systems. The absorption of RF radiation is considered in both bulk electrolyte and the region around the NPs. Simulations show a strong dependence of the heating rate on electrical conductivity of the electrolyte rather than on that of NPs properties. The obtained results indicate that NPs can act as sensitizers of the RF induced hyperthermia for biomedical applications.

Conference on Synthesis and Photonics of Nanoscale Materials XIII, San Francisco, CA, FEB 15-17, 2016; International audience; We overview our on-going activities on the improvement of physical sensitivity of plasmonic biosensors. Our approach is based on the employment of phase properties of light reflected from plasmonic transducer instead of amplitude ones in order to improve its detection limit in studies of biomolecular interactions between a target analyte and its corresponding receptor. Originally, phase-sensitive biosensing concept was demonstrated in conventional Surface Plasmon Resonance (SPR) geometry using a thin Au film in Kretschmann-Raether arrangement, but the resulting sensitivity had some limitations because of a rough relief of the gold film surface. We then demonstrate the possibility for the extension of this concept to novel nanoscale architectures of designed plasmonic metamaterials in order to further improve the sensitivity of plasmonic biosensing technology. The latter approach also profits from much enhanced electric field in coupled nanostructures exposed to illumination, therefore enabling spectroscopy analysis (Raman, Fluorescence, IR etc) methods to increase sensitivity level (potentially down to single molecule).

ABSRACT A novel theoretical scheme is presented for a surface plasmon-polariton (SPP) planar refractive index sensor based on one of the simplest integrated optical devices available, the Mach-Zehnder interferometer (MZI), to monitor relative phase variations in waveguides. An SPP is excited with the Bragg grating imprinted into core and buffer layers of one of the arms of the MZI. The main principle of operation of this device is based on the large phase change of the waveguide mode transmitted through the grating during the SPP excitation caused by the change in the refractive index of the sensed layer in contact with the SPP supporting metal layer.

Femtosecond laser ablation of a gold plate in aqueous solutions has been used to form colloidal gold nanoparticles. Using different chemical environments during the fabrication, this method makes it possible to functionalize nanomaterials by an appropriate capping ligand. In particular, we were able to control the size and the reactivity of gold particles by using different polymers (dextran and polyethylene glycol). The size of the nanoparticles, measured by transmission electron microscopy (TEM), was found to be as low as 5 nm, in some cases. The addition of these capping agents also significantly improved the long term stability of gold particles. The produced nanoparticles exhibited a strong absorption band near 520 nm due to the surface plasmon resonance and a photoluminescence signal in the violet-blue spectral range. The functionalized nanoparticles produced are of significance in view of their bio-imaging and bio-sensing applications.

The progress in the development of Si-based Surface Plasmon Resonance sensing technology is reported. This technology uses multi-layer structures with a gold film and a silicon prism in the Kretschmann-Raether geometry and makes potentially possible the miniaturization and integration of the sensor device on a silicon-based microplatform. We show conditions of the simultaneous excitation for two plasmon polariton modes over both sides of the gold film using different intermediate layers, between the high-refractive index silicon prism and the gold, and examine their response in configurations of the conventional and nanoparticle-enhanced sensing. The system has been calibrated in real – time measurements of protein (Concanavalin A) adsorption.

Femtosecond laser ablation technique has been used to process Si and Au targets in vacuum, air and water environment. The threshold of ablation was found to be much lower for Si compared to Au and that was related to much better radiation absorption of Si. The values of the threshold were almost identical for vacuum, air and water in the case of Si (0.4 J/cm 2 0.2 J/cm 2 in the single and multi-pulse irradiation regime, respectively) and Au (0.9 J/cm 2 and 0.3 J/cm 2 ). Craters on the surface of Si and Au were essentially similar for low fluences, suggesting an involvement of the same radiation-related mechanism of material removal, whereas for high fluences significant differences could take place. In particular, quite different crater morphologies were observed during the laser ablation in water, including ones with nanoporous layers for Si and ones with concentric spheres for Au. The differences of morphologies for high laser fluences were explained by the involvement of plasma-related effects under the processing in relatively dense media.

An overview of laser-assisted nanofabrication methods, which has been developed in the Laser Processing Laboratory, is presented. All methods imply the laser-related ablation of material from a solid target and the production of nanoparticles or nanostructures. We consider the nanofabrication process in both the gaseous and in the liquid ambience under different parameters of laser radiation. A particular attention is given on the absence or presence of the plasma-related absorption of the laser radiation, which make possible different nanofabrication regimes. The methods lead to a production of nanomaterials, which are of importance for photonics and biosensing applications.

The femtosecond laser ablation of gold in aqueous solution has been used to produce colloidal gold nanoparticles. We consider the effect of size reduction through the use of aqueous cyclodextrin (α-CD, β-CD or γ-CD) solutions. Both the size reduction and the colloid stability depend on the type of CD, with the smallest, almost monodispersed and extremely stable particles prepared with β-CD, followed by slightly larger ones fabricated in γ-CD and α-CD. Several studies were carried out to elucidate the nature of the interaction between the gold and CDs. In particular, we studied the influence of pH on the size distribution and the electric charge of the gold particles surface. We examined the gold surface composition and determined the nature of the chemical groups on the gold. This enabled us to develop a model of chemical interactions between the gold and the CDs, which includes both a hydrophobic interaction of the Au 0 with the interior cavity of the CD and a hydrogen bonding of -O - groups, on the partially oxidized gold surface, with -OH groups of the CDs. These nanoparticles are of importance in biosensing applications.

Surface Plasmon Resonance (SPR) effect is considered in conditions of the absorption sensing. This sensing implies a formation of a thin absorbent layer with non-zero imaginary part of the dielectric constant on the sensor surface. We study the sensing response of the prism-based coupling system to the thickness increase of different absorbent layers (Au, Cu, Pt, Ag, Al, Si) in both the Attenuated Total Reflection (ATR) and Kretschmann-Raether geometries. The obtained results are of importance for the characterization of the absorbent metal- or semiconductor-based layers and development of nanoparticle-enhanced SPR sensors

We study possibilities of implementation of Surface Plasmon Resonance (SPR) sensors on purely silicon platform, in which SPR-supporting Au film is used with a silicon prism in the Kretschmann-Raether geometry. Based on theoretical and experimental analyses we have determined the conditions and parameters of SPR excitations on such a platform in the infrared light for configurations of bio- and gas sensing. The approach enables one to apply well-developed silicon microfabrication and integration methods for SPR technique, opening up the possibilities to miniaturize SPR bio- and chemical sensors.

Germanium wafer surface is modified by a technique of CO2-laser induced air breakdown processing, which was recently introduced and used to produce photoluminescent Si-based nanostructured layers. Structural and optical properties of the Ge-based layers, formed under the irradiation spot as a result of the processing, are characterized by different techniques (SEM, XPS, FTIR, XRD, and PL). It has been found that the layers present a porous structure, containing nanoscale holes, and consist of Ge nanocrystals embedded into GeO2 matrices. They exhibited strong photoluminescence (PL) in the green range (2.2 eV), which was attributed to defects in GeO2 matrix due to the presence of Ge-O modes with some OH vibration in the FTIR spectra. The layers are of importance for local patterning of nanostructures on semiconductors.

Possibilities of the control of the size and size distribution of the colloidal gold particles produced by the 110-fs laser ablation from a gold plate in aqueous environment are studied. Compared to pure deionized water, significant reduction of the mean size and size dispersion of the produced particles was observed when the ablation was performed in aqueous solutions of cyclodextrins (CDs), while the efficiency of the size reduction depended on the concentration and type of the CD (α-CD, β-CD or γ-CD). In particular, ablation at 10 mM of β-CD led to a production of 2-2.4 nm particles with narrow size distribution of less than 1-1.5 FWHM, which were very stable under aerobic conditions without any protective agent present. In the UV-vis spectrum, the gold nanoparticles exhibited an absorption band at 520 nm due to the generation of plasmon resonances. The fabricated particles are of importance for biosensing applications.

A microfabrication system with the use of a femtosecond laser was designed for 3D processing of industrially important materials. The system includes a 120 fs, 1 kHz laser; beam delivery and focusing system, systems for automated 3D target motion and real-time imaging of the sample placed in a vacuum chamber. The first tests of the system on the processing of stainless steel and silicon are presented. We established thresholds and regimes of ablation for both materials. It was found that at relatively low laser fluences I 10 J/cm2 provides much higher ablation rate of 30-100 nm/pulse, giving an opportunity of fast high-quality processing of materials. This regime is well suited for drilling of through holes and fast cutting of materials. However, it was found that fast ablation regime imposes additional requirements on the quality of delivery and focusing of the laser beam because of the presence of parasitic ablation around the main spot on the tail of the radiation intensity distribution. As industrial machining examples, we demonstrate heat-affected-zone free drilling of through holes in a 50 μm thick stainless steel foil and cutting of a 50 μm thick Si wafer with a net cutting speed of 8 μm/sec.

Si/SiOx films were fabricated by Pulsed Laser Ablation from a silicon target in a residual gas. The films were crystalline with minimal grain size of 2-4 nm and had a porous morphology. The film structure was found to be extremely sensitive to deposition conditions with porosity depending on the gas pressure during the deposition. In particular, the increase of helium pressure from 0.2 to 4 Torr in different depositions led to a gradual porosity (P) increase from 10% to 95%. The porosity increase was accompanied by a slight increase of mean crystal size in the deposit. It has been established that photoluminescence (PL) properties were different for films with different porosities. For low porous films (P 40%) were mainly determined by post-deposition oxidation phenomena. They led to an enhancement of PL bands around 1.6-1.7 eV and 2.2-2.3 eV, which were independent of deposition conditions. Similar 2.2-2.3 eV signals were observed after strong film oxidation through a thermal annealing of films in air or through a silicon ablation in oxygen-containing atmosphere. Mechanisms of film formation and PL origin are discussed.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A novel dry, vacuum-free laser-assisted method for a fabrication of nanostructured Si/SiOx layers on a silicon wafer is demonstrated. This method uses the phenomenon of air optical breakdown to modify a semiconductor surface. Pulsed radiation from a CO2 laser was focused on a silicon wafer to initiate the optical breakdown in atmospheric pressure air. After several breakdown initiations near the threshold of plasma production, a gray-tint layer was formed under the radiation spot on the silicon surface. The size of the processed area could be controlled by varying the radiation focusing conditions. Properties of the layers were studied by optical and SEM microscopies, XPS, XRD, Specular X-ray Reflectivity and PL spectroscopy. It was found that the layers had the porosity of about 75-80% and contained nanoscale holes and channels. They consisted of silicon nanocrystals embedded in SiO2 matrix and exhibited strong photoluminescence (PL) at 1.9-2.0 eV, which could be seen by naked eyes. Possible mechanisms of nanostructure formation and PL origin are discussed. The method can be used for a controlled local patterning of photoluminescent nanostructured materials.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A method of Pulsed Laser Ablation (PLA) from a Si target in an inert He ambient has been applied in combination with different post-deposition oxidation procedures for the fabrication of Si/SiO x nanocrystalline structures on Si substrates. After the growth of a thin natural oxide layer on the film surface, the structures exhibited a strong visible photoluminescence (PL), which remained stable even under a prolonged continuous irradiation of the sample by an excitation laser light. The peak energy of the PL spectra could be finely varied between 1.58 and 2.15 eV by a change in the residual gas pressure during the deposition process. An effect of thermal annealing on the PL properties of the Si/SiO x films has been examined and compared with the results for Si-based films produced by thermal evaporation from a Si target in vacuum. For both deposition techniques, the thermal annealing led to a dramatic change of PL properties giving rise to a fixed PL peak around 2.2 eV. Photoluminescent properties of particles formed by PLA with natural oxidation were different than those of thermally oxidized amorphous Si films. A recombination through oxygen- related compounds in the upper film layer is considered as the most probable mechanism of PL.