Photoacoustic imaging (PAI) is a rapidly growing imaging modality, which combines high contrast of optical absorption with deep penetration depth of ultrasound. When combined with endogenous contrast agents based on light-absorbing nanoparticles (NPs), PAI can visualize various biological processes and tissues. Here, we describe a simple experimental setup based on a tissue-mimicking phantom with flexible optical properties for studying photoacoustic (PA) response of NPs. Our approach is based on a polyacrylamide gel phantom with independently variable optical absorption and scattering. The phantom allows one to model and study PA response of contrast agents with diverse spatial distributions and concentrations. To demonstrate high potential of the developed experimental setup, we prepared a phantom with optical properties matching human prostate tissue and performed a PAI of laser-synthesized titanium nitride (TiN) NPs, distributed in a disk-shaped area, located 10 mm under the phantom surface. We believe that our approach will contribute the successful development of clinical PAI with NPs-based contrast agents.
Newly emerging nanomaterials promise a major advancement of methods of nuclear and radiative medicine for cancer treatment, as they can be used as carriers of diagnostic or therapeutic radionuclides, contrast agents in nuclear imaging modalities (PET, SPECT) or sensitizers of radiative therapies (X-ray, ion beams, etc.). However, nanotechnology-based approaches have reported a limited success so far due to a lack of suitable functional nanoformulations, which are safe, non-toxic, excretable from the body and have favorable pharmacokinetics for effective accumulation in the tumor. As follows from the results of our on-going research activities, many of the above-stated problems can we solved by the employment of nanomaterials fabricated by clean laser-ablative synthesis. Here, we review our recent data on some promising nanomaterials, prepared by this method, including biodegradable silicon (Si) nanoparticles (NPs), 152Sm-enriched samarium oxide NPs, and elemental bismuth (Bi) NPs, which can be used either as carriers/agents in radionuclide therapy, or sensitizers in radiative diagnostics or therapy. Advantages of proposed approach include exceptional purity and flexibility in synthesizing of NPs of required physico-chemical parameters (controlled size, shape, composition, and surface conditioning of NPs). Advances in laser-ablative fabrication of novel nanomaterials open up avenues for future implementations of nuclear and radiative medicine approaches for safe and efficient theranostics of tumors and metastasis.
Titanium nitride (TiN) nanoparticles (NPs) prepared by methods of laser ablation in liquids present a novel object, which promises attractive biomedical applications. Here, we review our recent advances in the elaboration of femtosecond laser ablation technique from a TiN target in liquid medium (here, isopropanol) to maximize the efficiency of TiN NPs synthesis and optimize their characteristics. Our experiments showed that the synthesis productivity is dependent on lateral velocity of laser beam scanning during laser ablation with the achievement of productivity saturation at a certain relatively high velocity. The observed phenomenon was attributed to the interaction of laser pulses with cavitation bubbles generated during the ablation process. In addition, we assessed photo heating properties of the synthesized TiN NPs in the near-IR range. It was found that TiN NPs with sizes in 20-50 nm range have the highest heating rate and can be heated to maximal temperatures. As demonstrated by our recent tests in vitro and in vivo, this size range is optimal for biomedical applications, which promises successful applications of these nanoparticles in phototherapy and imaging modalities.
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.
Silicon (Si) nanoparticles (NPs) synthesized by pulsed laser ablation in water are explored as sensitizers of photothermal therapy under a laser excitation in the window of relative tissue transparency. Based on theoretical calculations and experimental data, it is shown that the NPs can be heated up to temperatures above 42–50 °C by laser diode irradiation at 808 nm in continuous wave (CW) and quasi-continuous wave (QCW) regimes. Profiting from the laser-induced heating, a high efficiency Si-NPs as sensitizers of the hyperthermia of cells in Paramecium Caudatum model is demonstrated. The QCW regime is found to be more efficient, leading to complete cell destruction even under relatively mild laser irradiation conditions. The obtained data evidence a great potential in using laser-ablated Si-NPs as sensitizers of photohyperthermia in antibacterial or cancer therapy applications
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.
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 situ temperature monitoring with photoacoustic measurements is introduced in an integrated setup, specifically designed for photothermotherapy treatmentof the glioblastoma, aided by nanoparticles and HIFU blood-brain barrier opening.
The presentation will overview our on-going activities on laser ablative synthesis of plasmonic colloidal nanomaterials and their biomedical applications. Our approach is based on ultra-short (fs) laser ablation from a solid target or already formed water-suspended colloids, which makes possible the fabrication of ultrapure bare (ligand-free) nanoparticles having controlled mean size and low size dispersion. The presentation will describe different approaches to achieve appropriate characteristics of nanomaterials (Au-based nanomaterials and alternative structures) and overview their biomedical applications. In particular, we show that Au nanoparticles can efficiently enhance Raman signals from different biological objects. Profiting from the observed enhancement and purity of laser-synthesized nanomaterials, we demonstrate successful identification of 2 types of bacteria (Listeria innocua and Escherichia coli). We also show that bare metal nanoparticles synthesized by laser ablation can provide an order of magnitude better response in glucose oxidation tasks, which promises their use as elecrocatalysts in bioimplantable therapeutic devices. Finally, we overview applications of bare plasmonic nanomaterials in phototherapy and tissue engineering tasks
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] Kögler 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 in deionized water were used to fabricate ultrasmall (< 2 nm), bare (ligand-free) organic luminophore DCEtDCS nanoparticles, which exhibit aggregation enhanced emission in the green range (533 nm) with the quantum yield exceeding 58% and provide no concentration quenching. In contrast to chemically synthesized counterparts, laser-synthesized DCEtDCS nanoparticles do not contain any organic impurities due to their preparation in aqueous medium and do not require surfactants to stabilize colloidal solutions, which makes them highly suitable for intracellular uptake and bioimaging. The highly negative surface charge of these nanoparticles impeded their cellular uptake, but when the surface was coated with chitosan, a cationic polymer, intracellular uptake in microglia was achieved. Using in vitro model, we finally demonstrate the efficient employment of ultrasmall and surfactant free fluorescent organic nanoparticles prepared by laser ablation as markers in bioimaging.
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.
A gold target was ablated by femtosecond laser radiation in aqueous solutions of preliminarily prepared Si nanoparticles. The ablation process led to the formation of Au-based spherical colloids with the mean size around 5–10 nm and a weak abundance of larger species. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) analysis revealed the presence of Au and Si in colloid composition, while the stoichiometry of colloids did not depend on laser fluence during the fabrication experiments. The formation of Au-Si nanohybrid structure was explained by an effect of the interaction of laser-ablated Au nanoclusters with water-dispersed Si nanoparticles. The fabricated structures can be of importance for biomedical, catalysis, and photovoltaics applications.
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