This work is dedicated to laser engineering of spherical resonant Mie-excitonic nanoparticles from layered materials, particularly Transition Metal Dichalcogenides (TMDC). The proposed approach leverages femtosecond laser ablation and fragmentation in liquids for the fabrication of water-dispersed ultra-stable spherical TMDC nanoparticles (NPs) of variable size (5 – 250 nm). Such nanoparticles demonstrate exciting optical and electronic properties inherited from the 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 nanoparticles.
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.
We investigate conditions of excitation and properties of Plasmonic Surface Lattice Resonances (PSLR) over glass substrate-supported Au nanoparticle dimers (~100-200 nm) arranged in a periodic metamaterial lattice, in Attenuated Total Reflection (ATR) optical excitation geometry, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. We show that spectral sensitivity of PSLR to RI variations is determined by the lattice periodicity (~ 320 nm per RIU change in our case), while ultranarrow resonance lineshapes (down to a few nm full-widthat-half-maximum) provide very high figure-of-merit values evidencing the possibility of ultrasensitive biosensing measurements. Combining advantages of nanoscale architectures, including a strong concentration of electric field, the possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise a drastic advancement of current state-of-the-art plasmonic biosensing technology.
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 bio-molecular interactions between a target analyte and its corresponding receptor. Originally, phase-sensitive bio-sensing 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 meta-materials in order to further improve the sensitivity of plasmonic bio-sensing 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).
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