Gold nanoantennas are a new type of nanostars with long spikes and small cores and the ability to adjust localized surface plasmon resonance in the range from 600 to 1600 nm by changing the shape and size of nanoparticles. In this work, the morphometric and optical properties of gold nanoantennas are investigated depending on the concentration of gold seeds and hydrochloric acid. Transmission electron microscopy (TEM) reveals a decrease in the spike length and the core diameter of nanoantennas under an increase in the seed concentration. The reaction rate decreases after the addition of hydrochloric acid. With a minimal addition of hydrochloric acid, the length of the spikes increases. However, with an increase in the hydrochloric acid concentration, the length of the spikes decreases. Increasing the concentration of both seeds and hydrochloric acid leads to a shift of the plasmon resonance towards shorter wavelengths. The cell viability test showed negligible in vitro citotoxicity of nanoantennas for two cell lines.
Tags based on surface-enhanced Raman scattering spectroscopy (SERS tags) contains a plasmon-resonant core and Raman reporter molecules located in the area of high local electromagnetic field. These tags are widely used in bioimaging and sensing. Gap enhanced Raman tag (GERT) is a novel type of SERS tag which consists of a plasmon core coated by noble metal shell with Raman reporter molecules embedded between metal layers. The optical properties of these particles are determined by the material and size of the core and shell, the thickness of the internal gap containing reporter molecules, and also by the laser wavelength. From the point of view of its optical and chemical properties, gold is one of the most suitable materials for the synthesis of the core and shell. However, it is necessary to select the optimal parameters for the synthesis of GERTs with the maximum enhancement of the SERS signal. In this work we examined the dependence of SERS signal of gold nanorod-based GERTs from the thickness of outer gold shell by using a Raman spectrometer with a wavelength of 785 nm, which is inside the transparency window of biological tissues. It is known that the intensity of SERS signal from the Raman reporter molecules incorporated inside the intermetallic gap is highly dependent from the gold shell thickness. We found that with a decrease in the gold shell thickness from 51 nm a gradual decrease in the intensity of the SERS signal is observed.
Gold nanostars are one of the new types of nanoparticles with advantages such as plasmon resonance tunability and low toxicity. Therefore, gold nanostars are promising candidates for various biomedical applications including bioimaging, cell optoporation and plasmonic photothermal therapy (PTT) in NIR I, II, and III optical transparency windows of biotissues. However, the stability and possible transformation of gold nanostars under laser irradiation still remains unexplored. In this work, we studied the photomodification of gold nanostars under the 1064-nm nanosecond pulsed laser irradiation by the transmission electron microscopy and spectrophotometry. The photostability of nanostars depends on their morphology and the plasmonic properties. Specifically, for large nanostars with a plasmon resonance at 950 nm remarkable changes occur at a threshold pulse energy of 5 μJ. At this threshold, a significant part of nanostars spikes melts and most of the nanostars start to transform into gold spheres. For higher pulse energies of about 50 μJ, all stars transform into spheres. For smaller gold stars with a plasmon resonance at 680 nm, the changes are less pronounced. Up to pulse energy of 50 μJ, they retain the shape of stars and have spikes on their surface. Moreover, the complete transformation of these stars into spheres does not occur up to pulse energy of about 150 μJ. The obtained results can be important for optimization of PTT treatment with gold nanostars and nanosecond laser irradiation.
It is now believed that the on-resonance excitation of the plasmonic nanoparticle is necessary to increase the Raman signal intensity of nearby molecules. On this basis, researchers try to fabricate rationally designed nanoparticles for surface-enhanced Raman scattering (SERS) applications with plasmon resonance close to wavelength of excitation. However, existing experiments show inconsistent results of measuring the dependence of the enhancement factor as a function of nanopaticle plasmon resonance. To fill the gap, we use the method of controllable etching to prepare set of Au nanorod colloids with the equal concentration, nanorod width, shape and tunable plasmon resonance that incrementally spanned 650-920 nm. Nanorods were functionalized with 4-nitrobenzenethiol and surface-enhanced Raman spectra were measured in colloid under 785 nm laser excitation. As a result we observe weak correlation between nanorod plasmon peak and SERS response. The ratio of SERS signals for on-resonance and of-resonance excitation was below 2. Nanorods were further overgrowth to have dumbbell morphology. This transformation leads to strong increase in SERS enhancement factor. Thus tuning of nanoparticles shape is more important factor towards highest SERS response compared to nanoparticle plasmonic peak.
The widespread use of SERS for bioimaging led to the development of the novel types of labels called SERS tags. SERS tags based on a metal core with adsorbed Raman reporters and coated with one or more metal shells are called nanomatryoshkas. In this work we investigated nanomatryoshkas based on gold nanorods coated by 4-nitrobenzenethiol Raman reporter molecules with gold and silver shell (AuNRs@NBT@Au and AuNRs@NBT@Ag, respectively). By changing the conditions of synthesis we can regulate the presence or absence of a gap inside the gold nanomatryoshkas. Moreover, it was found that for these particles the SERS enhancement factor does not depend on the presence of a gap, for both cases enhancement factor is about 4×105. For nanomatryoshkas with a silver shell, it was found that the absence of a visible gap is a feature of these particles, in good agreement with the literature data.
Polymeric nanoparticles (NPs) are widely used for drug delivery applications due to high biodegradability, low toxicity and high loading capacity. The focus of this study is the development of photosensitizer Photosens (PS) loaded albumin NPs for efficient photodynamic therapy (PDT). To fabricate PS-loaded bovine serum albumin nanoparticles (BSA-PS NPs), we used a coacervation method with glutaraldehyde followed by passive loading of PS. Successful loading of PS was confirmed by appearance of characteristic peak in absorption spectrum which allows to determine the PS loading in BSA NPs. The synthesized BSA-PS NPs demonstrated low toxicity to HeLa cells at therapeutic concentrations of loaded PS. Compared to free PS solution, the synthesized BSA-PS NPs generated the singlet oxygen more effectively under laser irradiation at 660 nm. In addition, due to presence of various chemical groups on the surface of BSA-PS NPs, they are capable to adsorb on cell surface and accumulate in cells due to cellular uptake mechanisms. Owing to combination of PD and cell uptake advantages, BSA-PS NPs demonstrated higher efficacy of photodynamic damage to cancer cells as compared to free PS at equivalent concentrations. These results suggest that non-targeted BSA-PS NPs with high PD activity and low-fabrication costs of are promising candidates for transfer to PD clinic treatments.
Gold nanoshells are promising nanoparticles for biomedical applications such as biosensing, photothermal therapy, and surface enhanced Raman scattering. However, existing synthesis protocols produce polydisperse samples with extinction plasmonic spectrum much broader than that predicted by electromagnetic Mie simulations. Here we report on improved synthesis of gold nanoshells using monodisperse silica cores with very narrow size distributions of separated samples. As a result we were able to fabricate high quality silica/gold nanoshells with very narrow plasmon resonance peak, which is in good agreement with Mie calculations based on polydisperse TEM models. TEM images revealed a presence of dimers and trimers in as-prepared nonseparated samples. We performed extensive finite difference time-domain (FDTD) simulations to show that the plasmonic response of aggregated nanoshells results in enhanced extinction across NIR spectral band and in a minor broadening of the main plasmonic peak. To summarize, the improved synthetic technology produces high quality monodisperse silica/gold nanoshells which optical properties are in excellent agreement with electromagnetic simulations based on TEM size distributions.
Plasmon-resonant nanoparticles attached to cell membranes, under laser treatment can temporarily increase membrane permeability. In this paper, the influence of continuous-wave and pulsed (nanosecond) laser irradiation on living cells incubated with gold nanoparticles was investigated. Gold nanospheres, nanostars, and nanorods with different functionalization were used as plasmonic agents. The dependence between increase of medium temperature on the irradiation time was showed for nanostars and nanorods with different surface properties. Cells samples incubated with gold nanorods showed the highest temperature increase. Feasibility of cell optoporation by the use of gold nanospheres with variable functionalization was demonstrated. The cell membrane permeability was successfully enhanced as shown by the uptake of the fluorescent dye upon nanosecond laser treatment. Toxicity of the nanoparticles was estimated by MTT assay.
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