Near-infrared Localized Surface Plasmon Resonance Research Articles

One-pot synthesis of wavy gold-silver alloy nanoplates with tunable elemental compositions: Optical and photothermal properties

We report a facile synthesis of AuAg alloy nanoplates in high purity, together with tunable elemental compositions and uniformity in size and morphology. The success of current work relies on the one-pot co-reduction of Au and Ag precursor in an ice-water bath with the presence of octadecyltrimethylammonium chloride (OTAC) as a capping agent. With the increase in Ag content, the localized surface plasmon resonance (LSPR) of AuAg alloy nanoplates exhibited a noticeable blue-shift from near-infrared (NIR) to visible region. Thanks to the well-defined NIR LSPR properties and broad spectral range, the current products exhibit a remarkably integrated high-quality photothermal feature as well as the efficient photothermal conversion. Meanwhile, the current AuAg alloy nanoplates demonstrate satisfying photothermal stability verified via continuous exposure and cyclic irradiation by an 808-nm laser. The present study offers a facile route to the preparation of two-dimensional AuAg alloy nanocrystals with tunable elemental compositions and validates their excellent responses towards photothermal measurements, which could find promising use in photothermy-based diagnosis and therapy.

Plasmonic Nanoassemblies: Tentacles Beat Satellites for Boosting Broadband NIR Plasmon Coupling Providing a Novel Candidate for SERS and Photothermal Therapy.

Optical theranostic applications demand near-infrared (NIR) localized surface plasmon resonance (LSPR) and maximized electric field at nanosurfaces and nanojunctions, aiding diagnosis via Raman or optoacoustic imaging, and photothermal-based therapies. To this end, multiple permutations and combinations of plasmonic nanostructures and molecular "glues" or linkers are employed to obtain nanoassemblies, such as nanobranches and core-satellite morphologies. An advanced nanoassembly morphology comprising multiple linear tentacles anchored onto a spherical core is reported here. Importantly, this core-multi-tentacle-nanoassembly (CMT) benefits from numerous plasmonic interactions between multiple 5 nm gold nanoparticles (NPs) forming each tentacle as well as tentacle to core (15 nm) coupling. This results in an intense LSPR across the "biological optical window" of 650-1100 nm. It is shown that the combined interactions are responsible for the broadband LSPR and the intense electric field, otherwise not achievable with core-satellite morphologies. Further the sub 80 nm CMTs boosted NIR-surface-enhanced Raman scattering (SERS), with detection of SERS labels at 47 × 10-9 m, as well as lower toxicity to noncancerous cell lines (human fibroblast Wi38) than observed for cancerous cell lines (human breast cancer MCF7), presents itself as an attractive candidate for use as biomedical theranostics agents.

Facile and rapid synthesis of emission color-tunable molybdenum oxide quantum dots as a versatile probe for fluorescence imaging and environmental monitoring.

Recent years have seen molybdenum oxide quantum dots (MoOx QDs) as a booming material due to their attractive physical and chemical properties. However, there is still a large demand for MoOx QDs with long-wavelength emission by a facile strategy but these are more challenging to obtain. Herein, we rationally designed and successfully prepared nitrogen and phosphorus co-doped green emitting MoOx QDs (N,P-MoOx QDs) through a microwave-assisted rapid method. They exhibit a maximum emission at 500 nm under a 430 nm excitation. Moreover, by controlling their sizes in the process, we find that such a strategy enables the tuning of the emission color of N,P-MoOx QDs from green to blue. N,P-MoOx QDs show a significant fluorescence response to pH changes, and also display pH-sensitive near-infrared localized surface plasmon resonance (LSPR) at 866 nm. An effective and simple pH probe with a dual-signal response is achieved using N,P-MoOx QDs. As environmental sensors, N,P-MoOx QDs can be applied for sensitive detection of the concentrations of permanganate and captopril, offering the linear range from 0.08 to 25 μM and 0.1 to 31 μM, respectively. Benefitting from the effect of doping nitrogen and phosphorus, the probe could detect a wide range of pH changes (2-9) and is endowed with superior biocompatibility. Further, it is successfully used to "see" the intracellular pH variation by fluorescence confocal imaging. These findings not only demonstrate the achievement of a promising multifunctional probe for biosensing and environmental detection, but also pave the way for the fabrication of transition metal oxide QDs with tunable optical properties.

Tunable Near-Infrared Localized Surface Plasmon Resonance of F, In-Codoped CdO Nanocrystals.

Nanocrystals (NCs) of transparent conducting oxides with a localized surface plasmon resonance (LSPR) in the near-infrared (NIR) spectral region show promising electrochromic properties for the development of a new generation of dynamic "smart windows". In this regard, we exploit thin films of F, In-codoped CdO (FICO) NCs as active coatings for electrochromic devices. The control over the dopants concentration in FICO NCs results in fine tuning of their LSPR across the NIR region of the electromagnetic spectrum. Highly transparent mesoporous electrodes were prepared from colloidal FICO NCs by in situ ligand exchange of the pristine organic capping ligands. This approach preserves the optical and electrical properties of native NCs and delivers highly homogeneous, nonscattering films with a good electronic coupling between the NCs. We achieved a dynamic control over the LSPR frequency by reversible electrochemical doping, hence a spectrally selective modulation of the optical transmittance in the NIR region of the solar spectrum, which carries nearly 50% of the whole solar heat. Spectroelectrochemical characterization, coloration efficiency, and switching kinetics results indicate that thin film based on FICO NCs are potential candidates for plasmonic electrochromic applications. Moreover, the high electron mobility and wide optical bandgap of FICO makes NCs of this material suitable for large-area devices capable of dynamically controlling the heat load coming from the solar infrared radiation, without affecting the visible light transmittance.

Semiconductor Plasmonic Nanocrystals with a Near-Infrared Localized Surface Plasmon Resonance

The techniques of preparation of layers of Cu2 – xSe semiconductor plasmonic nanocrystals (SPNC) with plasmonic resonances in near infrared region from toluene colloidal solution are described. It is shown that combining QDs with SPNC layers lead to the enhancement of optical response from the QDs. The PVA film makes it possible to optimize the QDs-SPNC interlayer distance and provide most efficient enhancement.

Controlled Synthesis of Cu2- xSe Nanoparticles as Near-Infrared Photothermal Agents and Irradiation Wavelength Dependence of Their Photothermal Conversion Efficiency.

The ability to manipulate the near-infrared (NIR) localized surface plasmon resonance absorbance of copper chalcogenide materials is of utmost importance for applications such as photothermal therapy (PTT). In this work, we manipulate the NIR absorbance of copper selenide (Cu2- xSe) nanoparticles (NPs) by precisely controlling their size and composition. We also introduce a facile method for transferring ultrasmall hydrophobic Cu2- xSe NPs into aqueous solution. We then elucidate the relationship between the irradiation wavelength and photothermal conversion efficiency for these materials. The resulting insights can advance the use of copper chalcogenide nanomaterials in PTT applications.

Vacancy engineering of Cu2-xSe nanoparticles with tunable LSPR and magnetism for dual-modal imaging guided photothermal therapy of cancer.

The vacancies in the semiconductor nanocrystals not only induce unique properties, but also provide spaces for engineering them with multifunctions by the introduction of other elements. Herein, the vacancy of Cu2-xSe nanoparticles was tuned by doping with magnetic ferric ions (Fe3+) at room temperature, and the position and intensity of the near-infrared localized surface plasmon resonance (LSPR) in the resultant nanostructure can be finely controlled by altering the feeding amount of Fe3+ ions. The results of the density-functional theory (DFT) calculations show that both doping and replacement reactions are favourable. Owing to its tunable near-infrared absorption and magnetic property, the obtained hybrid nanostructure was demonstrated to be a novel nanotheranostic agent for effective deep-tissue photoacoustic imaging, magnetic resonance imaging, and photothermal therapy of cancer.

Semiconductor Plasmonic Nanocrystals with a Near-Infrared Localized Surface Plasmon Resonance-=SUP=-*-=/SUP=-

Semiconductor Plasmonic Nanocrystals with a Near-Infrared Localized Surface Plasmon Resonance-=SUP=-*-=/SUP=-

Near-infrared localized surface plasmon resonance of self-growing W-doped VO2 nanoparticles at room temperature

Nanoparticles (NPs) of vanadium dioxide (VO2) in the metal state exhibit localized surface plasmon resonance (LSPR) at 1200–1600 nm, which fills the gap between the absorption ranges of silicon and the LSPR of conventional transparent conductor NPs (ZnO:Al, In2O3:Sn, etc.). However, two issues of the lithographic process for NP formation and the metal-insulator transition temperature (69 °C) higher than room temperature have made it difficult to use VO2 NPs for applications such as energy conversion devices, near infrared (NIR) light detectors, and bio-therapy. In this study, we developed a self-growing process for tungsten (W)-doped VO2 NPs that are in the metal state at room temperature, using sputter deposition and post-lamp annealing. The changes in the LSPR peak wavelengths with the NP size were well controlled by changing the deposited film thickness and oxygen pressure during the post-annealing treatment. The presented results resolve the difficulties of using the metal-insulator transition material VO2 for practical NIR utilization.

Strong Stimulated Mie Scattering From Plasmonic CuS Nanocrystals in Toluene or Pentane

We report here strong stimulated Mie scattering (SMS) from a grating formed by optically redistributed plasmonic CuS nanocrystals (NCs), which exhibit a strong near-infrared localized surface plasmon resonance. We demonstrate that CuS NCs dispersed in a solvent, such as toluene or pentane, interact strongly with light due to their large polarizability that arises from their high concentration of free charge carriers. The NCs redistribute in the intensity grating that is formed by the interference of forward pump light with backward Mie scattered light. This alignment generates a Bragg grating of CuS NCs, which produces efficient reflection to the plasmonically enhanced backward Mie scattering. We report SMS from CuS NCs suspended in toluene at varying concentrations, pumped by ~816-nm and ~10-ns laser pulses. At the optimum concentration and for a 2-cm cuvette length, the reflectivity (energy transfer efficiency from the input pump to the backward SMS) reached 29%, and the pump energy threshold was 4.8 times lower than that of stimulated Brillouin scattering in pure toluene. The time delay of the backward SMS pulse observed at lower pump energy levels is consistent with reflection from a grating formed by spatial redistribution due to drift mobility of nanoparticles. Changing the solvent from toluene to pentane that has lower viscosity, reduced the delay time, which is also consistent with the nanoparticle redistribution model. The temporal behavior, spectral line shape, and far-field distribution of the backward SMS are presented.

Roles of Sulfur Sources in the Formation of Alloyed Cu2–xSySe1–y Nanocrystals: Controllable Synthesis and Tuning of Plasmonic Resonance Absorption

Ternary alloyed Cu2–xSySe1–y nanocrystals (NCs) were synthesized by using a simple and phosphine-free colloidal approach, in which sulfur powder and 1-dodecanethiol (DDT) were used as sulfur sources. In both cases, the crystal phase transformed from cubic berzelianite to monoclinic djurleite structure together with the morphology evolution from quasi-triangular to spherical or discal with an increase of sulfur content. Accordingly, the near-infrared (NIR) localized surface plasmon resonance (LSPR) absorption of the as-obtained sulfur-rich NCs exhibited obvious red-shift of wavelength and widening of absorption width. When the sulfur powder was chosen as sulfur sources, the LSPR wavelength of the as-obtained alloyed Cu2–xSySe1–y NCs could be tuned from 975 to 1230 nm with a decrease of selenium content in the NCs. In contrast, the region of the red-shift could be up to 1250 nm for the alloyed NCs synthesized by incorporation of different DDT dosage into the reaction system. The different sulfur sources and the electron donating effects of the DDT as a ligand played an important role in the LSPR absorption tuning. This deduction could be testified by the post-treating the quasi-triangular Cu2–xSe NCs with DDT under different temperatures and over different reaction time, which exhibited a red-shift of LSPR wavelength up to 450 nm due to coordination of DDT to Cu atoms on the NC surface while incorporating some sulfur anions into the lattice. This study offers a convenient tool for tuning the LSPR absorption of copper chalcogenide NCs and makes them for application in biological and optoelectronic fields.

Synthesis of reduced-size gold nanostars and internalization in SH-SY5Y cells

The synthesis of large pentatwinned five-branched gold nanostars (GNS) has been modified so to obtain overall dimensions shrunk to 60% and a lower branches aspect ratio, leading to a dramatic blue shift of their two near-infrared (NIR) localized surface plasmon resonances (LSPR) absorptions but still maintaining one LSPR in the biotransparent NIR range. The interactions of polyethylene glycol (PEG) coated large and shrunk GNS with SH-SY5Y cells revealed that the large ones (DCI - diameter of the circumference in which GNS can be inscribed=76nm) are internalized more efficiently than the shrunk ones (DCI=46nm), correlating with a decreased cells surviving fraction.

Tuning and Locking the Localized Surface Plasmon Resonances of CuS (Covellite) Nanocrystals by an Amorphous CuPd x S Shell.

We demonstrate the stabilization of the localized surface plasmon resonance (LSPR) in a semiconductor-based core–shell heterostructure made of a plasmonic CuS core embedded in an amorphous-like alloyed CuPdxS shell. This heterostructure is prepared by reacting the as-synthesized CuS nanocrystals (NCs) with Pd2+ cations at room temperature in the presence of an electron donor (ascorbic acid). The reaction starts from the surface of the CuS NCs and proceeds toward the center, causing reorganization of the initial lattice and amorphization of the covellite structure. According to density functional calculations, Pd atoms are preferentially accommodated between the bilayer formed by the S–S covalent bonds, which are therefore broken, and this can be understood as the first step leading to amorphization of the particles upon insertion of the Pd2+ ions. The position and intensity in near-infrared LSPRs can be tuned by altering the thickness of the shell and are in agreement with the theoretical optical simulation based on the Mie–Gans theory and Drude model. Compared to the starting CuS NCs, the amorphous CuPdxS shell in the core–shell nanoparticles makes their plasmonic response less sensitive to a harsh oxidation environment (generated, for example, by the presence of I2).

Near infrared biosensor based on Classical Electromagnetically Induced Reflectance (Cl-EIR) in a planar complementary metamaterial

In the field of plasmonic metamaterials (MMs), the sub-wavelength metallic structures play a role similar to atoms in nature. Classical electromagnetically induced reflectance (Cl-EIR) is a classical phenomenon which is analogue to the EIR quantum phenomenon in atomic systems. A sensitive control of the Cl-EIR is crucial to a range of potential applications such as slowing light and biosensor. Here we report on our three-dimensional nanophotonic complementary planar metamaterial consisting of an array of three slot strips plasmonic that exhibits Cl-EIR phenomenon with magnetic and electric dipolar and quadruplar interaction between the plasmonic molecules. Simply by introducing symmetry broken of the proposed MM, the Cl-EIR can be dynamically tuned. We further demonstrate using a numerical simulation that the coupling between the plasmonic modes in one asymmetric case with changing the dielectric surrounding of the nano-structure to prove our design has a great potential for near-infrared localized surface plasmon resonance (LSPR) sensing applications. The changing of the used metal in thin-film was also proposed to explain the coupling effects between the bright and dark modes of the Cl-EIR electromagnetic spectra on sensitivity of our proposed nano-structure in plasmonic sensing. This work paves a promising approach to achieve plasmonic sensing devices. Actually, the reflection of more than 97% is observed which is very high for the EIR effect. Furthermore, the figure of merit (FOM) of 17.3 and the group index of 413 are obtained. These mentioned characteristics make the proposed metamaterial with potential to apply for ultrafast switches, bio-sensors, and slow-light devices.

Photothermal effect of gold nanostar patterns inkjet-printed on coated paper substrates with different permeability.

Inkjet printing of spherical gold nanoparticles is widely applied in the fabrication of analytical and diagnostics tools. These methods could be extended to non-spherical gold nanoparticles that can efficiently release heat locally when irradiated in the near infrared (NIR) wavelength region, due to localized surface plasmon resonance (LSPR). However, this promising application requires the ability to maintain high efficiency and tunability of the NIR LSPR of the printed nanoparticles. In this study stable inks containing PEGylated gold nanostars (GNS) were fabricated and successfully inkjet-printed onto differently coated paper substrates with different porosity and permeability. A pronounced photothermal effect was observed under NIR excitation of LSPR of the printed GNS patterns even at low laser intensities. It was found that beside the direct role of the laser intensity, this effect depends appreciably on the printing parameters, such as drop density (δ, drops/mm2) and number of printed layers, and, critically, on the permeability of the coated paper substrates. These results will promote the development of GNS-based printed platforms for local photothermal therapy.

Ultrafast Photodoping and Plasmon Dynamics in Fluorine-Indium Codoped Cadmium Oxide Nanocrystals for All-Optical Signal Manipulation at Optical Communication Wavelengths.

We show the ultrafast photodoping and plasmon dynamics of the near-infrared (NIR) localized surface plasmon resonance (LSPR) of fluorine-indium codoped cadmium oxide (FICO) nanocrystals (NCs). The combination of high temporal resolution and broad spectral coverage allowed us to model the transient absorption (TA) spectra in terms of the Drude model, verifying the increase in carrier density upon ultrafast photodoping. Our analysis also suggests that a change in carrier effective mass takes place upon LSPR excitation as a result of the nonparabolic conduction band of the doped semiconductor with a consequently high signal response. Both findings are combined in this new type of plasmonic material. The combination of large transmission modulation with modest pump powers and ultrafast recombination times makes our results interesting for all-optical signal processing at optical communication wavelengths. At the same time, our results also give insights into the physical mechanisms of ultrafast photodoping and LSPR tuning of degenerately doped semiconductor NCs.

Ratiometry, Wavelength, and Intensity: Triple Signal Readout for Colorimetric Sensing of Mercury Ions by Plasmonic Cu2-xSe Nanoparticles

In this study, we have reported a new colorimetric platform for sensitive and selective sensing of Hg2+ using near-infrared (NIR) plasmonic Cu2-xSe nanoparticles (NPs) as reporters. Because of ultrahigh affinity between Hg2+ and Se2–, the added Hg2+ can react with Cu2-xSe NPs and exchange their Cu+/Cu2+, yielding a HgSe layer around the host NPs. Accordingly, the absorption profiles of the Cu2-xSe NPs are modulated substantially: The absorbance at 400–600 nm is increased, and the NIR localized surface plasmon resonance dramatically decreases with a more than 150 nm bathochromic shift. Thus, the system possesses triple signal responses, namely, ratiometry, wavelength, and intensity, to the analytes simultaneously. Such uniquely multiple signal output not only provides more choices for the quantification, but also enhances the reliability in the analyte detection. By rationally choosing poly(allylamine hydrochloride) as the NP template, Hg2+ ions can be determined as ranging from 0–800 nM. The detection lim...

An easy hydrothermal synthesis of porous CuSySe1-y nanomaterials with broadly tunable near-infrared localized surface plasmon resonance

The ternary Cu2-xSySe1-y nanomaterials have attracted great attention due to their unique optical properties, but they are primarily synthesized by the hot-injection and high temperature solvent method, however they are complex and uneconomical. In the paper, we report a new facile method for the synthesis of monodispersed and uniform porous CuSySe1-y alloyed nanomaterials with tunable composition, size, and morphology. More importantly, the near-infrared localized surface plasmon resonance (NIR LSPR) wavelength of these CuSySe1-y alloyed nanomaterials can be broadly tuned from 1027 to 1400 nm, and the energy bandgap can be simultaneously tuned from 1.42 to 1.91 eV by adjusting the chalcogen ratio. This approach opens up a new route to access to synthesize other porous ternary alloyed nanomaterials with broadly tunable LSPR wavelength and energy bandgap, which will find potential applications in the photothermal therapy and photovoltaic conversion.

Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars.

The stability of thiol bonding on the surface of star-shaped gold nanoparticles was studied as a function of temperature in water and in a set of biologically relevant conditions. The stability was evaluated by monitoring the release of a model fluorescent dye, Bodipy-thiol (BDP-SH), from gold nanostars (GNSs) cocoated with poly(ethylene glycol) thiol (PEG-SH). The increase in the BDP-SH fluorescence emission, quenched when bound to the GNSs, was exploited to this purpose. A maximum 15% dye release in aqueous solution was found when the bulk temperature of gold nanostars solutions was increased to T = 42 °C, the maximum physiological temperature. This fraction reduces 3-5% for temperatures lower than 40 °C. Similar results were found when the temperature increase was obtained by laser excitation of the near-infrared (NIR) localized surface plasmon resonance of the GNSs, which are photothermally responsive. Besides the direct impact of temperature, an increased BDP-SH release was observed upon changing the chemical composition of the solvent from pure water to phosphate-buffered saline and culture media solutions. Moreover, also a significant fraction of PEG-SH was released from the GNS surface due to the increase in temperature. We monitored it with a different approach, that is, by using a coating of α-mercapto-ω-amino PEG labeled with tetramethylrhodamine isothiocyanate on the amino group, that after heating was separated from GNS by ultracentrifugation and the released PEG was determined by spectrofluorimetric techniques on the supernatant solution. These results suggest some specific limitations in the use of the gold-thiolate bond for coating of nanomaterials with organic compounds in biological environments. These limitations come from the duration and the intensity of the thermal treatment and from the medium composition and could also be exploited in biological media to modulate the in vivo release of drugs.

Size-, Shape-, and Composition-Controlled Synthesis and Localized Surface Plasmon Resonance of Copper Tin Selenide Nanocrystals

We report a robust methodology for synthesizing monodisperse copper-tin-selenide (CTSe) nanocrystals (NCs) of tunable size, shape, and composition including single-crystalline nanosheets, nanoplates, spheres, and tetrahedra. Both the identity and concentration of the selenium precursor play important roles in determining the morphology and crystal structure of the CTSe NCs. In contrast to previous studies, we demonstrated broad tunability of the Cu to Sn ratio. The size of CTSe NCs continuously decreased with increasing Sn incorporation. Moreover, the near-infrared (NIR) localized surface plasmon resonance (LSPR) in CTSe alloy NCs was tuned over a broad range by varying the Cu:Sn ratio. The LSPR red-shifted and decreased in intensity with increasing Sn content. This indicates that the free charge carrier concentration can be manipulated by varying the cation ratio. The cation deficiency responsible for self-doping in these NCs decreases with increasing Sn content. The resulting CTSe NCs and related materi...