Plasmonic Photothermal Heating Research Articles

Quantification and description of photothermal heating effects in plasmon-assisted electrochemistry

A growing number of reports have demonstrated plasmon-assisted electrochemical reactions, though debate exists around the mechanisms underlying the enhanced activity. Here we address the impact of plasmonic photothermal heating with cyclic voltammetry measurements and finite-element simulations. We find that plasmonic photothermal heating causes a reduction in the hysteresis of the anodic and cathodic waves of the voltammograms along with an increase in mass-transport limiting current density due to convection induced by a temperature gradient. At slow scan rates, a temperature difference as low as 1 K between the electrode surface and bulk electrolytic solution enhances the current density greater than 100%. Direct interband excitation of Au exclusively enhances current density by photothermal heating, while plasmon excitation leads to photothermal and nonthermal enhancements. Our study reveals the role of temperature gradients in plasmon-assisted electrochemistry and details a simple control experiment to account for photothermal heating.

Plasmonic Photothermal Heating of Gold Nanoshell Solutions

We present a theoretical approach to theoretically investigate how gold core-shellnanoparticles dispersed in water thermally respond to near-infrared-regime laser illumination. First, the absorption cross section of gold nanostructures is calculated using Mie theory. Second, we determine the absorbed power density when the solution is exposed by the laser light. Here, the solution of nanostructures is assumed to be uniform and homogenous. Third, we analytically solve the transient bioheat equation to calculate time-dependent temperature increase. Our theoretical calculations quantitatively agree with previous experiments without any adjustable parameter.This approach would provide a reliable tool to understand photothermal effects in unexplored structures.

Improving the performance of a photonic PCR system using TiO2 nanoparticles

Nucleic acid amplification using polymerase chain reaction (PCR) method has been widely used in different fields such as agricultural science, medicine, pathogen identification, and forensics to name a few. Today, it seems inevitable to have a robust, simple PCR system for diagnostics at the point-of-care (POC) level. Many photonic PCR systems have been proposed in the literature that benefit from plasmonic photothermal heating to achieve the common PCR thermal cycling. However, non-homogeneous temperature distribution is a challenge in some of them. In the present work, to achieve more efficient gene amplification, the effect of adding TiO2 nanoparticles has been investigated in a photonic PCR benefiting from plasmonic photothermal heating. The system enjoys higher heating and cooling rates than those of conventional PCR systems while having much lower energy consumption. The average heating and cooling rates are 4.44 °C/s and 2.65 °C/s, respectively. The system demonstrates acceptable temperature stability and accuracy with negligible deviation from the set points. Furthermore, the system is capable of amplifying eight gene samples simultaneously which makes it a viable choice for POC diagnostics. A part of the Alcohol Oxidase gene has been amplified using the plasmonic thermal cycler. It is demonstrated that adding TiO2 nanoparticles with a proper concentration to the sample provides a more specific band that can be ascribed to more homogeneous temperature distribution owing to enhanced thermal conductivity. The best amplification of the target gene has been achieved with a concentration of 0.4 nM of nanoparticles.

Multiphysics Modeling of Plasmonic Photothermal Heating Effects in Gold Nanoparticles and Nanoparticle Arrays.

Induced hyperthermia has been demonstrated as an effective oncological treatment due to the reduced heat tolerance of most malignant tissues; however, most techniques for heat generation within a target volume are insufficiently selective, inducing heating and unintended damage to surrounding healthy tissues. Plasmonic photothermal therapy (PPTT) utilizes light in the near-infrared (NIR) region to induce highly localized heating in gold nanoparticles, acting as exogenous chromophores, while minimizing heat generation in nearby tissues. However, optimization of treatment parameters requires extensive in vitro and in vivo studies for each new type of pathology and tissue targeted for treatment, a process that can be substantially reduced by implementing computational modeling. Herein, we describe the development of an innovative model based on the finite element method (FEM) that unites photothermal heating physics at the nanoscale with the micron scale to predict the heat generation of both single and arrays of gold nanoparticles. Plasmonic heating from laser illumination is computed for gold nanoparticles with three different morphologies: nanobipyramids, nanorods, and nanospheres. Model predictions based on laser illumination of nanorods at a visible wavelength (655 nm) are validated through experiments, which demonstrate a temperature increase of 5 °C in the viscinity of the nanorod array when illuminated by a 150 mW red laser. We also present a predictive model of the heating effect induced at 810 nm, wherein the heating efficiencies of the various morphologies sharing this excitation peak are compared. Our model shows that the nanorod is the most effective at heat generation in the isolated scenario, and arrays of 91 nm long nanorods reached hyperthermic levels (an increase of at least 5 °C) within a volume of over 20 μm3.

Surface plasmon resonance and defects on tungsten oxides synergistically boost high-selective CO2 reduction for ethylene

Photocatalytic CO2 reduction reaction (CO2-RR) driven by solar energy is one expected “green technology” to produce hydrocarbon, however, the high-valuble C2/Cx-compounds converted from CO2 face great challenges. Herein, high-selective ethylene production is achieved via photocatalytic CO2-RR by using plasmonic tungsten oxides as catalyst under solar light irradiation. Tungsten oxides (WO3-x-2) synthesized by using acid-assisted solvothermal method exhibits thin amorphous surface structure with abundant oxygen vacancies and low-valence tungsten ions (26.1 mol% W5+ and 7.1 mol% W4+). Under full-spectrum light irradiation, ethylene generation rate of WO3-x-2 is 61.6 μmol g − 1h − 1 (selectivity of 89.3%) and is 20-fold higher than that of WO3-x-0 with thick amorphous surface. The amorphous surface of tungsten oxides with abundant defects is clearly observed by atomic-resolution high-angle annular dark field scanning transmission electronic microscopy (HAADF-STEM). Light-dependent photocatalytic results demonstrate the synergetic effect of oxygen vacancies, plasmonic hot electrons and photothermal heating boosting CO2-RR on tungsten oxide catalysts for ethylene generation. One possible ethylene generation pathway is proposed based on the detected intermediates during CO2-RR. As far as we known, our work is the first report on plasmonic photocatalytic CO2-RR for high-selective ethylene generation.

Plasmonic photothermal heating of gold nanostars in a real-size container: multiscale modelling and experimental study

The ability of noble metal nanoparticles (NPs) to convert light into heat has triggered a lot of scientific interest due to the numerous potential applications, including, e.g. photothermal therapy or laser-based nanopatterning. In order for such applications to be practically implemented, the heating behaviour of NPs embedded in their surrounding medium has to be thoroughly understood, and theoretical models capable of predicting this behaviour must be developed. Here we propose a multiscale approach for modelling the photothermal response of a large ensemble of nanoparticles contained within a cm-scale, real-size container. Electromagnetic field, ray tracing and heat transfer simulations are combined in order to model the response of nanostars and nanospheres suspensions contained within a common Eppendorf tube. To validate the model, gold nanostars are then synthesised and characterized by electron microscopy and optical spectroscopy. Laser-induced heating experiments are conducted by irradiating colloid-filled Eppendorf tubes with a 785 nm continuous wave laser and monitoring by a thermographic camera. The experimental results confirm that the proposed model has potential for predicting and analysing the heating efficiency and temperature dynamics upon laser irradiation of plasmonic nanoparticle suspensions in real-scale containers, at cm3 volumes.

Cellulose paper support with dual-layered nano-microstructures for enhanced plasmonic photothermal heating and solar vapor generation.

Plasmonic nanoparticles, such as gold nanoparticles (AuNPs), have been actively applied in solar vapor generation for seawater desalination and water purification, owing to their photothermal heating performances. Such nanoparticles have been frequently anchored within porous supporting materials to ensure easy handling and water absorption. However, there has been limited progress in improving the transport efficiency of light to nanoparticles within porous supports to achieve more effective photothermal heating. Here, we show an enhanced light absorption of AuNPs by supporting on a cellulose paper with tailored porous structures for efficient photothermal heating. The paper consists of AuNP-anchored cellulose nanofibers and cellulose pulp as the top and bottom layers, respectively, which provides dual-layered porous nano–microstructures in the perpendicular direction. Then, the bottom layer with pulp-derived microstructures reflects the transmitted light back to AuNPs within the top layer, which improves their light absorptivity. Thus, under 1 sun illumination, the dual-layered paper demonstrates superior performance in photothermal heating (increases from 28 °C to 46 °C) and solar vapor generation (1.72 kg m−2 h−1) compared with the single-layered AuNP-anchored cellulose nanofiber paper even at the same AuNP content. Furthermore, the water evaporation rate per AuNP content of the dual-layered paper is more than 2 times higher than those of the state-of-the-art AuNP-anchored porous materials under the same light irradiation. This strategy enables the efficient use of precious plasmonic nanoparticles for further development of solar vapor generation.

Photothermal effects on protein adsorption dynamics of PEGylated gold nanorods

The effect of thermoplasmonic heating on the dynamics of the protein corona around polyethylene glycol (PEG) coated gold nanorods (GNRs) is reported. GNRs were surface-modified with densely packed shells composed of thiolated PEGs bearing carboxyl and/or amine end-terminal groups, which led to negatively, positively or neutral charged GNRs. The three types of PEGylated GNRs, although with subtle differences among them, present weak interactions (binding dissociation constants in the μM range) with the model protein bovine serum albumin (BSA), as determined by different methods including gel electrophoresis, laser Doppler anemometry and isothermal titration calorimetry (ITC). In general, plasmonic photothermal heating significantly changed the composition of the protein corona around GRNs, particularly, on the positively charged ones. Moreover, a pre-formed BSA corona on the PEGylated GNRs further decreased their already reduced uptake by cells. However, photothermal treatment of BSA-coated GNRs only produced a significant decreased internalization in the case of non-PEGylated control samples. Overall, our results indicate that differently surface charged PEGylations on GNRs affects the dynamics of protein corona formation, which is particularly relevant after photothermal treatment. Such effects are nonetheless non-significant concerning cellular uptake.

Monitoring the death of single BaF3 cells under plasmonic photothermal heating induced by ultrasmall gold nanorods

Morphological changes and trypan-blue staining are temporally tracked in single cellsviaoptical microscopy after plasmonic photothermal heating.

Laser Auto Fluorescence and Dye-enhanced Spectroscopic Detection of Normal and Cancerous Human Lung Cell Lines and Plasmonic Photothermal Heating

This work describes the results of laser autofluorescence, dye-enhanced fluorescence spectroscopy of normal MRC-5 and cancerous QU-DB human lung cell lines and the effect of gold nanoshells heating on the cells. It was shown that the intensity ratio of MRC-5 to QU-DB 80 (ΔR) and the shape factor (RP) can be appropriate indicators of normal and cancerous cells for primary and secondary peaks at 500 nm and 590 nm respectively. About 5 nm red shift was observed in the case of cancerous cells. Highest temperatures of about 51 and 39.5?C were achieved for (S3, S4) and (S5, S6) respectively. The percentage of damaged cells and nanoshells density are expected to decrease with radial distance from the center of the beam. The results also indicated an increasing degree of apoptosis with increasing the laser power, which critically governs the quality and the degree of laser-hyperthermia. The matrix temperature is thought to vary due to possible thermal overlapping of a larger fraction of NSs, agglomeration and clustering.

Remote Control of Mammalian Cells with Heat-Triggered Gene Switches and Photothermal Pulse Trains.

Engineered T cells are transforming broad fields in biomedicine, yet our ability to control cellular activity at specific anatomical sites remains limited. Here we engineer thermal gene switches to allow spatial and remote control of transcriptional activity using pulses of heat. These gene switches are constructed from the heat shock protein HSP70B' (HSPA6) promoter, show negligible basal transcriptional activity, and activate within an elevated temperature window of 40-45 °C. Using engineered Jurkat T cells implanted in vivo, we use plasmonic photothermal heating to trigger gene expression at specific sites to levels greater than 200-fold. We show that delivery of heat as thermal pulse trains significantly increase cellular thermal tolerance compared to continuous heating curves with identical area-under-the-curve (AUC), enabling long-term control of gene expression in Jurkat T cells. This approach expands the toolkit of remotely controlled genetic devices for basic and translational applications in synthetic immunology.

Chain Length and Solvent Control over the Electronic Properties of Alkanethiolate-Protected Gold Nanoparticles at the Molecule-to-Metal Transition.

Alkanethiolate protected gold nanoparticles are one of the most widely used systems in modern science and technology, where the emergent electronic properties of the gold core are valued for use in applications such as plasmonic solar cells, photocatalysis, and photothermal heating. Though choice in alkane chain length is not often discussed as a way in which to control the electronic properties of these nanoparticles, we show that the chain length of the alkyl tail exerts clear control over the electronic properties of the gold core, as determined by conduction electron spin resonance spectroscopy. The control exerted by chain length is reported on by changes to the g-factor of the metallic electrons, which we can relate to the average surface potential on the gold core. We propose that the surface potential is modulated by direct charge donation from the ligand to the metal, resulting from the formation of a chemical bond. Furthermore, the degree of charge transfer is controlled by differences between the dielectric constant of the medium and the ligand shell. Together, these observations are used to construct a simple electrostatic model that provides a framework for understanding how surface chemistry can be used to modulate the electronic properties of gold nanoparticles.

Investigation of thermal damage of tissues embedded with large blood vessels during plasmonic photo-thermal heating (PPTH)

Purpose – The large blood vessels (LBV) would act as a heat sink and hence play a significant role during photo-thermal therapy. Gold nanoshell was considered as a high-heat absorbing agent in photo-thermal heating to reduce the cooling effect of LBV. The heat sink effect of LBV results in insignificant irreversible tissue thermal damage. The paper aims to discuss these issues. Design/methodology/approach – In this paper, the thermal history of tissue embedded with LBV during photo-thermal heating were calculated using finite element-based simulation technique. A volumetric laser source term based on modified Beer-Lambert law was introduced to model laser heating. The numerically predicted temperature drop was validated against that of previously performed experiments by the authors on tissue mimic embedded with simulated blood vessels. In the later part of the study, Arrhenius equation was coupled with the energy equation to investigate and report the irreversible thermal damage to the bio-tissues. Findi...

Plasmonic Biofoam: A Versatile Optically Active Material.

Owing to their ability to confine and manipulate light at the nanoscale, plasmonic nanostructures are highly attractive for a broad range of applications. While tremendous progress has been made in the synthesis of size- and shape-controlled plasmonic nanostructures, their integration with other materials and application in solid-state is primarily through their assembly on rigid two-dimensional (2D) substrates, which limits the plasmonically active space to a few nanometers above the substrate. In this work, we demonstrate a simple method to create plasmonically active three-dimensional biofoams by integrating plasmonic nanostructures with highly porous biomaterial aerogels. We demonstrate that plasmonic biofoam is a versatile optically active platform that can be harnessed for numerous applications including (i) ultrasensitive chemical detection using surface-enhanced Raman scattering; (ii) highly efficient energy harvesting and steam generation through plasmonic photothermal heating; and (iii) optical control of enzymatic activity by triggered release of biomolecules encapsulated within the aerogel. Our results demonstrate that 3D plasmonic biofoam exhibits significantly higher sensing, photothermal, and loading efficiency compared to conventional 2D counterparts. The design principles and processing methodology of plasmonic aerogels demonstrated here can be broadly applied in the fabrication of other functional foams.

Nanoparticle-Assisted Heating Utilizing a Low-Cost White Light Source

In this experimental study, a filtered white light is used to induce heating in water-based dispersions of 20 nm diameter gold nanospheres (GNSs)—enabling a low-cost form of plasmonic photothermal heating. The resulting temperature fields were measured using an infrared (IR) camera. The effect of incident radiative flux (ranging from 0.38 to 0.77 W·cm−2) and particle concentration (ranging from 0.25–1.0 × 1013 particles per mL) on the solution's temperature were investigated. The experimental results indicate that surface heat treatments via GNSs can be achieved through complementary tuning of GNS solutions and filtered light.

Implantable Lanterns for Cancer Therapy

Implantable illumination devices enable selective thermal and drug therapy of deep tumors.

Plasmonic Photothermal Heating of Intraperitoneal Tumors through the Use of an Implanted Near-Infrared Source

Plasmonic nanomaterials including gold nanorods are effective agents for inducing heating in tumors. Because near-infrared (NIR) light has traditionally been delivered using extracorporeal sources, most applications of plasmonic photothermal therapy have focused on isolated subcutaneous tumors. For more complex models of disease such as advanced ovarian cancer, one of the primary barriers to gold nanorod-based strategies is the adequate delivery of NIR light to tumors located at varying depths within the body. To address this limitation, a series of implanted NIR illumination sources are described for the specific heating of gold nanorod-containing tissues. Through computational modeling and ex vivo studies, a candidate device is identified and validated in a model of orthotopic ovarian cancer. As the therapeutic, imaging, and diagnostic applications of plasmonic nanomaterials progress, effective methods for NIR light delivery to challenging anatomical regions will complement ongoing efforts to advance plasmonic photothermal therapy toward clinical use.

Photothermal Efficiencies of Nanoshells and Nanorods for Clinical Therapeutic Applications

With clinical trials for photothermal tumor ablation using laser-excited tunable plasmonic nanoparticles already underway, increasing understanding of the efficacy of plasmonic nanoparticle-based photothermal heating takes on increased urgency. Here we report a comparative study of the photothermal transduction efficiency of SiO2/Au nanoshells, Au2S/Au nanoshells, and Au nanorods, directly relevant to applications that rely on the photothermal response of plasmonic nanoparticles. We compare the experimental photothermal transduction efficiencies with the theoretical absorption efficiencies for each nanoparticle type. Our analysis assumes a distribution of randomly oriented nanorods, as would occur naturally in the tumor vasculature. In our study, photothermal transduction efficiencies differed by a factor of 3 or less between the different types of nanoparticle studied. Both experiment and theory show that particle size plays a dominant role in determining transduction efficiency, with larger particles more efficient for both absorption and scattering, enabling simultaneous photothermal heating and bioimaging contrast enhancement.