Surface Plasmon Resonance Of Gold Nanorods Research Articles

Transfers of the OAM and SAM densities of Bessel beam into the orbital and spin torques upon gold nanorod

The optomechanical interplay of a Bessel beam (an optical vortex) with a gold nanorod (GNR) in water is theoretically studied. The optical force and torque exerted on the GNR are analyzed using Maxwell's stress tensor to investigate the transfer rates of the orbital angular momentum (OAM) and the spin angular momentum (SAM) densities of Bessel beam into the orbital and spin torques upon GNR, respectively. From the numerical analysis, we find that the ratio of the orbital torque to the spin torque on the GNR matches the ratio of OAM to SAM of Bessel beam, corresponding to the order (topological charge) of the Bessel beam. This is to say that the transfer rate of the OAM density of Bessel beam into the orbital torque exerted on GNR nearly equals that of the SAM density into the spin torque. It implies that the spin-orbit interaction (SOI) of the optical vortex beam via a GNR is very weak. In addition, the spin torque is nearly equal to the corresponding zilch torque, the surface integral of Lipkin's zilch stress tensor. This could be because a GNR can be regarded as a perfect electric dipole particularly when the wavelength of the incident light is close to and little longer than the longitudinal surface plasmon resonance of GNR; the dipole's orientation is along the long axis of GNR. In contrast, the SOI via a spherical gold nanoparticle (GNP) is strong due to no preferred orientation for the equivalent dipole; a part of SAM of the optical vortex is transferred to the orbital torque upon GNP. Our results demonstrate that GNR, functioning as an ideal electric dipole, is a highly effective probe for detecting the OAM and SAM densities of an optical vortex individually through its distinct orbital and spin motions, without any crosstalk.

Designable Multiple Structural Colors Using Alkaline Periodate Oxidated Cellulose Nanocrystals and Gold Nanorods

AbstractStructural colors originating from ordered microstructures are popularly applied due to their versatile intrinsic advantages compared to dyes/pigments. Since the emergence of cellulose nanocrystals (CNCs) via alkaline periodate oxidation (PO‐CNCs) in 2019, here, their great potential as one‐dimensional nanomaterials for tunable optical materials combining with gold nanorods (GNRs) for the first time is demonstrated. The hybrid nanocomposite films with embedded and well‐organized PO‐CNCs and/or GNRs were prepared from hydrogel precursors after uniaxial stretching and air drying. In comparison with the solitary films containing pristine PO‐CNCs or GNRs, the birefringence of PO‐CNCs and surface plasmon resonance of GNRs synergistically expands the resulting color space. Based on their contributions, the solitary films containing only PO‐CNCs or GNRs can be stacked for widely spanning structural colors, such as red, green, and blue colors. Moreover, the relative angle between the stacked films can also be varied to manipulate the structural colors, providing a flexible method to construct designable optical materials. In brief, this study provides a general strategy for combining PO‐CNCs and GNRs into a novel series of nanocomposite materials and demonstrates their promising application potential in optics.

Biomimetic manganese-based theranostic nanoplatform for cancer multimodal imaging and twofold immunotherapy.

The limited clinical response and serious side effect have been challenging in cancer immunotherapy resulting from immunosuppressive tumor microenvironment (TME) and inferior drug targeting. Herein, an active targeting TME nanoplatform capable of revising the immunosuppressive TME microenvironment is designed. Briefly, gold nanorods (GNRs) are covered with silica dioxide (SiO2) and then coated manganese dioxide (MnO2) to obtain GNRs@SiO2@MnO2 (GSM). Myeloid-derived suppressor cells (MDSCs) membrane is further camouflaged on the surface of GSM to obtain GNRs@SiO2@MnO2@MDSCs (GSMM). In this system, GSMM inherits active targeting TME capacity of MDSCs. The localized surface plasmon resonance of GNRs is developed in near-infrared II window by MnO2 layer coating, realizing NIR-II window photothermal imaging and photoacoustic imaging of GSMM. Based on the release of Mn2+ in acidic TME, GSMM can be also used for magnetic resonance imaging. In cancer cells, Mn2+ catalyzes H2O2 into ·OH for (chemodynamic therapy) CDT leading to activate cGAS-STING, but also directly acts on STING inducing secretion of type I interferons, pro-inflammatory cytokines and chemokines. Additionally, photothermal therapy and CDT-mediated immunogenic cell death of tumor cells can further enhance anti-tumor immunity via exposure of CRT, HMGB1 and ATP. In summary, our nanoplatform realizes multimodal cancer imaging and dual immunotherapy.

Structural Colors by Synergistic Birefringence and Surface Plasmon Resonance.

One-dimensional nanomaterials including cellulose nanocrystals (CNCs) and gold nanorods (GNRs) are widely used in optical materials due to their respective inherent features: birefringence with accompanying light retardation and surface plasmon resonance (SPR). Herein, we successfully combine these properties of both nanorods to generate synergistic and readily tunable structural colors in hybrid composite polymer films. CNCs and GNRs are embedded either in the same or in separate films after unidirectional alignment in dynamic hydrogels. By synergistically leveraging CNCs and GNRs with diverse amounts in hybrid films or stacked separate films, wide-ranging structural colors are obtained, far beyond those from films solely with aligned CNCs or GNRs. Higher GNR contents enhance light absorption at 520 nm with promoted magenta colors, while more CNCs affect the overall phase retardation with light absorption between 400 and 700 nm between crossed polarizers. Moreover, adjusting the angles between films solely with CNCs or GNRs via a stacking/rotating technique successively manipulates colors with flexible film combinations. By rotating the films with aligned GNRs (0-180°), light absorption can traverse from ∼500 to 650 nm. Thus, tuning the adjustable synergism of birefringence of CNCs and SPR of GNRs provides great potential for structural colors, which enlightens inspirations for designing functional optical materials.

Plasmon mediated spectrally selective and sensitivity-enhanced uncooled near-infrared detector

Here, we present a high performance uncooled near-infrared (NIR) detector comprising of a giga hertz (GHz) solidly mounted resonator (SMR) and gold nanorods (GNRs) arrays. By coupling the localized surface plasmon resonances of GNRs, the resonator system exhibits optimized optical response to vis-NIR region. Both simulation and experiments demonstrate the hybrid GNRs-SMR exhibit significantly enhanced optical responsive sensitivity of NIR, the tunable aspect ratios (AR) of GNRs enable resonator respond sensitively to selected light. Specially, taking advantage of the acoustofluidic effect of SMR, the GNRs can be controllably and precisely modified on the microchip surface in an ultra-short time, which addresses one of the most fundamental challenges in the localized functionalization of micro/nano scale surface. The presented work opens new directions in development of novel miniaturized, tunable NIR detector.

Plasmonic‐Enhanced Cholesteric Films: Coassembling Anisotropic Gold Nanorods with Cellulose Nanocrystals

AbstractIncorporating photonic crystals with nanoplasmonic building blocks gives rise to novel optoelectronic properties that promise designing advanced multifunctional materials and electronics. Herein, the free‐standing chiral plasmonic composite films are designed by coassembling anisotropic plasmonic gold nanorods (GNRs) and rod‐like cellulose nanocrystals (CNCs). The effects of surface charge and concentration of the GNRs on the structure and optical properties of the CNC/GNR films are examined within this study. The CNC/GNR hybrid films retain the photonic characteristic of the CNCs host while concomitantly possessing the plasmonic resonance of GNRs. The negatively charged GNRs distribute uniformly in the layered CNCs host, inducing strong electrostatic repulsion among the CNCs and thus promoting the formation of a larger helical pitch than the case without GNRs. The positively charged GNRs decrease the chiroptical activity in the composite films with increasing the concentration of GNR, which is confirmed by the circular dichroism spectra. Notably, the surface plasmon resonances of GNRs enhance the fluorescence emission, which has been demonstrated by surface‐enhanced fluorescence signals in this work. This study sheds light on fabricating functional chiral plasmonic composite films with enhanced chiral plasmonics by utilizing CNCs as a dynamic chiral nematic template and adjusting surface charges.

Multispectral Plasmon of Anisotropic Core-shell Gold Nanorods@SiO2: Dual-band Absorption Enhancement with Coupling Dye Molecules

Direct evidence of effects of surface plasmon resonance(SPR) of gold nanorods(GNRs) on dual-band light absorption enhancement with coupling dye molecules was reported by introducing gold nanorod@SiO2(GNR@SiO2) core-shell nanoparticles into a photoelectric conversion system. GNR with asymmetric shape had unusual anisotropic SPR[transversal surface plasmon resonance(TSPR) and longitudinal surface plasmon resonance(LSPR)]. The excel-lent SPR of GNR made it a promising candidate as enhancing light absorption material to increase power conversion efficiency(PCE). The PCE was improved nearly 17.2% upon incorporating GNRs, mostly due to the increase in Jsc, while Voc and FF were unchanged. The improvement was mostly contributed by the SPR of the GNRs with coupling of N719. And there was also a complementary to N719 in visible light range. Therefore, SPR is an effective tool in improving the photocurrent and consequently enhancement of PCE. The TSPR and LSPR effects of GNRs on light harvesting were reflected in the increased monochromatic incident photon-to-electron conversion efficiency(IPCE). We also utilized finite-difference time-domain(FDTD) to investigate the light coupling of GNRs with TiO2. Compare to the base anode, the IPCE of optimized electrode showed significant improvement and peaks broadening at 500–600 nm and 610–710 nm. We got an increase in overall conversion efficiency from 6.4% to 7.5%.

Assembly of Gold Nanorods on HSA Amyloid Fibrils to Develop a Conductive Nanoscaffold for Potential Biomedical and Biosensing Applications

Today, Gold Nanorods have promised variety of applications in conjugation with biomolecules of interest. Discovery of functional amyloids has also been highlighted with possible use in designing high performance materials. To exploit dual properties of both Nano and Bio counterparts in new functional materials, this effort has focused on synthesis of a potential hybrid system of Gold nanorods (GNRs) and HSA amyloid fibrils to develop a conductive nanoscaffold. UV-Vis spectroscopy, Thioflavin T (ThT) assay, Far-UV Circular Dichroism (CD) spectropolarimetry, fluorescence and Transmission Electron microscopy were used to characterize formation of the nanostructures and amyloid fibrils. Surface plasmon resonance of GNRs was also monitored upon interaction with HSA amyloid fibrils, showing that the plasmonic component of the hybrid system has maintained its characteristic rod morphology without any perturbations. Analysis of Nyquist plots for the hybrid nanoscaffold showed that the electronic behavior of the hybrid system has been enhanced due to the presence of the assembled GNRs. Results of this investigation highlight the possibility of fabricating hybrid nano-bioscaffolds as promising candidates in versatile biomedical and biosensing applications.

Highly sensitive on-site detection of glucose in human urine with naked eye based on enzymatic-like reaction mediated etching of gold nanorods

Based on enzymatic-like reaction mediated etching of gold nanorods (GNRs), an ultrasensitive visual method was developed for on-site detection of urine glucose. With the catalysis of MoO42−, GNRs were efficiently etched by H2O2 which was generated by glucose-glucose oxidase enzymatic reaction. The etching of GNRs lead to a blue-shift of logitudinal localized surface plasmon resonance of GNRs, accompanied by an obvious color change from blue to red. The peak-shift and the color change can be used for detection of glucose by the spectrophotometer and the naked eyes. Under optimal condition, an excellent sensitivity toward glucose is obtained with a detection limit of 0.1μM and a visual detection limit of 3μM in buffer solution. Benefiting from the high sensitivity, the successful colorimetric detection of glucose in original urine samples was achieved, which indicates the practical applicability to the on-site determination of urine glucose.

Combined detection of breast cancer biomarkers based on plasmonic sensor of gold nanorods

In this study, a combined detection assay for determination of cancer antigen 15-3 (CA15-3) and copper level in breast cancer serum was developed by use of gold nanorod (GNR)-based plasmonic sensor. Rapid detection of tumor marker (CA15-3) can be accomplished through a simple transduction of optical signal induced by immune-reaction between CA15-3 and GNR@CA15-3 antibody. On the other hand, the copper-induced change of localized surface plasmon resonance of GNRs results in a direct readout of optical signal. Therefore, practical application for combined determination of CA15-3 and copper levels of human serum samples of breast cancer was performed. The results are close agreement with those given by the hospital or other standard approach, confirming this assay with high accuracy. The combined detection strategy provides potential applications for early diagnosing and monitoring the progress of malignant tumor.

Size-tunable synthesis of gold nanorods using pyrogallol as a reducing agent

A novel and facile seed-mediated method for the preparation of monodispersed gold nanorods (GNRs) is presented by introducing pyrogallol as a reductant. Fast Fourier transformation of high-resolution transmission electron microscopy reveals that the synthesized GNRs are single crystalline. The longitudinal surface plasmon resonance of GNRs can be finely tuned by varying silver ion concentrations or seed amounts. Also, both thick (diameter >30 nm) and thin (diameter <10 nm) GNRs with exceptional monodispersity can be well prepared by this method. These findings indicate that this method has a greater performance in controlling the morphology of GNRs than that of traditional approach with ascorbic acid as a reductant.

Pulsed laser induced microbubble in gold nanorod colloid

The characterization of a pulsed laser induced microbubble (PLIMB) in gold nanorod (GNR) colloid was studied experimentally. The generation of PLIMB is due to the optical breakdown in water. Using an ultrasonic transducer and a probing He–Ne laser associated with a photodetector, the photoacoustic (PA) signals and the bubble formation of the multi-cycled oscillation of a single PLIMB were measured simultaneously. Both results are in agreement to show that the lifetime of PLIMB is reduced as the gold concentration increases. This phenomenon is attributed to the plasmonic light scattering (Faraday–Tyndall effect) in GNR colloid; the energy for optical breakdown is reduced at the focus due to laser-beam defocusing. The effect is particularly pronounced at the longitudinal surface plasmon resonance of GNRs. In addition, the divergence angle of 532-nm CW laser beam through gold nanoparticle (GNP) colloid was measured. Our results show that the divergence angle increases as the concentration of GNP increases. This phenomenon again elucidates Faraday–Tyndall effect.

Effect of solution volume covariation on the growth mechanism of Au nanorods using the seed-mediated method

The effect of solution volume covariation on the growth mechanism of Au nanorods synthesized using a seed-mediated method was studied. The results from the ultraviolet–visible absorption spectra of gold nanorods (GNRs) revealed that the transverse surface plasmon resonance was ∼550nm for all GNR samples synthesized in various total volumes of growth solutions. The wavelength of longitudinal surface plasmon resonance of GNRs increased from 757 to 915nm, with the total volume of growth solution being raised from 10 to 320ml. Moreover, the calculated aspect ratio (AR) also increased from 3.55 to 5.21 while the total volume of growth solution increased from 10 to 320ml. Transmission electron microscopy microstructures showed that the growth mechanism of GNRs along 〈100〉 is in accordance with the hypothesis that the ratio of the number of monodispersed Au atoms existing in the growth solution to the number of seeds explain the behavior of Au atoms deposited on the nanorods with respect to all of the constituent concentrations in the growth solution on the AR of GNRs.

Manipulating the Collective Surface Plasmon Resonances of Aligned Gold Nanorods in Electrospun Composite Nanofibers

Surface plasmon resonance (SPR) is an interesting optical property that has been intensively studied in recent years. Herein, we report that the SPRs of gold nanorods (Au NRs) embedded in electrospun poly(vinyl alcohol) nanofibrous films can be manipulated via several approaches such as the change of Au NR percentage in the composite nanofibers, swelling-induced refractive index decrease of local environment, and swelling-induced increase of inter-rod distances among the embedded Au NRs. The electrospun composite nanofibrous films exhibit excellent sensing ability to the swelling solvents with short responsible time and remarkable reversibility. This study advances the fundamental understandings of plasmonic properties for electrospun composite nanofibrous films; thus, it can benefit the novel design of smart nanomaterials for broad sensing and nanophotonic applications.

Gold Nanorods Performing as Dual-Modal Nanoprobes via Metal-Enhanced Fluorescence (MEF) and Surface-Enhanced Raman Scattering (SERS)

The integration of metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS) onto single plasmonic nanoparticles is highly desirable to boost up accuracy and sensitivity in spectroscopic investigations. In this work, we demonstrate the feasibility of performing both MEF and SERS analysis on gold nanorods (GNRs) decorated with a unique molecular probe, here Rose Bengal (RB) fluorophore. While the cetyltrimethylammonium bromide layer on GNRs captures RB molecules preventing fluorescence quenching, the selective excitation of the two surface plasmon resonances of GNRs can trigger either the enhancement of fluorescence emission or Raman scattering. Both fluorescence enhancement mechanisms, i.e. increase of excitation rate and increase of quantum efficiency, promote an average 2.2-fold enhancement. For excitation with 785 nm laser line an average SERS enhancement of 1.7 × 105 is estimated and compared with the electromagnetic enhancement provided by finite-difference time-domain (FDTD) simulations. An extended dual-modal response of RB–GNRs conjugate is demonstrated by resonant excitation of both RB and GNRs with 532 nm laser line, which allows the surface-enhanced resonance Raman scattering (SERRS) and MEF signals to be detected simultaneously. The reporting abilities in SERS are demonstrated by conveying the Raman fingerprints of two molecular species concomitantly adsorbed on the surface of GNRs.

A gold nanorod-based optical DNA biosensor for the diagnosis of pathogens

A novel optical biosensor for detecting target DNA, utilizing gold nanorods (GNRs) as molecular probes is demonstrated. This sensor is based on simultaneous biorecognition-mediated hybridization of target DNA in a sandwich type manner with two different capture probe DNA sequences modified separately with identical sets of GNRs, which leads to aggregation of GNRs. The hybridization induced aggregation as revealed by TEM analysis, promotes the modulation of surface plasmon resonance of GNRs, which forms the basis of complementary target DNA detection from the Chlamydia trachomatis pathogen. Thermally induced reversible dissociation of hybridized DNA is demonstrated by melting analysis. The present sensing strategy is successfully demonstrated by detecting PCR amplified C. trachomatis pathogen gene isolated from human urine sample in a concentration range of 0.25–20 nM. Furthermore, this sensor displays excellent specificity by discriminating the target DNA versus other non-specific pathogenic genes.

Enhancing fluorescence of quantum dots by silica-coated gold nanorods under one- and two-photon excitation

Nano-composites of quantum dots (QDs) and gold nanorods (GNRs) or silica-coated GNRs (GNRs_SiO2) were synthesized. The attached GNRs modify the excitation intensity and spontaneous emission of QDs through the surface plasmonic effects. The fluorescence from QDs is enhanced and can be optimized by modifying the thickness of silica coated on GNRs, under both one- and two-photon excitations. The measurements of fluorescence intensity and lifetime demonstrate that the enhancement may be attributed to the matching of the localized surface plasmon resonance of GNR to the excitation wavelength. In addition to enhancing QD-fluorescence in QD-GNR@SiO2, GNRs also present as an effective contrast agent for bio-imaging, through light scattering and or two-photon emission, as well as for photo-thermal therapy. The composite's multifunctional characteristics are highly valuable and to be exploited in bio-applications.

Progesterone-binding cyst protein in breast tumor cytosol

In this study, a combined detection assay for determination of cancer antigen 15-3 (CA15-3) and copper level in breast cancer serum was developed by use of gold nanorod (GNR)-based plasmonic sensor. Rapid detection of tumor marker (CA15-3) can be accomplished through a simple transduction of optical signal induced by immune-reaction between CA15-3 and [email protected] antibody. On the other hand, the copper-induced change of localized surface plasmon resonance of GNRs results in a direct readout of optical signal. Therefore, practical application for combined determination of CA15-3 and copper levels of human serum samples of breast cancer was performed. The results are close agreement with those given by the hospital or other standard approach, confirming this assay with high accuracy. The combined detection strategy provides potential applications for early diagnosing and monitoring the progress of malignant tumor.