Localized Surface Plasmon Resonance Linewidth Research Articles

In Situ Photoreversible Tuning of Chemical Interface Damping in Single Gold Nanorods Through Cucurbit[8]uril-Based Host-Guest Interactions.

Chemical interface damping (CID) is a recently proposed plasmon-damping pathway based on the interfacial hot-electron transfer from metal to adsorbate molecules. However, the in situ reversible tuning of CID in single gold nanorods (AuNRs) has remained a considerable challenge. In this study, we used total internal reflection scattering microscopy and spectroscopy to investigate the CID induced by p-aminoazobenzene (p-AAB), which has fast photoisomerization characteristics, attached to single AuNRs. We demonstrated the in situ reversible tuning of CID in single AuNRs by switching between ultraviolet (UV, 365 nm) and visible (vis, 465 nm) irradiation to induce photoresponsive structural conversions between the cis and trans forms of p-AAB in ethanol, leading to different lowest unoccupied molecular orbital (LUMO) energies for both forms. The localized surface plasmon resonance (LSPR) line width was wide under vis irradiation but narrow under UV irradiation, indicating that hot electrons are more efficiently transferred to trans-p-AAB with a low LUMO energy level. We further investigated the in situ photoreversible tuning of CID by manipulating supramolecular host-guest interactions between cucurbit[8]uril (CB[8]) and p-AAB in the single AuNRs. Additionally, real-time in situ reversible tuning of CID in single AuNRs was achieved through photonic switching of the cis-trans forms of p-AAB inside CB[8]. The LSPR line width was narrow under vis irradiation but gradually widened under UV irradiation before narrowing again upon returning to vis irradiation, unlike the case with p-AAB only. These results can be ascribed to the fact that cis-p-AAB completely encapsulated within CB[8] in water is thermodynamically more favorable than trans-p-AAB. Therefore, we have discovered a new strategy for tuning the CID by performing p-AAB photoisomerization and adjusting the wavelength of incident light in single AuNRs. In addition, this study demonstrates that CID can be effectively applied to the development of biosensors to detect guest molecules and their structural changes inside the cavity of CB[8] in single AuNRs.

Tuning of chemical interface damping in single gold nanorods through pH-dependent host-guest interactions using cucurbit[6]uril.

Chemical interface damping (CID) in gold nanorods (AuNRs) arises from direct hot electron transfer from Au to adsorbed molecules. Despite recent studies on CID, its tunability in single AuNRs remains challenging. Herein, we present a method for in situ control of CID in single AuNRs using pH-dependent host-guest supramolecular interactions. We employ cucurbit[6]uril (CB[6]), a well-known host molecule capable of encapsulating and releasing guest molecules, along with bis(3-aminopropyl)amine (BAPA) as guest molecules forming a complex with CB[6] (CB[6]-BAPA). CID is induced by attaching the CB[6]-BAPA complex on AuNR surfaces through a strong Au-amine interaction. In addition, in situ tuning of CID is achieved by releasing CB[6] from the complex using a NaOH solution. Successful CB[6]-BAPA complex formation, their attachment onto AuNRs, and CB[6] release from the complex are confirmed through changes in the localized surface plasmon resonance (LSPR) peak and LSPR linewidth, alongside mass analysis. Therefore, this study offers a new method for in situ CID tuning using CB[6]-based pH-sensitive host-guest interactions in individual AuNRs. This study can be further used in CB[6]-based photochemical processes and biosensing studies.

Chemical interface damping in single gold nanorods coated with silver via hot electron‐mediated photoreduction

AbstractHerein, we investigated the photoreduction of silver (Ag) ions on gold nanorods coated with mesoporous silica shell (AuNRs@mSiO2) induced by hot electrons generated in Au via localized surface plasmon resonance (LSPR) excitation. In addition, we investigated chemical interface damping (CID) using pyridine as the adsorbate in single Ag‐coated AuNRs@mSiO2. The Ag deposition caused a blue shift and linewidth broadening of the LSPR peak of the AuNRs@mSiO2. The subsequent chemisorption of pyridine on Ag‐coated AuNRs@mSiO2 resulted in a red shift and additional LSPR linewidth broadening. Finally, we demonstrated real‐time time‐dependent changes in LSPR peak wavelength and linewidth during the sequential processes of hot electron‐mediated Ag deposition and pyridine adsorption on a single AuNR@mSiO2 in a flow cell. Therefore, we provided a deep understanding of hot electron‐triggered Ag coating and CID induced by pyridine adsorption in single AuNRs@mSiO2 coated with Ag.

Tale of Two Resonances: Waveguide–Plasmon Coupling and High Q-Factor Engineering on the Nanoscale

Localized surface plasmon (LSP) excitations provide an efficient strategy for advancing nanophotonic designs and applications where strong field enhancement and confinement are often required on the nanoscale. They represent an important plasmonic paradigm for achieving strong light–matter interactions in both linear and nonlinear regimes, enabling the development of high-performance chemical and biological sensing approaches and nonlinear optics with low light intensities. However, the LSP resonance line width, limited by both radiative and resistive losses of metallic nanostructures, is significantly larger than the line width of the waveguided modes supported by low-loss dielectric microcavities with a significantly lower field confinement. Hybrid microcavity–plasmonic systems are, therefore, often used to reduce the resonant line width which improves the detection spectral resolution while maintaining strong confinement. Employing the remarkable quality factors of whispering gallery mode (WGM) microresonators, the hybrid LSP-WGM systems demonstrate sensing capabilities down to the single-molecule level. In this Perspective, we review the recent advances in the hybridization of LSPs and WGMs, focusing on the fundamental understanding of the underlying coupling mechanisms and corresponding mode hybridization regimes. We further discuss opportunities for applying heterogeneous plasmonic–photonic integration to tailor the nanoscale light–matter interactions and realize novel waveguide–plasmon coupling based nontrivial responses and highlight their prospective applications in quantum optics, chiral spin-optics, nonlinear nanophotonics, and sensing.

Influence of oxygen plasma treatment on structural and spectral changes in gold nanorods immobilized on indium tin oxide surfaces.

Oxygen plasma treatment is commonly used to sterilize gold nanoparticles by removing chemical contaminants from their surface while simultaneously inducing surface activation and functionalization of nanoparticles for biological, electrocatalytic, or electrochemical studies. In this study, we investigate the influence of oxygen plasma treatment on structural and localized surface plasmon resonance (LSPR) spectral changes of anisotropic gold nanorods (AuNRs) immobilized on an indium tin oxide (ITO) glass substrate. Unlike AuNRs deposited on a glass slide, no noticeable structural change or deformation of AuNRs on ITO was observed while increasing the oxygen plasma treatment time. This result indicates that ITO provides structural stability to AuNRs immobilized on its surface. Additionally, single-particle scattering spectra of AuNRs showed the broadening of LSPR linewidth within 60s of oxygen plasma treatment as a result of the plasmon energy loss contributed from plasmon damping to ITO due to the removal of capping material from the AuNR surface. Nevertheless, an increase in the surface charge on the AuNR surface was observed by narrowing the LSPR linewidth after 180s of plasma treatment. The electrochemical study of AuNRs immobilized on ITO electrodes revealed the surface activation and functionalization of AuNRs by increasing plasma treatment. Hence, in this study, a significant understanding of oxygen plasma treatment on AuNRs immobilized on ITO surfaces is provided.

Single‐particle correlation study: Chemical interface damping in gold nanorods coated with mesoporous silica shell

AbstractChemical interface damping (CID) is the most recently suggested plasmon damping pathway induced by adsorbate molecules in gold nanoparticles. Despite recent advances in this field, CID has not been studied in gold nanorods coated with mesoporous silica shells (AuNRs@mSiO2). Herein, we conducted a single‐particle correlation study to elucidate CID using p‐nitrothiophenol (p‐NTP) as adsorbates in single AuNRs@mSiO2. Through surface‐enhanced Raman spectroscopy studies, we confirmed that p‐NTP with a strong electron‐withdrawing group was effectively adsorbed on the AuNR cores. Following the chemisorption of p‐NTP, a strong CID was observed with localized surface plasmon resonance (LSPR) linewidth broadening through the preferred interaction between sulfur and the Au surfaces. Furthermore, we presented the molecular binding effect on the LSPR linewidth of single AuNRs@mSiO2 during the reaction with p‐NTP in real‐time. Thus, the result further supported that the CID could be used to develop LSPR sensors having low sensitivity to the medium dielectric constant.

Single-particle spectroelectrochemistry: electrochemical tuning of plasmonic properties via mercury amalgamation in mesoporous silica coated gold nanorods without structural deformation.

This paper elucidates the mercury (Hg) amalgamation induced by electrochemical reduction on gold nanorods coated with mesoporous silica shell (AuNRs@mSiO2) using single-particle spectroelectrochemistry. First, the silica shell significantly enhanced the structural stability of AuNR cores after Hg amalgamation with the application of linear sweep voltages (LSVs). Thus, we were able to focus on the spectral changes of AuNRs@mSiO2 induced by the deposition of Hg without the disturbance of structural deformation, which also strongly affects localized surface plasmon resonance (LSPR) properties. Second, following the application of LSVs in the presence of Hg2+, a remarkable blueshift of the LSPR peak was observed, caused by the lowering of the work function due to the Hg adsorption, donating electron density to Au. Furthermore, the LSPR linewidth also dramatically increased after the Hg deposition with LSV. Lastly, the evolution of the Hg amalgamation process was directly observed by monitoring real-time LSPR peaks and LSPR linewidth shifts of a single AuNRs@mSiO2 in the Hg solution according to the application of the electrochemical potential. Moreover, the results showed the possibility of the in situ tuning of the LSPR properties of AuNRs@mSiO2 by Hg deposition via electrochemical potential manipulations without the disturbance of the structural variations of AuNR cores.

Chemical Interface Damping of Silver‐coated Gold Nanorods Using Supramolecular Host–Guest Chemistry

We present the chemical interface damping (CID) of single Ag‐coated Au nanorods (AuNRs@Ag) using cucurbit[7]uril (CB[7])‐based host–guest chemistry. The chemisorption of CB[7]‐NH2 onto an AuNR@Ag surface resulted in a redshift of its localized surface plasmon resonance (LSPR) scattering peak, with a considerably increased linewidth. This LSPR broadening was ascribed to CID caused by the formation of a strong nitrogen–Ag interaction during the chemisorption of CB[7]‐NH2 onto the AuNR@Ag surface. Furthermore, we observed additional broadening of the LSPR linewidth when the guest molecule (oxaliplatin) was encapsulated into CB[7]‐NH2 chemisorbed onto the AuNR@Ag surface.

Size-Induced Enhancement of Carrier Density, LSPR Quality Factor, and Carrier Mobility in Cr–Sn Doped In2O3 Nanocrystals

Heterovalent dopant ions, such as Sn4+, in In2O3 nanocrystals (NCs) provide free electrons for localized surface plasmon resonance (LSPR). But the same heterovalent dopants act as electron scattering centers, both independently and by forming complexes with interstitial oxygen, thereby increasing LSPR line width. Also, such complexes decrease free carrier density. These detrimental effects diminish the figure-of-merit of LSPR known as the quality factor (Q-factor). Herein, we designed colloidal Cr–Sn codoped In2O3 NCs, where both high carrier density and low carrier scattering can be achieved simultaneously, yielding a high LSPR Q-factor of 7.2, which is a record high number compared to prior reports of doped In2O3 NCs. Q-factors increase systematically from 3.2 for 6.6% Sn doped In2O3 NCs to 7.2 for 23.8% Cr–6.6% Sn codoped In2O3 NCs by increasing the Cr codoping concentration, which is also accompanied by an increase in NC size from 6.7 to 22.1 nm. Detailed characterization and analysis of LSPR spectra ...

Chemical interface damping of single gold nanorods with low sensitivity to the medium dielectric constant

Herein, we present scanning electron microscopy (SEM) correlated dark-field (DF) scattering studies of single gold nanorods (AuNRs). We demonstrate the effect of refractive index variation of the surrounding medium on the localized surface plasmon resonance (LSPR) linewidth in single AuNRs. The LSPR linewidth remains almost constant while increasing the dielectric constant of the medium, which is further verified by discrete dipole approximation (DDA) calculations. Furthermore, we demonstrate how thiol binding affects the LSPR linewidth of the longitudinal surface plasmon of single AuNRs. The thiol resulted in both a red shift and a strong damping with an increased LSPR linewidth.

Dynamics of Surface Plasmon Polaritons in Metal Nanowires

Metal nanostructures have found extensive use in a variety of applications in chemistry, including as substrates for molecular sensing and surface enhanced spectroscopy and as nanoscale heaters for photothermal therapy. These applications depend on the strong absorption and field enhancements associated with localized surface plasmon resonance (LSPR). This has led to a number of studies of how the LSPR line width, which measures energy losses for the coherent electron motion, depends on the size and shape of different types of metal nanoparticles, and the environment around the particle. Extended metal nanostructures, such as nanowires and nanoplates, display propagating surface plasmon modes, termed surface plasmon polaritons (SPPs), in addition to LSPRs. These modes are important for applications where metal nanostructures are used as waveguides. However, less is known about the damping of the propagating SPPs compared to the LSPRs. The energy losses for the propagating SPP modes can be investigated by ...

Plasmon-enhanced photoelectrochemical water splitting with size-controllable gold nanodot arrays.

Size-controllable Au nanodot arrays (50, 63, and 83 nm dot size) with a narrow size distribution (± 5%) were prepared by a direct contact printing method on an indium tin oxide (ITO) substrate. Titania was added to the Au nanodots using TiO(2) sols of 2-3 nm in size. This created a precisely controlled Au nanodot with 110 nm of TiO(2) overcoats. Using these precisely controlled nanodot arrays, the effects of Au nanodot size and TiO(2) overcoats were investigated for photoelectrochemical water splitting using a three-electrode system with a fiber-optic visible light source. From UV-vis measurement, the localized surface plasmon resonance (LSPR) peak energy (ELSPR) increased and the LSPR line width (Γ) decreased with decreasing Au nanodot size. The generated plasmonic enhancement for the photoelectrochemical water splitting reaction increased with decreasing Au particle size. The measured plasmonic enhancement for light on/off experiments was 25 times for the 50 nm Au size and 10 times for the 83 nm Au nanodot size. The activity of each catalyst increased by a factor of 6 when TiO2 was added to the Au nanodots for all the samples. The activity of the catalyst was proportional to the quality factor (defined as Q = E(LSPR)/Γ) of the plasmonic metal nanostructure. The enhanced water splitting performance with the decreased Au nanodot size is probably due to more generated charge carriers (electron/hole pair) by local field enhancement as the quality factor increases.