Strong Surface Plasmon Resonance Research Articles

β-cyclodextrin functionalized gold nanoparticles as an effective nanocatalyst for reducing toxic nitroaromatics

We demonstrated the effective reduction of the organic pollutants, the nitroaromatics, via green sustainable chemistry using high efficacy of the catalytic materials, i.e., β-cyclodextrin (β-CD) functionalized Au nanoparticles (AuNPs). Eco-friendly and biocompatible techniques were employed to fabricate gold nanoparticles (AuNPs) from an Au precursor (HAuCl4) using β-CD that plays as both reducing and surface-functionalizing agents. Detailed investigation of β-CD AuNPs formation, their sizes with morphologies, the surface charge, and the hydrodynamic size in a colloidal medium were performed by ultraviolet–visible (UV–vis) absorbance spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Zeta potential measurements, and the dynamic light scattering analysis, respectively. The plasmonic nanoparticle formation of the β-CD AuNPs led to the strong localized surface plasmon resonance peak at around the 520 nm wavelength. The catalytic activity of the β-CD AuNPs was evaluated using model reactions, including the catalytic conversion of nitroaromatics to the corresponding amino-aromatic compounds upon mixing sodium borohydride in a water medium. Chemical reactions of such catalytic reduction of nitroaromatics were tracked by UV–vis absorbance spectroscopy, showing high catalytic activity of β-CD AuNPs. We also provided a discussion on the possible pathways for the AuNPs-mediated catalytic reduction of nitroaromatics. The efficacy of the nanocatalysts presented to reduce nitroaromatics can hold a potential promise for detoxifying aquatic environments and their pharmaceutical applications.

Advanced refractive index sensor using 3-dimensional metamaterial based nanoantenna array

Photonic researchers have increasingly exploiting nanotechnology. Due to the advent of numerous prevalent nanosized manufacturing methods that enable adequate shaped nanostructures to be manufactured and investigated as a method of exploiting nano-structured. Owing of the variety of optical modes, hybrid nanostructures that integrate dielectric resonators with plasmonic nanostructures also offer enormous potentials. In this work, we have explored a hybrid coupled nano-structured antenna with stacked lithium tantalate (LiTaO3)/Aluminium oxide (Al2O3) multilayer operating at infrared ranging from 400 nm-2000 nm. Here, the sensitivity response has been explored of the hybrid nano-structured array made up of the gold metal elliptical disk placed on the top of a quartz substrate and excite the different modes in both materials. It shows large electromagnetic confinement at the separation distance (d) of the dimers due to strong surface plasmon resonance (SPR). The influence of the structural dimensions is investigated to optimise the sensitivity of stacked elliptical dimers. The designed hybrid coupled nano-structure with the combination of gold (Au) and Lithium tantalate (LiTaO3) /Aluminium oxide (Al2O3) with h 1 = h 2 = 10 nm each 10 layer exhibits bulk sensitivity (S), which is the spectrum shift unit per refractive index (RI) change in the surrounding medium was calculated to be 730 and 660 nm/RIU with major axis, (a) = 100 nm, minor axis, (b) = 10 nm, separation distance (d) = 10 nm, height, (h) = 100 nm (with or without stacked). The outcomes from the proposed hybrid nanostructure have been compared with a single metallic (only gold) elliptical paired nano-structure to show a significant improvement in the sensitivity using hybrid nano-structure. Depending on these findings, we demonstrated a roughly two-fold increase in sensitivity (S) by utilising a hybrid nano linked nano-structure with respect to identical nano structure, which competes with traditional sensors with the same height, (h) based on localised surface plasmon resonances. Our innovative plasmonic hybrid nanostructures provide a framework for developing plasmonic nanostructures for use in various sensing applications.

Silica–silver core–shell nanoparticles incorporated with cellulose filter paper as an effective colorimetric probe for mercury ion detection in aqueous media: Experimental and computational evaluations

This study investigates the facile and rapid detection of mercury ions using silica–silver core–shell nanoparticles (SiO2–AgNPs) incorporating a paper-based colorimetric sensor strip. A strong surface plasmon resonance peak at λ = 430 nm was observed for the resultant SiO2–AgNPs. The attachment of the AgNPs to the surface of SiO2 and the deposition of the AgNPs on the paper strip were confirmed using an electron microscope. The sensing of the SiO2–AgNPs toward the mercuric ion (Hg2+) in an aqueous solution indicated a rapid response in terms of a color change from yellowish-brown to colorless with a response time of 5–10 s. The prepared SiO2–AgNPs deposited on the paper strip exhibited high selectivity toward Hg2+ compared with other metal ions. The limit of detection for this assay was 1.13 nM, with an excellent correlation value of R2 = 0.9936. In addition, the complexation mode of the SiO2–AgNPs with Hg2+ was also elucidated via theoretical calculations using the density functional theory approach. This approach also provides insight into the complexation structure in terms of the electronic alteration of the SiO2–AgNPs prior to and following their interaction with Hg2+. Overall, the study demonstrates that SiO2–AgNP-based sensor materials can be utilized for the selective recognition of Hg2+ in aqueous solutions.

Biogenic Synthesis of Carboxymethyl Cashew Gum Modified Gold Nanoparticles and its Sensitive and Selective Calorimetric Detection of Hg2+ Ions and Catalytic Reduction of Methyl Red.

In the present study, we have successfully synthesized and characterized carboxy methyl cashew gum modified gold nanoparticles (CMCG-AuNPs) via a microwave-assisted method and used as a calorimetric probe for selective detection of Hg2+ ions as well as catalytic reduction of methyl red in an aqueous medium. The effect of different parameters including concentration and irradiation time on the formation of CMCG-AuNPs was also investigated. The presence of strong surface plasmon resonance (SPR) peak in the visible region indicated the formation of AuNPs. The characterization techniques were identified the interaction between the CMCG and AuNPs with estimation of size and morphology. The face centred cubic (FCC) crystal structure was identified by using XRD and supporting with SAED pattern. TEM images of CMCG-AuNPs were exhibited as polydispersed with spherical in shape and the average particle size was 12 ± 3nm. The synthesized CMCG-AuNPs were utilized to sensing Hg2+ ions in an aqueous medium, the presence of Hg2+ ions selectively among other metal ions, the CMCG-AuNPs were aggregated by changing the color from wine red to purple blue accompanied by change in the position of SPR peak and intensity. It was observed as a strong linear relationship based on the change in intensity, the limit of detection was determined to be 0.277nM. The catalytic activity was also examined for the reduction of methyl red (MR) in the presence of CMCG-AuNPs was completed within 12min and followed pseudo-first order kinetics with a rate constant of 0.261min-1. From the obtained results, the synthesized CMCG-AuNPs were useful for detection of heavy metal ions as well as toxic pollutants degradation via a green method, and utilized sensing, environmental, and biomedical application in future.

TiO2 Thickness-dependent charge transfer effect in p-aminothiophenol molecules chemisorbed on TiO2/Ni substrates

Semiconductors have been modulated in thickness to optimize their surface-enhanced Raman scattering (SERS) activity in noble metal/semiconductor SERS substrates. However, the charge transfer (CT) resonance mechanism caused by the change of the semiconductor thickness has not been fully clarified yet, due to the influence of the strong surface plasmon resonance (SPR) effect from the noble metals. Here, systems of p-aminothiophenol (PATP) molecules chemisorbed on TiO2/Ni nanopillar array films with precisely controlled TiO2 thicknesses (PATP/TiO2/Ni) were developed to systematically evaluate the TiO2 thickness-dependent CT mechanism on the premise of minimizing the SPR influence. Ultraviolet–visible, photoluminescence and X-ray photoelectron spectroscopy results demonstrated that four parts that ascribed to the SERS enhancement, photo-induced CT from Ni to TiO2, resonance excitation of TiO2, CT from TiO2 surface states to PATP molecules, and the molecular resonance of PATP molecules, are highly TiO2-thickness dependent. Hence the whole system exhibits a strong TiO2-thickness-dependent CT effect (at the two interfaces of Ni-TiO2 and TiO2-PATP) and SERS activity with a maximum SERS intensity at a TiO2 thickness of 40 nm. This work shall be valuable for future developing an optimal metal/semiconductor SERS substrates and obtaining an in-depth understanding of the semiconductor-thickness-dependent charge transfer mechanism for SERS applications.

A Metallic Niobium Nitride with Open Nanocavities for Surface-Enhanced Raman Spectroscopy.

The construction of open hot-spot structures that facilitate the entry of analytes is crucial for surface-enhanced Raman spectroscopy. Here, metallic niobium nitride (NbN) three-dimensional (3D) hierarchical networks with open nanocavity structure are first found to exhibit a strong visible-light localized surface plasmon resonance (LSPR) effect and extraordinary surface-enhanced Raman scattering (SERS) performance. The unique nanocavity structure allows easy entry of molecules, promoting the utilization of electromagnetic hot spots. The NbN substrate has a lowest detection limit of 1.0 × 10-12 M and a Raman enhancement factor (EF) of 1.4 × 108 for contaminants. Furthermore, the NbN hierarchical networks possess outstanding environmental durability, high signal reproducibility, and detection universality. The remarkable SERS sensitivity of the NbN substrate can be attributed to the joint effect of LSPR and interfacial charge transport (CT).

Tuning optical dispersion and localized surface plasmon resonance of 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag glass system

The optical dispersion properties of the 20Li2O-xBi2O3-(78-x)TeO2-1Er2O3-1Ag glass system were studied using the Wemple–DiDomenico fitting model. The single oscillator energy Eo and dispersion energy Ed decrease with increasing Bi2O3 concentration, with a maximum at x = 11 mol%.The large increase at x = 11 mol% can be attributed to the role of Bi2O3 as a glass former, which induces the formation of bonds in the glass network, thereby contributing to average bond strength and increasing Eo. The role of Bi2O3 as glass former may also induce minimal transformation of the glass network TeO2 to lower coordination number Nc, contributing to a maximum in Ed. Analytical expressions were also used to compute the complex dielectric properties of the glass samples. The εr and εi initially decreased at x ≤ 7 mol% before a maximum at x = 11 mol% possibly due to a decrease in polarization caused by blocking of Bi3+ ions to Li+ ions. By contrast, the maximum of εr and εi at x = 11 mol% may be attributed to the high field strength F of Bi3+ and Bi5+ ions, which increases the electronic polarizability of the glass samples. The behavior of the localized surface plasmon resonance was studied using coupling polarization approach, which revealed that the localized surface plasmon resonance of the Ag NP is dependent on the dielectric properties of Er3+ host glass. The electrical χ and Clausius–Mossotti polarizability αL showed a maximum at x = 13 mol%, which could be attributed to high real εr and imaginary dielectric constant εi, thus contributing to the polarizability of the glass samples and leading to strong localized surface plasmon resonance.

Biosynthesis of silver nanoparticles loaded PVA/gelatin nanocomposite films and their antimicrobial activities

A facile and novel method for producing silver nanoparticles (AgNPs) with star anise was performed. TEM analysis revealed the spherical shape with the average size of 10.98 nm and exhibited strong surface plasmon resonance (SPR) at 420 nm. AgNPs loaded PVA/gelatin nanocomposite films were confirmed by XRD and FTIR, which indicates the intermolecular hydrogen bonding between polymer matrix and AgNPs. The thermal stability of AgNPs loaded PVA/gelatin biofilms was increased owing to the reduced crystallinity, which correlated to the lower order of polymer structure of PVA during the embedding process with AgNPs. Accordingly, the biofilms demonstrated significant antimicrobial effects with a higher inhibition zone against E. coli, S. aureus, and C. albicans compared to pristine PVA/gelatin.

Green synthesis of gold nanoparticles using quercetin biomolecule from mangrove plant, Ceriops tagal: Assessment of antiproliferative properties, cellular uptake and DFT studies

Synthesis, structural elucidation and in vitro cytotoxic properties of quercetin gold nanoparticles (Qu-AuNPs) were derived from the mangrove plant, Ceriops tagal. UV–Visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) were used to characterize the quercetin Au-NPs while UV–Vis spectral analysis noted a strong surface plasmon resonance (SPR) band at 430 nm. From the FT-IR results, the peaks obtained indicate their relation to phenols, flavonoids, and anthocyanins with the inference of their role as reducing agents. Density functional theory (DFT) analysis revealed that the quercetin molecule was responsible for the reduction of Au3+ ions into Au0. The fluorescence property of the nanoparticles (NPs) has been confirmed with a fluorescence microscope. Moreover, the antiproliferative activity of these Qu-AuNPs has been evaluated using two different human cancer cell lines. Cell culture results demonstrated the potential efficacy of these nano-formulations against A549 and HeLa cell lines. Results of the A549 and HeLa cancer cell culture substantiate the potential efficacy of these nano-formulations against both the cell lines with IC50 values of 79.9 µg/ml and 73 µg/ml for A549 and HeLa cell lines, respectively.

Comprehensive study on the nonlinear optical response of MoO2 nanosheets in pulsed lasers

Molybdenum dioxide nanosheets (MoO2-NSs), as two-dimensional (2D) materials, have attracted broad attention owing to their high damage threshold, good stability, strong localized surface plasmon resonance (LSPR), affordability, and excellent physicochemical properties. In this work, we successfully synthesized high-quality MoO2-NSs through chemical vapor deposition synthesis method and characterized the morphology and structure of the prepared materials in detail. The saturable absorption characteristics of the MoO2-NSs were measured using Z-scan experiments for the first time. Additionally, the compact Q-switched laser and stable mode-locked laser were successfully realized based on a MoO2-NSs saturable absorber (SA). To the best of our knowledge, this is the first presentation of the application of MoO2-NSs SA in the field of ultrafast photonics. These findings indicate that high-quality MoO2-NSs can be an effective optical modulator for generating high-repetition-rate pulsed lasers, and exhibit promising potential applications in mode-locked ultrafast lasers.

Enhancing the Photocatalytic Activity of TiO2/Na2Ti6O13 Composites by Gold for the Photodegradation of Phenol

This study aims to synthesize Au/TiO2/Na2Ti6O13 composites to reduce the occurrence of recombination and increase photocatalytic activity in phenol degradation. Gold was used due to its high stability and strong surface plasmon resonance (SPR) properties which make it operate effectively in the visible light spectrum. The prepared composites were characterized using XRD, SEM, TEM, FTIR, and DRS. The results showed that the composite consisted of rutile TiO2 with a crystal size of 38–40 nm and Na2Ti6O13 with a crystal size of 25 nm. The gold in the composite has a crystallite size of 16–19 nm along with the percentage of gold added. Morphological analysis shows that the composite has the form of inhomogeneous spherical particles with gold spread among composites with sizes less than 20 nm. FTIR analysis showed the presence of Na–O and Ti–O–Ti bonds in the composite. The best composite was 3% Au/TiO2/Na2Ti6O13 which had high crystallinity, small particle size, and bandgap energy of 2.59 eV. Furthermore, it had an efficiency 205% better than without gold. After that, cost estimation is proposed as a large-scale application. This study describes the total cost, break-even analysis, and payback analysis for the commercialization needs of the designed photocatalytic catalyst.

SERS/NIR‐II Optical Nanoprobes for Multidimensional Tumor Imaging from Living Subjects, Pathology, and Single Cells and Guided NIR‐II Photothermal Therapy

AbstractMolecular imaging‐guided precision photothermal therapy has shown tremendous potential for invasively thermal ablation with solid tumors. However, it is still a pressing clinical need to develop precise and deep‐tissue multi‐scale imaging technologies easily integrated into a single system to boost accurate photothermal treatments. Herein, a SERS/NIR‐II optical nanoprobe assembled by gold nanostars, Raman molecular tags, and silver sulfide quantum dots through silica bridges (named AuDAg2S) is reported that allows the combination of the fingerprint‐style surface‐enhanced Raman scattering (SERS) imaging and second region near‐infrared (NIR‐II) in‐depth biological fluorescence imaging. It can also yield strong localized surface plasmon resonance for a satisfactory photothermal conversion efficiency of 67.1% at 1064 nm to effectively kill CT26 colon cancer cells. Moreover, the AuDAg2S nanoprobes can enhance the detection sensitivity up to the picomolar level and increase the depth of the NIR‐II fluorescence signal up to 1 cm under the excitation of the near‐infrared laser. As a result, the AuDAg2S nanoprobes can achieve multidimensional tumor imaging in levels of living subjects, histology, and single cell, and further guided deep NIR‐II photothermal anti‐tumor therapy in vivo. This study offers a promising approach for SERS/NIR‐II whole optical imaging for deep tumor photothermal treatment in future clinical applications.

Antimony speciation on a dithiothreitol-functionalized two-dimensional Au@Ag array by surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS), a fast and non-destructive detection technique, can be potentially used for the on-site analysis of antimony species. However, SERS quantification of antimony species has been rarely performed. This study fabricated a two-dimensional (2D) Au@Ag–dithiothreitol (DTT) array for antimony speciation analysis. This array was able to detect antimony at concentrations as low as Sb(III) = 1.05 µg·L−1 and Sb(V) = 3.81 µg·L−1. Moreover, it exhibited good uniformity with a relative standard deviation of 16.2% and recoveries of 88–93%. The results of three-dimensional finite-difference time-domain simulations revealed that the 2D Au@Ag array with 25 nm-Au cores, 6 nm-Ag shells, and 2 nm-interparticle gaps created a strong localized surface plasmon resonance. The DTT functionalization of the 2D Au@Ag array facilitated selective adsorption and SERS detection of antimony ions. By combining the electromagnetic and chemical mechanisms, antimony speciation analysis was successfully performed using the 2D Au@Ag–DTT array, suggesting a new on-site method for monitoring small molecules.

Fabrication and Characterization of Plasmonic Au Nanoparticles on ITO-Coated Glass Sheets

We report here the fabrication of sputter-deposited Au nanoparticles on ITO (Sn-doped indium oxide)-coated glass substrate. The effect of varying annealing parameters, viz., time and temperature in conjunction with varying thickness parameters has been thoroughly investigated. Synthesized Au nanoparticles were characterized using a field emission scanning electron microscope (FE-SEM), Rutherford backscattering (RBS) measurement, X-ray diffraction (XRD), and optical absorbance spectroscopy. The role of annealing temperature and time duration on the evolution of Au nanoparticles has been discussed in detail based on optical absorbance spectroscopy. The present study shows that 5 nm thickness Au thin film which was annealed at 500 °C for 90 min exhibited the strongest surface plasmon resonance (SPR) effect.

In Situ Surface Restraint-Induced Synthesis of Transition-Metal Nitride Ultrathin Nanocrystals as Ultrasensitive SERS Substrate with Ultrahigh Durability.

It is a major challenge to synthesize crystalline transition-metal nitride (TMN) ultrathin nanocrystals due to their harsh reaction conditions. Herein, we report that highly crystalline tungsten nitride (W2N, WN, W3N4, W2N3) nanocrystals with small size and excellent dispersibility are prepared by a mild and general in situ surface restraint-induced growth method. These ultrafine tungsten nitride nanocrystals are immobilized in ultrathin carbon layers, forming an interesting hybrid nanobelt structure. The hybrid WN/C nanobelts exhibit a strong localized surface plasmon resonance (LSPR) effect and surface-enhanced Raman scattering (SERS) effect, including a lowest detection limit of 1 × 10-12 M and a Raman enhancement factor of 6.5 × 108 comparable to noble metals, which may be one of the best records for non-noble metal SERS substrates. Moreover, they even can maintain the SERS performance in a variety of harsh environments, showing outstanding corrosion resistance, radiation resistance, and oxidation resistance, which is not available on traditional noble metal and semiconductor SERS substrates. A synergistic Raman enhancement mechanism of LSPR and interface charge transfer is found in the carbon-coated tungsten nitride substrate. A microfluidic SERS channel integrating the enrichment and detection of trace substances is constructed with the WN/C nanobelt, which realizes high-throughput dynamic SERS analysis.

Plasmonic photoelectrochemical reactions on noble metal electrodes of nanostructures

Plasmonic noble metal nanostructures have been targeted due to their strong surface plasmon resonance at photoelectrochemical interfaces. Recently, it has been concluded that, the plasmonic noble metal nanostructures on photoexcitation permit the transfer of effective hot carriers (hot electron/hole pair) to nearby adsorbed molecules where, the transformed hot carriers can efficiently decrease the activation barrier of a reaction. In this review, our recent achievements in the plasmon-mediated chemical reactions of organic molecules such as para -aminothiophenol, substituted para -aminothiophenol and para -nitrothiophenol at nanostructures modified noble metal electrodes using surface enhanced Raman spectroscopy, electrochemical methods, and theoretical calculations will be discussed.

Ultra-homogeneous Cu2−xSe nanoparticles as near-infrared II plasmonic phototheranstics for photothermal/chemodynamic synergistic therapy of liver cancer

Laser mediated photothermal/chemodynamic co-therapy is widely applied for anti-cancer treatment due to its good therapeutic effect. However, the laser wavelength for effectively targeting deep tumor tissues can decide whether or not it is a key premise of irradiation treatment. In this study, a super-homogenous and highly dispersive spherical nanoparticle Cu2-XSe was prepared, which displayed a strong surface plasmon resonance (SPR) peak in the near-infrared region (NIR)-II and high Fenton catalytic efficiency. The results of in vitro experiments showed that Cu2-XSe nanoparticles exhibited high photothermal conversion efficiency under the excitation of NIR-II laser irradiation, which significantly improved its ability to produce ·OH. In a tumor-bearing mouse model, the combination of Cu2-XSe and photothermal/chemodynamic co-therapy guided by the real-time photoacoustic imaging in the NIR-II could effectively inhibit tumor growth and exhibit good in vivo/in vitro biocompatibility. In summary, this Cu2-XSe nanoparticle-based NIR-II laser-mediated photothermal/chemodynamic co-therapy strategy is expected to provide a new option for the diagnosis and treatment of liver cancer.

New Chitosan-Grafted Thymol Coated on Gold Nanoparticles for Control of Cariogenic Bacteria in the Oral Cavity

Chitosan-grafted thymol (CST) coated on gold nanoparticles has been synthesized and characterized for the design of antimicrobial materials. CST was synthesized via adapting the Mannich reaction, and it acted as the capping agent for the synthesis of gold nanoparticles (AuNPs). The grafting of thymol onto the side chain of chitosan has provided a degree of substitution value (%DSNMR) of 10.0%, calculated by nuclear magnetic resonance spectroscopy. UV–visible spectrometry and elemental analysis were used to confirm the successful synthesis of CST through adapting the Mannich reaction. The appropriate concentration of CST for AuNP synthesis was found to be 0.020%w/v. A red-wine colloidal AuNP solution of 2.41–3.30 nM particle size exhibits a strong surface plasmon resonance at 502 nm, which shows negative charges at pH = 9 of −36.37 mV. This result evidenced that the AuNPs showed electrostatic repulsion and CST played a role as a capping agent to provide a good dispersion and stability state. CST coated on the AuNP surface was successfully utilized for the control of cariogenic bacteria in the oral cavity. The results obtained from this study show that the tuning of the capping agent used in the synthesis step strongly influences the latter antimicrobial activity of the nanoparticles against Streptococcus mutans ATCC 25175 and Streptococcus sobrinus ATCC 33402 activity, with an inhibition zone of 15.90 and 14.25 mm, respectively. The average minimum inhibitory concentration values against S. mutans ATCC 25175 and S. sobrinus ATCC 33402 were found to be 25 and 100 mg/L, respectively, whereas the minimum bactericidal concentration values were 100 and 200 mg/L, respectively.

Hot Hole Utilization in Au-TiO2 and Au-C3N4-TiO2 Core-Shell Heterojunctions for High Performance Photoelectrochemical Water Splitting

Gold nanoparticles (Au NPs) coated with TiO2 shells exhibit strong localized surface plasmon resonance (LSPR) peaks at ~550-600 nm. The Au plasmons decay in femtoseconds through both interband and intraband damping processes to produce hot electron-hole pairs. These hot carriers have excess energy at room temperature which can be utilized to generate electricity or drive a chemical reaction. However, the hot carriers experience ultrafast recombination and thermal relaxation in hundreds of femtoseconds to a few picoseconds due to electron-electron scattering and collisions with phonons. A Schottky barrier heterojunction between Au and a n-type semiconductor such as TiO2 is an ideal method to separate the hot carrier pairs. In Au-TiO2 Schottky junctions, hot electrons are injected into TiO2 through thermionic emission and/or field emission before recombination and thermal equilibration, at timescales of roughly 250 fs. However the harvesting of residual hot holes in Au remains problematic partly because of the difficulty in forming Schottky junctions between Au and p-type semiconductors. The harvesting of hot holes is particularly important considering that hot holes in Au are on average, more energetic than hot electrons.In this work, we use an innovative photoanode architecture to harvest hot holes. Our photoanode architecture consists of Au NPs coated with a thin layer of amorphous TiO2 and deposited on transparent conductive oxide (TCO)-coated glass substrates. Hot electrons are extracted from the Au into the TCO contact through the TiO2 shell. Hot holes tunnel through the TiO2 to reach the alkaline electrolyte whether they oxidize hydroxyl ions and dissolved oxygen species to generate oxygen. Another novelty is the use of a layer of graphitic carbon nitride (g-C3N4) quantum dots to pump the plasmon through exciton-to-plasmon energy transfer and increase the production of hot carriers. g-C3N4 works to enhance the plasmonic light harvesting due to the excellent overlap between the emission of g-C3N4 and the LSPR absorption band of Au. Photocurrent densities as high as 3.7 mA/cm2 were achieved under AM1.5G one sun illumination with concomitant high Faradaic efficiencies. Photoelectrochemical action spectra collected using filtered AM1.5G illumination and monochromatic LEDs revealed the prominent role of visible photons in water-splitting performed using Au-C3N4-TiO2 core-shell ternary heterojunctions. A key goal moving forward is to replace the noble metal (Au) with transition metal nitride plasmonic absorbers while sustaining the high level of photoelectrochemical performance.

Hybrid SERS platform by adapting both chemical mechanism and electromagnetic mechanism enhancements: SERS of 4-ATP and CV by the mixture with GQDs on hybrid PdAg NPs

Surface-enhanced Raman spectroscopy (SERS) is a versatile analytical technique widely adapted for the identification of target analytes even at an extremely low concentration. Herein, a unique hybrid SERS platform is demonstrated by utilizing the graphene quantum dots (GQDs) and hybrid PdAg NPs for the detection of 4-amino-thiophenol (4-ATP) and crystal violet (CV). GQDs offer the rich charge transfer to the LUMO and HOMO of 4-ATP and CV by the CM enhancement. A significant EM enhancement is achieved by the strong localized surface plasmon resonance (LSPR) of uniquely designed hybrid core-shell PdAg NP, possessing the narrow nano-gaps with the highly dense small Ag NPs and Pd core Ag shell configuration. As a result, orders of enhancement of originally weak 4-ATP and CV Raman signal is witnessed by the combination of electromagnetic mechanism (EM) and chemical mechanism (CM) enhancements on a single SERS substrate. The hybrid GQD/HNP SERS substrate demonstrates significantly improved hot spots and strongly localized electromagnetic fields as confirmed by the finite-difference time-domain (FDTD) simulations. A proper mixture ratio of GQDs and probe molecules presents largely enhanced SERS signals by a strong adsorption of probe molecules through π - π interaction and the enhancement factors vary by the mixture ratio depending on the adsorption kinetics and Raman cross-section of molecules.