Induced Surface Plasmon Resonance Research Articles

Multi-dimensional synergistically coupled signal enhancement on nano-micro hierarchical anemone-like substrates integrated SERS-based microfluidic sensor

We designed and prepared a novel anemone-like array substrate (ALAS) integrated pump-free microfluidic sensor based on surface-enhanced Raman spectroscopy (SERS). ALAS substrate forms ordered nanoantenna arrays on polystyrene (PS) nanospheres, which can improve the light-capturing efficiency of the substrate and induce surface plasmon resonance. It successfully achieved multi-dimensional enhancement of electric field coupling and further enhanced the Raman scattering signals of the Raman reporter molecules. Driven by a capillary pump, the seawater containing Hg2+ can be loaded in 100 s without the need for cumbersome syringe pumps. Our results demonstrated that the integrated sensor exhibits excellent responsiveness in detecting Hg2+ within the concentration range of 10−7 to 10−12 mol L−1. The detection limit can reach 1 pmol L−1. Therefore, we believe that this ALAS integrated microfluidic sensor provides a promising solution for the rapid and sensitive detection of Hg2+.

Improving thermal efficiency of solar stills: Bioactive nano-PCM and Cramer’s rule analysis

Green-sourced Petroselinum crispum leaf (P) was carefully harvested and underwent extraction processes. This material was then combined with TiO2 nanoparticles (T) into paraffin wax (P) to create the PTP nanocomposite, using an economically viable and environmentally friendly approach, with P serving as a consistent, reducing, and stabilizing element. The synthesized PTP was thoroughly analyzed using Spectrophotometer, Fourier-transform-IR spectroscopy, X-Ray diffraction, DSC, TGA, and SEM for characterization. The PTP samples were applied in constructing a Single Slope Wick Solar Still (SWS), aiming to induce surface plasmon resonance around 450 nm across the absorber plate. The excitation of PTP at SPR led to the release of significant heat, contributing to temperature increments of the aqueous medium by varying percentages (10 %, 20 %, 30 %, and 40 %) under different ratios upon exposure to solar radiation at the precise plasmon resonance wavelength. This study introduced the first-time application of Cramer's rule (determinant technique) in solving energy balance equations for temperature components. Evaluation revealed that incorporating 30 % PTP notably enhanced SWS efficiency, achieving an optimal distillate output of 8.70 l/m2day, including 1.95 l/m2 at night, resulting in an efficiency of 42.74 %.

Thermo-sensitive PLGA-PEG-PLGA hydrogel for sustained release of EGF to inhibit cervical cancer recurrence

Overexpression of epidermal growth factor receptor (EGFR) in cancer is a key cause of recurrence of cervical cancer (CC). Although the EGF-EGFR pathway has been studied for decades, preventing tumor growth and recurrence caused by peripheral EGF remains a great challenge. In this work, a strategy is proposed to reduce the stimulation of high concentration EGF on tumor growth by using a thermo-sensitive hydrogel. The hydrogel is a triblock copolymer composed of polyethylene glycol (PEG) and poly (lactide glycolide) (PLGA). Based on the excellent temperature sensitivity, carrier capacity, swelling property and biocompatibility, the hydrogel can absorb the liquid around the tumor by injection and release EGF continuously at low concentration. The inhibitory effect of hydrogel on tumor growth is fully confirmed by an implanted tumor mouse model with human cervical cancer cell lines (HeLa) using triple-immunodeficient NCG mice. Compared with free EGF, the EGF-loaded hydrogel can hardly induce surface plasmon resonance (SPR) response, which proves that hydrogel can effectively weaken cytoskeleton rearrangement and inhibit cell migration by continuously releasing low concentration EGF. In addition, the EGF-loaded hydrogel can reduce cell proliferation by delaying the progress of cell cycle progression. Taken together, the hydrogel can effectively protect tumor microenvironment from the stimulation of high concentration EGF, delay cancer cellular processes and tumor growth, and thus providing an approach for inhibiting tumor recurrence of CC.

Surface Plasmon Resonance-enhanced photocatalytic water-splitting for improved visible-light-driven H2 generation using Ag-modified twin crystal Cd0.5Zn0.5S photocatalysts

Photocatalytic hydrogen generation is a viable option among strategies to mitigate the energy crisis. This study investigates visible-light-driven H2 generation using Ag-doped twin crystal CdxZn1-xS photocatalysts synthesized through a solvothermal process. Ag nanoparticles induce Surface Plasmon Resonance (SPR), enhancing photo-response. Twin crystal 1 wt% Ag-doped Cd0.5Zn0.5S photocatalyst exhibits significant H2 evolution at 2458 μmol/gcat.h under visible light. Enhanced performance is attributed to dual-function Ag nanoparticles: SPR-enhanced light absorption, efficient electron transfer to the Cd0.5Zn0.5S conduction band, and the twin crystal structure facilitating electron-hole pair separation. Emphasis on optimal Ag loading and the crucial role of SPR in elevating photocatalyst efficiency.

Enhanced sunlight-driven catalysis for hydrogen generation and dye remediation using synergistic p-Co3O4/n-TiO2 nanocomposites.

In this study, p-Co3O4/n-TiO2 nanocomposites were synthesized using different ratios of cobalt and titanium precursors through a hydrothermal method. These nanocomposites demonstrated notable potential in photocatalytic applications for hydrogen production and orange-red dye degradation under sunlight. Various techniques, including XRD, Raman spectroscopy, XPS, FESEM, TEM, and BET analysis, were used to comprehensively characterize their structural, morphological, and optical properties. The nanocomposites exhibited both cubic and tetragonal phases of Co3O4 and TiO2, and their combined effect resulted in a narrowed band gap. Additionally, the presence of Co3O4 induced surface plasmon resonance on the TiO2 surface, effectively impeding electron-hole recombination. The nanocomposites displayed an average particle size of ∼20 to 30 nm with substantial visible light absorption. High crystallinity and well-dispersed nanocomposites were confirmed by XRD and Raman, with BET surface areas ranging between 49 and 106 m2 g-1. Notably, the p-Co3O4/n-TiO2 nanocomposite showed superior photocatalytic activity, achieving a maximum hydrogen generation rate of 1120 μmol h-1 g-1 and an 83% degradation efficiency of the orange-red dye within 6 minutes under sunlight. This study emphasizes the enhanced performance of the p-Co3O4/n-TiO2 nanocomposite, indicating its potential in photocatalytic applications, conforming to a pseudo-first-order kinetics model.

Mid-Infrared Gas Sensing Based on Electromagnetically Induced Transparency in Coupled Plasmonic Resonators.

The existence of surface plasmon polaritons in doped silicon micro-scale structures has opened up new and innovative possibilities for applications, such as sensing, imaging, and photonics. A CMOS-compatible doped Si plasmonic sensor is proposed and investigated. The plasmon resonance can be tuned by controlling the carrier density and dopant concentration. In this paper, we demonstrate that using silicon doped with phosphorus at a concentration of 5 × 1020 cm-3 can induce surface plasmon resonance in the mid-infrared region. Two ring resonators of two different radii based on metal-insulator-metal waveguide structures are studied individually. Then, the two ring resonators are integrated in the same device. When the two ring resonators are coupled and resonate at the same frequency; two distinct resonance spectral lines are generated with striking features that improve its potential use for sensing and modulation applications. The propagating plasmonic mode is studied, including its mode profile and bend loss. We evaluate the effectiveness of a microstructure gas sensor with dimensions of 15 μm × 15 μm by measuring its sensitivity and selectivity towards methane and ethane gases. Small alterations in the surrounding refractive index led to noticeable shifts in the resonance peak. The sensor achieved a sensitivity of 7539.9 nm/RIU at the mid-infrared spectral range around the 7.7 μm wavelength. Furthermore, by combining the resonators, we can achieve a smaller full width at half maximum (FWHM), which will ultimately result in greater sensitivity than using a single-ring resonator or other plasmonic resonator configurations. Once the sensitivity and selectivity of the sensor are measured, the FOM can be calculated by dividing the sensitivity by the selectivity of the sensor, resulting in an FOM of 6732.

Ultra-sensitive photoelectrochemical biosensor for determination of African swine fever virus based on surface plasmon resonance

Sensitive and specific detection of African swine fever virus (ASFV) is crucial for agricultural production and economic development due to the mortality and infectivity. In this study, a bismuth induced enhanced photoelectrochemical (PEC) biosensor based on in-situ loop mediated isothermal amplification (LAMP) was constructed using deposited bismuth nanoparticles loaded bismuth oxycarbonate (Bi/(BiO)2CO3) as photoactive material, using primers designed according to LAMP as recognition elements, and using in-situ LAMP to achieve nucleic acid amplification of target genes. As the Bi induced surface plasmon resonance (SPR) effect, enhanced light captures and effective electron hole separation, it could effectively enhance the photoelectric activity, so the prepared Bi/(BiO)2CO3 nanohybrid had higher photocurrent intensity and good stability. The constructed PEC biosensor has realized the detection of ASFV in real samples with good sensitivity, specificity and repeatability. In the range from 1.0 × 10−13 to 1.0 × 10−7 g/L, the photoelectric current decreased with the increase of the concentration of ASFV, and the detection limit was 3.0 × 10−14 g/L (about 0.048 copies/μL). Combining the advantages of LAMP with the excellent performance of PEC, it provides a simple, economical and efficient method for nucleic acid diagnosis, and also provides a new idea for biosensor detection.

SERS-Based Immunoassay of Myocardial Infarction Biomarkers on a Microfluidic Chip with Plasmonic Nanostripe Microcones

We developed a new plasmonic nanostripe microcone array (PNMA) substrate-integrated microfluidic chip for the simultaneous surface-enhanced Raman scattering (SERS)-based immunoassay of the creatine kinase MB isoenzyme (CK-MB) and cardiac troponin (cTnI) cardiac markers. The conventional immunoassay usually employs a microtiter plate as the solid capture plate to form the immunocomplexes. However, the two-dimensional (2D) surface of the microtiter plate limits the capture efficiency of the target antigens due to the steric hindrance effect. To address this issue, a gold film-coated microcone array with nanostripes was developed that can provide a large surface area for capture antibody conjugation and serve as a SERS-active substrate. This unique nano-microhierarchical structure showed an excellent light trapping effect and induced surface plasmon resonance to further enhance the Raman signals of the SERS nanoprobes. It significantly improved the sensitivity and applicability of SERS-based immunoassay on the microfluidic chip. With this integrated microfluidic chip, we successfully performed the simultaneous detection of CK-MB and cTnI, and the detection limit can reach 0.01 ng mL-1. It is believed that the PNMA substrate-integrated microfluidic chip would play a critical role in the rapid and sensitive diagnostics of cardiac diseases.

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Surface and Interface AnalysisVolume 55, Issue 2 p. 162-162 ERRATUMFree Access ERRATUM This article corrects the following: Gamma irradiation induced surface plasmon resonance of Cu nanoparticles in fullerene C60 Jyotsna Bhardwaj, Ritu Vishnoi, Amena Salim, Shriniwas Yadav, Sunil Ojha, Umesh Dwivedi, Asokan Kandasami, Pushpendra Kumar, Ganesh D. Sharma, Rahul Singhal, Volume 54Issue 11Surface and Interface Analysis pages: 1130-1141 First Published online: July 30, 2022 First published: 03 November 2022 https://doi.org/10.1002/sia.7168AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Gamma irradiation induced surface plasmon resonance of Cu nanoparticles in fullerene C60 In Bhardwaj et al,1 the name of the ninth author was misspelled in the original published article. The name “Ghanshyam Dutt Sharma” should have read as “Ganesh D. Sharma”. REFERENCE 1Bhardwaj J, Vishnoi R, Salim A, et al. Gamma irradiation induced surface plasmon resonance of Cu nanoparticles in fullerene C60. Surf Interface Anal. 2022; 54(11): 1130- 1141. doi:10.1002/sia.7137 Volume55, Issue2February 2023Pages 162-162 ReferencesRelatedInformation

Gamma irradiation induced surface plasmon resonance of Cu nanoparticles in fullerene C60

The present study reports the gamma irradiation‐induced surface plasmon resonance (SPR) of Cu nanoparticles (Cu‐NPs) that are embedded in the C60 fullerene matrix. These films were deposited by the thermal co‐evaporation technique. In this study, the fullerene C60 and CuC60 nanocomposite thin films were deposited separately and irradiated using gamma rays at various doses from 250 to 1000 kGy. A broad but well‐defined SPR peak is observed at approximately 618 nm after gamma irradiation at a dose of 1000 kGy as confirmed by UV–visible spectroscopy. An enhancement in the growth of Cu‐NPs with an average diameter of 46.05 nm is obtained at a dose of 1000 kGy. Raman spectroscopy confirms the ordering of fullerene C60 after gamma irradiation. However, the current–voltage measurements show that the resistivity of thin films remains approximately the same even after the highest doses of gamma irradiation. The electronic structures of these nanocomposite thin films were analyzed by X‐ray photoelectron spectroscopy. The incorporation of Cu‐NPs in fullerene C60 changes the nature of the surface from hydrophilic to hydrophobic. These results are understood based on the ionizing nature of the gamma rays.

(Invited) Revisiting Functions of Gold Nanoparticles in Photocatalysis

This presentation revisits the functions of gold nanoparticles in photocatalysis. In photocatalyst, gold nanoparticles not only induce surface plasmon resonance but also have other functions. This talk will discuss how to separate different functions of gold nanoparticles in photocatalysis.

(Keynote) Roles of Oxygen Vacancies in Metal Oxide Photocatalysts and Electrocatalysts

This talk concerns with the roles of oxygen vacancies in various metal oxide photocatalysts and electrocatalysts. A low level of oxygen vacancies in titanium oxide can induce shallow and deep sub-band gap Ti(III) states below the conduction band, which increases light absorption but not enhance photocatalytic activity. A high level of oxygen vacancies in metal oxides may generate an abundance of states near Fermi level and induce surface plasmon resonance.

Effect of ferroelectric polarization on piezo/photocatalysis in Ag nanoparticles loaded 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.1Ti0.9)O3 composites towards the degradation of organic pollutants

AbstractA 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.1Ti0.9)O3 (BCT‐BZT) ceramic was studied for photocatalysis and piezocatalysis effects using dye degradation (methylene blue, rhodamine B, and methyl orange) and bacterial (Escherichia coli) disinfection from aqueous solution. To examine the effect of ferroelectric polarization, BCT‐BZT powder was poled using the corona poling technique. Same time, BCT‐BZT was converted into Ag/BCT‐BZT composites as Ag induced surface plasmon resonance effect during photocatalysis. Piezocatalysis performance was assessed for dyes mineralization under ultrasonication. There was a significant impact of silver nanoparticles on the photo/piezocatalysis performance of BCT‐BZT. Similarly, electric poling has also played a positive role in improving the photo/piezocatalysis in view of various dye degradation. These samples also showed effective antibacterial performance.

A novel colorimetric biosensor for sensitive detection of aflatoxin mediated by bacterial enzymatic reaction in saffron samples

Aflatoxin is regarded as the potent carcinogenic agent which is secreted from fungi and present in some food products. So far, many detection methods have been developed to determine the trace amounts of aflatoxin in foods. In the present study a colorimetric competitive assay for detection of aflatoxin B1 (AFB1) has been developed based on interaction of gelatin functionalized gold nanoparticles (AuNPs@gelatin) in specific enzymatic reaction. Bacterial supernatant containing gelatinase enzyme were used as the substrate that could digest the coated gelatin on the surface of AuNPs and following in the presence of NaCl medium ingredient resulted to color change of AuNPs colloidal solution from red to purple. It was observed that with addition of aflatoxin to the bacterial supernatant, aflatoxin could interfere in aggregation of AuNPs and inhibited the process which subsequently prevent the expected color change induced by AuNPs aggregation. The supernatant containing AuNPs were investigated to analyze their induced surface plasmon resonance spectra through UV–visible spectroscopy. The absorption values were directly proportional with the applied AFB1 concentration. The experiment conditions including incubation time, AuNPs concentration and pH were investigated. The obtained results showed that through this approach we could detect the AFB1 in a linear range from 10 to 140 pg ml−1, with detection limit of 4 pg ml−1. Real sample assay in saffron samples showed recoveries percentage of 92.4%–95.3%. The applied approach proposed simple, cost effective and specific method for detection of AFB1 toxin in food samples.

Silicon-Based Ag Dendritic Nanoforests for Light-Assisted Bacterial Inhibition.

Silver dendritic nanoforests (Ag-DNFs) on silicon (Ag-DNFs/Si) were synthesized through the fluoride-assisted Galvanic replacement reaction (FAGRR) method. The synthesized Ag-DNFs/Si were characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), reflection absorbance spectrometry, surface-enhanced Raman scattering spectrometry, and X-ray diffractometry. The Ag+ concentration in ICP-MS measurements indicated 1.033 mg/cm2 of deposited Ag synthesized for 200 min on Si substrate. The optical absorbance spectra indicated the induced surface plasmon resonance of Ag DNFs increased with the thickness of the Ag DNFs layer. Surface-enhanced Raman scattering measurement and a light-to-heat energy conversion test presented the superior plasmonic response of Ag-DNFs/Si for advanced applications. The Ag-DNFs/Si substrate exhibited high antibacterial activity against Escherichia coli and Staphylococcus aureus. The large surface area of the dense crystal Ag DNFs layer resulted in high antibacterial efficiency. The plasmonic response in the metal–crystal Ag DNFs under external light illumination can supply energy to enhance bacterial inhibition. High-efficiency plasmonic heating by the dense Ag DNFs can lead to localized bacterial inhibition. Thus, the Ag-DNFs/Si substrate has excellent potential for antibacterial applications.

Facile Fabrication of a Novel Au/Phosphorus-Doped g-C3N4 Photocatalyst with Excellent Visible Light Photocatalytic Activity

The intrinsic disadvantages of pristine graphitic carbon nitride (g-C3N4) significantly restrict its applications in photocatalysis field. Hence, we have demonstrated facile thermal copolymerization and in situ photodeposition methods to fabricate a novel Au/phosphorus-doped g-C3N4 (Au/P-g-C3N4) photocatalyst. The results showed that phosphorus was doped into the structure of g-C3N4 and that the surface deposition of gold was successfully accomplished. The H2 generation rate of the optimal Au/P-g-C3N4 is 8.4 times compared with the pristine g-C3N4 under visible light irradiation. The enhancement of photocatalytic activity is due to the synergic effect between gold induced surface plasmon resonance and the modified structural and electronic properties of the g-C3N4 induced by the phosphorus dopant.

NIR-II driven plasmon-enhanced cascade reaction for tumor microenvironment-regulated catalytic therapy based on bio-breakable Au–Ag nanozyme

Emerging nanozymes with natural enzyme-mimicking catalytic activities have inspired extensive research interests due to their high stability, low cost, and simple preparation, especially in the field of catalytic tumor therapy. Here, bio-breakable nanozymes based on glucose-oxidase (GOx)-loaded biomimetic Au–Ag hollow nanotriangles (Au–Ag–GOx HTNs) are designed, and they trigger an near-infrared (NIR)-II-driven plasmon-enhanced cascade catalytic reaction through regulating tumor microenvironment (TME) for highly efficient tumor therapy. Firstly, GOx can effectively trigger the generation of gluconic acid (H+) and hydrogen peroxide (H2O2), thus depleting nutrients in the tumor cells as well as modifying TME to provide conditions for subsequent peroxidase (POD)-like activity. Secondly, NIR-II induced surface plasmon resonance can induce hot electrons to enhance the catalytic activity of Au–Ag–GOx HTNs, eventually boosting the generation of hydroxyl radicals (•OH). Interestingly, the generated H2O2 and H+ can simultaneously induce the degradation of Ag nanoprisms to break the intact triangle nanostructure, thus promoting the excretion of Au–Ag–GOx HTNs to avoid the potential risks of drug metabolism. Overall, the NIR-II driven plasmon-enhanced catalytic mechanism of this bio-breakable nanozyme provides a promising approach for the development of nanozymes in tumor therapy.

Green synthesis of silver nanoparticles using Tagetes erecta plant and investigation of their structural, optical, chemical and morphological properties

Presently, the green synthesis method of nanomaterials is well-recognized due to its inexpensive and environmentally friendly route. Silver nanoparticles (AgNPs) synthesized by the green synthesis method is suitable to manipulate the light interaction by inducing the surface plasmon resonance (SPR). Therefore, AgNPs demanded their potential application in plasmonic devices. This paper reports the green synthesis of AgNPs and the investigation of their properties. X-ray diffraction (XRD) study endorsed the presence of pure Ag phases with its face-centered cubic structure. The ultraviolet–visible (UV–vis) spectroscopy analysis evidenced the absorption peak at wavelength 420 nm, which is attributed to the induced surface plasmon resonance (SPR). Fourier transform infrared spectroscopy (FTIR), and Raman studies demonstrated the various vibration peaks concerning the elements present in the green synthesized AgNPs. The preparation of spherical Ag nanoparticles with their diameter from 24 to 49 nm is investigated by scanning electron (SEM) measurement. The energy-dispersive X-ray spectroscopy (EDAX) investigation endorsed the dominant peaks of Ag. Finally, the AgNPs used as the catalyst for the photodegradation study of Rhodamine B dye and the result is explored.

Ion irradiation (low & high energy ion) induced surface plasmon resonance in Cu(10%)C70 nanocomposite thin films

Cu-C70 nanocomposite thin films were deposited on glass, silicon and TEM grids by thermal co-evaporation; the thin films were irradiated by 350 keV Ar ions and 120 MeV Ag ions at different fluences, ranging from 1 × 1013 to 3 × 1016 ions cm−2 in a high vacuum chamber. Rutherford backscattering (RBS) of pristine film verified that the thickness and copper content of thin films were 30 nm and ∼10 at%, respectively. The modifications in structure and optical properties of irradiated thin films were studied by UV-visible absorption spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS); the results were compared with those of pristine film. Raman spectroscopy gave evidence of transformation of fullerene C70 matrix into amorphous carbon after irradiation by 350 keV Ar ions at a fluence of 3 × 1014 ions cm−2. At 1 × 1015 ions cm−2 fluence, a surface plasmon resonance band due to Cu nanoparticles appeared at ∼627 nm in the visible absorption spectrum. This band was seen to undergo blue shift at higher fluence values. TEM confirmed that increasing fluence brings about the coarsening of Cu nanoparticles (from 2.4 to 6.6 nm). Moreover, XPS study ruled out the possibility of formation of any Cu compound due to irradiation. In contrast, irradiation by 120 MeV Ag ion led to amorphization of Cu (10%) C70 nanocomposite thin films at higher fluences. The SPR band intensity at 627 nm was appreciably enhanced at a fluence of 3 × 1013 ions cm−2. The amorphization of C70 due to irradiation by 120 MeV Ag ion at fluence 3 × 1013 ions cm−2 was confirmed by the appearance of D and G band in the concerned Raman spectra. Moreover, this brings about a small increase in particle size. Both particle coarsening and amorphization of C70 were responsible for the emergence of SPR band due to copper.

Temperature induced surface plasmon resonance in Au/a-C nanocomposite thin film

Nanocomposite thin film containing Au nanoparticles in carbon matrix is developed using co-sputtering method in a high vacuum chamber (<10−6 torr). The atomic concentration of Au metal (6 at. %) is kept low so that the properties of matrix are not deteriorated much by the presence of metal. In order to enhance the growth of Au nanoparticles to an appreciable size, thermal annealing is performed on the as-deposited films at increasing temperatures from 100 to 500 °C in an inert atmosphere (continuous flow of Ar gas is maintained during heating and cooling). Annealing is performed for 1 hr on each sample. Growth of the Au nanoparticles and evolution of carbon matrix by thermal treatment is understood through TEM and Raman spectroscopy. TEM images of the as-deposited sample taken at different areas of the sample clearly indicate the spherical-shaped Au nanoparticles with an average diameter of ∼1.5 nm which is further increased up to ∼15.3 nm at the temperature of 500 °C. The results of Raman spectroscopy confirm the increase in the intensity of characteristic D and G bands of amorphous carbon with temperature. Surface plasmon resonance is successfully induced by temperature treatment at a wavelength of ∼548 nm at 400 °C, which is further enhanced at 500 °C. The growth of Au nanoparticles is also confirmed by X-ray diffraction study.