Surface Plasmon Resonance Absorption Research Articles

Polymer‐Protected Gold Nanoparticles for Photothermal Treatment of Ehrlich Adenocarcinoma: In Vitro and In Vivo Studies

AbstractPhotothermal therapy (PTT) is recognized as an effective tool for the treatment of cancer and it has attracted considerable attention of scientists. In this work, gold nanospheres (AuNSs) and gold nanorods (AuNRs) stabilized using poly(N‐vinylpyrrolidone) (PVP), pristine gellan gum (PGG), and poly(2‐ethyl‐2‐oxazoline)‐grafted gellan gum (GG‐g‐PEtOx) are synthesized and evaluated as PTT agents in Ehrlich cancer cells. The physicochemical characteristics of these AuNSs and AuNRs, including their surface plasmon resonance absorption spectra, size, zeta potential, and aspect ratio are studied using UV–vis‐spectroscopy, dynamic light scattering, zeta potential, transmission electron microscopy, and optical microscopy techniques. The polymer‐protected AuNSs exhibit light‐to‐heat conversion, raising the temperature from 37 to 43 °C when irradiated using a visible light source. In the case of AuNSs, considerable damage to Ehrlich cancer cells is observed following irradiation and 40 days of examination. However, with regard to AuNSs, the damage to Ehrlich cancer cells is slightly lower than observed in AuNRs. In vivo experiments demonstrate that laser irradiation of tumors in mice after injecting AuNSs leads to a statistically significant decrease in tumor size as compared to those not irradiated and the control samples.

Structural and optical properties of highly Ag-doped TiO2 thin films prepared by flash thermal evaporation

The present study investigates the structural and optical properties of silver (Ag)-doped titanium dioxide (TiO2) thin films prepared via flash thermal evaporation using TiO2 and Ag powders mixture at various mass ratios. The crystallinity and surface morphology of the films were studied by varying the percentage of Ag content. Structural properties were characterized using X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM), while optical properties were assessed through optical transmission spectra analysis. Results indicate that Ag doping enhances crystallinity, as evidenced by XRD and Raman spectroscopy, and induces surface plasmon resonance (SPR) absorption attributed to Ag nanoparticles. SEM micrographs reveal agglomerated silver particles on the film surface, confirming Ag diffusion during annealing. Surface analysis through Secondary Ion Mass Spectrometry (SIMS) measurements illustrated the diffusion of Ag within the TiO2 samples and its subsequent accumulation at the surface. We have suggested that the crystallization observed in the evaporated TiO2-Ag thin films may primarily result from the thermal diffusion of Ag metal rather than the annealing process alone. Optical transmission spectra demonstrate a shift in the absorption edge towards the visible region with increasing Ag concentration, indicating enhanced light absorption properties.

Ultra-broadband, high absorption, polarization-insensitive microwave absorbers designed based on multi-scale fractal metasurfaces

Microwave absorbers play an essential role in radar stealth applications. However, conventional microwave absorbers are hindered by limitations such as narrow bandwidth, large size, and inadequate absorption rates. Leveraging metasurfaces presents an ideal approach for creating microwave absorbers, but metasurface-based broadband absorbers typically entail intricate structures, natural absorbing materials, or electronic components, posing challenges in terms of fabrication and expansion. Here, we numerically demonstrate a simple multi-scale fractal metasurface microwave absorber, with the full width at half-maximum of band exceeding one optical octave. By integrating the localized surface plasmon resonance absorption band and the Salisbury-Screen-type absorption band, we achieve an average absorption of 90% ranging from 11.5 GHz to 27.1 GHz. Furthermore, this absorber exhibits excellent polarization insensitivity and maintains high absorption even at large incident angles. The device, offering both broadband absorption and a straightforward structure, holds significant promise for practical applications and widespread adoption.

Trifunctional Fe3O4@MIP nanocatalytic probe-gold nanosol SERS quantitative analysis of ultratrace dinotefuran

A new trifunctional magnetic nanosurface imprinted polymer (MMIP) nanoprobe (Fe3O4@MIP) were rapidly prepared by microwave digestion procedure, and the nanoprobe was characterized in details. It was found that the nanoprobe not only could specifically recognize dinotefuran (DNT), but also could catalyze the HAuCl4-pyruvate indication reaction to produce gold nanoparticles (AuNPs). The generated AuNPs have strong surface enhanced Raman scattering (SERS) effect using VB4r as molecular probes, resonant Rayleigh scattering (RRS) and surface plasmon resonance absorption (Abs) effect. After adding DNT, it specifically combined with Fe3O4@MIP to form Fe3O4@MIP-DNT conjugates with weak catalytic activity, and the SERS/RRS/Abs signal decreased linearly. Based on this, a new SERS/RRS/Abs trimode sensing platform was constructed for detection DNT with detection limit of 0.009, 0.01 and 0.35 nmol/L, respectively. Due to the unique magnetic properties of the nanoprobe, DNT could be easily and quickly identified, separated and enriched, the enrichment factor was up to 100 times. As a comparison, we also investigated the catalytic and specific recognition effects of MMIP nanoprobes prepared with different neonicotinoid insecticides template molecules and functional monomers.

Infrared light driven overall water vapor splitting on a plasmonic semiconductor p-n heterojunction photocatalyst

Photocatalytic overall water splitting (OWS) has yet to be realized on plasmonic semiconductor photocatalysts. In this work, we reported a plasmonic heterojunction of p-Cu1.81S/n-CdS with homogeneously distributed p-type and n-type domains in a single nanoparticle. The plasmonic heterojunction displays a strong localized surface plasmon resonance (LSPR) absorption peak at 1480 nm and can drive the OWS into hydrogen and oxygen under infrared light (IR) irradiation. The IR light-induced hot electrons and holes in Cu1.81S nanodisks alone can split water vapor into hydrogen and oxygen, but with poor efficiency. Surprisingly, the plasmonic p-Cu1.81S/n-CdS heterojunction shows significantly improved IR light-driven OWS performance. Under the irradiation of IR light (λ > 800 nm), the hydrogen and oxygen production rates were 0.73 mmol gcat−1 h−1 and 0.33 mmol gcat−1 h−1, respectively. The heterojunction photocatalyst delivered a solar-to-hydrogen conversion efficiency (STH) of 0.02 % under AM 1.5G irradiation. The present study has demonstrated that plasmonic semiconductors are promising photocatalysts for harvesting IR light for green hydrogen generation.

Smartphone-Integrated resorcinarene macrocycle capped silver nanoparticles (RMF-AgNPs) probe for enhanced La(III) detection in diverse environments

The demand for precise and responsive detection of Lanthanum (La(III)) is critical in key areas such as environmental monitoring, biomedical research, and industrial processes, underscoring the need for advanced sensor technologies. This research reports an efficient and cost-effective preparation of resorcinarene macrocycle framework (RMF) capped silver nanoparticles (RMF-AgNPs). These nanoparticles were then applied as a novel sensor for La(III), demonstrating dual functionality: they act as a colorimetric sensor and a paper-based probe. Unique in its class, the sensor excels in detecting La(III) at ultra-low concentrations, unaffected by other ions, and undergoes a significant color transition from yellow to grey in response to La(III) presence. This change is linked to the localized surface plasmon resonance (LSPR) absorbance alteration. Extensive analytical methods like FTIR, XPS, AFM, FESEM, DLS, Zeta potential, and UV–Vis spectroscopy confirmed that the sensor operates by aggregating nanoparticles induced by La(III). Adding to its practicality, we incorporated a smartphone interface with the paper-based sensor, enhancing its utility for on-the-spot, real-time detection. The sensor's efficacy was validated across various samples, including soil, rock, urine, drinking water, and industrial effluent, showing its versatility. With detection limits of 15 nM (colorimetric) and 280 nM (paper-based), and linear dynamic ranges from 0.05 to 100 µM and 0.5–100 µM respectively, this sensor marks a significant advancement, effectively bridging lab-based detection with field application needs.

Selective detection of thallium by prussian blue-coated gold nano-colorimetric probe

Thallium as a highly dispersed and toxic heavy metal element, is distributed in soil and water due to a result of industrial activities. Thallium is extremely accumulative, which not only makes it harmful to the environment, but also enriches in living organisms and eventually poses a serious threat to human health. In order to detect thallium ions in water quickly and effectively, a PB@AuNPs nano-colorimetric probe based on gold nanoparticles coated with soluble prussian blue was proposed and characterized by UV–visible photometer, dynamic light scattering particle size distribution, Fourier transform infrared spectroscopy and X-ray diffraction. When Tl+ ions were present in the test sample, PB@AuNPs tended to adsorb Tl+ in the system and agglomerated, which exhibited a remarkable color change from wine red to blue. Meanwhile, the intensity and displacement of surface plasmon resonance (SPR) absorption peak changed. PB@AuNPs nanoprobe exhibited a 0.67 μM of limit of detection (LOD) for UV–vis spectra under the optimal pH being 6 with a good linear relationship between the absorbance ratios and the concentrations of Tl+ ions in the range of 10.0 ∼ 30.0 μM, y = 0.04239 x − 0.07483, R2 = 0.99137. The results showed that PB@AuNPs nanoprobe had high selectivity and good anti-interference, which could be used in the detection of actual water samples.

Light erasable surface-enhanced Raman scattering substrates based on the metallic molybdenum dioxide nanospheres

Surface-enhanced Raman scattering (SERS) is a powerful label-free technique for the identification of molecules and molecular structures at extremely low concentrations. However, in most cases, the analytes will remain on SERS substrates, making the substrate a disposable consumable. Here, we propose a light erasable SERS substrate based on the metallic molybdenum dioxide (MoO2) nanospheres. The MoO2 nanospheres present a remarkable localized surface plasmon resonance (LSPR) absorption peak centered at 800 nm. Profiting from the local field magnification induced by the LSPR, MoO2 exhibits excellent SERS detection sensitivity towards rhodamine 6 G (R6G), rhodamine B (RhB), methyl blue (MB), crystal violet (CV) and Malachite Green (MG), with a detection limit of 10−7 M and a maximum enhancement factor up to 5.4 × 104. Moreover, the metallic MoO2 nanospheres possess a high photothermal conversion efficiency of 70.1% and good photothermal stability. The temperature of the MoO2 surface can reach 438 °C under 808 nm laser irradiation with a power density of 2.5 W cm−2, exceeding the decomposition temperature of most organic molecules. Thus, the residual probe molecules can be completely removed from the MoO2 substrate in less than 7.5 min under laser irradiation without compromising its SERS sensitivity and reproducibility. We anticipate our work will pave a new avenue for the development of reusable and highly sensitive SERS substrates.

Colorimetric Sensing of Antioxidant Capacity via Auric Acid Reduction Coupled to ABTS Oxidation.

In this study, a simple and sensitive colorimetric assay has been developed for total antioxidant capacity measurement. The assay is based on the absorption measurement of the bluish-green oxidized product (ABTS·+) formed as a result of the oxidation reaction of the chromogenic reagent ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) with gold(III). However, in the presence of antioxidants, the ABTS oxidation process is effectively suppressed due to the reduction of gold(III) ions to the zerovalent state forming gold nanoparticles (AuNPs). Relatively lighter colors and a significant decrease in absorbance are observed depending on the total antioxidant capacity. Taking advantage of this situation, qualitative and quantitative total antioxidant capacity (TAC) measurements, with the naked eye and UV-vis spectroscopy, respectively, could be successfully performed. The assay is named "auric reducing antioxidant capacity" (AuRAC) because the gold(III) ion-reducing ability of antioxidants is measured. The AuRAC assay was applied to dietary polyphenols, vitamin C, thiol-type antioxidants, and their synthetic mixtures. Trolox equivalent antioxidant capacity (TEAC) values obtained with the AuRAC assay were found to be compatible with those of the reference CUPRAC (cupric reducing antioxidant capacity) assay. The AuRAC assay was validated through linearity, additivity, precision, and recovery, demonstrating that the assay is reliable and robust. Compared to the simple TAC assays in the literature based on AuNP formation with subsequent surface plasmon resonance (SPR) absorbance measurement, this indirect assay has a smoother linear range starting from lower antioxidant concentrations. This method displays much higher molar absorption coefficients for antioxidant compounds than other conventional single electron transfer (SET) assays because 3-e- reduction of trivalent gold (i.e., Au(III) → Au(0)) produces three chromophore cation radicals (ABTS·+) of the assay reagent. The sensor has been successfully applied to complex matrices, such as tea infusions and pharmaceutical samples. The AuRAC assay stands out with its high molar absorptivity connected to enhanced sensitivity as well as its potential to convert into a paper-based colorimetric sensor.

Scalable synthesis of Au@CeO2 nanozyme for development of colorimetric lateral flow immunochromatographic assay to sensitively detect heart-type fatty acid binding protein

Nanozymes with core@shell nanostructure are considered promising biolabeling materials for their multifunctional properties. In this work, a simple one-pot strategy has been proposed for scalable synthesis of gold@cerium dioxide core@shell nanoparticles (Au@CeO2 NPs) with strong localized surface plasmon resonance (LSPR) absorption and high peroxidase-like catalytic activity by redox reactions of Ce3+ ions and AuCl4− ions in diluted ammonia solution under room temperature. A colorimetric lateral flow immunochromatographic assay (LFIA) has been successfully fabricated for sensitive detection of heart-type fatty acid binding protein (H-FABP, an early cardiac biomarker) by using the Au@CeO2 NPs as reporters. The as-developed LFIA with Au@CeO2 NP reporter (termed as Au@CeO2-LFIA) exhibits a dynamic range of nearly two orders of magnitude, and a limit of detection (LOD) as low as 0.35 ng mL−1 H-FABP with nanozyme-triggered 3,3′,5,5′-tetramethylbenzidine (TMB) colorimetric amplification. Furthermore, the practicality of Au@CeO2-LFIA has been demonstrated by profiling the concentrations of H-FABP in 156 blood samples of acute myocardial infarction (AMI) patients, and satisfactory results are obtained.

Dansyl-tagged xanthate ester as a capping agent to synthesize fluorescent silver nanoparticles with binding affinity toward serum albumin.

Developing multifunctional nanomaterials with distinct photochemical properties, such as high quantum yield, improved photostability, and good biocompatibility is critical for a wide range of biomedical applications. Motivated by this, we designed and synthesized a dansyl-tagged xanthate-based capping agent (DX) for the synthesis of fluorescent silver nanoparticles (AgNPs). The capping agent DX was characterized by 1 H and 13 C-NMR, LC-MS, and FT-IR. The synthesized DX-capped fluorescent AgNPs were thoroughly characterized by UV-visible spectroscopy, fluorescence spectroscopy, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), dynamic light scattering (DLS), and zeta potential. The fluorescent AgNPs showed distinct surface plasmon resonance absorption at λmax = 414 nm, fluorescence at λmax = 498 nm, quantum yield = 0.24, zeta potential = +18.6 mV, average size = 18.2 nm. Furthermore, the biological activity of the fluorescent AgNPs was validated by its interaction with the most abundant protein in the blood, that is, BSA (Bovine serum albumin) and HSA (Human serum albumin) with binding constant of 2.34 × 104 M-1 and 2.14 × 104 M-1 respectively. Interestingly, fluorescence resonance energy transfer (FRET) was observed between the fluorescent AgNPs and BSA/HSA with a FRET efficiency of 77.23% and 56.36%, respectively, indicating strong interaction between fluorescent AgNPs and BSA/HSA.

Bactericidal effect of nanosilver synthesized with Neolitsea cassia mucilaginous extract

This study focused on green synthesis of silver nanoparticles using mucilaginous leaf extracts of Neolitsea cassia and demonstrating the bactericidal effect of the product against Staphylococcus aureus and Escherichia coli, which are common in polluted water. A concentration series of silver nitrate was subjected to four treatments by mixing with separate (a) aqueous and (b) 80% methanol extracts of N. cassia leaves in (c) atmospheric and (d) nitrogen gaseous environments, for comparison. A linear increment of the dry weight of silver nanoparticles was observed with increasing silver nitrate concentration (r = 0.99, p = 0), resulting in higher yields from 80% methanol extracts in an atmospheric environment. As characterized by surface plasmon resonance absorption, energy-dispersive X-ray spectroscopy and scanning electron microscopy, quasi-spherical crystalline silver nanoparticles of 11.7 nm average diameter were synthesized. The disk diffusion method showed that the growth of E. coli and S. aureus in culture media was increasingly inhibited with increasing nanoparticle concentration (r = 0.95, p = 0 and r = 0.93, p = 0, respectively). It was concluded that 80% methanol extract in an atmospheric environment was the most productive way to green-synthesize silver nanoparticles from the mucilaginous sap of N. cassia.

A semi-solid, polychromatic dual-band electrochromic smart window: Visualizing sunlight and solar heat transmission

In this paper, a novel semi-solid, polychromatic dual-band electrochromic smart window was constructed by organically assembling monoclinic WO3-x nanowires (m-WO3-x NWs), AlCl3-polyvinyl alcohol (PVA) and polyaniline (PANI). The device not only presented the independent regulation of “bright”, “cool” and “dark”, but also exhibited excellent comprehensive performance, including large optical modulation (74.9 % and 79.1 % at 700 and 2000 nm, respectively.), short coloring/bleaching times (7.6/2.7 and 6.7/3.9 s at 700 and 1200 nm, respectively), and good stability and reversibility (the capacity decreased by 4.3 % and the coulombic efficiency stabled at 99.2 % after 1000 cycles). In addition, the multi-colored PANI endowed the window with the ability to visually monitor modulation modes, as well as indoor sunlight and thermal transmittance. The transparent, green, and blue represented “bright”, “cool”, and “dark” modes, and the depth of the color stood for the control effect in a certain mode. Moreover, the dual-band modulation and polychromatic conversion mechanisms of individual electrodes and the smart window prototype were also elucidated in detail. The modulation of near-infrared light mainly comes from the localized surface plasmon resonance (LSPR) absorption and the phase transition of m-WO3-x NWs, as well as the generated polarons and bipolarons of PANI. While the selective absorption of visible light was related to the bandgap transition of m-WO3-x NWs and the electronic transition of the quinone unit. Surprisingly, the smart window could achieve a maximum decrease of 4.3 °C by controlling the “bright-dark” mode transition in real application simulations, significantly boosting the process of low carbon environmental protection and the construction of energy-saving buildings.

Redox Chemistries for Vacancy Modulation in Plasmonic Copper Phosphide Nanocrystals.

Copper phosphide (Cu3-xP) nanocrystals are promising materials for nanoplasmonics due to their substoichiometric composition, enabling the generation and stabilization of excess delocalized holes and leading to localized surface plasmon resonance (LSPR) absorption in the near-IR. We present three Cu-coupled redox chemistries that allow postsynthetic modulation of the delocalized hole concentrations and corresponding LSPR absorption in colloidal Cu3-xP nanocrystals. Changes in the structural, optical, and compositional properties are evaluated by powder X-ray diffraction, electronic absorption spectroscopy, 31P magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, and elemental analysis. The redox chemistries presented herein can be used to access nanocrystals with LSPR energies of 660-890 meV, a larger range than has been possible through synthetic tuning alone. In addition to utilizing previously reported redox chemistries used for copper chalcogenide nanocrystals, we show that the largest structural and LSPR modulation is achieved using a divalent metal halide and trioctylphosphine. Specifically, nanocrystals treated with zinc iodide and trioctylphosphine have the smallest unit-cell volume (295.2 Å3) reported for P63cm Cu3-xP, indicating more Cu vacancies than have been previously observed. Overall, these redox chemistries present valuable insight into controlling the optical and structural properties of Cu3-xP.

Near-Infrared Responsive Ag@Au Nanoplates with Exceptional Stability for Highly Sensitive Colorimetric and Photothermal Dual-Mode Lateral Flow Immunoassay.

Lateral flow immunoassay (LFIA) has played a vital role in point-of-care (POC) testing on account of its simplicity, rapidity, and low cost. However, the low sensitivity and difficulty of quantitation limit its further development. Sensitive markers with new detection modes are being developed to dramatically improve LFIA's performance. Herein, a ligand-complex approach was proposed to uniformly coat a thin layer of Au onto Ag triangular nanoplates (Ag TNPs) without etching the Ag cores, which not only retain the unique optical properties from Ag TNPs but also acquire the surface stability and biocompatibility of gold. The localized surface plasmon resonance absorption of these Ag@Au TNPs could be finely adjusted from visible (550 nm) to the second near-infrared region (NIR-II) (1100 nm), and even longer, by simply adjusting the ratio between edge length and thickness. Utilizing the Ag@Au TNPs as new markers for LFIA, a highly sensitive colorimetric and photothermal dual-mode detection of the SARS-CoV-2 nucleocapsid protein was achieved with a very low background. The Ag@Au TNPs showed an exceedingly high photothermal conversion efficiency of 61.4% (ca. 2 times higher than that of Au nanorods), endowing the LFIA method with a low photothermal detection limit (40 pg/mL), which was 25-fold lower than that of the colorimetric results. The generality of the method was further verified by the sensitive and accurate analysis of cardiac troponin I (cTnI). This method is robust, reproducible, and highly specific and has been successfully applied to SARS-COV-2 detection in 35 clinical samples with satisfactory results, demonstrating its potential for POC applications.

Exploring the interplay of LSPR and CT: Hierarchical shell thickness optimization for advanced SERS sensing using AgNW@ZIF-8 Core@Shell substrates

Synergistic surface-enhanced Raman spectroscopy (SERS) substrates, leveraging the combined strengths of electromagnetic enhancement (EM) and chemical enhancement (CM), have been extensively explored in the literature. In this study, we introduce a distinctive approach to fabricating core@shell structures, specifically employing silver nanowire @ zeolite imidazole framework-8 (AgNW@ZIF-8) as synergistic SERS substrates. Notably, these substrates offer meticulous control over shell thickness through a straightforward post-synthesis procedure. Utilizing Ag nanowires as the plasmonic core, selected for their broader localized surface plasmon resonance (LSPR) absorption range compared to nanoparticles, we encapsulate them within ZIF-8, a metal-organic framework (MOF) recognized for its proficient charge transfer (CT) properties. Our investigation encompasses the SERS performance across various Raman-active molecules, considering their diverse sizes and distinct frontier molecular orbitals (FMO) energy levels. Additionally, we systematically explore the influence of alterations in shell thickness on SERS outcomes and scrutinize the impact of probe orientation. This comprehensive study not only advances the understanding of synergistic effects intrinsic to MOFs-metal SERS substrates but also provides valuable insights for the rational design of highly sensitive substrates tailored for practical applications.

The effect of photolysis of sodium citrate treated with gold chloride using coloured light on the generation of gold nanoparticles and the repression of WiDr colon cancer cells

Gold nanoparticles (GNPs) are usually formed via a wet chemical method using gold (III) chloride trihydrate (GC), which is treated with stable reducing agents such as sodium citrate (SC). This study determines the effect of coloured light on the formation of GNPs by irradiation of SC after the addition of GC (SCGC) and the effect of the SCGC photolytic procedure on the suppression of WiDr colon cancer cells by forming reactive oxygen species. The absorbance of surface plasmon resonance peaks at 523 nm are 0.069 and 0.219 for SCGC when treated with blue light illumination (BLI) and violet light irradiation (VLI), respectively, whereas green and red light treatments have little or no effect. Most GNPs have diameters ranging from 3 to 15 nm, with a mean of 6 nm, when SCGC is exposed to VLI for 1.5 h. Anionic superoxide radicals (O2•−) are formed in a charge-transfer process after SCGC under VLI treatment; however, BLI treatment produces no significant reaction. Moreover, SCGC under VLI treatment proves to be considerably more effective at inhibiting WiDr cells than BLI treatment, as firstly reported in this study. The reduction rates for WiDr cells treated with SCGC under BLI and VLI at an intensity of 2.0 mW/cm2 for 1.5 h (energy dose, 10.8 J/cm2) are 4.1% and 57.7%, respectively. The suppression rates for WiDr cells treated with SCGC are inhibited in an irradiance-dependent manner, the inhibition percentages being 57.7%, 63.3%, and 80.2% achieved at VLI intensities of 2.0, 4.0, and 6.0 mW/cm2 for 1.5 h, respectively. Propidium iodide is a fluorescent dye that detects DNA changes after cell death. The number of propidium iodide-positive nuclei significantly increases in WiDr cells treated with SCGC under VLI, suggesting that SCGC photolysis under VLI is a potential treatment option for the photodynamic therapy process.

The application of bacteria-derived dehydrogenases and oxidases in the synthesis of gold nanoparticles.

In this work the green synthesis of gold nanoparticles (Au-NPs) using the oxidoreductive enzymes Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH), Glomerella cingulata glucose dehydrogenase (Gc GDH), and Aspergillus niger glucose oxidase (An GOX)) as bioreductants was investigated. The influence of reaction conditions on the synthesis of Au-NPs was examined and optimised. The reaction kinetics and the influence of Au ions on the reaction rate were determined. Based on the kinetic study, the mechanism of Au-NP synthesis was proposed. The Au-NPs were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The surface plasmon resonance (SPR) absorption peaks of the Au-NPs synthesised with Mt CDH and Gc GDH were observed at 535nm, indicating an average size of around 50nm. According to the image analysis performed on a TEM micrograph, the Au-NPs synthesized with Gc GDH have a spherical shape with an average size of 2.83 and 6.63nm after 24 and 48h of the reaction, respectively. KEY POINTS: • The Au NPs were synthesised by the action of enzymes CDH and GDH. • The synthesis of Au-NPs by CDH is related to the oxidation of cellobiose. • The synthesis of Au-NPs by GDH was not driven by the reaction kinetic.

Full-spectrum Bi@SrTiO3 for bi-directional promotion effects on photocatalytic redox reaction: Insight into intermediates and mechanism

The development of full-spectrum photocatalysts active in the near-infrared (NIR) region has gained increasing attention for deleterious pollutant removal. The integration of plasmonic metals with semiconductors is an effective way to widen the light response range of photocatalysts due to the strong light absorption and fast plasmonic energy transfer of the localized surface plasmon resonance (LSPR). In this work, the full-spectrum responsive Bi@SrTiO3 was prepared via facile solvothermal chemical reduction. The optimal Bi@SrTiO3 achieves exceptional photocatalytic Cr(VI) reduction efficiency and tetracycline degradation, realizing bi-directional promotion effects on redox reaction. According to density functional theory (DFT) simulations, the extraordinary photocatalytic performance is attributed to the tunable built-in electric field (IEF) of the Ohmic contact. The favorable adaptability in real water and high stability of BSTO-25 were proved by experimental results. And the possible photocatalytic mechanism was proposed based on theoretical calculation and experimental results. Furthermore, the non-toxicity of the BSTO-25 was evaluated by E.coli cultivation, which further proves the feasibility of treating wastewater with BSTO-25. This work provides a new perspective on constructing full-spectrum-driven photocatalysts for applications dealing with environmental remediation.

Comparison of the antimicrobial photocatalytic activities of SiO2 and Au@SiO2 nanostructures in water decontamination.

Photocatalytic disinfection of Escherichia coli suspension by silicon dioxide nanoparticles and silicon dioxide/gold nanocomposite in a batch reactor is investigated experimentally and results are compared. Silica nanoparticles were synthesized by Stöber method and pulsed laser ablation method was employed to prepare gold nanoparticles in distilled water. Composition of two nanoparticles species was carried out, using the second harmonic pulse of Nd:YAG laser, whose wavelength is in the absorption spectra of gold nanoparticles. Results confirm a decrease in the bandgap energy of silica nanoparticles after composition. Escherichia coli were selected as an indicator of the microbial water contamination. Disk diffusion method was used to evaluate the antimicrobial potential of SiO2 and Au@SiO2 nanostructures. Photocatalytic activities of both nanostructures were examined in dark, and under the irradiation of UV and visible light. In all conditions, the performance of Au@SiO2 nanocomposites was higher than SiO2 nanoparticles. In dark condition the higher biocidal nature and activity of Au nanoparticles and for the case of UV radiation, decreasing the bandgap energy and recombination rate of SiO2 nanoparticles after composition with Au increased the efficiency. For the case of visible light radiation, surface plasmon resonances effects, and local heat of Au nanoparticles were responsible for increasing the efficiency. RESEARCH HIGHLIGHTS: Doping large bandgap semiconductors nanostructures, such as silica with metal nanoparticles, such as gold will improve their photocatalytic activity to work in visible light. In this mechanism, gold nanoparticles act as effective traps to prevent the recombination of photogenerated electron-hole pairs. Other mechanisms, such as Schottky barrier formation, surface plasmon resonance absorption of gold nanoparticles, and biocidal nature of the gold nanoparticles are effective in increasing the efficiency of Au doped silica nanostructures.