Plasmon Resonance Absorption Band Research Articles

Surface Modification of Gold Nanorods (GNRDs) Using Double Thermo-Responsive Block Copolymers: Evaluation of Self-Assembly and Stability of Nanohybrids.

A series of copolymers containing a thermo-responsive biocompatible first block of poly[di(ethylene glycol) methyl ether methacrylate)-co-(oligo(ethylene glycol) methyl ether methacrylate], P(DEGMA-co-OEGMA) were chain-extended to incorporate either poly(N-isopropylacrylamide), PNIPAAm or poly(N-isopropylacrylamide-co-butyl acrylate), P(NIPAAm-co-BA) as second thermo-responsive block using reversible addition-fragmentation chain transfer (RAFT) polymerization. P(DEGMA-co-OEGMA)-b-PNIPAAm copolymers showed two response temperatures at 33 and 43 °C in an aqueous solution forming stable aggregates at 37 °C. In contrast, P(DEGMA-co-OEGMA)-b-P(NIPAAm-co-BA) copolymers showed aggregation below room temperature due to the shift in response temperature provoked by the presence of hydrophobic butyl acrylate (BA) units, and shrinkage upon heating up to body temperature, while maintaining the second response temperature above 40 °C. The terminal trithiocarbonate group of the block copolymers was modified to a thiol functionality and used to stabilize gold nanorods (GNRDs) via the "grafting to" approach. The Localized Surface Plasmon Resonance (LSPR) absorption band of GNRDs with an aspect ratio of 3.9 (length/diameter) was located at 820 nm after surface grafting with block copolymers showing a hydrodynamic diameter of 160 nm at 37 °C. On the other hand, the stability of the P(DEGMA-co-OEGMA)-b-PNIPAAm@GNRDs and P(DEGMA-co-OEGMA)-b-P(NIPAAm-co-BA)@GNRDs nanohybrids was monitored for 8 days; where the LSPR absorption band did not shift or show any broadening. Aqueous dispersed nanohybrids were irradiated with a near-infrared laser (300 mW), where the temperature of the surroundings increased 16 °C after 16 min, where conditions for no precipitation were determined. These tailored temperature-responsive nanohybrids represent interesting candidates to develop drug nanocarriers for photo-thermal therapies.

Capping agent-free aqueous gold nanoparticles generated by an environmentally friendly plasma-liquid method

This study investigates a simple approach for synthesizing gold nanoparticles (Au NPs) using atmospheric pressure plasma without the need for reducing agents, additives, or capping agents. The size, morphology, optical properties, and aggregation stability of the synthesized Au NPs were characterized using scanning electron microscopy, UV-vis spectroscopy, and zeta potential analysis. The UV-vis absorption spectra of the gold nanoparticles, obtained at various Au3+ concentrations and treatment durations with anode plasma discharge, were analyzed. The UV-vis spectra revealed a surface plasmon resonance absorption band between 530–600 nm, indicative of Au NP formation. Results demonstrated that the size of Au NPs can be tuned within the range of 30–75 nm by adjusting the gold salt precursor concentration from 0.3 to 2.5 mmol/L. It was found that plasma treatment for 3–10 minutes, at different Au3+ concentrations, resulted in the formation of Au NPs with varying sizes and morphologies. The study showed that particles with different shapes – spherical, hexagonal, and triangular – were formed depending on the initial concentration of Au3+. The plasma-chemically synthesized nanoparticles at an Au3+ concentration of 0.06 mmol/L were predominantly spherical and exhibited the highest stability (lasting 12–24 hours), with a zeta potential of –20 to –22 mV, compared to samples with Au3+ concentrations ranging from 0.3 to 2.5 mmol/L.

Aggregated gold nanoparticles rich in electromagnetic field “hotspots” for surface enhanced Raman scattering

A simple method for one-step synthesis of aggregated gold nanoparticles (a-AuNPs) using single-layer carbon dots (s-CDs) as the capping agents has been proposed. The obtained a-AuNPs are mainly composed of several spherical AuNPs of 20–25 nm sized, which aggregate to form nanogaps of ∼1 nm. Furthermore, the obtained a-AuNPs produce a strong localized surface plasmon resonance (LSPR) absorption band centered at around 640 nm, which is quite close to the wavelength of the commonly used 633 nm laser in surface enhanced Raman scattering (SERS). Thus, under the irradiation of 633 nm laser, a lot of electromagnetic field “hot spots” are formed at around the nanogaps, and strong SERS activity is achieved. The obtained a-AuNPs are dropped on tin-foil wafers to fabricate SERS substrates, which show the advantages of high sensitivity, fast response, good repeatability and satisfactory stability. On the basis, a sensitive SERS sensor is developed to detect malachite green in aquaculture water, with a low detection limit of 1 × 10−9 mol/L.

Radiolytic reduction of silver nanoparticles probed in situ via Cherenkov spectroscopy

Expanding on our previous efforts demonstrating the feasibility of extracting chemical information in steady-state systems of nanoparticles under irradiation, we demonstrate that the Cherenkov spectra can be used to observe chemical changes in real-time, in situ, and for non-equilibrium systems under irradiation. This is done by way of a dose-resolved measurement of the localized plasmon resonance absorption band associated with the formation and growth of silver nanoclusters and nanoparticles produced via radiolytic reduction of a solution of silver ion under exposure to an electron beam. Additionally, the method utilized in this study provided a significant resolution with a simplified optical system. This paves the way for a technique to determine similar changes in the material in medicinal, industrial (nuclear industry), and research applications—and indeed in any application involving ionizing radiation.

Detection of miRNA-378 based on a catalytic hairpin self-assembly reaction combined with gold nanoparticle colorimetry

Recent studies have shown that abnormal miRNA-378 expression is a rule, rather than an exception, in cervical cancer and can be used as a diagnostic and prognostic biomarker to assess tumor initiation. In this study, we developed a general, sensitive strategy for detecting miRNA-378 using catalytic hairpin self-assembly (CHA) combined with gold nanoparticles (AuNP) colorimetry. The presence of miRNA-378 triggers the repeated self-assembly of two designed hairpin DNAs (H1 and H2) into dsDNA polymers, which leads to changes in the surface plasmon resonance absorption band and the macroscopic color of the AuNP colloids due to the formation of nanoparticle-DNA conjugates. This experimental phenomenon can be observed by ultraviolet-visible spectrometry or even with the naked eye. Using this method, miRNA-378 could be quantitatively detected at the picomolar level (as low as 20.7 pM). Compared with traditional methods, such as quantitative polymerase chain reaction and RNA blotting, this strategy has a simple operation, low cost, and high sensitivity and selectivity, and thus, exhibits significant potential for miRNA detection.

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.

Structural Color Materials with Color Mixing Effect Using Noble Metal‐Free Plasmonic Particles in SiO2–ZrN System

AbstractStructurally colored materials with a color mixing effect are developed using SiO2–ZrN core–shell particles, where ZrN nanoparticles used as shells exhibited localized surface plasmon resonances (LSPRs). ZrN nanoparticles (10–30 nm) are attached to monodispersed SiO2 particles by modifying SiO2 particles with polymers. The attached ZrN nanoparticles exhibited a plasmon resonance absorption band at 700 nm. These SiO2–ZrN core–shell particles have a highly monodisperse particle size and assemble into a particle‐stacked film with Bragg diffraction light in the visible spectrum. The particle‐stacked film of the SiO2–ZrN core–shell particles exhibited the maximum reflection depending on the particle size of the SiO2 core. The ratio of the reflection intensity in the long‐wavelength region corresponding to the ZrN absorption to that in the short‐wavelength region of the particle‐stacked film containing the ZrN shell is less than that of the ratio in only SiO2 particle‐stacked film. The results reveal that these particle‐stacked films exhibit a “color mixing effect” that combines specific wavelength absorption through plasmon resonance and specific wavelength diffraction owing to the periodic structure without using precious metals.

Antitumor activity of bimetallic silver/gold nanoparticles against MCF-7 breast cancer cells.

Breast cancer poses a global threat with rising incidence and high mortality. Conventional treatments, including chemotherapy, radiation, surgery, and immunotherapy, have side effects, such as resistance issues and adverse effects due to genetic mutations. Meanwhile, noble metal nanoparticles (NPs) synthesized using environmentally friendly methods offer alternative treatments. Bimetallic gold (Au) and silver (Ag) NPs, using natural compounds like starch as stabilizers, enhance biomedical applications, including breast cancer therapies. In this work, the optical properties, stability, and particle size of colloidal bimetallic Ag/Au NPs were analyzed using UV-visible spectroscopy and ζ-potential measurements. The structural properties of the NPs were studied by powder X-ray diffraction (PXRD), while the morphology, chemical composition and particle size were determined using scanning transmission electron microscopy (STEM). The antitumor properties of the Ag/Au NPs were analyzed on human breast cancer cells (MCF-7) using the MTT viability method, reactive oxygen species (ROS) production, and genotoxicity assays. Peripheral blood mononuclear cells (PBMCs) were used as a reference of healthy cells. UV-vis spectroscopy and EDX mapping analysis confirmed the synthesis of bimetallic Ag/Au NPs. Localized surface plasmon resonance (LSPR) absorption bands shifted from 407 nm (Ag) to 524 nm (Au) based on the chemical composition of the NPs. The Ag/Au NPs showed cytocompatibility in PBMCs and a dose-dependent anticancer effect against MCF-7 cancer cells, as well as cell death dependent on ROS production was observed, particularly in NPs with atomic compositions of 50 and 75 at% Ag. This biological activity of the bimetallic NPs was associated with genotoxic damage of 20-24% greater than that observed in the monometallic counterparts. This study demonstrated the synthesis of mono- and bimetallic Ag/Au NPs using a rapid, reproducible and environmentally friendly method, with successful biomedical application against human breast cancer MCF-7 cells.

Eco-Friendly Synthesis of Silver Nanoparticles Using Aqueous Extract of Ziziphus Spina-Christi Seeds: Characterization and Stability

In this study, silver nanoparticles (Ag-NPs) were prepared using an aqueous extract of Ziziphus Spina-Christi Seeds (ZSCS) powder as an eco-friendly material, reducing agent and capping ligand. The synthesized Ag-NP was characterized using UV-visible absorption spectroscopy (UV-Vis), Fourier transform infrared (FTIR), transmission electron microscopy (TEM) and dynamic light scattering (DLS). From The UV-Vis spectra, the surface plasmon resonance (SPR) absorption band at 443 nm confirmed the formation of Ag-NPs. The TEM results demonstrated that the synthesized Ag-NPs have mostly spherical shapes with a particle size of 21.54 nm. In addition, the particle size and the specific surface area (SSA) of Ag-NPs decreased with increasing ZSCS powder extract volume and AgNO3 concentration. The basic medium was found to be better than the acidic medium to prepare Ag-NPs. At a pH value equal to 9.5, within 30 minutes, the color of the solution was changed from colorless to brownish-orange. SPR absorption band of Ag-NPs demonstrated that the synthesized Ag-NPs have high stability over a period of 8 months. From FTIR results, the stretching of C-O group at 1223 and 1031 cm-1 disappeared after bioreduction of AgNO3, these results may be due to that Ag reduction was carried out by some hydroxyl groups that get oxidized at the expense of Ag+ because Ag+ is reduced to Ag-NPs.

Physicochemical robustness of pulse laser ablated silver-copper nanocomposoites against varied bacterial strains

Nanocomposites (NCs) of inorganic materials with controlled physicochemical characteristics became beneficial for diverse biomedicine and pharmacology applications. Thus, some new types of crystalline spherical silver (Ag)/copper (Cu) nanocomposites (Ag–CuNCs) were made at various laser fluences (ranged from 0 to 14.15 ± 3.9 J cm−2) using the pulsed laser ablation in liquid (PLAL) approach and characterized for the first time. The structures, morphologies, optical and bactericidal properties of these colloidal NCs were determined and the results for the best sample are presented. These NCs showed distinct surface plasmon resonance absorption bands at 402 and 580 nm accompanied by a blue shift. FTIR spectra verified the dispersion of pure Ag–CuNCs in deionized water and XRD pattern confirmed their crystalline nature. EDX analysis of samples confirmed their high purity with appropriate elemental distribution. HRTEM image of the optimum sample exhibited the presence of spherical Ag–CuNCs of mean diameter ≈ 6 ± 1.3 nm and lattice spacing of 0.073 nm and 0.155 nm. Model simulated optimized structure of Ag–CuNCs reaffirmed their stability and chemically reactive HOMO-LUMO isopotential surface. The antibacterial potential of the produced Ag–CuNCs was evaluated using the inhibition zone diameter (IZD) and optical density (at 600 nm) measurements. The optimum Ag–CuNCs prepared at 14.15 ± 3.9 J cm−2 when tested against E. coli, P. aeruginosa, B. subtilis and S. aureus bacteria showed the IZD of 23, 24, 21 and 22 mm, respectively. It was shown that by tuning the laser fluence, the physicochemical and bactericidal attributes of the proposed Ag–CuNCs can be customized, that may have significant implications for potential uses in nanomedicine.

Facile phytosynthesis of gold nanoparticles using Nepeta bodeana Bunge: Evaluation of its therapeutics and potential catalytic activities

In the present study, the ethanol extract of leaves of Nepeta bodeana Bunge was utilized in environmentally friendly synthesis of gold nanoparticles (AuNPs) via an immediate, one-step, and cost-effective process. The biosynthesized AuNPs were characterized using a variety of techniques, including UV–visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and laser Doppler electrophoresis (zeta potential), among others. Pink in hue, the manufactured AuNPs were practically spherical and had<20.5 nm in diameter. The peak of the localized surface plasmon resonance absorption band at 547 nm helped to explain the biogenic synthesis of AuNPs, which used the ethanolic extract of the Nepeta bodeana leaves. In addition to this, the biosynthesized AuNPs possessed the remarkable stability as a result of their zeta potential value of − 22.3 mV. The green synthesized AuNPs demonstrated the excellent catalytic activity because they were able to catalytically degrade methylene blue (MB) at a variety of concentrations. The results indicated that 94.2% of MB were degraded after 10 min. They also showed a remarkable antibacterial activity against both Gram-nrgative (Pseudomonas aeruginosa and Escherichia coli) and Gram-positive (Staphylococcus aureus and Bacillus cereus) bacteria. In addition, a proper antifungal activity with the minimum inhibitory concentration (MIC) values of 50 and 25 μg/mL against Candida albicans and Aspergillus niger, respectively, were determined. The phytosynthesized AuNPs indicated a considerable antioxidant activity of 83% and 74% in the applied DPPH and ABTS radical scavenging activity tests, respectively. The anti-inflammatory properties of the synthesized AuNPs were established to be dose-dependent and varied from 11% to 76%. The green synthesized AuNPs also exhibited a concentration-dependent cytotoxicity on human liver (HepG2) and breast (MCF-7) cancer cells, which were around 77.4 and 71.2% at 300 µg/mL, respectively. They showed as well a notable anti-diabetic activity with the 52% inhibition of α-amylase and the 62% glucose uptake activity by yeast cells at 300 µg/mL. All these findings suggested that the produced AuNPs could be explored for developing many therapeutic as well as catalytic useful products.

Surface grafted gold nanorods (GNRDs) using thermosensitive copolymers with various transition temperatures: Nanomaterials with potential application for photothermal therapy

A series of diblock copolymers containing a biocompatible polyethylene glycol (PEG) block and a thermoresponsive poly(N-vinyl caprolactam) (PNVCL) based block, were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The cloud point temperature (Tcp) in water of the diblocks was adjusted from 35 to 42 °C by adding N-vinyl pyrrolidone (NVP) units in the thermoresponsive block. The terminal trithiocarbonate group evolving from the RAFT agent used in the synthesis, was modified to thiol to stabilize gold nanorods (GNRDs) via a “grafting-to” approach. Stability of the PEG-b-P(NVCL-co-NVP)@GNRDs nanomaterials was monitored during 8 days; where the localized surface plasmon resonance (LSPR) absorption band did not shifted or showed any broadening. Aqueous dispersed samples were irradiated with near-infrared laser light for 10 min, observing a temperature increase from 25 to 50 °C depending on the laser optical power (between 100 and 500 mW); while no precipitation was observed. For temperatures above the cloud point temperature of the copolymers (Tcp), the formation of aggregates in sizes around 200 nm was observed without precipitation. This study demonstrates that the stabilization of gold nanorods by grafting with the title thermoresponsive block copolymers, and the observed temperature-dependent block-copolymer@GNRD aggregation, has potential uses in drug-delivery applications for photothermal therapy.

Gold Nanoparticles: A Didactic Step-by-Step of the Synthesis Using the Turkevich Method, Mechanisms, and Characterizations

In this study, gold nanoparticles (AuNPs) were synthesized using the Turkevich method. This article explains the didactic step-by-step synthesis, showing pictures of the entire process, including a well-explained mechanism and characterization study. Synthesis involves the reduction of NaAuCl4 using sodium citrate at high temperatures (approximately 90 °C). The two main mechanisms used to explain AuNPs synthesis via the Turkevich method are also discussed. The first mechanism considers that a nanowire intermediary and the other proposes that aggregate intermediates are not formed at any time during the synthesis. The materials (NaAuCl4 and AuNPs) were characterized using UV-Vis spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and dynamic light scattering (DLS). The UV-Vis spectrum exhibits an absorption maximum at 521 nm because of the surface plasmon resonance (SPR) absorption band of the AuNPs. The SEM images of NaAuCl4 show crystals with cubic shapes, while the AuNPs have an average particle size of approximately 16–25 nm and particles that appear mainly spherical. To confirm the particle shapes, AFM was conducted, and it was possible to clearly observe individual spherical nanoparticles and their aggregates, and the average diameter of these AuNPs was approximately 12–19 nm. The XRD pattern of AuNPs showed four main characteristic peaks corresponding to the (111), (200), (220), and (311) planes, confirming the presence of cubic (FCC) gold. The DLS presented an average particle size of 3.3 ± 0.9 nm and a polydispersity index (PDI) of 0.574. AuNPs were synthesized using a simple and rapid method. The resulting spherical and ultra-small particles can be used in several applications.

Photocatalytic and biological properties of silver nanoparticles synthesized using Callistemon lanceolatus leaf extract

Silver nanoparticles (AgNPs) have been extensively explored due to their diverse applications in catalysis, medicine, drug delivery, etc. Physical and chemical methods of synthesizing AgNPs pose a threat to the environment due to the use of toxic and non-biodegradable substances. Green synthesis of AgNPs due to its eco-friendly nature is considered a novel approach as it can be easily scaled up and avoid the use of toxic chemicals. The aqueous extract of leaves from Callistemon lanceolatus was used in the present study for the biosynthesis of AgNPs using the Box-Behnken design (BBD) of response surface methodology (RSM). The study involves the determination of antioxidant, antibacterial, and α-amylase inhibitory activities of biosynthesized AgNPs. In addition, the photocatalytic activity of the synthesized AgNPs was assessed through the degradation of methylene blue dye. The AgNPs showed a characteristic plasmon resonance absorption band around 424 nm. Furthermore, biosynthesized AgNPs were face-centered cubic (fcc) with an average diameter of 41.93 nm as determined by XRD and TEM analysis respectively. The chemical nature of biogenic AgNPs was ascertained using energy-dispersive X-ray (EDX) analysis. Similarly, biosynthesized AgNPs were also characterized using FTIR, SEM, and DLS analysis. The AgNPs showed potential DPPH radical scavenging (IC50 of 40.86 ± 1.8 µg/mL) and α-amylase inhibitory (85.3 % at 100 µg/mL) activities. They also possessed appreciable antibacterial activity with MIC and MBC values ranging from 40 to 80 µg/mL and 60–150 µg/mL respectively. The photocatalytic degradation of methylene blue dye by AgNPs showed a rate constant of 0.009 min−1. Also, AgNPs were effective in degrading the MB dye up to 91 % in 300 min with a concentration of 0.1 mg/mL. Additionally, the reusability of AgNPs as nano-catalyst showed a small decrease in their photo-catalytic activity after every consecutive cycle up to five cycles. It may be concluded that AgNPs produced from C. lanceolatus leaf extract may have biomedical uses and applications in the purification of water contaminated with organic dyes.

Reflective Fiber Temperature Probe Based on Localized Surface Plasmon Resonance towards Low-Cost and Wireless Interrogation.

Reflection fiber temperature sensors functionalized with plasmonic nanocomposite material using intensity-based modulation are demonstrated for the first time. Characteristic temperature optical response of the reflective fiber sensor is experimentally tested using Au-incorporated nanocomposite thin films deposited on the fiber tip, and theoretically validated using a thin-film-optic-based optical waveguide model. By optimizing the Au concentration in a dielectric matrix, Au nanoparticles (NP) exhibit a localized surface plasmon resonance (LSPR) absorption band in a visible wavelength that shows a temperature sensitivity ~0.025%/°C as a result of electron-electron and electron-phonon scattering of Au NP and the surrounding matrix. Detailed optical material properties of the on-fiber sensor film are characterized using scanning electron microscopy (SEM) and focused-ion beam (FIB)-assisted transmission electron microscopy (TEM). Airy's expression of transmission and reflection using complex optical constants of layered media is used to model the reflective optical waveguide. A low-cost wireless interrogator based on a photodiode transimpedance-amplifier (TIA) circuit with a low-pass filter is designed to integrate with the sensor. The converted analog voltage is wirelessly transmitted via 2.4 GHz Serial Peripheral Interface (SPI) protocols. Feasibility is demonstrated for portable, remotely interrogated next-generation fiber optic temperature sensors with future capability for monitoring additional parameters of interest.

Effect of various concentrated copper and plant extract concentrations on the antibacterial activity.

Copper nanoparticles (Cu NPs) were created using two methods, one with reducing and stabilizing agents and the other with green tea extract. The formation of Cu NPs has been described by spectra of UV-Vis absorption, which showed the surface plasmon resonance (SPR) at 620 and 630 nanometers, respectively. The position and shape of the surface plasmon resonance and plasmon absorption bands strongly depend on the reaction conditions. The crystalline morphology and size of the nanoparticles were determined by XRD, FESEM, and TEM studies. In both ways, the average particle size of Cu nanoparticles was found to be in the range of 28 nm and 142 nm for the chemical and green methods, respectively. The effectiveness of the materials prepared by both methods was high, and the antibacterial activity of the products prepared by both ways was against E. coli and S. aureus pathogens represented by inhibition zones ranging from 14–20 mm, 30–38 mm, and 11–18 mm, 20–24 mm, respectively.

Propofol-induced in-situ formation of silver nanoparticles: A sensing colorimetric method

A simple and eco-friendly colorimetric sensing method has been developed for the extremely effective detection of propofol in exhaled breath condensate (EBC). In this study, we put forward a Tollens' procedure, in which silver nanoparticles (AgNPs) were produced using propofol as a reducing agent. To verify the in-situ synthesis of AgNPs, the TEM images, and UV-Vis absorbance were recorded in the absence and presence of propofol. The solution turned from a colorless to yellow and deep yellow color due to the surface plasmon resonance absorption band of formed AgNPs. The intensity of nanoparticle absorbance was quantitatively correlated with the propofol concentration. The proposed sensor revealed good linearity over the range of 0.01–0.8 µg mL−1 at 422 nm with the detection limit of 8.8 ng mL−1 under optimum conditions. Finally, the proposed colorimetric sensor was successfully used for the determination of propofol in the EBC sample of patients receiving propofol.

Silver-platinum bimetallic nanoparticles as heterogeneous persulfate activator for the oxidation of malachite green

Fabrication of noble metal nanoparticles by using green chemical method with plant extract as reducing agent to the in situ oxidation toxic water contaminants have been the subject of various investigators due to their enhanced catalytic efficiencies. This paper describes the extraction of caffeic acid from Artemisia herba-alba aqueous extract, and preparation of silver (Ag), platinum (Pt), and silver-platinum (Ag-Pt) nanoparticles with caffeic acid as a reducing and capping agent. The as-prepared Ag-Pt NPs was used as a heterogeneous activator of persulphate (K2S2O8) for the in situ chemical oxidation of malachite green (MG). The Ag-Pt NPs shows no surface Plasmon resonance absorption band. The malachite green dye was completely decolorized in presence of Ag-Pt/K2S2O8 system. SO4-• and HO• radicals generated by the cleavage of S2O82- peroxide activation with Ag-Pt were responsible for the MG decolorization as well as mineralization. The Ag-Pt NPs acted as a sacrificial electron donor. The Ag-Pt NPs were characterized by using conventional techniques such as, UV–visible, FTIR, SEM, TEM, EDX, XPS, and XRD spectroscopic methods.

Quercetin- and caffeic acid-functionalized chitosan-capped colloidal silver nanoparticles: one-pot synthesis, characterization, and anticancer and antibacterial activities.

The presented study comprises the one-pot synthesis and the characterization of quercetin- and caffeic acid-functionalized chitosan-capped colloidal silver nanoparticles (Ch/Q- and Ch/CA-Ag NPs), and their antibacterial and anticancer activities. The formation of Ch/Q- and Ch/CA-Ag NPs has been confirmed by ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The characteristic surface plasmon resonance (SPR) absorption band has been found at 417 and 424 nm for Ch/Q- and Ch/CA-Ag NPs, respectively. The formation of a chitosan shell comprising quercetin and caffeic acid, which surround the colloidal core Ag NPs, was confirmed by UV-vis, and FTIR analyses, and monitored by TEM microscopy. The size of nanoparticles has been determined as 11.2 and 10.3 nm for Ch/Q- and Ch/CA-Ag, respectively. The anticancer activity of Ch/Q- and Ch/CA-Ag NPs has been evaluated against U-118 MG (human glioblastoma) and ARPE-19 (human retinal pigment epithelium) cells. Both NPs showed anticancer activity, but Ch/Q-Ag NPs seemed to be more effective on cancer cell lines (U-118 MG) in comparison to healthy ones (ARPE-19). Furthermore, the antibacterial activity of Ch/Q- and Ch/CA-Ag NPs against Gram-negative (P. aeruginosa and E. coli) and Gram-positive (S. aureus and S. epidermidis) bacteria was determined, and dose-dependent antibacterial effects were found.

Gold-silver alloy hollow nanoshells-based lateral flow immunoassay for colorimetric, photothermal, and SERS tri-mode detection of SARS-CoV-2 neutralizing antibody

Although many approaches have been developed for the quick assessment of SARS-CoV-2 infection, few of them are devoted to the detection of the neutralizing antibody, which is essential for assessing the effectiveness of vaccines. Herein, we developed a tri-mode lateral flow immunoassay (LFIA) platform based on gold–silver alloy hollow nanoshells (Au–Ag HNSs) for the sensitive and accurate quantification of neutralizing antibodies. By tuning the shell-to-core ratio, the surface plasmon resonance (SPR) absorption band of the Au–Ag HNSs is located within the near infrared (NIR) region, endowing them with an excellent photothermal effect under the irradiation of optical maser at 808 nm. Further, the Raman reporter molecule 4-mercaptobenzoic acid (MBA) was immobilized on the gold–silver alloy nanoshell to obtain an enhanced SERS signal. Thus, these Au–Ag HNSs could provide colorimetric, photothermal and SERS signals, with which, tri-mode strips for SARS-CoV-2 neutralizing antibody detection were constructed by competitive immunoassay. Since these three kinds of signals could complement one another, a more accurate detection was achieved. The tri-mode LFIA achieved a quantitative detection with detection limit of 20 ng/mL. Moreover, it also successfully detected the serum samples from 98 vaccinated volunteers with 79 positive results, exhibiting great application value in neutralizing antibody detection.