Plasmon Peak Research Articles

Triazole thiazole 4-Nitrobenzohydrazide Schiff base-stabilized silver nanoparticles for selective and efficient detection of neomycin

The widespread usage of antibiotics is leading to an increased negative impact on living organisms due to the consumption of polluted water containing drug residues. The emergence of drug-resistant bacteria has additionally manifested a growing need to identify commonly available medications in water sources. A rapid colorimetric nanosensor is developed in this study to selectively detect Neomycin, an antibiotic of class aminoglycosides. A straightforward reduction method was employed for the formation of Schiff base (4-nitrobenzohydrazide triazole thiazole) capped silver nanoparticles (4NHTS-AgNPs). Upon treatment with Neomycin, the colloidal solution of 4NHTS-AgNPs exhibited an immediate color change from yellow to red while no visible change was observed by addition of other competitive drugs. With an increase in drug concentration, the plasmonic characteristic peak of 4NHTS-AgNPs at 405 nm exhibited a progressive reduction. Furthermore, incubation with NeO resulted in a bathochromic shift and broadening to longer wavelength, specifically to 565 nm. The combined quenching and shift of the plasmonic peak were attributed to the aggregation of 4NHTS-AgNPs induced by the NeO through hydrogen bonding. The 4NHTS-AgNPs based sensor demonstrated a linear dynamic range of 0.02–100 μM, with a limit of detection and limit of quantification of 0.0061 μM and 0.020 μM, respectively. Even in the presence of interfering drugs and for real sample analysis, the selectivity of 4NHTS-AgNPs based sensor towards neomycin remained consistent.

Electrochemical insights into layered assemblies of silver nanoparticles, poly‐L‐lysine, and bovine serum albumin

AbstractThis study presents a comprehensive exploration of the electrochemical behavior of layer‐by‐layer assemblies comprising silver nanoparticles (AgNPs), poly‐l‐lysine (PLL), and bovine serum albumin (BSA) on gold surfaces. AgNPs were synthesized using the reduction of silver ions with the synergy of ascorbic acid and citrate in the presence of sodium chloride. The obtained silver nanoparticles were characterized using transmission electron microscopy, dynamic light scattering and UV‐Vis spectroscopy. A typical preparation produced AgNPs with a plasmon peak at 402 nm, a diameter of 27.5 nm and zeta potential of −37 mV. Employing a drop‐coating approach, we successfully achieved stable multilayers of AgNPs, PLL, and BSA. Cyclic voltammetry revealed well‐defined, bell‐shaped oxidation and reduction peaks of AgNPs within the multilayers, demonstrating complete conversion to AgCl and back to Ag. Notably, the stripping of AgNPs on a monolayer of PLL prepared at pH 4.00 resulted in the highest current intensity, contrasting with lower intensities observed for PLL monolayers prepared at pH 7.01 and pH 9.01. Despite the absence of a splitting reduction peak in the presence of biopolymer materials, a noteworthy observation emerged: the peak splitting exclusively occurred when PLL/AgNP layers, terminated with PLL, were exposed to BSA in the solution.

Silibinin-loaded chitosan-capped silver nanoparticles exhibit potent antimicrobial, antibiofilm, and anti-inflammatory activity against drug-resistant nosocomial pathogens

Nanoparticles capped with natural products can be a cost-effective alternative to treat drug-resistant nosocomial infections. Therefore, silibinin-loaded chitosan-capped silver nanoparticles (S-C@AgNPs) were synthesized to evaluate their antimicrobial and anti-inflammatory potential. The S-C@AgNPs plasmon peak was found at 430 nm and had a particle size distribution of about 130 nm with an average hydrodynamic diameter of 101.37 nm. The Scanning Electron Microscopy images showed the presence of sphere-shaped homogeneous nanoparticles. The Fourier Transform Infrared Spectroscopy analysis confirmed the loading of silibinin and chitosan on the AgNPs surface. The minimum inhibitory concentration of the S-C@AgNPs was reported between 3.12 μg/ml to 12.5 μg/ml and a minimum bactericidal concentration between 6.25 μg/ml to 25 μg/ml against drug-resistant nosocomial pathogens. Moreover, concentration-dependent significant inhibition of the biofilm formation was reported against P. aeruginosa (70.21%) and K. pneumoniae (71.02%) at 30 μg/ml, and the highest destruction of preformed biofilm was observed at 100 μg/ml against P. aeruginosa (89.74%) and K. pneumoniae (77.65%) as compared to individual bacterial control. Additionally, the fluorescence live/dead assay for bacterial biofilm confirmed that 100 µg/ml effectively inhibits the biofilm formed by these pathogens. S-C@AgNPs also showed anti-inflammatory activity, which is evident by the significant decrease in the proinflammatory cytokines and chemokines level in THP1 cells treated with LPS. This study concluded that S-C@AgNPs have potent antimicrobial, antibiofilm, and anti-inflammatory properties and could be a potential option for treating drug resistant nosocomial infections.

Synthesis and characterization of gold/nickel oxide nanoalloy via green laser irradiation

In the present study, a gold/nickel oxide (Au/NiO) nanoalloy was generated by irradiating two nano-metallic material solutions using a green laser. The produced Au/NiO nanocomposites were characterized by UV–Vis–NIR spectroscopy, an X-ray diffraction pattern, TEM and SEM imaging, and photoluminescence and DLS tests. Depending on the concentration of Au NPs in the suspension medium, the final characteristics of Au/NiO nanocomposites vary significantly. Au NPs exhibit an extremely high plasmonic absorption peak at approximately 530 nm. They melted by absorbing the energy of the second harmonic of the laser beam, forming an Au/NiO nanocomposite. Additionally, our results demonstrated that after irradiation with a green laser, the bandgap energy of samples was reduced to 5, 4.3, and 4 eV as the number of Au NPs in nanocomposite structures increased, indicating that the addition of gold to nickel oxide NPs improves their conductivity and reduces the bandgap energy of samples. Moreover, due to composition formation, the number and size of Au NPs dropped following green laser irradiation, while NiO NPs grew in size. This work created an AuNiO nanocomposite by laser ablation, which is a highly effective approach for fabricating nanostructures.

Engineering gold nanoworms with tunable longitudinal plasmon peak in the near infrared and their refractive index sensing properties.

The plasmonic properties of rod-shaped Au nanoparticles make them promising for numerous applications. The synthesis recipes for Au nanorods are well established and their longitudinal plasmon peak can be tuned over a wide wavelength range. Herein, we demonstrate that the longitudinal plasmon peak of gold NWs (NWs), which are bent nanorods, can be finely tuned in the near-infra-red region. The NWs were synthesized using a one-step reaction method. We have seen that the length and aspect ratio of NWs can be tuned by simply changing the pH of the reaction medium. Under higher pH reaction conditions, NWs with relatively smaller sizes were obtained. Similar to nanorods, NWs have a well-defined longitudinal plasmon peak, which scales linearly with their aspect ratio. Finite element analysis was used to model the optical properties of Au NWs. The simulated results matched well with the experimental spectra. The synthesized NWs have shown good refractive index sensitivities (RIS). The RIS of NWs increased with an increase in their aspect ratio. A maximum sensitivity value of 542 nm per RIU, was obtained for NWs with the plasmon peak at 1033 nm. The RIS values are comparable to that of Au nanorods and bipyramids.

Highly sensitive biofunctionalized nanostructures for paper-based colorimetric sensing of hydrogen peroxide in raw milk

Hydrogen Peroxide (H2O2) is a highly hazardous, toxic, and carcinogenic chemical compound utilised in various industries-based applications. Despite strict restriction, they are deliberately added to food items such as milk as preservatives to increase its shelf life. Herein, we have formulated a green rapid colorimetric nanosensor for detection of H2O2 in milk using cotton leaves as both reducing and functionalizing agent for synthesis of silver nanoparticles (AgNPs). UV–Vis spectra exhibit a strong plasmonic peak at around 434 nm. X-Ray Diffraction (XRD) analysis was performed to determine the crystallinity of the nanoparticles. Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscope (TEM) characterizations revealed spherical morphology with size approximately ∼16 nm. This functionalized nanoparticle could colorimetrically sense presence of H2O2 in milk samples both in liquid media and on paper substrates with Limit of Detection (LOD) of 8.46 ppm even in presence of other interfering substances in milk. This inexpensive route will pave the way for in depth research.

Seedless synthesis of Au nanoplates with tunable plasmonic peaks

Au nanoplates with tunable in-plane dipolar localized surface plasmon resonance peaks in a broad range from the visible to near-infrared region were obtained in high yield using a seedless wet chemical growth method after purification. Cetyltrimethylammonium chloride was used as a surfactant, while hydrogen peroxide and sodium borohydride were used as the weak and strong reducing agents, respectively. The edge length and in-plane dipolar localized surface plasmon resonance peak of the Au nanoplates could be adjusted by varying the amounts of hydrogen peroxide and sodium borohydride. The Au nanoplates were further used as the saturable absorber to generate pulsed laser output in a passively Q-switched solid-state laser at approximately 2 µm. Our study offers a new method for obtaining Au nanoplates with tunable plasmonic peaks over a broad range.

Green synthesis of gold nanoparticles using macroalgae Halimeda macroloba extract and their photocatalytic degradation of methylene blue and methyl orange

AbstractGreen synthesis of gold nanoparticles (AuNPs) is gaining attention of researchers because of their varieties of biomedical and environmental applications. This study reported the novel eco‐friendly synthesis of AuNPs using green macroalgae Halimeda macroloba (HM) extract and evaluate their photocatalytic potential. The green synthesized H. macroloba mediated gold nanoparticles (HM‐AuNPs) was characterized using UV–visible spectrophotometry, Fourier‐transform infrared (FT‐IR) spectroscopy, transmission electron microscope (TEM), scanning electron microscope‐energy dispersive spectroscopy, x‐ray photoelectron spectroscopy (XPS), and particle size distribution (PSD) anlaysis. The UV–visible spectrum shows a sharp intense plasmonic resonance peak at 543 nm. The bioactive compounds present in HM were primarily responsible for the biological reduction of gold ions validated by FT‐IR analysis. XRD analysis proved the crystalline face centered cubic structure of the HM‐AuNPs. The average particle size of 18.72 nm and morphological evidences were obtained from the images from TEM. The metallic form of biosynthesised HM‐AuNPs was confirmed by XPS results with a distinctive binding energy. The photocatalytic degradation ability of the green synthesized HM‐AuNPs was investigated against the methylene blue (MB) and methylene orange (MO) dyes under sunlight irradiation. The HM‐AuNPs exhibited 97.23% and 89.91% photocatalytic activity against MB and MO after 90 min of exposure to sunlight, respectively. The overall results of this research indicate that H. macroloba mediated HM‐AuNPs can be used as an effective option for the degradation of industrial dyes.

Antibacterial and anticancer activity of green synthesised silver nanoparticles using polysaccharides extracted from the marine alga Portieria hornemannii

The increasing incidence of cancer cases and multi-drug-resistant bacteria, which are major threats to humankind, forces the research world to innovate new molecules to deal with them. The main aim of the present work is to prepare silver nanoparticles using macroalgal polysaccharides and to study biological activities. The silver nanoparticles (NPs) were prepared using polysaccharides extracted from the marine macro alga Portieria hornemannii by stirring them with 1 mM silver nitrate after 24 h at 90 ºC. The formed silver nanoparticles were characterized using UV-visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR) analysis, Transmission Electron Microscopy (TEM) analysis, selected-area electron diffraction (SAED), and Energy Dispersive X-ray (EDX) analysis. UV-visible spectrum analysis revealed a surface plasmon peak at 380 nm, showing the development of silver nanoparticles. The nanoparticle size varied between 40 and 50 nm and the functional group was analyzed using FT-IR spectrum. The broadband was observed at 3304 cm-1 (hydroxyl and amino group) and the narrow band was observed at 2907 cm-1 (C–H stretching vibration), 1657 cm-1 (stretching of carbonyl groups), and 1001 cm-1 (C–O stretching vibration). The crystalline nature of silver NPs was confirmed by SAED. EDX analysis reveals the purity and the chemical composition of silver NPs. Nanoparticles were highly effective against Proteus mirabilis (24 mm zone of inhibition) and Bacillus substilis (24 mm zone of inhibition). The anticancer activity of the silver nanoparticles tested against colorectal adenocarcinoma cell lines increased at increasing concentrations of nanoparticles.

Self-assembly synthesis of two dimensional vanadium oxide nanotriangles for photocatalytic application

For the first time, we report a Two Dimensional Phase Transfer Reaction (2DPTR) between the three different phases of 2D nanosheets and their applications in catalysis and hydrogen evolution. Plasmonic two-dimensional (2D) nanomaterials have created a niche for themselves in a variety of applications due to their unique and tunable optical properties. In the present work, we report a simple method for the synthesis of three different phases of the 2D vanadium oxide nanosheets to convert to each other at room temperature (amorphous, nanoflakes and nanotriangles). We developed a two-step method that first involves probe ultrasonication to mediate the synthesis of 2D vanadium oxide nanoflakes (VNFs) at room temperature and secondly, their phase transformation to VNTs using hydrogen peroxide or Isopropyl Alcohol (IPA) as the phase transfer reagents. 2D VNTs have been studied for morphological, structural, and optical properties by using a variety of instruments, including TEM, UV–Vis, EPR, RAMAN, and XPS. Thus, after treatment with hydrochloric acid (HCl), the 2D vanadium oxide nanoflakes are easily converted to the 2D amorphous nanosheets (Vam) which then regain crystallinity in the form of VNTs after the addition of Hydrogen peroxide or IPA, with a plasmonic peak around 450 nm. Oxygen vacancies are created in the VNFs, after treatment with HCl, which results in the crystal lattice breakdown. These oxygen vacancies were filled up again when the nanoflakes were treated with hydrogen peroxide or IPA and then resulted in the formation of VNTs. The UV–vis spectroscopy was performed with different addition of concentrations of H2O2, the limit of detection 34.1 µM and linear range 0 to 1000 µM found. Also, a selectivity study proved H2O2 in these 2D VNTs. Vam and VNT also showed effective photocatalytic activity against KMnO4 which is a strong oxidizing reagent used in water treatment. The synthesis and plasmonic nature of the 2D VNTs and the photocatalytic activity of Vam and VNT present in this study is a pioneer report for these novel 2D nanomaterials and they can be further explored with many possibilities in many fields including sensing, catalysis, energy, biomedicine, and many other significant applications in the near future.

Optimization of Organic Capping Material on Silver Nanoparticles by Chemical Reduction and Its Functionalization for Plasmonic Sensor Application

The application of metal nanoparticles in medicine and optoelectronic devices recently has shown remarkable results. In the application of biosensor, metal nanoparticles are functionalized by the used of organic materials such as thiol-derivatives and citrate because of their high affinity to metal such as gold and silver also those organic material is dispersed in water that can be applied directly to bio-materials. Herein, we present the optimization study of capping molecules Trisodium citrate and 3-mercaptopropionic acid (3-MPA) on silver nanoparticles (AgNP) by used of modified chemical reduction and exchange ligand methods to form stable AgNP. The optimization of AgNP was done by varying the ratio among the concentration of the precursor (AgNO3), reducing agent and capping materials. Our colloidal AgNP products show bright yellow to yellow-brownish colour with the plasmonic peak for citrate capped AgNP (Ag-Citrate) at 410-424 nm, 3-MPA capped AgNP (Ag-MPA) by direct method at 428-440 nm, and 3-MPA capped AgNP (Ag-MPA) by ligand exchange method at 436-462 nm. The chemical characteristics of our Ag-citrate and Ag-MPA show the differences coordination of COO- between free citrate or 3-MPA and after citrate or 3-MPA capped on Ag. In our experiment, the TEM images for both samples of AgNPs show the spherical shape with the range of diameter size 5-38 nm which depends on the given ratio of material concentration in the synthesis process. Our AgNP solution results with the open capping of citrate or 3-MPA then can be applied as probe sensor for plasmonic sensor application.

Study on Magnetic and Plasmonic Properties of Fe3O4-PEI-Au and Fe3O4-PEI-Ag Nanoparticles.

Magnetic-plasmonic nanoparticles (NPs) have attracted great interest in many fields because they can exhibit more physical and chemical properties than individual magnetic or plasmonic NPs. In this work, we synthesized Au- or Ag-decorated Fe3O4 nanoparticles coated with PEI (Fe3O4-PEI-M (M = Au or Ag) NPs) using a simple method. The influences of the plasmonic metal NPs' (Au or Ag) coating density on the magnetic and plasmonic properties of the Fe3O4-PEI-M (M = Au or Ag) NPs were investigated, and the density of the plasmonic metal NPs coated on the Fe3O4 NPs surfaces could be adjusted by controlling the polyethyleneimine (PEI) concentration. It showed that the Fe3O4-PEI-M (M = Au or Ag) NPs exhibited both magnetic and plasmonic properties. When the PEI concentration increased from 5 to 35 mg/mL, the coating density of the Au or Ag NPs on the Fe3O4 NPs surfaces increased, the corresponding magnetic intensity became weaker, and the plasmonic intensity was stronger. At the same time, the plasmonic resonance peak of the Fe3O4-PEI-M (M = Au or Ag) NPs was red shifted. Therefore, there was an optimal coverage of the plasmonic metal NPs on the Fe3O4 NPs surfaces to balance the magnetic and plasmonic properties when the PEI concentration was between 15 and 25 mg/mL. This result can guide the application of the Fe3O4-M (M = Au or Ag) NPs in the biomedical field.

Simple method for optical characterization of surface agents on conjugated silver nanoparticles

In this study, a simple formula has been proposed to calculate the refractive index of surface agents of silver nanoparticles (Ag NPs) by using the plasmonic peak of the absorption spectra of dispersed Ag nano-colloids. The basis of the study is the shift in the localized surface plasmon resonance (LSPR) of Ag NPs upon alteration of surface agents. The color changes in a typical metal nano-colloid are mainly due to the shift in the LSPR, which is caused because of electrical interactions of surface agents on the particles. There are some theoretical models to simulate the absorption spectrum, but using these methods to evaluate the plasmonic peak is not facile for a wide range of users. Here, the required simulations were performed for different values of the refractive index of surface agents and particle sizes, and the absorption spectrum and dispersive curves were accordingly plotted. A simple formula was obtained between the wavelength of the plasmonic peak, the refractive index of the shell of surface agents, and the ratio of the hydrodynamic diameter to Feret size of the particles (R0). The refractive index of the surface agents can be calculated by n2=λmax−(202.3R02−748.6R0+947.4)−152.2R02+561.3R0−405.1, where λmax (in nanometer) is the wavelength of the absorption peak due to LSPR. This method can pave the way for experimenters to obtain the refractive index and consequently the type of surface agents around Ag NPs without the need for numerical or mathematical operations. It can also be useful in analyzing the spectral diagnosis of biological agents such as viral antibodies and antigens.

Modulating molecular plasmons in naphthalene via intermolecular interactions and strong light-matter coupling.

We conducted a theoretical investigation on the modulation of plasmon-like resonances in naphthalene - the so-called molecular plasmons - through intermolecular interactions and strong light-matter coupling. The configuration interaction with single excitations (CIS) approach and its quantum electrodynamics extension (QED-CIS-1) are used to describe the molecular plasmon states under these interactions. We detail the effects of changing intermolecular distances of the naphthalene dimer and incorporating the naphthalene molecule into optical cavities, both allowing for precise control of naphthalene's plasmonic responses. Our results show significant shifts of the plasmon peak in the absorption spectra of naphthalene, depending on the spatial configuration of the dimer and cavity parameters such as polarization, frequency, and coupling strength. Further investigation of the naphthalene dimer in a cavity reveals a synergistic effect on the plasmon peak when the two types of interactions are combined. This research provides insights into the plasmonic behavior of simple polyacenes like naphthalene and opens up possibilities for plasmon modulation in more complex systems.

Preparing and studying of Au Nanocomposites Synthesized with different polymer matrix

This work investigates the impact of several polymer matrix types, which are utilised as a capping layer around gold particles, on the optical properties. Nanocomposite materials consisting of gold and polymers such as polyethylene oxide, polyvinyl alcohol, and polyvinyl pyrrolidone were produced by a chemical reduction process. Tri sodium citrate was employed as the reducing agent. using the drop casting approach, nanocomposites based on gold were successfully put as a film on glass substrates.. An investigation was conducted to determine the influence of the polymer matrix type on the optical properties, including surface plasmon resonance, direct band gap, and indirect band gap. Furthermore, the absorption spectra of the materials that were synthesised demonstrated that the selection of the polymer that was utilised during the preparation process has a considerable impact on the location of the plasmonic absorption peak as well as the magnitude of the energy gap. Within the range of 1.9 to 2.3 electron volts (eV), the band gaps were found to be present.

The Impact of Polymer Matrix Type On the Optical Properties of Silver Nanocomposites

Nanocomposites materials of silver (Ag) with polyethene oxide, venal polyalcohol and polyvinyl pyrrolidone were synthesized by chemical reduction method using trisodium citrate (TSC) as a reduction agent. Silver based nanocomposites deposited as a film by dropcasting technique on (2x2 cm2) glass substrates. The effect of polymer matrix type on the optical properties (surface plasmon resonance, transmission and direct and indirect bandgap) were investigated. It was observed from the absorption spectra of the various synthesized materials that the type of polymer used in the preparation process significantly influences the location of the plasmonic absorption peak and the amount of the energy gap.

Continuous flow synthesis and simulation-supported investigation of tunable plasmonic gold patchy nanoparticles.

Plasmonic nanoparticles have intriguing optical properties which make them suitable candidates for sensing or theranostic applications. Anisotropic patchy particles, where metal is locally deposited on the surface of a core particle, exhibit plasmon resonances that can be specifically adjusted for these applications. However, many existing synthesis routes are complex, yield too little material, or provide particles with limited optical tunability. In this work, we present a simple and scalable continuous flow synthesis of gold-on-polystyrene patchy particles with widely adjustable optical properties. By increasing the chloride concentration in the electroless deposition of gold, we slow down the redox reduction kinetics and obtain a dense patch morphology as well as a reduced nucleation rate. The latter is counteracted by introducing a low-level seeding approach where a small number of gold nanocrystals heterocoagulate with the core particles prior to patch growth. Seeding and patch growth are performed in a continuous flow set-up with two T-shaped milli-mixers. The resulting patchy particle samples exhibit a tunable dipolar plasmon peak between 600 nm and 1100 nm. We also investigate the structure-property relationship for our gold patchy particles using finite element method simulations. After identifying a suitable patch shape model, we elucidate the influence of individual geometric parameters on the optical properties and show that the relationship holds true for a large range of patch coverages. Finally, we apply the relationship to explain the time-dependent change in the optical properties of as-synthesized patches by correlating it with the patch shape transformation revealed by electron microscopy.

Localized surface plasmon resonance effect of 3-mercaptopropionic acid capped on silver nanoparticles for sensing probe application

Metal nanoparticles such as gold and silver are often used in various nanotechnology applications due to the localized plasmon resonance effect that occurs when incident photons interact with metal nanoparticles. 3-mercaptopropionic acid (3-MPA) is one of the capping molecules that can be provided for surface functionalization on gold or silver core because it has thiol and carboxylic group as a linking biomolecule, and this allows the use of nanoparticles for biosensor applications. In this study, we successfully synthesized silver nanoparticles capped by 3-mercaptopropionic acid (AgMPA) by use of two kinds of methods i.e ligand exchange and direct reduction, which reveal the unique characteristic plasmonic peaks of AgNP around 430 nm and 436 nm, respectively with spherical shape of AgNP and diameter size about 6-20 nm. The transmittance spectra from Fourier Transform Infrared (FTIR) measurement shows that S-H coordination from 3-MPA is invisible after 3-MPA attach on Ag core due to the strong coordination between Ag and the sulfur (S) ion, while the broaden peaks at 1589 and 1385 cm-1 for AgMPA are assigned to asymmetric and symmetric vibrations of carboxylate groups which overlap between carboxylate from citrate and 3-MPA. Finally, the colorimetric detection using AgCA and AgMPA as sensing probe was carried out by use of Biocytin-Avidin system molecule as analyte, which resulted in the colour changed rapidly from yellow to transparent-yellow and the red-shifted of absorbance spectra indicating the attachment of analyte to functionalized molecule of our synthesized AgCA and AgMPA.

Gold nanomakura: nanoarchitectonics and their photothermal response in association with carrageenan hydrogels.

Photothermal conversion of light into heat energy is an intrinsic optical property of metal nanoparticles when irradiated using near-infrared radiation. However, the impact of size and shape on the photothermal behaviour of gold nanomakura particles possessing optical absorption within 600-700 nm as well as on incorporation in hydrogels is not well reported. In this study, nanomakura-shaped anisotropic gold nanoparticles (AuNMs) were synthesized via a surfactant-assisted seed-mediated protocol. Quaternary cationic surfactants having variable carbon tail length (n = 16, 14, 12) were used as capping for tuning the plasmon peak of gold nanomakura within a 600-700 nm wavelength. The aspect ratio as well as anisotropy of synthesized gold nanomakura can influence photothermal response upon near-infrared irradiation. The role of carbon tail length was evident via absorption peaks obtained from longitudinal surface plasmon resonance analysis at 670, 650, and 630 nm in CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM, respectively. Furthermore, the impact of morphology and surrounding milieu of the synthesized nanomakuras on photothermal conversion is investigated owing to their retention of plasmonic stability. Interestingly, we found that photothermal conversion was exclusively assigned to morphological features (i.e., nanoparticles of higher aspect ratio showed higher temperature change and vice versa irrespective of the surfactant used). To enable biofunctionality and stability, we used kappa-carrageenan- (k-CG) based hydrogels for incorporating the nanomakuras and further assessed their photothermal response. Nanomakura particles in association with k-CG were also able to show photothermal conversion, depicting their ability to interact with light without hindrance. The CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM after incorporation into hydrogel beads attained up to ≈17.2, ≈17.2, and ≈15.7 °C, respectively. On the other hand, gold nanorods after incorporation into k-CG did not yield much photothermal response as compared to that of AuNMs. The results showed a promising platform to utilize nanomakura particles along with kappa-carrageenan hydrogels for enabling usage on nanophotonic, photothermal, and bio-imaging applications.

Structural, electronic, mechanical, and optical properties of the lead-free halide perovskites XGeCl3(X = Cs, K, and Rb) for the photovoltaic and optoelectronic applications

The present investigations into the chloroperovskites CsGeCl3, KGeCl3, and RbGeCl3 are conducted by using the density functional theory-based CASTEP tool with the GGA-PBE method. The space group Pm-3m (221) is used. The computed values of lattice parameters are CsGeCl3: 5.34 Å, KGeCl3: 5.26 Å, and RbGeCl3: 5.29 Å, and also an inverse relationship between volume and density is observed. Total density of states (DOS) and partial density of states (PDOS) calculations are performed to assess the semiconducting properties of the materials. The calculated energy bandgaps, indicative of their direct semiconducting nature are as follows: CsGeCl3: 1.076 eV, KGeCl3: 0.874 eV, and RbGeCl3: 0.952 eV. In the context of mechanical properties, the various mechanical parameters are determined using single-elastic constants, revealing that XGeCl3 (X=Cs, K, Rb) exhibits mechanical stability and anisotropic characteristics. Furthermore, all materials are ductile and hard because Pugh's ratio is greater than 1.75 and Vicker's hardness is less than 40 GPa, respectively. All materials contain the same value of compressibility. Regarding optical characteristics, the loss function, refractive index, dielectric function, optical conductivity, absorption, and reflectivity are comprehensively studied. It is found that the strong peaks of absorption, conductivity (Re & Im), plasmon peak, dielectric functions (Im), refractive indices (Im), and reflectivity fall in the UV region (10 nm-400 nm), while the largest peaks of dielectric functions (Re) and refractive indices (Re) parts belong to the visible region (400 nm- 700 nm). These compounds hold significant promise for applications in photovoltaics and optoelectronics.