Absorption Spectra Of Gold Nanoparticles Research Articles

The impact of pH and temperature on the green gold nanoparticles preparation using Jeju Hallabong peel extract for biomedical applications.

The utilization of gold nanoparticles (AuNPs) has garnered significant attention in recent times, particularly in the field of biomedical research. The utilization of AuNPs in chemical synthesis procedures raises apprehensions regarding their potential toxicity in living organisms, which is inconsistent with their purported eco-friendly and cost-effective aspects. In this investigation, AuNPs were synthesized via the green synthesis approach utilizing Jeju Hallabong peel extract (HPE), a typical fruit variety indigenous to South Korea. The visible-range absorption spectrum of gold nanoparticles from green synthesis (HAuNPs) that are red wine in color occurs at a wavelength of λ = 517 nm. The morphology and particle size distribution were analysed using transmission electron microscopy (TEM) and ImageJ software. The TEM images reveal that the HAuNPs exhibit a high degree of dispersion and uniformity in their spherical shape, with an average size of approximately 7 nm. Moreover, elevating the initial pH level of the mixed solution has an impact on the decrease in particle dimensions, as evidenced by the blue shift observed in the UV-visible spectroscopy absorbance peak. Elevating the reaction temperature may accelerate the synthesis duration. However, it does not exert a substantial impact on the particle dimensions. The outcomes of an avidin-biocytin colorimetric assay provide preliminary analyses of possible sensor tunability using HAuNPs. The cytotoxicity of HAuNPs was evaluated through in vitro studies using the MTT assay on RAW 264.7 cell lines. The results indicated that the HAuNPs exhibited lower cytotoxicity compared to both chemically reduced gold nanoparticles (CAuNPs).

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.

A ratiometric fluorescence sensor based on the inner filtration effect of gold nanoparticles on quantum dots for monitoring dopamine

In this study, a smart phone assisted ratiometric fluorescence sensor was designed for detecting dopamine (DA). The ratiometric fluorescence sensor was prepared by simple physical mixing green quantum dots (GQDS) and red quantum dots (RQDS). DA could induce gold nanoparticles (AuNPs) aggregate via hydrogen-bonding interactions, and further changed the absorption spectrum of gold nanoparticles to overlap with a certain emission spectrum of ratiometric fluorescence sensor. AuNPs had inner filtration effect (IFE) on the ratiometric fluorescence sensor. Due to the IFE, the dispersive AuNPs could quench GQDS, whereas the clustered AuNPs could quench RQDS. With the addition of DA, the color of ratiometric fluorescence changed from orange red to green. To simplify the detection process, a smartphone was employed to detecting DA in human urine by measuring RGB value of fluorescence color changes with a detection limit of 86 nM. This proposed method has the advantages of low cost, easy prevalence and simple operation, thus provides a great promise for rapid detection of biomarker in biological samples.

Plasma resonance ultraviolet absorption spectroscopy of gold nanorods

Au nanorods were prepared by seed growth method. Based on the local surface plasmon resonance (SPR) absorption spectra of gold nanoparticles, the formation and growth kinetics of gold nanorods were observed and studied in real time. The effects of temperature and reaction time on the growth process of gold nanorods were emphatically investigated. It was found that the shift of SPR UV-vis absorption peak was closely related to the experimental conditions The influence factors and mechanism of SPR absorption peak shift are discussed. It is concluded that the moving direction of SPR peak is the result of the competition of particle size and charge transfer.

The effects of glucose and glucose oxidase on the Uv-vis spectrum of gold nanoparticles: A study on optical biosensor for saliva glucose monitoring.

In this study we have investigated the effect of glucose and glucose oxidase (GOD) on the absorption spectrum of gold nanoparticles (Au NPs) with 10-13 nm diameter, in order to improve optical methods of glucose monitoring using surface plasmon resonance of these particles. Different concentrations of glucose solution in water were prepared in the range of human saliva intensity. Two procedures are applied to study glucose effects on the particles; mixing the glucose to the nanocolloid and then adding the GOD, and reversely mixing the glucose and GOD solutions and then pouring in to the nanocolloid. Two different results were obtained that are analyzed based on optical properties. In each method, the effect of glucose and GOD on the size and Uv-vis spectrum of gold nanoparticles has been investigated. Results were interpreted by the physical concept of surface Plasmon resonance (SPR) of Au NPs. This study can open new insight about optical glucose sensing based on surface plasmon of metal nanoparticles.

Microfluidic Spectrophotometer for Neurotransmitter Detection Based on Gold Nanoparticles: Preliminary Results.

A microfluidic-based spectrophotometer for neurotransmitters sensing is presented in this paper. In addition, a neurotransmitter photo-fingerprint is analyzed to evaluate the feasibility of selective neurotransmitter detection using optical techniques. The aim of this work is to detect major neurotransmitters (NTs) using a compact, portable and cost effective optical system for selective and real time NT concentration monitoring. Micro-spectroscopic detection of NTs is challenging because most of them are transparent to visible light. Nevertheless, they interfere with the absorption spectrum of gold nanoparticles (Au-NP), which exhibit maximum absorbance in the range of 520 nm. We observed an Au-NP maximum absorbance shift of up to 4nm in presence of NTs. Based on this shift, it is possible to detect NTs using visible ligh by using vertical-cavity surface-emitting laser (VCSEL) as light sources and an integrated system-on-chip (SoC) spectrophotometer.

Determination of morphological characteristics of metallic nanoparticles based on modified Maxwell-Garnett fitting of optical responses

A modified effective medium theory (MEMT) is introduced to determine morphological characteristics and the volume fraction of colloidal metallic nanoparticles. By analyzing the optical absorption spectra of gold nanoparticles (NPs), this model is used to determine the distribution of prolate and oblate NPs and to demonstrate the presence of spherical NPs. In addition to interband transition, the model takes into account the longitudinal and transversal surface plasmon resonances. The results predicted by the MEMT theory were found to be in very good agreement with the shape distributions obtained by transmission electron microscopy. We found that fitting optical absorption spectra using MEMT provides a robust tool for measuring the shape and concentration of metallic NPs.

Pulse heating of water at the surface of gold nanoparticles: Femtosecond laser spectroscopy of energy relaxation of aqueous colloid of plasmonic nanoparticles under strong excitation conditions

The dynamics of differential absorption spectra of gold nanoparticles has been studied by femtosecond laser spectroscopy over a wide range of excitation energy density. The position of the plasmon resonance peak strongly depends on the dielectric properties of the medium, thereby allowing the use of plasmonic nanoparticles as an optical probe. It has been shown that femtosecond laser spectroscopy techniques, involving analysis of differential absorption spectra of gold nanoparticles in aqueous colloid nanolayer, make it possible to characterize the state of a water nanolayer surrounding the nanoparticle. In particular, at a high excitation energy density, the plasmon resonance absorption band exhibits spectral—kinetic features that suggest vaporization in the nanolayer around the gold particle.

Synthesis of Gold Nanoparticles with Polyamidoamine (Pamam) Generation 4 Dendrimer as Stabilizing Agent for CT Scan Contrast Agent

SummaryGold nanoparticles have great potential in biomedical applications as both a therapeutic and diagnostic agents. Pamam dendrimers are spherical, highly branched macromolecules with a narrow polydispersity to encapsulate and stabilize metal nanoparticles. In the preparation of metal nanoparticles, stabilizers play an important role in controlling particle size. The objectives of this study were to synthesize and characterize of gold nanoparticles. The gold nanoparticles were prepared by reduction of tetrachloroauric acid using sodium borohydride with and without addition of pamam generation 4 dendrimer as stabilizing agent. Gold nanoparticles stabilized pamam generation 4 dendrimer were characterized by Uv‐Vis spectrometry, transmission electron microscopy (TEM), dynamic light scattering (DLS) and zetasizer. The result showed that UV–vis absorption spectra of gold nanoparticles without pamam G4 dendrimer at 530 nm while absorption spectra of gold–pamam G4 dendrimer at 280 nm. The absorbance peak at 280 nm related to individual of gold nanoparticle encapsulated pamam dendrimer. TEM analysis exhibits the occurrence aggregation of gold nanoparticles without pamam G4 dendrimer. DLS analysis exhibit gold nanoparticles has a particles size 88‐252 nm while gold‐pamam G4 dendrimer nanoparticles 2‐15 nm. The addition of pamam generation 4 dendrimer on preparation of gold nanoparticles could prevent aggregation of nanoparticles through entrapment in cavity or core molecules. Au‐PAMAM G4 nanoparticles 0.1 mg/ml has a greater Hounsfield unit (HU) value than iodine at the same concentration, so it has better contrast properties.

A low-cost optical transducer utilizing common electronics components for the gold nanoparticle-based immunosensing application

We developed a cost-effective and convenient optical transducing platform for use in gold nanoparticle-based immunosensing applications. Two types of gold nanoparticles were prepared and used as optical signaling probes: spherical gold nanoparticles (GNPs) exhibiting maximal absorbance at 519nm and gold nanorods (GNRs) exhibiting maximal absorbance at 620nm. Common components used in electronics, including two types of laser diodes (λmax=532- and 635-nm), solar cells, and a multimeter, were reassembled to construct the optical transducing platform. Under the condition in which the emission spectra of lasers and the absorption spectra of gold nanoparticles are matched, laser intensity is decreased. In the designed transducing system, these changes in light intensity are directly indicated as alterations in the DC voltage signal. Based on this principle, we demonstrated the immunosensing applicability of the optical transducing platform. As model immunoreaction pairs, we used anti-mouse IgG/mouse IgG and anti-human IgG/human IgG; superparamagnetic microparticles (MPs) were conjugated with capture antibodies (anti-mouse IgG and anti-human IgG) and the GNPs and GNRs were conjugated with the target mouse IgG and human IgG (model antigens). When the capture antibody-modified MPs and the optical probes mixed in the platform's reaction channel, the optical probes bound to the MPs through an affinity-based reaction. Under a magnetic field, the biospecifically conjugated MP/GNP and MP/GNR complexes could be localized in the reaction channel. Consequently, the amounts of the GNPs and GNRs remaining in the solution were inversely proportional to the rate of the MP/GNP and MP/GNR reactions, and could be registered as DC voltage signals. Based on these results, we expect the novel transducing system and immunosensing strategy presented herein to be applied in practical optical immunosensing performed using key disease markers and their antibodies.

The redshift of surface plasmon resonance of colloidal gold nanoparticles induced by pressure with diamond anvil cell

Colloidal gold nanoparticles, extensively reagent-purified free and well size-controlled monodisperse, are chosen to study Surface Plasmon Resonance (SPR) under pressure with both in situ experimental measurements and theoretical calculations. The refractive index of water is enhanced by pressure up to 1.2 GPa, while the size, shape, and permittivity of gold nanoparticles change insignificantly. A redshift is shown in the absorption spectrum of gold nanoparticles during the process of increasing pressure and the absorption peaks corresponding to SPR of gold nanoparticles is found to be a linear dependence on the refractive index of water under pressure. It is very important to evaluate the wavelength of the absorption spectrum while we explore the phase transition of materials under pressure with surface enhanced Raman spectroscopy based on gold nanoparticles. These results provide us another method of tailoring SPR with pressure and enhancing the efficiency of detecting the weak optical signal under high pressure.

Spectral properties of the surface plasmon resonance and electron injection from gold nanoparticles to TiO2 mesoporous film: femtosecond study

Transient absorption spectra of gold nanoparticles (AuNPs) embedded in mesoporous TiO2 film were studied by a femtosecond laser photolysis pump-probe technique using 25 fs pulses at 740 nm (1.68 eV) and a low fluence of 24 μJ cm(-2). The shift of the bleaching peak in transient spectra by ∼100 meV is detected in the AuNP-TiO2 system, whereas the bleaching peak shift of the same AuNPs in aqueous colloids is not more than ∼5 meV. In addition to the thermal mechanism of the nonlinear response of AuNPs connecting with the electron gas heating and the smearing effect of the Fermi distribution, the electron transfer between AuNPs and TiO2 becomes important for the nonlinear response, in addition to the electron heating mechanism. The electron transfer can explain both the spectral shift and widening of the SPR band of AuNPs in TiO2.

Fragmentation of the gold nanoparticles using femtosecond Ti:Sapphire laser and their structural evolution

This paper reports the production of gold nanoparticles (NPs) with controlled morphology in an aqueous solution of sodium dodecyl sulfate (SDS) by Ti:Sapphire laser. When nanostructures were exposed to an additional laser irradiation/exposure at a particular wavelength corresponding to resonant excitation of surface plasmons or to an interband transition, a considerable size reduction of NPs from 78nm to 15nm has been achieved. This can simply be defined as size refining of NPs by a two-step laser ablation. The relationship between supercontinuum (SC) emission and absorption spectrum of gold NPs has been explored. Additionally the transformation of gold NPs into fractal-like structures has been examined. At longer exposure periods, it is observed that there is a tendency of assembling of NPs into one-dimensional (1d) nanostructures.

Liquid Sensor Using Localized Surface Plasmon Resonance of Gold Nanoparticles Deposited on Polydimethylsiloxane-Based Organic-Inorganic Hybrid Materials

In this paper, we fabricated gold nanoparticles (GNPs) on PDMS-based organic-inorganic hybrid materials in order to assembly liquid sensor using localized surface plasmon resonance. Using PDMS-based hybrid materials as a substrate enables us to control the structure of GNPs by synthesizing hybrid materials with the appropriate molar ratio of metal alkoxide to PDMS because the GNPs were deposited on (3-aminopropyl)triethoxysilane-modified inorganic parts of the hybrid materials by chemical adsorption. In addition, LSPR condition of GNPs deposited on the PDMS-based hybrid materials changes by not only refractive index of liquid surrounding GNPs but polarity of liquid because swelling of PDMS-based hybrid materials results in expansion of interparticle distance of GNPs. We measured absorption spectrum of GNPs as a function of time after the immersion to the liquids. We confirmed that time variation of the spectrum differs by changing the kind of sample liquid according to swelling characteristics of PDMS. This result suggests that the prepared GNPs deposited on hybrid material could work as a sensor for selective detection of the liquid sample.

Control of plasmon resonance of gold nanoparticles via excimer laser irradiation

A significant shift of the surface plasmon resonance absorption spectrum of gold nanoparticles was obtained by the oxidation of the nanoparticle surface via pulsed excimer laser irradiation. The high UV-light absorption of gold nanoparticles chemically produced by citrate reduction led to the important surface oxidation up to 26%. As a result of laser irradiation, the gold/gold oxide core-shell nanoparticles with little variation of the nanoparticle size were produced. After only 5 min of laser irradiation, a 12-nm blue shift in surface plasmon resonance was obtained. The possible mechanisms governing the modification in surface plasmon resonance by laser irradiation of gold nanoparticles were discussed.

Self-Assembly of Multipod-like Gold Nanoparticles in the Soft Template of SDS-PVP Clusters

Gold crystals are able to self-assemble into multipod-like nanoparticles through reducing HAuCl4 by sodium citrate in the soft template composed of sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP) clusters assisted by microwave irradiation. TEM image displayed directly that the reduced products possessed multipod-like morphology with equivalent diameter around 50 nm, and electron diffraction (ED) pattern indicated that the gold crystals were polycrystalline. XRD pattern suggested that the multipod-like nanoparticles were self-assembled into tiny pure gold crystals with diameter about 12.7 nm, which were grown preferentially along (111) lattice plane. The cluster of SDS-PVP had great influence on the size and shape of gold nanoparticles. At a fixed level of PVP, as the concentration of SDS increased, the shape of gold nanoparticles changed from sphere to multipod, and UV-Vis absorption spectrum of gold nanoparticles showed that absorption bands at 800 nm became stronger. The preferred multipod-like gold nanoparticles could be obtained easily and quickly by controlling the composition of the soft template of SDS-PVP clusters.

Fluorescent Property of Gold Nanoparticles with Different Surface Structures

Fluorescence spectra of naked gold nanoparticles, triphenylphosphine stabled gold nanoparticles, and 3-mercaptopropionic acid substituted gold nanoparticles were studied. It was found that fluorescence intensities of gold nanoparticles were highly sensitive to surface molecules. The fluorescence quenching effect of these gold nanoparticles on CdSe nanoparticles was also investigated. This quenching effect was related to the overlap degree between the absorption spectra of gold nanoparticles and the emission spectrum of CdSe nanoparticles, and was surface-dependent as well.