Presence Of AuNPs Research Articles

A detailed EIS study of boron doped diamond electrodes decorated with gold nanoparticles for high sensitivity mercury detection

This work compares the electrochemical impedance response of polished and unpolished boron doped diamond (BDD) electrodes, during mercury detection measurements. For each substrate type both bare electrodes and electrodes decorated with average diameter 30 nm AuNPs were used, to investigate the role of AuNPs during mercury sensing with diamond electrodes. In square wave anodic stripping voltammetry (SWASV) measurements for mercury detection, the mercury ions in the electrolyte are deposited onto, then stripped from the diamond electrode surface. To investigate the different electrode performances during these steps, the EIS measurements were made at the deposition and stripping potentials, alongside scans at open circuit potential for comparison. The performance of the electrodes is assessed in terms of their electron transfer rate (k0). The electrodes decorated with AuNPs are shown to have lower capacitance and higher reactivity than the bare pBDD and BDD electrodes, until the mercury concentration in the electrolyte is < 500 µM, when the sp2/sp3 carbon ratio at the surface of the electrodes has a greater influence on the sensitivity for mercury detection than the presence of AuNPs.

Synthesis of high crystallinity biphasic calcium phosphates/gold nanoparticles composites by solution combustion method with antimicrobial response

Calcium phosphates are biomaterials widely used in bone tissue engineering. In recent years, the alternative of obtaining these materials with antimicrobial properties, has been explored due to the multiple advantages that this would imply in the design of devices or implants that prevent the failure of these associated with bacterial colonization. The goal of the present work was obtaining gold nanoparticles supported on biphasic calcium phosphates (BCPs) with high crystallinity by one-step solution combustion technique, and with antimicrobial response, a fact that can significantly reduce the production cost of these materials. X-ray diffractograms (XRD) showed that prepared powders have high crystallinity owing to high temperatures during the combustion reaction, also Rietveld refinement showed that the inclusion of gold nanoparticles (AuNPs) influenced the phases’ ratio obtained. Furthermore, scanning electron microscopy (SEM) showed agglomeration of particles with morphologies with shape tending to be equigranular, while the presence of AuNPs was corroborated by transmission electron microscopy (TEM). All samples that were obtained in a single step, by solution combustion, showed antimicrobial behavior validated through the inhibition halos, whereas particles subjected to thermal treatment lost their antimicrobial response.

Colorimetric determination of acid phosphatase activity and inhibitor screening based on in situ polymerization of aniline catalyzed by gold nanoparticles.

A colorimetric assay for acid phosphatase (ACP) was constructed that isbased on in situ polymerization of aniline catalyzed by gold nanoparticles (AuNPs). Aniline can be polymerized by ammonium persulfate (APS) in acidic condition and form gold-polyaniline core-shell nanoparticles (Au@PANI NPs) in the presence of AuNPs with the assistance of sodium dodecyl sulfate (SDS). AuNPs were also found to accelerate the polymerization process of aniline and thus shorten the reaction time. Upon the introduction of ascorbic acid (AA), the oxidant APS was consumed via the redox reaction. That led to the suppression of the formation of PANI. Consequently, ACP activity can be supervised on the basis of hydrolysis of 2-phospho-L-ascorbic acid trisodium salt (AAP) catalyzed by ACP to release AA. With the increase of ACP activity, the intensity ratio of the absorbance at λ705 nm (A705) and the absorbance at λ530 nm (A530) gradually decreased and the color gradually changed from dark-green to light-green to blue-gray to purple and eventually to pink. This method for ACP determination worked in the range 0.40 to 2.00U·L-1. The detection limit is 0.043U·L-1. The assay was applied to determine ACP in human serum. The recovery ranged from 81.0 to 104.6%. Relative standard deviation was less than 5%. This suits the request forbiological sample analysis. Graphical abstract Schematic presentation of the colorimetric determination of acid phosphatase activity and inhibitor screening based on in situ polymerization of aniline catalyzed by gold nanoparticles. : acid phosphatase (ACP); : gold nanoparticles (AuNPs); : gold-polyaniline core-shell nanoparticles (Au@PANI NPs); ascorbic acid (AA); 2-phospho-L-ascorbic acid trisodium salt (AAP).

Reaction pathway change on plasmonic Au nanoparticles studied by surface-enhanced Raman spectroscopy

Gold nanoparticles (Au NPs) are nanoscale sources of light and electrons, which are highly relevant for their extensive applications in the field of photocatalysis. Although a number of research works have been carried out on chemical reactions accelerated by the energetic hot electrons/holes, the possibility of reaction pathway change on the plasmonic Au surfaces has not been reported so far. In this proof-of-concept study, we find that Au NPs change the reaction pathway in photooxidation of alkyne under visible light irradiation. This reaction produces benzil (COCO) without the presence of Au NPs. In contrast, as indicated by surface-enhanced Raman spectroscopic (SERS) results, the CC triple bonds (CC) adsorbed on Au NPs are converted into carboxyl (COOH) and acyl chloride (COCl) groups. The plasmonic Au NPs not only provide energetic charge carriers but also activate the reactant molecules as conventional heterogeneous catalysts. This study discloses the second role of plasmonic NPs in photocatalysis and bridges the gap between plasmon-driven and conventional heterogeneous catalysis.

β-Lactoglobulin-gold nanoparticles interface and its interaction with some anticancer drugs – an approach for targeted drug delivery

The protein-nanoparticle interface plays a crucial role in drug binding and stability, in turn enhancing efficacy in targeted drug delivery. In the present study, whey protein β-lactoglobulin (BLG) is conjugated with gold nanoparticles (AuNP) and its interaction with curcumin (CUR) and gemcitabine (GEM) has been explored. Further, AuNP-BLG conjugate interactions with anticancer drugs were characterized using dynamic light scattering (DLS), zeta potential, UV-visible, Raman spectroscopy, fluorescence, circular dichroism along with molecular dynamics simulation. The cytotoxicity studies were performed using breast cancer cell lines (MCF-7). ∼8 µM of BLG resides on AuNP (∼29 nm) surface revealed by DLS. Raman scattering of AuNP-BLG conjugate showed orientation of the central calyx of BLG towards solvent. BLG fluorescence confirmed the interaction between AuNP-BLG conjugate with drugs and indicated strong binding and affinity (for CUR KD = 3.71 x 108 M −1, n = 1.83, and for GEM KD = 3.78 x 103 M −1, n = 0.94), enhanced in the presence of AuNP. CD and Raman analysis exhibited selective hydrophilic and hydrophobic conformations induced by drug binding. Computational studies on BLG-drug complexes revealed that the residues Pro38, Leu39 and Met107 are largely associated with CUR binding, while GEM interaction is via hydrophilic contacts which significantly matches with spectroscopic investigation. IC50 values were calculated for all components of this loading system on MCF-7. The possible mechanisms of interaction between AuNP-BLG with anticancer drugs has been explored at the molecular level. We believe that these conjugates could be considered in the targeted drug delivery studies for cancer research. Communicated by Ramaswamy H. Sarma

Effect of Gold Nanoparticle Radiosensitization on Plasmid DNA Damage Induced by High-Dose-Rate Brachytherapy.

PurposeGold nanoparticles (AuNPs) are candidate radiosensitizers for medium-energy photon treatment, such as γ-ray radiation in high-dose-rate (HDR) brachytherapy. However, high AuNP concentrations are required for sufficient dose enhancement for clinical applications. Here, we investigated the effect of positively (+) charged AuNP radiosensitization of plasmid DNA damage induced by 192Ir γ-rays, and compared it with that of negatively (−) charged AuNPs.MethodsWe observed DNA breaks and reactive oxygen species (ROS) generation in the presence of AuNPs at low concentrations. pBR322 plasmid DNA exposed to 64 ng/mL AuNPs was irradiated with 192Ir γ-rays via HDR brachytherapy. DNA breaks were detected by observing the changes in the form of the plasmid and quantified by agarose gel electrophoresis. The ROS generated by the AuNPs were measured with the fluorescent probe sensitive to ROS. The effects of positively (+) and negatively (−) charged AuNPs were compared to study the effect of surface charge on dose enhancement.Results+AuNPs at lower concentrations promoted a comparable level of radiosensitization by producing both single-stranded breaks (SSBs) and double-stranded breaks (DSBs) than those used in cell assays and Monte Carlo simulation experiments. The dose enhancement factor (DEF) for +AuNPs was 1.3 ± 0.2 for SSBs and 1.5 ± 0.4 for DSBs. The ability of +AuNPs to augment plasmid DNA damage is due to enhanced ROS generation. While −AuNPs generated similar ROS levels, they did not cause significant DNA damage. Thus, dose enhancement using low concentrations of +AuNPs presumably occurred via DNA binding or increasing local +AuNP concentration around the DNA.Conclusion+AuNPs at low concentrations displayed stronger radiosensitization compared to −AuNPs. Combining +AuNPs with 192Ir γ-rays in HDR brachytherapy is a candidate method for improving clinical outcomes. Future development of cancer cell-specific +AuNPs would allow their wider application for HDR brachytherapy.

Modulation of enzyme activity at nano-bio interface: A case study with acetylcholinesterase and citrate synthase adsorbed on colloidal metal nanoparticles

The effects of colloidal gold and silver nanoparticles (Au and Ag NP, respectively) were studied on the activity of acetylcholinesterase (AChE), the key enzyme in the pathology of Alzheimer's Disease (AD) and citrate synthase (CS), the mitochondrial enzyme responsible for oxidative metabolism. Being established as a primary basis of neurodegeneration, mitochondrial dysfunction connects both these two enzymes with AD. The in-vitro enzymatic activities are modulated strongly in presence of NPs. The maximum AChE catalytic rate (Vmax) increases by 30% in presence of NP systems. The Michalis-Menten constant (Km) remains unaltered in presence of AuNP; while, ~61.23% increase is noted in presence of AgNP. For the two-substrate enzyme CS, NPs were found to affect only the pathway involving oxaloacetate (OAA) as substrate. In this case, Vmax and Km increased by 21.80% and 46.60%, respectively for AuNP; while the corresponding increase were 18.20% and 33.33%, respectively for AgNP. The binding of AChE on AgNP surface occurred through random contact within very short time scale, followed by slower interaction and contact optimization within tens of nanoseconds. A series of cationic surfactants exhibited optimistic results in restoring the intrinsic activity for both the enzymes. The results highlight neurotoxicity of metal NPs in certain cases like AD and emphasize their use in pharmacological milieu only with suitable accompanying delivery medium like surfactants.

Lavandula angustifolia NAMNAŻANA W KULTURACH IN VITRO NA POŻYWKACH ZAWIERAJĄCYCH AgNP i AuNPs – ALTERNATYWNE ROZWIĄZANIE DLA SYNTETYCZNYCH KONSERWANTÓW W KOSMETYKACH

We determined the preservation properties of Lavandula angustifolia propagated on media with gold or silver nanoparticles with a particle size of 13 and 30 nm. Cosmetic emulsions prepared by using lavender tissue that was propagated on media containing AuNPs and AgNPs showed increased preservative capacities when compared with the control ones. In the case of control cosmetic emulsions, which had no added plant tissues or dehydroacetic acid and benzoic acid (DHA BA), bacterial and fungal colonies appeared after the second week of the experiment. The addition of lavender tissue propagated on media without AuNPs or AgNPs protected the tasted samples from microbial contamination; in this case, bacterial contamination was detected after 4 weeks and fungal contamination after 6 weeks. The addition of lavender tissue propagated on medium containing AgNPs with a particle size of 13 nm at a concentration of 1 mg · dm−3 prolonged the time of detection of bacteria colonies to 8 weeks (0.9) and this result was close and comparable to the effect of DHA BA. Higher concentrations of AgNPs in the culture medium, as well as a larger particle diameter (30 nm), resulted in the decreased preservative capacity of plant tissues. The presence of AuNPs in the culture media showed a positive effect on the antimicrobial activity of lavender; however, to a lesser degree than in the case of AgNPs. Disintegrated fragments of lavender tissue propagated on media containing 1 mg ∙ dm−3 AgNPs with particle size of 13 nm can be used to preserve short shelf life cosmetic emulsions.

In silico modeling of cellular probabilistic nanoparticle radiosensitization in head and neck cancers.

Background: The use of gold nanoparticles (AuNPs) as radiosensitizers may offer a new approach in the treatment of head and neck cancers; minimizing treatment-associated toxicities and improving patient outcomes. AuNPs promote localized dose deposition; permitting improved local control and/or dose reduction. Aim: This work aimed to address the theoretical optimization of radiation doses, fractionation and nanoparticle injection schedules to maximize therapeutic benefits. Materials & methods: Probabilistic nanoparticle sensitization factors were incorporated into the individual cell-based HYP-RT computer model of tumor growth and radiotherapy. Results: Total dose outcomes across all radiation therapy treatment regimens were found to be significantly reduced with the presence of AuNPs, with bi-weekly injections showing the most decrease. Conclusion: Outcomes suggest the need for regular AuNP administration to permit effective radiosensitization.

Enzyme-Free Tandem Reaction Strategy for Surface-Enhanced Raman Scattering Detection of Glucose by Using the Composite of Au Nanoparticles and Porphyrin-Based Metal-Organic Framework.

In this work, an S hybrid nanosheet with multiple functions is synthesized by in situ modification of gold nanoparticles (AuNPs) onto two-dimensional (2D) metalloporphyrinic metal-organic framework (MOF) (Cu-tetra(4-carboxyphenyl)porphyrin chloride(Fe(III)), designated as AuNPs/Cu-TCPP(Fe). Cu-TCPP(Fe) nanosheets contribute peroxidase-like activity, and AuNPs have glucose oxidase (GOx) mimicking performance, which induce the cascade catalysis reactions to convert glucose into hydrogen peroxide (H2O2), and then, by using AuNP catalysis, H2O2 oxidizes the no Raman-active leucomalachite green (LMG) into the Raman-active malachite green (MG). Simultaneously, in the presence of AuNPs, sensitive and selective surface-enhanced Raman scattering (SERS) determination of glucose can be achieved. The bioenzyme-free SERS assay based on such AuNPs/Cu-TCPP(Fe) nanosheets is used for detection of glucose in saliva, showing good recovery from 96.9 to 100.8%. The work paves a new way to design a nanozyme-based SERS protocol for biomolecule analysis.

Mycosynthesis of biocompatible gold nanoparticles using Penicillium sp for bromothymol blue degradation

Introduction and Aim: The Biosynthesis of Gold nanoparticles (Au NPs) is an eco-friendly, cost effective and nontoxic alternative to chemical and physical methods. In the present study synthesis of Au NPs was performed by using a fungi Penicillium sp. isolated from agriculture soil.&#x0D; Materials and Methods: Fungi was isolated from the agricultural field and inoculated into Sabouraud Dextrose broth and incubated at 28º C in a shaker at 180 rpm for 96 to 120 hours. After incubation, the fungal culture was filtered and centrifuged, obtained fungal cell free extracts treated with 1mM gold salt (HAuCl4). The synthesis of Au NPs was confirmed by UV–visible spectroscopy and particles size was measured using Dynamic Light Scattering (DLS). Haemolytic assay of Au NPs was carried out using Chicken RBCs and results measured at 540 nm in UV-visible spectrophotometer. To study catalytic activity, Bromothymol blue (BB) was subjected to reduction by using sodium borohydride (NaBH4, 5.28X10-2 M) in the presence of Au NPs. Then the color change was monitored by visual observation.&#x0D; Results: The synthesis of Au NPs was preliminary observed by a color change from yellow to purple and confirmed by a peak at 560 nm using a UV–visible spectroscopy. The DLS analysis showed that the Au NPs were poly-dispersed and size ranges from 130 to 150 nm. The biosynthesised Au NPs was studied for their biocompatibility and dye degradation properties.&#x0D; Conclusion: The obtained results revealed that biosynthesized Au NPs shows a minimum level of toxicity to chicken erythrocytes and good catalytic activity towards the degradation of hazardous dye bromothymol blue. These nanoparticles could be potentially useful in various applications in medical and environmental fields.&#x0D;

Broadband light absorption by metal nanoparticle or quantum dot-coated silicon nanostructures for solar cell applications

Light absorption by metal nanoparticle (MNP) and quantum dot (QD) coated nanostructures is theoretically investigated for crystalline silicon (Si) solar cells. Despite light trapping by bare Si nanostructures, the near infrared region (NIR) of the solar spectrum remains unharvested owing to the indirect bandgap (1.1 eV) and low absorption coefficient of Si beyond visible wavelengths. In this work, periodic Si nanostructures, in the form of vertical nanowires (NWs), nanopyramids, and flat-topped nanocones, have been modeled, with their sidewalls decorated with spherical gold (Au) NPs. MNPs scatter light into neighboring Si and introduce localized plasmonic effects, thereby, offering strong broadband absorption and high conversion efficiency. Finite-difference time-domain (FDTD) analysis shows enhanced absorption beyond visible wavelengths, in the presence of Au NPs, for varying NP size and nanostructure periodicity. For 700 nm &lt; λ &lt; 1600 nm, the average absorption by Au NP coated Si nanopyramids and flat-topped nanocones is 5× higher than their bare counterparts. Moreover, Si QD/Si NW hybrid structures display better absorption characteristics than the Au NP/Si NW combination. The findings can be used to design and optimize highly efficient Si solar cells that combine light trapping nanostructures with broader, size tunable absorption profiles of plasmonic NPs and QDs.

Metal nanoparticle alters adenine induced charge transfer kinetics of vitamin K3 in magnetic field

In this article, we highlight the alterations in the photoinduced electron transfer (ET) and hydrogen atom transfer (HAT) pathways between an anti-tumor drug vitamin-K3 (MQ) and a nucleobase adenine (ADN) in the presence of gold (Au) and iron (Fe) nanoparticles (NPs). Inside the confined micellar media, with laser flash photolysis corroborated with an external magnetic field (MF), we have detected the transient geminate radicals of MQ and ADN, photo-generated through ET and HAT. We observe that the presence of AuNP on the MQ-ADN complex (AuMQ-ADN) assists HAT by limiting the ET channel, on the other hand, FeNP on the MQ-ADN complex (FeMQ-ADN) mostly favors a facile PET. We hypothesize that through selective interactions of the ADN molecules with AuNP and MQ molecules with FeNP, a preferential HAT and PET process is eased. The enhanced HAT and PET have been confirmed by the escape yields of radical intermediates by time-resolved transient absorption spectroscopy in the presence of MF.

Green synthesis of gold nanoparticles using cinnamon bark extract, characterization, and fluorescence activity in Au/eosin Y assemblies

This study reports the synthesis of gold nanoparticles (AuNPs) using an unconventional, eco-friendly method that utilizes cinnamon bark extract as a reducing agent and stabilizer. The synthesized AuNPs were characterized using UV–Vis spectroscopy and transmission electron microscopy (TEM). UV–Vis spectrum shows the surface plasmon resonance (SPR) peak around 535 nm. TEM shows the spherical shape of AuNPs and the particle size distribution at around 35 nm. The ability of the synthesized AuNPs as a quencher of eosin Y dye was monitored using a fluorometer. It was found that in the presence of AuNPs, the fluorescence peak of eosin is quenched. The fluorescence of the mixture of eosin and AuNPs is enhanced in the presence of bovine serum albumin (BSA) protein. TEM shows that the average size of the AuNPs is reduced from 35 to 5 nm with the addition of eosin, and the size of AuNPs then increased to 26 nm upon adding BSA to the mixture of ANPs and eosin. These fluorescence fluctuations may be used for trace identification and biosensing.

Multidonor surface energy transfer from Alexa Fluor dyes to gold nanoparticles: a quest for innovative sensor applications

We report energy transfer (ET) from two dyes: Alexa Fluor 514 (AF514) and Alexa Fluor 532 (AF532) to gold nanoparticles (AuNPs) of three different sizes (10, 30, and 53 nm) employing steady-state and time-resolved fluorescence measurements. The results show that the fluorescence intensity and fluorescence lifetimes of donor (D) molecules AF514 and AF532 decrease with increase in the concentration of acceptor (A) AuNPs (2 to 10 μM) upon interaction with AuNPs, thereby confirming the occurrence of ET between D and A. This clearly suggests that these two Alexa Fluor molecules act as efficient donors and AuNPs as excellent acceptors. Interestingly, the Forster distance (Ro) determined for these dyes varies from 212 to 550 Å with increasing size of AuNPs and suggests that the ET from AF514 and AF532 to AuNPs is essentially obeying surface energy transfer (SET) process following 1 / d4 distance dependence. As is well known, Forster resonance energy transfer is efficient for separation distances of up to 100 Å, beyond which its efficiency decreases. Thus, the present results follow dipole-surface type ET from molecule dipole (AF514 and AF532) to nanometal (Au) surface. The influence of size and distance on the SET from AF514 and AF532 to AuNPs is discussed. Further, the quenching of donor fluorescence in the presence of AuNPs and nonradiative ET are analyzed using Stern–Volmer plots. Our study is an experimental quest to explore the potential of such dye–noble metal NPs pairs performing as sensitive chemical and biosensors.

Microneedle-based transdermal electrochemical biosensors based on Prussian blue-gold nanohybrid modified screen-printed electrodes.

We report on the fabrication of a microneedle-based electrochemical biosensor for use in transdermal biosensing, which includes a screen-printed electrode containing a Prussian blue-gold nanohybrid as the working electrode. The Prussian blue gold nanohybrid is made from polyethylenime (PEI)- mediated simultaneous synthesis of Prussian blue (PBNP) and gold nanoparticles (AuNP), which forms a PBNP-AuNP nanohybrid with a remarkable change in the Prussian blue character. PEI-protected polycrystalline PBNPs can be synthesized in acidic media from the single precursor potassium ferricyanide [K3 Fe(CN)6 ] at 60°C. Since PEI also enables the controlled formation of gold nanoparticles (AuNPs) in the presence of formaldehyde, nanohybrids containing PBNPs and AuNPs may be prepared. Two different methods of PEI mediated synthesis of AuNP in the presence of PBNP were considered. In Method 1, AuNP and PBNP were made independently and mixed together in an appropriate ratio. In Method 2, PBNPs were made first, followed by PEI- and formaldehyde-mediated reduction of gold cations in the presence of PBNP. PBNP-AuNPs display a remarkable change in Prussian blue behavior such that the absorption maxima of PBNP-AuNPs made through Method 1 tend to increase at 670 nm as a function of gold concentration as compared with the control; the reverse was observed when PBNP-AuNPs were made through Method 2. As made PBNPs and PBNP-AuNPs made through Method 1 display excellent catalytic activity toward both reduction and oxidation of hydrogen peroxide based on peroxidase mimetic activity. In addition, the as-synthesized PBNPs displayed superparamagnetic behavior that can be manipulated in the presence of AuNPs. The results from peroxidase mimetic activity, chemiluminescence, cyclic voltammetry, and amperometry showed suitable analytical performance of the as-made PBNP-AuNP nanohybrid for biomedical applications.

The effect of ultrasound hyperthermia with gold nanoparticles on retinoblastoma Y79 cells

The purpose of this study was to evaluate the possible synergistic effect of gold nano-therapy (Au-NPs) on Y79 cells treated with ultrasonic hyperthermia. The cells in the presence and absence of gold nanoparticles were subjected to ultrasonic irradiation (3 MHz, 1 W/cm2, 40% pulse mode). Gold nanoparticles with an average diameter of 60 nm were synthesized. The cell viability of the Y79 cells was evaluated 48 h after performing 0.5–11 min hyperthermia with and without Au-NPs using the MTT assay. There was no cytotoxicity with 1.7 μg/mL Au-NP concentration. Moreover, the results revealed a significant difference in the cell viability between the control group and the groups with a hyperthermia period of more than 4 min. The results indicated that with increasing the concentration of Au-NPs (1.75, 3.5, 7, 14, 28 and 56 μg/mL), the cytotoxicity increased. The Y79 cell viability of 50% was caused for 9 min hyperthermia time alone and 4.5 min hyperthermia time in the presence of gold nanoparticles. The cell viability of the Y79 cells for a 0.5 to 11 min hyperthermia time, compared with the control group, was 93 to 27% and 95 to 32% with and without Au-NPs, respectively. It is concluded that the cells are more sensitive to hyperthermia induced by ultrasound irradiation in the presence of Au-NPs.

Effect of metallic nanoparticles on amyloid fibrils and their influence to neural cell toxicity

The modification of amyloid fibrils cytotoxicity through exogenous nanomaterials is crucial to understand the processes controlling the role of protein aggregation in the related diseases. The influence of nanoparticles on amyloid stability yields great interest due to the small size and high surface area-to-volume ratio of nanoparticles. Various physico-chemical parameters play a role in the interaction of proteins and nanoparticles in solution, thus influencing the disaggregation of preformed fibrils. We have examined the influence of two kinds of metallic nanoparticles on lysozyme amyloid fibrils using a multi-technique approach and focalized their impact on cytotoxicity on human neuroblastoma cells (SH-SY5Y). In particular, fluorescence, infrared and circular dichroism spectroscopies, optical and atomic force microscopy experiments have been carried out; the results are analyzed to rationalize the effects of these complexes on neural cell viability. It is remarkable, that the fibrils in the presence of AuNPs, unlike fibrils alone or with AgNPs, do not generate a significant cytotoxic effect even at high concentration and an amyloid degradation effect is visible.

Utilisation of the chemiluminescence method to measure the radiation dose enhancement caused by gold nanoparticles: A phantom-based study

Gold nanoparticles (AuNPs) are being investigated extensively for their role as radiosensitisers. Studies have shown that they are effective dose enhancing agents. One of the main factors that enables AuNPs to function as dose enhancing agents is their ability to generate reactive oxygen species under X-ray irradiation. In this study, we investigated this issue utilising a chemiluminescence technique with 3’-(p-aminophenyl) fluorescein (APF) in a phantom. First, we examined the time variation and dose response of the fluorescence intensity of APF for spherical 50 nm AuNPs exposed to a 6 MV photon beam. The APF reagent was added to the AuNPs suspension in a small tube fixed in a water phantom. The fluorescence intensities of APF were measured using a microplate reader. Next, based on the APF response, we evaluated the dose enhancements caused by AuNPs in a 6 MV flattening filter (FF) and flattening filter-free (FFF) photon beams and doses of either 2, 4, or 6 Gy. While the time variation of APF fluorescence intensity without AuNPs was less than 5% after X-ray irradiation, we observed an increase in the fluorescence intensity over time in the presence of AuNPs without the radiation. The APF signals had a linear response to X-ray irradiation in a dose-dependent manner. The measured dose enhancement ratios for the FFF beam were significantly higher than that for the FF beam in the presence of 30 μg/ml AuNPs. This result shows APF can successfully detect differences in dose enhancement between the FF and FFF beams using AuNPs. In conclusion, the chemiluminescence technique using APF is a useful and simple method to estimate the level of dose enhancement caused by nanoparticles in a phantom.

Gold Nanoparticle as a Lewis Catalyst for Water Elimination of Tyrosine-•OH Adducts: A Radiation and Quantum Chemical Study.

The role of gold nanoparticles (AuNPs) in the degradation of tyrosine intermediates formed during the radiation-induced •OH reaction with tyrosine at pH 6.5 is investigated by measuring the radiolytic yields, G, of tyrosine (-Tyr), dityrosine (DT), and 3,4 dihydroxyphenylalanine (DOPA). The G(DT) is doubled, whereas G(-Tyr) calculated is halved in the presence of 6.0 × 10-10 mol dm-3 AuNPs. Pulse radiolysis studies are carried out to elucidate the mechanism and nature of the transient formed in the reaction of •OH and •N3 with tyrosine. The formation of tyrosyl radical in the presence of AuNPs is found to be a major pathway through the decay of tyrosine-•OH adducts via the water elimination reaction, which is found to be 3× faster in the presence of AuNPs. Quantum chemical calculations on the system showed favorable formation of the tyrosine-AuNP complex. A new plausible mechanism of tyrosine-AuNP complex acting as a Lewis type catalyst in the decay of tyrosine-•OH adducts leading to reduced DOPA formation is proposed. The proposed mechanism is also complemented by the electronic spectra and energetics of the reaction of •OH with tyrosine using density functional theory calculations. Significantly, the H-shift reaction of ortho-tyrosine-•OH adducts is also found to be energetically viable. The investigation provides a new physical insight into the effect of AuNPs on the decay of free-radical transient species and demonstrates the potential of radiation chemical techniques and quantum chemical calculations as a tool for understanding the impact of metal nanoparticles in free-radical oxidation of amino acids, which is important in the use of metal nanoparticles for biomedical applications.