Absorption Of Gold Nanoparticles Research Articles

Thiolated Cyanines Appended to Partially Pegylated Gold Nanoparticles for Fluorescence Quenching of Two-Channel Photothermal Inks.

Following a new approach, we prepared a nanoink with two separate photothermally responsive absorption bands. One is the localized surface plasmon resonance (LSPR) absorption of gold nanoparticles (AuNP, d=17 nm), the second is the absorption band of two cyanine (Cy) dyes, Cy7-C6 or Cy7-C11, grafted to the AuNP surface through thiolated bridges of different lengths: the close proximity to the Au surface induces full quenching of the Cy fluorescence, resulting in thermal relaxation on irradiation. Attempts to full coat AuNP with the lipophilic Cy7-C6 and Cy7-C11 lead to precipitation from aqueous solutions. We thus prepared AuNP with partial pegylation (30, 50, or 70 %), using a long chain thiol-terminated PEG bearing a -COOH function. Addition until saturation of either Cy7-C6 or Cy7-C11 to the partially pegylated AuNP gave the AuNP@Cy/PEGX% hybrids (X=30, 50, 70) that are stable in water and in the water/alcohol mixtures used to prepare the nanoinks. Further overcoating of AuNP@Cy7-C6/PEG50 % with PAH (polyallylamine hydrochloride) avoids LSPR hybridization in the dry nanoink printouts, that present two separate bands. When irradiated with laser sources near their absorption maxima, the printouts of the AuNP@Cy7-C6/PEG50 %@PAH nanoink respond on two channels, giving different temperature increases depending on the irradiation wavelengths. This enhances the potentiality of use of these nanoinks for photothermal anticounterfait printouts, making more difficult to reproduce the correct ΔT vs λirradiation output.

A colorimetric detection of microRNA-148a in gastric cancer by gold nanoparticle–RNA conjugates

For the early diagnosis of gastric cancer, microRNA-148a (miRNA-148a) as a promising biomarker is measured by a simple colorimetric biosensor due to its unique surface plasmon resonance (SPR) absorption of gold nanoparticles (AuNPs). In the assay system, the sensing probes are facilitated by the conjugation of AuNPs with RNA probes (RNAP) via Au–S bonds, which align in a tail-to-tail fashion onto the target RNA. When miRNA-148a is introduced, a sandwich hybridization reaction is triggered between the AuNP–RNAP conjugates and targets, resulting in changes in the SPR absorption band, microscopic distribution and macroscopic color of the AuNP solution. Following this principle, this colorimetric method is able to quantitatively detect miRNA-148a at nanomolar level with a limit of ∼1.9 nM, and exhibits high sensitivity and selectivity by a low-cost UV–vis spectrometer or even the naked eye. Moreover, the AuNP network materials with a characteristic sharp ‘melting transition’ provide significant guidance for the reusability of DNA or RNA biosensors.

New detection method for nucleoside triphosphates based on carbon dots: The distance-dependent singlet oxygen trapping

The distance-dependent based sensing mechanism, such as fluorescence resonance energy transfer (FRET) and surface plasmon resonance (SPR) absorption of gold nanoparticles, has been used widely in visual detection. In this work, we report another distance-dependent detection method for nucleoside triphosphates (NTPs) based on carbon dots (CDs) (1O2 donor) and 9, 10-diphenylanthracene-2-boronic acid (DABA, 1O2 acceptor). The CDs can generate singlet oxygen (1O2) which allows diffusion within 200 nm. Thus, the distance between CDs and DABA decreased through binding of NTPs (<200 nm), leading to absorption changes of DABA under light irradiation due to 1O2 trapping. This sensing system (CDs@DABA) has high selectivity for the detection of NTPs due to the double molecular recognition and a linear response in the 0–80 μM concentration range was accomplished with the detection limit as low as 4.35 μM.

Photometric determination of the activity of cellulase and xylanase via measurement of formation of gold nanoparticles

We describe a colorimetric assay for the determination of the activity of cellulase and xylanase. Following enzymatic hydrolysis, reductive saccharides are produced which are capable of directly reducing auric acid to form gold nanoparticles (AuNPs). The AuNPs are of fuchsia color and possess a strong plasmonic absorption band at 550 nm. Reaction conditions such as temperature, reaction time, and pH of the solution were optimized. A linear relationship between the concentrations of saccharide and the plasmon absorption of gold nanoparticles at 550 nm allowed for quantitative detection of the saccharides formed in solution, from which the hydrolase activity can be calculated. The detection limits for cellulase and xylanase are 0.14 and 0.080 IU mL−1. The results were compared with those of the 3,5-dinitrosalicylic acid method and showed the established method to be reliable and accurate.

Fabrication and Photoelectric Properties of Large Area ZnO Nanorod with Au Nanospheres

Novel gold nanospheres top-contact ZnO nanorods arrays were fabricated via combination of self-assemble nanosphere lithography and low-cost hydrothermal chemical method. Gold nanoparticles of different geometries are used to enhance the fluorescent properties of ZnO nanorods based on localized surface plasmonic resonances. The results show that defect-related emission intensity ratio of the ZnO nanorods arrays can be improved up to two orders, and the defect-related emission peak red-shifted from 577 to 623 nm. This improvement is attributed to the enhanced localized surface plasmonic absorption of gold nanoparticles, which implies a promising application in surface plasmonic enhanced spectra.

INTERACTION OF METHOTREXATE WITH DNA USING GOLD NANOPARTICLES AS A PROBE

□ The use of gold nanoparticles as a probe to investigate the interaction of DNA with methotrexate is reported. Methotrexate has widespread use in the treatment of tumors and auto-immune diseases, and is an anti-metabolite of folic acid, having a direct or indirect effect on various molecular targets, which influences DNA replication and cell proliferation by integrating between the spaces between adjacent DNA base pairs. A simple method to monitor the interaction of DNA with methotrexate was developed, using ultraviolet – visible spectroscopy and spectroflurometry with gold nanoparticles as the probe. In a mixture of DNA and methotrexate, as the proportion of free DNA increased, the absorption of gold nanoparticles decreased and the fluorescence intensity increased. This article confirmed that as the interaction between DNA and methotrexate increased, less free DNA was available to bind with gold nanoparticles present in solution, reducing the absorption and enhancing the fluorescence of the nanoparticles. The limit of detection and limit of quantification were 160 ng/mL and 50 ng/mL, respectively. The results demonstrated the use of gold nanoparticles as a probe for the interaction of DNA with methotrexate, which may be an important tool to measure drug-induced DNA damage.

Size effect in plasmon absorption of gold nanoparticles upon adsorption of ozone

A size effect is revealed and analyzed for the shift of the plasmon absorption of gold nanoparticles upon ozone adsorption on their surface. The smaller the nanoparticles, the greater the shift of the band. At the same time, the shift of the Fermi level is a linear function of the inverse radius of nanoparticles. It is shown that the observed variations in the optical characteristics and the Fermi level may be explained within the framework of the model proposed for a decrease in the electron density of nanoparticles due to their partial binding by adsorbed ozone molecules.

Characterization of physicochemical properties of Miscanthus floridulus stems and study of their oil absorption ability using gold nanoparticles

Miscanthus floridulus, which originated from a high elevation mountain area in Taiwan, is a newly cultivated species of Miscanthus. Instead of Miscanthus × giganteus, M. floridulus can be used as an alternative fuel for energy production as well. Except for leaves, stems of M. floridulus count for a major portion of the biomass. In this study, the lignin and cellulose contents of M. floridulus stems were determined to be 22.33 ± 2.21% and 43.13 ± 2.79%, respectively. In addition, a new application of M. floridulus stems was proposed. Oil absorption ability represented by the amount of soybean and motor oils absorbed by one gram of pulverized M. floridulus stems was estimated to be 2.25 ± 0.25 and 2.33 ± 0.18 g, respectively. Gold nanoparticles were used to investigate the absorption ability of M. floridulus stems. The absorption of gold nanoparticles by M. floridulus stems was visualized using SEM and TEM. In addition, the IR spectrum of M. floridulus stems was recorded for comparison with other studies.

Redox of Flavonoids with Chlorauric Acid and Its Analytical Application

Four flavonoids including genistein,luteolin,daidzein and naringenin can reduce HAuCl4 to form gold nanoparticles in different acidity.There are good linear correlations between the signal of plasmon resonance absorption of gold nanoparticles and the concentration of four flavonoids.Thus,we developed a method to detect these four flavonoids respectively.By analyzing the molecular structure and calculating the electron cloud density distribution of the atoms using Materials-studio 4.0,we found that suitable pH for the reaction of different flavonoids and HAuCl4 was related to the number of phenolic hydroxyl group of flavonoid and electron cloud density distribution of alkaline oxygen atoms.

Gold Nanoparticle Arrays for Cancer Treatment and Diagnosis

In this paper we present a novel configuration of gold nanoparticle arrays (especially nanosandwiches) that absorb optical radiations efficiently. The absorbed radiations are then converted into heat in a pico second time scale ( because of the strong surface plasmon absorption of gold nanoparticles ) by the electron-phonon, and phonon-phonon processes. This heat severely damage cancer cells while normal cells are kept safe due to the higher concentration of nanoparticles selectively bound to the cancer cells of the tumor tissue. The surface plasmon absorption pattern obtained by the array of nanosandwiches is much better than all that obtained by other randomly distributed nanoshapes. Although this may be difficult in realization in the mean time, but it motivates the researchers to make this possible.

SU-FF-T-314: Initial Monte Carlo Analysis of the Dosimetric Effects of Gold Nanoparticle Radiosensitizers

Purpose:Monte Carlo simulations have been undertaken to quantify the dosimetry of tumors that have absorbed nanoparticlegold as radiosensitizers and irradiated with various radiotherapy modalities. Method and Materials: EGSnrcMP and BEAMnrcMP, well known and documented Monte CarloPhotonTransport simulation codes are used for therapy simulations. Previous measurements of uptake ratio's provide a basis for generating new radiation interaction cross sections for use in radiation transport simulations. Cross sections generated by the simulation software are checked against cross sections generated using the NIST (National Institute of Standards and Technology) Standard Reference Database 8 (XGAM) and found to agree to within about 0.5%. 250 kVp, and 6 MV and Ir‐192 HDR spectra provided with the EGS package where used as sources. Tumors containing 0.5% to 5% Au by weight (the balance made up by water) and sized from 0.5 to 3 cm were simulated at various depths and compared to pure water. The effects of normal tissue absorption of gold in media surrounding the tumor were also investigated. Results: As expected, 250 kVp orthovoltage units showed the largest benefit from nanoparticles. A 50% absorption increase in tumors absorbing 1.5% Au by weight. Ir‐192 therapy beams available from High Dose Rate Brachytherapy units treating 1.5% and 5% nanoparticlegold by weight showed a 13% and 38% increase in dose absorption rate for tumors 1cm from the source. 6MV photon beams treating a 3cm tumor at 10cm depth showed a modest 5% improvement. Surrounding media absorption of goldnanoparticles shifts both target and surrounding tissue absorption rates higher, but does not significantly change their relative absorption rates. Conclusion: These simulations suggest goldnanoparticles in some modalities are worth investigating as radiosensitizers. Initial research should focus on HDR modalities first.

Direct voltammetric determination of gold nanoparticles using graphite-epoxy composite electrode

A new voltammetric method for a direct determination of gold nanoparticles, based on adsorption and electrochemical detection of colloidal gold, is described. In this protocol, the absorption of gold nanoparticles onto the rough surface of graphite-epoxy composite electrode is followed by their electrochemical oxidation in 0.1 M HCl medium at a potential of +1.25 V. The resulting tetrachloroaurate ions generated near the electrode surface are detected by differential pulse voltammetry (DPV). The DPV response is linear in the range from 4.7 × 10 8 to 4.7 × 10 11 nanoparticles cm −3 with a limit of detection of 1.8 × 10 8 gold nanoparticles cm −3. The surface characteristics of the composite electrode are investigated and the parameters that affect the complete analytical detection process of gold nanoparticles are optimized.

Photoinduced Electron Transfer between Chlorophyll a and Gold Nanoparticles

Excited-state interactions between chlorophyll a (Chla) and gold nanoparticles have been studied. The emission intensity of Chla is quenched by gold nanoparticles. The dominant process for this quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles, although because of a small overlap between fluorescence of Chla and absorption of gold nanoparticles, the energy-transfer process cannot be ruled out. Photoinduced electron-transfer mechanism is supported by the electrochemical modulation of fluorescence of Chla. In absence of an applied bias, Chla cast on gold film, as a result of electron transfer, exhibits a very weak fluorescence. However, upon negatively charging the gold nanocore by external bias, an increase in fluorescence intensity is observed. The negatively charged gold nanoparticles create a barrier and suppress the electron-transfer process from excited Chla to gold nanoparticles, resulting in an increase in radiative process. Nanosecond laser flash experiments of Chla in the presence of gold nanoparticles and fullerene (C60) have demonstrated that Au nanoparticles, besides accepting electrons, can also mediate or shuttle electrons to another acceptor. Taking advantage of these properties of gold nanoparticles, a photoelectrochemical cell based on Chla and gold nanoparticles is constructed. A superior performance of this cell compared to that without the gold film is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode, leading to an enhancement in charge separation efficiency.