Diameter Of AuNPs Research Articles

Synthesis of Au Nanoparticles Attached to Large-Area Cu-Oxide Nanowires By Thermal Treatment for Artificial Photosynthesis Process

Developing materials for fuels based on solar utilization is a current need to solve the energy problem in the world society [1]. The proposal of heterostructures conformed by nanowires and nanoparticles has been suggested for solar energy recovery application [2] focused on the artificial photosynthesis process.In this work, heterostructures of copper oxide nanowires (CuO-Nw) and Gold nanoparticles (Au-Np) were achieved by thermal treatment. To grow the nanowires array, a Cu foil (99.99 % in purity) of 1 cm x 1 cm was chemically etched with 1 M nitric acid solution for 10 seconds, then it was isothermally heated in a horizontal furnace. The Oxygen atmosphere inside the furnace was controlled within 21 wt. % ± 1 wt. % content and a 20 L/min flux rate was used. The effect of temperature and time on density, diameter, and length of CuO-Nw was studied. The experiments were carried out at 400, 500 and 600 °C for 1h, 3h, and 5h. Afterward, Cu-O Nw were Au-coated by sputtering. Au films with 10 nm and 60 nm in thickness were deposited. In order to synthetize the Au-Np a thermal treatment was isothermally performed under Nitrogen atmosphere at 450 °C for 15 min. To guaranty reproducibility, the experiments were performed by triplicate in separated experiments.Field emission scanning electron microscopy images proved the achievement of heterostructures consisting of Au-Np attached to CuO-Nw walls. The average diameter of Au-Np was obtained about 60 nm and 80 nm. No organic contaminants were identified by Raman spectroscopy, thus, the proposed methodology is a clean and environment friendly process. Cyclovoltammetry curves were recorded by potentiometer chamber in alkaline medium to characterize the electrochemical response of samples. It was found that Au-coated heterostructures exhibit an enhancement in efficiency for oxygen evolution reaction against those containing CuO-Nw array alone. Acknowledgments The authors acknowledge the Secretaría de Investigación y Posgrado of the IPN for the economic support to this work. The authors have no conflict of interest to disclosure.

A novel fluorescence biosensor for the detection and imaging of tumor-related mRNA in living cells based on Au//hGNPs-FA nanocarrier

Au//hGNPs-FA nanocarriers-based novel fluorescence strategy for the detection and imaging of tumor-related mRNA in the living cells is described. Au//hGNPs-FA is a new nanocarrier with large capacity, high release efficiency and specificity. In Au//hGNPs-FA, ssDNA-bound gold nanoparticles (AuNPs-T1) could tightly combine with ssDNA-bound hollow gold nanospheres (hGNPs-T2) by hybridization of T1 and T2. Since AuNPs of diameter 16 nm could block the hGNPs’ pores of diameter 8.4 nm, the non-specific release of signal substances can be significantly reduced. New matching scheme of AuNPs and hGNPs not only utilized the powerful load capacity of hGNPs, but also realized efficient sealing and specific release. The results of extracellular experiments showed that the method can detect mRNA standards in the range of 1 pM to 20 nM, and the minimum detection limit is 850 fM. More importantly, combined with FA, the efficiency of Au//hGNPs-FA entering cells was increased by 20%. And, the fluorescence strategy could detect mRNA in living cells with high specificity and sensitivity, even in single cell with very low content. Therefore, the new strategy has the potential to monitor the expression of mRNA in tumor cells accurately.

Simple gold nanoparticles production method by ablated laser: Diameter modification

Recently, an improved interest in gold nanoparticles (AuNPs) with an interesting phenomenology such as plasmon resonance, has been aroused. There are many methods to synthesized AuNPs. We have successfully fabricated AuNPs base on laser ablation method. The pulsed Nd:YAG laser ablated at 1064 wavelength to a pure gold plate. The frequency was adjusted in low range to produce low energy density laser beam. Three different solution (aqueous, polyvinyl alcohol and polyethylene glycol) was applied to modify AuNPs diameter. The modified nanoparticles diameter was observed by mean UV-Vis spectroscopy exhibit different absorption peak wavelength. For comprehensive discussion, the spectrum was compared to simulation tool on MATLAB. Interestingly, AuNPs diameters have been modified by using different solution.

Inkjet‐Based Technology for Microencapsulation of Gold Nanoparticles within Biocompatible Hydrogels

AbstractHerein, an inkjet‐based technology as a versatile high throughput methodology for the microencapsulation of gold nanoparticles (AuNPs) inside a biocompatible chitosan hydrogel is described. This continuous automated inkjet production approach generates 30 µm diameter polymeric microcapsules and offers a high rate of production and nanoparticle encapsulation efficiency of 14 nm diameter AuNPs, precise control of the microcapsule size, and ease of scale‐up. The hybrid microcapsules demonstrate biocompatible cell‐adhesion properties and resist degradation over a large range of pH, making them particularly relevant for a variety of potential health applications.

Generalized preparation of Au NP @ Ni(OH)2 yolk-shell NPs and their enhanced catalytic activity

Yolk-shell nanostructures have attracted considerable attention because of their unique properties and promising applications. Yet, synthesis of well-defined yolk-shell structures with controllable composition remains a major challenge. Here, we report a general method to fabricate Au NP @ Ni(OH)2 yolk-shell NPs. Au cores with various diameters and shapes can be successfully encapsulated into the Ni(OH)2 shells by a similar approach. When the diameter of the core Au NPs changed from ~15 to ~90 nm, the size of the yolk-shell NPs accordingly grew from ~110 to ~380 nm, however, the shell thickness of the final yolk-shell NPs is in the narrow range of 18–20 nm. The synergistic contribution from both Au and Ni(OH)2 has endowed the yolk-shell heterostructure with enhanced catalytic activity. As shown in the oxygen-evolution reactions (OER) tests, the OER activity of Au NP @ Ni(OH)2 yolk-shell NPs is 8.7 and 86-fold higher than that of hollow Ni(OH)2 NPs alone and Au NP @C (5%) (Au NPs (5%) mixed with Carbon Black), respectively. In general, our method provides a simple and novel strategy towards the fabrication of yolk-shell structures with superior catalytic activity for OER.

Immunohistochemistry of IL-1β, IL-6 and TNF-α in spleens of mice treated with gold nanoparticles.

Gold nanoparticles (AuNPs) possess considerable biocompatibility and therefore gaining more attention for their biomedical applications. Previous studies have shown the transient increase in pro-inflammatory cytokines expression in different organs of rats and mice exposed to AuNPs. Structural changes in the spleen of mice treated with AuNPs have also been reported. This investigation was aimed to study the immunostaining of IL-1β, IL-6 and TNF-α in mice treated with different sizes of AuNPs. The animals were divided into 7 groups of 4 animals in each group. One group received saline and served as control. Two sets of three groups were treated with 5 nm, 20 nm and 50 nm diameter AuNPs. One set was sacrificed on day 1 and the other on day 7 following the AuNPs injections. Spleens were dissected out and promptly fixed in formalin for 3 days and then processed for IL-1β, IL-6 and TNF-α immunostaining using target-specific antibodies. The immunoreactivities of IL-1β and IL-6 were increased with the increase of AuNP size. The immunostaining of IL-1β in spleen of 20 nm AuNP treated mice was subsequently decreased on day 7 whereas it persisted in 50 nm AuNP group. The increase in the immunoreactivity of IL-6 on day 1 was decreased on day 7 in the spleens of mice treated with 20 nm or 50 nm AuNPs. The immunostaining of TNF-α was found to be negative in all the treatment groups. In conclusion, the size of AuNPs plays an important role in the expression of proinflammatory cytokines in mouse spleen; small size (5 nm) AuNPs caused minimal effect, whereas larger (50 nm) AuNPs produced intense immunostaining.

Size-controlled synthesis of gold nanoparticles by ultrafine bubbles and pulsed ultrasound

Size-controlled gold nanoparticles (AuNPs) were synthesized by ultrasonic irradiation of HAuCl4 aqueous solutions with the aid of ultrafine bubbles (UFBs) in the absence of any capping and reducing agents. Upon addition of air-UFBs, the mean diameter of the spherical AuNPs decreased. This result was attributed to the sonochemical reduction of gold ions in aqueous solution being accelerated by the UFBs. Moreover, the AuNPs were stable in a solution containing UFBs because AuNPs electrostatically adsorbed onto UFBs, whose lifetime in water was very long. Compared with the mean diameter of AuNPs synthesized with argon-, nitrogen- and oxygen-UFBs, that of AuNPs synthesized with air-UFBs was smaller. Pulsed ultrasound delivered with the same time-averaged power as continuous-wave irradiation further decreased the mean diameter of the AuNPs. Size-controlled synthesis of AuNPs without the use of a capping or reducing agent was successful through optimization of the number air-UFBs and the pulsed ultrasound conditions.

Acetylcholine and acetylcholinesterase inhibitors detection using gold nanoparticles coupled with dynamic light scattering

A novel sensitive method for the detection of acetylcholinesterase inhibitors is presented by using unmodified gold nanoparticle coupled with dynamic light scattering (DLS). The hydrolysis of acetylcholine (ACh) mediated by acetylcholinesterase (ACHE) yields the choline, which influences the gold nanoparticles (AuNPs) aggregation, and triggered the increase of their average diameter. The inhibition of the enzyme by pesticides (paraoxon) produces lower yields of choline, leading to less or no AuNP aggregate formation. This study is the first to describe a homogeneous AuNPs-based DLS nanosensor for ultrasensitive detection of paraoxon by measuring ACHE activity. The average diameter and count rate of unmodified AuNPs decreased with the increasing concentration of paraoxon, with a detection limit of 75.5 pmol.L−1. These results suggest that this DLS assay based on unmodified AuNPs could be used in the future for measuring ACHE activity and for non-selective detection of trace amounts of all ACHE inhibitors.

Microwave assisted synthesis of gold nanoparticles with Phyla nodiflora (L.) Greene leaves extract and its studies of catalytic reduction of organic pollutants

The synthesis of gold nanoparticles (AuNPs) has drawn attention over the past few years owing to their optical and physico-chemical properties. In this work, AuNPs were synthesized using Phyla nodiflora (L.) leaf extract by microwave irradiation method. This leaf extract act as reducing and stabilizing agent. The concentrations of Phyla nodiflora (L.) Greene leaf extract, HAuCl4 and duration of microwave irradiation were optimized for the better yield of AuNPs. The AuNPs formation was confirmed by different analytical techniques like UV–Vis spectrophotometry (UV), Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM). Under the optimal synthetic conditions, the average diameter and zeta potential of AuNPs synthesized were 10 ± 2 nm and −24.0 mV respectively. Phytochemicals present in the extract help to reduce Au+3 to Au0 and act as a stabilizer in the synthesis of AuNPs. Afterwards, the catalytic activity of AuNPs was studied in NaBH4 assisted reduction of p-nitrophenol (4-NP), Congo Red (CR) and Methylene Blue (MB). Thus, AuNPs synthesized with leaf extract could be an excellent catalyst for 4-NP, CR and MB in chemical industries.

Multiwalled Carbon Nanotubes/Gold Nanoparticles Hybrid Electrodes for Enzyme-Free Electrochemical Glucose Sensor.

We followed a facile strategy to fabricate glucose sensors using mildly oxidized multiwalled carbon nanotubes (MWCNTs), gold nanoparticles (AuNPs) and thiol acids including mercaptoacetic acid (MAA), mercaptopropionic acid (MPA), and mercaptosuccinic acid (MSA). The thiol acids separately bonded to MWCNTs anchored AuNPs of average diameter 14 nm, and yielded three different nanohybrids; MWCNTs-MAA-AuNPs, MWCNTs-MPA-AuNPs and MWCNTs-MSA-AuNPs. The nanohybrids after coating onto glassy carbon (GC) electrode resulted into enzyme free glucose sensors (GC-MWCNTs-MAA-AuNPs, GC-MWCNTs-MPA-AuNPs and GC-MWCNTs-MSA-AuNPs). Their electrocatalytic glucose sensing ability was examined through cyclic voltammetry and amperometry. GC-MWCNTs-MSA-AuNPs electrode showed high stability and activity in the electrocatalytic oxidation of glucose compared to other two sensors. It also showed a wide range of response for glucose concentration from 0.12 to 4.0 μM, and low detection limit of 0.036 μM (S/N = 3). The optimum rate of applied potential was 0.8 V/s, which proves the effective sensing of glucose. The selective sensing of glucose in the presence of H₂O₂, uric acid and blood cancer drug (imatinib mesylate) was verified through amperometry. The electrode can be a new addition to glucose sensors and bioanalytical techniques.

Water soluble gold nanoparticles based high relaxivity MRI contrast agents

Magnetic resonance imaging (MRI) is one of the modern diagnostic techniques that are being used for differentiating between normal and abnormal tissues. The sensitivity of MRI can be enhanced by the use of contrast agents. In this article, the synthesis and characterisation of new derivatives of gold nanoparticles for applications as MRI contrast agents is reported. Gold nanoparticles stabilised by dimethylaminopyridine (DMAP) molecules were prepared by reduction method. These nanoparticles were characterised by UV-visible spectroscopy, transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The presence of surface plasmon band at 525–530 nm in UV-visible spectra confirmed the formation of stable gold nanoparticles. Similarly, the TEM images showed the well dispersed spherical gold nanoparticles. The average diameter of AuNPs as calculated from TEM image analysis was found 2.25 nm. The DMAP molecules were then replaced by Gd-DTPA chelates along with butanethiol molecules. The butanethiol molecules are responsible for restricted tumbling of Gd-DTPA chelates that resulted in the 38% increase in relaxivity of gold nanoparticles based MRI contrast agents.

The Influence of the Parameters of a Gold Nanoparticle Deposition Method on Titanium Dioxide Nanotubes, Their Electrochemical Response, and Protein Adsorption.

The goal of this research was to find the best conditions to prepare titanium dioxide nanotubes (TNTs) modified with gold nanoparticles (AuNPs). This paper, for the first time, reports on the influence of the parameters of cyclic voltammetry process (CV) -based AuNP deposition, i.e., the number of cycles and the concentration of gold salt solution, on corrosion resistance and the capacitance of TNTs. Another innovation was to fabricate AuNPs with well-formed spherical geometry and uniform distribution on TNTs. The AuNPs/TNTs were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and open-circuit potential measurement. From the obtained results, the correlation between the deposition process parameters, the AuNP diameters, and the electrical conductivity of the TNTs was found in a range from 14.3 ± 1.8 to 182.3 ± 51.7 nm. The size and amount of the AuNPs could be controlled by the number of deposition cycles and the concentration of the gold salt solution. The modification of TNTs using AuNPs facilitated electron transfer, increased the corrosion resistance, and caused better adsorption properties for bovine serum albumin.

Ultrafast synthesis of gold nanoparticles on cellulose nanocrystals via microwave irradiation and their dyes-degradation catalytic activity

This study represents a well-dispersed gold nanoparticles (AuNPs) synthesis process via cellulose nanocrystals (CNC) which acts as both reducing and supporting agent. The synthesis process was ultrafast and completed in a few seconds using microwave irradiation. The entire synthesis process was cost-effective, sustainable and eco-friendly. The synthesized (AuNPs/CNC) nanocomposite was investigated by transmission electron microscopy, selected area electron diffraction, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffraction, and UV–vis spectroscopy. The obtained AuNPs were well accumulated on the CNC surface and had a uniform spherical shape with an average diameter of 8 ± 5.3 nm. The diameter of AuNPs could be altered by tuning the concentration of CNC suspension. The synthesized AuNPs/CNC nanocomposite film exhibited excellent degradation properties against various organic dyes, namely, Allura red, Congo red, Rhodamine B and Amaranth. The ultrafast degradation reactions followed pseudo first order kinetics. In the catalytic degradation reaction, AuNPs/CNC was transmitting electrons from a donor (NaBH4) to an acceptor (a dye).

Thiol-Mediated Multidentate Phosphorylcholine as a Zwitterionic Ligand for Stabilizing Biocompatible Gold Nanoparticles.

The increasing application of gold nanoparticles (AuNPs) in biomedicine requires extensive investigation of surface modification and stabilization to maximize their advantages for the diversity of more challenging biological utilization. Herein, a thiol-mediated multifunctional phospholipid ligand was designed while disclosing a zwitterionic nature to AuNPs. The ligand was synthesized by attachment to two bidentate lipoic acid (LA) anchor groups and incorporation of a zwitterionic phosphatidylcholine (PC) group, allowing for excellent hydrophilicity. As demonstrated through ultraviolet-visible spectroscopy, appropriate 7 nm diameter AuNPs modified with a 1,2-dilipoyl-sn-glycero-3-phosphorylcholine (di-LA-PC) compact ligand exhibited the best colloidal stability in a high NaCl concentration of up to 217 mM, different temperatures, and a wide range of pH values from 3 to 11 when compared to the traditional surfactants or thiol-contained amino acid surface modification cases. These AuNPs are also stable without specific interaction to positively/negatively charged proteins, possibly leading to prolonged blood circulation after in vivo administration. Moreover, much more resistance to ligand competition of dithiothreitol was found than other thiol-coated AuNPs, which further highlighted their affinity in an aqueous system. Biocompatibility of the zwitterionic ligand di-LA-PC-modified AuNPs was finally evaluated by hemolysis and cytotoxicity tests. Cumulatively, the remarkable stability and biocompatibility of AuNPs, multicoordinated with a di-LA-PC ligand, potentially motivated them as a practical alternative for surface tailoring in biotechnology.

Controlling Photocatalytic Reactions and Hot Electron Transfer by Rationally Designing Pore Sizes and Encapsulated Plasmonic Nanoparticle Numbers

Controlled self-assembly of different numbers of gold nanoparticles (AuNPs) in the highly ordered cylindrical anodic aluminum oxide nanopores was achieved by a facile ultrasonication method. The surface plasmon resonance bands became red-shifted by increasing the number of nanoparticles (N), in the top view, from monomer M1 (N = 1) to multimers of M2 (N = 3 ± 1), M3 (N = 5 ± 1), and M4 (N = 7 ± 1). The numerical calculations of the M2 model showed the best match of 2 nm nanogap among 28 nm diameter AuNPs in 53 nm diameter nanopores. When the number of AuNPs inside the nanopores increased, more hotspots were generated, which induced the plasmon-driven photocatalysis on AuNP clusters at the incident visible light of 633 nm. The enhanced photocatalytic reaction of 4-nitrobenzenethiol was observed after sequentially increasing the number of AuNPs, which began at M3 and was maximum for M4. The M3 configuration could be a magical number of AuNP clusters for the nanogap-induced photocatalysis under 633 nm irradiation (∼0.2 mW) for 12 min. Our methods should be helpful in adjusting photocatalysis by varying the numbers of nanoparticles inside the tunable nanopores.

Polyethyleneimine-oleic acid micelle-stabilized gold nanoparticles for reduction of 4-nitrophenol with enhanced performance

Noble metal nanoparticles have been drawing great attention for the treatment of water pollutants. The catalytic activity of noble metal nanoparticles is usually reduced due to their aggregation. Amphiphilic molecule micelles have potential to stabilize the noble nanoparticles against aggregation. In this study, a novel facile method was reported for preparing polyethyleneimine-oleic acid (PEI-oleic acid) micelle-stabilized gold nanoparticles (PO-AuNPsn), where the gold nanoparticles (AuNPs) were embedded in the shell area of micelles. When the molar ratio of [N] to [Au] was 50, 100, and 200, the mean diameter of AuNPs was 3.52 ± 0.42, 3.11 ± 0.28, and 2.85 ± 0.48 nm, respectively. The corresponding zeta potential of the PO-AuNPsn was determined to be 26.2, 28.9 and 35.7 mV, respectively. Furthermore, PO-AuNPsn remained stable in aqueous solution at room temperature for more than 1 month. More importantly, PO-AuNPsn had higher catalytic activity for 4-nitrophenol (4-NP) reduction in aqueous solution compared with previous reports, where PO-AuNPs200 showed a Knor value of 9367 s−1 g−1. It is believed that PO-AuNPsn showed high catalytic activity because of their small size, high stability, and the location of AuNPs in the shell area, which made it easier for AuNPs to contact with 4-NP. The method described in this report represents a new method to prepare small and stable noble metal nanoparticles for catalytic applications in the future.

Development of theranostic active-targeting boron-containing gold nanoparticles for boron neutron capture therapy (BNCT)

Successful boron neutron capture therapy (BNCT) requires sufficient and specific delivery of boron atoms to malignant cells. Gold nanoparticles (AuNPs) have been used as a useful delivery system for selectively releasing cytotoxic payloads in the tumor. However, studies demonstrating the in vivo distribution or pharmacokinetics of boron-containing AuNPs via noninvasive imaging are lacking. This study aims to develop theranostic AuNP-boron cage assemblies (B-AuNPs) and evaluate its feasibility for BNCT. The commercial citrate-coated AuNPs were subjected to PEGylation, azide addition, and carborane modification on the surface. To further arm the AuNPs, we conjugated anti-HER2 antibody (61 IgG) with boron-containing PEGylated AuNPs to form 61-B-AuNPs. The diameter and radiolabeling efficiency of boron-containing AuNPs were determined by dynamic light scattering (DLS) and radio thin-layer chromatography (radio TLC), respectively. Noninvasive single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging was performed to determine the pharmacokinetics of radioiodinated AuNPs in N87 gastric cancer xenografts, and the content of boron in tumor and muscle was assessed by inductively coupled plasma mass spectrometry (ICP-MS). After the 3-step modification, the diameter of B-AuNPs increased by ˜25 nm, and antibody conjugation did not affect the diameter of AuNPs. Radioactive iodine (I-123) was introduced in AuNPs by Click chemistry under copper catalysis. The radiolabeling efficiency of 123I-B-AuNPs and 123I-61-B-AuNPs was approximately 60 ± 5%. After purification, the radiochemical purity (RCP) of these NPs was greater than 90%. MicroSPECT/CT imaging showed that the tumor-to-muscle (T/M) ratio of 123I-B-AuNP-injected mice reached 1.91 ± 0.17 at 12 h post-injection, while that of 123I-61-B-AuNP-injected mice was 12.02 ± 0.94. However, the increased uptake of AuNPs by the thyroid was observed at 36 h after the administration of 123I-61-B-AuNPs, indicating antibody-mediated phagocytosis. The T/M ratio, assessed by ICP-MS, of B-AuNP- and 61-B-AuNP-injected mice was 4.91 ± 2.75 and 41.05 ± 11.15, respectively. We successfully developed detectable HER2-targeting boron-containing AuNPs with high RCP and an acceptable yield. Noninvasive imaging could be a valuable tool for the noninvasive determination of the pharmacokinetics of AuNPs and measurement of boron concentration in the tumor.

Nanoparticle Size Influences Localized Enzymatic Enhancement-A Case Study with Phosphotriesterase.

Enhancements in enzymatic catalytic activity are frequently observed when an enzyme is displayed on a nanoparticle (NP) surface. The exact mechanisms of how this unique interfacial environment gives rise to this phenomenon are still not understood, although evidence suggests that it can help alleviate some of the enzyme's rate-limiting mechanistic steps. The physicochemical limitations that govern when this process arises are also not known including, in particular, the range of NP size and curvature that are associated with it. To investigate the latter, we undertook a case study using the enzyme phosphotriesterase (PTE) and a series of differentially sized gold NPs (AuNPs). PTE, expressed with a terminal hexahistidine sequence, was ratiometrically coordinated to a series of increasing size AuNPs (diameter ≃ 1.5, 5, 10, 20, 55, 100 nm) surface-functionalized with Ni2+-nitrilotriacetic acid ligands and its activity assayed in a comparative format versus that of equivalent amounts of free enzyme controls. PTE-AuNP samples were prepared where the total PTE concentration and NP surface density were kept fixed by varying AuNP concentration along with the converse format. Assembly to the AuNPs increased PTE kcat ca. 3-10-fold depending upon NP size, with the smaller-sized particles showing the highest increase, while enzyme efficiency only increased 2-fold. Further kinetic testing suggested that the PTE enhancement again arose from alleviating its rate limiting step of enzyme-product release and not from a change in the activation energy. Comparison of kcat and enzyme specificity with AuNP diameter revealed that enhancement was directly correlated to AuNP size and curvature with the smaller NPs showing the largest kinetic enhancements. Kinetic simulations showed that almost all of the PTE enhancement variation across AuNP sizes could be reproduced by adjusting only the rate of enzyme-product dissociation. Understanding how NP size directly affects the enhancement of an attached enzyme can provide a rational basis for designing hybrid enzyme-NP materials that specifically exploit this emergent property.

Direct quantification of surface coverage of antibody in IgG-Gold nanoparticles conjugates

It is of paramount importance to be able to accurately quantify surface coverage of antibodies on gold nanoparticles (AuNP) so as to optimise the sensitivity of AuNP-based immunosensors. Herein, we developed a fluorescence-based method to directly quantify rabbit immunoglobulin G (IgG) used as antibody model bound to AuNP. Rabbit IgG was first labelled with fluorescein-5-isothiocyanate (FITC) prior to conjugation to AuNP via either physisorption or chemisorption. IgG-conjugated AuNP were treated with NaCN to dissolve the AuNP and restore the fluorescence emission that was quenched in the presence of the metallic colloids, followed by quantification of fluorescein by spectrofluorimetry. This direct assay gave about 4 IgG bound to each 15-nm diameter AuNP for both immobilization strategies. This surface coverage value was in good agreement with that determined from the theoretical value calculated from the Localized Surface Plasmon Resonance (LSPR) band shift. For comparison, we also applied two indirect methods based on the quantitation of excess IgG remaining in the supernatant using fluorescence assay or enzyme-linked immunosorbent assay (ELISA). The indirect assays, either fluorescence or ELISA, commonly used to assess the antibody coverage on AuNP, overestimated the IgG surface coverage to a large extent, since up to 3 to 4 times higher coverages were measured. Therefore, the direct fluorescence method reported in this paper appears as a valuable method for quantification of surface coverage of antibody on AuNP.

Selective and sensitive detection of L-Cysteine via fluorometric assay using gold nanoparticles and Rhodamine B in aqueous medium

An assay method based on fluorometric and colorimetric change was developed for selective sensing of important thiol containing amino acid L-Cysteine (L-Cys) by using gold nanoparticles (Au NPs) and Rhodamine B (RhB) in aqueous environment. This fluorometric assay is basically relies on the competitive binding between RhB and Au NPs via electrostatic interaction as well as strong thiol(-SH)-Au NPs bonding via chemisorption. Citrate stabilized Au NPs (diameter ∼27 nm) was synthesized by soft chemical method and characterized by UV–Vis absorption spectroscopy and Transmission electron microscopic (TEM) techniques. The change in non-radiative energy transfer between RhB and Au NPs are responsible for the observed drastic fluorescence quenching of RhB via FRET process. The recovery of fluorescence from the assay solution of RhB/Au NPs after addition of L-Cys was found linear over the concentration range 0.01 μM–1000 μM with experimental limit of detection (LOD) of 0.01 μM. The selective interaction of L-Cys with the mixed solution of RhB/Au NPs was reflected by the color change from wine to bluish-black of the final solution. The proposed fluorometric assay method accompanied with the observed colorimetric change could successfully differentiate other interfering amino acids including thiol (-SH) containing compounds namely L-Methionine, L-Homocysteine and antioxidant glutathione with the high degree of accuracy. Also the LOD is comparable to the concentration of L-Cys present in the blood plasma. The proposed sensing mechanism is also confirmed with pure human urine sample to detect the response of L-Cys in the urine. Therefore, this fluorometric assay technique for detection of L-Cys has great potential with the diagnostic impact for biomedical interest.