AuNPs Solution Research Articles

Gold Nanoparticles-based Colorimetric Sensor for Cysteine Detection

A simple, sensitive and selective colorimetric method for the detection of cysteine was demonstrated with unmodified gold nanoparticles (AuNPs) as probes. In this approach, the synthesized AuNPs solution was stabilized by the citrate anions as their repulsion protected the AuNPs from aggregation. Cysteine was added to AuNPs solution and was incubated to react for 3min. The resulting mixture color changes dramatically from red-purple-blue because cysteine induced the nanoparticle aggregation. These processes were studied and characterized by UV–vis spectroscopy, zeta potential and dynamic light scattering. Several parameters including AuNPs size, reaction time and media pH that governed the analytical performance of the method have been studied in detail and optimized. Under the optimized experimental conditions, cysteine could be selectively detected in a concentration range from 0.1 to 0.6ppm with a limit of detection as 0.01ppm at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.474 Abs/ppm. Some common interferents such as Na+, Cu2+, Cl− and urea showed no interference in the determination of cysteine by using AuNPs.

(Bio)-synthesis of Au NPs from soy isoflavone extracts as a novel assessment tool of their antioxidant capacity

In this work, (bio)-synthesis of Au NPs using selected isoflavone classes has been studied. To this end, relevant aglycones (genistein and daidzein) and their glycosides (genistin and daidzin) as well as complex soy-extracts with a well-documented composition have been explored. A sigmoidal curve described the (bio)-synthesis of Au NPs which was used to evaluate the antioxidant activity and to carry out a reliable comparison of the antioxidant activity of soy isoflavone extracts towards the assessment of two relevant parameters: the concentration value at which the absorption reaches its half-value; X50c, and Au NPs production, KAuNPs. Although both isoflavone classes generated Au NPs; however, genistein exhibited a marked bio-synthesis efficiency with the lowest X50c = 70 mg L−1 and the highest KAuNPs = 0.200 mg−1 L values. In addition, complex soy isoflavone extracts with high total isoflavone aglycone content exhibited higher bio-synthesis efficiency than those found with high total glycoside content. Interestingly, excellent correlations between X50c and total phenolics (TP) (from Folin–Ciocalteu (FC) assay as truly antioxidant capacity assay) (r = 0.93, p-value < 0.05) and KAuNPs and TP (r = 0.85, p-value < 0.10) were also obtained confirming the superior antioxidant activity of aglycones isoflavone class. UV-vis and TEM characterization revealed that both genistein standard and soy isoflavone extracts with a high aglycone content produced red colloidal solutions of Au NPs. In contrast, glycoside standards as well as soy isoflavone extracts with a high glycoside content, generated blue colloidal solutions. The overall results obtained from our studies allowed us to hypothesize that the high antioxidant activity found in soy isoflavone extracts could have a significant direct relationship with the (bio)-synthesis of Au NPs with a small diameter and with the strong red colour exhibited at 540 nm. All of this opens new avenues in a very important research field such as the bio-synthesis of Au NPs as a novel tool for evaluation of antioxidant activity of target extracts.

In vitro evaluation of gold nanoparticles toxicity towards human endothelial cells and comparison between static and flow conditions

In the last years metal nanoparticles has seen an escalation as new multi-functional platform for diagnostic and drug delivery, but, at the same time, awareness towards their impact on human and environmental health requires studies that characterize their potential cytotoxic effects (Dykman and Khlebtsov, 2012). In this work we investigate uptake and toxicity of gold nanoparticles (Au NPs) towards cells of the human vascular system (Human Umbilical Vein Endothelial Cells, HUVEC), because these are the first one to get in contact with NPs intravenously administered. The characterization of Au NPs is done by standard methods and by Two-Photon Fluorescence Correlation Spectroscopy. Au NPs uptake is investigated through transmission electron microscopy, fluorescence microscopy and ICPAES, and NPs toxicity is measured through standard bio-analytical tests. We have explored the cytotoxicity of Au NPs by evaluation of gene expression of inflammatory markers and by the cell production of reactive oxygen species (ROS) after incubation with Au NPs. In parallel, we propose and study a new in vitro model system, which consists in a linear microfluidic device (MFD) in polydimethylsiloxane. In this model we add shear stress associated with a flowing medium and a continuous infusion of Au NPs solution, since these phenomena are present when NPs are intravenously administrated (Mahto et al., 2010). The comparison between static and flow conditions shows that administration of equal concentrations of Au NPs under flow results in reduced sedimentation and uptake of NPs on the cells and in 20% lower cytotoxicity, providing new useful information to evaluate the therapeutic efficacy of nanoparticle-based formulations.

Preparation of flexible VOC sensor based on carbon nanotubes and gold nanoparticles

Novel flexible volatile organic compound (VOC) sensor was prepared by deposition of gold nanoparticle (AuNP) and amine modified multi-walled carbon nanotubes (MWCNT-NH2) on polyimide substrate via electrospraying technique. First, interdigitated electrodes (IDE) were fabricated on polyimide (Kapton®) substrate by photolithography. Then, the substrates were subjected to oxygen plasma etching, followed by electrospraying of AuNP and MWCNT-NH2 solution on the substrate. The thin films were characterized by FE-SEM and AFM as well as electrical conductivity measurement. Chemical sensing behaviors of the sensors were analyzed against polar (water, propanol and ethanol) and nonpolar (hexane, toluene, trichloroethylene and chloroform) VOCs. In addition, effect of the AuNP/MWCNT-NH2 ratio on the conductivity and sensing was investigated. Bending test (100 times) resulted in negligible resistance change, demonstrating the successful preparation of flexible sensor.

A colorimetric method for the molecular weight determination of polyethylene glycol using gold nanoparticles.

A gold nanoparticle (AuNP)-based colorimetric method was developed for the molecular weight (MW) determination of polyethylene glycol (PEG), a commonly used hydrophilic polymer. Addition of a salt solution to PEG-coated AuNP solutions helps in screening the electrostatic repulsion between nanoparticles and generating a color change of the solutions from wine red to blue in 10 min in accordance with the MW of PEG, which illustrates the different stability degrees (SDs) of the AuNPs. The SDs are calculated by the absorbance ratios of the stable to the aggregated AuNPs in the solution. The root mean square end-to-end length (〈h2〉1/2) of PEG molecules shows a linear fit to the SDs of the PEG-coated AuNPs in a range of 1.938 ± 0.156 to 10.151 ± 0.176 nm. According to the Derjaguin-Landau-Verwey-Overbeek theory, the reason for this linear relationship is that the thickness of the PEG adlayer is roughly equivalent to the 〈h2〉1/2 of the PEG molecules in solution, which determines the SDs of the AuNPs. Subsequently, the MW of the PEG can be obtained from its 〈h2〉1/2 using a mathematical relationship between 〈h2〉1/2 and MW of PEG molecule. Applying this approach, we determined the 〈h2〉1/2 and the MW of four PEG samples according to their absorbance values from the ordinary ultraviolet–visible spectrophotometric measurements. Therefore, the MW of PEG can be distinguished straightforwardly by visual inspection and determined by spectrophotometry. This novel approach is simple, rapid, and sensitive.

Visual chiral recognition of tryptophan enantiomers using unmodified gold nanoparticles as colorimetric probes

A simple protocol to distinguish enantiomers is extremely intriguing and useful. In this study, we propose a low-cost, facile, sensitive method for visual chiral recognition of enantimers. It is based on the inherent chirality of gold nanoparticles (AuNPs), and the unmodified AuNPs are used as chiral selector for d- and l-Tryptophan (Trp). In the presence of d-Trp, an appreciable red-to-blue color change of AuNPs solution can be observed, whereas no color change is found in the presence of l-Trp. The method can be used to detect d-Trp in the range of 0.2–10μM, and the limit of detection is 0.1μM. The chiral assay described in this work is easily readout with the naked eye or using a UV-vis spectrometer. Furthermore, the AuNPs can selectively adsorb d-Trp, and simple centrifugation can allow the precipitation of d-Trp with AuNPs and leave a net excess of the other enantiomer in solution, thus resulting in enantioseparation. In this method, AuNPs do not need any labeling or modifying with chiral molecules. The method is more attractive because of its high sensitivity, low cost, ready availability and simple manipulation.

A highly sensitive dual-readout assay based on poly(A) and gold nanoparticles for palmatine hydrochloride

This report presents a highly sensitive, poly(A)-stabilized gold nanoparticle-based assay with dual readouts (resonance light scattering and colorimetric) for detecting palmatine hydrochloride (PaH) in real samples. The detection mechanism is based on the fact that palmatine hydrochloride has strong affinity to poly(A), which can stabilize gold nanoparticles at high ionic strength, and cause the aggregation of poly(A)-stabilized AuNPs, resulting in the enhanced resonance light scattering (RLS). At the same time, the color change of poly(A)-stabilized AuNPs solution is from red to blue via purple. Thus a highly sensitive RLS assay for PaH has been developed with a linear range of 0.023–2.5μg/mL. The limit of detection (LOD, 3σ) is 2.3ng/mL. In this work, the reaction mechanism of this system was investigated by scanning electron microscope (SEM), dark-field light scattering images (DLSI), dynamiclight scattering (DLS) and circular dichroism (CD). This proposed method was also applied successfully for the determination of PaH in pharmaceutical preparations and urine samples with RSD⩽4.0%. The results are in good agreement with those from the official method.

Direct detection of hyaluronidase in urine using cationic gold nanoparticles: A potential diagnostic test for bladder cancer

Hyaluronidase (HAase) was reported as a urinary marker of bladder cancer. In this study, a simple colorimetric gold nanoparticle (AuNP) assay was developed for rapid and sensitive detection of urinary HAase activity. Charge interaction between polyanionic hyaluronic acid (HA) and cationic AuNPs stabilized with cetyl trimethyl ammonium bromide (CTAB) led to formation of gold aggregates and a red to blue color shift. HAase digests HA into small fragments preventing the aggregation of cationic AuNPs. The nonspecific aggregation of AuNPs in urine samples was overcome by pre-treatment of samples with the polycationic chitosan that was able to agglomerate all negatively charged interfering moieties before performing the assay. The developed AuNP assay was compared with zymography for qualitative detection of urinary HAase activity in 40 bladder carcinoma patients, 11 benign bladder lesions patients and 15 normal individuals, the assay sensitivity was 82.5% vs. 65% for zymography, while the specificity for both assays was 96.1%. The absorption ratio, A530/A620 of the reacted AuNP solution was used to quantify the HAase activity. The best cut off value was 93.5μU/ng protein, at which the sensitivity was 90% and the specificity was 80.8%.The developed colorimetric AuNP HAase assay is simple, inexpensive, and can aid noninvasive diagnosis of bladder cancer.

Stability of uncapped gold nanoparticles produced by laser ablation in deionized water: The effect of post-irradiation

Gold nanoparticle (AuNP) solution prepared by laser ablation in liquid (LAL) was irradiated by ns laser pulses to investigate the wavelength dependence on the size distribution of AuNPs and long-term stability of post-irradiated AuNP solutions. We have employed 266, 355, 532, and 1064nm lasers for post-irradiation source and found considerable wavelength dependence in the size distribution and stability of laser-generated AuNPs. Post-irradiation at 355nm was most effective to reduce the size distribution and to enhance the stability. The classical Derjaguin–Landau–Verwey–Overbeek theory was employed to explain the anomalous stability at 355nm.

Improving sensitivity of gold nanoparticle based fluorescence quenching and colorimetric aptasensor by using water resuspended gold nanoparticle

Gold nanoparticles (AuNPs) based fluorescence quenching or colorimetric aptasensor have been developed for many analytes recently largely because of the ease of detection, high sensitivity, and potential for high-throughput analysis. However, the effects of remnant non-AuNPs components in the colloid gold solution on these assays performance remain unclear. For the first time, we demonstrated that the remnant sodium citrate and the reaction products of three acids play counteractive roles in AuNPs based fluorescence quenching and colorimetric aptasensor in three ways in this study. First, the remnant sodium citrate in the colloid gold solution could increase the fluorescence intensity of FAM labeled on the aptamer that reduce the efficiency of AuNPs fluorescent quenching. Second, the reaction products of citric acid, HCl and ketoglutaric acid reduce the fluorescence recovery by quenching the fluorescence of FAM labeled on the aptamer dissociated from the surface of AuNPs upon addition of target. Lastly, the reaction products of three acids reduce the pH value of the colloid gold solution that reduce the sensitivity of AuNPs based colorimetric aptasensor by increasing the adsorption of aptamer to surface of AuNPs. With sulfadimethoxine and thrombin as model analytes, we found that water resuspended AuNPs can significantly increase the sensitivity by more than 10-fold for AuNPs based fluorescence quenching aptasensor. In the AuNPs based colorimetric aptasensor for sulfadimethoxine using the water resuspended AuNPs, the sensitivity also was increased by 10-fold compared with that of original AuNPs. The findings in this study provide theoretical guidance for further improving AuNPs based fluorescent quenching and colorimetric aptasensor by adjusting the composition of AuNPs solution.

Biosynthesis of gold nanoparticles using a kind of flavonol: Dihydromyricetin

The present paper investigated the biosynthesis of gold nanoparticles (AuNPs) using dihydromyricetin (DMY) without adding external surfactant, capping agent or template. The synthesized nanoparticles were characterized by using UV–vis spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and particle size analyzer. TEM images showed that anisotropic growth of AuNPs happened at pH=4.5 and 5.5 and relatively uniform small spherical shaped gold nanoparticles were obtained at pH=6.5 and 8.5. Furthermore, both the ratios of nHAuCl4/nDMY and process temperatures were discussed, respectively. DMY or DMY oxidation products which made AuNPs solution stable were directly adsorbed on the surface of AuNPs at the ratio of nHAuCl4/nDMY being 1:3 and 1:1 in the reduction process. Besides, the monodisperse and uniform AuNPs were easily obtained at higher temperatures (90°C). Based on the FTIR analysis, hydroxyl groups of DMY played an important reduction role during synthesis process. The experimental approach is simple, rapid, cost-effective and reproducible at room temperature.

Unmodified gold nanoparticles as a simple colorimetric probe for ramoplanin detection

In this paper unmodified gold nanoparticles (AuNPs) were used as a sensing element to detect ramoplamin. Detection relies on the fact that the dispersed AuNPs solution is red due to the intense surface plasmon absorption band at 530 nm whereas the AuNPs solution in the presence of ramoplanin is blue. Upon aggregation, there is a significant change in absorbance intensity at 620 nm. Based on the aggregation of AuNPs induced by ramoplanin, a simple colorimetric method was developed for determining the of ramoplanin concentration. Experimental conditions influencing the analytical performance such as particle size, amount of AuNPs, incubation time and pH were evaluated. Under the optimized experimental conditions, this method could detect ramoplanin in a linear range from 0.30 to 1.30 ppm with a detection limit of 0.01 ppm and exhibited good reproducibility, selectivity and recovery. Analysis time of this assay was only 2 min. To investigate its potential applicability, this assay was successfully applied for the determination of ramoplanin in urine samples without costly instruments.

Isothermal Strand-Displacement Polymerase Reaction for Visual Detection of the Southeast Asian–Type Deletion of α-Thalassemia

A rapid and reliable screening test for thalassemia carrier couples is the most effective strategy to decrease the risk of conceiving fetuses with severe thalassemia. We present an approach based on the isothermal strand-displacement polymerase reaction and the use of a lateral flow strip for the visual detection of an α-thalassemia Southeast Asian-type deletion. This assay was used to evaluate 86 clinical samples (72 cases of Southeast Asian-type deletions and 14 cases of other types of thalassemia), and the results obtained were 100% consistent with those obtained using conventional gap-PCR. The approach thus provides a simple, sensitive, rapid, and cost-effective method for the diagnosis of thalassemia genotypes.

Visual and surface plasmon resonance sensor for zirconium based on zirconium-induced aggregation of adenosine triphosphate-stabilized gold nanoparticles

Owing to its high affinity with phosphate, Zr(IV) can induce the aggregation of adenosine 5′-triphosphate (ATP)-stabilized AuNPs, leading to the change of surface plasmon resonance (SPR) absorption spectra and color of ATP-stabilized AuNP solutions. Based on these phenomena, visual and SPR sensors for Zr(IV) have been developed for the first time. The A660nm/A518nm values of ATP-stabilized AuNPs in SPR absorption spectra increase linearly with the concentrations of Zr(IV) from 0.5μM to 100μM (r=0.9971) with a detection limit of 95nM. A visual Zr(IV) detection is achieved with a detection limit of 30μM. The sensor shows excellent selectivity against other metal ions, such as Cu2+, Fe3+, Cd2+, and Pb2+. The recoveries for the detection of 5μM, 10μM, 25μM and 75μM Zr(IV) in lake water samples are 96.0%, 97.0%, 95.6% and 102.4%, respectively. The recoveries of the proposed SPR method are comparable with those of ICP-OES method.

Design of a Solid‐State Electrochemiluminescence Biosensor for Detection of PML/RARα Fusion Gene Using Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$‐AuNPs Aggregations on Gold Electrode

AbstractA solid‐state electrochemiluminescence (ECL) biosensor based on special ferrocene‐labeled molecular beacon (Fc‐MB) for highly sensitive detection of promyelocytic leukemia/retinoic acid receptor alpha (PML/RARα) fusion gene was developed successfully using Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$/2‐(dibutylamino)ethanol (DBAE) as detecting pattern. Such a special sensor involves two main parts, an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Ruthenium (II) tris‐(bipyridine) and Au nanoparticles (Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$‐AuNPs) onto the Au electrode (AuE) surface. The molecular beacon probe in which the ferrocene tag could effectively quench the ECL of the Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$acted as ECL intensity switch. The molecular beacon probe was designed with special base sequence, which could hybridize with its complementary target DNA. In the absence of a target, the hairpin structure of the probe forced the ferrocene (Fc) into close proximity with the ECL substrate, thus reducing ECL intensity. Target binding allowed the Fc away from the ECL substrate and resulted in an obvious increment in ECL intensity due to the decreased Fc quenching effect. The effect of the amount of Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ and the mixing procedure of Ru(bpy)${{{2+\hfill \atop 3\hfill}}}$ and AuNPs solution on the fabrication of ECL film had been investigated. As a result, the change of ECL intensity had a direct relationship with the logarithm of PML/RARα fusion gene concentration in the range of 0.05–500 pM with a detection limit of 7 fM, and the developed biosensor possessed good molecular recognizability in human serum. Thus, the approach holds promise for the early diagnostics and prognosis monitoring of APL and other diseases.

Gold nanoparticle-modified graphite pencil electrode for the high-sensitivity detection of hydrazine

A novel gold nanoparticle-modified graphite pencil electrode (AuNP-GPE) is prepared just by immersing a bare GPE in AuNP solution, followed by heating for 15min. The bare and modified GPEs are characterized by FE-SEM imaging and cyclic voltammetry. The AuNP-GPEs showed excellent electrocatalytic activities with respect to hydrazine oxidation, with good reproducibility. To reduce the quantification and detection limits, and increase the hydrazine sensitivity, the pH and square wave voltammetry parameters are optimized. A square wave voltammetry study as a function of the hydrazine concentration showed that the AuNP-GPE detector's quantification limit was 100nmolL−1 hydrazine, much lower than the value obtained using amperometry (10µmolL−1). The limits of detection (at 3σ) for hydrazine sensing at AuNP-GPEs using square wave voltammetry and amperometry were 42nmolL−1 and 3.07µmolL−1. Finally, the modified electrode was used to determine the hydrazine concentration in drinking water, and satisfactory results are obtained. This simple, rapid, low-cost method for fabricating a modified electrode is an attractive approach to the development of new sensors.

Effects of the Number of Satellites on Surface Plasmon Coupling of Core-Satellite Nanoassemblies

Noble metal nanoparticles have attracted much attention due to their unique optical properties, represented by surface plasmon resonance (SPR). The resonance frequency of the surface plasmon varies with the size, shape, material, and local environment of the nanoparticles. Another appealing means to tune the optical response of the nanoparticle systems is assembling nanoparticles, instead of modifying individual nanoparticles. Coupling of surface plasmons of nanoparticles in close proximity shifts the SPR band of the assembly from that of the individual nanoparticles. The shift naturally depends on the extent of the coupling, and thus on the detailed structure of assemblies such as interparticle distance, allowing for an infinitely fine control of the optical properties. Therefore, assembling nanoparticles in a controlled fashion is of paramount importance. Recently, we developed a novel method to prepare coresatellite nanoassemblies with well-defined and easily controllable structural parameters in a colloidal dispersion state. Selective desorption of large gold nanoparticles (AuNPs) against small AuNPs from glass substrates by sonication led to the production of ultrapure nanoassemblies. The nanoassemblies consist of large core AuNPs decorated by small satellite AuNPs with a distance defined by self-assembled monolayers (SAMs) of alkanedithiol linkers. Different lengths of the alkanedithiol linkers allowed us to measure the surface plasmon couplings between the AuNP core and satellites as a function of the interparticle distances. In complex nanoclusters, the surface plasmon coupling also depends on the number of nanoparticles that constitute the nanoclusters. For example, the surface plasmon coupling band continuously red-shifts as more nanoparticles are assembled in one direction. This is intuitively understood as the red-shifting longitudinal surface plasmon mode supported by elongated nanostructures. Contrary to linear assemblies, core-satellite nanoassemblies can be regarded as multiples of a size-asymmetric heterodimer consisting of a core and a satellite. In this simplified picture, the addition of satellites should not influence the surface plasmon coupling frequencies, although it will increase the intensity of the coupling. In this respect, it is intriguing to experimentally explore the surface plasmon coupling of the core-satellite nanoassemblies as a function of the number of satellites. The new assembly method we developed enables facile control over the number of satellites in the nanoassembly. The following process was used for the production of coresatellite nanoassemblies: (1) surface functionalization of glass substrates with amine, (2) adsorption of core AuNPs (50 ± 5 nm) on the glass substrate, (3) thiol-functionalization of the adsorbed core nanoparticles using 1,10-decanedithiol (DDT) SAMs, (4) adsorption of satellite AuNPs (13 ± 1 nm), and (5) selective desorption of the core-satellite nanoassemblies into ethanol by sonication. The immersion time in step 4, allowed for the satellite AuNPs in solution to interact with the core AuNPs on the glass substrate, determines the number of satellites covering the core nanoparticles (Figure 1(a)). Transmission electron microscopy (TEM) images of more than 100 final core-satellite

Logical regulation of the enzyme-like activity of gold nanoparticles by using heavy metal ions

In this study we employed self-deposition and competitive or synergistic interactions between metal ions and gold nanoparticles (Au NPs) to develop OR, AND, INHIBIT, and XOR logic gates through regulation of the enzyme-like activity of Au NPs. In the presence of various metal ions (Ag(+), Bi(3+), Pb(2+), Pt(4+), and Hg(2+)), we found that Au NPs (13 nm) exhibited peroxidase-, oxidase-, or catalase-like activity. After Ag(+), Bi(3+), or Pb(2+) ions had been deposited on the Au NPs, the particles displayed strong peroxidase-like activity; on the other hand, they exhibited strong oxidase- and catalase-like activities after reactions with Ag(+)/Hg(2+) and Hg(2+)/Bi(3+) ions, respectively. The catalytic activities of these Au NPs arose mainly from the various oxidation states of the surface metal atoms/ions. Taking advantage of this behavior, we constructed multiplex logic operations-OR, AND, INHIBIT, and XOR logic gates-through regulation of the enzyme-like activity after the introduction of metal ions into the Au NP solution. When we deposited Hg(2+) and/or Bi(3+) ions onto the Au NPs, the catalase-like activities of the Au NPs were strongly enhanced (>100-fold). Therefore, we could construct an OR logic gate by using Hg(2+)/Bi(3+) as inputs and the catalase-like activity of the Au NPs as the output. Likewise, we constructed an AND logic gate by using Pt(4+) and Hg(2+) as inputs and the oxidase-like activity of the Au NPs as the output; the co-deposition of Pt and Hg atoms/ions on the Au NPs was responsible for this oxidase-like activity. Competition between Pb(2+) and Hg(2+) ions for the Au NPs allowed us to develop an INHIBIT logic gate-using Pb(2+) and Hg(2+) as inputs and the peroxidase-like activity of the Au NPs as the output. Finally, regulation of the peroxidase-like activity of the Au NPs through the two inputs Ag(+) and Bi(3+) enabled us to construct an XOR logic gate.

Highly Robust, Recyclable Displacement Assay for Mercuric Ions in Aqueous Solutions and Living Cells

We designed a recyclable Hg(2+) probe based on Rhodamine B isothiocyanate (RBITC)-poly(ethylene glycol) (PEG)-comodified gold nanoparticles (AuNPs) with excellent robustness, selectivity, and sensitivity. On the basis of a rational design, only Hg(2+) can displace RBITC from the AuNP surfaces, resulting in a remarkable enhancement of RBITC fluorescence initially quenched by AuNPs. To maintain stability and monodispersity of AuNPs in real samples, thiol-terminated PEG was employed to bind with the remaining active sites of AuNPs. Besides, this displacement assay can be regenerated by resupplying free RBITC into the AuNPs solutions that were already used for detecting Hg(2+). Importantly, the detection limit of this assay for Hg(2+) (2.3 nM) was lower than the maximum limits guided by the United States Environmental Protection Agency as well as that permitted by the World Health Organization. The efficiency of this probe was demonstrated in monitoring Hg(2+) in complex samples such as river water and living cells.

Bioreduction of chloroaurate ions to gold nanoparticles by culture filtrate of Pleurotus sapidus Quél

The present study demonstrates an eco-friendly, non-toxic and cost-effective protocol for synthesis of gold nanoparticles (AuNPs) in aqueous medium using Pleurotus sapidus culture filtrate as the reducing and stabilizing agent. On treating chloroauric acid solutions with fungal culture filtrate, rapid reduction of chloroaurate ions is observed leading to the formation of highly stable AuNPs in solution. The particles thereby obtained were characterized by different spectroscopic and X-ray analysis. EDX-spectrum revealed the presence of gold in the nanoparticles. FTIR spectroscopy confirmed the presence of a protein shell outside the nanoparticles which in turn also support their stabilization. DLS and TEM analysis of the AuNPs indicated that they ranged in size from 15 to 100nm with average size of 65±5nm. A probable mechanism behind the biosynthesis is discussed, which leads to the possibility of using the present protocol in future “nano-factories”.