Presence Of Au3 Research Articles

Reductive carbon dots for reduction, ratiometric fluorescence determination, and intracellular imaging of Au3+

Many studies show that ortho-phenylenediamine (OPD) produces an oxidized fluorescent product when exposed to an oxidizing agent that enables the direct or indirect fluorescence detection of a range chemical and biochemical analytes. However, there is no report on this unique optical behavior for other two isomers of phenylenediamine. This study demonstrates that a simple hydrothermal treatment of para-phenylenediamine (PPD) in the presence of sulfuric acid results in the formation of fluorescent N, S-doped carbon dots (CDs) with triple functionalities including the reduction of Au3+ into gold nanoparticles (AuNPs), the stabilization of the produced AuNPs, and the determination of Au3+ concentration through an intrinsic ratiometric fluorescence signal. In the presence of Au3+, the blue emission of CDs at 437 nm quenched, and a green emission at 540 nm emerged. The linear concentration range for the determination of Au3+ was 20 nM–16 µM with a detection limit of 16 nM. Additionally, the dual emissive CDs-AuNPs hybrid probe showed potential for the indirect fluorescence ratiometric determination of cysteine and sulfide ions. The linear concentration range for cysteine and sulfide ions were 0.25–8 μM and 0.1–6 μΜ, with detection limits of 0.095 μM and 0.041 μM, respectively. Accordingly, CDs were applied to detect Au3+ and S2− in real water samples. Moreover, the synthesized CDs showed no cytotoxicity for HeLa cells up to 300 µg mL−1, as determined by the MTT assay. Therefore, their potential for intracellular imaging of Au3+ in living cells was also investigated.

Liposome-assisted chemical redox cycling strategy for advanced signal amplification: A proof-of-concept toward sensitive electrochemiluminescence immunoassay

This work presents a novel signal amplification strategy for electrochemiluminescence (ECL) biosensor based on liposome-assisted chemical redox cycling for in situ formation of Au nanoparticles (Au NPs) on TiO2 nanotubes (TiO2 NTs) electrode. The system was exemplified by ascorbic acid (AA)-loaded liposome, the redox cycling of AA utilizing tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of Au nanoclusters (Au NCs)/TiO2 NTs as working electrode to implement the ECL detection of prostate specific antigen (PSA). Specifically, the AA-loaded liposomes were used as tags to label the captured PSA through a sandwich immunoreaction. After the lysate of the liposome was transferred onto the interface of Au NCs/TiO2 NTs in the presence of Au3+ and TECP, the chemical redox cycling was triggered. In the cycling, Au3+ was directly reduced in situ by AA to form Au NPs on Au NCs/TiO2 NTs electrode, whereas the oxidation product of AA was reduced by TCEP to regenerate AA. The large loading capacity of the liposome and chemical redox cycling resulted in the incomplete reduction of the Au NCs to Au NPs on the TiO2 NTs electrode, enhancing the ECL intensity greatly. The multiple signal amplification strategy achieved an ultrasensitive detection for PSA with a detection limit down to 6.7 × 10−15 g mL−1 and a wide linear concentration range from 1.0 × 10−14 to 1.0 × 10−8 g mL−1. It is believed that this work is anticipated to extend the employment of advanced chemical redox cycling reaction in the field of ECL bioassays.

Neem seed derived green C-dots: A highly sensitive luminescent probe for aqueous Au3+ ions and nurtures green gold recovery

Highly luminescent green C-dots (NeCDs) were synthesized using neem seed kernel as the carbon precursor via one step microwave assisted pyrolysis. The brown NeCDs powder ensued after purification readily disperses in water (avg. particle size ~ 2 nm) and exhibits extensive surface functionalization of the carbon core by carboxyl and poly-hydroxyl functional groups. The aqueous solution of NeCDs is stable, has long shelf life and exhibit high photostability in different environments. In addition, NeCDs is found to be harmless and nontoxic towards A549 cells, and hence it was employed as a luminescent probe for multicolor cell imaging. Moreover, the photoluminescence (PL) of NeCDs solution (φf ~ 12.5%) is significantly/selectively quenched in the presence of Au3+ ions via two distinct deactivation processes viz donor excited photo-induced electron transfer and co-ordination induced aggregation. As a result, NeCDs exhibit the lowest ever reported limit of detection (LOD) of ~16 nM for aqueous Au3+ ions. Prolonged exposure (~ 24 h) to the poly-hydroxyl surface group of NeCDs chemically reduces the co-ordinated Au3+ ions at room temperature even in dark and produces urchin-like gold nanoparticles (UL-Au NPs), a simple and greener way to recover gold from aqueous medium.

An effective fluorescent optical sensor: Thiazolo-thiazole based dye exhibiting anion/cation sensitivities and acidochromism

Fluorescent 2,5-bis(4-hydroxyphenyl)thiazolo[5,4-d]thiazole (HPhTT) sensor molecule consisting of thiazolo-thiazole (TTz) binding central unit and phenolic signalling side groups was synthesized with a symmetric structure. The selectivity, sensitivity and reversibility properties of optical sensor towards cations and anions were investigated. TTz unit of the sensor was responsible from cation and proton interactions resulting with fluorescent quenching, while phenolic–OH groups were sensitive to anions with a deprotonation mechanism. The fluorescence quenching in the presence of Au3+ with high selectivity, sensitivity and fast response, making it clear that the sensor was very effective in detecting Au3+. Fluorescent sensor (HPhTT) was also found to be able to recognize AcO-, F- and CN– anions accompanied by obvious UV–vis absorption change and fluorescence switch-on response, and exhibited enhanced intramolecular charge transfer (ICT) strongly depending on the forming conjugated acid after addition of anions. Ratiometric detection and reversible usage of the sensor for AcO-, F- and CN– anions were also possible. The sensor showed remarkable detection ability in a pH > 9 media and it has also been demonstrated that it can be used successfully as a pH sensor in an aqueous media. A colour calculator study using F- anion to estimate colour change, colour purity and colour coordinates under UV light excitation with I550/I444 ratio indicated that HPhTT dye had a promising potential for fluorescent sensor studies.

A Rhodamine-based Fluorescent Chemodosimeter for Au3+ in Aqueous Solution and Living Cells.

A highly selective rhodamine hydrazide-based fluorescent chemosensor for Au3+ detection was developed. The aqueous solution of rhodamine N-hydroxysemicarbazide (RHS), in the presence of Au3+, exhibited a significant 55-fold turn-on fluorescence response at 591 nm and a colorimetric change from colorless to pink. Other interested ions including Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Pb2+, Mn2+, Co2+, Ni2+, Ag+, Cd2+, Cu2+, Hg2+, Zn2+, Sn2+, Fe2+, Fe3+, Cr3+, Ce3+ did not induce any distinct color/spectral changes. The irreversible detection mechanism occurred via Au3+-promoted 5-exo-trig ring closure to yield 1,3,4-oxadiazole-2-one product. The RHS probe is non-responsive to other biologically relevant metal ions and the limit of detection for Au3+ was calculated to be 0.5 µM with a linear range of 0 to 90 µM. Fluorescence bioimaging of Au3+ in HepG2 cells was also successfully demonstrated.

Sensitive detection of auric and sulphide ions using hybrid silver/nitrogen-doped carbon nanoparticles

Hybrid Silver/Nitrogen-doped Carbon nanoparticles (i.e., Ag/NCNPs) have been explored as a spectrophotometric probe for the sensing of Au3+ and S2− ions in water, where the nitrogen-doped luminescent-carbon nanoparticles (NCNPs), derived from microwave pyrolysis of aqueous mixture of dextrose and urea, served as a reducing as well as a stabilizing agent for the Ag+ ions in-situ. The detection has been monitored by correlating the attenuation of the localized surface plasmon resonance (LSPR) band intensity of Ag/NCNPs at ∼416 nm in presence of Au3+ and S2− ions. Successive oxidation of Ag in the formulation, in presence of Au3+ ions in the system and subsequent in-situ formation of Au is assigned to the gradual diminution of the LSPR band. Likewise, depreciation of the LSPR band in the presence of S2− ions has been related to the depletion of Ag via the in-situ formation of Ag2S. The limit of detection (LOD) for Au3+ and S2− ions was found to be as low as 0.16 μM and 0.18 μM, respectively, and the presence of other common water-soluble ions making no significant contribution endorses the high sensitivity and selectivity of the probe.

Water compatible triazole linked pyrene-C1-glucosyl fluorescent sensor for Au3+ and living cell imaging studies

Abstract We have reported a simple triazole linked pyrenyl appended carbohydrate-based ‘turn-off’ fluorescent sensor 1 for selective recognition of Au3+ in aqueous medium at physiological pH. The sensor provides important features such as high selectivity and sensitivity, low detection limit, reversibility and quick response time. The selectivity of 1 towards Au3+ ion is established by changes of absorbance and fluorescence in the presence of Au3+ ions. The formation of 1:1 complex (1-Au3+) was established by Job’s plot and supported by ESI-MS data. In addition, the sensor has been used for recognition of Au3+ ions in the living cells.

‘Mixing-and-measuring’ surface-enhanced Raman scattering (SERS) detection of Bacillus cereus for potentially aiding gold mine field exploration

Bacillus cereus, a common soil bacterium, has been shown to act as a biogeochemical indicator for concealed mineralisations, e.g., vein-type Au deposits. Field and cultivation-free detection of Bacillus cereus in the presence of Au3+ and other metal ions is significantly important but still almost blank in current biogeochemical prospecting of gold mine system. Herein, a self-established simple approach was slightly improved to make silver nanoparticles (Ag NPs) rapidly concentrated on every bacterial cell, and highly strong and distinct surface-enhanced Raman scattering (SERS) signals of Bacillus cereus free from any native fluorescence have been obtained in a so called ‘mixing-and-measuring’ manner. Furthermore, SERS was used for the first time to our knowledge to investigate the impacts of different concentrations of metal ions on Bacillus cereus, and successfully utilized for distinguishing Au3+ ions from other species. A more convincing multi-Raman criterion based on Raman bands, and further the entire Raman spectrum in combination with statistical analysis (e.g., principal component analysis (PCA)) were found capable of detecting spectral differences of Bacillus cereus in the presence of metal ions (Au3+, Ag+, Cu2+ and Zn2+) with different concentrations. An interesting phenomenon has been found that except for Au3+ ions, the highest permissive concentration of other metal ions for the detected Bacillus cereus is up to 10 μg/mL possibly due to their resistance to Au. The results also indicate that an effective biogeochemical exploration technique of SERS spectral response may be developed, where Bacillus cereus spore counts are measured in the field and used as a pre-screening method to target areas useful for further sampling and complete geochemical analysis.

Highly selective detection of Au3+ using rhodamine-based modified polyacrylic acid (PAA)-coated ITO

Rhodamine derivatives grafted on polyacrylic acid (PAA) were designed, synthesized and evaluated as a Au3+-selective chemosensor using the rhodamine ring-opening approach. The fluorogenic and chromogenic polymer chemosensors (PAA-Rho1-PAA-Rho4) were constructed via a coupling reaction between PAA and alkylene polyamine groups possessing a different number of donor atoms and chain lengths to yield PAA-Rho1 (84.2%), PAA-Rho2 (80.3%), PAA-Rho3 (91.9%), and PAA-Rho4 (85.1%). Chemical structures and purity of polymeric sensors were characterized by TGA, NMR, SEM and IR. The complexation studies indicate that PAA-Rho3 exhibited the highest selectivity and sensitivity responsive colorimetric and fluorescence Au3+-specific sensor when compared to other metal ions and polymeric sensors. The polymeric sensors are non-fluorescence in the spirolactam form and could be selectively converted into the fluorescence ring-opened amide form in the presence of Au3+, leading to the fluorescence enhancements and colorimetric changes. In addition, the fluorescent conjugated polymer film as the chemosensors were fabricated by chemical modification on ITO substrate, which created new fluorescent film sensors (PAA-Rho3-ITO). Further study showed that the sensing process is reversible by rinsing with EDTA solutions; the lower detection limit was less than that obtained from uncoated polymer film PAA-Rho3, and the response time was less than 40 s. The super sensitive response, good reversibility, and very fast response time, make the fluorescent film sensors a promising Au3+ sensor for environmental and biological applications.

A highly sensitive and selective fluorescein-based fluorescence probe for Au3+ and its application in living cell imaging

A new fluorescein-based fluorescent probe for the detection of Au3+ has been developed. This probe was derived from 4′,5′-fluoresceindicarboxaldehyde and exhibited highly selective and sensitive response toward gold(III) ions in aqueous solution. There is a good linear relationship between the fluorescence intensity at 523nm and the concentrations of Au3+ ranging from 0μM to 60μM, which makes it effective for the detection of Au3+. The limit of detection (LOD) was evaluated to be 0.07μM based on S/N=3. The fluorescence enhancement was attributed to the irreversible CN bond hydrolysis that occurred to this probe in the presence of Au3+, generating the fluorescent 4′,5′-fluoresceindicarboxaldehyde. Furthermore, the imaging experiments indicated that this probe is cell-permeable and can be used to detect Au3+ within living cell.

Modifications of the metal and support during the deactivation and regeneration of Au/C catalysts for the hydrochlorination of acetylene

The effect of the gold oxidation state and carbon structure on the activity of Au/C catalysts for the hydrochlorination of acetylene was investigated by a combined approach using TPR, XPS and porosimetry determinations. The activity of the catalyst in the synthesis of vinyl chloride monomer was found to be dependent on the presence of Au3+ species in the catalyst. However, by preparing catalysts with different Au3+ content it was possible to determine the existence of a threshold Au3+ amount, beyond which the excess of Au3+ was not active for the reaction. This was explained by the existence of active sites at the Au/C interface, and not just by the presence of Au3+ species on top of Au nanoparticles, as explained by current models for these catalysts. It was also possible to determine the existence of a subset of Au nanoclusters which do not take part in the reaction, as well as changes in the textural properties of the carbon that can affect its long term reusability.

The combination effects of trivalent gold ions and gold nanoparticles with different antibiotics against resistant Pseudomonas aeruginosa

Despite much success in drug design and development, Pseudomonas aeruginosa is still considered as one of the most problematic bacteria due to its ability to develop mutational resistance against a variety of antibiotics. In search for new strategies to enhance antibacterial activity of antibiotics, in this work, the combination effect of gold materials including trivalent gold ions (Au3+) and gold nanoparticles (Au NPs) with 14 different antibiotics was investigated against the clinical isolates of P. aeruginosa, Staphylococcus aureus and Escherichia coli. Disk diffusion assay was carried out, and test strains were treated with the sub-inhibitory contents of gold nanomaterial. Results showed that Au NPs did not increase the antibacterial effect of antibiotics at tested concentration (40 μg/disc). However, the susceptibility of resistant P. aeruginosa increased in the presence of Au3+ and methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid, up to 147 %. As an individual experiment, the same group of antibiotics was tested for their activity against clinical isolates of S. aureus, E. coli and a different resistant strain of P. aeruginosa in the presence of sub-inhibitory contents of Au3+, where Au3+ increased the susceptibility of test strains to methicillin, erythromycin, vancomycin, penicillin G, clindamycin and nalidixic acid. Our finding suggested that using the combination of sub-inhibitory concentrations of Au3+ and methicillin, erythromycin, nalidixic acid or vancomycin may be a promising new strategy for the treatment of highly resistant P. aeruginosa infections.

Accumulation and toxicity of gold in the rabbit lens in vitro

Gold compounds are used therapeutically and have been observed to accumulate in the human eye. In the present study, we have measured the accumulation and loss of gold (AuIII) in rabbit lenses in vitro using 195Au as a tracer. Accumulation increased progressively with time of incubation up to 24 hr. The highest concentration of Au3+ observed was about 16 mumol kg-1 wet wt. Rate of accumulation also rose with increase in the external concentration of Au3+, but the magnitude of the change exceeded the concentration difference. Autoradiography showed a high accumulation of 195Au in a central region of the anterior face of the lens, as has been observed in vivo in humans undergoing chrysotherapy. Loss (efflux) of accumulated 195Au was increased by the presence of Au3+ or dithiothreitol in the external media. Lanthanum (La3+), however, decreased the loss of such Au and promoted its accumulation. Gold can have a toxic effect on lenses as incubation for 7 days in a medium containing 10(-7) M Au3+ resulted in a marked gain of Na and loss of K. The results suggest that Au accretion occurs at surface sites associated with the anterior of the lens, but whether or not intracellular accumulation occurs is not clear. This Au, in excess, may have toxic effects on the tissue.