•Novel gold nanoclusters-based fluorescent sensors have been successfully constructed for H2S detection.•The sensors show high selectivity toward H2S over other anions, amino acids and thiols.•The sensors exhibit a stable response for H2S over a wide range from 0.002 μmol L−1 to 120 μmol L−1. The LOD is as low as 1.8 nmol L−1.As a highly toxic environmental pollutant and also an important gasotransmitter in diverse physiological processes, the selective and sensitive detection of hydrogen sulfide (H2S) is very significant. In this work, acetylcysteine stabilized gold nanoclusters (ACC@AuNCs)-based fluorescent sensors had been successfully constructed for H2S perception. The sensing principle was that H2S-induced fluorescence quenching of AuNCs which attributed to both the formation of Au2S between Au(I) in the AuNCs and H2S and the increased particle size. The proposed sensors showed high selectivity toward H2S over other anions, amino acids and thiols, and exhibited a stable response for H2S from 0.002 to 120 μmol L−1 with a detection limit of 1.8 nmol L−1. In addition, the practical application of the designed sensors was further evaluated with water and serum samples, and the tested results agreed well with those obtained by ICP-AES method. The satisfactory recoveries and good precision show that the proposed fluorescent sensors has potential application in biological and environmental fields.A novel gold nanoclusters-based fluorescent sensor have been successfully constructed for H2S detection. The sensors show high selectivity toward H2S over other anions, amino acids and thiols, and a wide linear range from 0.002 to 120 μmol L−1 H2S. The LOD of the sensors is as low as 1.8 nmol L−1. In addition, the practical application of the designed sensors is further evaluated with water and serum samples.Download high-res image (256KB)Download full-size image

•A novel fluorescent gold nanoclusters was obtained by a rapid one-pot synthesis.•The AuNCs was explored for selective and sensitive determination of Fe3+.•The MMTA-AuNCs show two wide linear ranges from 9.9 to 3000.0 nM and 3.0 to 1100 μM with a limit of detection of 3.0 nM.Herein, we demonstrate a straightforward synthesis of fluorescent gold nanoclusters (AuNCs), employing 2-Mercapto-4-methyl-5-thiazoleacetic acid (MMTA) as a reducing and protecting agent by a rapid one-pot synthesis method with a short time of 20 min. The as-synthesized MMTA-AuNCs exhibited bright blue emission with a strong peak centered at 430 nm and the quantum yield (QY) was evaluated to be 4.0%. Based on the fluorescence quenching mechanism of a surface chelating reaction between MMTA and ferric ion (Fe3+), the MMTA-AuNCs were exploited as a fluorescence sensor for sensitive and selective detection of Fe3+. Two linear ranges of 9.9–3000.0 nM and 3.0–1100 μM with a detection limit of 3.0 nM were obtained. The detection limit was lower than the maximum level (0.3 mg L−1, equivalent to 5.4 μM) of Fe3+ permitted in drinking water by the U.S. Environmental Protection Agency. Furthermore, the proposed fluorescent sensing system was successfully applied to the analysis of Fe3+ in real samples such as water and human serum samples with satisfactory recoveries. These results indicated that the as-prepared MMTA-AuNCs could pave an avenue for the development of sensing probes for detection of Fe3+ in environmental and biomedical applications.A novel fluorescent gold nanoclusters have been successfully obtained employing MMTA as both reducing and protecting agents with a short time of 20 min. The MMTA-AuNCs were exploited for sensitive and selective detection of Fe3+ ion. In addition, the as-fabricated fluorescent sensing system was successfully applied to the analysis of Fe3+ in water and serum samples with satisfactory recoveries.Download high-res image (216KB)Download full-size image

•A simple one-pot microwave-assisted synthesis method of gold nanoclusters was developed by employing chicken egg white as reducing/capping reagent.•The resultant AuNCs showed strong emission at 667 nm with quantum yield of 7.23%, large Stokes shift (>350 nm) and microsecond-scale lifetime.•The EW@AuNCs probe exhibits remarkable selectivity and ultra-high sensitivity toward Hg2+ with a detection limit as low as 20 pM.In this paper, we developed a simple one-pot method, employing inexpensive chicken egg white (EW) as a reducing/capping reagent, for microwave-assisted synthesis of water-soluble and well-dispersed chicken egg white-protected gold nanoclusters (EW@AuNCs) with far-red/near-infrared (FR/NIR) emission. The resultant AuNCs showed strong emission at 667 nm with a quantum yield of 7.23%. The excellent photostability, large Stokes shift (>350 nm), microsecond-scale lifetime and strong emission endowed EW@AuNCs potential as a sensing probe. The photoluminescence of EW@AuNCs could be quenched upon addition of either Hg2+ or Cu2+ ion. After ethylenediamine (En) was used as a masking agent, the EW@AuNCs offered highly selective for determination of Hg2+ ion. Also, the resultant EW@AuNCs probe exhibited ultra-high sensitivity toward Hg2+ ion with a detection limit as low as 20 pM, which is 500 times lower than the limit value (10 nM) defined by the U.S. Environmental Protection Agency in drinkable water. The proposed AuNCs probe for Hg2+ ion has a linear range of 0.0446–5.90 nM and good repeatable response to 2.0 nM Hg2+ with a relative standard deviation of 2.8% (n = 5). Additionally, the applicability of the sensing system was also verified by analysis of Hg2+ ion in tap water and pond water samples.

A highly selective and ultra-sensitive colorimetric assay has been developed for detecting the magnesium ion (Mg2+) based on pectinase (PE)-protected Au nanoparticles (PE-AuNPs). This is the first study reporting the use of pectinase for green synthesizing gold nanoparticles. Aggregation of PE-AuNPs was induced immediately following the addition of Mg2+ ion under Tris-HCl buffer at pH 4.0, yielding a color change from red to blue, and the characteristic surface plasmon resonance (SPR) peak of PE-AuNPs was red-shifted to 665 nm. The effects of parameters such as pH, the amount of PE-AuNPs, and incubation time on the sensitivity of colorimetric assay were investigated in detail. The Mg2+-induced aggregation of PE-AuNPs could be monitored by both the naked eye and UV–vis spectrophotometry. The lowest detection concentration with the naked eye is 0.52 μM. A linear relationship between the absorbance ratio (A665/A523) and Mg2+ concentration was observed in two ranges of Mg2+ concentration by UV–vis spectrophotometry, including 5.34 × 10−7 μM to 51.4 μM and 5.12 × 102 μM to 3.19 × 103 μM. The Mg2+ detection limit was determined to be 4.0 × 10−9 μM with UV–vis spectrophotometer. The proposed colorimetric assay possesses a highly selective response for Mg2+ over other metal ions. This method has been successfully applied to determine the Mg2+ ion in some water samples.

We report a facile strategy to synthesize ultrabright core–shell gold nanoclusters in one pot by using N-acetyl-L-cysteine (NAC) as both a reducing and protecting agent, in which the core is Au(0) atoms and the shell is oligomeric Au(I)–NAC complexes. The Au(0)@Au(I)–NAC core–shell nanoclusters (NCs) displayed excitation and emission bands at 340 and 590 nm, respectively. It showed a strong orange-yellow photoluminescence with a quantum yield of 14%. The thermogravimetric analysis and mass spectrometry data suggest that the as-synthesized NCs comprise mainly Au27NAC32, in which a uniquely high thiolate-to-Au ratio (1.2:1) endows the gold clusters better biocompatibility. The Au(0)@Au(I)–NAC core–shell NCs offered ultra-small size, excellent stability, large Stokes shift and microsecond-scale lifetime, and exhibited negligible cytotoxicity to cancer cells. Based on the excellent properties of the gold nanoclusters (AuNCs), cell experiments were conducted. Cytotoxicity studies showed that the AuNCs exhibited negligible effects in altering cell proliferation or triggering apoptosis. The as-synthesized AuNCs have been successfully applied as a photoluminescent probe for human bladder cancer cellular imaging.

•A highly selective and sensitive colorimetric method was developed for detecting Cysteine.•A novel synthesis method of gold nanoparticles was reported.•The proposed colorimetric assay of Cys could be operated by both the naked eye and UV-vis spectrophotometry.Herein, a novel, high sensitive, and specific colorimetric sensor for cysteine (Cys) based on pectinase protected gold nanoparticles (P@AuNPs) has been demonstrated for the first time. The P@AuNPs were synthesized by “MW-assisted heat method” and were characterized by UV–vis, TEM, FT-IR and zeta potential techniques. Cys could cause the aggregation of P@AuNPs due to formation of the strong covalent Au-S bond and electrostatic binding. As the Cys concentration increased, the color of the solutions gradually changed from wine-red to blue as well as the large absorption band shifted from 523 to 650 nm upon P@AuNPs aggregation. In addition, various experimental parameters such as pH, the amount of P@AuNPs and incubation time were investigated for the optimum sensing conditions. The concentration of Cys could be determined by monitoring with the naked eye or a UV–vis spectrometer. The proposed colorimetric sensor showed an extreme selectivity toward the determination of Cys in the presence of 20-fold all other different interferents. Under optimum conditions, this method exhibited two good linear ranges from 4.85×10−9 to 3.02×10−4 M (R2=0.996) and 3.25×10−3 to 1.03×10−2 M (R2=0.999), with a low detection limit of 4.6×10−9 M. Moreover, this colorimetric sensor was successfully applied to the detection of Cys in human urine samples, demonstrating its great value for practical application in biological systems.A highly selective and sensitive colorimetric method has been developed for detecting the Cysteine (Cys) based on pectinase (P) protected Au nanoparticles (P@AuNPs). Aggregation of P@AuNPs was induced following the addition of Cys, which attribute to formation of the strong covalent Au-S bond and electrostatic binding, which yielded a color change from wine-red to blue. The proposed colorimetric method for Cys could be operated by both the naked eye and UV–vis spectrophotometry. And the present AuNPs showed an extreme selectivity toward the determination of Cys in the presence of 20-fold of all other interferents. The detection limit is 4.6×10−9 M with UV–vis spectrophotometer. This method has been successfully proved in the detection of Cys in human urine samples with high reliability and applicability. So it would become promising assay platform for probing biothiols in biological systems.

We report a facile strategy to synthesize a novel fluorescent gold nanoclusters (NAC-AuNCs) in one step by using only the reactants of HAuCl4 and N-acetyl-l-cysteine. The as-prepared AuNCs exhibited a fluorescence emission at 590 nm and a quantum yield of 13.6%. On the basis of metallophilic Hg2+–Au+ interaction-induced fluorescence quenching mechanism, the fluorescent NAC-AuNCs offer highly sensitivity with a limit of detection of 0.2 nM for determination of Hg2+ ions, which is 50 times lower than the limit value (10 nM) defined by the U.S. Environmental Protection Agency in drinkable water. The proposed fluorescent probe has a linear response range of 2.0–3200 nM Hg2+ ions and good repeatable response to 20 nM Hg2+ with a relative standard deviation of 3.2% (n = 6). Also, the luminescence response of the NAC-AuNCs probe in the presence of EDTA is especially selective to Hg2+. The proposed method has been successfully applied for determination of Hg2+ in various water samples, and the results agreed well with those obtained by the ICP-AES method.

The uricase-gold nanoparticles (AuNPs) composite nanomaterial was covalently immobilized on a biofilm, eggshell membrane. The uric acid biosensor was constructed by positioning the immobilized biofilm on the surface of a Clark dissolved oxygen electrode. The scanning electron micrograph revealed that the uricase-AuNPs composite nanomaterial was successfully immobilized. The effects of enzyme loading, pH, concentration of phosphate buffer and temperature on the biosensor response have been studied in detail. The results showed that response time of the biosensor was 60 s, the linear range for the detection of uric acid varied from 1.0 µM to ~1.0 mM with a detection limit of 0.8 µM (S/N = 3) and relative standard deviation of 2.6% for 0.1 mM uric acid (n = 6). Some common potential interferents in samples demonstrated no interferences. The biosensor has been successfully applied to determine the uric acid level in urine and serum samples.