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Gold nanoclusters (AuNCs) possess weak intrinsic fluorescence, limiting their sensitivity in biosensing applications. This study addresses these limitations by developing a spatially confined dual-emission nanoprobe composed of silicon nanoparticles (SiNPs) and AuNCs. This amplified and stabilized fluorescence mechanism overcomes the limitations associated with using AuNCs alone, achieving superior sensitivity in the sensing platform. The nanoprobe was successfully employed for ratiometric detection of bleomycin (BLM) in serum samples, operating at an excitation wavelength of 365 nm, with emission wavelengths at 480 nm and 580 nm. The analytical performance of the system is distinguished by a linear detection range of 0–3.5 μM, an impressive limit of detection (LOD) of 35.27 nM, and exceptional recoveries ranging from 96.80 to 105.9%. This innovative approach significantly enhances the applicability and reliability of AuNC-based biosensing in complex biological media, highlighting its superior analytical capabilities. [ABSTRACT FROM AUTHOR]

Gold nanoclusters are a smart platform for sensing potassium ions (K+). They have been synthesized using bovine serum albumin (BSA) and valinomycin (Val) to protect and cap the nanoclusters. The nanoclusters (Val-AuNCs) produced have a red emission at 616 nm under excitation with 470 nm. In the presence of K+, the valinomycin polar groups switch to the molecule's interior by complexing with K+, forming a bracelet structure, and being surrounded by the hydrophobic exterior conformation. This structure allows a proposed fluorometric method for detecting K+ by switching between the Val-AuNCs' hydrophilicity and hydrophobicity, which induces the aggregation of gold nanoclusters. As a result, significant quenching is seen in fluorescence after adding K+. The quenching in fluorescence in the presence of K+ is attributed to the aggregation mechanism. This sensing technique provides a highly precise and selective sensing method for K+ in the range 0.78 to 8 µM with LOD equal to 233 nM. The selectivity of Val-AuNCs toward K+ ions was investigated compared to other ions. Furthermore, the Val-AuNCs have novel possibilities as favorable sensor candidates for various imaging applications. Our detection technique was validated by determining K+ ions in postmortem vitreous humor samples, which yielded promising results. [ABSTRACT FROM AUTHOR]

Sensors for which the output signal is an intensity change for a single-emission peak are easily disturbed by many factors, such as the stability of the instrument, intensity of the excitation light, and biological background. However, for ratiometric fluorescence sensors, the output signal is a change in the intensity ratio of two or more emission peaks. The fluorescence intensity of these emission peaks is similarly affected by external factors; thus, these sensors have the ability to self-correct, which can greatly improve the accuracy and reliability of the detection results. To accurately image glutathione (GSH) in cells, gold nanoclusters (AuNCs) with intrinsic double emission at wavelengths of 606 nm and 794 nm were synthesized from chloroauric acid. With the emission peak at 606 nm as the recognition signal and the emission peak at 794 nm as the reference signal, a near-infrared dual-emission ratio fluorescence sensing platform was constructed to accurately detect changes in the GSH concentration in cells. In vitro and in vivo analyses showed that the ratiometric fluorescent probe specifically detects GSH and enables ultrasensitive imaging, providing a new platform for the accurate detection of active small molecules. [ABSTRACT FROM AUTHOR]

When thiolactic acid–capped gold nanoclusters (AuNCs@TLA) with strong near-infrared (NIR, 800 nm) emission were applied to detect metal ions, only Ag+ induced the generation of two new emission peaks at 610 and 670 nm in sequence and quenching the original NIR emission. The new peak at 670 nm generated after the 800-nm emission disappeared utterly. The ratiometric and turn-on responses showed different linear concentration ranges (0.10–4.0 μmol·L−1 and 10–50 μmol·L−1) toward Ag+, and the limit of detection (LOD) was 40 nmol·L−1. Especially, the probe exhibited extremely high selectivity and strong anti-interference from other metal ions. Mechanism studies showed that the novel responses were attributed to the anti-galvanic reaction of AuNCs to Ag+ and formation of bimetallic nanoclusters. The two new emission peaks were due to the composition change and size growth of the metal core. Besides, bovine serum albumin (BSA) has been employed as a signal amplifier based on the assembly-induced emission enhancement properties of AuNCs, which improved the LOD to 10 nmol·L−1. Moreover, the ratiometric method is feasible for Ag+ detection in diluted serum with high recovery rates, showing large application potential in the biological system. The present study supplies a novel ratiometric probe for Ag+ with a two-stage response and provides a novel signal amplifier of BSA, which will facilitate and promote the application of NIR-emitted metal nanoclusters in biological system. [ABSTRACT FROM AUTHOR]

A two-photon excited ratiometric fluorescent pH sensor is reported by combining l-cysteine–protected AuNCs (Cys@AuNCs) with fluorescein isothiocyanate (FITC). Cys@AuNCs were synthesized through a one-step self-reduction route and showed pH-responsive photoluminescence at 650 nm. Benefiting from the opposite pH response of Cys@AuNCs and FITC, the fluorescence ratio (F515 nm/F650 nm) of FITC&Cys@AuNCs provided a large dynamic range of 200-fold for pH measurement in the response interval of pH 5.0–8.0. Based on the excellent two-photon absorption coefficient of Cys@AuNCs, the sensor was expected to achieve sensitive quantitation of pH in living cells under two-photon excitation. In addition, colorimetric biosensing based on enzyme-like metal nanoclusters has attracted wide attention due to their low-cost, simplicity, and practicality. It is crucial to develop high catalytic activity nanozyme from the viewpoint of practical application. The synthesized Cys@AuNCs exhibited excellent photoactivated peroxidase-like activity with high substrate affinity and catalytic reaction rate, promising for rapid colorimetric biosensing of field analysis and the control of catalytic reactions by photostimulation. [ABSTRACT FROM AUTHOR]

A creatively designed and constructed a multifunctional ratiometric fluorescence probe is reported by assembling glutathione (GSH)-protected gold nanoclusters (AuNCs) with fluorescein-doped mesoporous silica nanoparticle (FS) for the detection of Cu2+ and Ag+ ions, which could eliminate most interferences by self-calibration. Under the excitation at 450 nm, the fluorescence connected with AuNCs can rapidly respond by quenching or enhancement, respectively, for Cu2+ and Ag+ ions, while the fluorescein isothiocyante (FITC) fluorescence served as reference with negligible change. The fluorescence intensity ratio showed good linear relationships with Cu2+ and Ag+ concentrations in the range 0.5–10 μM and 0.1–8 μM, respectively. The detection limits were as low as 140 nM and 60 nM for Cu2+ and Ag+ ions, respectively. The color change induced by fluorescent intensity ratio variation could also be employed for visual discrimination. The AuNC-embedded FS (FS-Au) nanoprobe was successfully used for Cu2+ and Ag+ ion determination in drinking water and intracellular Cu2+ imaging, which exhibits promising prospects in cost-effective and rapid determination of both Cu2+ and Ag+ with good sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Quantitative detection of different types of reactive oxygen species (ROS) is vital for understanding the crucial roles of them in biological processes. However, few researches achieved the detection of multiple types of ROS with one probe until now. Given this, we designed and prepared fluorescent gold nanoclusters capped by dual ligand bovine serum albumin and lysozyme (BSA-LYS-AuNCs), which could detect 3 specific types of ROS based on its different fluorescent responses to H2O2, •OH and ClO−, respectively. The limit of detection (LOD) of H2O2, •OH, and ClO− was as low as 0.82 μM, 0.45 μM, and 0.62 μM. Moreover, as an important ROS type, ClO− was detected with high sensitivity and low LOD by BSA-LYS-AuNCs. It was also proved that the crosslinking of protein mainly contributed to the unique fluorescent characteristics of the probe exposing to ClO−. Furthermore, the fluorescent probe achieved the smart detection of hROS (including •OH and ClO−) and wROS (the form of H2O2) in the real sample, which could also been applied specifically to the detection of antioxidants, e.g. ascorbic acid. The gold nanoclusters developed have high potential for the smart detection of multiple ROS in the body fluid of organisms. [ABSTRACT FROM AUTHOR]

An innovative research has been conducted focused on demonstrating the ability of novel dual-emissive glutathione-stabilized gold nanoclusters (GSH-AuNCs) to perform bright near-infrared (NIR)–emitting contrast agents inside tissue-mimicking agarose-phantoms via two complementary confocal fluorescence imaging techniques. First, using a new and fast microwave-assisted approach, we synthesized photostable dual-emitting GSH-AuNCs with an average size of 3.2 ± 0.4 nm and NIR emission quantum yield of 9.9%. Steady-state fluorescence measurements coupled with fluorescence lifetime imaging microscopy (FLIM) assays performed on lyophilized GSH-AuNCs revealed that the obtained GSH-AuNCs exhibit PL emissions at 610 nm (red PL) and, respectively, 800 nm (NIR PL) in both solution and powder solid-state. Time-resolved fluorescence measurements showed that the two PL components are characterized by average lifetimes of 407 ns (red PL) and 1821 ns (NIR PL), respectively. Additionally, due to a partial overlap between the red PL and the absorption of the NIR PL, an energy transfer between the two coexisting emissive centers was discovered and confirmed via steady-state and time-resolved fluorescence measurements. Furthermore, the FLIM analysis performed on powder GSH-AuNCs under 640 nm, an excitation more suitable for bioimaging applications, revealed a homogeneous and photostable NIR PL signal from GSH-AuNCs. Finally, the ability of GSH-AuNCs to operate as reliable NIR-emitting contrast agents inside tissue-mimicking agarose-phantoms was demonstrated here for the first time via complementary FLIM and re-scan confocal fluorescence imaging techniques. In consequence, GSH-AuNCs show great promise for future in vivo imaging applications via confocal fluorescence microscopy. [ABSTRACT FROM AUTHOR]

Gold nanoclusters (AuNCs) are widely used in the fluorescence detection of biomolecules in human serum due to their good fluorescence properties, low toxicity, and better biocompatibility. However, the weak fluorescence intensity of AuNCs limits the fluorescence detection of molecules within a wide concentration range. It is reported that coating AuNCs in ZIF-8 with adjustable pore size can effectively improve the fluorescence intensity of AuNCs and broaden the detection range. And the AuNCs wrapped in the gaps of ZIF-8 can prevent the fluorescence quenching caused by the aggregation of AuNCs. However, ZIF-8 has high crystallinity, poor dispersion, and easy deposition, which reduces the fluorescence stability of the detection system and affects the detection. Based on the above research, the highly hydrophilic polymer PEI was modified to the surface of ZIF-8, and a kind of nanocomposite material AuNCs/ChOx@ZIF-8/PEI was obtained by co-encapsulating AuNCs prepared with glutathione as a ligand and cholesterol oxidase (ChOx) into ZIF-8 modified with PEI. The composite material emits strong red light at 650 nm under the excitation of 395-nm light, and the system can sensitively detect cholesterol (Chol) in human serum. Compared with other materials, the PEI-modified composite has better solubility and stability, so the detection effect of Chol is better. Encapsulation of ChOx in the ZIF-8 shell can protect the enzyme and increase the local concentration of ChOx, thereby speeding up the reaction rate. Compared with free AuNCs/ChOx, the quenching rate of AuNCs/ChOx@ZIF-8/PEI system is doubled. Secondly, the addition of Fe2+ to the detection process results in higher quenching rate and detection sensitivity. The system can detect Chol in the concentration range 0.1–2.4 μM, with a detection limit of 0.073 μM. The determination is a fast and sensitive strategy. In addition, the practicability of this assay in the detection of Chol in human serum has been verified. Due to its selectivity and sensitivity, it has potential application value in clinical diagnosis. [ABSTRACT FROM AUTHOR]

A dual-emission ratiometric fluorescent sensing system based on boron-doped carbon quantum dots (B-CQDs) and gold nanoclusters (AuNCs) has been developed for the determination of xanthine. The blue fluorescence of B-CQDs at 445 nm is then reduced by the AuNCs through the inner filter effect (IFE) under a single excitation wavelength of 370 nm. By the catalysis of xanthine oxidase (XOD), xanthine is oxidized by oxygen dissolved in the solution to produce H2O2. The horseradish peroxidase (HRP) catalyzes H2O2 to generate hydroxyl radicals, which can quench the fluorescence of AuNCs, leading to the recovery of the fluorescence of B-CQDs. Based on the relationship between the fluorescence intensity ratio (F445/F665) and the concentration of xanthine, the designed method exhibits a good linearity range of 1.2–500.0 μmol L −1 and a limit of detection of 0.37 μmol L −1. The ratiometric fluorescent is applied to determine xanthine in human urine samples. Good recoveries of spiked samples in the range 99.2–105.0% are obtained by the proposed assay, with relative standard deviations (RSD) ranging from 0.9 to 2.6%. [ABSTRACT FROM AUTHOR]

A core–shell QDs@mSiO2@y-AuNCs nanoprobe was prepared, and a new ratiometric fluorescent sensor for thiram detection was developed. The mechanism of thiram sensing was investigated using FTIR, surface-enhanced Raman, XPS spectra, etc. The sensing of thiram was mainly ascribed to the formation of Au–S bonds between thiram and Au atoms on y-AuNCs surface, resulting in the dissociation of 11-MUA ligand from the y-AuNCs surface and the charge transfer between thiram and y-AuNCs. In the ratiometric fluorescence detection of thiram based on QDs@mSiO2@y-AuNCs, a linear range of 0.5–60 ng/mL was obtained with a LOD of 0.19 ng/mL. Compared with the fluorescence detection based on y-AuNCs, the ratiometric fluorescence detection of thiram demonstrated 3-fold enhanced sensitivity. The improvement was ascribed to two aspects: the fluorescence emission of y-AuNCs was enhanced after they were loaded onto the QDs@mSiO2 nanoparticles; the ratiometric detection mode provided more precise sensing. The detection of thiram can be completed immediately after mixing the nanoprobe with thiram. Good recoveries of thiram in apple and pear samples were achieved. All the above results demonstrated the high potential of this method in practical applications. [ABSTRACT FROM AUTHOR]

A smartphone-based dual-wavelength digital imaging platform containing red (539–695 nm) and blue (389–511 nm) band-pass filters was developed for point-of-care (POC) testing of alkaline phosphatase (ALP) activity. The platform was based on dual-emitting fluorescent nanohybrids (AuNC@NAN), the ratiometric probe, which had a fluorescence "on-off-on-off" response. The probe comprised red-emitting gold nanoclusters (AuNCs) acting as the signal report units and blue-emitting N-(2-aminoethyl-1,8-naphthalimide) (NAN) acting as an internal reference. The different responses of the ratiometric probes resulted in a continuous color-multiplexing change from pink-red to dark-purple upon exposure to ALP. The dual-wavelength digital imaging platform was employed to acquire images of AuNC or NAN fluorescence signals without the influence of background light. Unlike the classical one-time digital imaging mode, the accurate red (R) and blue (B) channel values of the generated images can help to directly judge or eliminate the disturbance from unavoidable interfering factors. The R/B values were successfully employed for determining the ALP activity at a range 2.0 to 35.0 mU·mL−1 with the detection limit of 1.04 mU·mL−1. Such sensing imaging platform is also successful in determining ALP activity in human serum with 94.9–105% recoveries and relative standard deviation in the range 4.2–5.6%. [ABSTRACT FROM AUTHOR]

In present study, we discovered unusual solvent-mediated aggregation-enhanced emission (AEE) character of 11-mercaptoundecanoic acid capped gold nanoclusters (MUA-Au NCs). When aggregated in aqueous media, the MUA-Au NCs showed strong emission, which was weakened by adding ethanol. Interestingly, the suppressed emission was selectively enhanced in the presence of hydrogen sulfide (H2S) because H2S was absorbed onto Au NCs through the strong sulfur-gold bonding affinity. The hydrolyzed H2S, namely, HS−, made the Au NCs negatively charged, which aggregated again due to decreased solubility. The H2S-mediated fluorescence enhancement can be further amplified by introducing a hydrophilic thiolate (glutathione, GSH) onto the surface of Au NCs (GSH/MUA-Au NCs), which enabled sensitive determination of H2S. Under the optimized condition, a detection limit of 35 nM was achieved. The determination was not interfered by other anions such as F−, Cl−, Br−, I−, OAc−, N3−, NO3−, HCO3−, SCN−, SO32−, and SO42−. This excellent sensing performance allowed practical application of the GSH/MUA-Au NC-based sensing platform to accurate determination of H2S in human serum samples. [ABSTRACT FROM AUTHOR]

Nanosheets of cobalt oxyhydroxide (CoOOH) are found to exhibit oxidase-like activity and can catalyze the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by oxygen in weakly acidic solution even in the absence of hydrogen peroxide. On the basis of this property, a fluorometric assay was designed in which the blue oxidation product of TMB (oxTMB) reduces the intensity of the fluorescence of albumin-stabilized gold nanoclusters (BSA-AuNCs). The fluorescence of the AuNCs under 502 nm photoexcitation has a peak at 620 nm which overlaps the absorption band of oxTMB. As a result, fluorescence is reduced. The findings were used to develop a method for the fluorometric quantitation of ascorbic acid. Ascorbic acid is capable of destroying some of the CoOOH nanosheets, and hence catalytic oxidation is retarded and fluorescence will be less strongly reduced (i.e., reabsorbed). Fluorescence intensity increases in the 0.75 to 20 μM ascorbic acid concentration range, and the detection limit is 0.2 μM. The method is well reproducible (the relative standard deviation of 1.6% for 11 replicates at a 10 μM ascorbic acid level). The practicability of the method was demonstrated by the analysis of ascorbic acid in tablets and juices. [ABSTRACT FROM AUTHOR]

Gold-silver nanoclusters (Au-AgNCs) were synthesized by simultaneous chemical reduction of Au(III) and Ag(I) ions in one pot, using bovine serum albumin as both a template and a reductant. The Au-AgNCs have an average size of 2.4 nm and display strong red fluorescence (with an emission peak at 610 nm on excitation at 360 nm). The fluorescence quantum yield can reach 18.6%. Fluorescence is strongly quenched by hypochlorite, while other common anions have minor (or no) effects on fluorescence. Based on these findings, a fluorometric method was developed for the determination of hypochlorite. The method has a linear response in the 0.7 to 15 μM concentration range, with a limit of detection as low as 80 nM. It was successfully applied to the determination of hypochlorite in (spiked) tap water. [ABSTRACT FROM AUTHOR]

Hemoglobin-stabilized gold nanoclusters (Hb-AuNCs) were prepared by using hemoglobin as both reducing and stabilizing agents. The Hb-AuNCs display a strong catalytic effect on the chemiluminescence (CL) reaction of luminol with NaIO. The CL mechanism is discussed and the experimental variables are examined. It is found that dopamine strongly inhibits CL. This finding is exploited in a CL-based dopamine assay that works in the range between 0.3 and 9.0 nM and has a 0.1 nM detection limit. The relative standard deviation is 3.1% at a 5 nM dopamine level (for n = 11). The method was applied to the determination of dopamine in spiked human plasma with satisfactory results. [ABSTRACT FROM AUTHOR]

The authors describe a rapid and sensitive method for the determination of the activity of scavenging hydrogen peroxide in which glucose oxidase-stabilized gold nanoclusters (AuNCs) were employed as a fluorescent nanoprobe. The AuNCs are synthesized by a biomineralization process and display an intense blue fluorescence peaking at 450 nm and a quantum yield of 1.1% under 360-nm excitation. The Fenton reaction induces quenching of fluorescence, and this effect can be used to determine HO in the 0.5 to 10 μmol⋅L concentration range. The substances displaying HO scavenging activity prevent quenching and thus restore fluorescence. The intensity of restored fluorescence is directly related to the HO scavenging activity of the antioxidant. The method was applied to the determination of the HO scavenging activity of the model antioxidants ascorbic acid and tartaric acid which gave IC values of 7.4 and 19.1 μmol⋅L, respectively. [ABSTRACT FROM AUTHOR]

Gold nanoclusters (AuNCs) stabilized with bovine serum albumin were utilized as a fluorescent probe for ferrous ion. The detection scheme is based on the quenching of the fluorescence of the modified AuNCs by hydroxyl radical (•OH) that is generated in the Fenton reaction between Fe(II) and HO. Fe(II) can be quantified in the 0.08 to 100 μM concentration range, and the limit of detection is as low as 24 nM. The method also displays good accuracy and high sensitivity when employed to the determination of Fe(II) in rat cerebrospinal fluids (CSFs). When applied to CSFs of a rat model of Alzheimer's disease, it revealed enhanced levels of Fe(II) compared to a control, thereby showing the important physiological role of iron(II) in this disease. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We describe a sensitive fluorometric and colorimetric dual-readout probe for folic acid (FA). It is based on the use of the gold nanoclusters (AuNCs) and cysteamine-modified gold nanoparticles (cyst-AuNPs). The bovine serum albumin stabilized AuNCs exhibit strong fluorescence emission at 652 nm. Upon addition of cyst-AuNPs, the fluorescence intensity of the AuNCs showed dramatic decrease due to the surface plasmon enhanced energy transfer process. This is due to an FA-induced aggregation of the cyst-AuNPs which shifts the absorption peaks from 530 to 670 nm. Thus, the surface plasmon enhanced energy transfer between cyst-AuNPs and AuNCs is weakened and the fluorescence intensity of AuNCs is recovered. The fluorescence intensity of the AuNCs/cyst-AuNPs system is proportional to the concentration of FA in the range from 0.11 to 2.27 μmol L. The dual-readout probe reported here was successfully applied to the determination of FA in spiked serum samples and folic acid tablets. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Heating and drying of the mixture of glutathione-etched gold nanoparticles (Au-SG) and β-cyclodextrin (β-CD) results in the formation of β-CD-capped and glutathionate-protected Au nanoclusters (Au(SG)@β-CD). Their particle size, composition, and number of gold atoms and the capping molecules were characterized by scanning electron microscopy, fluorescence, UV-vis absorption, FT-IR spectroscopy and mass spectrometry. The fluorescence of these nanoclusters is specifically enhanced by the addition of Ag(I) ions to the aqueous solution. This effect was exploited to develop a selective and sensitive method for the fluorometric determination of Ag(I) in water in the concentration range between 0.5 nM and 0.1 μM, with a detection limit at 0.3 nM (at a signal-to-noise ratio of 3). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We have developed a novel resonance light scattering (RLS) assay for the sensitive and selective determination of iodide. It is based on the use of histidine-stabilized gold nanoclusters (His-AuNCs) which undergo fusion and aggregation in the presence of iodide. The resulting enhancement in the intensity of RLS is proportional to the concentration of iodide in the 0.01 to 8.0 μM range, and the detection limit is as low as 1.8 nM at a signal-to-noise ratio of 3. This 'turn-on' method is highly selective for iodide and not interfered by other ions commonly present. It was applied to the determination of iodide in (spiked) real water samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Fluorescent gold nanoclusters (AuNCs) were synthesized using a drug target bacterial enoyl-ACP reductase (FabI) as a template. The physical and chemical properties of the AuNCs were studied by UV-vis absorption, fluorescence, X-ray photoelectron spectroscopy and TEM. The AuNCs-FabI conjugate was prepared by in situ reduction of tetrachloroaurate in the presence of FabI. The conjugated particles were loaded onto nylon membranes by taking advantage of the electrostatic interaction between the negatively charged AuNCs@FabI and the nylon film which is positively charged at pH 7.4. This results in the formation of a test stripe with sensor spots that can be used to detect Hg(II) ion in the 1 nM to 10 μM concentration range. The test stripes are simple, convenient, selective, sensitive, and can be quickly read out with bare eyes after illumination with a UV lamp. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

New bimetallic gold/silver nanoclusters (NCs) are reported that display strong blue fluorescence with excitation/emission maxima at 370/455 nm, decay times of around 14 ns for the main components, and a quantum yield of around 20%. The NCs were synthesized by using L-tryptophan (L-Trp) as the template to react with tetrachloroauric acid and silver nitrate at 120 °C for 4 h in a one-pot reaction. Their fluorescence is around 5 times stronger than that of pure gold nanoclusters. The fluorescence of the bimetallic NCs is strongly reduced in the presence of the antitumor drugs methotrexate (MTX) and doxorubicin (DOX) due to an inner filter effect. Response to MTX is linear in the 2.5–150 μM concentration range, and to DOX in the 2.5–150 μM concentration range. The detection limits are as low as 2.5 nM and 3 nM, respectively. The recoveries from spiked serum are between 87.7% - 101.2% for MTX and between 86.2%–105.4% for DOX. [ABSTRACT FROM AUTHOR]

A fluorometric assay was constructed for supersensitive determination of Cu2+ and Co2+ based on their quenching effect on the orange fluorescence of methionine-capped gold nanoclusters (Met-AuNCs). A simple one-step method was developed for the preparation of the Met-AuNCs, employing L-methionine as both a reducing and protecting reagent. Within 10 min, water soluble Met-AuNCs were obtained with an average size of 2.4 nm. Under photoexcitation at 370 nm, the Met-AuNCs possess a maximum emission at 580 nm and a quantum yield of 2.3%. The response is fast (1 min), and the selectivity for Cu2+ and Co2+ is high over other metal ions. The detection limits for Cu2+ and Co2+ are around 47 and 420 pM, respectively. The effects were used to design a test paper for visual detection of Cu2+ and Co2+. Using this test paper, 1 μM of Cu2+/Co2+ can be detect under the UV lamp (365 nm excitation). It is perceived to be a promising tool for the rapid on-site determination of Cu2+ and Co2+ in real water samples. [ABSTRACT FROM AUTHOR]

A ratiometric fluorometric assay for mercury(II) ion is described. It is making use of glutathione-stabilized gold nanoclusters (GSH-AuNCs) modified with tetraphenylporphyrin tetrasulfonic acid (TPPS). The resultant GSH-AuNC/TPPS nanocomposite displays dual emission (at 572 and 664 nm) under a single excitation wavelength of 365 nm. Mercury(II) ion intensively quenches the yellow fluorescence of GSH-AuNCs (peaking at 572 nm) but has a negligible effect on the red fluorescence of TPPS (at 664 nm). The ratio of fluorescence intensities at 572 and 664 nm drops linearly with Hg(II) ion concentration in the 0.02-2.0 μmol·L−1 range, and the detection limit is 7 nmol·L−1 (3sb/S). The relative standard deviation (RSD) of the assay is 2.0% at a 0.5 μmol·L−1 concentration level (n = 11). The method was successfully applied to the determination of Hg(II) ion in spiked water samples, with recoveries within the range of 87.5-107.5%. [ABSTRACT FROM AUTHOR]

A fluorometric turn-on assay is described for ascorbic acid (AA). It is based on the controlled release of polyallylamine-stabilized gold nanoclusters (polyallylamine-AuNCs) from MnO2 nanosheets. In an aqueous solution of near-neutral pH value, the positively charged capped AuNCs are adsorbed on the surface of the negatively charged MnO2 nanosheets. The adsorption leads to the quenching of the fluorescence of the AuNCs. However, in the presence of AA, MnO2 is reduced to Mn2+. This causes the destruction of the MnO2 nanosheets. As a result, the fluorescence of the polyallylamine-AuNCs at 615 nm is recovered. This method for determination of AA is inexpensive, sensitive, and selective. It works in the 0.01 to 200 μM concentration range and has a 3.2 nM detection limit (for S/N = 3). [ABSTRACT FROM AUTHOR]