Luminescent silver nanoclusters for efficient detection of adenosine triphosphate in a wide range of pH values

In this work, polymethacrylic acid (PMAA)-templated silver nanoclusters (Ag NCs) were developed as the fluorescent probe for the efficient and sensitive detection of adenosine triphosphate (ATP) in a wide range of pH values. The fluorescence intensity of the Ag NCs could keep stable with pH values ranging from 2.5 to 9.3. The detection of ATP was based on the quenching of the fluorescent Ag NCs in the presence of ATP. The fluorescence quenching of the Ag NCs with increasing ATP concentration was studied at pH 2.5, 4.5, 7.0 and 8.5 which involved a wide pH environment in body fluids. The limit of detection (LOD) for ATP was as low as 0.1 mmol/L in an acidic environment with pH of 2.5 and all the linear correlation coefficients were satisfactory under wide-span pH values from 2.5 to 8.5. In addition, the sensitive determination of ATP was also achieved by adding copper ions (Cu²⁺). The high selectivity and rapid detection process proved that the fluorescent probe had great potential to detect ATP in biological samples under different pH conditions.     

Luminescent silver nanoclusters for efficient detection of adenosine triphosphate in a wide range of pH values

In this work, polymethacrylic acid (PMAA)-templated silver nanoclusters (Ag NCs) were developed as the fluorescent probe for the efficient and sensitive detection of adenosine triphosphate (ATP) in a wide range of pH values. The fluorescence intensity of the Ag NCs could keep stable with pH values ranging from 2.5 to 9.3. The detection of ATP was based on the quenching of the fluorescent Ag NCs in the presence of ATP. The fluorescence quenching of the Ag NCs with increasing ATP concentration was studied at pH 2.5, 4.5, 7.0 and 8.5 which involved a wide pH environment in body fluids. The limit of detection (LOD) for ATP was as low as 0.1 mmol/L in an acidic environment with pH of 2.5 and all the linear correlation coefficients were satisfactory under wide-span pH values from 2.5 to 8.5. In addition, the sensitive determination of ATP was also achieved by adding copper ions (Cu²⁺). The high selectivity and rapid detection process proved that the fluorescent probe had great potential to detect ATP in biological samples under different pH conditions.     

Zinspy sensors with enhanced dynamic range for imaging neuronal cell zinc uptake and mobilization

Thiophene moieties were incorporated into previously described Zinspy (ZS) fluorescent Zn(II) sensor motifs (Nolan, E. M.; Lippard, S. J. Inorg. Chem. 2004, 43, 8310-8317) to provide enhanced fluorescence properties, low-micromolar dissociation constants for Zn(II), and improved Zn(II) selectivity. Halogenation of the xanthenone and benzoate moieties of the fluorescein platform systematically modulates the excitation and emission profiles, pH-dependent fluorescence, Zn(II) affinity, and Zn(II) complexation rates, offering a general strategy for tuning multiple properties of xanthenone-based metal ion sensors. Extensive biological studies in cultured cells and primary neuronal cultures demonstrate 2-{6-hydroxy-3-oxo-4,5-bis[(pyridin-2-ylmethylthiophen-2-ylmethylamino)methyl]-3H-xanthen-9-yl}benzoic acid (ZS5) to be a versatile imaging tool for detecting Zn(II) in vivo. ZS5 localizes to the mitochondria of HeLa cells and allows visualization of glutamate-mediated Zn(II) uptake in dendrites and Zn(II) release resulting from nitrosative stress in neurons.     

Uptake and imaging of glycine functionalized gold nanoclusters in Spodoptera frugiperda (Sf9) cells

Journal of Cluster Science - Fluorescent gold nanoclusters (Au NCs) have attracted considerable interest in biological application. Here, we reported a novel Au NCs with blue fluorescence,...     

Low energy structures of gold nanoclusters in the size range 3–38 atoms

Using a combination of first principles calculations and empirical potentials we have undertaken a systematic study of the low energy structures of gold nanoclusters containing from 3 to 38 atoms. A Lennard-Jones and many-body potential have been used in the empirical calculations, while the first principles calculations employ an atomic orbital, density functional technique. For the smaller clusters (n=3–5) the potential energy surface has been mapped at the ab initio level and for larger clusters an empirical potential was first used to identify low energy candidates which were then optimised with full ab initio calculations. At the DFT-LDA level, planar structures persist up to six atoms and are considerably more stable than the cage structures by more than 0.1 eV/atom. The difference in ab initio energy between the most stable planar and cage structures for seven atoms is only 0.04 eV/atom. For larger clusters there are generally a number of minima in the potential energy surface lying very close in energy. Furthermore our calculations do not predict ordered structures for the magic numbers n=13 and 38. They do predict the ordered tetrahedral structure for n=20. The results of the calculations show that gold nanoclusters in this size range are mainly disordered and will likely exist in a range of structures at room temperature.     

Protein-templated gold nanoclusters as fluorescence probes for the detection of methotrexate

In this contribution, bovine serum albumin stabilized gold nanoclusters as novel fluorescent probes were successfully utilized for the detection of methotrexate for the first time. Our prepared gold nanoclusters exhibited strong emission with peak maximum at 633.5 nm. However, the addition of methotrexate induced the strong fluorescence intensity of the gold nanoclusters to decrease. The decrease in fluorescence intensity of the gold nanoclusters caused by methotrexate allowed the sensitive detection of methotrexate in the range of 0.0016 μg mL(-1) to 24 μg mL(-1). The detection limit for methotrexate is 0.9 ng mL(-1) at a signal-to-noise ratio of 3. The present sensor for methotrexate detection possessed a low detection limit and wide linear range. In addition, the real samples were analyzed with satisfactory results.     

Amperometric determination of hydrogen and hydroxyl ion concentrations in unbuffered solutions in the pH range 5–9

Hydrogen and hydroxyl ion concentrations can be determined by ion-selective amperometry in the pH range 5–9 in unbuffered solutions. The working electrode is a plasticized PVC membrane electrode loaded with the neutral hydrogen ion carrier tridodecylamine. Measurements are made in a flow-injection system.     

Preparation of orange-red fluorescent gold nanoclusters using denatured casein as a reductant and stabilizing agent,and their application to imaging of HeLa cells and for the quantitation of mercury(II)

We describe a method for the preparation of water-soluble gold nanoclusters (Au-NCs) from chloroauric acid using denatured-casein as both a reducing and stabilizing agent. The resulting Au-NCs were characterized by photoluminescence, UV–vis absorption, and X-ray photoelectron spectroscopies, and by transmission electron microscopy. The Au-NCs have an average diameter of 1.7 ± 0.2 nm and exhibit orange-red fluorescence emission peaking at 600 nm (with a Stokes’ shift as large as 237 nm), a quantum yield of 4.3 %, and good stability over the physiologically relevant range of pH values and ionic strength. Cytotoxicity studies showed the Au-NCs to display negligible effects in terms of altering cell proliferation or triggering apoptosis. Fluorescence imaging of HeLa cancer cells was accomplished by loading such cells with the Au-NCs. The fluorescence of the Au-NCs is found to be strongly quenched by Hg(II) ions, and thus the Au-NCs can be used for detecting and, possibly, imaging of Hg(II). An assay was worked out for the determination of Hg(II), and its limit of detection is 1.83 nM, which is 5.5 times lower than the maximum allowed concentration of Hg(II) in drinking water as defined by the US EPA.

Denatured-casein was firstly used as a reductant and stabilizing agent in facile preparation of orange-red fluorescent AuNCs for imaging of HeLa cells and for the quantitation of mercury(II)

     

Fluorescent photoionic devices with two receptors and two switching mechanisms: applications to pH sensors and implications for metal ion detection

Two leading designs of fluorescent sensors are combined to yield the novel hybrid system of the ‘Fluorophore-Receptor₁-Spacer-Receptor₂’ format. We use 4-(dialkylaminoalkylamino)-7-nitrobenzo-2-oxa-1,3-diazoles as examples. The emission from internal charge transfer excited states in the present instances are highly responsive to N-H deprotonation as well as being quenched by intramolecular tertiary amine groups via photoinduced electron transfer (PET). When applied to pH sensing, this leads in favourable cases to two steps in the fluorescence-pH profile which can be viewed as a multi-stable photoionic device, even though single steps are more usual. The former situation is favoured when the two proton-associated equilibria are sufficiently separated on the pH scale and when the PET process is of moderate efficiency. These systems have the added feature of excitation/emission wavelengths in the visible region. As a secondary theme, we point out that caution is required when designing sensors for transition metal ions from systems with intrinsically proton-sensitive fluorescence due to receptors either integrated with or spaced from the fluorophore.     

Rare earth ions-enhanced gold nanoclusters as fluorescent sensor array for the detection and discrimination of phosphate anions

The discrimination and detection of phosphate anions have attracted extensive attention due to their important roles in various biological processes. Compared with sensors to detect one individual phosphate at a time, sensor arrays are able to discriminate multiple phosphates simultaneously. In this study, we developed a rare earth ions enhanced AuNCs-based sensor array to achieve facile and rapid identification of phosphate anions (PPi, ADP and ATP). The rare earth ions (i. e., Ce³⁺, Gd³⁺, Tm³⁺ and Yb³⁺) can significantly enhance the fluorescence of AuNCs through aggregation-induced emission effect. And the subsequent addition of phosphate anions can recover the fluorescence of the AuNCs-rare earth ions assembly. Thanks to the different numbers of phosphate group and different steric hindrance effects of phosphate anions, the recovery fluorescence of AuNCs-rare earth ions assembly induced by PPi, ADP or ATP are respectively distinct. Thus the sensor array composed of AuNCs and different rare earth ions is able to distinguish those phosphate anions. Finally, the sensor array was successfully demonstrated to identify the phosphates in blind samples.     

Structure–Property Investigations of Substituted Triarylamines and Their Applications as Fluorescent pH Sensors

Fourteen triphenylamine derivatives functionalized with fluorophenyl, methoxyphenyl, and pyridinyl groups as respective donors and acceptors were synthesized and characterized. Their photophysical properties were systematically investigated in various solvents with different polarities. The solvent‐dependent Stokes shifts of these compounds were observed and analyzed by the Lippert–Mataga equation. The synthesized compounds, especially tris(4‐(pyridin‐4‐yl)phenyl) amine, presented pH‐dependent absorptions and emissions, indicating that these compounds might be used as pH sensors.     

On the photodissociation of ozone in the range of 5–9 eV

The photoabsorption spectrum of ozone in the UV range (5–9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 ¹A′ (3 ¹A₁), 6 ¹A′ (4 ¹A₁), and 4 ¹A″ (2 ¹B₁). Excitation of the state 8 ¹A′ (¹B₂) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 ¹A′ and 4 ¹A″) different from the state excited in the Hartley band (3 ¹A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited ¹A′ as well as the ¹A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to and O(¹D) + O₂(¹Δ_g), the next higher spin-allowed channel, , also is likely to be a major product channel, in agreement with experimental observations.     

A rational approach to tuning the pKa values of rhodamines for living cell fluorescence imaging

A novel strategy to systematically tune the pK(a) values of rhodamines is described. This strategy was applied to rationally develop compound 1e with a pK(a) of 6.5, the highest among rhodamine amide derivatives, and it could be employed to detect acidic pH variations in living cells with a turn-on signal.     

Determination of pH values over the temperature range –60°C for some operational reference standard solutins and values of the conventional residual liquid-junction potentials

Direct measurements of the pH of six new operational standard solutions for the British Standard pH scale are reported from measurements with hydrogen gas electrodes in cells with liquid junctions reproducibly formed in vertical capillary tubes (1 mm internal diameter). Comparison with assigned pH values from cells without liquid junction enables values of the conventional residual liquid-junction potential to be calculated.     

Calculation of the relative free energy of oxidation of azurin at pH 5 and pH 9

Free energy calculations are described for the small copper‐containing redox protein Azurin from Pseudomonas aeruginosa. A thermodynamic cycle connecting the reduced and oxidized states at pH 5 and pH 9 is considered, allowing for an assessment of convergence in terms of hysteresis and cycle closure. Previously published thermodynamic integration (TI) data is compared to Hamiltonian replica exchange TI (RE‐TI) simulations using different simulation setups. The effects of varying simulation length, initial structure, position restraints on particular atoms, and the strength of temperature coupling are studied. Although the overall simulation times are too short to observe an experimentally described peptide plane rotation, it is found that RE‐TI simulations do stimulate the distribution of conformational changes over the relevant values of the TI coupling parameter λ. This results in significantly improved values for hysteresis and cycle closure when compared to regular TI. © 2012 Wiley Periodicals, Inc.     

Buffers for the physiological pH range: Thermodynamic constants of substituted aminopropanesulfonic acids from 5 to 55°C

ThepK ₂ values for 3-[(l,l-Dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO), and 3-[N,N-Bis(-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) have been determined at 12 temperatures over the range 5 to 55‡C by measurements of the emf of cells without liquid junction containing hydrogen and silver-silver chloride electrodes. The values of pK ₂ for AMPSO and DIPSO were found to be 9.138 and 7.576, respectively, at 25‡C. The thermodynamic quantities, δG‡, δH‡, δS‡, and δC _p ^‡ were calculated from the change of the equilibrium constants with temperature. These buffer substances are useful as secondary pH standards in the physiological region of pH 7 to 9. Camille and Henry Dreyfus Fellow, 1994–1996.