Intrinsic dual emissive insulin capped Au/Ag nanoclusters as single ratiometric nanoprobe for reversible detection of pH and temperature and cell imaging.

pH and temperature are two important characteristics in cells and the environment. These, not only in the well-done regulation of cell functions but also in diagnosis and treatment, have a key role. Protein-protected bimetallic nanoclusters are abundantly used in the building of biosensors. However, insulin-stabilized Au-Ag nanoclusters with dual intrinsic emission have not been investigated yet. In this work, Dual emissive insulin templated Au-Ag nanocluster (Ins(Au/Ag)NCs) were first synthesized in a simple and green one-put manner. The two emission wavelengths of, as-prepared NCs centered at 410 and 630 nm, excited in one excitation wavelength (330 nm). These two emission peaks were assigned to the di-Tyrosine cross-linked formation and bimetallic nanoclusters respectively. Further analysis displayed that each emission band of Ins(Au/Ag)NCs responded to one variable whilst another peak remained constant; For blue and red emission wavelengths, pH dependency and thermo-responsibility were observed respectively. As-prepared nanoprobe with the intrinsic dual emissive feature was used for ratiometric determination of these parameters, each with a discrete response from another. The linear range of 6.0-9.0 for pH and 1 to 71 °C for temperature was obtained, which comprises the physiological range of pH and temperature and afforded intracellular sensing and imaging capability. As-prepared NCs probe show excellent biocompatibility and cell membrane permeability, and so were successfully applied as direct ratiometric pH and temperature probes in HeLa and HFF cells. More interestingly, this dual emissive nanoprobe is capable of distinguishing cancer cells from normal ones.

Engineering of Hole Transporting Interface by Incorporating the Atomic-Precision Ag6 Nanoclusters for High-Efficiency Blue Perovskite Light-Emitting Diodes.

Properties of the underlying hole transport layer (HTL) play a crucial role in determining the optoelectronic performance of perovskite light-emitting devices (PeLEDs). However, endowing the current HTL system with a deep highest occupied molecular orbital (HOMO) level concurrent with high hole mobility is still a big challenge, in particular being an open constraint toward high-efficiency blue PeLEDs. In this regard, employing the poly(9-vinylcarbazole) as a model, we perform efficient incorporation of the atomic-precision metal nanoclusters (NCs), [Ag6PL6, PL = (S)-4-phenylthiazolidine-2-thione], to achieve significant tailoring in both HOMO energy level and hole mobility. As a result, the as-modified PeLEDs exhibit an external quantum efficiency (EQE) of 14.29% at 488 nm. The presented study exemplifies the success of metal NC involved HTL engineering and offers a simple yet effective additive strategy to settle the blue PeLED HTL dilemma, which paves the way for the fabrication of highly efficient blue PeLEDs.

Fluorescence Quenching of Tyrosine-Ag Nanoclusters by Metal Ions: Analytical and Physicochemical Assessment.

A new synthesis method is described for the first time to produce silver nanoclusters (AgNCs) by using the tyrosine (Tyr) amino acid. Several important parameters (e.g., molar ratios, initial pH, reaction time etc.) were optimized to reach the highest yield. The formed Tyr-AgNCs show characteristic blue emission at λem = 410 nm, and two dominant fluorescence lifetime components were deconvoluted (τ1 ~ 3.7 and τ2 ~ 4.9 ns). The NCs contained metallic cores stabilized by dityrosine. For possible application, the interactions with several metal ions from the tap water and wastewater were investigated. Among the studied cations, four different ions (Cu2+, Ni2+, Fe3+, and Rh3+) had a dominant effect on the fluorescence of NCs. Based on the detected quenching processes, the limit of detection of the metal ions was determined. Static quenching (formation of a non-luminescent complex) was observed in all cases by temperature-dependent measurements. The calculated thermodynamic parameters showed that the interactions are spontaneous ranked in the following order of strength: Cu2+ > Fe3+ > Rh3+ > Ni2+. Based on the sign and relations of the standard enthalpy (ΔH°) and entropy changes (ΔS°), the dominant forces were also identified.

Pre etched Ag nanocluster as SERS substrate for the rapid quantification of AFB1 in peanut oil via DFT coupled multivariate calibration.

The current study extends the use of surface-enhanced Raman spectroscopy (SERS) combined with density functional theory (DFT) and multivariate calibration towards the rapid quantification of aflatoxin B1 (AFB1) in peanut oil samples. It reports the design of pre etched Ag nanocluster as an active SERS substrate for quantifying AFB1, after being impregnated on its surface. The SERS spectra of AFB1@pre etched Ag nanocluster was recorded and its respective theoretical spectrum was calculated by density functional theory (DFT) to assign the characteristic peaks. The baseline drift and rotation effects were masked by the first-order derivative preprocessing method followed by multivariate calibration. The BP-AdaBoost model exhibited optimum prediction (Rp = 0.9283 and 0.9332) ability over the concentration range 5-100 and 100-1000 ngmL-1, respectively. The limit of detection calculated was 5.0 ngmL-1 and the obtained recoveries were in the range from 90.4% to 113.1% in spiked peanut oil samples. Additionally, precision analysis revealed an RSD ca. 5%, suggesting the applicability of the pre etched Ag nanocluster SERS substrate towards AFB1 detection. Thus, the proposed SERS platform exploiting DFT and BP-AdaBoost model was found reproducible for the quantification of AFB1 in peanut oil.

Hybridization induced fluorescence enhanced DNA-Ag nanocluster/aptamer probe for detection of prostate-specific antigen.

In this work, a label-free Ag nanocluster (AgNC)-based fluorescent probe is proposed to detect tumor marker, prostate-specific antigen (PSA). In the experiments, DNA sequences containing segments complemented to different parts of PSA aptamer were used to synthesize DNA-Ag nanoclusters (DNA-AgNC). Some of the obtained specific DNA-AgNC exhibited significant fluorescence increase after hybridization with PSA aptamer. Based on this, a simple DNA-AgNC/aptamer hybridization probe was fabricated for PSA detection using fluorescence quenching, because competitively specific binding between PSA and its aptamer inhibited the fluorescence enhancement effect of PSA aptamer on DNA-AgNC. The sequence of template DNA, pH and salt concentration of binding buffer, and the concentration of aptamer were optimized. Under optimum conditions, the concentration of PSA within the range of 2-150 ng mL-1 with the detection limit of 1.14 ng mL-1 was detected (3σ; n = 7). This approach was also successfully applied to determine PSA in spiked serum samples. As is well known, this was the first report to realize PSA detection using fluorescent AgNC-based probe. This work would provide reference for construction of AgNC-based probes for detecting other proteins.

Photoluminescence enhancement of silver nanoclusters assembled on the layered double hydroxides and their application to guanine detection.

Development of the fluorescent and stability-enhanced scheme for silver nanoclusters is challengeable. In the present study, silver nanoclusters stabilized by nuclear fast red sodium salt (NFR) were assembled with Mg2Al-layered double hydroxide (LDH) nanosheets. The as-prepared films (AgNCs-NFR/LDH UTFs) were confirmed by powder X-ray diffraction (XRD), UV-vis, fluorescence spectra,atomic force microscope (AFM) and scanning electron microscope (SEM). Owing to the confined effects of 2D layered LDH nanosheets, the fluorescence intensity and photostability of AgNCs-NFR/LDH UTFs have improved significantly in comparing with that of AgNCs-NFR solution. By introducing Cu2+ ions as a modulator, AgNCs-NFR/LDH UTFs were applied successfully to determination guanine in the concentration range of 10-20 µM and 20-100 µM. The limit of detection was 1.85 µM guanine. Moreover, the selectivity for guanine over the other nucleotide bases (such as adenine, thymine, cytosine and uracil) and some potential interfering substances were investigated. The constructed sensor films were simple and economic which avoided a sophisticated synthetic process, and the detected reactions completed within 5 min. Therefore, this paper provides a new opportunity for fabrication the nanocomposite sensor based on AgNCs-NFR/LDH for guanine sensing.

Silver nanoclusters stabilized with denatured fish sperm DNA and the application on trace mercury ions detection.

In this study, fluorescent silver nanoclusters (Ag NCs) were synthesized using denatured fish sperm DNA as the template. In contrast to other methods, this method did not use artificial DNA as the template. After their reaction with denatured fish sperm DNA, Ag+ ions were reduced by NaBH4 to form Ag NCs. The Ag NCs showed a strong fluorescence emission at 650 nm when excited at 585 nm. The fluorescence intensity increased fourfold at pH 3.78, controlled with Britton-Robinson buffer solution. The fluorescence of the Ag NCs was quenched in the presence of trace mercury ions (Hg2+ ) in a weakly acidic medium and nitrogen atmosphere. The extent of the fluorescence quenching of Ag NCs strongly depends on the Hg2+ ion concentration over a linear range from 2.0 nmol L-1 to 3.0 µmol L-1 . The detection limit (3σ/k) for Hg2+ was 0.7 nmol L-1 . Thus, a sensitive and rapid method was developed for the detection of Hg2+ ions.

Synthesis and sensing integration: A novel enzymatic reaction modulated Nanoclusters Beacon (NCB) "Illumination" strategy for label-free biosensing and logic gate operation.

A novel fluorescent label-free "turn-on" NAD(+) and adenosine triphosphate (ATP) biosensing strategy is proposed by fully exploiting ligation triggered Nanocluster Beacon (NCB). In the presence of the target, the split NCB was brought to intact, which brought the C-rich sequence and enhancer sequence in close proximity resulting in the lightening of dark DNA/AgNCs ("On" mode). Further application was presented for logic gate operation and aptasensor construction. The feasibility was investigated by Ultraviolet-visible spectroscopy (UV-vis), Fluorescence, lifetime and High Resolution Transmission Electron Microscopy (HRTEM) etc. The strategy displayed good performance in the detection of NAD(+) and ATP, with the detection limit of 0.002nM and 0.001mM, the linear range of 10-1000nM and 0.003-0.01mM, respectively. Due to the DNA/AgNCs as fluorescence reporter, the completely label-free fluorescent strategy boasts the features of simplicity and low cost, and showing little reliance on the sensing environment. Meanwhile, the regulation by overhang G-rich sequence not relying on Förster energy transfer quenching manifests the high signal-to-background ratios (S/B ratios). This method not only provided a simple, economical and reliable fluorescent NAD(+) assay but also explored a flexible G-rich sequence regulated NCB probe for the fluorescent biosensors. Furthermore, this sensing mode was expanded to the application of a logic gate design, which exhibited a high performance for not only versatile biosensors construction but also for molecular computing application.

H2 adsorption on Ag-nanocluster/single-walled carbon nanotube composites: a molecular dynamics study on the effects of nanocluster size, diameter, and chirality of nanotube.

The H2 physisorption on AgN (with N = 32, 108, 256, 500, and 864)/carbon nanotube (CNT; in armchair and zigzag structures with diameters between 0.54 and 2.98 nm) composites were studied by molecular dynamic simulation to investigate the effect of nanocluster size, diameter, and chirality of nanotube on the adsorption phenomena. The calculations indicate that the effects of nanocluster properties are more important than those of the nanotube, in such a way that increase of nanocluster size, decreases the H2 adsorption. Also, the diameter and chirality of CNTs have considerable influence on the adsorption phenomena. As the diameter of nanotube is increased, the amount of adsorption is decreased. Moreover, H2 molecules have more tendencies to those nanoclusters located on the armchair nanotubes than the zigzag ones. Another important result is the reversibility of H2 adsorption on these materials in which the structure of composite in vacuum and after reduction of H2 pressure to zero, is not changed, considerably.