Photoluminescent AuCu bimetallic nanoclusters as pH sensors and catalysts

Revealing the alloying and dealloying behaviours in AuAg nanorods by thermal stimulus

Binary metallic nanocrystals are attractive as they offer an extra degree of freedom for structure and phase modulation to generate synergistic effects and extraordinary properties. However, whether the binary structures and phases at the nanoscale still follow the rules established on the bulk counterparts remains unclear. In this work, AuAg nanorods were used as a sample to probe into this issue. An in situ heating method by combining aberration-corrected transmission electron microscopes with a chip-based heating holder was employed to perform the heating experiments. It was found that the AuAg nanorods, which initially possessed heterostructures, can be designed and engineered to be gradient phase alloys with thermal pulses over 350 °C. Atomic diffusion inside the rod structures did not alter the shape of the rods but provided a route to fine-tune their properties. At higher temperatures, the discrepant sublimation behaviours between Au and Ag lead to dealloying of the nanorods. Durative sublimation of the Ag element can continuously tailor the lengths of the nanorods while concentrating the Au composition simultaneously. Especially, nearly pure Au nanocrystals can be obtained with the depletion of Ag by sublimation. These findings give insights into the nanoscale structure and phase behaviours in binary alloys and provide an alternative way to fine-tune their structure, phase, and properties.

Synthesis of gold and copper bimetallic nanoclusters with papain for fluorescence detection of cortisone in biological samples

In this work, bimetallic gold and copper nanoclusters (Au-Cu NCs) were fabricated by using papain as a ligand. The as-synthesized papain-Au-Cu NCs displayed red fluorescence at 365 nm of UV lamp. The as-prepared papain-Au-Cu NCs display a strong fluorescence at 656 nm when excited at 390 nm. Papain encapsulated Au-Cu NCs exhibit distinct interaction site towards cortisone, which results red fluorescence "turn-off". Papain-Au-Cu NCs exhibited a rapid response and remarkable fluorescence quenching with the addition of cortisone as a biomarker. The developed probe is demonstrated for the quantification of cortisone by plotting the calibration graph between the fluorescence ratio (I₀/I) and cortisone concentration (0.031-1.00 μM) with an impressive detection limit of 1.89 nM. Interestingly, the response of papain-Au-Cu NCs towards other biomarkers and common interfering species is quite silent, signifying the selectivity of papain-Au-Cu NCs for the detection of cortisone. The probe was successfully applied to assay cortisone biomarker in urine and plasma samples. More importantly, the analytical validation of the probe was assessed by assaying cortisone in intra- and inter-day, demonstrating papain-Au-Cu NCs could serve as promising probe for the rapid detection of cortisone in biological samples.

Influence of Pt alloying on the fluorescence of fully inorganic, colloidal gold nanoclusters

Noble metal alloy nanoclusters (NCs) are interesting systems as the properties of two or more elements can be combined in one particle, leading to interesting fluorescence phenomena. However, previous studies have been exclusively performed on ligand‐capped NCs from wet chemical synthesis. This makes it difficult to differentiate to which extent the fluorescence is affected by ligand‐induced effects or the elemental composition of the metal core. In this work, we used laser fragmentation in liquids (LFL) to fabricate colloidal gold‐rich bi‐metallic AuPt NCs in the absence of organic ligands and demonstrate the suitability of this technique to produce molar fraction series of 1nm alloy NC. We found that photoluminescence of ligand‐free NCs is not a phenomenon limited to Au. However, even minute amounts of Pt atoms in the AuPt NCs lead to quenching and red‐shift of the fluorescence, which may be attributed to the altered surface charge density.

Synthesis of metal nanoclusters and their application in Hg2+ ions detection: A review

Mercuric (Hg²⁺) ions released from human activities, natural phenomena, and industrial sources are regarded as the global pollutant of world's water. Hg²⁺ ions contaminated water has several adverse effects on human health and the environment even at low concentrations. Therefore, rapid and cost-effective method is urgently required for the detection of Hg²⁺ ions in water. Although, the current analytical methods applied for the detection of Hg²⁺ ions provide low detection limit, they are time consuming, require expensive equipment, and are not suitable for in-situ analysis. Metal nanoclusters (MNCs) consisting of several to ten metal atoms are important transition missing between single atoms and plasmonic metal nanoparticles. In addition, sub-nanometer sized MNCs possess unique electronic structures and the subsequent unusual optical, physical, and chemical properties. Because of these novel properties, MNCs as a promising material have attracted considerable attention for the construction of selective and sensitive sensors to monitor water quality. Hence this review is focused on recent advances on synthesis strategies, and optical and chemical properties of various MNCs including their applications to develop optical assay for Hg²⁺ ions in aqueous solutions.

Transferrin Coated d-penicillamine-Au-Cu Nanocluster PLGA Nanocomposite Reverses Hypoxia-Induced EMT and MDR of Triple-Negative Breast Cancers

Triple-negative breast cancer (TNBC), the most aggressive subtype of breast cancer, lacks effective targeted therapies due to negative expression of the targetable bioreceptors. Additionally, hypoxic condition in solid tumors contributes to the epithelial to mesenchymal transition (EMT), which aggravates cancer progression, multidrug resistance (MDR), migration, and stemness of the TNBC. A therapeutic module has been established in this regard by coating PLGA nanoparticle with d-penicillamine templated Au-Cu bimetallic nanoclusters. Further, the resultant nanomaterials were coated with recombinant transferrin protein to specifically target transferrin receptor overexpressing TNBC. The synthesized nanocomposites showed strong orange emission band at 630 nm with fluorescence quantum yield of 2%, rendering it suitable for theranostic applications. Experimental results demonstrated efficient cellular internalization and significant innate anti-cell proliferative potential of the nanocomposites. The fabricated nanocomposites were also able to induce cell death in spheroids, which was confirmed by live/dead dual staining results. Furthermore, when EMT-induced TNBC cells were treated with nanocomposites, they generated reactive oxygen species (ROS), depolarized the mitochondrial membrane potential, and induced apoptosis. Gene expression by real-time PCR indicated that treatment of EMT-induced TNBC cells with nanocomposites facilitated mesenchymal to epithelial transition (MET). In MDA-MB-468 cells, treatment with nanocomposites resulted in a 1.35-fold rise in E-cadherin an epithelial marker and a 1.36-fold decrease in vimentin a mesenchymal marker. Similarly, 2.87-fold and 1.76-fold decrease in stemness markers ALDH1A3 and EpCAM were observed in MDA-MB-231. Furthermore, 4.63-fold decrease in expression of ABCC1, a prominent contributor of MDR, was observed in MDA-MB-231. Protein expression studies revealed that nanocomposites reduced p-STAT-3 by 1.61-fold in MDA-MB-231 and by 7.8-fold in MDA-MB-468. Importantly, nanocomposites downregulated the expression of β-catenin by 3-fold in MDA-MB-231 and by 3.11-fold in MDA-MB-468. Downregulation of EMT with concomitant alteration of STAT-3 and β-catenin signaling pathways led to reduced migration ability of the TNBC cells.

A fluorescent PET probe based on polyethyleneimine-Ag nanoclusters as a reversible, stable and selective broad-range pH sensor

In this work, nanoclusters (NCs) of Cu and Ag capped with hyperbranched polyethyleneimine (PEI) were prepared using chemical reduction by a one-step hydrothermal method. The PEI coated-NCs were characterized by high-resolution transmission electron microscopy, ζ potential, thermogravimetric analysis, dynamic light scattering, Fourier-transform infrared, UV-visible, and fluorescence spectroscopy. The PEI-NCs exhibited strong absorption and fluorescence, high stability, and excellent water dispersibility. The resulting PEI-NCs showed a reversible and linear response of fluorescence intensity with pH over a wide range (3-11); however, PEI-AgNCs showed a better reversibility and sensitivity than PEI-CuNCs. Unlike several types of pH sensors based on modified NCs, which are based on a nanoparticle aggregation/disaggregation mechanism, the response of our sensor is based on a photoinduced electron transfer process, which gives it a high reversibility. This method was successfully applied in pH measurements in tap water and green tea samples, with excellent results, indicating its practical utility for these applications. A visual device was obtained by immobilizing PEI-AgNCs into agarose hydrogels at different pH values. The results show that the proposed sensor can be used as a pH visual detector. Besides, the light emission of the nanosensor was corroborated by fluorescence microscopy, confirming that the nanosensor based on PEI-AgNCs has great potential to be used in cellular imaging.

pH-modulated aggregation-induced emission of Au/Cu nanoclusters and its application to the determination of urea and dissolved ammonia

A fluorescence platform is designed based on aggregation-induced emission of Au/Cu nanoclusters (Au/Cu NCs) driven by pH value. When pH increases from 6.0 to 7.0, Au/Cu NCs change from aggregation to dispersion, accompanied by the oxidation of Cu cores. Under the catalysis of urease, urea is hydrolysed to release ammonia, which further undergoes a hydrolysis reaction to produce OH^-, causing the pH to increase. The fluorescence of Au/Cu NCs quenches linearly at 590 nm with the excitation wavelength at 320 nm when the concentration of urea varies from 5.0 to 100 μM. The limit of detection (LOD) and limit of quantification (LOQ) of urea are 2.23 and 7.45 μM, respectively. Combined with headspace single-drop microextraction technology, Au/Cu NCs are employed to monitor dissolved ammonia with low-cost and simple operation. The linear range of dissolved ammonia is from 20 to 300 μM. The LOD and LOQ of dissolved ammonia are 7.04 and 23.4 μM, respectively. The relative standard deviation (RSD) values of the intra-day and inter-day precision of urea are 2.4-3.0% and 3.0-3.7%, respectively, and those of dissolved ammonia are in the range 3.4-5.1% (intra-day precision) and 4.2-5.8% (inter-day precision). No interferences have been indentified in the determination of urea and dissolved ammonia. Finally, the proposed method has been applied to determine urea in human urine samples and dissolved ammonia in water samples with satisfactory results.Graphical abstract The pH increase produces the dispersion and decomposition of Au/Cu NCs, leading to the fluorescence quenching. Both urea and dissolved ammonia are detected successfully because they cause the pH change to alkaline.

A review on metal nanozyme-based sensing of heavy metal ions: Challenges and future perspectives

Large scale mining, manufacturing industries, exploitation of underground water, depletion of groundwater level, and uncontrolled discharge of industrial wastes have caused severe heavy metal ion pollution to the environment throughout the world. Therefore, the rapid detection of such toxic metal ions is inevitable. However, conventional methods require sophisticated instruments and skilled manpower and are difficult to operate in on-field conditions. Recently, metal nanozyme-based assays have been found to have the potential as an alternative to conventional methods due to their portability, simplicity, and high sensitivity to detect metal ion concentration to as low as parts per trillion (ppt). Metal nanozyme-based systems for heavy metal ions enable rapid and cheap screening on the spot with a very simple instrument such as a UV-vis absorption spectrophotometer and therefore, are convenient for use in field operations, especially in remote parts of the world. The sensing mechanism of a nanozyme-based sensor is highly dependent on its surface properties and specific interactions with particular metal ion species. Such method often encounters selectivity issues, unlike natural enzyme-based assays. Therefore, in this review, we mainly focus our discussion on different types of target recognition and inhibition/enhancement mechanisms, and their responses toward the catalytic activity in the sensing of target metal ions, design strategies, challenges, and future perspectives.

Dopamine-Modified AuCu Bimetallic Nanoclusters as Charge Transfer-Based Biosensors for Highly Sensitive Glycine Detection

Glycine is the simplest amino acid in living organisms and plays important roles in biology and medicine. However, few biosensors for glycine sensing have been reported. Herein, we present a facile strategy to construct dopamine-modified AuCu bimetallic nanoclusters (denoted as AuCu NC-DA) as charge transfer-based biosensors for highly sensitive glycine sensing. The AuCu NCs stabilized by bovine serum albumin (BSA) exhibited a fluorescence maximum at 400 nm. Because of the high affinity of BSA for dopamine (DA), the surface of the AuCu NCs was modified with DA without any complicated chemical reactions, resulting in fluorescence quenching through a charge transfer process. Among 20 amino acids, AuCu NC-DA exhibited an off/on fluorescence switching response specifically toward glycine through the formation of hydrogen bonds with oxidized DA, which inhibited the charge transfer process, leading to the emergence of a new emission peak at 475 nm. Spectroscopic and thermodynamic results combined with molecular docking analyses provided comprehensive understanding of the sensing mechanism. Furthermore, we showed that AuCu NC-DA was able to sense glycine in cells by imaging. Finally, the practicability of AuCu NC-DA for glycine detection was validated in milk drink samples. This study presents a promising type of a charge transfer-based sensor.

Photonic crystal enhanced gold-silver nanoclusters fluorescent sensor for Hg2+ ion

Luminescent nanoclusters (NCs) have attracted much attention because of their good photostability and low toxicity, however, the low quantum yield is still a deficiency, and many increasing efforts are being devoted to enhance the luminescence intensity of NCs. In this paper, a method of enhancing the fluorescent signal of gold-silver nanoclusters (AuAgNCs) by photonic crystals (PhCs) was proposed. The fluorescent intensity of AuAgNCs on PhCs can be enhanced 8.0-fold in comparison to the control sample without PhCs. Furthermore, a novel fluorescence sensor of AuAgNCs based on PhCs is used for the sensitive and selective detection of Hg²⁺ ion in the aqueous solution, the detection limit is 0.35 nM due to the PhCs enhancement effect for the fluorescence. This proposed method may not only develop a highly sensitive method for determination of Hg²⁺ ion, but also expand the application of AuAgNCs in ultra-trace analysis.

Recent progress in copper nanocluster-based fluorescent probing: a review

Copper nanoclusters (CuNCs) are an attractive alternative to other metal nanoclusters. The synthesis of CuNCs is highly efficient and fast, with low-cost and without any complicated manipulation. Because of their tunable fluorescence and low toxicity, CuNCs have been highly exploited for biochemical sensing. This review (with 172 refs.) summarizes the progress that has been made in the field in the past years. Following an introduction into the fundamentals of CuNCs, the review first focuses on synthetic methods and the fluorescence properties of CuNCs (with subsections on the use of proteins, peptides, DNA and other molecules as templates). This is followed by a section on the use of CuNCs in fluorometric assays, with subsections on the detection of small molecules, proteins, nucleic acids, various other biomolecules including drugs, and of pH values. A further large chapter summarizes the work related to environmental analyses, specifically on determination of metal ions, anions and pollutants. Graphical abstract Schematic representation of the synthesis and potential applications of copper nanocluster (CuNCs) in biochemical analysis, emphatically reflected in some vital areas such as small molecule analysis, biomacromolecule monitoring, cell imaging, ions detection, toxic pollutant, etc.

AuCu bimetal nanoclusters as high-performance mimics for ultrasensitive recognition of biomolecules

Introducing novel mimic materials as alternatives for natural enzymes challenges the analysts. Study on the peroxidase-like materials is an active field in analytical research areas. Herein, Au/Cu bimetal nanoclusters (Au/Cu NCs) are introduced as highly efficient peroxidase mimics, which were investigated using fluorometric and colorimetric techniques. A comprehensive comparison between the catalytic activity of Au, Cu, and their bimetal NCs, with different ratios of Au/Cu was performed using some different peroxidase substrates (including 3,3′,5,5′-tetramethylbenzidine (TMB), o-phenylenediamine dihydrochloride (OPD), and terephthalic acid (TA)). Additionally, different capping agents were applied for the synthesis of NCs, and it was found that penicillamine-capped NCs with 50% Cu have higher activity than other synthesized NCs. Analytical application of the novel mimic for H2O2 detection caused a linear calibration in a wide linear range of 0.001–3 μmol/L, and a great detection limit (3S) of 0.18 nmol/L, using a sensitive fluorescence system. The developed system was also sensitive for recognizing glucose and cholesterol in blood samples, after their enzymatic oxidation and production of H2O2. Detection limits of 55 and 15 nmol/L were obtained for glucose and cholesterol, respectively. The presented method also showed good reliability, which was validated by certified reference materials.

Fluorescence lifetime-based pH sensing by platinum nanoclusters

In this work, we report for the first time the application of ultrasmall Pt nanoclusters (Pt NCs) as a fluorescence-lifetime-based pH sensor. The fluorescence properties of our prepared Pt NCs show strong pH dependence, due to the change of the surface states of Pt NCs under alkaline/acidic conditions. Interestingly, both the fluorescence intensity and the fluorescence lifetime of Pt NCs exhibit a good linear relationship in the physiologically relevant pH range of 6.02-7.54. Our Pt NC-based pH sensor possesses many important features as an attractive sensor, including high anti-jamming capability, excellent stability and good reversibility. Moreover, the use of fluorescence lifetime as the optical readout signal rather than the intensity makes the present pH sensor more reliable in practical applications because the fluorescence lifetime is invariant to the probe concentration or changes in excitation conditions. Application of the Pt NC-based system for pH detection in real water samples and simulated intracellular environment samples has also been successfully demonstrated.

Rapid synthesis of Au/Ag bimetallic nanoclusters with highly biochemical stability and its applications for temperature and ratiometric pH sensing

Herein, we developed a simple and rapid strategy to synthesize gold/silver bimetallic nanoclusters (Au/Ag NCs) with highly biochemical stability by a one-pot route. The Au/Ag NCs were obtained via a chemical reduction procedure in alkaline aqueous solution at 75 °C within only 20 min by employing bovine serum albumin (BSA) as both ligand and reductant. The as-obtained Au/Ag NCs displayed bright orange fluorescence with an emission peak located at 570 nm and temperature-dependent fluorescence property, which were utilized as fluorescent thermometer directly. More intriguingly, the Au/Ag NCs were very stable against various pH values, ions, biothiols, H₂O₂, fetal bovine serum (FBS), RPMI 1640 medium and amino acids. Taking advantage of the excellent biochemical stability, a ratiometric fluorescence biosensor, fluorescein-5-isothiocyanate (FITC)-Au/Ag NCs, was constructed for pH sensing based on the incorporation of FITC into the Au/Ag NCs. Furthermore, the ratiometric pH sensor was also successfully applied on the model of HeLa cells.

Investigation of high contrast and reversible luminescence thermochromism of the quantum confined Cs4PbBr6 perovskite solid

Thermochromism of organic/inorganic halide perovskites has attracted particular interest due to their potential applications as photoluminescence (PL)-based temperature sensors. However, despite the outstanding PL characteristics, their use as a thermochromic material in practical temperature ranges has been limited because of their poor thermal stability. In this study, we used the quantum confinement effect and exceptional PL quantum efficiency of the Cs4PbBr6 perovskite to demonstrate their high on/off ratio (20) and reversible PL thermochromism in the solid state in practical temperature ranges including room temperature (RT). Systematic photophysical and optical characterization studies, including exciton-phonon scattering, exciton binding energy, exciton decay dynamics, and crystal structure change, were performed to investigate the origin of this unique thermochromic PL property. The results showed that the efficient and highly reversible thermochromic PL emission of the Cs4PbBr6 perovskite is due to its desirable optical properties such as highly luminescent emission, efficient PL quenching at high temperatures, and thermally reversible structural changes.

Bimetallic AuCu nanoclusters-based florescent chemosensor for sensitive detection of Fe3+ in environmental and biological systems

Assays of ferric ion (Fe³⁺) with high sensitivity and selectivity have been required to evaluate its amount in environmental and biological systems. Herein, a novel fluorometric penicillamine-capped bimetallic gold-copper nanoclusters (PA-AuCu bi-MNCs) sensor was constructed for facile, environmentally friendly and quantitative detection of Fe³⁺ through inner filter effect (IFE) mechanism. One-step green synthetic approach was applied for the synthesis of AuCu bi-MNCs by using d-penicillamine (D-PA) as template and stabilizer. In the presence of Fe³⁺, the emission of the PA-AuCu bi-MNCs was hindered that caused selective quenching of the fluorescence intensity. The response to Fe³⁺ allows for two linear dynamic ranges of 5.0 × 10^-7 M-7.0 × 10^-6 M and 7.0 × 10^-6 M-1.0 × 10^-4 M with a detection limit of 0.1 μM, which is approximately 53 times lower than the maximum level (5.37 μM) of Fe³⁺ in drinking water that had been reported by the World Health Organization. The independency of the system from most of the interferences is the important feature of this work. Beside the appropriate selectivity of the proposed method, it shows a considerable operation in various environmental samples including rain water, three types of river water and also in human blood serum as a biological matrix.

Photoluminescent Ag nanoclusters for reversible temperature and pH nanosenors in aqueous solution

A facile, straightforward, and green method was reported for the preparation of water-soluble and highly luminescent silver nanoclusters (AgNCs) using captopril (Capt) as a stabilizing agent. The as-prepared Capt@AgNCs exhibited bright red emission with a strong peak centered at 637 nm and showed low toxicity and good stability. Interestingly, the AgNCs displayed temperature sensitivity based on obvious temperature dependence of the fluorescence emission intensity. Furthermore, the AgNCs showed a good reversible and linear response to the environment temperature over the range from 10 °C to 45 °C with a high resolution and activation energy, which allowed its potential application as a fluorescent nanothermometer. In addition, the AgNCs were prepared to monitor pH via the fluorescence intensity of AgNCs responding sensitively to pH fluctuating within a wide range from 2.08 to 6.06. The study provides promising applications as a convenient and eco-friendly fluorescent temperature and pH nanosenser in environmental and biological fields. Graphical abstract Novel silver nanocluster-based fluorescent nanosensors have been successfully constructed for temperature detection. The nanosensors showed a good reversible and linear response to the environment temperature over the range from 10 °C to 45 °C. In addition, the AgNCs described here are employed as pH sensors by virtue of the fluorescence intensity of their sensitive response to fluctuating pH in a linear range of 2.08-6.06.

Fluorescence red-shift of gold-silver nanoclusters upon interaction with cysteine and its application

In this work, gold-silver alloy nanoclusters (AuAg NCs) were demonstrated as a novel probe for fluorescent detection of cysteine (Cys). The alloy nanoclusters were fabricated by bovine serum albumin as a template and NaBH₄ as a reducer. They showed a red emission at 650 nm. The interaction between AuAg NCs and Cys was investigated. The thiol group in Cys molecules has strong affinity on the surface of metals, which results in variation of fluorescence peak wavelength. It was further demonstrated that this red-shift of fluorescence had a good linear relationship with the concentration of Cys in the range of 2-100 μM. The method was successfully applied for human plasma analysis with satisfactory results. This novel strategy was expected to provide a potential opportunity for extending the application of novel metal nanoclusters in fluorescence.

In Situ Generation of Fluorescent Copper Nanoclusters Embedded in Monolithic Eggshell Membrane: Properties and Applications

Luminescent metal nanoclusters have attracted considerable research attention in recent years due to their unique properties and extensive usage in many fields. Three different synthetic routes were developed to in situ generate orange and red emitting copper nanoclusters embedded in monolithic eggshell membrane (Cu NCs@ESM) using different reducing reagents including N₂H₄·H₂O, NH₂OH·HCl and Vitamin C at room temperature for the first time. The routes are extremely facile, low-cost and versatile. The obtained Cu NCs@ESM nanocomposites exhibit excellent photostability and chemical stability, laying the foundation for various practical applications. Fluorescent surface patterning was demonstrated based on the proposed strategy easily. Significantly, the Cu NCs@ESM shows selective fluorescence quenching response to Hg2+ ions and good catalytic activity for methylene blue (MB) reduction degradation making it ideal as portable sensing strip and recyclable catalyst. The work provides a general strategy for the fabrication of other various monolithic nanomaterials with potential applications.

Synthesis and Properties of the Self-Assembly of Gold-Copper Nanoparticles into Nanoribbons

We report the efficient wet-chemical production of self-assembled gold-copper bimetallic nanoparticles (diameter of ∼2 nm) into two-dimensional flexible ribbonlike nanostructures. The direct observation of a layered arrangement of particles into nanoribbons was provided through high-resolution transmission electron microscopy and electron tomography. These nanoribbons showed photoluminesce and efficient photocatalytic activity for the conversion of 4-nitrophenol. The thermal stability of the nanoribbons was also measured by in situ heat treatment in the electron microscope, confirming that the self-assembled gold-copper nanoribbons efficiently supported up to 350 °C. The final morphology of the nanoparticles and their ability to self-assemble into flexible nanoribbons were dependent on concentration and the ratio of precursors. Therefore, these experimental factors were discussed. Remarkably, the presence of copper was found to be critical to triggering the self-assembly of nanoparticles into ordered layered structures. These results for the synthesis and stability of self-assemblies of metallic nanoparticles present a potential extension of the method to producing materials with catalytic applications.

BSA capped bi-functional fluorescent Cu nanoclusters as pH sensor and selective detection of dopamine

Illustration of the preparation of bi-functional BSA-CuNCs, the pH sensing and the detection of dopamine (DA).

Solvent Polarity-Dependent Behavior of Aliphatic Thiols and Amines toward Intriguingly Fluorescent AuAgGSH Assembly

Highly stable fluorescent glutathione (GSH)-protected AuAg assembly has been synthesized in water under UV irradiation. The assembly is composed of small Ag₂/Ag₃ clusters. These clusters gain stability through synergistic interaction with Au(I) present within the assembly. This makes the overall assembly fluorescent. Here, GSH acts as a reducing as well as stabilizing agent. The assembly is so robust that it can be vacuum-dried to solid particles. The as-obtained solid is dispersible in nonaqueous solvents. The interaction between solvent and the assembly provides stability to the assembly, and the assembly shows fluorescence. It is interesting to see that the behavior of long-chain aliphatic thiols or amines toward the fluorescent assembly is altogether a different phenomenon in aqueous and nonaqueous mediums. The assembly gets ruptured in water due to direct interaction with long-chain thiols or amines, whereas in nonaqueous medium, solvation of added thiols or amines becomes pronounced, which hinders the interaction of solvent with the assembly. However, the fluorescence of the assembly is always quenched with thiols or amines no matter what the solvent medium is. In aqueous medium, the fluorescence quenching by aliphatic thiol or amine becomes pronounced with successive decrease in their chain length, whereas in nonaqueous medium, the trend is just reversed with chain length. The reasons behind such an interesting reversal of fluorescence quenching in aqueous and nonaqueous solvents have been discussed explicitly. Again, in organic solvents, thiol or amine-induced quenched fluorescence is selectively recovered by Pb(II) ion without any alteration of excitation and emission maxima. This phenomenon is not observed in water because of the ruptured fluorescent assembly. The fluorescence recovery by Pb(II) and unaltered emission peak only in nonaqueous solvent unequivocally prove the engagement of Pb(II) with thiols or amines, which in turn revert the original solvent-supported stabilization of the assembly.

Longitudinal Study of the Effects of Environmental pH on the Mechanical Properties of Aspergillus niger

The regulation of environmental pH is key to the health of an ecosystem, influencing the metabolic activity, growth, and development of organisms within it. Although pH values can be measured by a wide range of readily available technologies ranging from fluorescent dyes and nanosensors, these cannot reveal the history of environmental pH from before monitoring begins. This information is sometimes crucial for piecing together what has happened to an ecosystem, and our long-term goal is therefore to develop technologies capable of obtaining it. Here, we propose monitoring environmental pH over time by tracking mechanical properties of a common fungus. As a first step toward obtaining a time history of pH, we evaluate the effect of pH upon the effective indentation modulus of spores and hyphae of Aspergillus niger. We report that the indentation modulus of this phosphorus-solubilizing fungus, obtained through atomic force microscopy and nanoindentation, correlated with environmental acidity. We observed a significant, monotonic increase in moduli over the course of incubation in an acidic environment, but no change in moduli over time for incubation in a neutral environment. Results show promise for using our scheme to detect and track environmental pH over time, and more broadly for using a microorganism's mechanical properties as a biomarker for environmental detection.

Multifunctional Zn(II) Complexes: Photophysical Properties and Catalytic Transesterification toward Biodiesel Synthesis

Using 4-substituted derivatives of phenol-based compartmental Schiff-base hydroxyl-rich ligand, four multifunctional binuclear Zn(II) complexes have been synthesized and characterized. The photophysical properties of these complexes were explored in the solid state, in solutions, and in poly(methyl methacrylate) (PMMA) matrix, which revealed their good potential as tunable solid state emitters. Some of these complexes acted as efficient catalysts for the transesterification of esters and canola oil showing their potential in biodiesel generation. Mechanistic investigations using ESI-MS revealed that the transesterification catalyzed by these complexes proceeds through two types of acyl intermediates.

Synthesis, Optical Properties, and Sensing Applications of Gold Nanodots

In this Personal Account, we briefly address our journey in developing photoluminescent nanomaterials for sensing purposes, with a focus on gold nanodots (Au NDs). Their synthetic strategies, optical properties, and sensing applications are emphasized. The Au NDs can be simply prepared from the etching of small-sized Au nanoparticles (<3 nm in diameter) by thiol compounds such as 11-mercaptoundecanoic acid under alkaline conditions. This simple approach allows the preparation of various functional Au NDs by choosing different thiol compounds as etching agents. Since the optical properties of Au NDs are highly dependent on the core and shell of each Au ND, the selection of etching reagents is important. Over the years we have developed various sensing systems using Au NDs for the detection of metal ions, anions, and proteins, based on analyte-induced photoluminescence quenching/enhancement of Au NDs as a result of changes in their oxidation state, shell composition, and structure.

pH-Sensitive gold nanoclusters: preparation and analytical applications for urea, urease, and urease inhibitor detection

Herein, we reported for the first time a facile synthetic process of gold nanoclusters (AuNCs) by using N-acetyl-L-cysteine both as a reducing agent and as a protection ligand. Based on the pH stimuli-responsive properties of the as-prepared AuNCs, we constructed a pH-sensing platform for the detection of urea, urease, and urease inhibitors.

Bimetallic silver nanoparticle–gold nanocluster embedded composite nanoparticles for cancer theranostics

A bimetallic silver nanoparticle based gold nanocluster module has been developed for theranostic cellular application by a rapid and simple galvanic exchange method.

Ultra sensitive and wide-range pH sensor based on the BSA-capped Cu nanoclusters fabricated by fast synthesis through the use of hydrogen peroxide additive

This study reports a new pH sensor based on BSA-capped copper nanoclusters. The proposed pH sensor provides better sensitivity and a wider ranging pH response compared with other metal nanoclusters reported in the literature.

The isomeric effect of mercaptobenzoic acids on the preparation and fluorescence properties of copper nanoclusters

Copper nanoclusters (Cu NCs) aggregates prepared from copper nitrate and mercaptobenzoic acid (MBA) isomers show differential optical properties.