Differential Interaction of Metal Ions with Gold Nanoclusters and Application in Detection of Cobalt and Cadmium

Binding Investigation of Some Important Metal Ions Copper (I), Nickel (II), and Aluminium (III) with Bovine Serum Albumin Using Valid Spectroscopic Techniques

Studies based on the interaction of metals with proteins resulted in the development of promising metal-based compounds with encouraging medicinal potential. This study was aimed to utilize FT-IR and UV-Vis spectroscopic techniques to analyze the interactions of biologically significant metal ions, such as Al3+, Ni+2, and Cu+, with bovine serum albumin (BSA). Different concentrations of metal ions were interacted with BSA, and the complexes were analyzed using the two techniques. The change in the BSA secondary structure components such as β-sheet, β-antiparallel, α-helix, β-turn, and random coil were analyzed using second derivative resolution enhancement. The FT-IR spectroscopy suggested a marked decrease in the C=O stretching (corresponding to amide I) and C=N stretching (corresponding to amide II) intensities. Interestingly, upon complexation, a marked reduction (22.58–29.03%) in the α-helical component was observed with a considerable increase in the random coil component. The intensity of the absorption peak of BSA obtained using UV was observed to increase consecutively as the concentration of Cu+, Al3+, and Ni2+ ions increased. The binding constants for the BSA-Cu+, BSA-Ni+2, and BSA-Al+3 complexes were calculated to be 3.46 × 104 M−1, 1.28 × 104 M−1, and 2.08 × 104 M−1, respectively. It was concluded that the binding interaction decreased in the order Cu+ > Al3+ > Ni2+. These findings were similar to our previous findings using affinity capillary electrophoresis (ACE). Therefore, it can be inferred that the FT-IR and UV techniques might be utilised effectively to assess the metal-protein interaction and can have wide application in routine analysis. These techniques have several advantages in being simple, easy-to-perform, rapid, and affordable over other high-end techniques.

Synthesis of Orange-Red Emissive Au-SG and AuAg-SG Nanoclusters and Their Turn-OFF vs. Turn-ON Metal Ion Sensing

Synthesis of luminescent metal cluster for selective sensing of specific analyte with detail mechanistic understanding is very important for real world applications as well as for developing new emissive materials. In the present work, we have synthesized L-glutathione stabilized gold (Au-SG) and gold-silver bimetallic (AuAg-SG) clusters under identical experimental conditions with orange red emissive characteristics for both. Detail photo physical analysis reveals that both clusters are phosphorescent in nature with moderate quantum yield of 7% and 19% for Au-SG and AuAg-SG respectively and their excited state lifetime values are in the range of 1-2 μs. While Au-SG cluster showed luminescence quenching response (turn-off) in presence of Fe³⁺ and Hg²⁺ ions, AuAg-SG cluster showed turn-off response for Cu²⁺, Fe³⁺ and Hg²⁺, but luminescent enhancement (turn-on) response for Cd²⁺ ions. The highest detection limit obtained for Cu²⁺ ion by AuAg-SG cluster is 20 nM while for Cd²⁺ ion it is 75 nM. From Time Correlated Single Photo Counting (TCSPC) and Dynamic Light Scattering (DLS) measurements we postulated that except Cd²⁺, all other metal ions cause aggregation of clusters through ligation with SG ligands while Cd²⁺ ion does not induce any cluster aggregation but binds to cluster surface atoms. The near constant life time values of both clusters during gradual addition of respective metal ions confirms static quenching/enhancement process through formation of stable ground state adducts.

Luminescent Gold Nanocluster-Methylcellulose Composite Optical Fibers with Low Attenuation Coefficient and High Photostability

Because of their lightweight structure, flexibility, and immunity to electromagnetic interference, polymer optical fibers (POFs) are used in numerous short-distance applications. Notably, the incorporation of luminescent nanomaterials in POFs offers optical amplification and sensing for advanced nanophotonics. However, conventional POFs suffer from nonsustainable components and processes. Furthermore, the traditionally used luminescent nanomaterials undergo photobleaching, oxidation, and they can be cytotoxic. Therefore, biopolymer-based optical fibers containing nontoxic luminescent nanomaterials are needed, with efficient and environmentally acceptable extrusion methods. Here, such an approach for fibers wet-spun from aqueous methylcellulose (MC) dispersions under ambient conditions is demonstrated. Further, the addition of either luminescent gold nanoclusters, rod-like cellulose nanocrystals or gold nanocluster-cellulose nanocrystal hybrids into the MC matrix furnishes strong and ductile composite fibers. Using cutback attenuation measurement, it is shown that the resulting fibers can act as short-distance optical fibers with a propagation loss as low as 1.47 dB cm^-1 . The optical performance is on par with or even better than some of the previously reported biopolymeric optical fibers. The combination of excellent mechanical properties (Young's modulus and maximum strain values up to 8.4 GPa and 52%, respectively), low attenuation coefficient, and high photostability makes the MC-based composite fibers excellent candidates for multifunctional optical fibers and sensors.

Glutathione stabilized green-emission gold nanoclusters for selective detection of cobalt ion

A glutathione stabilized Au nanoclusters (GSH-Au NCs) was synthesized here and used to selective detection of cobalt ion. The as-prepared GSH-Au NCs had strong green light emission around 500 nm, and the features of the NCs have been systematically characterized by UV-vis absorption, X-ray photoelectronic spectroscopic, Fourier transform infrared spectroscopy and transmission electron microscope characterization. The interactions between the GSH-Au NCs and metal ions was studied, and the results indicated that the fluorescence of the GSH-Au NCs could be quenched in the presence of Co²⁺ ion at pH of 6.0. The quenching ratio was linear with the concentration of Co²⁺ ions, and the calibration curve was I₀/I = 0.1187c_co + 0.6085 in the Co²⁺ concentration ranges from 2.0 to 50.0 μM with correlation coefficient (R²) of 0.9950 and the limit of detection (LOD, 3σ) of 0.124 μM. In addition, we collected environmental water samples to test the reliability of the method and demonstrated this method is simple, rapid, and selective.

Copper nanoclusters with/without salicylaldehyde-modulation for multifunctional detection of mercury, cobalt, nitrite and cyanide ions in aqueous solution and bioimaging

The sensitive determination of multiple heavy metal ions and toxic anions is important in biological and environmental fields. Here we report a facile strategy to construct a multifunctional chemosensor for the detection of Hg²⁺, [Formula: see text]Co²⁺, and CN^- in aqueous solution based on the fluorescent copper nanoclusters (Cu NCs). It was interesting to find that salicylaldehyde (SA) could effectively modulate the fluorescence property and sensing behavior of Cu NCs. In the absence of SA, Cu NCs showed 'on-off' fluorescence responses at the addition of Hg²⁺ and [Formula: see text] under different quenching mechanisms. Upon the presence of SA, Cu NCs exhibited a strong intramolecular charge transfer emission at 500 nm, accompanied by the decrease of the initial fluorescence of Cu NCs at 430 nm. This fluorescence on-state of Cu NC-SA at 500 nm was found to be exclusively turned off by Co²⁺ and enhanced by CN^-. Spectroscopy results combined with thermodynamic analysis provided sufficient information to deduce the sensing mechanisms. Finally, the Cu NCs showed high biocompatibility and were able to be used for fluorescence bioimaging in living cells. This study provided a novel and simple strategy to construct the multifunctional chemosensors for bioanalytical applications.

Metal Nanostructures for Environmental Pollutant Detection Based on Fluorescence

Heavy metal ions and pesticides are extremely dangerous for human health and environment and an accurate detection is an essential step to monitor their levels in water. The standard and most used methods for detecting these pollutants are sophisticated and expensive analytical techniques. However, recent technological advancements have allowed the development of alternative techniques based on optical properties of noble metal nanomaterials, which provide many advantages such as ultrasensitive detection, fast turnover, simple protocols, in situ sampling, on-site capability and reduced cost. This paper provides a review of the most common photo-physical effects impact on the fluorescence of metal nanomaterials and how these processes can be exploited for the detection of pollutant species. The final aim is to provide readers with an updated guide on fluorescent metallic nano-systems used as optical sensors of heavy metal ions and pesticides in water.