Dual-functional cellulase-mediated gold nanoclusters for ascorbic acid detection and fluorescence bacterial imaging

Protein-protected metal nanomaterials are becoming the most promising fluorescent nanomaterials for biosensing, bioimaging, and therapeutic applications due to their obvious fluorescent molecular properties, favorable biocompatibility and excellent physicochemical properties. Herein, we pioneeringly prepared a cellulase protected fluorescent gold nanoclusters (Cel-Au NCs) exhibiting red fluorescence under the excitation wavelength of 560 nm via a facile and green one-step method. Based on the fluorescence turn-off mechanism, the Cel-Au NCs were used as a biosensor for specificity determination of ascorbic acid (AA) at the emission of 680 nm, which exhibited satisfactory linearity over the range of 10-400 µM and the detection limit of 2.5 µM. Further, the actual sample application of the Au NCs was successfully established by evaluating AA in serum with good recoveries of 98.76%-104.83%. Additionally, the bacteria, including gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and gram-negative bacteria (Escherichia coli), were obviously stained by Cel-Au NCs with strong red emission. Thereby, as dual-functional nanoclusters, the prepared Cel-Au NCs have been proven to be an excellent fluorescent bioprobe for the detection of AA and bacterial labeling in medical diagnosis and human health maintenance.

Copper nanoclusters: designed synthesis, structural diversity, and multiplatform applications

Atomically precise metal nanoclusters (MNCs) have gained tremendous research interest in recent years due to their extraordinary properties. The molecular-like properties that originate from the quantized electronic states provide novel opportunities for the construction of unique nanomaterials possessing rich molecular-like absorption, luminescence, and magnetic properties. The field of monolayer-protected metal nanoclusters, especially copper, with well-defined molecular structures and compositions, is relatively new, about two to three decades old. Nevertheless, the massive progress in the field illustrates the importance of such nanoobjects as promising materials for various applications. In this respect, nanocluster-based catalysts have become very popular, showing high efficiencies and activities for the catalytic conversion of chemical compounds. Biomedical applications of clusters are an active research field aimed at finding better fluorescent contrast agents, therapeutic pharmaceuticals for the treatment and prevention of diseases, the early diagnosis of cancers and other potent diseases, especially at early stages. A huge library of structures and the compositions of copper nanoclusters (CuNCs) with atomic precisions have already been discovered during last few decades; however, there are many concerns to be addressed and questions to be answered. Hopefully, in future, with the combined efforts of material scientists, inorganic chemists, and computational scientists, a thorough understanding of the unique molecular-like properties of metal nanoclusters will be achieved. This, on the other hand, will allow the interdisciplinary researchers to design novel catalysts, biosensors, or therapeutic agents using highly structured, atomically precise, and stable CuNCs. Thus, we hope this review will guide the reader through the field of CuNCs, while discussing the main achievements and improvements, along with challenges and drawbacks that one needs to face and overcome.

Fluorescence-tunable copper nanoclusters and their application in hexavalent chromium sensing

Generally, metal nanoclusters are synthesized using only a single ligand. Thus, the properties and applications of these nanomaterials are limited by the nature of the ligand used. In this study, we have developed a new synthetic strategy to prepare bi-ligand copper nanoclusters (Cu NCs). These bi-ligand Cu NCs are synthesized from copper ions, thiosalicylic acid, and cysteamine by a simple one-pot method, and they exhibit high quantum yields (>18.9%) and good photostability. Most interestingly, the fluorescence intensities and surface properties of the Cu NCs can be tailored by changing the ratio of the two ligands. Consequently, the bi-ligand Cu NCs show great promise as fluorescent probes. Accordingly, the Cu NCs were applied to the inner-filter-effect-based detection of hexavalent chromium in water. A wide linear range of 0.1–1000 μM and a low detection limit (signal-to-noise ratio = 3) of 0.03 μM was obtained. The recoveries for the real sample analysis were between 98.3 and 105.0% and the relative standard deviations were below 4.54%, demonstrating the repeatability and practical utility of this assay.

Generally, metal nanoclusters are synthesized using only a single ligand.

Interaction of proteins with lemon-juice/glutathione-derived carbon nanodot: Interplay of induced-aggregation and co-solubilization

The accumulation of protein aggregates (tau) causes Alzheimer's disease (AD), Parkinson's disease (PD), and a range of neurodegenerative diseases. To develop a less toxic and bio-derived nanomaterials for inhibition of protein-aggregation, carbon nanodot has been used for this study. Nanodot have generated huge interest in biomedical applications owing to unique emission property and good biocompatibility. A carbon nanodot is synthesized from a natural resource-lemon juice and glutathione. The synthesized nanodot possesses excitation-independent emission and nano-sheet like with high graphitic content. Interaction of protein with CND is monitored by intrinsic fluorescence (trp residues), FT-IR and circular dichroism spectroscopy. Whereas it solubilizes the protein aggregates at its higher concentration. Both induced-aggregation and co-solubilization are sequence-independent and dictated by nanodot. The study may shed light on the role of glutathione in glutathione-dependent glyoxalase system toward defence against glycation product.