Thiolate-protected metal nanoclusters (or thiolated metal NCs) have recently emerged as a promising class of functional materials because of their well-defined molecular structures and intriguing molecular-like properties. Recent developments in the NC field have aimed at exploring metal NCs as novel luminescent materials in the biomedical field because of their inherent biocompatibility and good photoluminescence (PL) properties. From the fundamental perspective, recent advances in the field have also aimed at addressing the fundamental aspects of PL properties of metal NCs, shedding some light on developing efficient strategies to prepare highly luminescent metal NCs. In this Perspective, we discuss the physical chemistry of a recently discovered aggregation-induced emission (AIE) phenomenon and show the significance of AIE in understanding the PL properties of thiolated metal NCs. We then explore the unique physicochemical properties of thiolated metal NCs with AIE characteristics and highlight some re...

Luminescent Metal Nanoclusters with Aggregation-Induced Emission.

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease.

Aqueous solution properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) amphiphilic copolymer (Pluronic L64:  EO13PO30EO13) were studied in the presence of various alkali halide salts (LiCl, KCl, NaCl, NaBr, and NaI), sodium thiocyanate (NaSCN), and urea ((NH2)2CO). Differential scanning calorimetry (DSC) was employed for the determination of both the unimer-to-micelle transition (critical micellization temperature, CMT) and the phase separation (cloud point, CP). DSC is particularly useful in the case of Pluronic L64 where the detection of the CMT by optical techniques is hindered by the presence of a hydrophobic impurity. The presence of LiCl, KCl, NaCl, and NaBr decreased both CMT and CP (in the order Cl- > Br- and Na+ > K+ > Li+), whereas addition of NaSCN and urea resulted in a CMT and CP increase (in the order NaSCN > urea). NaI appeared to be an intermediate case as it decreased the CMT but increased the CP. Variation of the anion type (rather than...

Differential scanning calorimetry investigation of the effect of salts on aqueous solution properties of an amphiphilic block copolymer (poloxamer)

Plasmonic nanostructures possessing unique and versatile optoelectronic properties have been vastly investigated over the past decade. However, the full potential of plasmonic nanostructure has not yet been fully exploited, particularly with single-component homogeneous structures with monotonic properties, and the addition of new components for making multicomponent nanoparticles may lead to new-yet-unexpected or improved properties. Here we define the term "multi-component nanoparticles" as hybrid structures composed of two or more condensed nanoscale domains with distinctive material compositions, shapes, or sizes. We reviewed and discussed the designing principles and synthetic strategies to efficiently combine multiple components to form hybrid nanoparticles with a new or improved plasmonic functionality. In particular, it has been quite challenging to precisely synthesize widely diverse multicomponent plasmonic structures, limiting realization of the full potential of plasmonic heterostructures. To address this challenge, several synthetic approaches have been reported to form a variety of different multicomponent plasmonic nanoparticles, mainly based on heterogeneous nucleation, atomic replacements, adsorption on supports, and biomolecule-mediated assemblies. In addition, the unique and synergistic features of multicomponent plasmonic nanoparticles, such as combination of pristine material properties, finely tuned plasmon resonance and coupling, enhanced light-matter interactions, geometry-induced polarization, and plasmon-induced energy and charge transfer across the heterointerface, were reported. In this review, we comprehensively summarize the latest advances on state-of-art synthetic strategies, unique properties, and promising applications of multicomponent plasmonic nanoparticles. These plasmonic nanoparticles including heterostructured nanoparticles and composite nanostructures are prepared by direct synthesis and physical force- or biomolecule-mediated assembly, which hold tremendous potential for plasmon-mediated energy transfer, magnetic plasmonics, metamolecules, and nanobiotechnology.

Multicomponent Plasmonic Nanoparticles: From Heterostructured Nanoparticles to Colloidal Composite Nanostructures.

One of the biggest impacts that the nanotechnology has made on medicine and biology, has been in the area of drug delivery systems (DDSs). Many drugs suffer from serious problems concerning insolubility, instability in biological environments, poor uptake into cells and tissues, sub-optimal selectivity for targets and unwanted side effects. Nanocarriers can be designed as DDSs to overcome many of these drawbacks. One of the most versatile building blocks to prepare these nanocarriers is the ubiquitous, readily available and inexpensive protein, serum albumin. Areas covered: This review covers the use of different types of albumin (human, bovine, rat, and chicken egg) to prepare nanoparticle and microparticle-based structures to bind drugs. Various methods have been used to modify the albumin structure. A range of targeting ligands can be attached to the albumin that can be recognized by specific cell receptors that are expressed on target cells or tissues. Expert opinion: The particular advantages of albumin used in DDSs include ready availability, ease of chemical modification, good biocompatibility, and low immunogenicity. The regulatory approvals that have been received for several albumin-based therapeutic agents suggest that this approach will continue to be successfully explored.

Albumin nanostructures as advanced drug delivery systems

The effect of the anionic surfactant sodium dodecyl sulfate (SDS) on the protein human serum albumin (HSA) was studied using steady-state spectroscopy, time-resolved measurements, and circular dichroism spectroscopy. The binding of SDS to the domain IIA of HSA, housing the single tryptophan amino acid residue (Trp214), was monitored, and it was found that this addition of the surfactant takes place in a sequential manner depending upon the concentration of the added surfactant. Both fluorescence intensity and lifetimes of HSA decreased with the increasing concentration of SDS, and the surfactant molecules serve the role of a quencher for the fluorescence of Trp214. Circular dichroism data also support the structural changes induced by SDS. The 17 disulfide bridges present in HSA provide the necessary structural rigidity to the protein. Stern-Volmer plots and thermodynamic parameters have been used to characterize the sequential binding of SDS to HSA, and these parameters not only confirm that the binding is spontaneous in nature but also is quite strong, depending on the concentration of the added surfactant.

Spectroscopic Probing of the Microenvironment in a Protein−Surfactant Assembly

The binding of the antibiotic tetracycline hydrochloride (TC) to three proteins was investigated by steady-state, time-resolved, and circular dichroism spectroscopy. The tryptophan (Trp) amino acid residues were used as an intrinsic fluorophore to decipher the structure-function relationship. As monitored by CD spectroscopy, the addition of TC causes the protein to alter some of its helical content although such changes are only marginal. The gradual decrease in fluorescence intensity of Trp can be ascribed to static quenching which takes place by the interaction of the drug with the protein. Besides Trp quenching, there is evidence of fluorescence resonance energy transfer (FRET) in all three proteins with different values of efficiency of energy transfer. Various quenching/binding and thermodynamic parameters associated with such drug-protein interactions have been estimated. The results thus obtained can provide guidelines to synthetic chemists to design and synthesize target-oriented drugs.

Exploring the Mechanism of Fluorescence Quenching in Proteins Induced by Tetracycline

The mechanism by which the protein bovine serum albumin undergoes unfolding induced by the anionic surfactant sodium dodecyl sulphate (SDS) and then the subsequent refolding brought in by β-Cyclodextrin (β-CD) was studied by steady-state fluorescence, time resolved measurements and Circular Dichroism (CD) spectroscopy. The prominent findings of this investigation are (i) SDS unfolds the protein in a sequential manner passing through three different phases of binding of SDS followed by a saturation phase; (ii) the refolding process is initiated through inclusion/removal of SDS molecules by β-CD and hence this also seems to happen in a phased manner; (iii) the process of refolding seems to be reversible to the unfolding process but the protein does not regain all its structure on refolding; (iv) however, CD results reveal almost 100% recovery of the secondary structure lost during SDS induced unfolding. We have conclusively proved that there is a marginal structural gain of the native protein at low surfactant concentration and β-CD also induces a marginal structural loss to the native protein. The unfolding process induced by SDS seems to be spontaneous and the binding of SDS to BSA is rather strong, as revealed by thermodynamic parameters.

Reversibility in protein folding: effect of β-cyclodextrin on bovine serum albumin unfolded by sodium dodecyl sulphate

Binding, unfolding and refolding dynamics of serum albumins☆☆☆

To address the concern of material chemists over the issue of stability and photoluminescent (PL) characteristics of Cu nanoclusters (NCs), herein we present an efficient protocol discussing PL Cu NCs (Cu/HSA) having blue emission and high photostability. These PL NCs were illustrated as efficient probes for Forster resonance energy transfer (FRET) with a compatible fluorophore (Coumarin 153). Our spectroscopic results were well complemented by our molecular docking calculations, which also favored our proposed mechanism for Cu NC formation. The beneficial aspect and uniqueness of these nontoxic Cu/HSA NCs highlights their temperature-dependent PL reversibility as well as the reversible FRET with Coumarin 153, which enables them to be used as a nanothermometer and a PL marker for sensitive biological samples.

Uttam Anand

Papers

Spectroscopic Probing of the Microenvironment in a Protein−Surfactant Assembly

Exploring the Mechanism of Fluorescence Quenching in Proteins Induced by Tetracycline

Reversibility in protein folding: effect of β-cyclodextrin on bovine serum albumin unfolded by sodium dodecyl sulphate

Binding, unfolding and refolding dynamics of serum albumins☆☆☆

Photostable Copper Nanoclusters: Compatible Förster Resonance Energy-Transfer Assays and a Nanothermometer.