Protein-Mediated Synthesis of Nanosized Mn-Doped ZnS: A Multifunctional, UV-Durable Bio-Nanocomposite

Tunable structural and optical properties of AgxCuyInS2 colloidal quantum dots

Herein is discussed tunable absorption and emission properties of AgxCuyInS2 quantum dots involving wurtzite to chalcopyrite phase transformation dependent on Ag+ dopant content.

Silk Cocoon-Derived Protein Bioinspired Gold Nanoparticles as a Formidable Anticancer Agent

We synthesized bioinspired sericin encapsulated gold nanoparticles (SGNPs) using HAuCl4 as the starting material in a bottom-up approach. Further, two-dimensional (2D) and three-dimensional (3D) conformational changes (folding and unfolding) in sericin were studied using circular dichroism (CD) and fluorescence spectroscopy, respectively, during and after the synthesis of particles. Finally, the synthesized SGNPs were characterized using several physical techniques to ensure their correct synthesis and study the size, stability, and charge over the surface of particles. At the beginning of the reaction, when gold was in the ionic form (Au+3), sericin exhibited maximum electrostatic interaction and underwent unfolding. Au+3 reduced to Au during the reaction, and sericin regained its 3D confirmation due to a decrease in its native electrostatic interactions. However, CD revealed the same patterns of unfolding and folding; a decrease in α helix and an increase inβ3 pleated sheets were noticed. Although the 3D structure of sericin was restored after the synthesis of SGNPs, it was substantially altered. In addition, certain changes in the 2D structure were observed; however, these did not alter the activity of sericin. Furthermore, Fourier-transform infrared spectroscopy (FTIR) confirmed these findings. The SGNPs were found to be effective against lung cancer (A549 cells), with an IC50 of 145.49 βM, without exerting any toxic effects on normal cells (NRK cells). The effectiveness of SGNPs was examined by MTT cytotoxicity and nuclear fragmentation assays. Furthermore, we assessed their ability to produce excessive ROS and release Cyt-c from the mitochondria for caspase-3-mediated apoptosis.

Tuneable luminescence properties of EDTA-assisted ZnS:Mn nanocrystals from a yellow-orange to a red emission band

Luminescence technology has been improved with the help of semiconductor nanoparticles that possess novel optical and electrical properties compared with their bulk counterpart. The aim of this study was to design semiconductor nanocrystals in their pure (ZnS) or doped form (ZnS:Mn) with different concentrations of Mn²⁺ ions by a wet chemical route stabilized by ethylenediamine tetra-acetic acid (EDTA) and to evaluate their luminescence properties. The nanocrystals were characterized by physicochemical techniques such as X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), EDS, and ultraviolet (UV)-visible light and photoluminescence (PL) studies. These results showed the presence of cubic phase and spherically shaped nanocrystals. A blue shift with respect to their bulk counterpart was observed. PL emission spectra were observed with a fixed blue peak and the yellow-orange bands were red shifted towards the red region under the same excitation wavelength. The orange-red bands were attributed to the radiation transition of electrons in 3d5 unfilled shells of Mn²⁺ ions [⁴ T₁ (⁴ G)-⁶ A₁ (⁶ S)]; the ZnS matrix varied with Mn²⁺ concentration. Shift and increase in the intensity of the PL and absorption bands were observed with increase in Mn content. The study showed that Mn²⁺ -doped ZnS nanocrystal emission bands can be tuned from the yellow-orange to the red regions under a controlled synthesis process and could be used as promising luminescent emitters in the biology field upon functionalization with suitable materials. Further studies on construction with various other materials will be useful for practical applications.

Glucose oxidase-directed, instant synthesis of Mn-doped ZnS quantum dots in neutral media with retained enzymatic activity: mechanistic study and biosensing application

Protein-directed synthesis of quantum dots (QDs) is a "greener" alternative to the current high-temperature and aqueous synthetic protocols, which provide water-soluble, biocompatible protein-functionalized QDs in one-pot. However, the protein activity in such synthetic schemes is a critical issue, since the synthetic conditions (for instance, high pH of the precursors, long time of synthesis, and disruption of disulfide bonds) are not suitable for retaining the activity (especially for enzymes). Herein, we present a facile and instant glucose oxidase (GOD)-directed strategy for the preparation of highly luminescent, phosphorescent Mn-doped ZnS (Mn-ZnS) QDs in one-step at room temperature and in neutral aqueous media. With such mild synthetic conditions, the enzymatic activity of GOD was totally retained. Furthermore, we also carried out GOD-directed synthesis of QDs with several other conditions that are reported in the literature. It turned out that the GOD enzymatic activity under these synthetic conditions was lower than that of the proposed protocol, indicating that mild synthetic conditions are the prerequisite for retaining the enzymatic activity. Importantly, the as-prepared GOD-mediated Mn-ZnS QDs exhibited high photostability, high salt tolerance and colloidal stability, and can be stored for months at 4 °C or 25 °C without changing their phosphorescent intensity and enzymatic activity. Via selective chemical modification, the exact functional groups (amino acid residues) of GOD in directing the synthesis of Mn-ZnS QDs were studied in detail. It turned out to be imidazole in histidine residues but not thiol in cysteine residues that directed the formation of Mn-ZnS QDs, and this was further confirmed with several other proteins for synthesis of Mn-ZnS QDs. The as-prepared GOD-capped Mn-ZnS QDs were employed as phosphorescent probes for background-free sensing of glucose in serum samples.

Highly selective colorimetric bacteria sensing based on protein-capped nanoparticles

A rapid and cost effective colorimetric sensor has been developed for the detection of bacteria, and Bacillus subtilis was selected as an example to demonstrate the feasibility of the sensing system.