Probing the Structural Degradation of CsPbBr3 Perovskite Nanocrystals in the Presence of H2O and H2S: How Weak Interactions and HSAB Matter.

Structural degradation of all inorganic CsPbBr3 in the presence of moisture is considered as one of its major limitations to use as an active component in various light-harvesting and light-emitting devices. Herein, we used two similar molecules, H2O and H2S, with similar structures, to follow the decomposition mechanism of CsPbBr3 perovskite nanocrystals. Interestingly, H2O acts as a catalyst for the decomposition of CsPbBr3, which is in contrast to H2S. Our experimental observations followed by density functional theory (DFT) calculations showed that the water molecule is intercalated in the CsPbBr3 perovskite whereas H2S is adsorbed in the (100) planes of CsPbBr3 by a weak electrostatic interaction. According to Pearson's hard-soft acid-base theory, both cations present in CsPbBr3 prefer soft/intermediate bases. In the case of the water molecule, it lacks a soft base and thus it is not directly involved in the reaction whereas H2S can provide a soft base and thus it gets involved in the reaction. Understanding the mechanistic aspects of decomposition can give different methodologies for preventing such unwanted reactions.

Quantum Dot-Based Fluorometric Sensor for Hg(II) in Water Customizable for Onsite Visual Detection.

An easy naked-eye detection technique for mercuric ions in water using silanized quantum dots is demonstrated. Cadmium selenide quantum dots were synthesized and rendered water soluble by silica overcoating. The quantum dot emission was instantly turned off by the mercuric ions in the analyte, enabling visual detection. The emission quenching was associated with a concomitant bathochromic shift, both in the absorption and emission profiles. The underlying mechanism is a permanent surface modification of quantum dots by mercuric ions, altering the electronic structure and, in turn, the photophysical properties. The results confirmed the potential of this simple system to be customized for on-site visual detection of mercury contamination in water bodies, biological fluids, and soil with high selectivity and sensitivity.

Effective cellular internalization of silica-coated CdSe quantum dots for high contrast cancer imaging and labelling applications.

The possibility of developing novel contrast imaging agents for cancer cellular labelling and fluorescence imaging applications were explored using silica-coated cadmium selenide (CdSe) quantum dots (QDs). The time dependent cellular internalization efficiency study was carried out using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and Confocal Laser Scanning Microscopy (cLSM) after exposing QDs to stem cells and cancer cells. The strong fluorescence from the cytoplasm confirmed that the QDs were efficiently internalized by the cells. The internalization maxima were observed at the fourth hour of incubation in both stem and cancer cells. Further, the in vitro fluorescence imaging as well as localization study of QDs were performed in various cells. Moreover, high contrast in vivo tumor imaging efficiency of silica-coated CdSe QDs was performed in ultrathin sections of tumor mice, and the results confirmed its effective role in cellular imaging and labelling in cancer and other diseases.