Quantum dots (QDs) are usually used as fluorescent probe, and they are difficult to use in colorimetric detection. However, in this report carboxyl-functionalized CdS (COF-CdS) QDs were synthesized in aqueous solution for colorimetric detection following a classic method. On the basis of inducing the aggregation of COF-CdS QDs, a simple naked eye colorimetric method with high sensitivity and selectivity was developed for the sensing of Co(2+) ions in aqueous solutions. The Co(2+) ions induced COF-CdS QDs results in a marked enhancement of the UV-vis absorption spectra at 360 nm, and the process was accompanied by a visible color change from colorless to yellowish brown within 5 min, which proves a sensitive detection of Co(2+) ions. The sensing of Co(2+) ions can therefore be easily achieved by a UV-vis spectrophotometer or even by the naked eye. Under the optimized circumstances, this method yields excellent sensitivity (LOD = 0.23 μg mL(-1)) and selectivity toward Co(2+) ions. The calibration plot of (A - A(0)) at 360 nm against concentration of Co(2+) ions was linear over the range from 0.5 to 14 μg mL(-1) with a correlation coefficient of 0.9996. The accuracy and reliability of the method were further ascertained by recovery studies via standard addition method with percent recoveries in the range of 99.63-102.46%. The plausible mechanism for the color change reaction has also been discussed. Our attempt may provide a cost-effective, rapid, and simple solution for the inspection of Co(2+) ions in the presence of a complex matrix from environmental aqueous samples.

The fluorescence quenching spectrum of bovine serum albumin (BSA) was investigated in the presence of felodipine (FLD) by spectroscopic methods including fluorescence spectroscopy and UV-Vis absorption spectroscopy. Stern-Volmer quenching was successfully applied and the corresponding thermodynamic parameters, namely enthalpy change (DeltaH), free energy change (DeltaG) and entropy change (DeltaS) at different temperatures (304, 314 and 324 K) were calculated according to the Van't Hoff relation. This revealed that the hydrophobic interaction plays a major role in stabilizing the complex. The fluorescence spectrum of BSA was studied in presence of various concentrations of SDS surfactant. The distance (r) between donor (BSA) and acceptor (FLD) was obtained according to fluorescence resonance energy transfer (FRET). The synchronous fluorescence spectroscopy was used to investigate the effect of FLD on BSA molecule. The result shows that the conformation of BSA was changed in the presence of felodipine.

Platinum(II) complexes [Pt(pap)(an-cat)] (1) and [Pt(pap)(py-cat)] (2) with 2-(phenylazo)pyridine (pap), 4-[2-[(anthracen-9-ylmethylene)amino]ethyl]benzene-1,2-diol (H2an-cat), and 4-[2-[(pyren-1-ylmethylene)amino]ethyl]benzene-1,2-diol (H2py-cat) were prepared, and their photoinduced cytotoxicity was studied. The complexes were found to release catecholate ligand in the presence of excess glutathione (GSH), resulting in cellular toxicity in the cancer cells. The catecholate complex [Pt(pap)(cat)] (3) was prepared and used as a control. Complex 3, which is structurally characterized by X-ray crystallography, has platinum(II) in a distorted square-planar geometry. The complexes are redox-active, showing responses near 0.6 and 1.0 V versus SCE in N,N-dimethylformamide/0.1 M tetrabutylammonium perchlorate corresponding to a two-step catechol oxidation process and at -0.3 and -1.3 V for reduction of the pap ligand. Complex 1 showed remarkable light-induced cytotoxicity in HaCaT (human skin keratinocytes) and MCF-7 (human breast cancer) cells, giving IC50 value of ∼5 μM in visible light of 400-700 nm and >40 μM in the dark. The 2',7'-dichlorofluorescein diacetate (DCFDA) assay showed the generation of reactive oxygen species (ROS), which seems to trigger apoptosis, as is evident from the annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) assay. The fluorescence microscopic images showed significant nuclear localization of the complexes and free ligands. A mechanistic study revealed possible reduction of the coordinated azo bond of pap by cellular GSH, releasing the catecholate ligand and resulting in remarkable photochemotherapeutic action of the complexes.

CoFe 2 O 4 -BaTiO 3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ε ) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ε ) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.

A novel, simple but highly selective fluorescent probe is developed for the direct detection of sulfide ions [S(2-)] based on the fluorescence quenching of the functionalized CdS QDs in aqueous solution at trace levels and successfully applied for quantitation of S(2-) from water samples in a complex matrix exclusive of pretreatment by standard addition method.

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Graphical representation of the binding of CURNPs to Cu2+(fluorescence off) and release of CURNPs (fluorescence on) by the reaction of S2−with copper bound to CURNPs.