Netaji K. Desai

Cetyltrimethylammonium Bromide Capped 9-Anthraldehyde Nanoparticles for Selective Recognition of Phosphate Anion in Aqueous Solution Based on Fluorescence Quenching and Application for Analysis of Chloroquine

Cetyltrimethylammonium bromide (CTAB) capped 9-Anthraldehyde nanoparticles (9-AANPs) in aqueous suspension prepared by reprecipitation method are seen brick shaped in Scanning Electron Microscope image. The Dynamic Light Scattering histogram of nanoparticle suspension reveals narrow particle size distribution and average particle size is 89 nm. The positive zeta potential 20.8 mV measured on zeta sizer indicates high level stability of nanoparticle suspension. The blue shift of 65359.47 cm−1 observed in the UV-Visible absorption spectrum of CTAB capped 9-AANPs from the absorption maximum of dilute solution of 9-Anthraldehyde (9-AA) in acetone is an indication of formation of H-bonded aggregates by π stacking effect. The strong Aggregation Induced Enhanced Emission (AIEE) of CTAB capped 9-AANPs at 537 nm is selectively quenched with addition of phosphate anion solution. The fluorescence quenching results of the nanoparticle in aqueous solution fit into conventional Stern–Volmer relation in the range of phosphate ion concentration of 0–40 μM. The possible mechanism of fluorescence quenching of nanoparticle is explained by considering adsorption of phosphate anion electrostatistically on positively charged surface of nanoparticle generated by CTAB cap. The Langmuir adsorption plot constructed for PO43− adsorption on the basis of fluorescence quenching results of CTAB capped 9-AANPs is linear. The estimated value of Langmuir constant (K) and Stern – Volmer constant (Ksv) are in close agreement within experimental limits. The sensing method of phosphate ion based on fluorescence quenching of 9-AANPs is applied successfully for quantification of phosphate from pharmaceutical tablet chloroquine phosphate and hence to determine the amount of chloroquine.

Fluorescence quenching studies of CTAB stabilized perylene nanoparticles for the determination of Cr(VI) from environmental samples: spectroscopic approach

Cetyl trimethyl ammonium bromide (CTAB) stabilized perylene nanoparticles (PNPs) were prepared by a modified reprecipitation method in aqueous solution under ultrasonic treatment. A spectrofluorimetric method for the quantitative determination of hexavalent chromium (Cr(VI), dichromate species) based on the fluorescence (FL) quenching of CTAB-stabilized PNPs (CTAB-PNPs) in aqueous solution was proposed. Under the most favourable conditions, the FL intensity of PNPs monitored at an excitation wavelength of λex = 382 nm was quenched by the successive addition of increasing concentrations of dichromate ions. The FL quenching results were found to fit the Stern–Volmer (S–V) relationship in the range of 0.5–50 μg mL−1 with a correlation coefficient of 0.9997. The limit of detection (LOD) was 0.008 μg mL−1. The method based on FL quenching was successfully applied for the quantitative analysis of Cr(VI) in water samples collected from different environments.

Off–on fluorescent polyanthracene for recognition of ferric and fluoride ions in aqueous acidic media: application in pharmaceutical and environmental analysis

Fluorescent polyanthracene prepared by a chemical oxidative route was shown to sense ferric ions (Fe3+) in aqueous acidic solutions. The fluorescence titration indicates that the intensity of fluorescence of the polyanthracene (PAT) was gradually quenched by the successive addition of an Fe3+ ion solution (‘Off-fluorescence’). The fluorescence quenching data fit well into the conventional Stern–Volmer relationship. A mechanism of Photoinduced Electron Transfer (PET) is proposed to explain the observed ‘Off fluorescence’ state of the PAT. Based on the strong affinity of Fe3+ to F− ions, the mixture of polyanthracene–F− ions exhibiting ‘On fluorescence’, could behave as a fluorescent ‘On type probe’. Thus a method using a single probe for the detection of both Fe3+ and F− ions is developed using a fluorescence ‘Off–On’ approach, and is successfully applied for the determination of these ions in commercial samples.