Prasad G. Mahajan

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.

Selective sensing of Fe2+ ions in aqueous solution based on fluorescence quenching of SDS capped rubrene nanoparticles: application in pharmaceutical formulation

The nanoparticles of highly fluorescent rubrene prepared by reprecipitation method using sodium dodecyl sulphate (SDS) exhibited narrower particle size distribution when examined by the Dynamic Light Scattering (DLS) technique. The average particle size obtained is 87.2 nm and the zeta potential −13.8 mV given by a zetasizer indicated that the rubrene nanoparticles (RUBNPs) entrapped in SDS surfactant are negatively charged therefore changing the photo absorption and emission properties of the aqueous suspension of nanoparticles. The red shifted UV-photo absorption band of RUBNPs in comparison with the absorption band of rubrene in tetrahydrofuran (THF) solution is because of J-type aggregates in the aqueous suspension of nanoparticles, which also results in Aggregation Induced Enhanced Emission (AIEE) at λmax = 564 nm. The presence of Fe2+ in the aqueous suspension of RUBNPs showed quenching of fluorescence at 564 nm and the quenching results fit into a conventional Stern–Volmer relation in the concentration range of 0–80 μg mL−1 of Fe2+ ions solution with a good linear relationship. The possible mechanism of fluorescence quenching of RUBNPs is explained by considering the adsorption of the Fe2+ cation electrostatically on the negatively charged surface of the nanoparticle generated by SDS capping. The proposed sensing method of RUBNPs for selective detection of Fe2+ ion is successfully applied for the quantification of Fe2+ from pharmaceutical tablets.

Pyrene nanoparticles as a novel FRET probe for detection of rhodamine 6G: spectroscopic ruler for textile effluent

An aqueous suspension of pyrene nanoparticles (PyNPs) stabilized by sodium lauryl sulfate exhibit red shifted aggregation induced enhanced emission (AIEE) in the spectral region where Rhodamine 6G (R6G) absorbs strongly. Dynamic light scattering results of the aqueous suspension show a narrow particle size distribution with an average size of 38 nm and the zeta potential of −22 mV predicted a high degree of stability and surface charge modification of the nanoparticles. The negative zeta potential allowed cationic R6G to adsorb on the oppositely charged surface of the nanoparticles and both the molecules bind within the close distance required for efficient fluorescence resonance energy transfer (FRET) to take place from PyNPs to R6G. Systematic FRET experiments performed by measuring quenching of fluorescence of PyNPs with successive addition of R6G solution exploited the use of the PyNPs as a novel probe first time for the detection and estimation of R6G from textile effluents with a Limit of Detection (LOD) equal to 8.905 × 10−6 mol L−1 by fluorimetric measurements. The quenching results obtained at different constant temperatures were found to fit the well-known Stern–Volmer relation and were used further to estimate photokinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (ΔH), Gibbs free energy change (ΔG) and entropy change (ΔS). The mechanism of binding and quenching of fluorescence of PyNPs by R6G is proposed based on the thermodynamic parameter, the energy transfer efficiency, critical energy transfer distance (R0) and distance of approach between donor–acceptor molecules (r). The fluorescence quenching results are used further to develop analytical methods for estimation of R6G from industrial textile effluents.

Polyvinyl pyrrolidone capped fluorescent anthracene nanoparticles for sensing fluorescein sodium in aqueous solution and analytical application for ophthalmic samples.

Based on the known complexation ability between polyvinyl pyrrolidone (PVP) and fluorescein sodium (FL Na(+)), fluorescent PVP capped anthracene nanoparticles (PVP-ANPs) were prepared using a reprecipitation method for detection of fluorescein in aqueous solution using the fluorescence resonance energy transfer (FRET) approach. A dynamic light scattering histogram of PVP-ANPs showed narrower particle size distribution and the average particle size was 15 nm. The aggregation-induced enhanced emission (AIEE) of PVP-ANPs was red shifted from its monomer by 1087.22 cm(-1). The maximum emission was seen to occur at 420 nm. The presence of FL Na(+) in the vicinity of PVP-ANPs quenched the fluorescence of PVP-ANPs because of its adsorption on the surface of PVP-ANPs in aqueous suspension. The FL Na(+) and PVP-ANPs were brought close enough, typically to 7.89 nm, which was less than the distance of 10 nm that is required between the energy donor-acceptor molecule for efficient FRET. The quenching results fit into the Stern-Volmer relationship even at temperatures greater than ambient temperatures. The thermodynamic parameters determined from FRET results helped to propose binding mechanisms involving hydrophobic and electrostatic molecular interaction. The fluorescence quenching results were used further to develop an analytical method for estimation of fluorescein sodium from ophthalmic samples available commercially in the market.

Fluorimetric detection of Sn2 + ion in aqueous medium using Salicylaldehyde based nanoparticles and application to natural samples analysis

The fluorescent 2-[(E)-(2-phenylhydrazinylidene)methyl]phenol nanoparticles (PHPNPs) were prepared by a simple reprecipitation method. The prepared PHPNPs examined by Dynamic Light Scattering show narrower particle size distribution having an average particle size of 93.3nm. The Scanning Electron Microphotograph shows distinct spherical shaped morphology of nanoparticles. The blue shift in UV-absorption and fluorescence spectra of PHPNPs with respect to corresponding spectra of PHP in acetone solution indicates H- aggregates and Aggregation Induced Enhanced Emission (AIEE) for nanoparticles. The nanoparticles show selective tendency towards the recognition of Sn(2+) ions by enhancing the fluorescence intensity preference to Cu(2+), Fe(3+), Fe(2+), Ni(2+), NH4(+), Ca(2+), Pb(2+), Hg(2+) and Zn(2+) ions, which actually seem to quench the fluorescence of nanoparticles. The studies on Langmuir adsorption plot, fluorescence lifetime of PHPNPs, DLS-Zeta sizer, UV-visible and fluorescence titration with and without Sn(2+) helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Sn(2+) and their binding ability during complexation. The fluorescence enhancement effect of PHPNPs induced by Sn(2+) is further used to develop an analytical method for detection of Sn(2+) from aqueous medium in environmental samples.

A highly selective and sensitive single click novel fluorescent off–on sensor for copper and sulfide ions detection directly in aqueous solution using curcumin nanoparticles

Based on curcumin nanoparticles (CURNPs) in the aqueous system a fluorescent nanosensor was prepared by a simple reprecipitation method and characterized. It can display off-type fluorescence with high selectivity toward Cu2+ among other metal ions in aqueous solution having an excellent detection limit. Furthermore, the in situ generated CURNPs–Cu2+ ensemble could recover the quenched fluorescence upon the addition of S2− resulting in an on-type sensing with a detection limit in the nanogram range in the same medium, which overcomes the detection limit of the method reported in the literature. No interference was observed from other anions, making it a highly sensitive and selective sulfide probe. The fluorescence lifetime, particle size and zeta potential studies of CURNPs with and without Cu2+ and S2− helped to propose a suitable mechanism of fluorescence ‘off–on’ of nanoparticles by Cu2+ and S2−. In addition, the stoichiometry and binding ability of CURNPs during complexation with Cu2+ was estimated by Jobs, Hills and Benesi–Hildebrand plots. The fluorescence ‘off–on’ results are used further to develop analytical methods for estimation of Cu2+ and S2− ions from environmental water samples without any interference.

TNPs as a novel fluorescent sensor for the selective recognition of fast green FCF: a spectrofluorimetric approach

Fluorescent tetracene nanoparticles (TNPs) have been prepared by a reprecipitation method using cetyl trimethyl ammonium bromide (CTAB) as a stabilizer. These TNPs are more photostable against photobleaching and have a high solubility in water, minimizing the utilization of hazardous organic solvents when compared with single organic fluorophores in sensing applications. The method is based on the fluorescence quenching of the TNPs, which are used as a novel fluorescent sensor for the selective recognition of the fast green FCF dye in aqueous solution. The fluorescence intensity of the TNPs was quenched by the successive addition of increasing concentrations of the fast green FCF dye. The fluorescence quenching results were found to fit the Stern–Volmer (S–V) relationship in the range of 0.5–7.0 µg L−1 with a correlation coefficient of 0.999. The limit of detection (LOD) was 0.136 µg L−1. Moreover, the excited state lifetime of the TNPs remains unchanged even after increasing the concentration of the fast green FCF dye, which suggests that the fast green FCF dye was adsorbed over the surface of the nanoparticles to form a non-fluorescent ground state complex i.e. the nature of the quenching process is static. The proposed method was successfully applied for the quantitative analysis of the fast green FCF dye in commercial samples with no necessity of prior separation of analyte molecules from the interfering constituents.

Carbazole based nanoprobe for selective recognition of Fe3 + ion in aqueous medium: Spectroscopic insight

A simple carbazole based nanoprobe prepared by reprecipitation method shows selective sensing behavior for Fe3+ ion in aqueous medium. The prepared SDS capped 9-phenyl carbazole nanoparticles (9-PCzNPs) has narrower particle size distribution with an average diameter 35nm and zeta potential of -34.3mV predicted a good stability with negative surface charge over the nanoparticles. The Field Emission Scanning Electron Microscopy (FE-SEM) image showed cubic shape morphology of nanoparticles. The aqueous suspension of SDS capped 9-phenyl carbazole nanoparticles exhibited aggregation induced enhanced red shifted intense emission in comparison with the emission arising from dilute solution of 9-phenyl carbazole in DCM. The cation recognition test based on fluorescence change shows Fe3+ ion induce significant fluorescence quenching, however remaining cations responds negligibly. The obtained quenching data fit into Stern-Volmer relation in the concentration range of 0.0-1.0μg·mL-1 of Fe3+ ion solution and the detection limit is 0.0811μg·mL-1. The probable mechanism of fluorescence quenching of SDS capped 9-PCzNPs is because of adsorption of Fe3+ ion over the negatively charged surface of NPs through electrostatic interaction. Thus the proposed method was successfully applied for the detection of Fe3+ ion in environmental water sample.

Serendipitous formation of novel class of dichromeno pyrano pyrimidinone derivatives possessing anti-tubercular activity against M. tuberculosis H 37 Rv

One pot three-component reaction of salicylaldehyde, barbituric acid, and 4-OH coumarin catalyzed by ionic liquid, 1-(ethylaceto acetate)-1-(2-hydroxyethyl) piperidinium tetrachloroaluminate [EAHEPiPY]+ [AlCl4]− in water resulted into unexpected formation of a novel class of dichromeno pyrano pyrimidinone derivatives. Synthesized compounds exhibited excellent in vitro anti-tubercular activity against M. tuberculosis H37Rv.Graphical abstract