Fluorescence-based logic gate for sensing of Ca2+ and F- ions using PVP crowned chrysene nanoparticles in aqueous medium.

Polyvinyl pyrrolidone (PVP) crowned chrysene nanoparticles (CHYNPs) were prepared by using a reprecipitation method. Dynamic light scattering (DLS) and scanning electron microscope (SEM) studies indicate that the monodispersed spherical nanoparticles bear a negative charge on their surfaces. The bathochromic spectral shift in the UV-visible and fluorescence spectrum of CHYNPs from chrysene (CHY) in acetone solution supports the J- type aggregation of nanoparticles. The aggregation-induced enhanced emission of CHYNPs at 486 and 522 nm decreases by increasing the concentration of the Ca2+ ion solution. It can display an ON-OFF type fluorescence response with high selectivity towards Ca2+ ions aqueous medium. Furthermore, the in situ generated PVP-CHYNPs-Ca2+ ensemble could recover the quenched fluorescence upon the addition of fluoride anions resulting in an OFF-ON type sensor. The present method has a correlation coefficient R2 = 0.988 with a detection limit of 1.22 µg/mL for Ca2+ in the aqueous medium. The fluorescence changes of PVP crowned CHYNPs upon the addition of Ca2+ and F- can be utilized as an INHIBIT logic gate at the molecular level, using Ca2+ and F- chemical inputs and the fluorescence intensity signal as output.

Fluorescence resonance energy transfer from tryptophan to folic acid in micellar media and deionised water.

The fluorescence resonance energy transfer (FRET) from tryptophan (Trp) to folic acid (FA) in aqueous sodiumdodecyl sulphate, cetyltrimethyl ammonium bromide, and Brij-35 as well as deionised water was investigated using steady state and time resolved fluorescence techniques. The data obtained from steady state fluorescence spectral studies and time resolved measurement indicated that the FRET from Trp to FA occurred most effectively in aqueous sodium dodecyl sulphate micellar solutions. The distance between Trp and FA were evaluated. Binding constant, number of binding sites and thermodynamic parameters were determined for Trp-FA interactions in deionised water. The values of the thermodynamic parameters suggest that the hydrophobic forces and hydrogen bonding are the key interacting forces between Trp-FA interaction.

Spectrofluorimetric determination of 5-fluorouracil by fluorescence quenching of 9-anthracenecarboxylic acid.

Photo-induced intermolecular electron transfer (PET) interaction between excited singlet (S(1)) state of 9-anthracene carboxylic acid (9-ANCA) and DNA bases of pyrimidines as uracil and 5-fluorouracil (5-FU) has been studied in water and ethanol solutions using steady-state fluorescence spectroscopy. The intensity of all emission bands of 9-ANCA was quenched in presence of uracil and 5-FU by electron transfer reaction without formation of an exciplex. It was found that uracil and 5-fluorouracil acts as effective electron donors and simultaneously quench the fluorescence of electron-accepting sensitizer 9-ANCA. The quenching by diffusion-controlled rate coincides well with the dynamic Stern-Volmer correlation. The bimolecular quenching rate constant (k(q)(ss)) and electron transfer rate constant (k(et)) observed are seen to be much higher for 5-fluorouracil than those for uracil. The thermodynamic parameters estimated by using the Rehm-Weller equation were used to propose a suitable mechanism for PET occurring between uracils and 9-ANCA. The proposed method was used to determine 5-fluorouracil from pharmaceutical samples with satisfactory results. The technique is more selective, sensitive and relatively free from coexisting substances.

Interaction between felodipine and bovine serum albumin: fluorescence quenching study.

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.

Spectroscopic studies on the interaction between norfloxacin and p-amino benzoic acid: analytical application on determination of norfloxacin.

Fluorescence (Förster) Resonance Energy Transfer (FRET) between norfloxacin (NF) and p-amino benzoic acid (PABA) has been investigated by fluorescence and UV-vis absorption spectroscopy. It was found that the quenching of fluorescence of PABA is followed by simultaneous sensitization of NF fluorescence. The hydrophobic and electrostatic interaction plays an important role to stabilize the complex. The binding constant (K), binding site number (n) and corresponding thermodynamic parameters like free energy change (DeltaG), enthalpy change (DeltaH) and entropy change (DeltaS) were determined according to van't Hoff equation. Using FRET, the distance (r) between donor (PABA) and acceptor (NF) was obtained. This method is simple, selective and relatively free of interference from co-existing substances. The method was successfully applied to the determination of norfloxacin from pharmaceutical tablets.