Fluorescence Enhancement Based Quantification of Human Serum Albumin from Biological Sample Using Indole Based Nanosuspension: Molecular Interactions and Molecular Docking Studies.

Fluorescent 3-[(E)-(2-phenylhydrazinylidene) methyl]-1H-indole (PHI) was synthesized by condensation of indole-3-carboxaldehyde and phenyl hydrazine in presence of acetic acid and ethanol and after spectral characterization used further to prepare its aqueous nano suspension by reprecipitation method using polyvinylpyrrolidone (PVP) as stabilizer. The average particle size of nano suspension measured by Dynamic Light Scattering (DLS) was found 77.5 nm while FESEM microphotograph showed spherical morphology. The blue shift in the absorption spectrum and stokes shifted fluorescence of nanosuspension of PHI compared to its monomer spectrum in dilute solution indicate formation of H-type aggregate by face to face overlapping of the molecules.The aggregation induced enhanced emission (AIEE) of PVP capped nanosuspension of PHI is increased appreciably by presence of aqueous solution of human serum albumin (HSA). A suitable mechanism of molecular binding interactions based on complex formation between PHI nanoaggregate and HSA through PVP is proposed. Fluorescence life time, zeta potential and particle size data of PHI nanoparticles (PHINPs) obtained in presence of different amounts of HSA are in support of molecular interactions leading to complex formation. The molecular docking studies showed that HSA and PVP capped PHINPs exhibit strong hydrogen bonding interaction. The fluorescence enhancement effect induced in PHI nanosuspension is used further to develop analytical method for quantitative estimation of HSA in aqueous biological sample solution.

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.

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.

A novel pyrimidine derivative as a fluorescent chemosensor for highly selective detection of aluminum (III) in aqueous media.

An efficient fluorescent chemosensor Al(3+) receptor based on pyrimidine derivative,2-amino-6-hydroxy-4-(4-N,N-dimethylaminophenyl)-pyrimidine-5-carbonitrile (DMAB), has been synthesized by three-component condensation of aromatic aldehyde, ethyl cyanoacetate and guanidine hydrochloride in ethanol under alkaline medium. High selectivity and sensitivity of DMAB towards Aluminum ion (Al(3+)) in water: ethanol and acetate buffer at pH 4.0 makes it suitable to detect Al(3+) with steady-state UV-vis and fluorescence spectroscopy. Method shows good selectivity towards Al(3+) over other coexisting metal ions tested, viz. Fe(2+), Ni(2+), Cu(2+), Co(2+), Pb(2+), Sb(3+), Na(+), Ca(2+), Mg(2+), Zn(2+), Hg(2+), Ba(2+), Cd(2+) and K(+). A good linearity between the Stern-Volmer plots of F0/F versus concentration of Al(3+) was observed over the range from 10 to 60 µg mL(-1) with correlation coefficient of 0.991. The accuracy and reliability of the method were further confirmed by recovery studies via standard addition method with percent recoveries in the range of 101.03-103.44% and lowest detection limit (LOD=7.35 µg mL(-1)) for Al(3+) was established. This method may offer a new cost-effective, rapid, and simple key to the inspection of Al(3+) ions in water samples in the presence of a complex matrix and can be capable of evaluating the exceeding standard of Al(3+) in environmental water samples. The probable mechanism for fluorescence quenching was also discussed.

Fluorescence enhancement effect for the determination of adenosine 5'-monophosphate with 9-anthracene carboxylic acid-cetyl trimethyl ammonium bromide system.

A fluorimetric method based on fluorescence enhancement effect was developed for the determination of adenosine 5'-monophosphate (AMP) with 9-anthracene carboxylic acid (9-ANCA)-cetyl trimethyl ammonium bromide (CTAB) system. Fluorescence intensity of 9-ANCA was decreased by the addition of CTAB but addition of AMP again rose the intensity of 9-ANCA gradually. The observed fluorescence enhancement is attributed to the competitive binding reaction of 9-ANCA and adenosine to CTAB. The enhancement in the fluorescence intensity was found proportional to the concentration of AMP over the range 2.0 × 10(-4) to 1.2 × 10(-3) mol dm(-3). The ion pair complex is formed spontaneously between 9-ANCA and CTAB. Since the binding interaction is larger for the adenosine-CTAB pair, the fluorophore 9-ANCA will be released. The quantum yield of free 9-ANCA is higher therefore its fluorescence observed at 417 nm wavelength is enhanced. This mechanism of competitive molecular interaction is further confirmed by conductometric measurements. The method was applied successfully for the determination of AMP from pharmaceutical sample. The method is more selective, sensitive and relatively free from interferences.