Anionic micelle-induced fluorescent sensor activity enhancement of acridine orange: Mechanism and pH effect

Fluorescence Quenching of Carbazole by Selected Phenols in a Cationic Micellar System of Cetyltrimethyl Ammonium Bromide (CTAB)

A group of selected phenols i.e., picric acid, p-Nitrophenol, m-Nitrophenol, o-Nitrophenol, and phenol interactions were studied with a fluorescent probe carbazole in a micellar system of CTAB. CTAB concentration was optimized for maximum quenching of carbazole for each studied phenol. Interaction was studied in 0.02 and 0.1 mol/dm³ CTAB. All the studied phenols resulted in the quenching of carbazole in both CTAB concentrations though lower CTAB concentration was found optimum for highest quenching of the probe carbazole. Carbazole fluorescence quenching with phenols were explained with the help of Stern-Volmer equation that produced the constants of Stern-Volmer ([Formula: see text]). [Formula: see text] shows the sensitiveness of the method for the studied phenol and were observed in the order picric acid > phenol > m-Nitrophenol > p-Nitrophenol > o-Nitrophenol. Detection threshold (DT) and quantification threshold (QT) were observed in the order 1.76 [Formula: see text] 10^-7 - 6.30 [Formula: see text] 10^-7 mol/dm³ and 5.898 [Formula: see text] 10^-7 - 2.11 [Formula: see text] 10^-6 mol/dm³ respectively. The method is reproducible and is effective for the determination of studied phenols in the samples.

The vibronic absorption spectra and electronic states of acridine orange in aqueous solution

The time-dependent density functional theory (TD-DFT) was used to obtain vibronic absorption spectra of acridine orange dye (AO) in an aqueous solution that were in good agreement with the experiment. The protonated and neutral forms of the dye have been investigated. The results of calculations using various functionals and basis sets have been analyzed. The best agreement with experiment was given by the level of theory X3LYP/6-31G(d,p). AO molecular orbitals involved in electronic transitions due light absorption in the visible region of the spectrum have been obtained. The dipole moments and atomic charges of the ground and excited states of the AO molecule have been calculated. Maps of the electrostatic potential have been drawn. An insignificant photoinduced electron transfer was found in the central ring of the chromophore of the dye molecule. According to our calculations, the vibronic coupling and the Boltzmann distribution play a significant role in the absorption spectra of the AO.

Pendant-drop method coupled to ultraviolet-visible spectroscopy: A useful tool to investigate interfacial phenomena

UV-vis spectroscopy is a powerful tool to investigate surface phenomena. Surface tension measurements coupled to spectroscopic techniques can help to elucidate how the interface organization influences the electronic properties of molecules. However, appreciable sample volumes are usually necessary to achieve strong signals during conduction of experiments. This study reports on the simultaneous acquisition of surface tension data and UV-vis spectra by axisymmetric drop shape analysis (ADSA) coupled to diffuse reflectance (DRUV) spectrophotometry using a pendant microliter-drop that requires small sample volumes and low analyte concentrations. Three example systems gave evidence of the applicability of this technique: (a) disaggregation of an organic dye driven by surfactant as a function of the surface tension and alterations in the UV-vis spectra, (b) activity of a glycosylphosphatidylinositol anchored enzyme estimated from formation of a colored product, and (c) interaction between this enzyme and biomimetic membrane systems consisting of dipalmitoylphosphaditylcholine and cholestenone. Apart from using smaller sample volume, this coupled technique allowed to investigate interfacial organization in the light of electronic spectra obtained in loco within a shorter acquisition time. This procedure provided precise interfacial information about static and dynamic systems. This has been the first study describing the kinetic activity of an enzyme in the presence of phospholipid monolayers through simultaneous determination of the surface tension and UV-vis spectra.

Delivery of fluorophores by calcium phosphate-coated nanoliposomes and interaction with Staphylococcus aureus biofilms

The delivery capacity and mechanical stability of calcium phosphate (CaP) coated 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) liposomes free and adsorbed on bacterial surface was investigated introducing either acridine orange (AO) or 5,10,15,20-Tetrakis(1-methyl-4-pyridinio)porphyrin (TMP) in the aqueous core of the liposomes. The obtained nanomaterials were thoroughly characterized by electron and optical microscopy and by fluorescence techniques. Distribution of the AO and TMP molecules between the aqueous liposomes core and the outer solution was demonstrated by the band shifts and broadening of the excitation-emission matrices and the modified Stern-Volmer model for fluorescence quenching. In aqueous suspensions, c.a. 40% of AO was released to the outer solution while only a small percentage of TMP was observed to reach the outer liposome surface. The nanoliposomes adhesion capacity and the leaking of fluorophore molecules to Staphylococcus aureus (S. aureus) biofilms were further evaluated. A close interaction between liposomes and S. aureus biofilm was evidenced by TEM and SEM imaging. Epifluorescence experiments demonstrated that CaP-coated liposomes have good biofilm staining capability after two hours incubation of the biofilms with the liposomes, thus supporting an important release of the fluorophores when in contact with the biofilm. Altogether, the obtained results strongly suggest that CaP-coated liposomes are capable of activating drug release when in presence of S. aureus biofilms and smears. The studies herein presented, indicate that CaP-coated liposomes are potential vehicles for the selective delivery of drugs to S. aureus biofilms, as is the case of the singlet oxygen photosensitizer TMP, a well known photodynamic antibacterial agent.

Bispyrene/surfactant-assembly-based fluorescent sensor array for discriminating lanthanide ions in aqueous solution

Lanthanides are valuable nonrenewable resources and widely used in a variety of industries. Detection and identification of lanthanide ions are in high demand but challenging because of the similarity among lanthanide ions. In the present work, a fluorescent sensor array of three cationic bispyrene derivatives mixed with anionic surfactant assemblies was developed. The sensor array exhibits cross-reactive responses to lanthanide ions when tested in aqueous solution. The combination of fluorescence variations at both monomer and excimer emission of each of the bispyrene sensor elements provides a six-signal recognition pattern for lanthanide ions. Principle component analysis illustrates that the sensor array could at least identify 6 of the 14 similar lanthanide ions including La(3+), Pr(3+), Nd(3+), Eu(3+), Ho(3+), and Er(3+). UV-vis absorption measurements rule out the possibility of binding lanthanides with fluorophores. Fluorescence titration experiments in both cationic and neutral surfactant aqueous solutions reveal that the three fluorophores show slight fluorescence responses to the lanthanide ions, indicating that electrostatic attraction between lanthanide ions and anionic surfactant plays an important role in the sensing behavior of the sensor array. Control experiments with divalent metal ions find no cross-reactive responses, suggesting that the stronger electrostatic interaction with trivalent lanthanide ions is responsible for the multiple fluorescence responses.

Control of H-dimer formation of acridine orange using nano clay platelets

Acridine orange (AO) forms dimer even in aqueous solution. In layer-by-layer (LbL) film of AO dimeric sites predominate over monomeric sites. This communication reports the control of H-dimer of AO in LbL film by incorporating nano clay platelets. This was studied by using UV-Vis absorption spectroscopy. Atomic force microscopic (AFM) image of the LbL film was taken to confirm the presence of nano clay platelets in the LbL film.

Investigating the binding of acridine, acridine orange, and acridine yellow G to humic acid through fluorescence quenching

A fluorescence quenching method was used to determine the equilibrium binding constants for the association of acridine, acridine orange, and acridine yellow G to humic acid. The fluorescence of each polycyclic aromatic nitrogen heterocycle (PANH) was monitored as aliquots of humic acid were added, and a Stern-Volmer plot was produced in which the slope is the equilibrium constant of the binding reaction. The quenching experiments were performed at temperatures of 30, 35, 40, and 45 °C. A van't Hoff plot generated from the equilibrium binding constants as a function of temperature for a given PANH resulted in a linear plot. Calculation of the ΔHbinding, ΔGbinding, and ΔSbinding for each PANH leads to the conclusion that the equilibrium binding constant, and ΔGbinding, may be predictors of bioavailability. The other thermodynamic quantities, ΔHbinding and ΔSbinding, are helpful in understanding the relative binding of the compounds. For example, acridine yellow G appears to be the least bioavailable of the three PANHs studied because of its strong ΔHbinding = -29.8 kJ/mol, which leads to ΔGbinding = -0.71 kJ/mol. While acridine orange and acridine have similar ΔHbinding values, acridine orange is more likely to bind to humic acid because the ΔSbinding for the process is less negative. Thermodynamic values and equilibrium binding constants for all three compounds are reported.

A simple approach to detect caffeine in tea beverages

The photophysical properties of commercially available dye Acridine Orange (AO) describe an excellent probe for selective and sensitive detection of caffeine in aqueous solution. AO exists in monomer-dimer equilibrium in water. AO monomer is a fluorophore, but the dimer is not. Addition of caffeine to the AO leads to a shift in the monomer-dimer equilibrium toward the direction of AO monomer (fluorophore) and results in enhancement of AO fluorescence intensity. Enhancement of AO fluorescence intensity in the presence of caffeine has been treated as a signal for caffeine sensor. Furthermore, the caffeine-induced shift in AO monomer-dimer equilibrium is attributed to the binding of caffeine with AO monomer, and the binding constant was higher at a low pH range (pH ~2) compared to pH ~7, which results in superior caffeine sensitivity at pH ~2. Finally, caffeine content in commercial tea beverages has been evaluated and compared with the value obtained with a standard HPLC method.