Steady-state Fluorescence Methods Research Articles

Detailed physicochemical study and thermodynamic aspects of the interaction between nonionic cellulose derivative hydroxyethyl cellulose and anionic surfactant sodium N-dodecanoyl sarcosinate in aqueous media

BackgroundThe scheme of this work was to study the interaction between hydroxyethyl cellulose (HEC), a non-ionic, water soluble biopolymer and sodium N-dodecanoyl sarcosinate (SDDS), a novel, environmentally friendly amino acid-based anionic surfactant in aqueous medium. The study of this type of interaction is relatively less complicated compared to that between a polymer and a surfactant with opposite charges. MethodsThe critical micelle concentration (CMC) of HEC-induced SDDS has been determined by various physicochemical methods such as tensiometry, conductometry, fluorimetry and microcalorimetry. Several thermodynamic and surface parameters related to the binding of SDDS with HEC have been assessed. The aggregation number (Nagg) of SDDS micelles in the presence of non-ionic HEC polymer has been measured by the steady-state fluorescence method. The hydrodynamic diameter (Dh) and zeta potential (ζ) of the polymer-surfactant aggregate have been measured by the dynamic light scattering method. The interaction study has further been amplified by detecting the change in the surface morphology of the polymer due to surfactant binding using Field Emission Scanning Electron Microscopy (FESEM) and high resolution transmission electron microscopy (HR-TEM) imaging in solvent-free state, as well as visualization of the HEC-SDDS micelle in the solution phase using fluorescence microscopy technique. Significant findingsFrom a physicochemical point of view, hydrophobic synergism seems to be important for understanding the interaction pattern of HEC-SDDS combination. In each scenario, the CMC of SDDS decreases with an increase in weight percentage of HEC. The aggregation number (Nagg) of SDDS micelles is also found to decrease with an increase in weight percentage of HEC in the medium. The hydrodynamic diameter (Dh) and zeta potential (ζ) of the polymer-surfactant aggregate, these two parameters have been found to be strongly dependent on the amphiphile concentration. Finally, investigations of the surface morphologies by taking Field Emission Scanning Electron Microscopy (FESEM), high resolution transmission electron microscopy (HR-TEM) and fluorescence microscopy techniques assist the experimental data.

Size-dependent solvatochromism of CdS nanoparticles: Experimental absorption and fluorescence analyses

Owing to the quantum confinement effect, a nanocrystal shows a unique blend of molecular and solid properties: discrete energy levels with large polarizabilities which could respond to solvent environments. In this paper, we used steady-state fluorescence and absorption spectroscopy to study the size-dependent solvatochromism of CdS nanoparticles. The dipolar character of the ground state and the first excited state of the nanoparticle were also investigated with in the framework of Onsager reaction field theory using Ooshika–Mataga–Lippert equation. The results of the present study revealed that the solvatochromic responses were size dependent. Additionally, the responses increased with the particle size up to a certain size beyond which the response started to fall again. Hence, fine-tuning the nanoparticle's solvatochromic response and band gap is possible by appropriate choice of size. Moreover, size-dependent dipole moment values of CdS nanoparticles were determined. Based on the findings of the present study it was noted that steady-state fluorescence and absorption spectroscopy methods can efficiently be used to study the size-dependent solvatochromism of CdS nanoparticles.

Detail study on the interaction between perfluorooctanoic acid (PFOA) with human hemoglobin (Hb)

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are often referred to as legacy perfluoroalkyl substances (PFAS). Human exposure to PFAS leads to severe negative health impacts including cancers, infertility, and dysfunction in the kidneys. Steady-state absorbance, fluorescence, and circular dichroism (CD) methods were used to study the interactions between PFOA and Hb. The results demonstrate the presence of multiple PFOA binding sites on the Hb protein. The detailed analysis of the ferric hemoglobin protein (met Hb) absorbance data as a function of PFOA concentration indicates the presence of at least two binding sites with equilibrium dissociation constants of 0.8 ± (0.2) × 10−6 M and 63 ± (15) × 10−5 M. A competitive binding study with 1,8-ANS showed PFOA can bind to the same binding site as 1,8-ANS on the Hb protein. The titration curve for PFOA binding to Hb in its CO bound form (CO-Hb) yields a single equilibrium dissociation constant of 139 ± (20) × 10−6 M. PFOA binding at low concentrations occurs at the high-affinity sites leading to the destabilization of the protein structure as reflected by changes in the CD spectrum. PFOA interactions with Hb also interfere with the kinetics of CO association to this protein. The rate for CO association to Hb increases at low PFOA concentrations, whereas at elevated PFOA concentrations, the ligand association is biphasic as a new kinetic process with a different rate constant was observed. Overall, this study provides a detailed explanation of PFOA-induced structural and conformational changes to the Hb protein based on the spectroscopy data.

Micellization Behavior of Conventional Cationic Surfactants within Glycerol-Based Deep Eutectic Solvent.

The aggregation behavior of two cationic surfactants, i.e., cetyldimethylethanolammonium bromide (CDMEAB) and cetyltributylphosphonium bromide (CTBPB), within an aqueous deep eutectic solvent (DES) is studied. The synthesized DES is composed of 1:2 mole ratio of choline chloride and glycerol and is further characterized by Fourier transform infrared (FTIR) and 1H NMR spectroscopy techniques. The critical micellar concentration (CMC), micellar size, and intermolecular interaction in surfactants within Gly-based DES solutions are investigated by various techniques including surface tension, conductivity, fluorescence, dynamic light scattering (DLS), FTIR, 1H NMR, and two-dimensional (2D) nuclear Overhauser effect spectroscopy (NOESY). The various interfacial properties and thermodynamic parameters are determined in the presence of 5 wt % glyceline (Gly)-based DES in an aqueous solution. The CMC, aggregation number (Nagg), and Stern–Volmer constant (Ksv) have also been determined by a steady-state fluorescence method. DLS is used to obtain information regarding the size of the aggregates formed by the cationic surfactants in DES solutions. FTIR spectroscopy is used to study the surfactant–DES interactions that tune the micellar structure of the surfactants within the Gly-based DES solution. The functional groups involved in the interactions (H-bonding and electrostatic) are the head groups (HO–CH2–CH2–N+ ion for CDMEAB and quaternary phosphonium (P+) ion for CTBPB) of the surfactants with the −OH-containing Gly DES. The hydrophobic moieties are involved in the hydrophobic interactions. The 1H NMR data show that differences in chemical shifts can provide significant information about the interactions taking place within the system. 1H NMR and NOESY techniques are further employed to strengthen our claim on the feasible structural arrangements within the aqueous surfactant–DES self-assembled structures. It is observed that both the cationic surfactants, i.e., CDMEAB and CTBPB, form self-assembled nanostructures in the Gly-based DES solutions. The present results are expected to be useful for colloidal solutions of DES and their mixtures with water.

Effect of Acetonitrile on the Colloidal Behavior of Conventional Cationic Surfactants: A Combined Conductivity, Surface Tension, Fluorescence and FTIR Study

A comprehensive study the effect of acetonitrile (ACN) with four cationic surfactants, viz. tetradecyltrimethylammonium bromide (TTAB), cetyltrimethylammonium bromide (CTAB), cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) was made by using the conductivity, surface tension, fluorescence and FTIR techniques. Significant micellar, interfacial and thermodynamic properties were studied by the tensiometeric and conductivity methods. The critical micelle concentration (CMC), aggregation number (Nagg), and Stern–Volmer constants (Ksv) have also been studied by the steady state fluorescence method using pyrene as probe. The fluorescence study also supports the CMC results obtained from conductivity and surface tension. FTIR was used to ascertain that the strength of intermolecular interactions such as hydrogen bonding, ion–ion pair interactions and induced dipole interactions between the surfactants and ACN depend upon the head-group of the surfactants. The interaction of surfactants with ACN is energetically favorable and occurs via direct interactions between the surfactants and ACN. The results further revealed that the strength of interactions between the surfactants and ACN follows the order: TTAB > CTAB > CPC > CPB.

Characterization of a New Electron Donor–Acceptor Dyad in Conventional Solvents and Ionic Liquids

Ionic liquids are being tested as potential replacements for current electrolytes in energy-related applications. Electron transfer (ET) plays a central role in these applications, making it essential to understand how ET in ionic liquids differs from ET in conventional organic solvents and how these differences affect reaction kinetics. A new intramolecular electron donor-acceptor probe was synthesized by covalently linking the popular photoacceptor coumarin 152 with the donor dimethylaniline to create the dyad "C152-DMA" for potential use in probing dynamical solvent effects in ionic liquids. Molecular dynamics simulations of this dyad show the considerable conformational flexibility of the linker group but over a range of geometries in which the ET rate parameters vary little and should have minimal effect on reaction times >100 ps. Steady-state and time-resolved fluorescence methods show the spectra of C152-DMA to be highly responsive to solvent polarity, with ET rates varying over the range of 108 to 1012 s-1 between nonpolar and high-polarity conventional solvents. The sensitivity to hydrolysis in the presence of acidic impurities limits the dyad's use to ionic liquids of high purity. The results in the few ionic liquids examined here suggest that in addition to solvent polarity, electron transfer in C152-DMA also depends on solvent fluidity or solvation times.

Effects of polymer concentration and type on the interactions between 1-methyl-3-tetradecylimidazolium bromide and polymers in aqueous solution

The interactions between the long-chain ionic liquid of 1-methyl-3-tetradecylimidazolium bromide (C14mimBr) and five polymers have been studied in detail using surface tension, electric conductivity, isothermal titration microcalorimetry (ITC), and steady-state fluorescence methods. The polymers used include neutral polymers of polyethylene glycol (PEG) and polyvinyl alcohol (PVA), triblock copolymers of PEO13PPO30PEO13 (L64) and PEO79PPO30PEO79 (F68), and polyelectrolyte of sodium carboxymethylcellulose (NaCMC). This paper focuses on the effects of polymer concentration and type on the surfactant-polymer interactions. The curves in the absence and in the presence of the polymer have more or less differences, exhibiting the cooperative interaction of the surfactant and five polymers. Although the effects of each polymer addition on the surfactant aggregates can be proved by various techniques, for one system, the inflection points on the curves from different method are difficult to unify and an attempt to show the concurrence of the data is only diluting the essence of this area. It is concluded that the interacting intensity between C14mimBr and the polymer has the order of NaCMC > L64 >F68 >PVA > PEG, which is determined by the strong electrostatic attraction, relatively strong hydrophobic interaction, and/or weak ion-dipole interaction relating to the polymer structure. Due to the precipitation formation of NaCMC and cationic surfactant aqueous solution, copolymers especially the existence of PPO chain not only has a good synergistic effect with surfactant, but also can adjust the viscosity of the system.

BODIPY parent compound: Excited triplet state and singlet oxygen formation exhibit strong molecular oxygen enhancing effect

Excited triplet state (T1) properties and formation efficiency are key issues in photodynamic therapy (PDT) and organic light emitting diode (OLED). We report hereby the T1 properties, T1 formation efficiency and mechanism for BODIPY parent compound (BDP) using laser flash photolysis technique. We also disclose the singlet oxygen 1O2(1Δg) formation ability of BDP based on NIR phosphorescence and chemical trapping method. More importantly we show that molecular oxygen can strongly increase the T1 and singlet oxygen formation efficiency of BDP up to 5-fold compared to its intrinsic ability due to intersystem crossing. Combining with time-resolved and steady state fluorescence methods, we conclude that the oxygen enhancing mechanism is due to that the energy transfer from the excited singlet state (S1) of BDP to molecular oxygen leads to both T1 and 1O2 formation: BDP(S1) + O2 → BDP(T1) + 1O2(1Δg). This O2 enhancing mechanism for T1 and 1O2 formation is important to understand and design BODIPY photosensitizers in various applications including PDT and OLED.

Ultrafast electron-transfer in a fully conjugated coumarin-ferrocene donor-acceptor dyads

A series of a fully conjugated ferrocene-containing coumarins and B,O-chelated coumarins was prepared and characterized by a variety of spectroscopic (UV–vis, NMR, and mass spectrometry), electrochemical (CV and DPV) and spectroelectrochemical methods. The photophysical properties of the target compounds were investigated by steady-state fluorescence and ultrafast transient absorption spectroscopy methods. Selective photoexcitation of the coumarin core was followed by ultrafast electron transfer from the ferrocene fragment, resulting in formation of a charge-separated Fc+-coumarin-. state. This charge-separated state undergoes ultrafast ground state recovery in 20–25 ps, shortening the excited state lifetime of the organic coumarin precursors (1.2–1.5 ns) by almost two orders of magnitude. Formation of the charge-separated states was supported by the experimental (steady-state fluorescence oxidative titrations) and theoretical DFT and TDDFT calculations.

Studies on photosensitization of TiO2 nanoparticles by novel 1,3,4-oxadiazoles derivatives

In the present work, photosensitization of TiO2 nanoparticles (<25 nm) from three novel 1,3,4-oxadiazole derivatives namely TTO, TBO and TMO has been investigated using steady-state absorption, steady-state fluorescence and time-resolved fluorescence methods. Increase in absorbance and broadening of the absorption spectra for all the dyes in the presence of different concentrations of TiO2 nanoparticles confirm the possibility of interactions involving dyes and nanoparticles. Fluorescence quenching has been observed for all the dyes in the presence of colloidal TiO2 nanoparticles. Analysis of the cyclic voltammetric experimental data using Rehm-Weller relation shows that, fluorescence quenching is due to electron transfer from dye to TiO2 nanoparticles and confirms the photosensitization of TiO2 nanoparticles. Theoretical studies too confirmed the electron transfer from dye to TiO2 nanoparticles Hence, we infer that dyes used in the present studies may be useful for dye-sensitized solar cell (DSSC). Further, Stern-Volmer studies suggest that, the fluorescence quenching mechanism follows dynamic process along with minor static quenching. The apparent association constant (ks) of the interaction is also calculated using Benesi-Hildebrand model.

Comparative effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability of phospholipase A2

Herein, we have investigated the effect of cationic gemini surfactant (hexanediyl-α,ω-bis-(N-(2-hydroxyethyl)N-methylhexadecylammonium bromide), (16-6-16MEA) and its monomeric counterpart (N-(2-hyroxyethyl)N, N-dimethylhexadecylammonium bromide), (16MEA) on the conformational stability of phospholipase A2 (PLA2). The interaction of gemini surfactant and its monomeric counterpart with PLA2 was characterized by utilizing steady-state fluorescence, time-resolved fluorescence, CD spectroscopy, and computational methods. The steady-state fluorescence results suggested the involvement of static quenching mechanism which was further supported by time resolved fluorescence measurements. The Stern-Volmer equation was utilized to calculate the value of Stern-Volmer quenching constant KSV. The stoichiometric binding ratio of PLA2 with 16MEA and 16-6-16MEA was observed to be 1:1. The far-UV CD spectra for PLA2 revealed similar alteration in secondary structure, in presence of 16MEA and 16-6-16 MEA, which was further supported by computational methods.

Fluorimetric Studies of a Transmembrane Protein and Its Interactions with Differently Functionalized Silver Nanoparticles

Transmembrane proteins play important roles in intercellular signaling to regulate interactions among the adjacent cells and influence cell fate. The study of interactions between membrane proteins and nanomaterials is paramount for the design of nanomaterial-based therapies. In the present work, the fluorescence properties of the transmembrane receptor Notch2 have been investigated. In particular, the steady-state and time-resolved fluorescence methods have been used to characterize the emission of tryptophan residues of Notch2 and then this emission is used to monitor the effect of silver colloids on protein behavior. To this aim, silver colloids are prepared with two different methods to make sure that they bear hydrophilic (citrate ions, C-AgNPs) or hydrophobic (dodecanethiol molecules, D-AgNPs) capping agents. The preparation procedures are tightly controlled to obtain metal cores with similar size distributions (7.4 ± 2.5 and 5.0 ± 0.8 nm, respectively), thus, making the comparison of the results easier. The occurrence of strong interactions between Notch2 and D-AgNPs is suggested by the efficient and statistically relevant quenching of the stationary protein emission already at low nanoparticle (NP) concentrations (ca. 12% quenching with [D-AgNPs] = 0.6 nM). The quenching becomes even more pronounced (ca. 60%) when [D-AgNPs] is raised to 8.72 nM. On the other hand, the addition of increasing concentrations of C-AgNPs to Notch2 does not affect the protein fluorescence (intensity variations below 5%) indicating that negligible interactions are taking place. The fluorescence data, recorded in the presence of increasing concentrations of silver nanoparticles, are then analyzed through the Stern-Volmer equation and the sphere of action model to discuss the nature of interactions. The effect of D-AgNPs on the fluorescence decay times of Notch2 is also investigated and a decrease in the average decay time is observed (from 4.64 to 3.42 ns). The observed variations of the stationary and time-resolved fluorescence behavior of the protein are discussed in terms of static and collisional interactions. These results document that the capping shell is able to drive the protein-particle interactions, which likely have a hydrophobic nature.

Studies on the interaction between 7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one and cadmium sulfide quantum dots

Quantum dots (QDs) are well known for their optical properties which differ from those of bulk semiconductors. Herein, we have created an energy transfer platform that combines CdS QDs with a coumarin based dye C485 [7-(dimethyl amino)-4-(trifluoromethyl)-2H-1-benzopyran-2-one]. Spectroscopic studies of energy transfer between the dye donor and CdS QDs as acceptors reveal the occurrence of dynamic quenching. Analysis of the steady-state and time resolved fluorescence measurements of C485 in the presence of CdS QDs infers fluorescence resonance (Förster type) energy transfer (FRET) as responsible for the quenching phenomena. The energy transfer efficiency as well as energy transfer distance for the donor-acceptor pair is calculated using steady-state fluorescence method. Luminescence enhancement of CdS QDs play a critical role in device performance for solar applications and also in the field of biological applications.

Probing the stereoselective interaction of ofloxacin enantiomers with corresponding monoclonal antibodies by multiple spectrometry

Although stereoselective antibody has immense potential in chiral compounds detection and separation, the interaction traits between stereoselective antibody and the corresponding antigenic enantiomers are not yet fully exploited. In this study, the stereospecific interactions between ofloxacin isomers and corresponding monoclonal antibodies (McAb-WR1 and McAb-MS1) were investigated using time-resolved fluorescence, steady-state fluorescence, and circular dichroism (CD) spectroscopic methods. The chiral recognition discrepancies of antibodies with ofloxacin isomers were reflected through binding constant, number of binding sites, driving forces and conformational changes. The major interacting forces of McAb-WR1 and McAb-MS1 chiral interaction systems were hydrophobic force and van der Waals forces joined up with hydrogen bonds, respectively. Synchronous fluorescence spectra and CD spectra results showed that the disturbing of tyrosine and tryptophan micro-environments were so slightly that no obvious secondary structure changes were found during the chiral hapten binding. Clarification of stereospecific interaction of antibody will facilitate the application of immunoassay to analyze chiral contaminants in food and other areas.

Aggregation behaviors of amine-oxide gemini surfactants

ABSTRACTThe micellar aggregation of a series of gemini surfactants [N, N’-dimethyl-N, N’-bis(2-alkylamideethyl)-ethylenediamine oxide (alkyl = C11H23, C13H27, C15H31)] in aqueous media has been investigated. The results show that there is an excellent agreement among the critical micelle concentration (CMC) values obtained by surface tension and steady-state fluorescence methods. Because of the occurrence of self-coiling or the formation of pre-micellization, the CMC values, the I1/I3 values, and the micelle aggregation numbers (Nagg) at CMC (Nm) increase with the hydrophobic alkyl chain length increasing. Besides, vesicles are observed above the CMC for all these surfactants.

Enhance the fluorescence and singlet oxygen generation ability of BODIPY: Modification on the meso-phenyl unit with electron withdrawing groups

Abstract Herein, meso -R-carboxyphenyl substituted BODIPY compounds were synthesized and characterized (R = CH 3 , COOH, NO 2 , H and Br 4 ). The fluorescence, excited triplet state and singlet oxygen formation properties for these compounds were measured in nonpolar and polar solvents by UV–vis absorption, steady-state and time-resolved fluorescence methods, as well as laser flash photolysis technique. These BODIPYs exhibit very different fluorescence quantum yield and lifetime value, as well as singlet oxygen formation capability in polar solvents. In contrast, these compounds show very similar spectral shape and position, emit bright green fluorescence in non polar solvents. The introduction of an ortho -COOH on the benzene unit leads to a 20-fold increase in the fluorescence quantum yield. The further introduction of an electron withdrawing NO 2 or COOH on the phenyl makes the BODIPY dye show much higher capability to generate singlet oxygen (up to 5-fold increase) and causes a sharp decrease in both fluorescence quantum yield and lifetime value. The increase in solvent polarity enhances singlet oxygen generation and intramolecular fluorescence quenching. The results are explained by the presence of intramolecular photoinduced electron/charge transfer from BODIPY core to the carboxyphenyl moiety.

Photoinduced Electron Transfer-based Halogen-free Photosensitizers: Covalent meso-Aryl (Phenyl, Naphthyl, Anthryl, and Pyrenyl) as Electron Donors to Effectively Induce the Formation of the Excited Triplet State and Singlet Oxygen for BODIPY Compounds.

Pristine BODIPY compounds have negligible efficiency to generate the excited triplet state and singlet oxygen. In this report, we show that attaching a good electron donor to the BODIPY core can lead to singlet oxygen formation with up to 58 % quantum efficiency. For this purpose, BODIPYs with meso-aryl groups (phenyl, naphthyl, anthryl, and pyrenyl) were synthesized and characterized. The fluorescence, excited triplet state, and singlet oxygen formation properties for these compounds were measured in various solvents by UV/Vis absorption, steady-state and time-resolved fluorescence methods, as well as laser flash photolysis technique. In particular, the presence of anthryl and pyrenyl showed substantial enhancement on the singlet oxygen formation ability of BODIPY with up to 58 % and 34 % quantum efficiency, respectively, owing to their stronger electron-donating ability. Upon the increase in singlet oxygen formation, the fluorescence quantum yield and lifetime values of the aryl-BODIPY showed a concomitant decrease. The increase in solvent polarity enhances the singlet oxygen generation but decreases the fluorescence quantum yield. The results are explained by the presence of intramolecular photoinduced electron transfer from the aryl moiety to BODIPY core. This method of promoting T1 formation is very different from the traditional heavy atom effect by I, Br, or transition metal atoms. This type of novel photosensitizers may find important applications in organic oxygenation reactions and photodynamic therapy of tumors.

Analysis of the photophysical properties of zearalenone using density functional theory

The intrinsic photophysical properties of the resorcylic acid moiety of zearalenone offer a convenient label free method to determine zearalenone levels in contaminated agricultural products. Steady-state fluorescence and density functional methods were applied to investigate the role of structural chemistry on zearalenone detection. Geometry optimization calculations using the B3LYP density functional identified a tautomeric form of zearalenone. Excited state geometries for zearalenone and a tautomeric form were obtained by MNDO semi-empirical optimizations. Steady-state fluorescence studies suggest that fluorescence quenching at neutral pH is associated with water interactions. Time-dependent density functional and ground state calculations indicate that the anionic and dianionic forms of zearalenone possess lower band gaps, excitation energies, and the lowest unoccupied molecular orbitals are positioned over the non-fluorophoric portion of zearalenone. These results suggest that deprotonation of one or more of the phenolic hydroxyls diminishes the intensity of the fluorescence emission of zearalenone.

Charged and confused: Meso-tetrakis(p-methoxycarbonyl-phenyl) N-confused porphyrin as a precursor to water soluble variants

A metal-free meso-tetrakis([Formula: see text]-methoxycarbonylphenyl) N-confused porphyrin (1) was prepared as the precursor for water-soluble derivatives by the reaction between pyrrole, methyl-4-formylbenzoate, and MSA. Tautomeric behavior of the porphyrin 1 in polar and non-polar solvents was probed by [Formula: see text]H NMR, UV-vis, MCD, steady-state fluorescence, and high-resolution ESI methods and was found to be similar to the previously reported metal-free N-confused porphyrins. The electronic structure and the nature of the excited states in 1 were correlated with the results obtained by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations.

Role of ammonium ion on the aggregation and adsorption properties of sodium dodecylsulfate

ABSTRACTThe role of mixed counterion toward the aggregation behavior of sodium dodecylsulfate (SDS) is quantified by determining the critical micelle concentration (cmc) of SDS micelle in the presence of added NH4Cl salt. The dependence of cmc of SDS on added salt is explained in the light of the modified Corrin–Harkins equation and the nonlinearity of this plot is shown due to the exchange of Na+ ion by added ion. The aggregation number (N) of SDS micelle is also calculated using the steady-state fluorescence method, where sudden change in N value was observed in two different concentration regions of the modified CH plot. Furthermore, the hydrodynamic diameter (dH) of dodecyl sulfate micelles was determined using the dynamic light scattering method. In scattering studies, a sharp change in the value of dH occurred at around 50 mM of added salt, which might hint toward the shape change of dodecyl sulfate micelle. The surface excess values of SDS in the presence of mixed inorganic counterion are also calculated in the light of the Gibbs adsorption isotherm.