Stern-Volmer Relationship Research Articles

Enhanced explosive sensing based on bis(methyltetraphenyl)silole nanoaggregate

New photoluminescent bis(methyltetraphenyl)silole nanoaggregates for the detection of trinitrotoluene (TNT) were developed by using aggregation-induced emission property. Bis(methyltetraphenyl)silole nanoaggregates exhibited that photoluminescence (PL) intensity was increased when the water fraction was increased to 90% by volume. Relative PL efficiency of bis(methyltetraphenyl)silole nanoaggregates was exponentially increased to the percent of water fraction and particle diameter was dependent on solvent composition. Particle size of bis(methyltetraphenyl)silole nanoaggregates was tuned by controlling the water fraction by volume. Absolute quantum yield of bis(methyltetraphenyl)silole nanoaggregates in 90% water volume fraction were 32.4%, which increases by about 40 times. Detection of TNT was achieved from the quenching PL measurement of bis(methyltetraphenyl)silole nanoaggregates by adding the TNT. A linear Stern-Volmer relationship was observed for the detection of TNT.

Syntheses and photophysical properties of diaminotetraphenylporphyrins and their corresponding polyimides

Two free base porphyrins, 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin (cis-DATPP), 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin (trans-DATPP), and their zinc metalated analogues (cis-ZnDATPP and trans-ZnDATPP) were synthesized. A series of their corresponding polyimides were obtained by the condensed polymerization of the respective monomeric isomer DATPP with a 1:1 ratio of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA). The inclusion of PFMB and 6FDA into the polymeric backbone causes the polymers to be moderately to highly soluble in organic polar solvents. The molar content of the respective DATPP monomer varied between 5 and 30%. All compounds were structurally characterized by 1H NMR and ATR-IR spectroscopy and the porphyrin content in the polyimides was determined by UV–Visible absorption spectroscopy. Photophysical properties consisted of measuring both the UV–Visible (ground state) absorption and fluorescence (excited state) spectra, fluorescence quantum yields (Φf), and fluorescence lifetimes (τf) in dichloromethane and N,N-dimethylacetamide. Fluorescence quenching was also measured and observed by the Stern-Volmer relationship, using 9,10-anthraquinone (AQ) as the quencher molecule. Both the bimolecular rate constant of fluorescence quenching (kq) and the Stern-Volmer constant (KQ) were calculated from this relationship. Furthermore, deviations from linearity depicted in the Stern-Volmer plots for TPP and ZnTPP at higher concentrations of AQ were also measured as a means of examining and explaining the simultaneous occurrence of dynamic (collisional) quenching and static quenching in the mechanisms of fluorescence quenching. It was found in this work that the significantly larger values in the static quenching constant (KS) than in the dynamic quenching constant (KD) are indicative that static quenching and ground state complex formation between the fluorophore and quencher is the dominant mechanism of fluorescence quenching of these systems at higher quencher concentrations.

Photochemical Reaction Between 1,2‐Naphthoquinone and Adenine in Binary Water‐Acetonitrile Solutions

The photochemical reaction between 1,2-naphthoquinone (NQ) and adenine was investigated using nanosecond time-resolved laser flash photolysis. With photolysis at 355nm, the lowest triplet state T1 of NQ was produced via intersystem crossing from its singlet excited state. The triplet-triplet absorption of the state contributes three bands of transient spectra at 374, 596 and 650nm, respectively, in pure acetonitrile and binary water-acetonitrile solutions. In the presence of adenine, the observation of A·+ (at 363nm) and NQ+H· radical (at 343 and 485nm) indicates a multistep mechanism of electron transfer process followed by a proton transfer between 3 NQ* and adenine. By fitting with the Stern-Volmer relationship, the quenching rate constant kq of 3 NQ* by adenine in binary water-acetonitrile solutions (4/1, volume ratio, v/v) is determined as 1.66×109 m-1 s-1 . Additionally, no spectral evidence confirms the existence of electron transfer between 3 NQ* with thymine, cytosine and uracil.

Spectroscopic investigations on the interaction of thioacetamide with ZnO quantum dots and application for its fluorescence sensing

The purpose of the present work was to develop a method for the sensing of thioacetamide by using spectroscopic techniques. Thioacetamide is a carcinogen and it is important to detect its presence in food-stuffs. Semiconductor quantum dots are frequently employed as sensing probes since their absorption and fluorescence properties are highly sensitive to the interaction with substrates present in the solution. In the present work, the interaction between thioacetamide and ZnO quantum dots has been investigated by using UV–visible, fluorescence and infrared spectroscopy. Besides, dynamic light scattering (DLS) has also been utilized for the interaction studies. UV–visible absorption studies indicated the bonding of the lone pair of sulphur atom of thioacetamide with the surface of the semiconductor. The fluorescence band of the ZnO quantum dots was found to be quenched in the presence of micromolar concentrations of thioacetamide. The quenching was found to follow the Stern-Volmer relationship. The Stern-Volmer constant was evaluated to be 1.20×105M−1. Infrared spectroscopic measurements indicated the participation of the NH2 group and the sulphur atom of thioacetamide in bonding with the surface of the ZnO quantum dots. DLS measurements indicated that the surface charge of the semiconductor was shielded by the thioacetamide molecules.

Luminescent determination of ascorbic acid in dietary supplements

The article presents the results of the ascorbic acid (AA) determination with using a complex of an Tb (III) ion with ciprofloxacin (CF) as a lanthanide luminescent marker. The luminescent properties of the Tb (III)-CF complex in the presence of AA were studied. The excitation and luminescence spectra, triplet level of ligand, the kinetics of the luminescence decay of the Tb(III)-CF complex in the presence of AA were analyzed. The excitation spectrum of the Tb (III)- CF complex has broad bands with maxima at 302 and 355 nm that corresponding to the n→π* electronic transition in the absorption spectrum of ligand. The luminesce spectra demonstrate the emission transitions arising from 5D4 energy level to 7Fj multiplet ground state. The luminescence of the Tb(III)-CF complex was found to be quenched by AA. It was established that the lifetime of the excited 5D4 state of the Tb (III) ion decreases with AA concentration increasing up to 0,25 mg/сm3. Luminescence quenching of the Tb (III)-CF complex by AA follows the Stern-Volmer relationship of AA. The Stern-Volmer constant K is 2478 dm3/mol. The biomolecular quenching rate constant kq is 1,25∙107 dm3/mol. The effect of luminescence quenching of the Tb (III)-CF complex was used to developing the procedure for determining of AA in the dietetic additives «Asvitol» and «Ascorbic acid». The linear calibration plot for AA was obtained over the concentration range of 0,02 to 0,25 mg/сm3.

Lanthanide-organic frameworks based on terphenyl-tetracarboxylate ligands: syntheses, structures, optical properties and selective sensing of nitro explosives

Three isostructural three-dimensional (3D) lanthanide-based metal-organic frameworks [Ln2L(H2L)(NMP)2]·H2O (Ln=Sm ( 1 ), Eu ( 2 ), Gd ( 3 ); H4L=1,1′:4′,1″-terphenyl-2′,4,4″,5′-tetracarboxylic acid; NMP= N -methyl-2-pyrrolidone) have been synthesized and structurally characterized. In 1 – 3 , two Ln3+ ions are doubly-bridged by two oxygen atoms of two carboxylate groups to form the dinuclear Ln2(OCOO–)2 unit. Each Ln2(OCOO–)2 unit links with four H2L2− ligands and four L4− ligands to lead to the 3D framework, which can be rationalized as a new trinodal 4,4,8-connected (44.62)(45.6)(412.616) topological network by considering the dinuclear Ln2(OCOO–)2 units as 8-connected nodes and L4−/H2L2− ligands as planar 4-connected nodes, respectively. 1 and 3 exhibit blue emission originated from the ligand with the emission maximum at 384 nm, while 2 shows intense characteristic red emission of Eu3+ ions and weak ligand-centered emission. Moreover, 2 has fluorescent quenching response towards the aromatic nitro compounds, especially for the 3,4-dinitrotoluene (3,4-DNT) with the linear Stern-Volmer relationship in the concentration range of 0–1 mM and the quenching constant ( K sv) of 2.084×103 M−1.

Bimolecular Photoinduced Electron Transfer in Static Quenching Regime: Illustration of Marcus Inversion in Micelle.

Ultrafast bimolecular photoinduced electron transfer (PET) between six coumarin dyes and four viologen molecules in the stern layer of sodium dodecyl sulfate micelle have been studied using femtosecond broadband transient absorption spectroscopy and femtosecond fluorescence up-conversion spectroscopy over a broad reaction exergonicity (ΔG0). Emanating the formation of radical cation intermediates of viologen molecules using the transient absorption and the fast decay component of coumarins using the fluorescence up-conversion studies the forward bimolecular electron transfer rate (ket) have been measured with high accuracy. The relationship of ket with ΔG0 found to follow a Marcus type bell-shaped dependence with an inversion at -1.10 eV. In this report, we have studied PET reaction using ultrafast spectroscopy at the quencher concentration where static quenching regime prevails. Moreover, the incompetency of Stern-Volmer experiments in studying ultrafast PET has been revealed. In contrary to previous claims, here we found that the ket is lower for lower lifetime coumarins, indicating that static, nonstationary and stationary regime of quenching have the minimal role to play to in the bimolecular electron transfer process. By far, this report is believed to be the most efficient and immaculate way of approaching Marcus inverted region problem in the case of bimolecular PET and settles the long-lasting debate of whether the same can be observed in micellar systems.

A LED-based fiber-optic sensor integrated with lab-on-valve manifold for colorimetric determination of free chlorine in water

In this work, a colorimetric methodology was developed for free chlorine determination by constructing a fiber-optic sensor (FOS) which was designed by using a small LED as light source and two silica fibers as light transmission elements. Then the FOS was integrated with the sequential injection lab-on-valve (SI-LOV) manifold to fabricate a FOS-SI-LOV system for free chlorine detection. The colorimetric determination was based on the reaction between N,N-diethyl-p-phenylenediamine (DPD) reagent and free chlorine, which would produce a chromophore showing maximum absorbance at 511 and 551nm and detected by a micro spectrometer detector. By choosing a green LED with emission wavelength at 520nm as light source, the chlorine concentration could be simply evaluated according to Beer's law. The developed FOS-SI-LOV system showed improved performances of wide linear range (10–400μgL−1), low detection limit (3.5μgL−1, 3σ), fast analysis (6.85s) and excellent repeatability (0.0083 RSD, n=8) for chlorine determination. The proposed FOS-SI-LOV system has been applied to on-line and real-time chlorine determination in different water samples with excellent selectivity. Furthermore, this FOS-SI-LOV methodology provided a colorimetric and fluorescence detection platform for other hazardous species monitoring in water environment based on Beer's law and Stern-Volmer relationship, respectively.

Facile Design of a Plasmonic Nanolaser

A spaser consists of a plasmonic noble-metal nanostructure that acts as nanocavity, when incorporated or surface-coupled two-level emitters constitute the nanoscale gain medium. Suited two-level emitters are, for instance, laser dyes. Optical pumping may provide efficient excitation energy transfer between the two-level emitters in the gain medium and the surface plasmons sustained in the nanocavity. Strong resonant coupling of the surface plasmon modes to the gain medium may establish an inherent feedback amplification mechanism which finally drives the spaser action. In this contribution, we demonstrate that spaser emission can be generated by amplifying longitudinal surface plasmon modes in gold nanorods by optically pumping surface-attached resonantly-coupled laser dyes. Therefore, we synthesized gold nanorods whose longitudinal surface plasmon resonance peak was adjusted between 680 and 700 nm. The gain medium was realized by electrostatically attaching the laser dye phthalocyanine tetrasulfonate via the positively-charged CTAB (cetyltrimethylammonium bromide) bilayer to the gold-nanorod surface. Phthalocyanine tetrasulfonate exhibits fluorescence at 700 nm. Fluorescence quenching experiments unambiguously gave indication of resonant excitation energy transfer. The fluorescence intensity ratio I F 0 / I F follows the Stern–Volmer relationship, and the Stern–Volmer coefficient was determined as KSV = 1.22 × 106 M−1. The spaser emission was observed in fs transient absorption spectra as an ultrafast decaying narrow emission peak around 716 nm.

CdTe quantum dots capped with different stabilizing agents for sensing of ochratoxin A

Cadmium telluride (CdTe) quantum dots (QDs) were prepared from aqueous solution with different capping agents of thioglycolic acid (TGA) and L-cysteine. Photoluminance spectra of CdTe QDs were used as a property of optical sensor for ochratoxin A (OTA) in the concentration range of ng/mL. It was found that L-cysteine capped CdTe QDs have linear response to OTA concentration in the range from 0.5 to 10ng/mL. By applying Stern–Volmer relationship, it was found that a very good linearity (R2=0.99) is observed in the concentration range from 0.5 to 10ng/ml, Ksv was 3.48 ×104Lg−1 and the minimum of detection was 0.5ng/ml. TGA capped CdTe QDs have a fair of linearity of R2 equals to 0.8929 in the concentration range from 5 to 30ng/ml of OTA and Ksv was 1.4×105Lg−1 with the minimum of detection of 5ng/ml. The mechanism of the effect of pH on the fluorescence of CdTe QDs was proposed and the low fluorescence intensity of CdTe QDs in acidic media was attributed to protonation of the surface binding thiolates and consequently the dissociation of CdTe QDs.

(Invited) Utilization of Photoluminescence from Semiconductor Nanoparticles to Prove Electron Transfer Reactions Influenced By Their Surface Conditions

Semiconductor nanoparticles, or quantum dots, have many advantages as photoluminescent materials such as the broad and intense optical absorption and single, narrow, and size-tunable emission. However, they have different types of fragility when compared to other organic/inorganic fluorophores. The importance of the surface on photoluminescence property is well-known by nanoparticle chemists but has hardly been investigated from both qualitative and quantitative points of view. The band edge emission can be observed when photogenerated excitons are confined in a particle having no defect levels: the whole structure including particle core, shell, and insulating ligands bound to the nanoparticle surface is essential to a high luminescence. The present study demonstrates a simple and efficient method to investigate the condition of ligands, which typically consist of organic molecules like alkylamines, carboxylates, and thiols. The emission quenching of these nanoparticles were observed when small electron acceptors like quinones were introduced to the nanoparticle solution, because these small molecules unexpectedly penetrated the protecting ligand layers. The mathematical analyses revealed that there were many defects in the ligand layer even if they are commonly used molecules and believed to be appropriate for the synthesis and storage of nanoparticles. Figure 1a shows the photoluminescence intensity ratio (I 0/I – 1) when the CdSe nanoparticles capped with n-alkylamine ligands were quenched by 1,4-benzoquinone introduced as an electron acceptor. The magnitude of quenching became greater with the alkyl moiety of the ligands became smaller. Although it is generally expected to be straight when the quenching mechanism follows the Stern-Volmer relationship that describes the photoinduced electron transfer between the species both dissolved and moving freely, they were all concave up. To reveal the origin of the curvatures, a model of quenching was developed. A nanoparticle has several voids of ligands on its surface, and through which the quenchers (1,4-benzoquinone) approach to the nanoparticle core to the distance that the electron transfer is possible (Figure 1b). A mathematical analysis with taking statistical distributions into account, was conducted following the proposed model, and they provided good fits with curvatures with three important parameters; the number of accessible sites existing on a nanoparticle, electron transfer rate, and the adsorption coefficients of quenchers to the nanoparticles. None of these parameters are available with conventional analysis methods, and all of them should be very import to address the intrinsic weakness of semiconductor nanoparticle fluorophores.Time variations on the magnitude of quenching were also observed during the storage of as-prepared nanoparticles. The nanoparticle surface became gradually damaged during the storage in a pure chloroform solution, while the nearly-perfect surface was formed when only a small amount of additional ligands given in the storage solution, which were proved quantitatively for the first time by our methods. Figure 1

Molecularly imprinted fullerene-silica nanocomposite particles for sensitive and selective recognition of diethylstilbestrol

A highly sensitive, molecularly imprinted fluorescent sensor was fabricated using a C60 fullerene as the signal transducer and silica as the imprinting matrix. The incorporation of C60 and the formation of diethylstilbestrol (DES) imprinted sites in the silica network were achieved by the sol–gel method. C60 has a narrow band gap between the ground and excited states, resulting in a weak photoluminescence. However, C60 showed a strong emission when it was incorporated into a molecularly imprinted silica matrix. DES imprinted fullerene-silica nanocomposite particles (MIFSNCs) showed an intense fluorescence emission with the peak maximum at ∼600nm. The fluorescence intensity of MIFSNCs significantly decreased with increasing DES concentration. MIFSNCs exhibited a linear Stern–Volmer relationship for DES and its structural analogs. The quenching constant of MIFSNCs for DES was about five times higher than those for DES analogs, indicating the highly selective recognition property.

Luminescence Quenching and Enhancement by Adsorbed Metal Ions with Ruthenium Diimine Complexes Immobilized on Silica Polyamine Composites.

Luminescent ruthenium diimine complexes have been covalently bound to the surface of a silica polyamine composite (SPC) using peptide coupling agents. The loading of the complexes using this route is quite low (~0.01-0.04 mmol/g) leaving sufficient surface amines to coordinate added metal ions. When the composite particles containing the Ru complexes are exposed to solutions of Cu2+, Ni2+ or Zn2+, luminescence is quenched with efficiencies that follow concentration dependence and the relative binding affinities of the ions. When heavy metal ions such as mercury or lead are adsorbed onto the same surface, luminescence is enhanced by a factor of ~3.5. When the complexes are exposed to these metals in solution, no quenching or enhancement is observed. Both phenomena were shown to be the result of adsorption of the cations onto the polyamine surface by using the Stern-Volmer relationship. The mechanism of both quenching and enhancement is discussed and the options for further development of this novel metal sensing technique are presented.

Triazine-Carbon Nanotubes: New Platforms for the Design of Flavin Receptors.

The synthesis of functionalised carbon nanotubes as receptors for riboflavin (RBF) is reported. Carbon nanotubes, both single-walled and multi-walled, have been functionalised with 1,3,5-triazines and p-tolyl chains by aryl radical addition under microwave irradiation and the derivatives have been fully characterised by using a range of techniques. The interactions between riboflavin and the hybrids were analysed by using fluorescence and UV/Vis spectroscopic techniques. The results show that the attached functional groups minimise the π-π stacking interactions between riboflavin and the nanotube walls. Comparison of p-tolyl groups with the triazine groups shows that the latter have stronger interactions with riboflavin because of the presence of hydrogen bonds. Moreover, the triazine derivatives follow the Stern-Volmer relationship and show a high association constant with riboflavin. In this way, artificial receptors in catalytic processes could be designed through specific control of the interaction between functionalised carbon nanotubes and riboflavin.

THE INFLUENCE OF SOL-GEL COATED LENGTH AND WITHDRAWAL RATE ON PLASTIC OPTICAL FIBER CORE TOWARDS OXYGEN GAS SENSING SENSITIVITY

The fabrication and characterization of an optical fiber oxygen sensor based on oxygen fluorescence quenching are described. The sensors are prepared by coating the oxygen sensitive indicator (tris-BP ruthenium (II) chloride and platinum octaethylporphyrin) that is immobilized by the sol-gel route onto the uncladded middle portion of a multimode plastic optical fiber. A design of experiment based on two parameters which are the uncladded coated length and withdrawal rate was carried out in order to identify the optimum setting that gives the highest fluorescence emission which leads to better sensitivity. The sensitivity of the optical oxygen sensor is quantified in terms of the ratio I0/I where I0 and Irepresent the fluorescence intensities in pure nitrogen and pure oxygen environments, respectively. Both ruthenium and platinum coated fiber produced a linear Stern-Volmer relationship which indicate the homogeneous environment of the luminophore. The experimental result reveals that the optimized setting for ruthenium sol-gel coated fiber is 5 mm decladded length and 120 mm/min withdrawal rate while for platinum sol-gel coated fiber is 8 mm decladded length and 160 mm/min withdrawal rate.

The investigation of the photophysical properties of α-chlorocurcumin and α-methylcurcumin

The electronic properties of α-chlorocurcumin and α-methylcurcumin was theoretically investigated at the B3LYP/6-311++G(d,p) level of theory. The thermodynamics quantities were estimated by calculating the frequencies of the molecules. Three main isomers were predicted after full geometry optimization of various suggested isomers within the tautomeric mixture of each molecule; the cis -enol, trans -enol and the trans -diketo isomers. Their stability was in the sequence: cis -enol > trans -diketo > trans -enol. The stabilization energy for the cis -enol with respect to trans -diketo and trans -enol in chlorocurcumin is 8.44 and 12.59 kcal/mol, respectively, while in methylcurcumin, it is 4.80 and 10.79 kcal/mol, respectively. The fluorescence spectra were recorded for the investigated compounds in several protic and aprotic solvent with different dielectric constants and H-bonding abilities. The emission maxima are within the range 487 to 571 nm in ethylene glycol, while they are within the range 475 to 557 nm in n -hexane. The fluorescence quantum yields of both compounds are low and lower than those of curcumin. The quantum yield of chlorocurcumin ranges from Φ Fl = 0.008 in MeOH to Φ Fl = 0.058 in toluene, while for methylcurcumin it ranges from Φ Fl = 0.007 in DMF to Φ Fl = 0.0524 in ethylene glycol. The fluorescence of both compounds quenched by water and their fluorescence life times are estimated from the slopes of the linear curves that obtained from Stern-Volmer relationship to be 1.44 and 1.40 psec for chlorocurcumin and methylcurcumin, respectively.

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.

Efficient Fluorescence Quenching of tert-butyl substituted Phthalocyanines with Picric Acid

Two tert-butyl substituted phthalocyanines(Pcs), in metal-free and metallated forms, were synthesized and the fluorescence responses toward various nitro derivatives, including picric acid(PA), 2,4-dinitrotoluene(DNT), 1,4-dinitrobenzene(DNB), 4-nitrotoluene(NT), nitrobenzene(NB), 1,4-benzoquinone(BQ), and nitromethane(NM) were investigated. Among the various nitro derivatives, current Pc derivatives exhibited efficient and exclusive fluorescence quenching in the presence of picric acid, which was readily observed by a naked eye. Quenching efficiency was estimated by the Stern-Volmer relationship, in which quenching constant, KSV, was calculated to be in the range of 10 4 M -1 . It was also found out that the aggregational behaviors of these Pcs are heavily dependent on the nature of solvent systems, subsequently affecting the quenching efficiency.

Luminescence quenching of [Os(bpy)3]2+ by Mn7+, Cr6+ and Ce4+ ions in acidic aqueous solution

Luminescence quenching of [Os(bpy)3]2+ by Mn7+, Cr6+ and Ce4+ ions in acidic aqueous media are studied. Ground state interactions between [Os(bpy)3]2+ and these ions show ground state association with stoichiometric ratios in accordance with the electron transfer process. Positive deviation is observed from the linear Stern–Volmer relationship which with the ground state association is in support of static quenching mechanism. Benesi-HildEbrand equation was used to evaluate the association constant which were found to be 5×103M−1, 6.6×104M−1 and be 1.1×105M−1 for association of [Os(bpy)3]2+ with Ce4+, Cr6+ and Mn7+, respectively, based on luminescence intensity measurements. Different models for static luminescence quenching were employed to discuss the results.

Model of dynamics of intracellular chloride based on fluorescent imaging

Fluorescent indicators are relatively non-invasive probe that allow the measure of ion concentrations in brain slices and neuron cultures using microscopy imaging. Most fluorescent ion indicators bind selectively with a certain ion, causing a decrease in fluorescence in a process known as quenching. Under steady state conditions, a fluorescence measurement, made at a specific point and time, is directly related to the local ion concentration at the same point and time, typically via the Stern-Volmer relationship. However, this is usually no longer true under the dynamic conditions inside a cell when transmembrane currents are active. While calcium ions (Ca²+) dynamics have been well analyzed theoretically [1], chloride ions (Cl-) indicators have been experimentally shown to exhibit changes in the timescale of minutes following the transient bathing with a GABA A agonist – leading to the interpretation that Cl- dynamics are very slow [2]. In this follow-up of a theoretical analysis of chloride indicator dynamics [3], we present novel contributions to the understanding of Cl- dynamics through the computational modeling of a recently built genetic membrane-bound fluorescent indicator (mbYFPQS, [4]). This indicator, obtained by adding a palmitoylation sequence to a previously described chloride indicator (YFPQS) to target the protein to the plasma membrane of cultured midbrain neurons, offers the possibility to study the mechanisms of Cl- transmembrane exchanges with an unprecedented resolution. We designed a computational model allowing the study of Cl- based on a detailed multi-compartmental conductance model that includes (a) Cl- pumps as well as (b) the interaction of Cl- with the mbYFPQS indicator as a system of non-linear differential equations derived from biophysical and chemical kinetic theory. To constrain the model parameterizations, we relied on fluorescent measurements of mbYFPQS recorded in rat cultured midbrain cells, and during which the extracellular medium was replaced several times by a muscimol bath followed by a wash solution. Using tools from the optimization theory to fit the model outputs with these experimental data, we were able to find broad plausible boundaries for parameters such as the Cl- leak pump kinetics as well as the forward/backward binding rates with the fluorescent indicator. However, the observed data did not have a sufficient temporal precision to derive precise estimates of these parameters. We also established through a sensitivity analysis on the membrane indicator density that orders of magnitude from 10-11 (e.g., as dense as pumps) to 10-18 M.cm−2 (e.g., as dense as postsynaptic densities) did not change the best fit parameter ranges nor the overall goodness-of-fit with experimental data, thus validating the widespread assumption that binding dynamics are independent from the indicator concentration in neurons.