The Binding Mechanism Between Cyclodextrins and Anticancer Drug Noscapine: A Spectroscopic and Molecular Docking Study.

In this paper the binding of noscapine (NOS) as an anticancer drug with poor bioavailability and low solubility with beta and methyl-beta cyclodextrins (ß-CD and M-ß-CD) as the biocompatible drug carriers were discussed using ultraviolet-visible, fluorescence and nuclear magnetic resonance spectroscopy, as well as molecular docking. The absorption of NOS changed when it was bound to both cyclodextrins, resulting in a hyperchromic shift. It formed a 1:1 stoichiometry inclusion complex with both cyclodextrins according to the Benesi-Hildebrand equation. The binding affinity was larger in NOS-M-ß-CD (5.9 (± 0.66) × 103 M- 1) than NOS-ß-CD (3.7 (± 0.22) × 103 M- 1) complex. The fluorescence emission band of NOS at 408 nm was quenched when NOS was complexed with ß-CD, and enhanced in the presence of M-ß-CD, while the shoulder at 350 nm was enhanced selectively when NOS was complexed with M-ß-CD. The fluorescence quenching of NOS with ß-CD showed a negative deviation from the Stern-Volmer. The thermodynamic parameters have been estimated with the help of the Van't Hoff equation in different temperatures, and a dynamic mechanism was proposed for quenching. Also, both ΔH and ΔS have positive values thus the main interactions result in hydrophobic forces. Moreover, the negative value of ΔG indicates that the bonding process is spontaneous. 1H NMR chemical shift changes were observable for NOS and both CDs protons due to the chemical environment changes of some nuclei upon complexation. The molecular docking results revealed that the 1:1 inclusion complex possesses a good molecular shape complementarity score for their most probable structures, and indicated that the M-ß-CD inclusion system gave the higher complexation efficiency. The binding energy values for ß-CD and M-ß-CD were determined to be -6.7 and - 9.5 kcal/mol, respectively. These findings suggest the same as the result of experimental tests that the NOS-M-ß-CD complex is more stable than the NOS-ß-CD complex.

Elucidating the Mechanism of Copper-Induced Photoluminescence Quenching in 2-Phenylbenzimidazole-5-Sulfonic Acid.

To explore the possible impact of 2-Phenylbenzimidazole-5-sulfonic acid (PBSA) on the function of a sunscreen, in this work we investigate the binding of copper metal ions (Cu2+) to PBSA. Due to the existence of an intrinsic interaction phenomenon between Cu2+ ions and PBSA molecules, the photoluminescence (PL) quenching arises owing to the charge transfer from PBSA to Cu2+ ions. The mechanism of fluorescence quenching is probed experimentally following excitation at 306 nm by evaluating various quenching parameters with the help of the Stern-Volmer plot. Through the assessment of the values of the Stern-Volmer constant ( K SV = 45.2 M - 1 ) and bimolecular quenching rate constant ( k q = 0.77 × 10 10 M - 1 . s - 1 ), it is deduced that the dynamic mode of PL quenching is operative between PBSA and Cu2+ ions. We evaluate the number of binding sites (n = 1) that advocate the presence of a single binding site in PBSA for Cu2+ ions. The numerical value of standard Gibbs free energy change, Δ G o ~ -27.485 kJ.mol-1 implies the spontaneous binding between Cu2+ ions and PBSA molecules. The results obtained give an insight into the mechanism of metal-induced PL quenching of water soluble PBSA sunscreen.

Influence of millimeter range electromagnetic waves on bovine serum albumin interaction with acridine orange.

The effect of non-ionizing millimeter range electromagnetic waves (MM EMW) (30-300 GHz) on the bovine serum albumin (BSA) interaction peculiarities with acridine orange (AO) has been studied in vitro. The frequencies 41.8 and 50.3 GHz were chosen, since the first one is nonresonant frequency for the water, while the second one is resonant for water. The binding constant and number of binding sites were calculated at both irradiation presence and absence. AO was revealed to bind to BSA, while after the protein irradiation the interaction force strengthens. However, it was also shown that there are differences of the interaction parameters while irradiating by 41.8 or 50.3 GHz. AO binds to BSA, irradiated by MM EMW with the frequency 41.8 GHz much more weaker, than to that, irradiated by MM EMW with the frequency 50.3 GHz.

The manuscript is devoted to the study of the effect of millimeter range electromagnetic waves with the frequencies 41.8 and 50.3 GHz on the model biological system, being on molecular level of organization. Nowadays millimeter range electromagnetic waves compose a significant part of electromagnetic pollution in the environment and affect biological material, besides these waves are used in extremely high frequencies-therapy ((30­300 GHz), which are millimeter range electromagnetic waves (1­10 mm)). On the other hand, the problem of their effect mechanism is mainly connected to water, since the resonant frequencies for water molecules are in the interval of millimeter waves. In the present study, as such biological molecule, the bovine serum albumin has been chosen, which interacts with acridine orange. Serum albumins are known to carry and transport various endogenous and exogenous agents, including drugs throughout circulatory system. In turn, acridine orange has been extensively used for biological staining to differentiate DNA from RNA by fluorescence emission for years, Nowadays, it is considered as a promising agent for antitumorous treatment and diagnosis.The data obtained show that the interaction between bovine serum albumin and acridine orange changes, when the solution of albumin is irradiated by the millimeter waves with the frequencies 41.8 and 50.3 GHz. However, the interaction alteration depends on the frequency as well. Thus, the irradiation with the frequency 41.8 GHz makes insignificant changes, while that with the frequency 50.3 GHz induces significant changes of measured parameters. The studies were conducted by absorption, fluorescence and CD spectroscopy methods.

Development of a Sensitive and Selective Method for the Determination of some Selected Aldehydes Based on Fluorescence Quenching.

Phenanthrene fluorescence quenching in anionic micellar system of sodium dodecyl sulphate (SDS) was explored for the development of a sensitive and selective method for a group of selected aldehydes (2,6-dichlorobenzaldehyde, 4-(dimethylamino)benzaldehyde, 4-aminobenzaldehyde, 4-nitrobenzaldehyde, 2-chlorobenzaldehyde, benzaldehyde and 2-methoxybenzaldehyde). Experiments were performed in 0.02 mol L- 1 SDS. All the studied aldehydes quenched the fluorescence intensity of the probe (phenanthrene). Stern-Volmer equation was useful in explaining the phenanthrene quenching by the studied aldehydes. Stern-Volmer constants ([Formula: see text]) were obtained as a result of using the Stern-Volmer equation that gives the information in respect of sensitivity of the method for the studied aldehydes. Greater the [Formula: see text] higher will be the sensitivity and vice versa. [Formula: see text], detection limit (DL) and quantification limit (QL) were observed in the order 2,6-dichlorobenzaldehyde > 4-dimethylaminobenzaldehyde > 4-aminobenzaldehyde > 4-nitrobenzaldehyde > 2-chlorobenzaldehyde > benzaldehyde > 2-methoxybenzaldehyde. Phenanthrene fluorescence quenching by the studied aldehydes is useful for their determination in environmental samples.

Ecofriendly Approach for the Determination of Selected Aldehydes by Fluorescence Quenching of L-Tryptophan.

It is a fluorescence-based study to examine the interaction between L-tryptophan and a selection of aldehydes, namely furfural (furan-2-carbaldehyde), 3-hydroxybenzaldehyde, salicylaldehyde (2-hydroxybenzaldehyde), 3-nitrobenzaldehyde, and 4-bromobenzaldehyde. The investigation took place in an aqueous environment, revealing that all five aldehydes induced quenching of the fluorescence intensity of L-tryptophan. By employing the Stern-Volmer equation to describe the quenching process, we constructed Stern-Volmer plots and derived Stern-Volmer constants. These constants (KSV) ranged from 2.87 × 104 mol L- 1 to 5.75 × 104 mol L- 1. Notably, the values of the Stern-Volmer constants varied among the different aldehydes, with the following order: 3-hydroxybenzaldehyde(3-HBA) > 4-bromobenzaldehyde (4-BBA) > 3-nitrobenzaldehyde > furan-2-carbaldehyde > salicylaldehyde. Consequently, our findings highlighted 3-hydroxybenzaldehyde as the most potent quencher, while 2-hydroxybenzaldehyde displayed the least sensitivity to quenching. Additionally, we determined the detection and quantification limits for the investigated aldehydes, resulting in ranges of 3.87 × 10- 12 to 8.25 × 10- 6 and 1.29 × 10- 11 to 2.75 × 10- 5, respectively. This research paves the way for the development of novel fluorescence probe-based sensors and offers valuable techniques for analyzing aldehydes within environmental and biological samples.

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.

Investigating the Effect of Silver Nanoparticles on the Fluorescence Intensity of Bambuterol and its Active Metabolite Terbutaline Using FRET.

Silver nanoparticles (AgNPs) were found to significantly quench the fluorescence of bambuterol hydrochloride (BAM) and its active metabolite terbutaline sulfate (TER). The intrinsic fluorescence intensity of each of BAM (at 264/292 nm) and TER (at 276/306 nm) decreased by the gradual addition of AgNPs. Quenching of the steady state fluorescence of BAM and TER probably resulted from the energy transfer to the photo-excited state of AgNPs. The estimated Stern-Volmer quenching constant at several temperature settings proved that the quenching mechanism of the two drugs was dynamic quenching in case of BAM while it was static quenching in case of TER. The number of binding sites, binding constants, and corresponding thermodynamic parameters depending on the interaction system were estimated at 293, 313, and 333 °K and the results obtained were interpreted.

Interaction of an Aldose Sugar with Photoinduced Electron Transfer (PET) and Non-PET Based Acridinedione Dyes in Water: Hydrogen-bonding Evidences from Fluorescence Spectral Techniques Assisted by Molecular Docking Approach.

Fluorescence spectral techniques aided by molecular docking (Mol.Doc) approach were employed in probing the molecular interactions existing between D-glucose and resorcinol based acridinedione (ADR) dyes. ADR dyes has been classified into PET and non-PET dyes based on the substitution in the 9th position of acridinedione ring structure. Addition of glucose to PET dye (ADR1) resulted in a decrease in the absorbance whereas to that of ADR2 dye (non-PET character in aqueous medium) resulted in a significant increase in the absorbance. The formation of an isosbestic point reveals the existence of a ground state interaction existing between the dye and sugar molecule. Addition of glucose to PET dye resulted in a drastic increase in the fluorescent enhancement (FE) and subsequent addition resulted in a marked decrease in the fluorescent intensity with no apparent shift of emission maximum. Interestingly, neither characteristic shift nor variation in emission intensity was observed in the case of ADR2 dye. Fluorescence lifetime studies of ADR1 dye in the presence of glucose illustrate the existence of multiple distinguishable micro environments of dye. Mol.Doc studies authenticate the co-existence of hydrogen bonding (HB) and hydrophobic interaction wherein the dye and sugar molecule acts as HB donor and acceptor resulting in a stable conformer. These conformers are governed predominantly by HB interactions. The nature of interaction of a simple sugar with ADR dyes are explored in depth by fluorescent techniques in coordination with docking studies is imparted in the present study.

Biocompatible Carbon Dot Decorated α-FeOOH Nanohybrid for an Effective Fluorometric Sensing of Cr (VI) in Wastewater and Living Cells.

This article reports the fluorometric detection of toxic hexavalent chromium Cr (VI)) in wastewater and Cr (VI) contaminated living cells using in-situ grown carbon quantum dots into the goethite (α-FeOOH) nano-matrix. The synthesized nano-hybrid shows enormous potential in determining the chromium contamination levels in various types of water samples. This selective fluorometric probe is enormously sensitive (LOD 81 nM) toward hexavalent chromium, which makes it a dedicated chromium sensor. Moreover, the sensing mechanism has been assessed using Stern-Volmer's equation and fluorescence lifetime experiments showing the simultaneous occurrence of photoinduced electron transfer and the inner filter effect. This chromium sensor has also been employed to assess the contamination level in real-life industrial wastewater. The performance of this probe in a real-life wastewater sample is quite commendable. Further, this biocompatible fluorometric probe has been used to demonstrate the in-vitro sensing of Cr (VI) in HeLa cells. The rapid detection mechanism of hexavalent chromium in living cells has been validated using theoretical docking simulations. Henceforth, this fluorometric sensor material could open new avenues not only in wastewater monitoring but also in biomedical applications.

Plasmonic Surface of Metallic Gold and Silver Nanoparticles Induced Fluorescence Quenching of Meso-Terakis (4-Sulfonatophenyl) Porphyrin (TPPS) and Theoretical-Experimental Comparable.

Colloidal metallic nanoparticles have attracted a lot of interest in the last two decades owing to their simple synthesis and fascinating optical properties. In this manuscript, a study of the effect of both gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs) on the fluorescence emission (FE) of TPPS has been investigated utilizing steady-state fluorescence spectroscopy and UV-Vis spectrophotometry. From the observed electronic absorption spectra, there is no evidence of the ground state interaction between metallic Au NPs or Ag NPs with TPPS. On the other side, the FE spectra of TPPS have been quenched by both Ag and Au NPs. Via applying quenching calculations, Ag NPs showed only traditional static fluorescence quenching of TPPS with linear Stern-Volmer (SV) plots. On the contrary, quenching of TPPS emission by Au NPs shows composed models. One model is the sphere of action static quenching model that prevails at high quencher concentrations leading to non-linear SV plots with positive deviation. However, at low Au NPs concentrations, traditional dynamic quenching occurs with linear SV plots. The quantum calculations for TPPS structure have been obtained using Gaussian 09 software: in which the TPPS optimized molecular structure was achieved using DFT/B3LYP/6-311G (d) in a gaseous state. Also, the calculated electronic absorption spectra for the same molecule in water as a solvent are obtained using TD/M06/6-311G + + (2d, 2p). Furthermore, the theoretical and experimental results comparable to UV-Vis spectra have been investigated.

Interactions of Environmental Pollutant Aromatic Amines With Photo Excited States of Thiophene Substituted 1,3,4-Oxadiazole Derivative: Fluorescence Quenching Studies.

In the present work, the fluorescence quenching of novel thiophene substituted1,3,4-oxadiazole derivative 2-(4-(4-vinylphenyl) phenyl)-5-(5-(4-vinylphenyl)thiophen-2-yl)-1,3,4-oxadiazole (TSO) by five different environmental pollutant aromatic amine derivatives like 2,4-dimethylaniline, 3-chloroaniline, 4-chloroaniline, o-anisidine, and m-toluidine has been studied at room temperature through steady-state and time-resolved methods. It is observed that, the quenching efficiency is highest in the case of o-anisidine and least in the case of 3-chloroaniline. The fluorescence quenching mechanism between TSO and aromatic amines is analysed through different quenching models. The results suggest that, the fluorescence quenching is due to diffusion assisted dynamic or collisional quenching according to the sphere of action static quenching model and according to the finite sink approximation model, the bimolecular quenching reactions are due to the collective effect of dynamic and static quenching. Further, cyclic voltammetry and DFT studies suggest that the fluorescence quenching is due to electron transfer. Binding equilibria analysis confirms the 1:1 stoichiometric ratio between fluorophore and the quencher.

Analysis of the Equilibrium Distribution of Ligands in Heterogeneous Media-Approaches and Pitfalls.

The equilibrium distribution of small molecules (ligands) between binding agents in heterogeneous media is an important property that determines their activity. Heterogeneous systems containing proteins and lipid membranes are particularly relevant due to their prevalence in biological systems, and their importance to ligand distribution, which, in turn, is crucial to ligand's availability and biological activity. In this work, we review several approaches and formalisms for the analysis of the equilibrium distribution of ligands in the presence of proteins, lipid membranes, or both. Special attention is given to common pitfalls in the analysis, with the establishment of the validity limits for the distinct approaches. Due to its widespread use, special attention is given to the characterization of ligand binding through the analysis of Stern-Volmer plots of protein fluorescence quenching. Systems of increasing complexity are considered, from proteins with single to multiple binding sites, from ligands interacting with proteins only to biomembranes containing lipid bilayers and membrane proteins. A new formalism is proposed, in which ligand binding is treated as a partition process, while considering the saturation of protein binding sites. This formalism is particularly useful for the characterization of interaction with membrane proteins.

Pyrene Interaction with Selected Amines in Aqueous Sodium Dodecyl Sulphate (SDS).

Pyrene interaction with a group of selected amines such as i.e. benzylamine, phenethylamine, trimethylamine, 1-phenylethylamine was studied in aqueous sodium dodecyl sulfate. All the four amines quenched the fluorescence intensity of pyrene in aqueous SDS. Pyrene acts as a sensitive and selective sensor for the detection of amines in environmental samples. Two different SDS concentrations (0.05 mol L- 1 and 0.1 mol L- 1) were used to get the optimum SDS concentration for maximum quenching and best detection and quantification limits. Lower SDS concentration (0.05 mol L- 1) was found the optimum for maximum quenching, lower detection and quantification limits. Fluorescence quenching of pyrene by the studied amines was treated with the Stern-Volmer equation that resulted in a Stern-Volmer constants (Ksv). Ksv reflects the sensitivity of pyrene for studied amines. Ksv varied between 1.962 × 104 - 0.020 × 103 mol L- 1. A sensitivity, detection limit (DL), quantification limit (QL) of pyrene for studied amines was found in the order Benzylamine > phenethylamie > trimethylamine > 1-phenylethylamine. DL varied from 4.53 × 10- 7 to 4.55 × 10- 4 mol L- 1 and QL varied from 1.51 × 10- 6 to 1.52 × 10- 3 mol L- 1. Method showed excellent reproducibility and is fruitful for the studied amines in environmental samples.

Analysis of Fluorescence Quenching of Coumarin Derivative under Steady State and Transient State Methods.

Nature has gifted us many organic molecules which have remarkable influence in our daily life. Amongst many organic molecules, heterocyclic organic molecules have gained potential applications in the advanced field of biomedicine, pharmaceutical, electronics and many more. In the present work fluorescence quenching of biologically active fluorescent probe 8EMOHCC by aniline in different solvents have been studied at room temperature. To understand the molecular behaviour in different media, solvents of different refractive index and dielectric constant have been used. Spectroscopic measurement techniques such as UV/Vis spectroscopy and time related single photon counting are employed to characterise the molecule at room temperature. The fluorescence quenching study shows linear dependence of SV-plot in solvents of different dielectric constants. It reveals that quenching reactions are dynamic in nature. Various parameters of quenching have been determined and identified the type of quenching involved in the quenching reaction. Further, kq is found to be greater than [Formula: see text] in ACN, methanol, propanol and dioxane. Activation energy of quenching (Ea) is found to be greater than energy of diffusion (Ed) in ACN, methanol, propanol, THF solvents and Ed > Ea in dioxane, indicating that quenching reaction is not solely controlled by material diffusion but also activation process.

Study of Interfacial Charge Transfer from an Electron Rich Organic Molecule to CdTe Quantum Dot by using Stern-Volmer and Stochastic Kinetic Models.

Photoinduced electron transfer (PET) from N-methylaniline (NMA) to a photoexcited CdTe quantum dot (QD*) is studied in toluene. The PET mechanism at low to moderate quencher (NMA) concentrations (<0.08 M) remains mostly collisional with some contributions from QD-NMA complex formation. However, at high quencher concentrations (>0.10 M), QDs form larger numbers of static complexes with NMA molecules leading to a steep positive deviation in the steady-state Stern-Volmer curves. An isothermal titration calorimetry (ITC) study confirms the formation of QD-NMA complexes (K∼150 M-1 ) at high quencher concentrations. Fitting our experimental data using a stochastic kinetic model indicates that the number of NMA molecules attached per QD at highest NMA concentration (∼0.16 M) used in this study decreases from ∼0.76 to ∼0.47 with reducing the QD size from ∼5.2 nm to ∼3.2 nm. However, the PET rate increases with decreasing QD size, which is commensurate with the observation that the chemical driving force (ΔG) increases with decreasing the QD particle size. We have analyzed the PET kinetics mainly by using Stern-Volmer fittings. However, in some cases Tachiya's stochastic kinetic model is used for stoichiometric analysis, which seems to be useful only at high quencher concentrations. The measured PET rate coefficients in all the cases are found to be at least an order of magnitude lower when compared to the diffusion-controlled rate of the reaction medium.

Fluorescence quenching of the SYBR Green I-dsDNA complex by in situ generated magnetic ionic liquids.

Magnetic ionic liquids (MILs) with metal-containing cations are promising extraction solvents that provide fast and high efficiency extraction of DNA. Hydrophobic MILs can be generated in situ in a methodology called in situ dispersive liquid-liquid microextraction. To consolidate the sample preparation workflow, it is desirable to directly use the DNA-enriched MIL microdroplet in the subsequent analytical detection technique. Fluorescence-based techniques employed for DNA detection often utilize SYBR Green I, a DNA binding dye that exhibits optimal fluorescence when bound to double-stranded DNA. However, the MIL may hinder the fluorescence signal of the SYBR Green I-dsDNA complex due to quenching. In this study, MILs with metal-containing cations were selected and their fluorescence quenching effects evaluated using FÓ§rster Resonance Energy Transfer and quantified using Stern-Volmer models. The MILs were based on N-substituted imidazole ligands (with butyl- and benzyl- groups as substituents) coordinated to Ni2+ or Co2+ metal centers as cations, and paired with chloride anions. The effects of NiCl2 and CoCl2 salts and of the 1-butyl-3-methylimidazolium chloride ionic liquid on the fluorophore complex were also studied to understand the components of the MIL structure that are responsible for quenching. The metal within the MIL chemical structure was found to be the main component contributing to fluorescence quenching. FÓ§rster critical distances between 11.9 and 18.8 Å were obtained for the MILs, indicating that quenching is likely not due to non-radiative energy transfer but rather to spin-orbit coupling or excited-state electron transfer. The MILs were able to be directly used in qPCR and fluorescence emission measurements using a microplate reader for detection, demonstrating their applicability in fluorescence-based detection methods. Graphical abstract.

Spectrofluorimetric study on fluorescence quenching of tyrosine and l-tryptophan by the aniracetam cognition enhancer drug: quenching mechanism using Stern-Volmer and double-log plots.

A novel approach on fluorescence quenching of tyrosine and l-tryptophan is presented for spectrofluorimetric determination of aniracetam in drug substances and products. The quenching mechanism was investigated using Stern-Volmer plots and ultraviolet spectra figures of quencher-fluorophore mixtures. Binding constant and stoichiometry were calculated using double-log plots. The spectrofluorimetric method was optimized for the experimental conditions affecting fluorescence quenching including fluorophore concentration, diluent, and reaction time. Moreover, the pH-rate profile of aniracetam was studied using simple kinetics and found to be stable within the pH range 5-8. Fluorescence quenching of tyrosine and l-tryptophan were observed on addition of aniracetam in aqueous medium at pH 5.5-6.5. Aniracetam quenched the fluorescence of tyrosine and l-tryptophan in the concentration range 1-20 µg/ml and 0.3-20 µg/ml, respectively, with binomial relationships between quenching values (ΔF) and aniracetam concentration. Limits of detection were found to be 0.10 µg/ml for tyrosine-aniracetam and 0.14 µg/ml for l-tryptophan-aniracetam. Method validation was performed as per ICH guidelines and demonstrated that the developed spectrofluorimetric method was accurate, precise, specific, and suitable for analysis of aniracetam in routine quality control laboratories. All experimental materials and solvents used are eco-friendly, indicating that the cited spectrofluorimetric procedure is an excellent green method.

Homogeneous immunoassay for alpha-fetoprotein based on the quenching of the fluorescence of quantum dots by antibody labelled with complexed copper ion tags.

A homogeneous fluorescent immunoassay is described for the determination of alpha fetoprotein (AFP) relying on the interaction between copper ion complex and quantum dots (QDs). The copper ion complex-labelled antibody can be employed as a quencher of fluorescence of QDs and capture probe of AFP in homogeneous solution. The labelled antibody is mixed with QDs to form the immune ensemble probe. Upon the addition of AFP, the labelled antibody is stripped away from QDs by antigen-antibody combination leading to the increase in the fluorescence signal. Thus, the determination of AFP can be realized by fluorometry (best measured at excitation/emission wavelengths of 360/520 nm). The fluorescence intensity shows a good linear relationship with the AFP concentration ranging from 40 to 640 ng mL-1, and the LOD is 26 ng mL-1. The proposed method provides a new approach to incorporate metal complexes into QD-based biomolecule sensing. Graphical abstract Schematic presentation of a fluorescent probe comprised of quantum dots and antibody labelled with copper ion complex for homogeneous immunoassay of α-fetoprotein. The target antigen can break up the ground state QD/labelled antibody complex to set free the fluorescent QDs.

A fluorometric optical fiber nanoprobe for copper(II) by using AgInZnS quantum dots.

An optical fiber nanoprobe is presented for fluorometric determination of copper(II). The method based on the use of water-dispersible AgInZnS quantum dots (QDs) deposited at the end of an optical fiber in a poly(vinyl alcohol) matrix. The fluorescnece of the QDs, best measured at excitation/emisssion wavelengths of 365/570 nm, is quenched by Cu(II) due to both static and electron transfer from the QDs to Cu(II). This is experimentally confirmed by photoluminescence and UV-vis absorption spectra, and measurement of luminescence lifetimes. The probe is highly selective and possesses a linear detection range that extends from 2.5 to 800 nM. Graphical abstractSchematic representation of an optical fiber nanoprobe based on hydrophilic AgInZnS quantum dots for fluorometric determination of copper(II). The fluorescence is quenched by Cu(II) due to static quenching and dynamic quenching. It has a detection range of 2.5-800 nM.

A Polynomial-Exponent Model for Calibrating the Frequency Response of Photoluminescence-Based Sensors.

In this work, we propose a new model describing the relationship between the analyte concentration and the instrument response in photoluminescence sensors excited with modulated light sources. The concentration is modeled as a polynomial function of the analytical signal corrected with an exponent, and therefore the model is referred to as a polynomial-exponent (PE) model. The proposed approach is motivated by the limitations of the classical models for describing the frequency response of the luminescence sensors excited with a modulated light source, and can be considered as an extension of the Stern-Volmer model. We compare the calibration provided by the proposed PE-model with that provided by the classical Stern-Volmer, Lehrer, and Demas models. Compared with the classical models, for a similar complexity (i.e., with the same number of parameters to be fitted), the PE-model improves the trade-off between the accuracy and the complexity. The utility of the proposed model is supported with experiments involving two oxygen-sensitive photoluminescence sensors in instruments based on sinusoidally modulated light sources, using four different analytical signals (phase-shift, amplitude, and the corresponding lifetimes estimated from them).