Langmuir Binding Isotherm Research Articles

Development of a Point-of-Care SPR Sensor for the Diagnosis of Acute Myocardial Infarction.

A novel point-of-care surface plasmon resonance (SPR) sensor was developed for the sensitive and real-time detection of cardiac troponin I (cTnI) using epitope-imprinted molecular receptors. The surface coverage of a nano-molecularly imprinted polymer (nanoMIP)-functionalized SPR sensor chip and the size of nanoMIPs (155.7 nm) were characterized using fluorescence microscopy and dynamic light scattering techniques, respectively. Atomic force microscopy, electrochemical impedance spectroscopy, square wave voltammetry and cyclic voltammetry techniques confirmed the successful implementation of each step of the sensor fabrication. The SPR bio-detection assay was initially established by targeting the cTnI peptide template, and the sensor allowed the detection of the peptide in the concentration range of 100-1000 nM with a correlation coefficient (R2) of 0.96 and limit of detection (LOD) of 76.47 nM. The optimum assay conditions for protein recognition were subsequently determined, and the cTnI biomarker could be detected in a wide concentration range (0.78-50 ng mL-1) with high reproducibility (R2 = 0.91) and sensitivity (LOD: 0.52 ng mL-1). The overall sensor results were subjected to three binding isotherm models, where nanoMIP-cTnI interaction followed the Langmuir binding isotherm with the dissociation constant of 2.99 × 10-11 M, indicating a very strong affinity between the cTnI biomarker and epitope-imprinted synthetic receptor. Furthermore, the selectivity of the sensor was confirmed through studying with a control nanoMIP that was prepared by imprinting a non-specific peptide template. Based on the cross-reactivity tests with non-specific molecules (i.e., glucose, p53 protein, transferrin and bovine serum albumin), the nanoMIP-SPR sensor is highly specific for the target biomarker. The developed biomimetic sensor, relying on the direct assay strategy, holds great potential not only for the early and point-of-care testing of acute myocardial infarction but also for other life-threatening diseases that can be diagnosed by determining the elevated levels of certain biomarkers.

FRET-based Solid-state Luminescent Glyphosate Sensor Using Calixarene-grafted Ruthenium(II)bipyridine Doped Silica Nanoparticles.

Calixarene-functionalized luminescent nanoparticles were successfully fabricated for the FRET-based selective and sensitive detection of the organophosphorus pesticide glyphosate (GP). p-Tert-butylcalix[4]arene was grafted on the surface of [Ru(bpy)3 ]2+ incorporated SiNps to produce self-assembled nanosensors (RSC). FRET was switched on in the presence of GP by means of energy transfer due to binding with p-tert-butylcalix[4]arene grafted on the surface of the RSC. The FRET efficiency of the GP-RSC system was increased gradually with the addition of GP. The FRET efficiency was evaluated as 87.69 % and a high binding affinity was established by the binding constant value, 1.16×107 M-1 , using a Langmuir binding isotherm plot. The estimated limit of detection (LOD) was 7.91×10-7 M, which was lower than the Environmental Protection Agency (EPA) recommendation. The probe also effectively responds to real sample analysis. The sensitivity and selectivity was realized due to the efficient FRET towards the fluorescence properties of the [Ru(bpy)3 ]2+ complex.

A Novel Fluorescent Nanoparticle for Sensitive Detection of Cry1Ab Protein In Vitro and In Vivo

Here, we report the synthesis and characterization of CoFe2O4 doping Ag2S dendrimer-modified nanoparticles (CoFe2O4-Ag2S DMNs) in Cry1Ab protein detection and imaging. The near-infrared Ag2S quantum dots were first prepared by using the thermal decomposition method, followed by modification of the water-soluble quantum dots using the method of solvent evaporation and ligand exchange, and finally the fluorescent magnetic bifunctional nanoparticles were obtained by binding with CoFe2O4. As-prepared CoFe2O4-Ag2S DMNs were characterized by fluorescence (FL) spectroscopy and transmission electron microscopy (TEM). Results showed that Ag2S DMNs could sensitively detect Cry1Ab both in vitro and in vivo. In vitro, the enhanced FL intensity as a function of the concentration is notably consistent with the Langmuir binding isotherm equation in the range of 0-200ng/mL of Cry1Ab proteins. The detection limit of this method was found to be 0.2ng/mL. Meanwhile, the fluorescence wavelength was extended to the second near-infrared range (NIR-II, 1.0~1.4μm), which enables in vivo imaging. This study highlights the importance of NIR QDs doping magnetic materials as a new method to trace Bacillus thuringiensis (Bt) in insects and their potential applications in in vivo NIR tissue imaging.

Thioglycolic acid-CdTe quantum dots sensing and molecularly imprinted polymer based solid phase extraction for the determination of kanamycin in milk, vaccine and stream water samples

Kanamycin is an antibiotic from the aminoglycoside class used to treat a myriad of infections. Aminoglycosides enhanced the photoluminescence of the thioglycolic acid modified CdTe quantum dots (TGA-CdTe QDs) following a Langmuir binding isotherm model. Binding constants were calculated indicating strong interactions between surface of nanoparticles and aminoglycosides. For kanamycin, the equilibrium binding constant was of 5.6×107Lmol−1. Based on this, a sensitive and selective method was developed for kanamycin determination based on the enhanced photoluminescence of TGA-CdTe QDs. Solid phase extraction with a new molecularly imprinted polymer, made using kanamycin as a template, provided high selectivity towards aminoglycosides. Under adjusted conditions, the two orders of magnitude analytical curve (linearized Langmuir binding isotherm) was constructed from 1.4×10−8molL−1 (limit of quantification) to 1.6×10−6molL−1 (8.1–92.8ngmL−1) of kanamycin sulphate. The proposed procedure was tested for the determination of kanamycin in milk and yellow fever vaccine with recoveries between 86.6 and 93.7%. In addition, the kanamycin effect on TGA-CdTe QDs was also demonstrated under capillary electrophoresis regime, indicating another possibility for selective sensing.

금속이온에 의한 CdSe 나노결정의 형광 소광 및 회복 특성

CdSe 기반 나노결정의 구리이온에 의한 형광 소광 특성 및 아연이온에 의한 형광 회복 특성을 관찰하였다. 구리이온이 첨가되었을 경우, CdSe 양자점에서는 매우 빠르고 급격한 형광 소광 특성을 보이는 반면에 CdSe 나노라드의 경우에서는 형광이 서서히 소광되는 특성을 보인다. 구리이온으로 형광을 소광시킨 CdSe/CdS(핵/껍질) 양자점에 아연이온이 첨가되면 소광된 양자점의 형광이 회복된다. 용액 내 1 μM의 아연농도에서 양자점의 형광이 50% 증가됨을 확인하였으며, 아연 농도가 증가함에 따라 양자점의 형광세기가 증가되며 이는 Langmuir binding isotherm 모델로 해석할 수 있다. 이러한 연구를 바탕으로 CdSe 기반의 나노결정을 이용한 형광 화학 센서를 구현할 수 있을 것으로 기대한다. Copper ion induced photoluminescence (PL) quenching dynamics and recovery of the PL by zinc ions were investigated for CdSe based nanocrystals. When copper ions were added, CdSe quantum dots showed fast and dramatically PL quenching whereas PL of CdSe nanorod gradually decreased. In the presence of zinc ions, the PL of CdSe/CdS (core/shell) nanocrystals that have quenched by copper ions was efficiently recovered. It showed that the PL intensity of nanocrystals increased by 50% in a solution containing 1 μM zinc ions. The PL intensity was increasing with increasing zinc ions, and could be described by Langmuir binding isotherm model. We showcase that the CdSe based nanocrystals can be used as fluorescence turn-on sensor.

Polyamidoamine functionalized CdTeSe quantum dots for sensitive detection of Cry1Ab protein in vitro and in vivo

To evaluate the possibility of sensitive detection of Cry1Ab protein in vivo and in vitro, polyamidoamine (PAMAM) dendrimers functionalized CdTeSe QDs were prepared by using solvent evaporation method and Cry1Ab was bound on the surface of NIR QDs through hydrogen bond. Transmission electron microscope (TEM) was used to examine the structure and properties of PAMAM-functionalized CdTeSe quantum dots. Fluorescence microscopy was used to detect the fluorescence of the nanoparticles. The results showed that PAMAM-functionalized CdTeSe QDs can detect Cry1Ab protein both in vitro and in vivo with sensitivity. In vitro, the enhanced fluorescence (FL) intensity as a function of concentration matched Langmuir binding isotherm equation very well in the range of 0–200ng/mL of Cry1Ab proteins. The detection limit of this method was found to be 3ng/mL. In vivo, the water-soluble NIR-QD nanoparticles were found in the midgut of pest by fluorescence microscopy, indicating that these bioprobes are useful for real-time detection of Cry1Ab. The prepared PAMAM functionalized QDs could serve as excellent NIR optical imaging probes to detect the transgenic ingredients in genetically modified (GM) research.

Determination of captopril using selective photoluminescence enhancement of 2-mercaptopropionic modified CdTe quantum dots

A photoluminescent probe for the determination of captopril is proposed based on the enhancement of luminescence from 2-mercaptopropionic modified CdTe quantum dots (2-MPA-CdTe QDs). Under optimum conditions, the calibration model (the Langmuir binding isotherm) was linear up to 4.8 × 10−4 mol L−1 with equilibrium binding constant of 3.2 × 104 L mol−1 and limit of detection (xb + 3 sb) of 2.7 × 10−7 mol L−1 (59 ng mL−1). The approach was tested in the determination of captopril in pharmaceutical formulations and the results were in agreement with the ones obtained using reference method. The possible mechanism of interaction is also investigated by Raman and electronic absorption spectroscopy and dynamic light scattering.

Subpicogram Per Milliliter Detection of Interleukins Using Silicon Photonic Microring Resonators and an Enzymatic Signal Enhancement Strategy

The detection of biomolecules at ultralow (low to subpicogram per milliliter) concentrations and within complex, clinically relevant matrices is a formidable challenge that is complicated by limitations imposed by the Langmuir binding isotherm and mass transport, for surface-based affinity biosensors. Here we report the integration of an enzymatic signal enhancement scheme onto a multiplexable silicon photonic microring resonator detection platform. To demonstrate the analytical value of this combination, we simultaneously quantitated levels of the interleukins IL-2, IL-6, and IL-8 in undiluted cerebrospinal fluid in an assay format that is multiplexable, relatively rapid (90 min), and features a 3 order of magnitude dynamic range and a limit of detection ≤1 pg/mL. The modular nature of this assay and technology should lend itself broadly amenable to different analyte classes, making it a versatile tool for biomarker analysis in clinically relevant settings.

Cadmium Tellurium Quantum Dots in Sol-Gel-Derived Silica Spheres Coated with Calix[6]Arene as an Optical Probe for Dalapon

This paper reports a new optical probe for detect dalapon. We have synthesized the luminescent and stable CdTe quantum dots(QDs) capped with calix[6]arene(C[6]/SiO2/CdTe) via the sol-gel technique in aqueous media. These hybrid organic-inorganic compounds are characterized by IR spectroscopy, ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), and fluorescence. We found that the C[6]/SiO2/CdTe were more stable and had higher fluorescence than the SiO2/CdTe nanoparticles (NPs). The C[6]/SiO2/CdTe show selectivity and sensitivity to dalapon via significant fluorescence intensity decrease. It can be ascribed to the Stern-Volmer equation. Under the optimal conditions, the relative fluorescent intensity was decreased linearly with increasing dalapon concentration in the range of 1.0–25.0 nmol/L with a detection limit of 0.262 nmol/L of dalapon. The possible underlying mechanism is discussed by Langmuir binding isotherm.

Calcium and Phosphatidylserine Inhibit Lipid Electropore Formation and Reduce Pore Lifetime

Molecular dynamics simulations of electroporation of homogeneous phospholipid bilayers show that the pore creation time is strongly dependent on the magnitude of the applied electric field. Here, we investigated whether heterogeneous bilayers containing phospholipids with zwitterionic and anionic headgroups exhibit a similar dependence. To facilitate this analysis we divide the life cycle of an electropore into several stages, marking the sequence of steps for pore creation and pore annihilation (restoration of the bilayer after removal of the electric field). We also report simulations of calcium binding isotherms and the effects of calcium ions on the electroporation of heterogeneous lipid bilayers. Calcium binding simulations are consistent with experimental data using a 1:2 Langmuir binding isotherm. We find that calcium ions and phosphatidylserine increase pore creation time and decrease pore annihilation time. For all systems tested, pore creation time was inversely proportional to the bilayer internal electric field.

Physico-Chemical Aspects of Quantum Dot–Vasodialator Interaction: Implications in Nanodiagnostics

The present work describes a comprehensive study on the interactions between the two components, namely, CdTe quantum dots (QDs) and tyrosine-bradykinin (tyr-BK), and explores the feasibility of probing bradykinin by a simple and fast quantum dot based optical method. The optical spectroscopic studies suggest that three amino acids of bradykinin are possibly involved in interactions between QDs and tyr-BK, leading to a conformational change in bradykinin. It was also observed through isothermal calorimetry that the interaction between CdTe QDs and bradykinin is an entropy driven process. The luminescence of QDs increases significantly even in the presence of micromolar concentrations of tyr-BK. The luminescence enhancement follows the Langmuir binding isotherm, and its dependence on size of QD, solvent polarity, and salt effect has also been investigated. The luminescence lifetime measurements indicate a possible association of QDs and tyr-BK. The present strategy is able to detect bradykinin in the range...

Ultrasensitive Detection of Glyphosate Using CdTe Quantum Dots in Sol-Gel-Derived Silica Spheres Coated with Calix[6]arene as Fluorescent Probes

We have developed a simple method for the preparation of highly fluorescent and stable, water-soluble CdTe quantum dots in sol-gel-derived composite silica spheres which were coated with calix[6]arene. The resulting nanoparticles (NPs) were characterized in terms of UV, fluorescence and FT-IR spectroscopy and TEM. The results show that the new NPs display more intense fluorescence intensity and are more stable than its precursors of the type SiO2/CdTe. Under the optimum, the novel NPs exhibit a higher selectivity and ultrasensitive fluorescence probes for the determination of gly-phosate over other pesticides, the fluorescence intensity increase with the concentration of glyphosate in the range from 1.0 to 25.0 nmol/L and the detection limit is low to 0.0725 nmol/L. A mechanism is suggested to explain the inclusion process by a Langmuir binding isotherm.

Ultrasensitive detection of mercury(II) ion using CdTe quantum dots in sol-gel-derived silica spheres coated with calix[6]arene as fluorescent probes

We have developed a simple method for the preparation of highly fluorescent and stable, water-soluble CdTe quantum dots in sol-gel-derived composite silica spheres that were coated with calix[6]arene. The resulting nanoparticles (NP) were characterized in terms of UV, fluorescence and FT-IR spectroscopy and by TEM. The results show that the new NPs display more intense fluorescence intensity and are more stable than its precursors of the type SiO2/CdTe. In addition, the new NPs exhibit a higher selectivity for the determination of Hg2+ than for other metal ions. Under the optimum conditions, the relative fluorescence intensity decreases with the concentration of Hg2+ in the range from 2.0 to 14.0 nmol L−1 and the detection limit is 1.55 nmol L−1. The method is based on the quenching of fluorescence by Hg2+ and expected to serve as a practical fluorescence test for rapid detection of Hg2+. A mechanism is suggested to explain the inclusion process by a Langmuir binding isotherm, and fluorescence quenching is best described by the Stern-Volmer equation.

Quantum dot based probing of mannitol: An implication in clinical diagnostics

We demonstrate that mannitol, an important diuretic, can be determined with cysteine-capped CdS quantum dots (QDs) using optical spectroscopy. Unique luminescence enhancement of QDs was observed on interaction with mannitol. The binding between QDs and mannitol was monitored by UV–vis, Fourier transform infra-red and Raman spectroscopy. The binding constant was determined following the Langmuir binding isotherm. A quantitative correlation between mannitol concentration and PL enhancement of CdS QDs has been established. We also observed that possible interfering agents, such as, urea, uric acid, creatinine, some metal ions, glucose, sorbitol or sucrose had no significant effect on luminescence of CdS QDs. The proposed strategy can be a very fast, simple and potential tool for the monitoring of diuretics and assaying intestinal permeability.

Electrochemical probe for the monitoring of DNA–protein interactions

Self-assembly of thiol-terminated oligonucleotides on gold substrates provides a convenient way for DNA-functionalized surfaces. Here we describe the development of an electrochemical assay for the detection of DNA–protein interactions based on the modification of the electrochemical response of methylene blue (MB) intercalated in the DNA strands. Using a functionalized electrode with double stranded DNA carrying T3 RNA polymerase binding sequence, we show a substantial attenuation of the current upon the DNA–protein interaction. Moreover, a Langmuir binding isotherm for T3 RNA polymerase (T3 Pol) gives a dissociation constant K D equal to 0.46 ± 0.23 μM. Such value is 100 times lower than the calculated K D for the non-specific interaction of bovine serum albumin (BSA) with T3 Pol promoter. In addition, the use of the T7 RNA polymerase (T7 Pol) promoter instead of the T3 Pol promoter induces an increase of K D from 0.46 μM to more than 25 μM. Accordingly, this strong decrease in the affinity of T3 Pol towards an off-target DNA promoter reveals an electrochemical sequence-specific discrimination of DNA–protein interactions. In conclusion, our results show that the developed electrochemical test allows the monitoring of DNA–protein interactions with high specificity and with an in situ protein detection threshold at a nanomolar range.

Distribution and accessibility of cyclodextrins covalently bound onto silica gel

Silica gel coated with a layer of β-cyclodextrins is a well investigated system. Earlier literature studies suggest that the coating changes the mesoporous structure of the silica gel and that the coating obtained might be heterogeneous. From surface area measurements it was found that the average pore diameter and accessible pore volume was reduced after grafting with 3-glycidyloxypropyltrimethoxysilane and β-cyclodextrin, but the change was reversible by simple pyrolysis of the organic compounds. To investigate the amount of accessible β-cyclodextrin on the silica particles, a Langmuir adsorption study was used. From the Langmuir binding isotherm it was found that the 8 Anilinonaphtalene-1-sulfonic acid ammonium (1,8 ANS) guest had a much larger stability constant with surface bound β-cyclodextrin compared to that found for free β-cyclodextrin. The accessible amount of β-cyclodextrin was found to be approximately 12% lower than the total amount of β-cyclodextrin indicating that some β-cyclodextrin is inaccessible for complex formation on the silica particles. The distribution of the cyclodextrin on the particle was investigated using the enhanced fluorescence of 1,8 ANS when complexed to β-cyclodextrin using confocal laser scanning microscopy. The confocal images of the particle show that the β-cyclodextrin was positioned on the outer layer of the particle, explained by the difficulty of diffusion of the β-cyclodextrin into the small pores. It was observed that smaller particles (>20 μm) has a more homogeneous distribution of β-CD compared to larger particles where a heterogeneous distribution was observed.

Bending affects entropy of semiflexible polymers: Application to protein-DNA complexes

We discuss a class of generalized wormlike chain models of polymers with spontaneous curvature and show that the density of states and consequently the entropy of such natively bent polymers are higher than that of straight ones. This effect changes the classical Langmuir binding isotherm by giving rise to enhanced binding of DNA-bending proteins.

CdTe nanocrystals as luminescent probes for detecting ATP, folic acid and l-cysteine in aqueous solution

CdTe quantum dots capped by short-chain thioglycolic acid (TGA) are prepared in aqueous solution. In this study, we report the effect of adenosine 5′ triphosphate (ATP), folic acid and l-cysteine on the photoluminescence intensity of CdTe nanocrystals in pH 7.4 Tris-HCl buffer solutions. The luminescence of CdTe nanocrystals is quenched in the presence of ATP or folic acid, which is related to their concentrations. The relationship between the luminescence intensity of CdTe nanocrystals and the concentration of ATP or folic acid is described by the Stern–Volmer equation. The emission intensity of CdTe nanocrystals is enhanced in the presence of l-cysteine. The relationship between the emission intensity of CdTe nanocrystals and the concentration of l-cysteine agrees with Langmuir binding isotherm equation in the range of 5 × 10 −6 to 2 × 10 −4 mol/L. These results show that CdTe nanocrystals can be potentially used as luminescence probes for detecting ATP, folic acid and l-cysteine.

Luminescence switching of CdTe quantum dots in presence of p-sulfonatocalix[4]arene to detect pesticides in aqueous solution

A simple, rapid, and sensitive identification method of fenamithion and acetamiprid is developed using supramolecular nano-sensitizers combining of CdTe quantum dots (QDs) and p-sulfonatocalix[4]arene as additive by fluorescent spectroscopic technique in water. Depending on p-sulfonatocalix[4]arene, the selectivity of CdTe QDs is tuned between fenamithion and acetamiprid. The luminescence of free CdTe QDs is quenched selectively to fenamithion. While in the presence of p-sulfonatocalix[4]arene, it shows that the fluorescence intensity of QDs is enhanced selectively to acetamiprid due to the cooperation of QDs and p-sulfonatocalix[4]arene. Based on the response characteristics of the QDs, a fluorescent method is performed for tuning selective determination of the pesticides. Under optimum conditions described, it is found that the pesticides effect on the luminescence of the CdTe QDs in concentrations dependence are described by a Stern–Volmer-type equation or a Langmuir binding isotherm equation in the range of 0–10 −4 M (fenamithion) and 0–10 −3 M (acetamiprid), with the corresponding detection limits (3 σ) of 1.2 × 10 −8 M (fenamithion) and 3.4 × 10 −8 M (acetamiprid), respectively. The possible mechanism is discussed.

Single quantum dot-micelles coated with gemini surfactant for selective recognition of a cation and an anion in aqueous solutions

The synthesis of quantum dot coated with cetyltrimethyl ammonium bromide (CTAB) and gemini surfactant [C 12 H 25 N + (CH 3 ) 2 (CH 2 ) 4 (CH 3 ) 2 N + C 12 H 25 ]·2Br − (C 12-4-12 ) in aqueous solution have been described. It is characterized by photoluminescent spectroscopy, UV–vis spectroscopy and transmission electron microscopy (TEM), etc. In comparison with CTAB-coated QDs, the QDs coated with C 12-4-12 respond selectively to both transition metal ion copper and fluoride ion in aqueous media. When Cu 2+ is bound to C 12-4-12 -coated QD micelles, the fluorescence intensity is quenched. Linear relationships are found between the relative fluorescence intensity and the concentration of Cu 2+ in the range 0–500 μM, which is best described by a Stern–Volmer-type equation. Meanwhile, it is found that F − enhanced the luminescence of the C 12-4-12 -coated QD micelles in a concentration dependence that is described by a Langmuir binding isotherm equation in the range 0–300 μM. The limits of detection of Cu 2+ and F − are 1.1 and 0.68 μM, respectively. The possible mechanism is discussed.