分子光谱法研究硫普罗宁修饰的CdTe量子点与血红蛋白相互作用

以N-(2-巯基丙酰基)-甘氨酸(硫普罗宁,TP)为稳定剂,采用水相法合成了荧光较好的水溶性CdTe量子点(TP-CdTe QDs)。本文通过共振瑞利散射光谱(RRS)、荧光光谱(FL)和紫外光谱(UV-Vis),探讨了TP-CdTe QDs与血红蛋白通过静电引力相互作用的机理.研究发现TP-CdTe QDs与血红蛋白通过静电引力相互作用以后,TP-CdTe QDs荧光猝灭发生猝灭同时荧光光谱发生蓝移,体系的共振瑞利散射光谱强度增大.血红蛋白通过静态猝灭,动态猝灭和光诱导电子转移的方式猝灭TP-CdTeQDs的荧光。同时对体系共振瑞利散射增强的原因进行了讨论。     

Interaction of CdTe Quantum Dots with 2,2-Diphenyl-1-Picrylhydrazyl Free Radical: A Spectroscopic, Fluorimetric and Kinetic Study

The interaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH^●) free radical with thiol-capped CdTe quantum dots (QDs) has been studied by UV–vis spectroscopy, steady state and time resolved fluorescence measurements. Addition of DPPH^● radical to CdTe QDs resulted in fluorescence quenching. The interaction occurs through static quenching as this was confirmed by fluorescence lifetime measurements. Time course absorption studies indicates that DPPH^● may be reduced by interaction with QDs to the substituted hydrazine form (2,2-diphenyl-1-picrylhydrazine) DPPH-H. The mechanism of fluorescence quenching of CdTe QDs by DPPH^● is proposed.     

Study on the interaction of CdTe quantum dots with ferulic acid and protocatechuic aldehyde by optical spectroscopy

Luminescent CdTe quantum dots (QDs) were synthesized using thioglycolic acid (TGA) as a stabilizing agent in aqueous medium and were characterized by Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In weak basic media the fluorescence of TGA-CdTe QDs was quenched notably by ferulic acid (FA) and protocatechuic aldehyde (PA), and the quenching values were proportional to the concentration of the quenchers in a certain range. The addition of bovine serum albumin (BSA) to TGA-CdTe QDs-FA and TGA-CdTe QDs-PA systems rendered a large recovery of the fluorescence of TGA-CdTe QDs.     

Two distinct photoluminescence responses of CdTe quantum dots to Ag (I)

Four sizes of water-soluble thiol-capped CdTe quantum dots (QDs) have been synthesized and used to investigate the photoluminescence (PL) responses to Ag⁺ ions. For small particles, the CdTe QDs exhibit PL enhancement in the presence of lower concentration of Ag⁺ but show obvious quenching with the further increase of Ag⁺; for larger particles, however, PL of CdTe QDs is quenched all the time with the Ag⁺ addition, no PL enhancement is observed. Mechanism study shows that small QDs with more traps on the particle surface are effectively passivated by initial adsorbed Ag⁺, which accounts for the PL enhancement observed; after the initial traps are saturated, the excess Ag⁺ facilitates nonradiative recombination, resulting in PL quenching. For larger particles, the nonradiative recombination dominates the whole process even for the lower concentration of Ag⁺, due to the fewer traps on the QD surface. Compared with larger particles, the small CdTe QDs are more suitable for sensing Ag⁺ because of the more sensitive and selective PL response. To our best knowledge, this is the first systematical study on the interaction of Ag⁺ with different-sized CdTe QDs.     

Mechanistic Aspects of Quantum Dot Based Probing of Cu (II) Ions: Role of Dendrimer in Sensor Efficiency

Selective quenching of luminescence of quantum dots (QDs) by Cu²⁺ ions vis-à-vis other physiologically relevant cations has been reexamined. In view of the contradiction regarding the mechanism, we have attempted to show why Cu²⁺ ions quench QD-luminescence by taking CdS and CdTe QDs with varying surface groups. A detailed study of the solvent effect and also size dependence on the observed luminescence has been carried out. For a 13% decrease in particle diameter (4.3 nm →3.7 nm), the quenching constant increased by a factor of 20. It is established that instead of surface ligands of QDs, conduction band potential of the core facilitates the photo-induced reduction of Cu (II) to Cu (I) thereby quenching the photoluminescence. Taking the advantage of biocompatibility of dendrimer and its high affinity towards Cu²⁺ ions, we have followed interaction of Cu²⁺-PAMAM and also dendrimer with the CdTe QDs. Nanomolar concentration of PAMAM dendrimer was found to quench the luminescence of CdTe QDs. In contrast, Cu²⁺-PAMAM enhanced the fluorescence of CdTe QDs and the effect has been attributed to the binding of Cu²⁺-PAMAM complex to the CdTe particle surface. The linear portion of the enhancement plot due to Cu²⁺-PAMAM can be used for determination of Cu²⁺ ions with detection limit of 70 nM.     

A Comparative Study on the Sensitive Detection of Hydroxyl Radical Using Thiol-capped CdTe and CdTe/ZnS Quantum Dots

Four types of water-soluble luminescent quantum dots (QDs) whose surface was functionlaized with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), or glutathione (GSH), were investigated for the sensitive and selective detection of hydroxyl radical (^●OH) in aqueous media. It was found that the type of capping agent and QD influenced the sensitivity of the probe. The order of sensitivity of the probe was: GSH-CdTe@ZnS > MPA-CdTe@ZnS > TGA-CdTe > MPA-CdTe QDs. Under the optimum conditions, a limit of detection as low as 8.5?×?10^-8?M was obtained using GSH-CdTe@ZnS. The effects of foreign reactive oxygen species and the Fenton reactants and products as possible interferences on the proposed probe were negligible for CdTe@ZnS QDs. Besides, experimental results indicated that CdTe@ZnS QDs were more attractive for the selective recognition of ^●OH than CdTe QDs. The mechanistic reaction pathway between the QDs and ^●OH is proposed.     

Sensitive Detection of Luteolin Using Thioglycolic Acid–Capped Cadmium Telluride/Cadmium Sulphide Quantum Dots as the Fluorescent Probe

ABSTRACT

A sensitive and simple method for the determination of luteolin (LTL) was developed based on the fluorescence quenching effect of LTL for thioglycolic acid–capped (TGA-capped) CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3 to 20.0 µg · mL^?1 with a correlation coefficient of 0.9972, and the detection limit was 7.2 ng · mL^?1. The fluorescence quenching mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-Vis) absorption, fluorescence (FL) spectroscopy. The proposed method was successfully applied to the determination of LTL in commercial capsules and human urine samples. It manifested several advantages such as high sensitivity, short analysis time, low cost, and ease of operation.     

Spectroscopic Studies on the Thermodynamics of L-Cysteine Capped CdSe/CdS Quantum Dots��BSA Interactions

CdSe/CdS quantum dots (QDs) capped with L-cysteine can provide an effective platform for the interactions with bovine serum albumin (BSA). In this study, absorption and fluorescence (FL) spectroscopy were used to study the binding reactions of QDs with BSA, respectively. The binding constant (??10⁴ M^-1) from FL quenching method matches well with that determined from the absorption spectral changes. The modified Stern-Volmer quenching constant (5.23?×?10⁴, 5.22?×?10⁴, and 4.90?×?10⁴ M^-1) and the binding sites (??1) at different temperatures (304 K, 309 K, and 314 K) and corresponding thermodynamic parameters were calculated (?G?<?0, ?H?<?0, and ?S?<?0). The results show the quenching constant is inversely correlated with temperature. It indicates the quenching mechanism is the static quenching in nature rather than dynamic quenching. The negative values of free energy (?G?<?0) suggest that the binding process is spontaneous, ?H?<?0 and ?S?<?0 suggest that the binding of QDs to BSA is enthalpy-driven. The enthalpy and entropy changes for the formation of ground state complex depend on the capping agent of QDs and the protein types. Furthermore, the reaction forces were discussed between QDs and BSA, and the results show hydrogen bonds and van der Waals interactions play a major role in the binding reaction.     

The double-effect mechanism between Fe3O4 nanoparticles and MSA-capped CdTe QDs

Water-soluble mercaptosuccinic acid (MSA)-capped CdTe quantum dots (QDs) of two sizes and superparamagnetic Fe₃O₄ nanoparticles have been synthesized and used to investigate the effect of the mechanism of Fe₃O₄ nanoparticles on the fluorescence intensity of QDs. In the presence of a low concentration of Fe₃O₄ nanoparticles, the CdTe QDs with smaller particle size exhibit fluorescence quenching while fluorescence enhancement of CdTe QDs with larger particle size was observed, and the fluorescence intensity changes with the excitation wavelength and the concentration of Fe₃O₄ nanoparticles. The mechanism study shows that there is a double-effect between the Fe₃O₄ and CdTe QDs: one is the fluorescence quenching effect due to Fe₃O₄ strong absorption of excitation and emission light, the other is the fluorescence enhancement effect resulting from a localized electromagnetic field caused by the absorption of exciting light. The fluorescence of CdTe QDs with lower concentration of Fe₃O₄ nanoparticles was determined via the synergy of the double-effect. To our best knowledge, this is the first systematic study on the interaction between Fe₃O₄ nanoparticles and CdTe QDs, which finds the fluorescence enhancement effect in the presence of low concentration of Fe₃O₄.     

Photoinduced interaction between MPA capped CdTe QDs and certain anthraquinone dyes

Photoinduced interaction of mercapto propionic acid (MPA) capped CdTe quantum dots (QDs) with certain anthraquinone dyes namely alizarin, alizarin red S, acid blue 129 and uniblue has been studied by steady state and time resolved fluorescence measurements. Addition of anthraquinone dyes to CdTe QDs results in the reduction of electron hole recombination has been observed (i.e., fluorescence quenching). The Stern-Volmer constant (K_SV), quenching rate constant (k_q) and association constants (K) were obtained from fluorescence quenching data. The interaction of anthraquinone dyes with QDs occurs through static quenching was confirmed by unaltered fluorescence lifetime. The occurrence of electron transfer quenching mechanism has been proved by the negative free energy change (ΔG_et) obtained as per the Rehm-Weller equation.     

Interaction Between Isoquercitrin and Bovine Serum Albumin by a Multispectroscopic Method

ABSTRACT

The interaction of isoquercitrin and bovine serum albumin (BSA) was investigated by means of fluorescence spectroscopy (FS), resonance light scattering spectroscopy (RLS), and ultraviolet spectroscopy (UV). The apparent binding constants (K _a) between isoquercitrin and BSA were 5.37 × 10⁵ L mol^?1 (293.15 K) and 2.34 × 10⁵ L mol^?1 (303.15 K), and the binding site values (n) were 1.18 ± 0.03. According to the Förster theory of non-radiation energy transfer, the binding distances (r) between isoquercitrin and BSA were 1.94 and 1.95 nm at 293.15 K and 303.15 K, respectively. The experimental results showed that the isoquercitrin could be inserted into the BSA, quenching the inner fluorescence by forming the isoquercitrin–BSA complex. The addition of increasing isoquercitrin to BSA solution leads to the gradual enhancement in RLS intensity, exhibiting the formation of the aggregate in solution. It was found that both static quenching and non-radiation energy transfer were the main reasons for the fluorescence quenching. The entropy change and enthalpy change were negative, which indicated that the interaction of isoquercitrin and BSA was driven mainly by van der Waals interactions and hydrogen bonds. The process of binding was a spontaneous process in which Gibbs free energy change was negative.     

Studies on Interaction of CdTe Quantum Dots with Bovine Serum Albumin Using Fluorescence Correlation Spectroscopy

Luminescent quantum dots (QDs) have widely used in some biological and biomedical fields due to their unique and fascinating optical properties, meanwhile the interaction of QDs with biomolecules recently attract increasing attention. In this paper, we employed fluorescence correlation spectroscopy (FCS) to investigate the nonspecific interaction between CdTe QDs and bovine serum albumin (BSA) as a model, and evaluate their stoichiometric ratio and association constant. Our results documented that BSA was able to bind to CdTe QDs and form the QD–BSA complex by a 1:1 stoichiometric ratio. The association constant evaluated is 1.06 ± 0.14 × 10⁷ M⁻¹ in 0.01 M phosphate buffer (pH = 7.4). Furthermore, we found that QD–BSA complex dissociated with increase of ion strength, and we speculated that the interaction of CdTe QDs with BSA was mainly attributed to electrostatic attraction. Our preliminary results demonstrate that fluorescence correlation spectroscopy is an effective tool for investigation of the interaction between quantum dots (or nanoparticles) and biomolecules.     

Au纳米颗粒和CdTe量子点复合体系发光增强和猝灭效应

利用金属蒸发真空多弧离子源注入机, 将Au离子注入到高纯石英玻璃来制备镶嵌有Au 纳米颗粒的衬底材料, 随后将化学方法合成的CdTe量子点旋涂在玻璃衬底上制备了Au纳米颗粒和CdTe量子点复合体系. 通过对镶嵌有Au纳米颗粒的衬底进行热退火处理来控制Au纳米颗粒的生长和分布, 系统研究了Au纳米颗粒的局域表面等离子体共振对CdTe量子点光致发光性能的影响. 利用光学吸收谱、原子力显微镜、透射电子显微镜和光致发光谱对样品进行了表征和测试. 光致发光谱表明, Au纳米颗粒的局域表面等离子体对CdTe量子点的发光有增强效应也有猝灭效应. 深入分析了Au纳米颗粒和CdTe量子点之间的相互作用过程, 提出了关于Au-CdTe 纳米复合体系中CdTe 发光增强和猝灭的新机理. 该实验结果为利用金属纳米颗粒表面等离子体技术制备高发光性能的光电子器件提供了较好的参考.     

Determination of l-proline based on anodic electrochemiluminescence of CdTe quantum dots

A novel flow injection method for detection of l-proline was proposed in the presence of CdTe quantum dots (QDs). This method is based on the enhanced anodic electrochemiluminescence (ECL) emission of CdTe QDs l-proline in aqueous system. CdTe QDs were modified with thioglycolic acid to obtain stable water-soluble QDs and intensive anodic ECL emission in Na₂CO₃–NaHCO₃ buffer solution at an indium tin oxide (ITO) electrode, which was used for the sensitive detection of ECL enhancement using our homemade flow cell. Under the optimal conditions, the ECL intensity was correlated linearly with the concentration of l-proline over the range of 1.0×10^?8?1.0×10^?4 g mL^?1 (r=0.9996) and the detection limit was 5.0×10^?9 g mL^?1. The relative standard deviation was 1.12% for 6.0×10^?5 g mL^?1 l-proline (n=11). The possible mechanism was discussed. This method put forward a new efficient ECL methodology for enhancement-related determination of l-proline successfully.     

A simple fluorescence quenching method for roxithromycin determination using CdTe quantum dots as probes

A new method for the determination of roxithromycin based on the fluorescence quenching of 3-mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) was developed. In ethanol medium, the fluorescence of CdTe quantum dots at 552 nm was quenched in the presence of roxithromycin. Based on this a simple, sensitive, and selective method for rapid determination of roxithromycin was described. Reaction time, interfering substances on the fluorescence quenching, and mechanism of the interaction of CdTe QDs with roxithromycin were investigated. After optimization, the proposed method allows the determination of roxithromycin over the range 25.0-350.0 μg ml⁻¹. The detection limit is 4.6 μg ml⁻¹. The proposed method was successfully applied to commercial capsules and tablets with satisfactory results. The recovery of the method was in the range of 96.8-102.5%.     

Interaction of Folic Acid with Mn2+ Doped CdTe/ZnS Quantum Dots: In Situ Detection of Folic Acid

To utilize the nanomaterials as an effective carrier for the drug delivery applications, it is important to study the interaction between nanomaterials and drug or biomolecules. In this study GSH functionalized Mn²⁺-doped CdTe/ZnS QDs has been utilized as a model nanomaterial due to its high luminescence property. Folic acid (FA) gradually quenches the FL of GSH functionalized Mn²⁺???doped CdTe/ZnS QDs. The Stern-Volmer quenching constant (K_sv), binding constant (K_s) and effective quenching constant (Ka) for the FA-QDs system is calculated to be 1.32?×?10⁵ M^?1, 1.92?×?10⁵ and 0.27?×?10⁵ M^?1, respectively under optimized condition (Temp. 300 K, pH 8.0, incubation time 40 min.). The effects of temperature, pH, and incubation time on FA-QDs system have also been studied. Statistical analysis of the quenched FL intensity versus FA concentration revealed a linear range from 1?×?10^?7 to 5.0?×?10^?5 for FA detection. The LOD of the current nano-sensor for FA was calculated to be 0.2 μM. The effect of common interfering metal ions and other relevant biomolecules on the detection of FA (12.0 μM) have also been investigated. L-cysteine and glutathione displayed moderate effect on FA detection. Similarly, the common metal ions (Na⁺, K⁺, Ca²⁺ and Mg²⁺) produced minute interference while Zn²⁺ Cu²⁺ and Fe³⁺ exert moderate interference. Toxic metal ions (Hg²⁺ and Pb²⁺) produced severe interferences in FA detection.

Graphical abstract

GSH-Mn²⁺ CdTe/ZnS QDs based Fluorescence Nanosensor for Folic acid

     

Analysis of the binding mechanism between o-phenylenediamine and bovine hemoglobin by molecular spectroscopy and molecular modeling methods

Abstract

This study was aimed to reveal the binding mechanism between bovine hemoglobin and o-phenylenediamine by using molecular spectroscopy techniques and molecular modeling methods. The experimental results revealed that the fluorescence quenching mechanism was a combined dynamic and static quenching. The binding constant was (1.17?±?0.02)×10⁴ L/mol, and only a single binding site exists. The binding distance was 2.46?nm. The binding process was a spontaneous reaction, dominated by hydrophobic forces. The molecular docking simulations have also confirmed the results of the spectroscopic methods. The results reported here may significantly help understanding the interaction mechanism of o-phenylenediamine and hemoglobin.     

Adsorption Kinetics and Binding Studies of Protein Quantum Dots Interaction: A Spectroscopic Approach

Protein Quantum dots interaction is crucial to investigate for better understanding of the biological interactions of QDs. Here in, the model protein Bovine serum albumin (BSA) was used to evaluate the process of protein QDs interaction and adsorption on QDs surface. The modified Stern-Volmer quenching constant (K_a), number of binding sites (n) at different temperatures (298 308 and 318 K?±?1) and corresponding thermodynamic parameters (ΔG?<?0, ΔH?<?0, and ΔS?>?0) were calculated. The quenching constant (K_s) and number of binding sites (n) is found to be inversely proportional to temperature. It signified that static quenching mechanism is dominant over dynamic quenching. The standard free energy change (ΔG?<?0) implies that the binding process is spontaneous, while the enthalpy change (ΔH?<?0) suggest that the binding of QDs to BSA is an enthalpy-driven process. The standard entropy change (ΔS?>?0) suggest that hydrophobic force played a pivotal role in the interaction process. The adsorption process were assessed and evaluated by pseudofirst-order, pseudosecond-order kinetic model, and intraparticle diffusion model.     

Photoluminescence quenching of CdTe/CdS core-shell quantum dots in aqueous solution by ZnO nanocrystals

Photoluminescence (PL) properties of 3-mercaptopropionic acid (MPA) coated CdTe/CdS core-shell quantum dots (QDs) in aqueous solution in the presence of ZnO colloidal nanocrystals were studied by steady-state and time-resolved PL spectroscopy. The PL quenching of CdTe/CdS core-shell QDs with addition of purified ZnO nanocrystals resulted in a decrease in PL lifetime and a small red shift of the PL band. It was found that CdTe(1.5 nm)/CdS type II core-shell QDs exhibited higher efficiency of PL quenching than the CdTe(3.0 nm)/CdS type I core-shell QDs, indicating an electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals. The experimental results indicated that the efficient electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals could be controlled by changing the CdTe core size on the basis of the quantum confinement effect.     

Study on the Interaction of the CpG Alternating DNA with CdTe Quantum Dots

A novel sensitive method for detection of DNA methylation was developed with thioglycollic acid (TGA)-capped CdTe quantum dots (QDs) as fluorescence probes. Recognition of methylated DNA sites would be useful strategy due to the important roles of methylation in disease occurrence and developmental processes. DNA methylation occurs most often at cytosine-guanine sites (CpG dinucleotides) of gene promoters. The QDs significantly interacted with hybridized unmethylated and methylated DNA. The interaction of CpG rich methylated and unmethylated DNA hybrid with quantum dots as an optical probe has been investigated by fluorescence spectroscopy and electrophoresis assay. The fluorescence intensity of QDs was highly dependent to unmethylated and methylated DNA. Specific site of CpG islands of Adenomatous polyposis coli (APC), a well-studied tumor suppressor gene, was used as the detection target. Under optimum conditions, upon the addition of unmethylated dsDNA, the fluorescence intensity increased in linear range from 1.0?×?10^??10 to 1.0?×?10^??6M with detection limit of 6.2?×?10^??11 M and on the other hand, the intensity of QDs showed no changes with addition of methylated dsDNA. We also demonstrated that the unmethylated and methylated DNA and QDs complexes showed different mobility in electrophoresis assay. This easy and reliable method could distinguish between methylated and unmethylated DNA sequences.