Fluorescence Intensity Of Quantum Dots Research Articles

One-step assembly of TA-FeIII supramolecular shell on AgNPs surface for regulating fluorescence intensity of quantum dots

During surface-enhanced fluorescence processes, the spatial spacing layer on the surface of noble metals plays an important role in regulating the fluorescence intensity. We propose a method for regulating fluorescence intensity using the AgNPs@TA-FeIII composite nanostructured materials as the substrate and using characteristic fluorescence of graphene quantum dots as the detection signal. Tannins-FeIII (TA-FeIII) nanofilms were prepared with a one-step assembly method, which is simple, fast, green, and safe. This work is expected to help the application of polyphenol metal nanofilm technology in the field of surface enhanced fluorescence (SEF).

Fluorescent Alloyed CdZnSeS/ZnS Nanosensor for Doxorubicin Detection

Doxorubicin (DOX) is widely used in chemotherapy as an anti-tumor drug. However, DOX is highly cardio-, neuro- and cytotoxic. For this reason, the continuous monitoring of DOX concentrations in biofluids and tissues is important. Most methods for the determination of DOX concentrations are complex and costly, and are designed to determine pure DOX. The purpose of this work is to demonstrate the capabilities of analytical nanosensors based on the quenching of the fluorescence of alloyed CdZnSeS/ZnS quantum dots (QDs) for operative DOX detection. To maximize the nanosensor quenching efficiency, the spectral features of QDs and DOX were carefully studied, and the complex nature of QD fluorescence quenching in the presence of DOX was shown. Using optimized conditions, turn-off fluorescence nanosensors for direct DOX determination in undiluted human plasma were developed. A DOX concentration of 0.5 µM in plasma was reflected in a decrease in the fluorescence intensity of QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, for 5.8 and 4.4 %, respectively. The calculated Limit of Detection values were 0.08 and 0.03 μg/mL using QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, respectively.

КВАНТОВЫЕ ТОЧКИ СУЛЬФИДА КАДМИЯ, ПОЛУЧЕННЫЕ С ИСПОЛЬЗОВАНИЕМ БЕЛКОВ-ПОРИНОВ, КАРРАГИНАНОВ, ХИТОЗАНОВ И ЛИПОПОЛИСАХАРИДОВ

Quantum dots (QDs) are a new generation of fluorochromes with significant advantages over traditional organic dyes. QDs based on CdS are promising materials for optics, optoelectronics, biology, and medicine. QDs in the form of colloidal solutions are of great scientific and practical interest. CdS quantum dots were synthesized by chemical condensation in an aqueous solution using Yersinia pseudotuberculosis porin proteins, positively (chitosan) and negatively (carrageenan, lipopolysaccharide) charged polysaccharides. The maxima of the emission spectra for all samples were 450 nm, which indicates the same QD size; is determined by the size of the "cells" of the grid matrix, which limit the size of the QD. It was shown that the fluorescence intensity of QDs synthesized in LPS solutions was two times higher than that of other samples. The fluorescence of the samples and the maxima of the emission spectra (450 nm) are preserved during intensive dialysis against buffers, which indicates the stability of QDs and the possibility of using the obtained labeled preparations. Keeping samples at pH 3 leads to a significant decrease in fluorescence, especially for acidic polysaccharides. Anionic oxygen of phosphate, hydroxyl groups of sugar, nitrogen atoms can interact with metal ions, which are precursors (precursors) for CdS nanocrystals. It was found that the interaction with porin-specific IgG leads to a significant change in the luminescence intensity of QD-porin samples. This is of interest from the point of view of chemical sensing and opens the prospect of using QD-labeled porin-based nanostructures as biosensors.

Highly stable and recoverable humidity sensor using fluorescent quantum dot film.

Fluorescent sensors are resistant to electromagnetic interference and are electrically insulated, allowing for highly accurate measurements. Quantum dots (QDs) serve as outstanding sensing materials owing to the unique optical properties such as tunable photoluminescence (PL), excellent visible light activity, and high chemical and physical stability. In this paper, we develop an optical humidity sensor based on a QDs nanocomposite film. The film is made of polyvinyl alcohol (PVA), SiO2 microsphere (SM), and QDs through the layer-by-layer self-assembly method. The mechanism of humidity detection is moisture-induced quenching of the QDs fluorescence intensity. The results reveal that our sensor shows a good linear response to relative humidity in the range of 5% to 97%, a fast response-recovery time of 25 s and 20 s, and good repeatability for more than 50 cycles as well as high stability for over 180 days. Possessing the remarkable property, optical humidity sensors are envisaged for great potential applications in environmental monitoring.

The Optimized Quantum Dots Mediated Thermometry Reveals the Efficiency of Myosin Extracted from Muscle Mini Bundles

The biophysical function of myosin in vitro has been extensively investigated in different motility assays. However, the study of myosin ATPase properties at the fiber level is still limited. In this study we aimed to optimize quantum dots (QD) mediated thermometry to measure the efficiency of myosin extracted from muscle mini bundles. A reduction in fluorescent intensity of QD reflects an increase in temperature caused by the heat release during ATP hydrolysis, denoting the efficiency of the motor protein myosin. The procedure for extracting myosin was modified from the single fiber in vitro motility assay, and the concentration of myosin was represented by the extracted total protein since the ratio of extracted myosin to total protein was constant. Moreover, the efficiency of myosin extracted from preparations containing different isoform compositions revealed that slow myosin has a lower efficiency than fast myosin, i.e., a higher amount of heat was released resulting in faster decay of QD fluorescence intensity. Thus, the optimized QD mediated thermometry provides a new sensitive approach to evaluate myosin function from a thermometrical perspective based on minimal muscle tissue.

The optimized quantum dot mediated thermometry reveals isoform specific differences in efficiency of myosin extracted from muscle mini bundles

The biophysical function of myosin in vitro has been extensively investigated in different motility assays, but the study of myosin ATPase properties at the fiber level is insufficiently investigated. In this study, quantum dot (QD) mediated thermometry measurements were optimized to measure the efficiency of myosin extracted from muscle mini bundles. A reduction in fluorescent intensity of QD reflects an increase in temperature caused by the heat released during ATP hydrolysis and denotes the efficiency of the motor protein myosin. The procedure for extracting myosin was similar to the single fiber in vitro motility assay with some small modifications, and the concentration of myosin was represented by the extracted total protein since the ratio of extracted myosin to total protein was constant. Moreover, the efficiencies of myosin extracted from preparations containing different myosin heavy chain isoforms reveal lower efficiency of slow compared to fast myosin isoforms. Specifically, more heat was released in slow myosin enzymatic reaction, resulting in faster decay of QD fluorescence intensity. Hence, the optimized QD mediated thermometry provides a novel and sensitive approach to evaluate efficiency of myosin ATPase obtained from small muscle samples, representing a significant advantage in the clinical evaluation of neuromuscular disorders.

Фотомодуляция люминесценции наносфер с квантовыми точками CdSe/ZnS в полимерных пленках

The results of studies of the spectral-kinetic (absorption and fluorescent) characteristics of the polymer nanospheres created by us (containing luminescent inorganic CdSe/ZnS quantum dots and photochromic diarylethene molecules) incorporated into a polymer film are presented. A reversible modulation of the fluorescence intensity of quantum dots, caused by the photoisomerization of diarylethene molecules, was found. It is shown that nanospheres in polymer matrices exhibit higher efficiencies of both photoinduced modulation of QD radiation and Förster resonance energy transfer (FRET) from QDs to the cyclic isomer of DAE as compared to solutions. The results can be used, for example, to create luminescent photocontrolled panels based on films containing fluorescent nanoparticles.

Luminescence photomodulation of nanospheres with CdSe/ZnS quantum dots in polymer films

The results of studies of the spectral-kinetic (absorption and fluorescent) characteristics of the polymer nanospheres created by us (containing luminescent inorganic CdSe/ZnS quantum dots and photochromic diarylethene molecules) incorporated into a polymer film are presented. A reversible modulation of the fluorescence intensity of quantum dots, caused by the photoisomerization of diarylethene molecules, was found. It is shown that nanospheres in polymer matrices exhibit higher efficiencies of both photoinduced modulation of QD radiation and Forster resonance energy transfer (FRET) from QDs to the cyclic isomer of DAE as compared to solutions. The results can be used, for example, to create luminescent photocontrolled panels based on films containing fluorescent nanoparticles. Keywords: photochromism, fluorescence, quantum dot, Forster resonance energy transfer, polymer nanospheres, polymer films

The Preparation of CuInS2-ZnS-Glutathione Quantum Dots and Their Application on the Sensitive Determination of Cytochrome c and Imaging of HeLa Cells.

Cytochrome c (Cyt c), one of the most significant proteins acting as an electron transporter, plays an important role during the transferring process of the energy in cells. Apoptosis, one of the major forms of cell death, has been associated with various physiological regularity and pathological mechanisms. It was found that Cyt c can be released from mitochondria to cytosol under different pathological conditions, triggering subsequent cell apoptosis. Herein, we developed a fluorescence nanoprobe based on negatively charged CuInS2-ZnS-GSH quantum dots (QDs) for the sensitive determination of Cyt c. CuInS2-ZnS-GSH QDs with high photochemical stability and favorable hydrophilicity were prepared by a simple hot reflux method and emit a bright orange-red light. The electron-deficient heme group in Cyt c is affiliated with the electron-rich CuInS2-ZnS-GSH QDs through the photo-induced electron transfer process, resulting in a large decrease in fluorescence intensity of QDs. A good linearity for concentration of Cyt c in the range of 0.01–7 μmol L–1 is obtained, and the detection limit of Cyt c is as low as 1.1 nM. The performance on the detection of Cyt c in spiked human serum and fetal bovine serum samples showed good recoveries from 85.5% to 95.0%. Furthermore, CuInS2-ZnS-GSH QDs were applied for the intracellular imaging in HeLa cells showing an extremely lower toxicity and excellent biocompatibility.

A Ratiometric Optical Dual Sensor for the Simultaneous Detection of Oxygen and Carbon Dioxide

Simultaneous detection of carbon dioxide (CO2) and oxygen (O2) has attracted considerable interest since CO2 and O2 play key roles in various industrial and domestic applications. In this study, a new approach based on a fluorescence ratiometric referencing method was reported to develop an optical dual sensor where platinum (II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) complex used as the O2-sensitive dye, CdSe/ZnS quantum dots (QDs) combined with phenol red used as the CO2-sensitive dye, and CdSe/ZnS QDs used as the reference dye for the simultaneous detection of O2 and CO2. All the dyes were immobilized in a gas-permeable matrix poly (isobutyl methacrylate) (PolyIBM) and subjected to excitation using a 380 nm LED. The as-obtained distinct fluorescence spectral intensities were alternately exposed to analyte gases to observe changes in the fluorescence intensity. In the presence of O2, the fluorescence intensity of the Pt (II) complex was considerably quenched, while in the presence of CO2, the fluorescence intensity of QDs was increased. The corresponding ratiometric sensitivities of the optical dual sensor for O2 and CO2 were approximately 13 and 144, respectively. In addition, the response and recovery for O2 and CO2 were calculated to be 10 s/35 s and 20 s/60 s, respectively. Thus, a ratiometric optical dual gas sensor for the simultaneous detection of O2 and CO2 was successfully developed. Effects of spurious fluctuations in the intensity of external and excitation sources were suppressed by the ratiometric sensing approach.

New properties of carbon nanomaterials through zinc doping and application as a ratiometric fluorescence pH sensor

Fluorescence intensity of carbon nanomaterials (CNMs) synthesized with ethanolamine hardly changed with pH value. Doping Zinc into CNMs improved optical properties of CNMs. On the one hand, the fluorescence quantum yield of CNMs increased, on the other hand, the fluorescence intensity of Zn-doped CNMs decreased with pH value. Coupling Zn-doped CNMs with ZnCdS quantum dots (QDs) as a dual emission system, the blue fluorescence intensity of CNMs (I450) decreased while the orange fluorescence intensity of QDs (I580) enhanced with pH value increasing. The ratio (I450/I580) varied linearly with pH value in the range of 1–9 and correlation coefficient (R2) was 0.991. Furthermore, using the system as a ratiometric fluorescence pH sensor to determine ascorbic acid, a good linear relationship (R2 = 0.998) was found when the concentration of ascorbic acid ranged from 0–1600 μM and limit of detection (LOD) was as low as 0.082 μM.

Synthesis of luminescent biotinylated multivalent dendrimer encapsulated quantum dots and investigation on its physico-chemical interactions with biological receptor avidin

It is challenging to design and characterize molecular recognition pair consisting of both targeting and imaging property and it is also of particular interest to inquire into the limits of the affinity that can be achieved with designed bio-conjugate. This paper presents functionalization of luminescent quantum dots (QDs) employing multivalent dendrimer molecules conjugated with biotin as targeting moiety and photo-physical and thermodynamic behavior of this bio-conjugate in terms of highly affinic binding with avidin. It is demonstrated that fluorescence intensity of QDs remained almost unaffected when synthesized conjugate interacts with avidin and this is considered to be an important requisite for applications in imaging and sensing. The observed changes in average emission lifetime as well as values of lifetime components of avidin indicate the binding of biotin with tryptophan moiety of avidin. Calorimetric investigation reveals that binding of avidin with biotin-dendrimer conjugate is exothermic process accompanied with favorable enthalpy (ΔH = −21.6 kcal/mol) and unfavorable entropy (ΔS = −43.7 cal/mol/deg). These findings may help design of multiplexed assays where dendrimer conjugated QDs based probe molecules are immobilized via the avidin-biotin interactions which can have implications in development of immuno-histochemical techniques.

Potential Application of Perovskite Glass Material in Photocatalysis Field

So far, the application of inorganic glass materials in the field of photocatalysis has not been explored. First, phase separation induced CsPbBr3 quantum dot glasses, as an unprecedented method, is proposed in this work. The results show that the fluorescence intensity of quantum dots (QDs) glass is increased by 1.5 times compared with the initial intensity after the thermal cycle, showing excellent thermal stabilities. Furthermore, the quantum dots glass material is used for the first time in antibiotic residues degradation. The concentration of TC-HCl in 20 mg/L is degraded by 73% in 1 h, and the photocatalytic efficiency reaches 85% of the initial value after three cycles, revealing favorable water stabilities. In this paper, quantum dot glass material breaks the inherent thinking of the preparation methods, and it explores the feasibility application in fields of photocatalyst and brings unexpected changes to the application of glass material in the future.

Monitoring of Cell‐Dependent Reduced States Using Aptamer‐Functionalized Reduction‐Sensitive Quantum Dots

Conjugation of quantum dot (QD) with oxidized nile blue (NB) is known to be able to strongly decrease fluorescence intensity of QD. In the present study, NB‐conjugated QD (QD‐NB) was functionalized with anti‐human epidermal growth factor receptor 2 aptamer to form aptamer‐functionalized QD‐NB (Apt‐QD‐NB), as a new biosensing platform to monitor aptamer‐dependent internalizations and reduction‐dependent transformations. Our study shows that more QD fluorescence signals in cells can be induced by the specific internalization of higher amounts of Apt‐QD‐NB and that the higher ratio of reduced NB over oxidized NB resulting from the different reducing environment of the cells can lead to brighter QD signals. Apt‐QD‐NBs are expected to be used as optical labels that can monitor intracellular metabolic pathways at the single‐cell level, because the use of Apt‐QD‐NBs to investigate drug effectiveness and cellular redox conditions offers exciting opportunities for drug screening.

Preparation of novel fluorescence nanosensor κC - CdTe/ZnS quantum dots for high accurate detection of Epirubicin

Measurement of biologically active compounds in living systems by highly sensitive methods seems to be attractive nowadays. So, design of fluorescence-based quantum dots nanosensors to detect low concentrations of pharmaceutical compounds is a highly attractive area of research. However, reaching the higher fluorescence intensity of quantum dots and reducing the low toxicity of quantum dots by ligand (polymer) exchange method are two more important items. Here, the preparation of novel fluorescence nanosensors κC-CdTe/ZnS quantum dots is reported. After structure confirmation by different analysis methods such as FTIR, TGA, and TEM, fluorescence intensity response of κC-CdTe/ZnS QDs with Epirubicin drug investigated. Based on obtained results, not only this nanosensor developed but also the fluorescence quenching was explained by the typical Stern–Volmer equation. The best linear quenching equation for entitled nanosesor in the presence of Epirubicin is F0/F = 0.0379Q + 1.15 (R2 = 0.99). Moreover, the detection limit of Epirubicin was found around 0.05 × 10−6 mol/L at 25 °C. All of the results showed that this method could be a reliable and suitable approach for the determination of Epirubicin in commercial tablets.

Quantum dots based “On-Off” fluorescence probe for the selective detection of Cu2+ ion: Application to real sample analysis

Abstract Turn ‘On-Off’ quantum dot-based fluorescent probe has been developed for the selective detection of Cu2+. This strategy achieved by consecutively fluorescence enhancement and quenching of mercapto propionic acid (MPA) capped cadmium sulphide quantum dots (MPA-CdS QDs) by the addition of D-penicillamine (D-PA) and Cu2+ respectively. After successive addition of Cu2+in CdS QDs-(D-PA) system, the fluorescence intensity of quantum dots decrease due to the removal of D-PA molecules from the surface of QDs as well as selective ion exchange process takes place between Cu2+ and Cd2+ at the surface of QDs. At optimal conditions, probe offers a good response in the linear range between 4 ng/mL and 40 ng/mL with LOD 2.71 ng/mL. This reported strategy is a very simple and selective towards Cu2+. Hence, a new method for the potential detection of Cu2+ in real pharmaceutical samples can be developed by using QDs-based fluorescence probe.

Quantum Dot-Based F0F1-ATPase Aptasensor for Vibrio parahaemolyticus Detection

Sensitive detection of pathogenic bacteria is of great significance for food safety and public health. This study aimed to report a novel F0F1–ATPase aptasensor based on quantum dots (QDs) for quantitative detection of Vibrio parahaemolyticus. The fluorescent QDs were labeled onto the surface of chromatophores to act as an indicator. Aptamer target to V. parahaemolyticus was linked to the “rotator” e-subunit of F0F1–ATPase within chromatophores to act as a recognition element. On the basis of aptamer and V. parahaemolyticus binding, the loading of e-subunit was increased and the rotation rate of F0F1-ATPase was decreased, resulting in a decrease in the concentration of H+ out of the chromatophores. The increased pH value induced the increased fluorescence intensity of QDs. By using this fluorescent signal strategy in the detection, a limit of detection (LOD) as low as 7 cfu/mL was successfully achieved for ultrasensitive detection of V. parahaemolyticus. This aptasensing assay had no serious cross reaction with interfering species, and was successfully applied to the determination of V. parahaemolyticus in spiked shrimp and salmon samples. The F0F1-ATPase aptasensor provides a promising method for pathogenic bacteria detection in food safety and other application.

A general strategy for label-free homogeneous bioassays based on selective recognition and silver ion-mediated conformational switch

Simple, sensitive, and cost-effective detection of biomolecules is important to clinical analysis and treatment. Herein, a novel fluorescence turn-off method for the homogeneous detection of DNA and proteins was developed using selective recognition reaction and silver ion-mediated conformational switch. In this work, we discovered the new phenomenon that cadmium telluride (CdTe) quantum dots (QDs) could selectively differentiate silver ions (Ag+) from the cytosine (C)-Ag+-cytosine (C-Ag+-C) hairpin structure, owing to the ability of Ag+ to quench CdTe QDs which the C-Ag+-C complex didn't possess. With this method, the C-Ag+-C hairpin probe formed, followed by the reaction with the target DNA, thus the C-Ag+-C was opened and free Ag+ were released. This initiated the selective recognition reaction with CdTe QDs, leading to the decrease in the CdTe QDs fluorescence intensity. Therefore, the DNA concentration could be quantitatively measured by indirectly monitoring the fluorescence signal of CdTe QDs. Furthermore, the application of this sensor was extended to the detection of prostate-specific antigen (PSA) by employing its aptamer as the recognize elements, with the similar strategy used for the target DNA assay. Under the optimized conditions, this strategy achieved good analytical performance for both DNA assay with a limit of detection of 0.12 nM and linear dynamic range of 5–100 nM, and PSA assay with a limit of detection of 0.01 ng/mL and the linear dynamic range of 0.1–2.5 ng/mL. This new fluorescence method is simple in design and operation, with no need for oligonucleotide labeling and separation, and it has great potential to be applied in clinical diagnosis.

Immobilization of gold nanoparticles with rhodamine to enhance the fluorescence resonance energy transfer between quantum dots and rhodamine; new method for downstream sensing of infectious bursal disease virus.

Infectious bursal disease virus is a causative agent of one of the most important disease which causes frequent tragic disaster in the poultry industry all over the world. Therefore, in the present study a new fluorescence resonance energy transfer-based technique was developed to detect VP2 gene of infectious bursal disease virus using two oligonucleotide probes labeled with quantum dots and rhodamine- immobilized gold nanoparticles (AuNPs-Rh). Quantum dots labeled with an amino-modified first oligonucleotide, and AuNPs-Rh labeled with thiol-modified second oligonucleotides were added to the DNA targets upon which hybridization occurred. In the presence of target the AuNPs-Rh will be located in the vicinity of the quantum dots and leads to the fluorescence resonance energy transfer to be occurred and subsequently the fluorescence intensity of quantum dots was stimulated. The immobilization of rhodamine to the surface of AuNPs increased the fluorescence intensity of rhodamine. The maximum fluorescence resonance energy transfer efficiency for the developed sensor is monitored at a quantum dots-PA/AuNPs-Rh-PT molar ratio of 1:10. Moreover, the feasibility of the developed nanobiosensor was demonstrated by the detection of a synthetic 49-mer nucleotide derived from infectious bursal disease virus and the limit of detection was estimated as 3 × 10-8 M. The developed DNA detection scheme is a simple, rapid and efficient technique which does not need excessive washing and separation steps.

Study of energy transfer mechanism from CdS quantum dots to Rhodamine 101 in reverse micelle medium

In this study, fluorescence resonance energy transfer (FRET) between CdS quantum dots (QDs) and Rhodamine 101 was investigated in reverse micelles. CdS QDs as donor were synthesized by using reverse micelle method. The particle sizes of CdS QDs were found as 1.18 ± 0.05 for QD1 and 2.11 ± 0.25 nm for QD2 with TEM measurements. It was determined that the fluorescence intensity of the QDs quenched as the concentration of Rh101 increased. The effect of the concentration of dye on the quenching of the fluorescence intensity of QDs was evaluated by the Stern-Volmer approach and KSV and kq values were calculated. It was observed that the quenching was not diffusion controlled. The FRET parameters were also calculated by using fluorescence spectroscopy. The distances between donor-acceptor (r) were also calculated as 4.74 nm for QD1 and 2.26 nm for QD2. The steady-state transfer efficiencies were calculated as 0.24 and 0.53 for QD1 and QD2, respectively. The time-resolved transfer efficiencies were also determined as 0.11 for QD1 and 0.48 for QD2. The results demonstrated that the novel donor-acceptor pairs may play an important role in the applications of many research areas such as FRET-based nanosensors and light harvesting devices.