Fluorescence Intensity Of CdTe Quantum Dots Research Articles

Y3+@CdTe quantum dot nanoprobe as a fluorescence signal enhancement sensing platform for the visualization of norfloxacin.

Quinolone antibiotics (norfloxacin) pose a serious threat to animal and human health due to their misuse and difficulty in being broken down in surface water and food. Rapid and effective detection of norfloxacin (NOR) is essential for environmental testing and ecosystems. In this study, yttrium was coordinated with mercaptopropionic acid (MPA)-modified CdTe quantum dots (QDs) to obtain a novel fluorescence sensor Y3+@CdTe QDs for the sensitive detection of NOR. NOR can bind to Y3+ to form a complex (NOR-Y3+). This complex enhances the luminescence of NOR and blue-shifts to 423 nm. The fluorescence intensity of NOR-Y3+ at 423 nm (I423) gradually increased with increasing NOR concentration; meanwhile, the fluorescence intensity of CdTe QDs at 634 nm (I634) gradually decreased due to aggregation induction. The ratio of I423 to I634 was used for the quantitative determination of NOR. The linear range of the constructed fluorescent probes was from 1.0 to 150.0 μM, with a detection limit of 31.8 nM. CdTe QDs act as a red fluorescent background, and with the addition of NOR, the color of the system transitions from red to purple and finally blue. This method was rapid (immediate) and visual, providing a simple analysis of various actual samples (tap water, lake water, honey, milk and human serum) for NOR.

Surface functionalized quantum dots as biosensor for highly selective and sensitive detection of ppb level of propafenone.

Monodispersed CdTe quantum dots (QDs) were prepared by using thioglycolic acid as surfactants in aqueous solution. The thioglycolic acid was chemically adsorbed on the surface of CdTe QDs that enables the QDs positively charged. In week acidic media, propafenone is positively charged, which can combine with the CdTe QDs to form larger ion-association complex via electrostatic attraction and hydrogen bond. Moreover, the formed ion-association complex could increase the intensity of resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling-scattering (FDS) of CdTe QDs, and quench the CdTe QDs fluorescence. Importantly, under optimal experimental conditions, the increased RRS, SOS and FDS intensity, and quenched fluorescence intensity of CdTe QDs were in direct proportion to the propafenone concentration in a certain range, respectively. Among them, the RRS method exhibited the highest sensitivity. In a wide concentration range of propafenone from 0.003 to 7.0 μg mL-1, the detection limit could reach 0.96 ng mL-1, which was much lower than previously reported methods. To simulate practical applications, the possible foreign interfering substances were also investigated, such as common ions, amino acid, and glucide. The proposed method here is rapid, sensitive and shows promising application for detection of ppb level of propafenone in human serum.

Amphiphilic CdTe Quantum Dots@Layered Double Hydroxides/Arachidate Nanocomposite Langmuir-Blodgett Ultrathin Films: Its Assembly and Response Mechanism as VOC Fluorescence Sensors.

Amphiphilic biomembrane structures determine significant biological functions and are extensively used as structure models to learn from and study nature. Many biomimetic amphiphilic membranes have been established to connect natural and artificial substances. In this paper, taking advantage of the intercalation and assembly properties of the layered double hydroxides (LDHs), the amphiphilic LDHs/arachidic acid (AA) nanocomposite Langmuir-Blodgett (LB) ultrathin films (UTFs) were fabricated by the LB technology. The CdTe quantum dots (QDs) were incorporated into the LB monolayers via a layer-by-layer (LbL) method based on the electrostatic interaction between LDHs and CdTe QDs. The amphiphilic (CdTe QDs@LDHs/AA) n nanocomposite LB UTFs were composed of CdTe QDs@LDHs hydrophilic segments and hydrophobic layers formed by the long alkyl chain of AA. Because of the spacing effect of amphiphilic AA, the fluorescence intensity of CdTe QDs was enhanced about 10-fold, and the fluorescence lifetimes (38.96 ns vs 17.63 ns) and quantum yield (QY %) (17.56 vs 5.96) have been improved compared to that of the counterpart by the LbL method. The fluorescence intensity of CdTe QDs increased by about fivefolds in the presence of LDHs compared with the counterpart without LDHs, which can be attributed to the two-dimensional confinement effect of LDHs. The amphiphilic nanocomposite LB UTFs were used to detect volatile organic compounds (VOCs) with various polarities. The amphiphilic nanocomposite LB UTFs exhibited two kinds of fluorescence response to VOCs: irreversible fluorescence quenching for amine VOCs with strong polarity and reversible fluorescence enhancement for non-amine VOCs. The fluorescence response mechanism was investigated and can be attributed to the amphiphilic structure of the LB UTFs and the selective adsorption of different VOC molecules. Therefore, this fluorescence quenching/enhancement dual-model response of amphiphilic nanocomposite LB UTFs can be applied into the selective detection of VOCs.

Amplified fluorescence resonance energy transfer sensing of prostate specific antigen based on aggregation of CdTe QDs/antibody and aptamer decorated of AuNPs-PAMAM dendrimer

In this work, a simple and sensitive approach for detection of prostate-specific antigen (PSA) based on the fluorescence resonance energy transfer (FRET) from cadmium telluride (CdTe) quantum dots (QDs) to gold nanoparticles (AuNPs)-polyamidoamine (PAMAM) is described. In this FRET system, CdTe QD modified with antibody (Ab) acts as donor and aptamer decorated PAMAM-AuNPs is used as acceptor in the QDs-Ab/AuNPs-PAMAM/aptamer system. Detection of PSA is achieved by monitoring immunocomplex between PSA and aptamer, while the fluorescence intensity of CdTe QDs decreased during PSA addition. A linear relationship between the concentrations of the PSA antigen and the fluorescence-quenching intensities is obtained when QDs is closed to the AuNPs surface as a result of sandwich structure of QDs-Ab/PSA/AuNPs-PAMA/aptamer. Under the optimized conditions, the linear range of PSA antigen is extended from 0.01 ng mL−1 to 100 ng mL−1 with limit of detection (LOD) of 1 pg mL−1. A superior sensitivity is achieved due to the superior fluorescence properties of CdTe QDs along with highly loading ability of dendrimer and high selectivity of sensor toward PSA displayed due to more specificity of aptamer. The presented assay was further applied for PSA detection in human serum samples with satisfactory results. Due to high selectivity, simplicity and sensitivity of the proposed strategy, it could be developed for sensing of other targets by varying the recognition probes.

Facile Synthesis and Properties of Aqueous CdTe Quantum Dots for High-Sensitive Copper (II) Ion Detection

The synthesis of aqueous MPA-capped CdTe quantum dots (QDs) via a facile one-pot route was developed. The particle size, optical properties and crystal structure of the as-synthesis QDs were investigated by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV-vis absorption and photoluminescence (PL) spectra, respectively. Meanwhile, the effect of reaction conditions, including reaction time, pH and the quantity of sodium citrate (SC) on the growth of CdTe QDs were discussed. Then, the obtained CdTe QDs were successfully used for the detection of trace Cu[Formula: see text] with high sensitivity and excellent selectivity. The fluorescence intensity of CdTe QDs with Cu[Formula: see text] concentration showed a linear relationship in the range from [Formula: see text] mol/L to [Formula: see text][Formula: see text]mol/L. The correlation coefficient (R) is 0.9980 and limit of detection (LOD) is [Formula: see text][Formula: see text]mol/L. Moreover, the concentration of Cu[Formula: see text] in tap water samples was determined based on this sensing system and the recovery test was satisfactory.

Determination of superoxide anion radical by modified CdTe quantum dots

Abstract A novel fluorescence probe for determination of superoxide anion radical (O2 −) was developed with CdTe quantum dots(QDs) modified by thiophene-2-formaldehyde shrinked l -cysteine Schiff base, which was characterized by Fourier transform infrared (FT-IR), thermal gravimetric analysis (TGA), ultraviolet-visible (UV–vis) and fluorescent spectrum. The particle size of CdTe QDs was 3.1 nm as confirmed by X-ray powder diffraction pattern (XRD) and Transmission Electron Microscope (TEM) in presence of β-cysteamine (CA). The fluorescent results showed that the fluorescence intensity of CdTe QDs was decreased with modified Schiff base at 305 nm, but enhanced at 610 nm with O2 − and showed an apparent linear dependence in the concentration scope of 2.0 × 10−5–1.0 × 10−4 mol L−1 (r = 0.9934) with a detection limit of 1.8 × 10−6 mol L−1, which exhibited high selectivity and stability towards O2 −.

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

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

Highly sensitive colorimetric and fluorescent sensor for cyanazine based on the inner filter effect of gold nanoparticles

Cyanazine residue poses a great threat to human health and its derivatives would remain in soils, natural waters, and other environmental domains for a long time. Herein, a simple, rapid, and ultra-sensitive analytical method for the determination of cyanazine (CZ) based on inner filter effect (IFE) of Au nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs) is first described in this study. With the presence of citrate-stabilized AuNPs, the fluorescence of GSH-capped CdTe QDs was remarkably quenched by AuNPs via IFE. The fluorescence of the AuNP–CdTe QD system was recovered upon addition of CZ. CZ can adsorb on to the surface of AuNPs due to its cyano group that has good affinity with gold, which could induce the aggregation of AuNPs accompanying color change from red to blue. Thus, the IFE of AuNPs on CdTe QDs was weakened, and the fluorescence intensity of CdTe QDs was recovered accordingly. A good linear correlation for detection of CZ was exhibited from 0.05 to 9 μM, and the detection limit reached 0.1568 μM, which was much lower than the safety limit required by the USA, the UK, and China. In order to probe into the selectivity of AuNPs towards CZ over other pesticides, various frequently used pesticides were mixed with AuNPs. AuNP composite solution shows good selectivity towards CZ among other pesticides. This method was successfully carried out for the assessment of CZ in real samples with satisfactory results, which revealed many advantages such as high sensitivity, low cost, and non-time-consuming compared with traditional methods.

Visual and fluorescent assays for selective detection of beta-amyloid oligomers based on the inner filter effect of gold nanoparticles on the fluorescence of CdTe quantum dots

Beta-amyloid (Aβ) peptides are the major constituents of senile plaques in the brains of Alzheimer’s disease (AD) patients. Aβ monomers (AβMs) can coalesce to form small, soluble oligomers (AβOs), followed by reorganization and assembly into long, thread-like fibrils (AβFs). Recently, soluble AβOs have been regarded as reliable molecular biomarkers for the diagnosis of AD because of their high toxicity for neuronal synapse and high concentration levels in the brains of AD patients. In this work, we reported a label-free, sensitive and selective method for visual and fluorescent detection of AβOs based on the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). Specifically, the fluorescence of CdTe QDs was quenched significantly by AuNPs through the IFE. PrP(95–110), an AβOs-specific binding peptide from cellular prion protein, triggered the aggregation and color change of AuNPs suspension; thus, the IFE of AuNPs on the fluorescence of CdTe QDs was weakened and the fluorescence intensity was recovered. However, in the presence of AβOs, the specific interaction of AβOs and PrP(95–110) prevented the absorption of PrP(95–110) onto the surface of AuNPs. As a result, the aggregation of AuNPs was inhibited and the fluorescence intensity of CdTe QDs was quenched again. This label-free method is specific for detection of AβOs but not for AβMs and AβFs. The detection limits were found to be 0.5nM for the visual assay and 0.2nM for the fluorescent detection. We believe that this work would be valuable for many investigations related to AD diagnosis and drug discovery.

Improving optical properties of CdTe quantum dots by a new multidentae biopolymer based on salep

In this work, we have successfully modified aqueous CdTe quantum dots (QDs) by a biopolymer based on poly (2-hydroxyethyl methacrylate) grafted onto salep via a facile method at room temperature. The obtained QDs were characterized using Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TG), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The size of the prepared QDs was estimated around 1.5nm by TEM and XRD. Optical properties of modified QDs were monitored by absorption and fluorescence spectrophotometers. It was found that the fluorescence intensity of CdTe QDs was enhanced after coating by biopolymer. Finally, the fluorescence intensity of CdTe QDs was investigated at different temperatures and times.

Synthesis of Two Different Sizes of CdTe Quantum Dots for Detection of Copper(II) in Seawater

The use of CdTe quantum dots (QDs) as fluorescent probes for detection of copper(II) in seawater was evaluated, and the relationship between the size of CdTe QDs and fluorescent response in seawater was investigated. The fluorescence intensity of CdTe QDs was quenched linearly as the concentration of copper(II) increased, and the quenching efficiency increased as the size of the CdTe QDs decreased. The smaller CdTe QDs (emission peak at 518 nm, average diameter of ~2.1 nm) achieved a detection limit of copper(II) of 0.48 μg L−1 under optimal experimental conditions. No significant influence was found for pH in the range from 7.0 to 9.0 in seawater. In contrast, the emission maxima of the CdTe QDs exhibited a slight red shift and the intensity of fluorescence decreased significantly as salinity was increased. Based on the performance of CdTe QDs in this study, small CdTe QDs display enormous potential for detection of copper(II) in seawater.

Luminescence switching of CdTe quantum dots in presence of water-soluble spironaphthoxazine

The typical reaction of spironaphthoxazine is the conversion between the non-polar spiro form and polar merocyanine form. Quantum dots (QDs) have unique optical properties and several advantages over conventional organic dyes. In this work, the CdTe QDs containing a water-soluble spironaphthoxazine was used as the optical probe photoisomerization between spiro and merocyanine. The initial bright fluorescence of CdTe QDs was effectively quenched by water-soluble spironaphthoxazine using UV irradiation. Reversible modulation of fluorescence intensity of CdTe QDs was achieved using alternating irradiation with UV and visible light. The possible mechanism is discussed.

A novel β-Cyclodextrin-QDs optical biosensor for the determination of amantadine and its application in cell imaging

In this paper, a novel optical biosensor for amantadine (AD) determination has been constructed successfully based on the fluorescence resonance energy transfer (FRET) between water-soluble β-Cyclodextrin (β-CD)-functionalized CdTe quantum dots (QDs) and Rhodamine B (RB). RB could enter the cavity of β-CD by hydrophobic interaction, and the process of FRET between QDs and RB occurred. However, the process of FRET was switched off with the addition of AD, due to its larger hydrophobic association constant with β-CD than that of RB. The fluorescence intensity of CdTe QDs (donor) would increase gradually with the increasing concentration of AD, which shown a good linear relationship in the range of 1×10−5–1.6×10−4mol/L with a correlation coefficient R2=0.998. We also obtained a satisfactory result using this spectrophotometric method for the determination of AD in pharmaceutical formulation. Furthermore, β-CD-functionalized CdTe QDs with AD in the cavity were incubated with target HepG2 cells and could be observed in the cytoplasm of cells. The β-CD-functionalized CdTe QDs could act as a visible biomarker for AD in cancer cells fluorescence imaging, which presents a potential application in biomedical field.

Cooperative antimicrobial activity of CdTe quantum dots with rocephin and fluorescence monitoring for Escherichia coli

In this study, the cooperative antibacterial efficiency of CdTe quantum dots (QDs) and rocephin against Escherichia coli (E. coli) was investigated. Colony-forming capability assay and diameter of inhibition zone (DIZ) measurement showed the antibiotic action of CdTe QDs-rocephin complex was better than the superposition of pure CdTe QDs and rocephin. The fractional inhibitory concentration index (FICI) indicated that CdTe QDs-rocephin complex could achieve great cooperative antimicrobial effects. The infrared ray (IR) spectrum, photoluminescence (PL) spectrophotometry, and detection of reactive oxygen species (ROS) indicated that CdTe QDs and rocephin formed a stable antimicrobial group through electrostatic attraction and hydrogen bonds and then killed the E. coli together. Meanwhile, the fluorescence intensity of CdTe QDs and the optical density (OD) value of E. coli showed a good linear relationship. Thus, dynamic monitoring to total bacterial concentration in the antibacterial process was realized by the CdTe QDs.

Determination of vanadium(V) with CdTe quantum dots as fluorescent probes

CdTe quantum dots (QDs) were modified with thioglycolic acid (TGA) and synthesized in aqueous medium. The optimum fluorescence intensity was found to be at pH 6.24 with a CdTe QDs concentration of 4.96 x 10(-7) mol L(-1). The quenched fluorescence intensity of CdTe QDs is linearly proportional to V(V) concentration from 10 to 200 ng mL(-1) with correlation coefficient R = 0.9985. The limit of detection for V(V) was 2.07 ng mL(-1). The proposed method was successfully applied to the analysis of trace amounts of V(V) in water samples with recovery of 96.5-101.8%, and the results were in good agreement with those of electrothermal atomic absorption spectrometry.

Water-soluble multicolored fluorescent CdTe quantum dots: Synthesis and application for fingerprint developing

Multicolored water-soluble fluorescent CdTe quantum dots (QDs) have been synthesized by using Te, NaBH 4, and CdCl 2 as precursors and several mercapto-based compounds as modifiers. The effects of ratio of the precursor, type of modifier, refluxing time and initial pH value of the reaction on fluorescence intensity of CdTe QDs have been studied. XRD, HRTEM and fluorescence spectra were employed to characterize these samples. It is found that CdTe QDs with a crystalline size of 3–4 nm are homogeneously embedded in the organic matrix. The maximum fluorescence emission peaks of CdTe QDs solutions shifted from 525 nm to 591 nm according to the refluxing time. The fingerprint details on the surface of smooth objects were clearly developed with CdTe QDs solution under irradiation of UV lights.

Ultrasensitive Detection of Trace Protein by Western Blot Based on POLY-Quantum Dot Probes

In this study, we describe an ultrasensitive quantum dots (QDs)-based Western blot. With the high affinity of avidin-functionalized POLY-QDs and simplification of the detection process, this enabled the quantitative analysis of protein by Western blotting. To prepare the POLY-QDs, CdTe quantum dots were first coated with biotinylated denatured bovine serum albumin and then, via the effect of the biotin-avidin system, the biotinylated denatured bovine serum albumin-coated QDs, which had strong fluorescence, were linked together. With this series of modifications, the fluorescence intensity of CdTe QDs was significantly increased. Using the POLY-QDs as labels, the signal of Western blotting was more sensitive in tracing the protein than traditional dyeing. In the present study, trace protein A was applied to POLY-QDs-based Western blotting as a model. The linearity of this method was from 30 pg to 1.5 ng, and the sensitivity was up to low pictogram values. The final fluorescence signal on the polyvinylidenedifluoride (PVDF) membrane was retained for at least 40 min. The results of this study indicate that the POLY-QDs-based Western blot is an excellent quantitative analytical method for trace protein analysis.

Ionic Liquids (ILs) Detection Based on its Enhancing Effect on the Photoluminescence of CdTe Quantum Dots (QDs)

In this paper, a method for the determination of ILs, specifically 1-butyl-3-methyl imidazolium bromide( BMIB), was developped using mercaptoacetic acid (MAA) capped CdTe QDs as fluorescence probe. Under optimum conditions, the enhancement of fluorescence intensity of CdTe QDs was linearly in proportion to the concentration of BMIBin the range of 9.1x10-5-1.1x10-2 mol L-1 with a correlation coefficient of 0.996. The detection limit was 6.9x10-5 mol L-1. The proposed method was applied to the determination of trace BMIB in river water and tap water samples with satisfactory results. Keywords: Ionic liquids, 1-Butyl-3-methylimidazolium bromide, CdTe quantum dots, Fluorescence enhancement