Thioglycolic Acid-capped CdTe Quantum Dots Research Articles

Modeling and optimization of the ratio of fluorophores: a step towards enhancing the sensitivity of ratiometric probes.

In the ratiometric fluorescent (RF) strategy, the selection of fluorophores and their respective ratios helps to create visual quantitative detection of target analytes. This study presents a framework for optimizing ratiometric probes, employing both two-component and three-component RF designs. For this purpose, in a two-component ratiometric nanoprobe designed for detecting methyl parathion (MP), an organophosphate pesticide, yellow-emissive thioglycolic acid-capped CdTe quantum dots (Y-QDs) (analyte-responsive), and blue-emissive carbon dots (CDs) (internal reference) were utilized. Mathematical polynomial equations modeled the emission profiles of CDs and Y-QDs in the absence of MP, as well as the emission colors of Y-QDs in the presence of MP separately. In other two-/three-component examples, the detection of dopamine hydrochloride (DA) was investigated using an RF design based on blue-emissive carbon dots (B-CDs) (internal reference) and N-acetyl L-cysteine functionalized CdTe quantum dots with red/green emission colors (R-QDs/G-QDs) (analyte-responsive). The colors of binary/ternary mixtures in the absence and presence of MP/DA were predicted using fitted equations and additive color theory. Finally, the Euclidean distance method in the normalized CIE XYZ color space calculated the distance between predicted colors, with the maximum distance defining the real-optimal concentration of fluorophores. This strategy offers a more efficient and precise method for determining optimal probe concentrations compared to a trial-and-error approach. The model's effectiveness was confirmed through experimental validation, affirming its efficacy.

A highly selective and simple fluorescent probe for salbutamol detection based on thioglycolic acid-capped CdTe quantum dots.

In this paper, a highly fluorescent water-soluble CdTe quantum dots (CdTe QDs) stabilized with thioglycolic acid (TGA) were synthesized for the quantitative and selective determination of salbutamol (SAL). When ten different of 2.09×10-6 mol L-1 alpha-2 adrenoceptor agonist were added to 4.38×10-4 mol L-1CdTe QDs solution, the fluorescence signal of the CdTe QDs quenched obviously by SAL with 57.32% and 0.815% - 7.00% for other nine kinds of veterinary medicine, such as tulobuterol, fenoterol, phenylethanamine A, simatero, penbutolol, clenbuterol, ractopamine, terbutaline and clorprenaline. The result shows that the CdTe QDs is highly sensitive sensor for SAL. The quenching mechanism has been investigated by absorption spectroscopy and KSV at different temperatures, and shew a static quenching process than dynamic quenching. Under the optimal conditions, respectively the straight line equation (F0/F=0.1491×106 C+1.3078) was found between the relative fluorescence intensity and the concentration of SAL was in the range of 6.27×10-8 to 2.09×10-7 mol L-1, and the limit of detection was 4.2×10-8 mol L-1. The proposed method has been applied to the determination of SAL in pig urine samples.

Aptamers-Based Sensing Strategy for 17β-Estradiol Through Fluorescence Resonance Energy Transfer Between Oppositely Charged CdTe Quantum Dots and Gold Nanoparticles.

A novel aptamers-based fluorescence resonance energy transfer (FRET) assay was developed employing the oppositely charged thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) and cysteamine-stabilized gold nanoparticles (cysteamine-AuNPs). The fluorescence of TGA-CdTe QDs was significantly quenched with addition of cysteamine-AuNPs via the FRET. The FRET process can be modulated by 17β-estradiol in that the specific recognition between 17β-estradiol and aptamers could show different effects on the aptamers-mediated aggregation of cysteamine-AuNPs, and correspondingly adjust the FRET process. The feasibility of the method has been demonstrated by carrying out the detection of 17β-estradiol with the wide linear range from 0.5·ng mL-1 to 150 ng·mL-1 and the low detection limit of 0.057 ng·mL-1. The established assay exhibited favorable selectivity towards 17β-estradiol over other endocrine disrupting compounds and probably coexisting chemicals in real samples. Furthermore, the assay has been successfully applied to detect 17β-estradiol in real tap water samples and feeds samples with good performance. The results were in full consistence with those from HPLC method, indicating the reliability of the detection system. The aptamers-based FRET assay is expected to offer a new opportunity for the rapid analysis of 17β-estradiol in real samples.

Boric Acid-Based Dual Modulation Photoluminescent Glucose Sensor Using Thioglycolic Acid-Capped CdTe Quantum Dots

Most luminescent glucose sensors based on the interaction of glucose with organic boric acids or borates. Herein, a new luminescent glucose sensor is designed using thioglycolic acid-capped CdTe quantum dots in the presence of cheap inorganic boric acid. Both peak position and intensities change upon the addition of glucose because of the interaction of boric acid with glucose and thioglycolic acid-capped CdTe quantum dots, which enables glucose detection by either color change or intensity change. The luminescent intensities change linearly with glucose concentrations in the ranges from 0.03 to 1 mM and 1–25 mM with a detection limit of 10 µM (S/N = 3). Moreover, glucose concentrations can be conveniently detected by color change in the range from 1 mM–25 mM. It displays a highly selective response to glucose over other interfering but biologically important saccharides, amino acids, and common ions. A thioglycolic acid-capped CdTe QD-based sensor can detect glucose with wide linear range by change in intensity or color in the presence of cheap inorganic boric acid.

Flow-based determination of methionine in pharmaceutical formulations exploiting TGA-capped CdTe quantum dots for enhancing the luminol-KIO4 chemiluminescence

A novel flow-injection chemiluminescence method (FI-CL) was established for the determination of methionine in this paper, based on its strong enhancement on CL intensity of the luminol-KIO4 system catalyzed by thioglycolic acid-capped CdTe quantum dots in alkaline media. Under the optimized conditions, the relative CL intensity was in proportion to methionine concentration in the range from 1.0×10−8 to 1.0×10−5gmL−1 with a detection limit of 6.6×10−9gmL−1 (3σ). The relative standard deviation (RSD) of the CL intensity for 1.0×10−6gmL−1 standard methionine solution was 0.97% (n=11). The proposed method was successfully applied to determine methionine in commercial pharmaceutical formulations with recoveries between 98.0% and 101.9%. The possible CL mechanism was discussed as well.

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.

Sensitive arginine sensing based on inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

Arginine plays an important role in many biological functions, whose detection is very significant. Herein, a sensitive, simple and cost-effective fluorescent method for the detection of arginine has been developed based on the inner filter effect (IFE) of citrate-stabilized gold nanoparticles (AuNPs) on the fluorescence of thioglycolic acid-capped CdTe quantum dots (QDs). When citrate-stabilized AuNPs were mixed with thioglycolic acid-capped CdTe QDs, the fluorescence of CdTe QDs was significantly quenched by AuNPs via the IFE. With the presence of arginine, arginine could induce the aggregation and corresponding absorption spectra change of AuNPs, which then IFE-decreased fluorescence could gradually recover with increasing amounts of arginine, achieving fluorescence “turn on” sensing for arginine. The detection mechanism is clearly illustrated and various experimental conditions were also optimized. Under the optimum conditions, a decent linear relationship was obtained in the range from 16 to 121μgL−1 and the limit of detection was 5.6μgL−1. And satisfactory results were achieved in arginine analysis using arginine injection, compound amino acid injection, even blood plasma as samples. Therefore, the present assay showed various merits, such as simplicity, low cost, high sensitivity and selectivity, making it promising for sensing arginine in biological samples.

SERS and integrative imaging upon internalization of quantum dots into human oral epithelial cells.

CdTe quantum dots (QDs) are widely used in bio-applications due to their size and highly efficient optical properties. However internalization mechanisms thereof for the variety of freshly extracted, not cultivated human cells and their specific molecular interactions remains an open topic for discussion. In this study, we assess the internalization mechanism of CdTe quantum dots (3.3 nm) capped with thioglycolic acid using non cultivated oral epithelial cells obtained from healthy donors. Naked gold nanoparticles (40 nm) were successfully used as nanosensors for surface-enhanced Raman spectroscopy to efficiently identify characteristic Raman peaks, providing new evidence indicating that the first interactions of these QDs with epithelial cells occurred preferentially with aromatic rings and amine groups of amino acid residues and glycans from trans-membrane proteins and cytoskeleton. Using an integrative combination of advanced imaging techniques, including ultra-high resolution SEM, high resolution STEM coupled with EDX spectroscopy together with the results obtained by Raman spectroscopy, it was determined that thioglycolic acid capped CdTe QDs are efficiently internalized into freshly extracted oral epithelial cells only by facilitated diffusion, distributed into cytoplasm and even within the cell nucleus in three minutes.

CdTe quantum dots and gold nanoparticle based spectral methods for determination of lincomycin

Two novel and convenient methods for the determination of lincomycin (LCM) in aqueous solutions have been developed. The first method was based on the enhanced fluorescence of thioglycolic acidcapped CdTe quantum dots (TGA-CdTe QDs) by LCM. For the second method, the introduction of LCM could induce the aggregation of gold nanoparticles (AuNPs), displaying distinct changes in color and in UVvis spectra. Under optimal conditions, the enhanced fluorescence intensity was linearly proportional to LCM concentration in the range of 1–240 μg mL−1 with a detection limit of 2.63 × 10−1 μg mL−1. The second platform is capable of determining LCM in ranges from 1.00 × 10−3 to 2.00 × 10−2 μg mL−1 and from 3.00 × 10−2 to 1.20 × 10−1 μg mL−1 with a detection limit of 1.27 × 10−4 μg mL−1. Both methods were used for rapid detection of LCM in real samples with satisfactory results. Comparisons between the two methods were made.

Determination of Tigecycline by Quantum Dots/Gold Nanoparticles-based Fluorescent and Colorimetric Sensing System

In this study, two simple and sensitive methods for detection of tigecycline are developed based on thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) and unmodified gold nanoparticles (AuNPs), respectively. The first method was based on the fluorescence quenching of CdTe QDs by the addition of tigecycline. For the second method, the introduction of tigecycline could induce the aggregation of gold nanoparticles, displaying distinct changes in color and in UV-vis spectra. Under optimal conditions, the relative fluorescence intensity of CdTe QDs decreased linearly with the increasing concentration of tigecycline in the range of 0.11-35.56 ug mL-1 with a detection limit of 3.93×10-2 ug mL-1. While the colorimetric sensor could detect tigecycline in linear range from 5.98×10-3 to 1.44×10-1 ug mL-1 and from 0.30 to 2.99 ug mL-1 with a detection limit of 1.07×10-3 ug mL-1. Moreover, both the proposed methods were applied to real sample with satisfactory results. Finally, comparisons between these two methods were made. Keywords: Colorimetric, fluorescence quenching, gold nanoparticles, quantum dots, tigecycline.

Investigation of ultrafast relaxation dynamic process of water-soluble TGA-CdTe quantum dots

In the present paper, we study the average fluorescence lifetimes, detected by using the time-correlated single-photon-counting (TCSPC) technique, of three thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs), which are ～6 ns, ～9 ns and ～11 ns; and the fluorescence kinetic process includes two parts:the slow process and the fast process. With the increase of the particle size, the slow process becomes longer, but the fast process becomes shorter. Afterwards, by using both femtosecond transient absorption and fluorescence up-conversion time-resolved spectrum techniques, we have investigated the interband relaxation process of three TGA-CdTe QD samples, with the nanoparticle diameters of 2.3, 2.8 and 3.5 nm. Investigation indicates that for the three QD samples, exciton filling rate becomes slower in the highest excited state and the lowest excited state, among them, the time of exciton filling increases from 0.33 to 0.79 ps for the highest excited state, while the time of exciton filling increases from 0.53 ps to 1 ps for the lowest excited state. Moreover, the two kinds of experiment provide complementary information and obtain the full image of interband relaxation process. Result shows that the bleach recovery of the 1 S transition shows an initial rise, but the fluorescence up-conversion signal for the 1 S transition is slower in rise time, which can provide help in the application of optoelectronic devices.

Turn-on electrochemiluminescence sensing of Cd2+ based on CdTe quantum dots

A simple and sensitive method for the detection of cadmium ion was proposed based on the electrochemiluminescence (ECL) of thioglycolic acid capped-CdTe quantum dots (CdTe QDs). The ECL of CdTe QDs was firstly quenched by introduction of S2− and was restored due to following addition of Cd2+, on the basis of which, a “turn-on” ECL method for the detection of Cd2+ was demonstrated. The ECL of CdTe QDs exhibited linear response toward Cd2+ concentration in the range from 6.3nM to 3.4μM (R=0.999) with a detection limit of 2.1nM. The proposed assay was simple, sensitive, selective, and practicable in real water samples.

Structural, optical, and electrical properties of thioglycolic acid-capped CdTe quantum dots thin films

Water-soluble cadmium telluride (CdTe) quantum dots (QDs) were synthesized using thioglycolic acid as capping agent; this reaction was carried out at pH = 10.2 and refluxed at 100°C for 18 h. The CdTe QDs prepared at various reflux times from 1 to 18 h were coated on the glass substrates to obtain thin films of the CdTe QDs with the same thickness. The CdTe thin films were characterized by X-ray diffraction, ultraviolet-vis spectroscopy, and photoluminescence spectroscopy. The absorption thresholds of the CdTe thin films are blueshifted by about 0.65 eV with respect to the bulk value (1.5 eV), due to the quantum size effect as expected from the nanocrystalline nature of the CdTe QDs. X-ray diffraction showed that the films consisted of small CdTe nanocrystallites, 2.91 to 3.57 nm in size, showing quantum size effects. The effects of temperature on the electrical properties of the films were studied in detail. Electrical resistivity measurements were carried out for different films in the temperature range from 343 to 463 K. It is shown that activation energy increases by increasing the reflux time.

An improved method for ratiometric fluorescence detection of pH and Cd2+ using fluorescein isothiocyanate–quantum dots conjugates

In this study, thioglycolic acid capped-CdTe quantum dots (QDs) were modified by polyethylenimine (PEI), and then combined with fluorescein isothiocyanate (FITC) to fabricate FITC–CdTe conjugates. The self-assembly of FITC, CdTe and PEI was ascribed to electrostatic interactions in aqueous solution. The resulting conjugates were developed toward two routes. In route one, ratiometric photoluminescence (PL) intensity of conjugates (IFITC/IQDs) was almost linear toward pH from 5.3 to 8.7, and a ratiometric PL sensor of pH was favorable obtained. In route two, firstly added S2− induced remarkable quenching of QDs PL peak (at the “OFF” state), which was restored due to following addition of Cd2+ (at the “ON” state). In the conjugates, successive introduction of S2− and Cd2+ hardly influenced on FITC PL peaks. According to this PL “OFF-ON” mode, a ratiometric PL method for the detection of Cd2+ was achieved. Experimental results confirmed that the IFITC/IQDs exhibited near linear proportion toward Cd2+ concentration in the range from 0.1 to 15μM, and the limit of detection was 12nM. Interferential experiments adequately testified that the proposed sensors of pH and Cd2+ were practicable in real samples and complex systems. In comparison with conventional analytical techniques, the ratiometric PL method was simple, rapid, economic and highly selective.

Spectral method determination of kanamycin sulfate using both gold nanoparticles and quantum dots

Two novel methods for the determination of kanamycin sulfate (Kan) have been developed. The first method was based on the enhanced fluorescence of thioglycolic acid-capped CdTe quantum dots by Kan in aqueous solutions. The second method was a simple colorimetric method to detect trace amounts of Kan with unmodified gold nanoparticles as the sensing probe. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of Kan between 1.80 × 10−2 μg mL−1 and 8.00 × 10−1 μg mL−1. The linear ranges of the colorimetric sensor for Kan were from 3.75 × 10−3 μg mL−1 to 4.25 × 10−2 μg mL−1 and from 4.40 × 10−2 μg mL−1 to 9.88 × 10−2 μg mL−1, respectively. Comparisons between the two methods were made. Both methods were used for rapid detection of Kan in real samples with satisfactory results.

Electrochemical reduction of dioxygen on a thioglycolic acid-capped CdTe quantum dots modified glassy carbon electrode

A novel modified electrode was constructed by immobilizing thioglycolic acid-capped CdTe quantum dots (QDs) on a glassy carbon electrode (GCE) using Nafion ionomers. The results obtained by electrochemical impedance spectroscopy, cyclic voltammetry, and rotating disk electrode using the modified QDs–Nafion/GCE in a 0.20 M phosphate buffer of pH 7.0 revealed that the QDs act as effective mediators for the electrocatalytic reduction of dioxygen.

Sensitive fluorescent detection of melamine in raw milk based on the inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

A simple, rapid and sensitive fluorescent assay for determination of melamine has been developed based on inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). When thioglycolic acid-capped CdTe QDs was mixed with citrate-stabilized AuNPs, the fluorescence of CdTe QDs was significantly quenched via the IFE of AuNPs. With the presence of melamine, melamine could induce the aggregation and corresponding absorbance change of AuNPs, which then resulted in the recovery of IFE-decreased emission of CdTe QDs. Under the optimum conditions, the detection limit for melamine in raw milk was 0.02mgL−1. The application of this method in samples of melamine-spiked raw milk suggested a recovery between 103% and 104%. Therefore, the obvious merits provided by the present assay, such as simplicity, rapidity, low cost, and high sensitivity, would make it promising for on-site screening of melamine adulterant in raw milk.

Investigations on the photoinduced interaction of water soluble thioglycolic acid (TGA) capped CdTe quantum dots with certain porphyrins

The photoinduced interaction of TGA capped CdTe quantum dots (QDs) with porphyrins such as meso-tetrakis(4-sulfonatophenyl)porphyrin [TSPP], meso-tetrakis(4-carboxyphenyl)porphyrin [TCPP], meso-tetrakis (4-N-methylpyridyl)porphyrin [TMPyP] and meso-tetraphenylporphyrin [TPP] has been studied by using absorption, steady state and time resolved fluorescence spectroscopy. The QD surface was negatively charged due to thiol capping agent containing carboxylic group. Positively charged TMPyP interacts with QDs through charge transfer mechanism, negatively charged porphyrins (TCPP and TSPP) interacted through energy transfer mechanism and the neutral one (TPP) does not have any interaction. The Stern–Volmer constant, quenching rate constant, association constants, rate of electron transfer and energy transfer parameters were calculated from the fluorescence data. Effect of molecular structure has also been studied.

Effects of size, capping agent, and concentration of CdSe and CdTequantum dots doped into a nematic liquid crystal on the optical and electro-optic properties of the final colloidal liquid crystal mixture

To investigate size and capping agent-dependent alignment and electro-optic effects of quantum dots (QDs) in nematic LCs, mixtures of a nematic phenylpyrimidine LC (LC1) doped with hexadecylamine-capped CdSe and thioglycolic acid-capped CdTe QDs were prepared and investigated by polarized optical microscopy between plain, untreated glass slides and in ITO-coated glass cells with rubbed polyimide alignment layers as well as by electro-optic analysis. The five investigated CdSe QDs, varying in size from 2.5 to 5.2 nm, show fluorescence emission maxima ranging from 480 to 610 nm, and the four CdTe QDs, varying in size from 3.2 to 4.0 nm, emit light from 530 to 610 nm depending on their size. The CdSe QDs favoring homeotropic anchoring of the nematic LC induce vertical alignment at 1 and 2 wt% in LC1 between plain glass slides and only at 1 wt% in the planar cells, except for CdSe QD emitting at 590 nm (CdSe590), which induces vertical alignment independent of the substrate only at 1 wt%. Concentrations above 2 wt% of the CdSe QDs in LC1 show planar alignment mainly due to aggregation of the QDs in LC1 at these higher concentrations. On the contrary, the CdTe QDs favoring planar anchoring of the nematic LC induce homeotropic alignment of LC1 at concentrations above 2 wt% between plain glass slides. All QDs are effective in reducing the threshold voltage (Vth) and the splay elastic constant (K11). The most drastic reduction over the entire temperature range, however, was observed for the smallest CdSe480 QDs, which showed the least tendency of all investigated QDs to aggregate in LC1.

A simple fluorescence quenching method for berberine determination using water-soluble CdTe quantum dots as probes

A novel method for the determination of berberine has been developed based on quenching of the fluorescence of thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) by berberine in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of berberine between 2.5 × 10 −8 and 8.0 × 10 −6 mol L −1 with a detection limit of 6.0 × 10 −9 mol L −1. The method has been applied to the determination of berberine in real samples, and satisfactory results were obtained. The mechanism of the proposed reaction was also discussed.