Mercaptopropionic Acid-capped CdTe Quantum Dots Research Articles

Portable smartphone-assisted RGB-dependent ratiometric sensing platform for the detection of tetrachloro-p-benzoquinone in river samples

Tetrachloro-p-benzoquinone (TC-PBQ) can be harmful to the environment as a pesticide residue, but its analytical detection has been largely neglected. In this work, a smartphone-assisted RGB-dependent TC-PBQ ratiometric sensing platform for rapid recognition is introduced. Here, the red-emitting mercaptopropionic acid-capped CdTe quantum dots (MPA-capped CdTe) as the reaction unit can be quenched by TC-PBQ, while the blue-emitting carbon dots (CDs) as the reference signal remain unchanged. The limit of detection (LOD) of the sensing platform can reach 59 nM in aqueous solution. By constructing an analysis model with the system RBG value, the smartphone-assisted sensor-coated fluorescent test paper can complete the qualitative and quantitative visual detection of TC-PBQ (LOD is 93 nM). The applicability of smartphone-dependent RGB analysis significantly simplifies and speeds up the operation process, which provides a new analytical method for real-time analysis of TC-PBQ in real samples.

Toward visual chiral recognition of amino acids using a wide-range color tonality ratiometric nanoprobe

Chiral recognition has long been a challenging issue to deal with in biological systems, drug design and food authentication. Implementing nanoparticle-based probes with intrinsic or induced chirality in this field has addressed several issues concerning sensitivity, reliability, rapidness and the cost of chiral sensing platforms. Yet, research into chiral nanoprobes that can be used for visual monitoring of chiral substances is still in its infancy. As part of this study, a visual chiral recognition platform has been developed in which a combination of blue-emitting carbon dots (BCDs) and mercaptopropionic acid-capped CdTe quantum dots (MPA-QDs) with inherent chiroptical activity were employed for enantiomeric detection. The ratiometric probe displayed unique fluorescence response patterns in the presence of arginine (Arg) and histidine (His) enantiomers. Upon addition of l-amino acids, successive enhancement and quenching of emission intensity as well as a red-shift in emission wavelength of MPA-QDs were observed. The emission color of the nanoprobe changed from green to pink-red and green to brick-red red by increasing the concentration of L-Arg and L-His, respectively.In contrast, their d-amino acid equivalents have a negligible influence on the emission color and fluorescence signal of the developed nanoprobe. Due to the enantioselective vibrant color changes of the nanoprobe, RGB analysis was applied for the determination of enantiomeric excess (ee) in racemic mixture with satisfactory results, allowing smartphone-based onsite visual evaluation of ee (%). Circular dichroism, lifetime, size distribution and ζ-potential measurements were employed to study the chiroselective responses. First-principle calculations were also carried out with density functional theory (DFT) to confirm the experimental observation. Furthermore, chiroselective response patterns of the ratiometric nanoprobe were manipulated to construct a logic gate system mimicking AND, OR, and INHIBIT functions. The capability of the proposed chiral platform in visual monitoring of the fraction of enantiomers in racemic mixtures has a great potential for rapid and onsite visual discrimination of chiral compounds in the field of clinical diagnostics and drug analysis.

Conformational and functional effects of MPA-CdTe quantum dots on SOD: Evaluating the mechanism of oxidative stress induced by quantum dots in the mouse nephrocytes.

The application of quantum dots (QDs) is restricted by the biosafety issue. QDs contribute to the adverse effects of organisms probably because of the ability to induce oxidative stress via changing the activity of antioxidant enzyme, for example, superoxide dismutase (SOD). But the underlying molecular mechanisms still remain unclear. This study investigated the harmful effects of oxidative stress induced by mercaptopropionic acid capped CdTe QDs (MPA-CdTe QDs) on the mouse primary nephrocytes as well as the structure and function of SOD molecule and explored the underlying molecular mechanism. After 24-hour MPA-CdTe QD exposure, the activation level of extracellular regulated protein kinase (ERK) signaling pathway and cysteinyl-directed aspartate-specific proteases (Caspases) significantly increased, which led to the increasing level of reactive oxygen species (ROS) and cell apoptosis; the group pretreated with ROS scavenger N-acetyl-L-cysteine (NAC) significantly reduced the apoptotic cell percentage, indicating that ROS played a critical role in QD-induced cytotoxicity. Further molecular experiments showed that the interacting processes between the MPA-CdTe QDs and SOD were spontaneous which changed the conformation, secondary structure of SOD. The interaction significantly resulted in the tightening of polypeptide chains and the shrinkage of SOD, leading to the inhibition of molecular SOD activity. This study demonstrates the adverse effects of QDs, revealing their potential risk in biomedical applications.

A magnetic nanoparticle based immunoassay for alternariol monomethyl ether using hydrogen peroxide-mediated fluorescence quenching of CdTe quantum dots.

The authors describe a fluorometric immunoassay for alternariol monomethyl ether (AME). It is making use of magnetic nanoparticles and quenching of the fluorescence of mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) by H2O2. Catalase (CAT) was labeled with AME as a competitive antigen to competitively bind to magnetic nanoparticles carrying monoclonal antibodies (mAbs) with free AME in samples. The effects of the concentration and pH value of buffer, the concentrations of H2O2 and CAT-AME, and the incubation time of H2O2 and MPA-CdTe QDs were optimized. Under optimal conditions and in combination with magnetic separation, the quenching of the fluorescence of the MPA-CdTe QDs (excitation at 310nm, emission at 599nm) can be used to quantify AME with a detection limit of 0.25pg·mL-1 and the linear range from 0.25 to 7.5pg·mL-1. The immunoassay also has a lower cross-reactivity to AME analogues. It was evaluated by analyzing fruit samples spiked with AME. The recoveries from spiked fruits ranged from 87.2% to 92.0%. Graphical abstract Schematic presentation of a fluorometric immunoassay for alternariol monomethyl ether (AME) using magnetic nanoparticles (MNPs) for the rapid separation and purification. The method is based on quenching of the fluorescence of mercaptopropionic acid-capped CdTe quantum dots (MPA-CdTe QDs) by H2O2 for the fluorescence signal output, and on the use ofcatalase (CAT) with its high catalytic activity.

Preparation of fluorescent CdTe@CdS core@shell quantum dots using chemical free gamma irradiation method

This study investigates pH dependent gamma radiation effects on Mercaptopropionic Acid (MPA) capped CdTe quantum dots (QDs). Gamma radiation, as fast and chemical free catalyser, causes CdS Shell formation on MPA capped CdTe QDs at very high alkaline environment. UV–vis absorption spectroscopic results showed that, with increase in gamma radiation doses, the absorption peak of CdTe QDs decreased to lower wavelength (decrease in particle size) in both acidic & neutral medium (as synthesised), and it increased towards longer wavelength in basic medium indicating the possibility of growth of CdS shell over CdTe core QDs. X-ray diffractogram studies have revealed that the peaks of CdTe QDs shift towards higher angles after irradiation, supporting the notion of the core@shell particle structure of CdTe@CdS. TEM images confirmed the extra stretch around core particles from CdS material resulted in increase of average size of QDs. EDX study revealed the chemical composition of material system. X-ray photoelectron spectroscopic results revealed the shift in the binding energy of both Cd and S thereby indicating the change in the coordination condition after irradiation promoted the particles’ formation of core@shell in nature. The systematic photoluminescence spectroscopic investigation at all possible pH values against ascended gamma radiation doses revealed the formation of CdS shell over CdTe core at optimum pH value (i.e. only at basic pH 12). Contrarily, photo-oxidation of QDs’ was observed at neutral (and below) pH values towards gamma irradiation. The quantum yield is increased only after introducing external shell source material at highest alkaline media confirming the formation of CdS shell on CdTe core.

Fluorescence ELISA for sensitive detection of ochratoxin A based on glucose oxidase-mediated fluorescence quenching of CdTe QDs

The present study described a novel fluorescence enzyme-linked immunosorbent assay (ELISA) used to detect ochratoxin A (OTA) by using the glucose oxidase (GOx)-mediated fluorescence quenching of mercaptopropionic acid-capped CdTe quantum dots (MPA-QDs), in which GOx was used as an alternative to horseradish peroxidase (HRP) for the oxidization of glucose into hydrogen peroxide (H2O2) and gluconic acid. The MPA-QDs were used as a fluorescent signal output, whose fluorescence variation was extremely sensitive to the presence of H2O2 or hydrogen ions in the solution. Under the optimized conditions, the proposed fluorescence ELISA demonstrated a good linear detection of OTA in corn extract from 2.4 pg mL−1 to 625 pg mL−1 with a limit of detection of 2.2 pg mL−1, which was approximately 15-fold lower than that of conventional HRP-based ELISA. Our developed fluorescence immunoassay was also similar to HRP-based ELISA in terms of selectivity, accuracy, and reproducibility. In summary, this study was the first to use the GOx-mediated fluorescence quenching of QDs in immunoassay to detect OTA, offering a new possibility for the analysis of other mycotoxins and biomolecules.

Mercaptopropionic acid-capped CdTe quantum dots as fluorescence probe for the determination of salicylic acid in pharmaceutical products.

Mercaptopropionic acid (MPA)-capped cadmium telluride (CdTe) quantum dot (QDs) fluorescent probes were synthesized in aqueous solution and used for the determination of salicylic acid. The interaction between the MPA-capped CdTe QDs and salicylic acid was studied using fluorescence spectroscopy and some parameters that could modify the fluorescence were investigated to optimize the measurements. Under optimum conditions, the quenched fluorescence intensity of MPA-capped CdTe QDs was linearly proportional to the concentration of salicylic acid in the range of 0.5-40 µg mL(-1) with a coefficient of determination of 0.998, and the limit of detection was 0.15 µg mL(-1). The method was successfully applied to the determination of salicylic acid in pharmaceutical products, and satisfactory results were obtained that were in agreement with both the high pressure liquid chromatography (HPLC) method and the claimed values. The recovery of the method was in the range 99 ± 3% to 105 ± 9%. The proposed method is simple, rapid, cost effective, highly sensitivity and eminently suitable for the quality control of pharmaceutical preparation. The possible mechanisms for the observed quenching reaction was also discussed.

A novel multi-commutated method for the determination of hydroxytyrosol in enriched foods using mercaptopropionic acid-capped CdTe quantum dots

Hydroxytyrosol (HXT) has been reported to have beneficial effects for human health, such as antioxidant and antimicrobial properties and an important contribution to the prevention of cardiovascular disease. Hence, exhaustive research is currently being performed to prepare functional foods, such as tomato juice or milk, with HXT. This paper presents a multi-commutated flow method based on the quenching effect that HXT has on the fluorescence of water-soluble mercaptopropionic acid-capped CdTe quantum dots. Under optimal conditions a linear working range was obtained for concentrations between 10 and 250 ng µl−1. In order to demonstrate the suitability of the proposed method for the determination of HXT, HXT-enriched samples were prepared. Using a QuEChERS (quick, easy, cheap, effective, rugged and safe) procedure for extraction, HXT was determined in the prepared functional foods (milk, infant formula, tomato juice and tomato soup). Recoveries of 100% ± 8%, relative standard deviations (RSDs) lower than 5% and high sample throughput of 70 samples per h show the potential of the system for the analysis of HXT in food samples.

Rapid Fluorimetric Quantitation of Ibandronate by Coupling Quantum Dots and Multicommutated Flow Injection Analysis

Ibandronate is a potent nitrogen-containing bisphosphonate with a tertiary amine group, which does not easily form chromophore derivatives that can be detected by UV light of fluorescence emission. Here, a simple and straightforward automated multicommutated flow system, making use of water-soluble mercaptopropionic acid-capped CdTe quantum dots, was implemented for the fluorescence quantitation of ibandronate in pharmaceutical formulations. The developed approach was based on the analyte ability to establish surface interactions that resulted in quenched nanocrystals fluorescence intensity, being this effect proportional to the target compound’s concentration. Size and concentration of quantum dots and pH of the media were some of the most relevant and influencing parameters studied. The proposed methodology allowed the determination of ibandronate in the range of 20-200 µg mL-1, with good repeatability (RSD<3%) and a sampling frequency of about 70 samples per hour. The results obtained in the analysis of pharmaceuticals showed excellent agreement with those provided by the manufacturer.

Hydrothermal synthetic mercaptopropionic acid stabled CdTe quantum dots as fluorescent probes for detection of Ag+

Mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) with particle size 3nm have been successfully synthesized in aqueous medium by hydrothermal synthesis method. And the effects of different metal ions on MPA capped CdTe QDs fluorescence were studied using fluorescence spectrometry. The results demonstrated that at the same concentration level, Ag+ could strongly quench CdTe QDs fluorescence, and the other metal ions had little effect on CdTe QDs fluorescence except Cu2+. On the basis of this fact, a rapid, simple, highly sensitive and selective method based on fluorescence quenching principle for Ag+ detection in aqueous solution was proposed. Under optimal conditions, the quenched fluorescence intensity (F0–F) increased linearly with the concentration of Ag+ ranging from 4×10−7 to 32×10−7molL−1. The limit of detection for Ag+ was 4.106×10−8molL−1. The obtained plot of F0/F versus [Ag+] was an upward curvature, concave towards the y-axis, rather than a straight line. The modified form of the Stern–Volmer equation was third order in Ag+ concentration. According to the modified Stern–Volmer equation, it can be inferred that dynamic quenching and static quenching simultaneously occurred when Ag+ interacted with MPA capped CdTe QDs. At the same time other factors might also influence the quenching process. Based on this study, hydrothermal synthesized MPA capped CdTe QDs with particle size 3nm may be used as a novel fluorescence probe to quantificationally and selectively detect Ag+.

Photophysical behavior of zinc monoaminophthalocyanines linked to mercaptopropionic acid-capped CdTe quantum dots

Photosensitizing properties of zinc monoaminophthalocyanine ( 2) {in the absence or presence of mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs)} were compared with those of mono-aminophenoxy zinc phthalocyanine ( 3), zinc tetrasulfonated phthalocyanine and zinc phthalocyanine. Complexes 2 and 3 were also linked to the MPA capped CdTe quantum dots through the formation of an amide bond. High triplet state quantum yields were obtained for the linked QD–phthalocyanine derivatives (complexes 2 and 3) compared to when complexes 2 and 3 were mixed with MPA QDs without a chemical bond.

Photoinduced interaction between MPA capped CdTe QDs and certain anthraquinone dyes

Abstract 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 (Δ G et ) obtained as per the Rehm–Weller equation.

Electrochemiluminescence of CdTe quantum dots as labels at nanoporous gold leaf electrodes for ultrasensitive DNA analysis

A new electrochemiluminescence (ECL) DNA assay is developed using quantum dots (QDs) as DNA labels. When nanoporous gold leaf (NPGL) electrodes are used, sensitivity of the ECL assay is remarkably increased due to ultra-thin nanopores. In this assay, target DNA (t-DNA) is hybridized with capture DNA (c-DNA) bound on the NPGL electrode, which is fabricated by conjugating amino-modified c-DNA to thioglycolic acid (TGA) modified at the activated NPGL electrode. Following that, amino-modified probe DNA is hybridized with the t-DNA, yielding sandwich hybrids on the NPGL electrode. Then, mercaptopropionic acid-capped CdTe QDs are labeled to the amino group end of the sandwich hybrids. Finally, in the presence of S(2)O(8)(2-) as coreactant, ECL emission of the QD-labeled DNA hybrids on the NPGL electrode is measured by scanning the potential from 0 to -2V to record the curve of ECL intensity versus potential. The maximum ECL intensity (I(m,ECL)) on the curve is proportional to t-DNA concentration with a linear range of 5 x 10(-15) to 1 x 10(-11)mol/L. The ECL DNA assay can be used to determine DNA corresponding to mRNA in cell extracts in this study.