Oriented surface imprinted 96-well microplate-based fluorescent biosensor for glycoprotein detection by boronate affinity sandwich assay

Glycoproteins perform vital functions in numerous biological processes and have important clinical implications. Many glycoproteins have been used as biomarkers and therapeutic targets for disease diagnosis. Due to low concentration of glycoprotein biomarkers and the presence of high-abundance interfering species in biological samples, a selective and sensitive detection method for glycoprotein is essential for real-world applications. In this study, we develop an oriented surface imprinted microplate-based fluorescent biosensor by boronate-affinity sandwich assay (BASA) for the specific, sensitive and high throughput determination of glycoproteins in complex samples. The structure of the BASA is based on sandwich formation between boronate affinity-oriented surface-imprinted microplates, target glycoproteins, and boronate affinity fluorescence probes. The imprinted microplates ensure the high specificity, high affinity and high throughput, while the fluorescence probes, consisting of boronic acid-modified CdTe QDs, provide high sensitivity. The proposed approach could exhibit a wide linear range of 1 ng/mL-105 ng/mL, with a low LOD of 0.528 ng/mL using horseradish peroxidase (HRP) as a model glycoprotein. As compared with traditional "turn off" fluorescent sensor, the developed "turn on" fluorescent sensor provided three orders of magnitude higher sensitivity at least. The fluorescent biosensor achieved average recoveries ranging from 96.8 % to 106.0 % in urine samples.

A Highly Efficient Fluorescent Turn-Off Nanosensor for Quantitative Detection of Teicoplanin Antibiotic from Humans, Food, and Water Based on the Electron Transfer between Imprinted Quantum Dots and the Five-Membered Cyclic Boronate Esters

Teicoplanin has been banned in the veterinary field due to the drug resistance of antibiotics. However, teicoplanin residue from the antibiotic abuse of humans and animals poses a threat to people's health. Therefore, it is necessary to develop an efficient way for the highly accurate and reliable detection of teicoplanin from humans, food, and water. In this study, novel imprinted quantum dots of teicoplanin were prepared based on boronate affinity-based precisely controlled surface imprinting. The imprinting factor (IF) for teicoplanin was evaluated and reached a high value of 6.51. The results showed excellent sensitivity and selectivity towards teicoplanin. The relative fluorescence intensity was inversely proportional to the concentration of teicoplanin, in the range of 1.0-17 μM. And its limit of detection (LOD) was obtained as 0.714 μM. The fluorescence quenching process was mainly controlled by a static quenching mechanism via the non-radiative electron-transfer process between QDs and the five-membered cyclic boronate esters. The recoveries for the spiked urine, milk, and water samples ranged from 95.33 to 104.17%, 91.83 to 97.33, and 94.22 to 106.67%, respectively.

Visual detection of H2O2 and glucose by HBcAb-HRP fluorescence-enhanced CdTe QDs/CDs ratiometric fluorescence sensing platform

This study presents the development of a sensitive and simple enhanced ratiometric fluorescence sensing platform in the consist of CdTe quantum dots (QDs), carbon dots (CDs), and hepatitis B core antibody labeled with horseradish peroxidase (HBcAb-HRP) for the visual analysis of H2O2 and glucose. The sulfur atoms in HBcAb-HRP have a strong affinity for Cd(II), which effectively enhances the fluorescence intensity of the CdTe QDs due to the generation of more radiative centers at the CdTe/Cd-SR complex. In the presence of H2O2, the Cd-S bonds are oxidized to form disulfide products and results in linear fluorescence quenching, while CDs maintain stable. Becasue glucose can be converted into H2O2 with the aid of glucose oxidase, this sensing platform can also be used for analyzing glucose. The detection limits for H2O2 and glucose are 2.9 μmol L-1 with RSD of 2.6% and 1.6 μmol L-1 with RSD of 2.4% respectively. In addition, under UV lamp irradiation, the orange-yellow CdTe QDs gradually quench with increasing H2O2 and glucose, while the blue CDs remain unchanged. A color change from orange-yellow to blue enables a visual semi-quantitative determination of H2O2 in commercial contact lens solution and glucose in human serum without any pretreatment. Thus, this CdTe QDs/CDs ratiometric sensing platform has significant potential for the rapid analysis of H2O2 and glucose in actual application.

Efficient Gamma Ray Detection Using CdTe/CdS Core/Shell Quantum Dots: A Simple and Rapid Fluorescence Approach

Gamma rays, as hazardous nuclear radiation, necessitate effective and rapid detection methods. This paper introduces a low-cost, fast, and simple fluorescence method based on CdTe/CdS core/shell quantum dots for gamma-ray detection. CdTe/CdS quantum dots, subjected to gamma irradiation from a 60Co source under various conditions, were investigated to assess their fluorescence sensor capabilities. The obtained results showed that an increase in CdTe/CdS nanoparticle size was associated with decreased sensitivity, while a reduction in CdTe/CdS concentration correlated with increased sensitivity. To further validate the practicality of CdTe/CdS core/shell quantum dots in gamma-ray detection, the structural properties of the quantum dots were meticulously studied. Raman spectroscopy, X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) analysis were conducted before and after gamma-ray radiation. The results demonstrated the crystalline stability of CdTe/CdS core/shell quantum dots under gamma irradiation, highlighting their robust structural integrity. In conclusion, the experimental findings underscore the exceptional potential of CdTe/CdS quantum dots as an off-fluorescence probe for simple, low-cost, fast, and on-site detection of gamma rays. This research contributes to the advancement of efficient and practical methods for gamma-ray sensing in various applications.

Xylenol orange-modified CdTe quantum dots as a fluorescent/colorimetric dual-modal probe for anthrax biomarker based on competitive coordination

Bacillus anthracis spores can make humans infected with vicious anthrax, so it is significant to detect their biomarker 2,6-pyridinedicarboxylic acid (DPA). The development of dual-modal methods for DPA detection that are more flexible in practical applications remains a challenge. Herein, colorimetric xylenol orange (XO) was modified on fluorescent CdTe quantum dots (QDs) for dual-modal detection of DPA through competitive coordination. After the binding of XO on CdTe QDs via coordination with Cd²⁺, CdTe QDs displayed quenched red fluorescence and the bound XO was presented as red color. The competitive coordination of DPA with Cd²⁺ made XO released from CdTe QDs, causing the enhanced red fluorescence of CdTe QDs and the yellow color of free XO. On this basis, DPA was rapidly (1 min) quantified through fluorescent and colorimetric modes within the ranges of 0.1-5 μM and 0.5-40 μM, respectively. The detection limits for DPA were calculated as low as 42 nM and 240 nM, respectively assigned to fluorescent and colorimetric modes. The level of urinary DPA was further measured. Satisfactory relative standard deviations (fluorescent mode: 0.1%-10.2%, colorimetric mode: 0.8%-1.8%) and spiked recoveries (fluorescent mode: 100.0%-115.0%, colorimetric mode: 86.0%-96.6%) were obtained.

Combination of colorimetry, inner filter effect-induced fluorometry and smartphone‑based digital image analysis: A versatile and reliable strategy for multi-mode visualization of food dyes

Herein, a multi-mode visualization platform was initiated for in-situ detection of food dyes (FDs) by combining colorimetry, fluorometry and smartphone‑based digital image analysis, in which water-dispersible quantum dots (QDs) were served as nanoprobes. Colorimetry was achieved by color comparison, while both fluorometry and fluorescence quantification were performed through inner filter effect (IFE)-induced fluorescence quenching, then color information (RGB & gray-scale values) of colorimetry and fluorometry was picked by a smartphone to reconstruct digitized alignments. Since IFE mechanism was concentration-dependent but did not rely on the interaction between fluorophore and quencher, the whole process of fluorescence response could be finished within 10 s, and both color gradients and fluorescence changes showed fine mappings to FDs concentrations in the range of 1.0 × 10^-3∼0.035 mg/mL for brilliant blue, and 1.0 × 10^-4∼0.1 mg/mL for Allura red and sunset yellow. As a proof-of-concept, the in-situ multi-mode visualization of these FDs in real beverages was experimentally proved to be highly feasible and reliable as compared with instrumental techniques like UV-vis/fluorescence spectrometry, along with HPLC. Finally, this strategy was extended to the multi-mode visualization of non-food dyes in three simulated wastewater samples with high credibility by contrast with the true additive amounts of model dyes.

Molecularly imprinted probe based on CdTe QDs and magnetic nanoparticles for selective recognition of malachite green in seawater and its sensing mechanisms

A magnetic molecularly imprinted probe (MMIP@QD) was synthesized by reverse microemulsion method using CdTe QDs, Fe₃O₄, and molecularly imprinted polymer as the fluorophore, magnetic carrier, and recognition sites, respectively. The nanoparticle was characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry (VSM). In the optimal experimental condition, fluorescent emission intensity (measured at excitation wavelengths of 350 nm) was quenched linearly with increasing malachite green (MG) concentration from 0.8 to 28.0 μM with LOD of 0.67 μM. Simultaneously, it was observed that the maximum absorption wavelength was blue shifted gradually with the increase of MG concentration. The inner filter effect, static quenching, and band gap transition were interpreted as the mechanisms of fluorescence quenching and wavelength shift. Thermodynamic studies indicated that the quenching reaction proceeded spontaneously. The developed sensor was applied to detect MG in seawater samples. Satisfactory recoveries of MG in spiked seawater ranged from 83.6 to 122.1% with RSD < 1.8%.

Boronate affinity-based template-immobilization surface imprinted quantum dots as fluorescent nanosensors for selective and sensitive detection of myricetin

In order to prepare a kind of efficient fluorescence sensors for determination of cis-diol-containing flavonoids, novel imprinted quantum dots for myricetin (Myr) were prepared based on boronate affinity-based template-immobilization surface imprinting. The obtained boronate affinity-based surface imprinted silica (imprinted APBA-functionalized CdTe QDs) was used as recognition elements. The quantum dots were used as signal-transduction materials. Under the optimum conditions, according to fluorescence quenching of imprinted APBA-functionalized CdTe QDs by Myr, the imprinting factor (IF) for Myr was evaluated to be 7.88. The result indicated that the boronate affinity functionalized quantum dots coated with imprinted silica were successfully prepared. The prepared imprinted APBA-functionalized CdTe QDs exhibited good sensitivity and selectivity for Myr. The fluorescence intensity was inversely proportional to the concentration of Myr in the 0.30-40 μM concentration range. And its detection limit was obtained to be 0.08 μM. Using the fluorescence sensors, the detection of Myr in real samples was successfully carried out, and the concentration of Myr in green tea and apple juice samples was evaluated to be 2.26 mg/g and 0.73 mg/g, respectively. The recoveries for the spiked green tea and apple juice samples were 95.2-105.0% and 91.5-111.0%, respectively. This study also provides an efficient fluorescent detection method for cis-diol-containing flavonoids in real samples.

CdTe QDs@ZIF-8 composite-based recyclable ratiometric fluorescent sensor for rapid and sensitive detection of chlortetracycline

The residue problem in animal food products caused by the abuse of chlortetracycline (CTC) is one of the food safety issues that have attracted much attention. Herein, a composite was generated by embedding CdTe quantum dots (QDs) into ZIF-8 for ratiometric fluorescent analysis of CTC. With adding CTC, the green luminescence of CTC appeared under the sensitization effect of Zn²⁺ in ZIF-8, but the red luminescence of CdTe QDs was reduced by the inner filtration effect of CTC. On this basis, CTC was detected by the composite with a short response time of 1 min, and the limit of detection was calculated to be 37 nM that was 17 times lower than the maximum residue limit of CTC in animal food products (626 nM). Excellent recyclability of the composite was also observed, and CTC was consecutively measured at least six times. The composite was used to determine CTC in basa fish and pure milk with satisfactory recoveries (91.0-110.0%). Portable test strips were further manufactured and the visual determination of CTC was obtained. These results convictively demonstrate that CdTe QDs@ZIF-8 composite as a recyclable ratiometric fluorescent sensor achieves the rapid and sensitive measurement of CTC residue in animal food products.

Resistive Switching in CdTe/CdSe Core–Shell Quantum Dots Embedded Chitosan-Based Memory Devices

In this paper, we report on the resistive switching (RS) and conduction mechanisms in devices consisting of CdTe/CdSe core–shell quantum dots embedded chitosan composites active layer. Two devices with active layers sandwiched between (1) Al and Ag, and (2) ITO and Ag electrodes were studied. Both devices exhibited bipolar memory behavior with [Formula: see text] V and [Formula: see text][Formula: see text]V, for the Al-based device, while [Formula: see text] V and [Formula: see text][Formula: see text]V were observed for the ITO-based device, enabling both devices to be operated at low powers. However, the switching mechanisms of both devices were different, i.e., RS in Al device was attributed to conductive bridge mechanism, while space-charge-limited driven conduction filament attributed the switching mechanism of the ITO device. Additionally, the Al-based device showed long retention ([Formula: see text][Formula: see text]s) and a reasonable large ([Formula: see text]) ON/OFF ratio. Additionally, for this device, we also observed sweeping cycle-induced reversal of voltage polarity of the [Formula: see text] and [Formula: see text]. In contrast, we observed that increasing sweeping cycles resulted in an exponential decrease of the OFF-state resistance of the ITO-based device.

Synthesis of Novel Heteroleptic Oxothiolate Ni(II) Complexes and Evaluation of Their Catalytic Activity for Hydrogen Evolution

Two heteroleptic nickel oxothiolate complexes, namely [Ni(bpy)(mp)] (1) and [Ni(dmbpy)(mp)] (2), where mp = 2-hydroxythiophenol, bpy = 2,2′-bipyridine and dmbpy = 4,4′-dimethyl-2,2′-bipyridine were synthesized and characterized with various physical and spectroscopic methods. Complex 2 was further characterized by single crystal X-ray diffraction data. The complex crystallizes in the monoclinic P 21/c system and in its neutral form. The catalytic properties of both complexes for proton reduction were evaluated with photochemical and electrochemical studies. Two different in their nature photosensitizers, namely fluorescein and CdTe-TGA-coated quantum dots, were tested under various conditions. The role of the electron donating character of the methyl substituents was revealed in the light of the studies. Thus, catalyst 2 performs better than 1, reaching 39.1 TONs vs. 4.63 TONs in 3 h, respectively, in electrochemical experiments. In contrast, complex 1 is more photocatalytically active than 2, achieving a TON of over 6700 in 120 h of irradiation. This observed reverse catalytic activity suggests that HER mechanism follows different pathways in electrocatalysis and photocatalysis.

Photoelectrochemical hydrogen evolution using CdTexS1-x quantum dots as sensitizers on NiO photocathodes

The design of active photocathodes for the hydrogen evolution reaction (HER) is a crucial step in the development of dye-sensitized photoelectrochemical cells (DS-PECs) aimed at solar-assisted water splitting. In the present work, we report on the use of orange CdTexS1-x quantum dots (QDs) with an average diameter of ca. 3.5 nm, featuring different capping agents (MAA, MPA, and MSA) for the sensitization of electrodes based on nanostructured NiO. Photoelectrochemical characterization of the resulting NiO|QDs electrodes in the presence of [CoIII(NH3)5Cl]Cl2 as an irreversible electron acceptor elects MAA-capped QDs as the most active sample to achieve substantial photocurrent densities thanks to both improved surface coverage and injection ability. Functionalization of the NiO|QDs electrodes with either heterogeneous Pt or the molecular nickel bis(diphosphine) complex (1) as the hydrogen evolving catalysts (HECs) yields active photocathodes capable of promoting hydrogen evolution upon photoirradiation (maximum photocurrent densities of -16(±2) and -20(±1) μA·cm-2 for Pt and 1 HECs, respectively, at 0 V vs. NHE, 70-80% faradaic efficiency, maximum IPCE of ca. 0.2%). The photoelectrochemical activity is limited by the small surface concentration of the QD sensitizers on the NiO surface and the competitive light absorption by the NiO material which suggests that the match between dye adsorption and the available surface area is critical to achieving efficient hydrogen evolution by thiol-capped QDs.

Discrimination of copper and silver ions based on the label-free quantum dots

A simple and fast method for copper ions (Cu²⁺) and silver ions (Ag⁺) detection was established with cadmium telluride quantum dots (CdTe QDs) as fluorescent probes. In the presence of Cu²⁺ or Ag⁺, the fluorescence intensity of TGA-CdTe QD can be significantly quenched, which fitted a linear relationship between the fluorescence quenching degree (F₀-F)/F₀ and the concentration of metal ions. In this work, the lowest detected concentration for Cu²⁺ and Ag⁺ was 35.0 nM and 25.3 nM, respectively. In addition, the differentiation of Cu²⁺ and Ag⁺ at different concentrations was realized with the principal component analysis (PCA). Furthermore, Cu²⁺ was successfully detected in body fluids. This method provides a good potential for copper ions and silver ions detection with simplicity, rapidity, and excellent selectivity.

Reactivity and Mechanism of Photo- and Electrocatalytic Hydrogen Evolution by a Diimine Copper(I) Complex

The tetrahedral copper(I) diimine complex [Cu(pq)2]BF4 displays high photocatalytic activity for the H2 evolution reaction with a turnover number of 3564, thus representing the first type of a Cu(I) quinoxaline complex capable of catalyzing proton reduction. Electrochemical experiments indicate that molecular mechanisms prevail and DFT calculations provide in-depth insight into the catalytic pathway, suggesting that the coordinating nitrogens play crucial roles in proton exchange and hydrogen formation.

The role of the capping agent and nanocrystal size in photoinduced hydrogen evolution using CdTe/CdS quantum dot sensitizers

Hydrogen production via light-driven water splitting is a key process in the context of solar energy conversion. In this respect, the choice of suitable light-harvesting units appears as a major challenge, particularly as far as stability issues are concerned. In this work, we report on the use of CdTe/CdS QDs as photosensitizers for light-assisted hydrogen evolution in combination with a nickel bis(diphosphine) catalyst (1) and ascorbate as the sacrificial electron donor. QDs of different sizes (1.7-3.4 nm) and with different capping agents (MPA, MAA, and MSA) have been prepared and their performance assessed in the above-mentioned photocatalytic reaction. Detailed photophysical studies have been also accomplished to highlight the charge transfer processes relevant to the photocatalytic reaction. Hydrogen evolution is observed with remarkable efficiencies when compared to common coordination compounds like Ru(bpy)₃²⁺ (where bpy = 2,2'-bipyridine) as light-harvesting units. Furthermore, the hydrogen evolution performance under irradiation is strongly determined by the nature of the capping agent and the QD size and can be related to the concentration of the surface defects within the semiconducting nanocrystal. Overall, the present results outline how QDs featuring large quantum yields and long lifetimes are desirable to achieve sustained hydrogen evolution upon irradiation and that a precise control of the structural and photophysical properties thus appears as a major requirement towards profitable photocatalytic applications.

Synthesis of pH Sensitive Dual Capped CdTe QDs: Their Optical Properties and Structural Morphology

We herein report five different types of thiol dual capped cadmium tellurite quantum dots (CdTe QDs) namely glutathione-mercapto-propanoic acid (QD 1), glutathione-thiolglycolic acid (QD 2), L-cysteine-mercapto-propanoic acid (QD 3), L-cysteine- thiol-glycolic acid (QD 4) and mercapto-propanoic acid-thiol-glycolic (QD 5). Dual-capped CdTe QDs were prepared using a one pot synthetic method. Cadmium acetate and sodium tellurite were respectively used as cadmium and tellurium precursors. Photo-physical properties of the synthesized QDs were examined using UV-Vis and photoluminescence spectroscopy while structural characterization was performed by means of transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The influence of pH on QD characteristics (fluorescence intensity) was studied using phosphate and citrate buffers and continuous titration with HCl (0.1 N). UV-vis and photoluminescence spectra exhibited sharp absorption band edge with high intensities and improved colloidal stability. All the QDs were found to be in nano-size rang. TEM analysis revealed the presence of spherical nanoparticles while FTIR evidenced successful dual-capping of QDs. Upon pH changes, QDs 3 and 4 demonstrated more remarkable variations in fluorescence intensity than QDs 1 and 2. The pH-sensitivity of these QDs represents a promising feature for further development of potential theranostic nano-devices.

Determination of cis-diol-containing flavonoids in real samples using boronate affinity quantum dots coated with imprinted silica based on controllable oriented surface imprinting approach

Novel boronate affinity imprinted quantum dots (BA-CdTe@MIPs QDs) were used to develop a selective and sensitive fluorescent nanosensor for determination of cis-diol-containing flavonoids such as quercetin (Qu), baicalein (Bai) and luteolin (Lut) based on controllable oriented surface imprinting approach. The boronate affinity imprinted silica was used as recognition elements. Under the optimum conditions, the imprinting factor (IF) for Qu, Bai and Lut was evaluated to be 9.42, 6.58 and 10.91, respectively. The results indicated that the boronate affinity quantum dots coated with imprinted silica were successfully prepared. The obtained BA-CdTe@MIPs QDs provided high selectivity and high sensitivity for cis-diol-containing flavonoids such as quercetin and luteolin. The BA-CdTe@MIPs QDs exhibited linear decrease in fluorescence intensity with the increase of concentration of quercetin in the 0.05-25 μM concentration range. The detection limit (LOD) is evaluated to be 0.02 μM. The obtained fluorescent nanosensor could be successfully applied to efficient detection of cis-diol-containing flavonoids in onion skin and human urine samples. The recoveries for the spiked onion skin and urine samples were evaluated to be 83.50-104.00% and 86.67-105.00%, respectively. Clearly, this study provides a rapid and efficient fluorescent detection tool for cis-diol-containing flavonoids in real samples.

An indirect ELISA-inspired dual-channel fluorescent immunoassay based on MPA-capped CdTe/ZnS QDs

To meet the need for high-throughput immunoassays, many multiplex fluorescent immunoassays have been proposed. Most of them need different kinds of fluorescent label indicators during the test. In this work, a novel indirect ELISA-inspired dual-channel fluorescent immunoassay based on 3-mercaptopropionic acid capped CdTe/ZnS quantum dots (QDs) was constructed. The ELISA wells were coated with two kinds of antigen-QD complex. When the primary antibodies were present in a sample, they mediated the binding of a secondary antibody-DNA-gold nanoparticle complex to the antigen-QD complex. Then the gold nanoparticles quenched the fluorescence of the QDs and a decrease in fluorescence intensity was observed. Thus, the amount of primary antibody could be estimated from the decrease of fluorescence intensity. Owing to the wide absorption range and the relatively narrow emission band of the QDs, the dual-channel fluorescent immunoassay system could work at the same excitation wavelength and the emission wavelengths of each channel had no interference. As a result, two different kinds of primary antibody could be detected at the same time in one ELISA well, which simplified the operation and greatly improved the efficiency. Besides, only one type of secondary antibody needs to be added to the prepared microtiter plates, which further simplified the operation during the detection procedure. This dual-channel fluorescent immunoassay system will provide new insights into high-throughput immunodetection. Graphical abstract.

Preparation of Fluorescent Molecularly Imprinted Polymers via Pickering Emulsion Interfaces and the Application for Visual Sensing Analysis of Listeria Monocytogenes

In this work, a novel molecularly imprinted polymer (MIP) with water-soluble CdTe quantum dots (QDs) was synthesized by oil-in-water Pickering emulsion polymerization using whole Listeria monocytogenes as the template. Listeria monocytogenes was first treated by acryloyl-functionalized chitosan with QDs to form a bacteria-chitosan network as the water phase. This was then stabilized in an oil-in-water emulsion comprising a cross-linker, monomer, and initiator, causing recognition sites on the surface of microspheres embedded with CdTe QDs. The resulting MIP microspheres enabled selective capture of the target bacteria via recognition cavities. The target bacteria Listeria monocytogenes was detected. Scanning electron microscopy (SEM) characterization showed that the MIPs had a rough spherical shape. There was visual fluorescence detection via quenching in the presence of the target molecule, which offered qualitative detection of Listeria monocytogenes in milk and pork samples. The developed method simplified the analysis process and did not require any sample pretreatment. In addition, the fluorescence sensor provided an effective, fast, and convenient method for Listeria monocytogenes detection in food samples.

Detection and Imaging of Hydrogen Sulfide in Lysosomes of Living Cells with Activatable Fluorescent Quantum Dots

The simple, sensitive, and specific detection of hydrogen sulfide (H₂S) is of great importance because of its crucial role in food safety, environmental pollution, and various pathological and physiological processes. Here, we reported activatable fluorescence nanoprobe-based quantum dots (QDs) for sensitive and selective monitoring of H₂S in red wine, environmental water samples, and lysosome of live cancer cells. The nanoprobe was prepared through a strong electrostatic interaction between thioglycolic-acid-stabilized CdTe QDs and p-amino thiophenol capped silver nanoparticles (AgNPs) that resulted in the formation of the assembled nanostructure, called QD/AgNP nanocomplexes. The initial fluorescence of QDs was effectively quenched by the AgNPs because of the inner filter effect. Upon interaction with H₂S, the strong etching ability of H₂S to AgNPs could trigger the disassembly of QD/AgNP nanocomplexes and generate Ag₂S on the surface of QDs, achieving a shell-core Ag₂S/CdTe QDs with remarkable fluorescence as a result of the termination of inner filter effect. The aqueous solution studies displayed that the assembled QD/AgNP nanoprobe was sensitive to detect H₂S, with a detection limit of 15 nM. In addition, this assembled QD/AgNP nanoprobe showed a high specificity toward H₂S over other anions and biologically relevant species. The subsequent fluorescence imaging studies demonstrated that the assembled QD/AgNP nanoprobe exhibited high ability to enter into cellular lysosome and generated an enhancement fluorescence, which was used for endogenous H₂S detection in lysosome of living cancer cells. This proposed nanoprobe revealed a more simple, rapid, time-saving, low-cost, sensitive, and selective process for monitoring of H₂S in further environmental pollution, food safety, and clinical diagnosis of H₂S-related diseases.

Development of a portable device for Ag+ sensing using CdTe QDs as fluorescence probe via an electron transfer process

Ag⁺ as one of the most commonly seen toxic heavy metal ions is involved in numerous vital biological processes, which would cause fatal damages and environmental contamination when Ag⁺ is excessive. In the present work, CdTe quantum dots (QDs) with green, orange, and red emission capped by mercaptoacetic acid (TGA) were synthesized at one time by controlling the synthesis time and utilized for Ag⁺ detection. Both fluorescence spectral red-shift and intensity decrease could be used for Ag⁺ discrimination. Fluorescence lifetime, Zeta potential, and XRD, etc. were carried out to analyze the detection mechanism. Results displayed that surface passivation and electron transfer due to binding effects of Ag⁺ to Te atom on traps of QDs could be relied on to explain the sensing mechanism. Additionally, in accordance with PCA analysis, Ag⁺ could be also be successfully differentiated from Hg²⁺ and the other metal ions. Importantly, a home-made portable device based on a 32 bit embed Micro Control Unit (MCU) system was first proposed for Ag⁺ detection. The power supply system adopt the mini-sized lithium cell instead of the power supply system, which ensure its practical applicability. The relative position of light source and detector is set at 90° to minimize the interference. According to the detection results, the linear detection range using the device was from 5 nM to 200 nM (with a larger coefficient of determination, R²), and the detection limit was calculated to be about 5 nM, which indicated that this proposed method and device could fulfil the practical application requirements.

Selective and Sensitive Detection of Silver(I) Ion Based on Tetracationic Complex and TGA/GSH Co-capped Quantum Dots as an Effective Fluorescent Sensing Platform

CdTe quantum dots capped with glutathione (GSH) and thioglycolic acid (TGA) were synthesized and the interaction between QDs and tetracationic Fe complex was investigated. Based on the specific interaction between Ag⁺ and cytosine bases (C), we designed a label-free DNA sensor for the detection of Ag⁺ in aqueous solution. Furthermore, tetracationic Fe complex with a higher positive charge is demonstrated to improve the sensitivity of the sensor. A detection limit of 3.3 nmol dm^-3 was obtained, which was lower than in previous reports. This sensor also exhibits promising potential for real sample analysis.

Toxicological Evaluation of Luminescent Silica Nanoparticles as New Drug Nanocarriers in Different Cancer Cell Lines

Luminescent mesoporous silica nanoparticles, CdTeQDs@MNs@PEG1, SiQDs@Isoc@MNs and SiQDs@Isoc@MNs@PEG2, were successfully synthetized and characterized by SEM, TEM, XRD, N₂ nitrogen isotherms, ¹H NMR, IR, absorption, and emission spectroscopy. Cytotoxic evaluation of these nanoparticles was performed in relevant in vitro cell models, such as human hepatoma HepG2, human brain endothelial (hCMEC/D3), and human epithelial colorectal adenocarcinoma (Caco-2) cell lines. None of the tested nanoparticles showed significant cytotoxicity in any of the three performed assays (MTT/NR/ LDH) compared with the respective solvent and/or coating controls, excepting for CdTeQDs@MNs@PEG1 nanoparticles, where significant toxicity was noticed in hCMEC/D3 cells. The results presented reveal that SiQDs-based mesoporous silica nanoparticles are promising nanoplatforms for cancer treatment, with a pH-responsive drug release profile and the ability to load 80% of doxorubicin.

Visual detection of melamine by using a ratiometric fluorescent probe consisting of a red emitting CdTe core and a green emitting CdTe shell coated with a molecularly imprinted polymer

A composite ratiometric fluorescent probe is described for visual detection of melamine (MEL) in milk samples. It is based on the use of red emitting and green emitting CdTe quantum dots, and a mesoporous molecularly imprinted polymer. The red emitting QDs are embedded in the silica microsphere to serve as a core, and the green emitting QDs are coated on the surface of the silica microsphere as a shell. A molecularly imprinted polymer (MIP) with specific recognition sites for MEL was placed on the shell. If MEL is bound by the MIP, the green fluorescence is quenched due to hydrogen bond interaction. The red emission, in contrast, remains unchanged. Quenching leads to a change in the color of fluorescence from red-green to purely red. This effect allows for visual and instrumental detection of MEL. The mesoporous structure of the MIP reduces the mass transfer resistance and enhances the accessibility of sites for MEL. Response is linear in the 50-1000 ng mL^-1 MEL concentration range, and the limit of detection is 13 ng mL^-1. The fluorescent probe was successfully applied to the analysis of MEL-spiked milk samples and gave recoveries between 94.1 and 98.7%, with 3.6-5.1% relative standard deviations. Graphical abstract Schematic of the preparation and detection of the composite probe. The probe was applied for the selective recognition and visual detection of melamine (MEL).

Novel fluoroimmunoassays for detecting ochratoxin A using CdTe quantum dots

Novel direct and indirect competitive fluorescence-linked immunosorbent assays (cFLISA and icFLISA) for detection of ochratoxin A (OTA) were described using CdTe quantum dots (QDs) as fluorescent label. CdTe QDs were successfully synthesized, which had an emission wavelength of 615 nm. The high purity monoclonal antibody against OTA was prepared through cell thawing and the octylic acid-ammonium sulfate method. The OTA MAbs were successfully coupled with CdTe QDs, and which also retained the original biological activity. The 50% inhibition values (IC₅₀ ) of the cFLISA and icFLISA were 0.630 ng/mL, 0.234 ng/mL, the limits of detection (LOD) were 7.06 × 10^-3 and 4.15 × 10^-3  ng/mL, and detection ranges were 7.06 × 10^-3 - 18.34 ng/mL and 4.15 × 10^-3 - 4.88 ng/mL, in-order. The recoveries were 96.0-104.7% along with coefficients of variation (CVs) below 10%. The FLISA provided novel method for determination of OTA and the potential of MAb-CdTe QDs for the establishment of fluorescent immunochromatographic test strip.

Impact of D2O/H2O Solvent Exchange on the Emission of HgTe and CdTe Quantum Dots: Polaron and Energy Transfer Effects

We have studied light emission kinetics and analyzed carrier recombination channels in HgTe quantum dots that were initially grown in H2O. When the solvent is replaced by D2O, the nonradiative recombination rate changes highlight the role of the vibrational degrees of freedom in the medium surrounding the dots, including both solvent and ligands. The contributing energy loss mechanisms have been evaluated by developing quantitative models for the nonradiative recombination via (i) polaron states formed by strong coupling of ligand vibration modes to a surface trap state (nonresonant channel) and (ii) resonant energy transfer to vibration modes in the solvent. We conclude that channel (i) is more important than (ii) for HgTe dots in either solution. When some of these modes are removed from the relevant spectral range by the H2O to D2O replacement, the polaron effect becomes weaker and the nonradiative lifetime increases. Comparisons with CdTe quantum dots (QDs) served as a reference where the resonant energy loss (ii) a priori was not a factor, also confirmed by our experiments. The solvent exchange (H2O to D2O), however, is found to slightly increase the overall quantum yield of CdTe samples, probably by increasing the fraction of bright dots in the ensemble. The fundamental study reported here can serve as the foundation for the design and optimization principles of narrow bandgap quantum dots aimed at applications in long wavelength colloidal materials for infrared light emitting diodes and photodetectors.

Temperature-Dependent Exciton and Trap-Related Photoluminescence of CdTe Quantum Dots Embedded in a NaCl Matrix: Implication in Thermometry

Temperature-dependent optical studies of semiconductor quantum dots (QDs) are fundamentally important for a variety of sensing and imaging applications. The steady-state and time-resolved photoluminescence properties of CdTe QDs in the size range from 2.3 to 3.1 nm embedded into a protective matrix of NaCl are studied as a function of temperature from 80 to 360 K. The temperature coefficient is found to be strongly dependent on QD size, with the highest sensitivity obtained for the smallest size of QDs. The emission from solid-state CdTe QD-based powders is maintained with high color purity over a wide range of temperatures. Photoluminescence lifetime data suggest that temperature dependence of the intrinsic radiative lifetime in CdTe QDs is rather weak, and it is mostly the temperature-dependent nonradiative decay of CdTe QDs which is responsible for the thermal quenching of photoluminescence intensity. By virtue of the temperature-dependent photoluminescence behavior, high color purity, photostability, and high photoluminescence quantum yield (26%-37% in the solid state), CdTe QDs embedded in NaCl matrices are useful solid-state probes for thermal imaging and sensing over a wide range of temperatures within a number of detection schemes and outstanding sensitivity, such as luminescence thermochromic imaging, ratiometric luminescence, and luminescence lifetime thermal sensing.

Optical and cytotoxicity properties of water soluble type II CdTe/CdSe nanoparticles synthesised via a green method

We herein report the optical and cytotoxicity properties of highly luminescent water soluble mercaptopropanoic acid (MPA) capped CdTe/CdSe core shell nanoparticles (NPs). The synthesis of the CdTe/CdSe NPs was carried out via a simple, one pot and economical route, involving the use of greener materials under ambient environment in the absence of an inert atmosphere. The temporal evolution of the size and optical properties of the nanomaterials was investigated by varying the reaction time and stability of the as-synthesised material at pH 12. The as-synthesised nanomaterials were characterised using UV-vis absorption and photoluminescence (PL) spectroscopy. The nanoparticles obtained were of high quality with high absorption and emission features. Addition of Se precursor to produce CdSe layer on the CdTe NPs core surface resulted in significant red shirt of both the absorption and emission maxima. The stability study showed that the emission maximum peak positions and FWHM remain the same with increase in emission intensity for all the NPs during the aging period. The cytotoxicity assay showed very high cell viability for the CdTe/CdSe NPs produced at 7 h compared with those produced at 30 mins as the concentration increased from 0.1 to 60 ug/ml. The lower cytotoxicity at the higher reaction time was attributed to the higher stability of the material and hence lower release of Cd2+.

Synthesis and enhanced fluorescence of Ag doped CdTe semiconductor quantum dots

Doping with intentional impurities is an intriguing way to tune the properties of semiconductor nanocrystals. However, the synthesis of some specific doped semiconductor nanocrystals remains a challenge and the doping mechanism in this strongly confined system is still not clearly understood. In this work, we report, for the first time, the synthesis of stable and water-soluble Ag-doped CdTe semiconductor quantum dots (SQDs) via a facile aqueous approach. Experimental characterization demonstrated the efficient doping of the Ag impurities into the CdTe SQDs with an appropriate reaction time. By doping 0.3% Ag impurities, the Stokes shift is decreased by 120 meV, the fluorescence intensity is enhanced more than 3 times, the radiative rate is enhanced 4.2 times, and the non-radiative rate is efficiently suppressed. These observations reveal that the fluorescence enhancement in Ag-doped CdTe SQDs is mainly attributed to the minimization of surface defects, filling of the trap states, and the enhancement of the radiative rate by the silver dopants. Our results suggest that the silver doping is an efficient method for tuning the optical properties of the CdTe SQDs.

Color-tunable luminescent CdTe quantum dot membranes based on bacterial cellulose (BC) and application in ion detection

Color-tunable luminescent membranes of CdTe QDs on bacterial cellulose (BC) nanofibers were successfully fabricated by in situ synthesis in aqueous solution.