Fluorescent Quantum Dots Research Articles

A metal-organic framework and quantum dot-based ratiometric fluorescent probe for the detection of formaldehyde in food.

Agreen and sensitive ratio fluorescence strategy was proposed for the detection of formaldehyde (FA) in food based on a kind of metal-organic frameworks (MOFs), MIL-53(Fe)-NO2, and nitrogen-doped Ti3C2 MXene quantum dots (N-Ti3C2 MQDs) with a blue fluorescence at 450nm. As a type of MOFs with oxidase-like activity, MIL-53(Fe)-NO2 can catalyze o-phenylenediamine (OPD) into yellow fluorescent product 2,3-diaminophenazine (DAP) with a fluorescent emission at 560nm. DAP has the ability to suppress the blue light of N-Ti3C2 MQDs due to inner filter effect (IFE). Nevertheless, Schiff base reaction can occur between FA and OPD, inhibiting DAP production. This results in a weakening of the IFE which reverses the original fluorescence color and intensity of DAP and N-Ti3C2 MQDs. So, the ratio of fluorescence intensity detected at respective 450nm and 560nm was designed as the readout signal to detect FA in food. The linear range of FA detection was 1-200µM, with a limit of detection of 0.49µM. The method developedwas successfully used to detect FA in food with satisfactory results. It indicates that MIL-53(Fe)-NO2, OPD, and N-Ti3C2 MQDs (MON) system constructed by integrating the mimics enzyme, enzyme substrate, and fluorescent quantum dots has potential application for FA detection in practical samples.

Confined Unimolecular Micelles for Directed Self-Assembly of Ultrastable Multiple-Responsive Ratiometric Fluorescent Ultrasmall Nanoparticle Assemblies.

Ultrasmall fluorescent nanomaterials have been widely studied as novel fluorescent probes; however, these nanomaterials are prone to structural damage or aggregation, and the sensitivity and accuracy of most single emission fluorescence probes were very low. Therefore, the controlled synthesis of stable dual-emission ratiometric fluorescence ultrasmall assembly probes still remains a challenge. Herein, star-like polymer unimolecular micelles were utilized as a scaffold template to encapsulate fluorescent ultrasmall carbon quantum dots (CQDs) and gold nanoclusters (AuNCs) via the polymer template directed self-assembly strategy to obtain multiple-responsive ratiometric fluorescent assemblies. The assemblies were ultrastable, well-defined, and nearly monodispersed with controlled size, regular morphology, and pH- and thermal-responsiveness. The assemblies can be applied to realize rapid, sensitive, quantitative, and specific detection of Cu2+ and GSH. Moreover, the convenient rapid real-time detection was realized via the combination of the visualized paper-based sensor, and the multilevel information encryption was also achieved.

Rapid detection of chlortetracycline and metacycline in food based on the fluorescence quenching effect of ZnS@CdS quantum dots

Excessive accumulation of tetracycline can not only cause harm to the environment, but also threaten human health through the food chain. In order to reduce the likelihood of people being harmed by these drugs, new methods for the detection of chlortetracycline (CTC) and metacycline (MTC) based on the ZnS@CdS quantum dot (QDs) fluorescence quenching reaction were established. High quality CdS QDs capped by mercaptopropionic acid and ZnS were prepared, which were characterized by transmission electron microscopy, fluorescence, ultraviolet visible spectra, fourier transform infrared, X-ray diffraction and thermogravimetric analysis. The study showed that there was an interaction between CTC/MTC and ZnS@CdS QDs, and the electrostatic force was the main force. The Stern-Volmer analysis showed that the quenching was static, which was further proved by fluorescence lifetime experiment. Under the optimized experimental conditions, linear calibration curves for detecting CTC/MTC were obtained with a limit of detection of 12.91/12.10 ng mL−1. The contents of CTC/MTC in milk, tangerine, beef and pork samples were detected. The recoveries of CTC/MTC were satisfactory. The established method had good analytical performance and can be used for the detection of more actual samples.

Light-triggered reactions in a new “light” of nanoparticles engineering

This study presents an innovative light-triggered synthesis of nanoparticles (NPs) utilizing UV radiation (λ = 254 nm), thiols (non-toxic mercaptosuccinic acid, MSA), and metal ions (Cu2+, Zn2+, Cd2+, Se4+). Efficient formation of various nanoparticles is achieved by exposing a precursor blend of metal ions and thiols (MSA) to ultraviolet light in compact volumes, like UV-transparent 96-well plates (50 – 300 μL per well) or plastic tubes (1.5 – 50 mL). This process effectively produces different types of nanoparticles, including fluorescent zinc-cadmium quantum dots (ZnCd QDs), non-fluorescent copper nanoparticles (CuNPs), and selenium nanoparticles (SeNPs). The scalability of the method allows for easy upscaling using larger test tubes or downsizing by depositing precursors (10 – 100 μL) on a paper matrix, where UV treatment not only induces NP formation in solution but also facilitates their anchoring to the paper surface. The developed one-pot in situ approach offers a cost-effective, user-friendly, and energy-efficient method for NP production and chemical engineering on paper surfaces. The technique is promising for a wide range of applications, such as interferometric measurement using ZnCd QDs, bactericidal effects of CuNPs against methicillin-resistant Staphylococcus aureus (MIC100 = 0.14 mg/mL), and visible light switchable (ON/OFF) nanozymatic reactors employing SeNPs. We suggest light-triggered chemistry based on thiols and metal ions for effective “soft” synthesis of various nanoparticles and NPs-based devices.

Hydrochromic convertibility on fiberized self-assembling of copper-based perovskite quantum dots

Halide perovskite presents great competitive advantages in the new generation of stimuli-responsive materials, while the tuning of fluorescence emission is still limited by irritative factors and external conditions. Herein, anti-solvent assisted crystallization and in-situ synthesis are innovatively combined to accomplish the fiberized self-assembly of copper-based perovskite quantum dots economically and environmentally, which makes humidity a novel stimulus for luminescence regulation. Under the excitation of medium-wave UV, the original Cs3Cu2I5-CsCu2I3@polyacrylonitrile (CCI@PAN) fibers exhibit a main emission peak of 460 nm with a shoulder at 550 nm, and the intensity of shoulder peak is gradually increased with the continuous addition of moisture. Switching from blue to yellow fluorescence is achieved in CCI@PAN fiber membrane by the introduction of water, which is attributed to the ultra-high solubility of CsI in water. Moreover, owing to the spatial limitation of the nanofibers, the unique incomplete reversibility exhibited by the nanofiber membrane during water removal predicts that the nanofiber membrane can be used as a permanent recording material. Overall, this work deeply explores the influence of humidity on the fluorescence and structure of perovskite quantum dots, providing a method to synthesize innovative perovskite nanofiber composites based on emission conversion, which has broad prospects in advanced anti-counterfeiting, biological protection display, information encryption and smart wearable devices.

Sustainable carbon quantum dots enhanced photoluminescence for bioimaging applications: An in vitro and in silico analysis

This study explores the synthesis and characterization of glucose-based carbon quantum dots (CQDs) for potential applications in the field of photoluminescence. The unique properties of CQDs are investigated, highlighting their distinct features compared to traditional carbon dots. Here, commercially available L-glucose is a precursor that has been chosen as the starting material to produce fluorescent carbon quantum dots (CQDs). The low to high quantum yield CQDs were reduced by chemical reduction method using sodium borohydride and then thiol (L-cysteine) induced for the stabilizer to stabilize rigidified reduced CQDs-L-cysteine (r-CQDs-Cys). The effect of pH and the ligand effect have been investigated for the photoluminescence (PL) studies of r-CQDs-Cys, yielding emission responses that were tuned according to the pH and ligand. The optimized CQDs to r-CQDs-Cys shows the quantum yield (QY) increased from 8.56 % to 42.72 %. The fluorescent QY of the synthesized CQDs investigated for the cytotoxicity test explicates that 90 % of the cells (MCF7) maintain their normal morphology even at higher concentrations of r-CQDs-Cys at 100 µg/mL. This Cytotoxicity test suggests that r-CQDs-Cys are non-toxic biocompatible and the binding energy value −6.8 kcal/mol of the carbon quantum dots was confirmed by in-silico studies. A total of 13 hydrogen bonds, 2 carbon bonds, and one Pi bond were formed during the interaction of the MCF7 cancer cell line with carbon quantum dots. The overall results confirmed that r-CQDs-Cys enhanced QY, fluorescence emission, and superior water solubility of the while compared to others which made them suitable for bio-imaging applications.

CsPbBr3 perovskite quantum dots-based Janus membrane with multifunction of luminescence, magnetism and aeolotropic electroconductivity

Lead halide perovskite quantum dots (QDs) are promising semiconductors for next-generation photoelectric devices. However, the development of perovskite QDs-based multifunctional materials still needs to be addressed in order to further advance the application of perovskite QDs. Herein, a successful synthesis of Janus microfibers array Janus membrane (JMAJM) with up-down structure and multifunction of luminescence, magnetism and electroconductivity is firstly achieved based on CsPbBr3 QDs through a parallel electrospinning. JMAJM comprises up-down two layers tightly bonded together. The up-layer of JMAJM is luminescence/magnetism Janus microfibers array (L/M-JMAJM) constructed by [CsPbBr3/polymethyl methacrylate (PMMA)]//[CoFe2O4/PMMA] Janus microfibers as building elements. The down-layer of JMAJM is luminescence/electroconductivity Janus microfibers array (L/E-JMAJM) fabricated by [CsPbBr3/PMMA]//[polyaniline (PANI)/PMMA] Janus microfibers as building elements. Two independent microcosmic regions are designed and realized in a Janus microfiber, confining luminescence with magnetic or conductive substances into their respective regions, thus minimizing adverse effects of other dark-colored functional substances on the fluorescence of CsPbBr3 QDs. This peculiar Janus microfiber enables the effective separation and high integration of CsPbBr3 QDs with other functional substances. The up-down structure of JMAJM ensures a high integration of luminescence, magnetism and conductivity. Meanwhile, JMAJM addresses the environmental instability of CsPbBr3 QDs while simultaneously endows perovskite QDs-based materials with additional functions to realize multifunction. Under ultraviolet excitation, fluorescence characteristics of the CsPbBr3 QDs in JMAJM are maintained, exhibiting a vibrant green emission at 517 nm. Meanwhile, JMAJM achieves a maximum saturation magnetization of 20.32 emu·g−1, high conductance of 10-2 S and aeolotropic electroconductivity degree of 107. The combination of micro-partition with macro-partition in JMAJM receives superior concurrent luminescence-magnetic-conductive multifunction. This work provides a novel idea and strategy for advancing perovskite QDs-based multifunctional materials.

A waterborne polyurethane‐based fluorescent tunable carbon quantum dot

AbstractFluorescent tunable materials have potential applications in lighting, display, anti‐counterfeiting, biological probes, and so on. Herein, carbon quantum dots (CQDs) with blue fluorescence (BCDs), and yellow fluorescence (YCDs) were synthesized by solvothermal method using bio‐based citric acid and lignin as carbon sources, respectively. BCDs and YCDs were anchored on polyurethane chains to prepare waterborne polyurethane‐based blue fluorescent carbon quantum dots (BCDs1.0‐WPU) and waterborne polyurethane‐based yellow fluorescent carbon quantum dots (YCDs1.0‐WPU), respectively. Compared with the corresponding BCDs and YCDs, the fluorescence intensity of both BCDs1.0‐WPU and YCDs1.0‐WPU is markedly enhanced, and the emission peaks obviously show a hypochromatic shift. A waterborne polyurethane‐based fluorescent tunable carbon quantum dots (BCDsxYPDs1‐x‐WPU) is prepared by mixing the ratio of BCDs1.0‐WPU and YCDs1.0‐WPU with the RGB method. It is noteworthy that BCDsxYCDs1‐x‐WPU not only achieves a fluent change of fluorescence from blue to yellow but also emits strong white fluorescence (CIE coordinates: X = 0.28, Y = 0.32). The absolute value of the Zeta potential of BCDsxYCDs1‐x‐WPU is greater than 40, indicating good storage stability. Furthermore, the thermal decomposition temperature is above 225 °C, implying good thermal stability. Furthermore, BCDsxYCDs1‐x‐WPU uses water as a continuous phase and has potential applications in environmentally friendly luminescence, anti‐counterfeiting and biological probes.

Onion-like multicolor thermally activated delayed fluorescent carbon quantum dots for efficient electroluminescent light-emitting diodes

Carbon quantum dots are emerging as promising nanomaterials for next-generation displays. The elaborate structural design is crucial for achieving thermally activated delayed fluorescence, particularly for improving external quantum efficiency of electroluminescent light-emitting diodes. Here, we report the synthesis of onion-like multicolor thermally activated delayed fluorescence carbon quantum dots with quantum yields of 42.3–61.0%. Structural, spectroscopic characterization and computational studies reveal that onion-like structures assembled from monomer carbon quantum dots of different sizes account for the decreased singlet-triplet energy gap, thereby achieving efficient multicolor thermally activated delayed fluorescence. The devices exhibit maximum luminances of 3785–7550 cd m−2 and maximum external quantum efficiency of 6.0–9.9%. Importantly, owing to the weak van der Waals interactions and adequate solution processability, flexible devices with a maximum luminance of 2554 cd m−2 are realized. These findings facilitate the development of high-performance carbon quantum dots-based electroluminescent light-emitting diodes that are promising for practical applications.

ZnS@ fluorenone derived multifunctional quantum dots for simultaneous recognition of bovine serum albumin (BSA) and copper ions (Cu2+) in aqueous blood and urine samples

An efficient synthesis of water-stable and fluorescent ZnS quantum dots has been executed beginning with its organic predecessor possessing fluorenone for sensing bovine serum albumin (BSA) among other proteins. Moreover, the organic predecessor of quantum dots has also been utilized for sensing of F- ions with binding constant of 1.8 × 104 M−1. Various spectroscopic techniques such as high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (PXRD), UV-visible (UV-vis), Fourier transform infrared (FTIR), thermogravimetric (TGA), Energy dispersive X-ray analysis (EDX), circular dichroism (CD) and Fluorescence (FL) spectroscopy have been utilized for the characterization of the developed quantum dots. The emission properties of quantum dots made them useful for the sensing of BSA and Cu2+ accompanied with secondary sensing of urea. The LODs value for BSA and Cu2+ were calculated as 213 and 211 nM, respectively. Demonstrating remarkable efficacy, these quantum dots have been successfully employed for the discernment of BSA in human blood and urine samples, achieving an outstanding recovery rate of up to 99.8%.

Room temperature, ultrafast and one-step synthesis of highly fluorescent sulfur quantum dots probe and their logic gate operation

The direct and rapid conversion of abundant and cheap elemental sulfur into fluorescent sulfur quantum dots (SQDs) at room temperature is a critical and urgent challenge. Conventional synthesis methods require high temperatures, high pressures, or specific atmospheric conditions, making them complex and impractical for real applications. Herein, we propose a simple method for synthesizing SQDs simply by adding H2O2 to an elemental sulfur-ethylenediamine (S-EDA) solution at room temperature. Remarkably, within a mere 10 min, SQDs with a photoluminescence quantum yield of 23.6 % can be obtained without the need for additional steps. A comprehensive analysis of the mechanism has demonstrated that H2O2 is capable of converting Sx2− ions generated in the S-EDA solution into zero-valent sulfur atoms through oxidation. The obtained SQDs can be utilized as a fluorescent probe for detection of tetracycline (TC) and Ca2+ ions with the limit of detection (LOD) of 0.137 μM and 0.386 μM respectively. Moreover, we have developed a sensitive logic gate sensor based on SQDs, harnessing the activated cascade effect to create an intelligent probe for monitoring trace levels of TC and Ca2+ ions. This paper not only presents a viable approach for ultrafast and scalable synthesis of SQDs at room temperature, but also contributes to the efficient utilization of elemental sulfur resources.

Lateral flow assemblies and allied application of carbon quantum dots derived from cigarette tobacco in biosensing, anticounterfeiting and fluorescent films: Theoretical and experimental overview

The bio-sensing activity of fluorescence based nanoprobes is one of the most significant aspects to scrutinize the analytical pursuance in modern security and lateral flow assays. Herein, potent transmogrification of waste cigarette tobacco into fluorescent carbon quantum dots (CQDs) has been achieved by calcination approach. The waste transformation to CQDs holds diverse benefits, comprising high quantum yield, low toxicity and scale up synthesis. The developed CQDs were able to identify tetracycline with phenomenal selectivity and sensitivity through fluorescence based method. The sensing mechanism was fully explored using Density Functional Theory (DFT) and Molecular docking studies. Governing features comprising tetracycline concentration, interfering studies, and real water analysis on the identification of tetracycline were also investigated. Along with, the prepared CQDs act as colorimetric probe, facilitating the detection of tetracycline with the naked eye. The lateral flow device was constructed for the on-site detection of tetracycline in real water samples. To the best of our knowledge, the present work represents a novel approach to designing CQDs and demonstrates their significant potential for application in anticounterfeiting measures and lateral flow devices. This work holds significant prospective as the prepared CQDs was fully utilized to its maximum usage in developing films and fluorescent anti-counterfeiting applications. Concisely, current work opens up distinctive opportunities for rapid on-site, real-time and visualized surveillance of tetracycline using CQDs prepared with a quite simple green approach.

Continuous Detection of Cobalt Ions and Pyrophosphates by NAC-CdTe Quantum Dots Fluorescence Probes.

In this work, a simple and sensitive N-acetyl-L-cysteine (NAC)-covered CdTe quantum dots (NAC-CdTe QDs) fluorescence probe for continuous detection of Co2+ and pyrophosphate ions (PPi, P2O74-) was synthesized. The fluorescence of the quantum dots was significantly quenched by Co2+ through the coordination of Co2+ and the carboxyl groups on the NAC-CdTe quantum dots. Interestingly, the combination of NAC-CdTe quantum dots with Co2+ yields a new fluorescence probe of Co2+-modified NAC-CdTe QDs (Co2+@NAC-CdTe). The addition of PPi restored the fluorescence due to the competition between PPi and carboxyl groups with Co2+ causing Co2+ to detach from the surface of Co2+@NAC-CdTe quantum dots. Thus, a sensitive and reversible detection of Co2+ and PPi had been successfully established. The Co2+@NAC-CdTe quantum dots fluorescence probe exhibits excellent selectivity and high sensitivity toward PPi detection with low detection limit of 0.28μM. In addition, the novel fluorescence probe was successfully applied to detect the concentration of PPi in environmental water samples and in-vitro cells imaging.

Fluorescence modulation of quantum dots in subsurface defects of optical elements by a linearly polarized light.

The limited excitation efficiency of quantum dots in the detection of subsurface defects in optical elements by quantum dot fluorescence gives rise to insufficient accuracy. To enhance the excitation efficiency of quantum dots, we studied the modulation of the polarization direction of linearly polarized incident light on quantum dot fluorescence. We first apply density matrix evolution theory to study the quantum dots interacting with linearly polarized incident light and emitting fluorescence. The fluorescence intensity exhibits cosine oscillations versus modulated laser polarization. It reaches a maximum value at the polarization angle zero, and then decreases as the angle becomes larger until π/2. The experimental results for the quantum dot in both solutions and subsurface defect of optical elements confirmed these results. For optical elements tagged with CdSe/ZnS quantum dots, the fluorescence intensity increases by 61.7%, and the area for the detected subsurface defects increases by 142.9%. Similarly, for C and InP/ZnS quantum dots, there are also increases in both the fluorescence intensity and the area of subsurface defects. Our study suggests that the subsurface defect detection in optical elements by the linearly polarized incident light could enhance the detection accuracy of subsurface defects in optical elements, and potentially achieve super-resolution imaging of subsurface defects.

Analyte-perturbed balance between reducibility and fluorescence of Ti3C2 MXene quantum dots for label-free, dual-mode detection of silver ions

BackgroundAs an emerging and attractive low-dimensional functional materials, Ti3C2 MXene quantum dots (QDs) enlarge the toolbox of fluorescence sensing. However, monochromatic fluorescence, which only provide one single signal, is often beset by challenges such as false-positive readouts and limitations in selectivity. Consequently, to improve the sensing accuracy by means of cross-verified dual-signal authentication, the endeavor to engineer dual-mode nanoprobes based on Ti3C2 QDs, incorporating both the capability of fluorescence and an alternative sensing mechanism, emerges as a compelling avenue. ResultsHere, based on the alterations in colorimetric and fluorescent signals of Ti3C2 QDs with the addition of Ag+, we propose a dual-mode sensor obviating the necessity for nanoprobe labeling. Owing to the decent reducibility of Ti3C2 QDs, Ag+ is adsorbed and reduced, resulting in the generation of plasmonic Ag nanoparticles (NPs), which simultaneously trigger colorimetric responses of the solution and enhance the fluorescent emission of Ti3C2 QDs. The confluence of colorimetry and fluorometry within this strategy optimally harnesses the modulating role of the acquired Ag NPs on the reducing capability and fluorescence characteristics of Ti3C2 QDs. The equilibrium imparts versatility and promising prospects to this analyte-triggered label-free method, which enables a remarkable specificity and an excellent detecting limit (0.45 μM) for Ag+. SignificanceThe balance between reducibility and fluorescence of Ti3C2 QDs for dual-mode detection is inventively demonstrated. With the exemplification of a direct influence of both features of the nanoprobe via the introduction of analytes, this study opens the feasibility of the analyte-perturbed felicitous equilibrium, which endows label-free methods with versatility and promising prospects. This design may evoke more biosensing strategies with the function of double-signal mutual verification.

Preparation of 3D pomegranate‐like quantum dot nanobeads and its application to highly sensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is often used as a major indicator for evaluating aflatoxin contamination in food, and its accurate and sensitive detection is of great significance. Herein, the high-quality CdSe/ZnS fluorescent quantum dot nanobeads (QBs) with 3D pomegranate were prepared by the dual-protecting microemulsion method, which showed excellent stability in different environments. AFB1 were detected by competitive quantum dot-based fluorescence-linked immunosorbent assay (QLISA) using 3D pomegranate-like QBs and single-core silica-encapsulated quantum dots (QD@SiO2). After optimization of the reaction conditions, the quantitative detection range of AFB1 by single-core QD@SiO2 as fluorescent probe was 0–100 ng/mL, with the half maximal inhibitory concentration (IC50) of 3.01 ng/mL and the limit of detection (LOD) of 0.12 ng/mL; whereas the quantitative detection range of AFB1 by fluorescent QBs was 0–100 ng/mL, with the IC50 of 1.76 ng/mL and the LOD of 1.03 pg/mL. Compared to single-core QD@SiO2, the fluorescent QBs was 120-fold more sensitive. The detection of AFB1 was also achieved in negative corn and peanut samples, indicating the possibility of its application to the detection of real food samples. The high performance of competitive QLISA using 3D pomegranate-like QBs as fluorescent probes offer highly sensitive and accurate quantitative detection of analytes in food safety monitoring.

Eu3+-based InP/ZnS quantum dot fluorescence platform for multi-color and sensitive visualization of tetracycline

A turn-on type ratiometric fluorescence sensing system of blue quantum dot Eu-MPA-InP/ZnS was established for multi-color visualization determination of tetracycline (TC). Mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) both modify the hydrophilicity of InP/ZnS QDs and serve as a scaffold for coordinating of Eu3+ ions. The blue fluorescence of Eu-MPA-InP/ZnS at 478 nm is reduced by the TC through the inner filter effect (IFE) under a single excitation wavelength of 365 nm. Rich colour gradients and a highly discriminative colour change were features of this multicolour response to TC, which allowed visual quantification of TC in a dose-dependent manner. Furthermore, by cross-linking Eu-MPA-InP/ZnS with agarose (Aga.), a mouldable Eu-MPA-InP/ZnS@Aga 96-well gel sensing device was designed to serve as a handheld sensor for on-site detection of TC. This probe expands the use of InP QDs in analytical sensing and has been effectively applied to the visual detection of tetracycline in milk and the environment.

Borophene Quantum Dots as Novel Peroxidase-Mimicking Nanozyme: A Dual-Mode Assay for the Detection of Oxytetracycline and Tetracycline Antibiotics.

The greater advantages and wide applications of zero-dimensional nanodots inspire researchers to develop new materials. Therefore, novel borophene quantum dots (QDs) were prepared by a hydrothermal liquid exfoliation technique using water medium. The borophene QDs proved to be highly stable in water medium for more than 120 days. The synthesized borophene QDs revealed intrinsic peroxidase mimetic activity using two chromogenic substrates, 3,3',5,5'-tetramethylbenzidine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS). The excellent intrinsic peroxidase activity toward TMB and ABTS substrates was executed using optimal reaction conditions (pH, borophene QDs' concentration, incubation time, and temperature). The formation of hydroxyl radicals in the presence of H2O2 upon TMB and ABTS oxidation played a significant role in the peroxidase reaction. The borophene QDs further proved to be successful for the colorimetric detection of antibiotics (oxytetracycline and tetracycline) using both TMB and ABTS peroxidase substrates. The limit of detection (LOD) for oxytetracycline and tetracycline was found to be 1.10 and 1.02 μM using TMB and 1.03 and 1.02 μM using ABTS chromogenic substrates, respectively. In addition, the fluorescence sensing of oxytetracycline and tetracycline over borophene QDs was also examined. The high fluorescence of borophene QDs (turn ON) was quenched (turn OFF) by oxytetracycline and tetracycline through the inner filter effect mechanism. The LOD of the fluorescence sensing of oxytetracycline and tetracycline was 1.14 and 1.08 μM, respectively. Interestingly, the borophene QDs could be used for the sensitive and selective colorimetric and fluorometric sensing of oxytetracycline and tetracycline after 120 days of storage. The synthesized borophene QDs with long-term stability and real sample analysis provide new insight as nanozymes with higher peroxidase mimetic and fluorescence performance and can be further exploited for medical diagnosis and environmental toxicants' detection.

One-step hydrothermal synthesis of sulfur quantum dots for detection of Hg2+ ions and latent fingerprints

High blue-emitting sulfur quantum dots (SQDs) with quantum yields of up to 58.7% were prepared using elemental sulfur using a facile ethylenediamine-assisted hydrothermal acceleration method at 60 °C for 7 h. In the presence of ethylenediamine, bulk sublimated sulfur powder can be broken down into fine particles of sulfur-nitrogen compounds and then oxidized to produce SQDs. HRTEM analysis of the morphology of SQDs showed that SQDs had a quasi-spherical shape with a size of 3.2 nm. In this process, under the influence of ethylenediamine, sublimated sulfur is rapidly converted from zero-valent sulfur to polysulfide with simple heating, greatly improving manufacturing efficiency. Synthesized fluorescent sulfur quantum dots (SQDs) were used in this study as fluorescent probes for quantitative detection of Hg2+. The SQD served as an effective Hg2+ detection probe with a detection limit of 2.7 μM through an efficient on-off switching mechanism in response to Hg2+. In addition, latent fingerprints were recognized using SQD powder, and fingerprints were detected on the surfaces of various media, such as paper, glass, and aluminum foil. The synthesized SQDs have a high potential for sensing applications of various luminescent materials.

PH response mechanism of bifunctional fluorescent carbon quantum dots and application in cancer detection and bioself-targeting imaging

The development of fluorescent probes suitable for lysosome visualisation as well as real-time tracking is crucial because lysosomes play a crucial role in numerous metabolic activities and diseases. In this paper, nitrogen-doped carbon quantum dots (NCQDs) enriched with a large number of hydroxyl, amino, and carboxyl groups were prepared by a simple solvothermal method using tartaric acid and 4-aminosalicylic acid as raw materials. The fluorescence intensity of NCQDs decreased with increasing pH (1–13) due to protonation and deprotonation as well as hydrolysis of surface groups in alkaline environment and detachment of chromophores. This enabled the NCQDs to achieve label-free and rapid visualisation of pH in cells. The disparity in pH levels between cancer cells and normal cells resulted in varying fluorescence brightness of NCQDs observed in these two cells, which enabled the differentiation of cancer cells from normal cells. Most importantly, when NCQDs entered the cell, lysosomes could provide protons for NCQDs, and the protonation of NCQDs' surface groups led to stronger fluorescence after endocytosis of NCQDs in lysosomes. Thus, lysosomal targeted imaging could be achieved without the need to introduce lysosomal-targeted ligands, and NCQDs had a higher biocompatibility and stability compared to commonly used commercial dyes, which made it the ideal choice of lysosomal-targeted fluorescent probes.