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Understanding the cytotoxicity of fluorescent carbon dots (CDs) is crucial for their applications, and various biochemical assays have been used to study the effects of CDs on cells. Knowledge on the effects of CDs from a biophysical perspective is integral to the recognition of their cytotoxicity, however the related information is very limited. Here, we report that atomic force microscopy (AFM) can be used as an effective tool for studying the effects of CDs on cells from the biophysical perspective. We achieve this by integrating AFM-based nanomechanics with AFM-based imaging. We demonstrate the performance of this method by measuring the influence of CDs on living human neuroblastoma (SH-SY5Y) cells at the single-cell level. We find that high-dose CDs can mechanically induce elevated normalized hysteresis (energy dissipation during the cell deformation) and structurally impair actin skeleton. The nanomechanical change highly correlates with the alteration of actin filaments, indicating that CDs-induced changes in SH-SY5Y cells are revealed in-depth from the AFM-based biophysical aspect. We validate the reliability of the biophysical observations using conventional biological methods including cell viability test, fluorescent microscopy, and western blot assay. Our work contributes new and significant information on the cytotoxicity of CDs from the biophysical perspective., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

A sensitive method for the detection of β-glucuronidase was established using functionalized carbon dots (β-CD-SiCDs) as fluorescent probes. The β-CD-SiCDs were found to be obtained through in situ autopolymerization by mixing the solutions of methyldopa, mono-6-ethylenediamine-β-cyclodextrin and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane at room temperature. The method has the characteristics of low energy consumption, simple and rapid. β-CD-SiCDs exhibited green fluorescence at 515 nm emission with a quantum yield of 7.9 %. 4-nitrophenyl-β-D-glucuronide was introduced as a substrate for β-glucuronidase to generate p-nitrophenol. Subsequently, p-nitrophenol self-assembled with β-CD-SiCDs through host-guest recognition to form a stable inclusion complex, resulting in the fluorescence quenching of β-CD-SiCDs. The linear range of β-CD-SiCDs for detecting β-glucuronidase activity was 0.5-60 U L -1 with a detection limit of 0.14 U L -1 . For on-site detection, gel reagents were prepared by a simple method and the images were visualized and quantified by taking advantage of smartphones, avoiding the use of large instrumentation. The constructed fluorescence sensing platform has the benefits of easy operation and time saving, and has been successfully used for the detection of β-glucuronidase activity in serum and cell imaging., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A ratiometric fluorescence strategy was proposed based on carbon dots (CDs) and self-assembled copper nanoclusters (CuNCs) driven by Al 3+ ions for S 2- detection. Si-CDs/CuNCs@Al 3+ exhibits blue and red emission under single excitation. Interestingly, the red emission of the CuNCs was regularly quenched while the blue fluorescence emission of the CDs was preserved after continuous addition of S 2- . The fluorescence spectrometer-based S 2- linear range is from 0.5 to 40 μM, with a low detection limit (LOD) of 0.16 μM. The fluorescence response of Si-CDs/CuNCs@Al 3+ to S 2- exhibits a distinct color change process (red to pink to blue), implying feasibility of visual analysis. A portable fluorescence sensing platform was established using the color-to-value conversion function of a smartphone for accurate visualization and quantitative identification of S 2- without spectrometer. The fluorescent test strips prepared with Si-CDs/CuNCs@Al 3+ can conduct on-site visual analysis of S 2- in the water environment more conveniently and quickly. The linear range of S 2- detection based on the smartphone-integrated test strip sensing platform is 1-40 μM, and the LOD is 0.42 μM. This work provides a new horizon for target on-site analysis in environmental samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

A novel fluorescent probe based on molecularly imprinted polymers (MIPs) coupled with carbon quantum dots (CQDs) was fabricated and successfully used for selective recognition of mesotrione. In this probe, the biomass-derived CQDs were prepared through a hydrothermal method using mango peels as carbon source, and the whole synthesis procedure was green without chemical reagents. The CQDs were encapsulated into MIPs by using sol-gel technology. After removal of the template molecule mesotrione, specific binding sites are formed and there is electrostatic attraction between the probe and the template molecule. The synthetic CQDs@MIPs were able to selectively capture the target mesotrione with fluorescence quenching via the specific interaction between mesotrione and the recognition cavities. The probe was used for determination of mesotrione in corn to verify the practicality of the proposed method. The detection limit of mesotrione was 4.7 nmol L -1 , and the linear range was 15 nmol L -1 to 3000 nmol L -1 . Meanwhile, the recoveries of this method for mesotrione were 91.4-96.2%, and the relative standard deviations (RSDs) were 3.2-6.1%. This work provides a novel research method to synthesize CQDs@MIPs with high selectivity (imprinting factor = 5.6), and which can be used for convenient, rapid recognition and sensitive detection of trace compounds from complex matrices.

The concentration of L-cysteine (Cys) and glutathione (GSH) is closely related to the critical risk of various diseases. In our study, a new rapid method for the determination of Cys and GSH in water and urine samples has been developed using a fluorescent probe technique, which was based on crystal violet (CV)-functionalized CdTe quantum dots (QDs). The original QDs emitted fluorescence light, which was turned off upon adding CV. This conjugation of CV and QDs could be attributed to electrostatic interaction between COO - of mercaptopropionic acid (MPA) on the surface of QDs and N + of CV in aqueous solution. In addition, Förster resonance energy transfer (FRET) also occurred between CdTe QDs and CV. After adding Cys or GSH to the solution, Cys or GSH exhibited a stronger binding preference toward Cd 2+ than Cd 2+ -MPA, which disturbed the interaction between MPA and QDs. Thus, most MPA was able to be separated from the surface of QDs because of the participation of Cys or GSH. Then, the fluorescence intensity of the CdTe QDs was enhanced. Good linear relationships were obtained in the range of 0.02-40 μg mL -1 and 0.02-50 μg mL -1 , and the detection limits were calculated as 10.5 ng mL -1 and 8.2 ng mL -1 , for Cys and GSH, respectively. In addition, the concentrations of biological thiols in water and urine samples were determined by the standard addition method using Cys as the standard; the quantitative recoveries were in the range of 97.3-105.8%, and relative standard deviations (RSDs) ranged from 2.5 to 3.7%. The method had several unique properties, such as simplicity, lower cost, high sensitivity, and environmental acceptability. Graphical abstract Crystal violet-functionalized CdTe quantum dots for detecting L-cysteine and glutathione with switch-on fluorescent strategy.

A newly designed fluorescence probe made from a hybrid quantum dot/mesoporous silica/molecularly imprinted polymer (QD/MS/MIP) was successfully created, and the probe was used for the detection of tetracycline (TC) in serum sample. QD/MS/MIP was characterized by transmission electron microscope, Fourier transform infrared spectroscopy, UV spectroscopy, X-ray powder diffraction, nitrogen adsorption-desorption experiment and fluorescence spectroscopy. Tetracycline, which is a type of broad-spectrum antibiotic, was selected as the template. The monomer and the template were combined by covalent bonds. After the template was removed to form a binding site, a hydrogen bonding interaction formed between the hole and the target molecule. Moreover, when rebinding TC, a new complex was produced between the amino group of QD/MS/MIP and the hydroxyl group of TC. After that, the energy of the QDs could transfer to the complex, which explains the fluorescence quenching phenomenon. The fluorescent intensity of QD/MS/MIP decreased in 10 min, and an excellent linearity from 50 to 1000 ng mL(-1) was correspondingly obtained. This composite material has a high selectivity with an imprinting factor of 6.71. In addition, the confirmed probe strategy was successfully applied to serum sample analyses, and the recoveries were 90.2%-97.2% with relative standard deviations of 2.2%-5.7%. This current work offers a novel and suitable method to synthesize QD/MS/MIP with a highly selective recognition ability. This composite material will be valuable for use in fluorescence probe applications.

A newly designed molecularly imprinted polymer (MIP) material was fabricated and successfully utilized as recognition element to develop a quantum dots (QDs) based MIP-coated composite for selective recognition of the template cyphenothrin. The MIP-coated QDs were characterized by fluorescence spectrophotometer, Fourier transform infrared spectroscopy, transmission electron microscope, dynamic light scattering and X-ray powder diffraction. The fluorescence of the coated QDs is quenched on loading the MIP with cyphenothrin, and the effect is much stronger for the MIP than for the non-imprinted polymer, which indicates the MIP could as a recognition template composite. This method can detect down to 9.0 nmol L(-1) of cyphenothrin in water, and a linear relationship has been obtained covering the concentration range of 0.1-80.0 μmol L(-1). The method has been used in the determination of cyphenothrin in water samples and gave recoveries in the range from 88.5% to 97.1% with relative standard deviations in the range of 3.1-6.2%. The present study provides a new and general strategy to fabricate inorganic-organic MIP-coated QDs with highly selective recognition ability in aqueous media and is desirable for chemical probe application., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A sensitive and effective strategy for the detection of cytochrome c (Cyt c) and trypsin was developed using biomass nitrogen-doped carbon quantum dots (N-CQDs) as the fluorescence probe. N-CQDs were synthesized through a one-pot hydrothermal method by utilizing cellulolytic enzyme lignin as the carbon source and ammonia as the solvent and nitrogen source. The obtained N-CQDs had good water solubility and stable optical properties. The introduction of nitrogen increased fluorescence quantum yield (QY) to 8.23%, which was almost four times as high as that before nitrogen doping. The N-CQDs were fabricated as a label-free biosensor to detect Cyt c and trypsin. The fluorescence of N-CQDs was quenched with positively charged Cyt c due to electrostatic induction aggregation and static quenching. However, Cyt c tended to be hydrolyzed into small peptides in the presence of trypsin, which caused fluorescence recovery of the N-CQDs/Cyt c complex. A wide linear response range was achieved for Cyt c within 1–50 μM and the developed N-CQDs/Cyt c complex displayed a linear response for trypsin within 0.09–5.4 U/mL. The detection limits were 0.29 μM for Cyt c and 0.013 U/mL for trypsin, respectively. Furthermore, this assay had been applied to Cyt c and trypsin detection in serum samples with the recoveries in the range of 94.6–98.5% and 95.5–102.0%, respectively. The established method was sensitive, selective, easy to operate, and low cost, which proved its potential application in clinical diagnosis. [ABSTRACT FROM AUTHOR]

A multifunctional nanocomposite for highly sensitive and rapid detection of tetracycline hydrochloride (TC) has been developed using magnetic quantum dots (MQDs). The thiolated quantum dots (QDs) were conjugated with amino-coated Fe3O4 and subjected to crosslinking modification with EDC/NHS through covalent binding. The obtained MQDs were shown to possess superparamagnetic characteristics and fluorescence properties and exhibit a strong orange metal-to-ligand charge transfer emission. The MQDs were characterized by fluorescence spectrophotometry, X-ray powder diffraction, Fourier transform infrared spectroscopy, physical property measurement and transmission electron microscopy. The multifunctional nanomaterial shows excellent fluorescence properties that allow for highly sensitive and short response time for TC detection. Under optimum conditions, a linear calibration plot of the quenched fluorescence intensity at 593 nm against the concentration of TC was observed in the range from 10 to 700 nmol L−1 with a detection limit of 1.2 nmol L−1. The recovery detected with this method was from 95.7% to 99.3% with a relative standard deviation (R.S.D.) below 3%. This method manifested several advantages such as high sensitivity, non-toxicity, short analysis time, low cost and ease of operation. [ABSTRACT FROM AUTHOR]

A new dual-emission ratiometric fluorescent probe was synthesized and successfully used for the determination of Malachite Green (MG) in fish farming water. The ratiometric fluorescent probe was successfully composited by sol-gel method using C3N4 and CdTe quantum dots as fluorescent materials combined with mesoporous molecularly imprinted polymers. MG quenches the red fluorescence of the CdTe QDs (with excitation/emission wavelengths at 350/680 nm) while the blue fluorescence of C3N4 (with excitation/emission wavelengths at 350/458 nm) remains unchanged. The change of fluorescence color and fluorescence intensity ratio can be successfully used for quantification of malachite green. In addition, the mesoporous structure has a large surface and good adsorption capacity for malachite green. The normalized intensity of fluorescence increases linearly in the 50–1000 ng·mL−1 MG concentration range, and the detection limit is 10 ng·mL−1. The imprinting factor is 3.2. The nanoprobe was applied to the determination of MG in fish farming water samples. Recoveries and relative standard deviations were 92.5–97.8% and 2.5–6.2%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dual-emission ratiometric fluorescent probe for carbimazole detection was prepared. • Establishment of a portable sensing platform combining test strips and smartphones. • The method is convenient and fast, which allows the on-site detection of carbimazole. • Real sample analysis results of the smartphone-assisted platform are satisfactory. The ratio-based probe improves detection precision and accuracy by minimizing the effects of various experimental conditions. Herein, we constructed a ratio fluorescent probe (Si NPs/TGA-functionalized CdTe) using silicon nanoparticles (Si NPs) as the background signal and mercaptoacetic acid-functionalized cadmium telluride quantum dots (TGA-functionalized CdTe) as the responding unit. The interaction between Carbimazole (CBZ) and sulfhydryl groups on the surface of TGA-functionalized CdTe led to a decrease in the fluorescence intensity of the probe, and the color of the solution turned red and pink turned blue. Meanwhile, a test paper-based detection method integrated with the smartphone sensing platform was established to analyze the red, green, and blue (RGB) values in the images of Si NPs/TGA-functionalized CdTe solution before and after the addition of CBZ based on the change of hue, and an analytical model was constructed based on the R/B value and CBZ concentration, realizing rapid visual detection and analysis of CBZ. In addition, the constructed smartphone sensing platform was applied to the detection of CBZ in human urine, and the limit of detection the fluorescence analysis method and the smartphone sensing platform were 40 nM and 63 nM, with the recoveries of 96.5 %-102.7 % and 90.6 %-107.2 %, and the relative standard deviations of 2.7 %-4.1 % and 3.5 %-6.8 %, respectively. This work provides a significant improvement in the proportional sensing of CBZ in human urine and broadens the use of portable quantitative sensing devices in chemical sensing applications. [ABSTRACT FROM AUTHOR]

This study describes the fabrication, performance and characterization of a luminescence temperature sensor based on ordered all-quantum-dot (QD) multilayers. Highly photoluminescent and stable CdSe/ZnS core-shell QDs modified with two types of surface functional groups (-NH 2 and –COOH) were prepared via aqueous route. Ordered thin films (film-A), based on alternate assembly of CdSe/ZnS–COOH (negatively charged) and CdSe/ZnS–NH 2 (positively charged), were fabricated through electrostatic layer-by-layer (LBL) self-assembly technique. The temperature-dependent fluorescent properties of film-A (temperature-dependent photoluminescence; transient spectroscopy) were compared with that of a QD-polymer film (PDDA-CdSe/ZnS–COOH films; film-B) also prepared using electrostatic LBL self-assembly. Compared with film-B, film-A showed significant temperature sensitivity and fluorescence lifetime over the range 50–300 K. In addition, structural characterization of CdSe/ZnS–COOH and CdSe/ZnS–NH 2 QDs were symmetrically characterized by transmission electron microscope (TEM) and the average diameters of the two QDs were both around 4.2 nm. The two functional groups (-COOH and –NH 2) were confirmed by X-ray photoelectron spectroscopy (XPS). The results suggested that ordered all-QD multilayer films may have good potential in applications requiring sensors for optical thermometry. • Ordered thin film based on alternate assembly of CdSe/ZnS–COOH and CdSe/ZnS–NH 2 (film-A) have been fabricated through electrostatic layer-by-layer (LBL) self-assembly technology for the first time. • The all-QD films via electrostatic LBL self-assembled exhibited significant temperature sensitivity over the range 50-300 K. • This ordered all-OD film would have potential application in field of fluorescence thermometry. [ABSTRACT FROM AUTHOR]

Preparation and application of ratiometric fluorescent sensing platform for dual-mode TC-PBQ sensing. [Display omitted] • Fluorescent test paper coated with dual emission ratiometric fluorescent sensor. • The system exhibited a wide range of color changes in the presence of TC-PBQ. • Introduces a reliable portable smartphone-assisted RGB-dependent sensing model. • Realization of rapid and visual on-site detection of TC-PBQ in river water. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hybrid materials of BSN-CQDs and vanadium oxide nanoribbons have been prepared. • A method for detection of α-glucosidase has been established. • The "turn-on" and "turn-off" processes have been obtained. • The satisfactory monitor results have been obtained. A sensitive and effective strategy for the screening of α-glucosidase and its inhibitors was established based on carbon quantum dots (CQDs) and vanadium oxide nanoribbons. B,S,N co-doped CQDs (BSN-CQDs) were prepared by one-step microwave hydrothermal method using o-phenylenediamine, boric acid, and thiourea as raw materials. The prepared CQDs emitted yellow fluorescence (λ em = 565 nm) under excitation of 410 nm, and the quantum yield was 15.3%. The fluorescence of CQDs was firstly quenched by the vanadium oxide nanoribbons via inner filter effect. Then, 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA2G) was introduced as a substrate of α-glucosidase to produce ascorbic acid (AA). Vanadium oxide nanoribbons could be converted to V4+ by AA, which led to fluorescence recovery. After adding inhibitors (anti-diabetic drugs), the α-glucosidase activity was inhibited and the degree of fluorescence recovery was reduced. The established nanoprobe showed a response linearity to α-glucosidase in the range of 0.01–5 U mL−1, with a low detection limit of 0.003 U mL−1. This platform was applied for the screening of acarbose, with a detection limit of 0.02 μM. The constructed sensing strategy had the advantages of high selectivity, sensitivity, and was successfully used for α-glucosidase detection in serum samples and anti-diabetic drugs screening. [ABSTRACT FROM AUTHOR]