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Acid-sensitive CdTe quantum dots-loaded alginate hydrogel (CdTe QDs-AH) beads were designed for the visual detection of SO 2 residues. As proof of concept, two types of CdTe QDs were selected as model probes and embedded in AH beads. The entire test was performed within 25 min in a modified double-layer test tube with one bead fixed above the sample solution. Adding citric acid and heating at 70 ℃ for 20 min transformed the sulfites in the solution into SO 2 gas, which then quenched the fluorescence of the CdTe QDs-AH beads. Using this assay, qualitative, naked-eye detection of SO 2 residues was achieved in the concentration range of 25-300 ppm, as well as precise quantification was possible based on the difference in the average fluorescence brightness of the beads before and after the reaction. Five food types were successfully analysed using this method, which is simpler and more economical than existing methods, and does not require complex pretreatment., 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 Ltd. All rights reserved.)

Epinephrine (EP) is a catecholamine hormone with a variety of physiological activities. Monitoring the concentration of EP in drugs, food, biological samples and cosmetics is of great significance for their quality control. Herein, a novel fluorescence sensing method was designed for the high-specificity detection of EP based on N-doped carbon quantum dots (N-CDs). The EP could interact with the fluorescent senor of N-CDs which emits blue fluorescence to produce concentration- dependent fluorescence quenching through the photo-induced electron transfer (PET). The established sensing method has good linearity in the range of 0.5-10 μM with the LOD of 0.15 μM. More importantly, it is highly selective because similar components with phenolic hydroxyl groups or primary amino groups, even norepinephrine (NEP), could not interfere with the detection. This method can provide a low-cost, rapid and simple new way for the detection of EP, and has a good application prospect in point-of-care assay and in situ test., 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 fluorescent probe based on N/S doped carbon dots (N/S-CQDs) and mercaptoacetic acid capped CdTe quantum dots (TGA-CdTe QDs) with sensitized and self-calibration functions was constructed to sensitively detect multiple tetracycline antibiotics (TCs). N/S-CQDs could attach stably to TGA-CdTe QDs and form a new composite ratiometric fluorescent probe that had a more than tenfold increase in sensitivity to TCs compared with each single QD. The probe could detect four common TCs as the color of the probe changed from bright red to dark red, and the limit of detection (LOD) was 1.47 × 10 -2 -1.78 × 10 -2 mg/L. Practical applications of the probe in food and urine were also verified with recovery rates of 95.21%-104.97%. Due to the abundant spectral fingerprints provided by both QDs, this novel probe could accurately recognize not only different single TCs but also mixed TC samples even in actual samples combined with chemometrics., 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. Published by Elsevier Ltd.)

Copper (Cu 2+ ), as a heavy metal, accumulates in the human body to a certain extent, which can induce various diseases and endanger human health. Rapid and sensitive detection of Cu 2+ is highly desired. In present work, a glutathione modified quantum dot (GSH-CdTe QDs) was synthesized and applied in a "turn-off" fluorescence probe to detect Cu 2+ . The fluorescence of GSH-CdTe QDs could be rapidly quenched in the presence of Cu 2+ through aggregation-caused quenching (ACQ), resulting from the interaction between the surface functional groups of GSH-CdTe QDs and Cu 2+ and the electrostatic attraction. In the range of 20-1100 nM, the Cu 2+ concentration showed a good linear relationship with the fluorescence decline of the sensor, and the LOD is 10.12 nM, which was lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, aiming to attain visual analysis, colorimetric method was also used for rapidly detecting Cu 2+ by capturing the change in fluorescence color. Interestingly, the proposed approach has successfully been applied for the detection of Cu 2+ in real samples (i.e., environment water, food and traditional Chinese medicine) with satisfactory results, which provides a promising strategy for the detection of Cu 2+ in practical application with the merits of being rapid, simple and sensitive., 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.)

The inappropriate application of aminoglycoside antibiotics (AGs) in food products has led to the accumulation of AG residues in the human body. In this study, a novel fluorescent sensor based on mercaptosuccinic acid (MSA)-modified CdTe quantum dots (QDs) were designed for the rapid visual detection of a representative AG, neomycin (NEO). The proposed sensor showed excellent performance toward NEO determination, with a detection limit of 1.60 × 10 -8  mol/L. Furthermore, MSA-CdTe QDs can be applied to the visual detection of NEO, where the fluorescence changes from bright yellow to dark red with increasing NEO concentration. Most importantly, high selectivity of MSA-CdTe QDs toward NEO was achieved even in the presence of other antibiotics, which are common interfering agents, with a recovery rate in actual samples as high as 95.66 %-100.77 % and an RSD of less than 3.15 %., 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 Elsevier Ltd. All rights reserved.)

Background: Ascorbic acid (AA) is an essential nutrient for humans, which must be obtained from vegetables, fruits, and other foods. The content of AA has become an important standard to evaluate the quality and nutritional value of food. The fluorescence sensing method based on nanomaterials is a good alternative for the rapid detection of AA. In this study, we developed an inner filter effect-based fluorescent probe that hybridized nitrogen-doped carbon dots (NCDs) with cobalt oxyhydroxide nanoflakes (CoOOH NFs)., Results: An optimal NCDs was successfully selected because it has a strong fluorescence at 430 nm and the most significant quenching phenomenon with CoOOH NFs due to the inner filter effect. When adding AA into the NCDs-CoOOH NFs probe solution, a specific redox reaction will occur between the enediol group of AA and the CoOOH NFs to interfere with the quenching ability of CoOOH NFs and recover the fluorescence of NCDs. The recovered fluorescence intensities demonstrated a linear relationship with the concentrations of AA. The assay based on the NCDs-CoOOH NFs probe allows AA to be tested in a wide range of 5-200 μmol L -1 with a detection limit of 2.31 nmol L -1 . Furthermore, to evaluate its practical application, the NCDs-CoOOH NFs fluorescence probe was utilized to analyze AA in vegetable, fruit, and serum matrixes with satisfactory results., Conclusion: An inner filter effect-based fluorescence probe for the rapid detection of AA was developed, and it has a good potential to be applied in both food and clinical testing. © 2022 Society of Chemical Industry., (© 2022 Society of Chemical Industry.)

A novel dual-channel sensor array based on the "off" and "off-on" phenomenon of ZnCdSe quantum dots (QDs) - KMnO 4 system was established for the effective distinguish of 30 green teas with various species, grades and origins. Starting from optimization of QDs for the construction of the sensing system, their sensitivity and selectivity performances towards 10 representative green teas were tested first and the sensor systems based on ZnCdSe QDs were finally established. An obvious "off" response brought by the interactions between amino acids, quercetin, et al. and ZnCdSe QDs was obtained while an "off-on" phenomenon brought by the interactions between catechins and the ZnCdSe-KMnO 4 system had also been verified. Furthermore, based on the differential fluorescence "off-on" response of seven catechins, the qualitative and quantitative analyses of these catechins were successfully carried out with the linear range from 0.5 to 10 µg/mL. Most importantly, through adopting the dual-channel sensor, 30 green teas with different species, origins and grades can be accurately identified with the LDA model according to the spectral signals and the recognition accuracy could achieve 100 %., 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 Elsevier Ltd. All rights reserved.)

In recent years, antibiotic residues in food have been of great concern to regulators and consumers. In this study, a novel fluorescent sensor based on S, N-doped carbon quantum dots (S, N-CQDs) was established for rapid detection of tetracycline antibiotics (TCs). Through the internal filter effect (IFE), QDs fluorescence can be effectively quenched by TCs, endowing it an "off" condition. Under the optimal conditions, the TC concentration in the range of 1.88-60 μmol/L had a good linear relationship with the change of QDs fluorescence intensity, and the limit of detection (LOD) was calculated as 0.56 μmol/L (S/N = 3). Furthermore, the proposed "Turn-off" sensor could be employed to quickly and accurately quantify TCs residues even in milk, honey and tap water. The recovery rate was as high as between 93.61% and 102.31%. The established sensor has great application value in the fields of food safety and drug analysis, and provides broad prospects for the future food industry., 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.)

Mercury ions and thiophanate methyl (TM), are common contaminants present in the environment and food products. These contaminants cause neurovirulence and carcinogenicity effect on the human body. Herein, thioctic acid-carbon dots (SCDs) was synthesized and applied in a fluorescent "turn-off-on" probe to detect Hg 2+ and TM. The presence of other common metal ions and pesticides did not affect the response of the developed sensor. Further investigation revealed that the fluorescent "turn-off-on" model were static, wherein the "turn-off" was induced by an electron transfer effect, while the "turn-on" was caused by the formation of TM-Hg complexes. Under optimal conditions, the fluorescence sensor method exhibited limits of detection as low as 33.3 nmol/L and 7.6 nmol/L for Hg 2+ and TM, respectively. The developed sensor was designed to detect Hg 2+ and TM in real tap water, grape juice and Citri Reticulatae Pericarpium (CRP) water samples., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

As a special carrier of traditional Chinese culture, baijiu is rich in terms of types and ingredients. Its quality analysis and control are always important and complex issues that urgently need reliable evaluation methods. In this study, four different modified CdTe quantum dots (QDs) were used to characterize their sensing performance to various baijiu. A sensor array was then constructed through the complementary properties of differential fluorescence signals. To achieve an accurate and rapid evaluation of different baijiu types, a linear discriminant analysis (LDA) was introduced to extract and process spectral information. And the array was able to distinguish commercial baijiu samples with different aroma-types, brands, qualities and storage years with a recognition rate of 100%. In addition, according to the heat map, the organic acids in baijiu were shown to be the main components causing the fluorescence change through electron transfer (hydrogen bond) and resonance energy transfer among QDs and acids. Furthermore, using the partial least squares regression (PLSR) model, five representative organic acids were accurately quantified with a quantitative range of 10 μmol/L-80 μmol/L with a high selectivity. This QDs fluorescence sensing strategy provides an accurate, simple, and fast baijiu sensing method, which provides a potential use for on-line baijiu monitoring., 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 © 2021 Elsevier B.V. All rights reserved.)

Caffeine naturally occurs in tea and cocoa, which is also used as an additive in beverages and has pharmacological effects such as refreshing, antidepressant, and digestion promotion, but excessive caffeine can cause harm to the human body. In this work, based on the specific response between nano zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H-porphine (nano ZnTPyP)-CdTe quantum dots (QDs) and caffeine, combined with chemometrics, a visual paper-based sensor was constructed for rapid and on-site detection of caffeine. The fluorescence of QDs can be quenched by nano ZnTPyP. When caffeine is added to the system, it can pull nano ZnTPyP off the surface of the QDs to achieve fluorescence recovery through electrostatic attraction and nitrogen/zinc coordination. The detection range is 5 × 10 -11 ~3 × 10 -9  mol L -1 , and the detection limit is 1.53 × 10 -11  mol L -1 (R 2  = 0.9990) (S/N = 3). The paper-based sensor constructed exhibits good results in real samples, such as tea water, cell culture fluid, newborn bovine serum, and human plasma. Therefore, the sensor is expected to be applied to the rapid instrument-free detection of caffeine in food and biological samples.Graphical abstract.

The needing of rapid and sensitive detection method for pesticides is increasing, to facilitate its detection without complicated instruments. Herein, a novel paper-based senor was developed for the visual detection of three carbamate pesticides (metolcarb, carbofuran, and carbaryl) based on CdTe quantum dots (QDs) and nano zinc 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H-porphine (nano ZnTPyP) with a "turn-off-on" mode. This fluorescence sensing model could be applied in the highly selective and sensitive detection of carbamate pesticides both by fluorescence spectrometry or paper-based sensors. Based on the extracted RGB color values of paper, the partial least squares regression (PLSR) was used to accurately quantify the concentrations of carbamate pesticides in different food matrices (apple, cabbage and tea water). This method featured in high speed, low price and high accuracy, and provided a new strategy for the detection of food safety., 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 © 2020 Elsevier Ltd. All rights reserved.)

Silver ions, as a commonly used industrial heavy metal, tends to deposit in the body and induce many diseases. In this work, modified CdTe QDs with green and red emission were synthesized to assemble dual-QDs, which could be efficient and selective utilized for Ag + determination through the electron transfer progress between surface functional group of dual-QDs and Ag + , and the aggregation of Ag + on the surface of dual-QDs. Under the appropriate pH value and volume ratio, the interaction between the surface functional groups of assembled dual-QDs reduce the affinity of Hg 2+ in this system. The fluorescent signal of dual-QDs simultaneously attenuation or enhancement in the same proportion remove the interference of Cu 2+ and other metal ions. Therefore, this method can selectively detect Ag + without any masking agents. The linear region of detection was from 0 to 800 nmol/L (R 2  > 0.998), and low of detection (LOD) was 7.7 nmol/L, which could meet the corresponding standards of World Health Organization (WHO) and Environmental Protection Agency (EPA). This effective proposed dual-QDs ratios fluorescent probe has been applied to detect Ag + in real environment water, tea and Citri Reticulatae Pericarpium (CRP) water., 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 © 2020 Elsevier B.V. All rights reserved.)

Colorimetric sensor array is a sensitive, rapid, and inexpensive detection technology which simulates human olfaction system based on various organic dyes. In this work, a sensor array based on acid-sensitive CdTe QDs coupled with chemometrics method was developed and proved to be a rapid, accurate and sensitive method for identification of 32 kinds of Chinese traditional cereal vinegars (CTCV). The specificity of identification of this method was mainly depends on the organic acids and melanoidins of CTCV. Among them, organic acids can quench the fluorescence of QDs through enhancing their electron transfer (hydrogen bond) and resonance energy transfer, and the fluorescence intensity of melanoidin was closely related to the brewing technology and aging year of CTCV. The types and aging time of 32 CTCV can be 100% identified at a dilution of 1000 by partial least squares discriminant analysis, when the latent variables were 4. And only one kind of QDs is needed instead of various organic dyes to this kind of colorimetric sensor array. Except for vinegar, this method can also be used in the identification of other food which rich in organic acid., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Carbon quantum dots (CQDs), especially originated from biomass, have emerged as a rising star for the construction of metal ion sensor because they can serve as sensitive, selective and biocompatible probes. The present work describes a novel kind of ascorbic acid (AA)-enhanced CQDs which are synthesized with a kind of famous green teas, Maojian, serving as carbon source. Compared with the CQDs only based on Maojian teas, citric acid (CA)-enhanced and ascorbic acid (AA)-enhanced CQDs had the enhanced fluorescence intensity, and different response characteristics. In addition, the (AA)-enhanced CQDs showed more sensitive and specific fluorescence response to Hg 2+ than simple ones, with a detection limit of 6.32 × 10 -9  nmol·L -1 . A linear response range from 2.00 × 10 -7  mol·L -1 to 6.00 × 10 -5  mol·L -1 was also achieved. The (AA)-enhanced CQDs also demonstrate good stability. They could effectively sense the Hg 2+ in complex samples including waste water, tea and rice. Therefore, these versatile (AA)-enhanced CQDs fluorescence method hold a promising potential in other promising applications such as pharmaceutical quality, environmental quality, and food safety monitoring., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Fluorescent "turn-off" sensors based on double quantum dots (QDs) has attracted increasing attention in the detection of many materials due to their properties such as more useful information, higher fluorescence efficiency and stability compared with the fluorescent "turn-off" sensors based on single QDs. In this work, highly sensitive and specific method for recognition of 53 different famous green teas was developed based on the fluorescent "turn-off" model with water-soluble ZnCdSe-CdTe double QDs. The fluorescence of the two QDs can be quenched by different teas with varying degrees, which results in the differences in positions and intensities of two peaks. By the combination of classic partial least square discriminant analysis (PLSDA), all the green teas can be discriminated with high sensitivity, specificity and a satisfactory recognition rate of 100% for training set and 100% for prediction set, respectively. The fluorescent "turn-off" sensors based on the single QDs (either ZnCdSe QDs or CdTe QDs) coupled with PLSDA were also employed to recognize the 53 famous green teas with unsatisfactory results. Therefore, the fluorescent "turn-off" sensors based on the double QDs is more appropriate for the large-class-number classification (LCNC) of green teas. Herein, we have demonstrated, for the first time, that so many kinds of famous green teas can be discriminated by the "turn-off" model of double QDs combined with chemometrics, which has largely extended the capability of traditional fluorescence and chemometrics, as well as exhibits great potential to perform LCNC in other practical applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Fluorescent "turn-off" sensors based on water-soluble quantum dots (QDs) have drawn increasing attention owing to their unique properties such as high fluorescence quantum yields, chemical stability and low toxicity. In this work, a novel method based on the fluorescence "turn-off" model with water-soluble CdTe QDs as the fluorescent probes for differentiation of 29 different famous green teas is established. The fluorescence of the QDs can be quenched in different degrees in light of positions and intensities of the fluorescent peaks for the green teas. Subsequently, with aid of classic partial least square discriminant analysis (PLSDA), all the green teas can be discriminated with high sensitivity, specificity and a satisfactory recognition rate of 100% for training set and 98.3% for prediction set, respectively. Especially, the "turn-off" fluorescence PLSDA model based on second-order derivatives (2nd der) with reduced least complexity (LVs = 3) was the most effective one for modeling. Most importantly, we further demonstrated the established "turn-off" fluorescent sensor mode has several significant advantages and appealing properties over the conventional fluorescent method for large-class-number classification (LCNC) of green teas. This work is, to the best of our knowledge, the first report on the rapid and effective identification of so many kinds of famous green teas based on the "turn-off" model of QDs combined with chemometrics, which also implies other potential applications on complex LCNC classification system with weak fluorescence or even without fluorescence to achieve higher detective response and specificity., (Copyright © 2017 Elsevier B.V. All rights reserved.)

As a popular detection model, the fluorescence "turn-off" sensor based on quantum dots (QDs) has already been successfully employed in the detections of many materials, especially in the researches on the interactions between pesticides. However, the previous studies are mainly focused on simple single track or the comparison based on similar concentration of drugs. In this work, a new detection method based on the fluorescence "turn-off" model with water-soluble ZnCdSe and CdSe QDs simultaneously as the fluorescent probes is established to detect various pesticides. The fluorescence of the two QDs can be quenched by different pesticides with varying degrees, which leads to the differences in positions and intensities of two peaks. By combining with chemometrics methods, all the pesticides can be qualitative and quantitative respectively even in real samples with the limit of detection was 2 × 10(-8) mol L(-1) and a recognition rate of 100%. This work is, to the best of our knowledge, the first report on the detection of pesticides based on the fluorescence quenching phenomenon of double quantum dots combined with chemometrics methods. What's more, the excellent selectivity of the system has been verified in different mediums such as mixed ion disruption, waste water, tea and water extraction liquid drugs., (Copyright © 2016 Elsevier B.V. All rights reserved.)

BACKGROUND: Ethyl carbamate (EC) is a potentially toxic carcinogen produced during fermentation and storage of fermented foods, and many countries have set thresholds for its content in food. Therefore, sensitive, rapid and accurate detection of EC is meaningful to ensure the quality of fermented food. RESULTS: This study introduces a CdTe quantum dots/nano‐5,10,15,20‐tetrakis (4‐methoxyphenyl)‐porphyrin (nano TPP‐OCH3) fluorescence sensor system detection of EC. The specificity of this sensing mainly relies on a photo‐induced electron transfer and electrostatic force interaction between EC and nano TPP‐OCH3. This sensor presented a linear range of 10 to 1000 μg L−1 (R2 = 0.9903) with a low detection limit of 7.14 μg L−1. Meanwhile, the recovery (91.19–101.09%) and precision [relative standard deviation (RSD) = 0.64–3.05%] of the sensor for the analysis of fermented food (yellow rice wine, soy sauce, Chinese spirits, Pu‐erh tea) samples were good and could meet the requirements of practical detection. Moreover, the detection results of fermented food (yellow rice wine, soy sauce, Chinese spirits, Pu‐erh tea) samples by this sensor are basically consistent with those of high‐performance liquid chromatography with fluorescence detector (HPLC‐FLD). CONCLUSION: This method was expected to provide a potential platform for sensitive and accurate detection of EC in food safety monitoring, which would provide knowledge of the flavor and quality related to fermented food. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

BACKGROUND: The quality of tea is influenced by numerous factors, especially l‐theanine, which is one of the important markers used to evaluate the sweetness and freshness of tea. Sensitive, rapid, and accurate detection of l‐theanine is therefore useful to identify the grade and quality of tea. RESULTS: A high‐sensitivity, paper‐based fluorescent sensor combined with chemometrics was established to detect l‐theanine in tea water based on CdTe quantum dots / corn carbon dots and nano tetra pyridel‐porphine zinc (ZnTPyP). To verify the reliability of this method, fluorescence spectra and fluorescence‐visualized paper‐based sensors were compared. The fluorescence spectrum method demonstrated a linear range of 1 to 10 000 nmol L−1 and a limit of detection (LOD) of 0.19 nmol L−1. In the fluorescence‐visualized paper‐based sensors there was a linear range of 10–1000 nmol L−1, and the LOD was 10 nmol L−1. Partial least squares discriminant analysis (PLSDA) and partial least squares regression analysis (PLSR) were used successfully to determine l‐theanine accurately in tea water with this approach. The accuracy of the PLSDA model was 100% both in the training set and the predicting set, and the correlation coefficient between the actual concentration and the predicted concentration was greater than 0.9997 in the PLSR model. CONCLUSION: This fluorescence‐visualized paper‐based sensor, combined with chemometrics, could be applied efficiently to the practical analysis of tea water samples, which provides a new idea to ensure the flavor and quality of tea. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Fluorescent TiO2/carbon quantum dots (CQDs) nanocomposites are prepared through incorporating CQDs into TiO2 nanofilms, which are regarded as pressure sensitives to fabricate fluorescent pressure sensors for the first time. The TiO2/CQDs sensors emit bright white fluorescence, and the fluorescence intensity of the TiO2/N-doped CQDs (NCQD) sensor is much higher than the TiO2/undoped CQDs (UCQD). The current response of the TiO2/CQDs sensors have a good linear relationship with the applied pressure (R2 > 0.96), while that of the pure TiO2 sensor does not. Furthermore, the sensitivity of the TiO2/NCQD sensor is 2.27 times larger than that of the TiO2/UCQD sensor. In addition, the thickness of the nanocomposite film has a great influence on pressure sensing. The fluorescence and sensing performance of the fluorescent pressure sensors based on TiO2/CQDs nanocomposite films are expected to be further simultaneously optimized by modulating CQDs for dynamically monitoring indoor security, such as recognizing the hit from the outdoor and simultaneously generating a self-warning signal of abnormal ultraviolet illumination from the surroundings. [ABSTRACT FROM AUTHOR]

Highlights • A new on-off-on fluorescent assay for detecting chiral amino acids was developed. • Chiral nano ZnTPyP was synthesized for chiral recognition of amino acids. • The assay method was reliable and robust with high selectivity and sensitivity. • It realized accurate detection of amino acids in biological environment. Abstract Interests in the recognition of chiral amino acids have grown tremendously in recent years, particularly in the fields of food analysis and pharmaceutical studies. Herein, an innovative "on-off-on" fluorescent assay has been developed for the sensitive and selective determination of chiral Proline (Pro), Lysine (Lys), and Serine (Ser). This detection platform is constructed by exploiting the fluorescence quenching ability of chiral self-assembly zinc 5, 10, 15, 20-tetra(4-pyridyl)-21 H -23 H -porphine (ZnTPyP) to CdTe quantum dots (CdTe QDs). CdTe QDs can act as signal switches whose fluorescence signals can effectively quenched by chiral nano ZnTPyP and then restored in the presence of enantiomer amino acids. The coupling use of CdTe QDs and chiral nano ZnTPyP also permits quantitative analysis of d -Pro, d -Lys, l -Ser with detection limits of 4.46 × 10−10 mol L−1, 7.13 × 10−11 mol L−1, and 3.35 × 10−11 mol L−1, respectively. The approach is also suitable for the effective detection of the three amino acids in complex biological matrices. This rapid, robust and reliable strategy for recognizing enantiomer amino acids has not been reported. The proposed method can be a powerful and valuable technology in the areas of drug discovery and food chemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel sensor was established by N-acetyl-L-cysteine capped CdTe QDs. • The sensor could detect atractylodin in Atractylodis Rhizome. • The sensor showed good selectivity and sensitivity for atractylodin. • The sensor could achieve analysis for Atractylodis Rhizome origin identification. The economic and medicinal value of Atractylodis Rhizoma (AR) is intricately tied to its geographical origin and mainly depends on the atractylodin (IUPAC Name: 2-[(1E,7E)-nona-1,7-dien-3,5-diynyl]furan) content in it. In this study, a green fluorescent sensor using N-acetyl-L-cysteine (NAC, IUPAC Name: (2R)-2-acetamido-3-sulfanylpropanoic acid)-capped CdTe quantum dots (QDs) was developed for the detection of AR origin discrimination. Both electron transfer and internal filtration effects was introduced into sensor to improve the sensitivity and selectivity. The sensors can achieve visual quantitative analysis of atractylodin using the partial least squares regression (PLSR) model. This model with a detection limit of 0.321 µg /mL and the quantification range of 0.002–0.030 mg /mL. Furthermore, the visual sensor also could be applied to the quantification of atractylodin in the actual AR samples with recoveries as high as 95.36 % to 105 %. Their sensor was also able to identify different origin of AR with an accuracy of 100 % for the training set and 95.29 % for the prediction set using the partial least squares discriminant analysis (PLSDA) model. The method offers direction for verifying the authenticity of traditional Chinese medicine and precise analysis of intended constituents in complex systems. [ABSTRACT FROM AUTHOR]

The price and quality of goji berries (GB) are closely linked to their origins. Therefore, identifying the geographical origins of GB produced in specific origin is important. In this work, a fluorescent sensor based on a glutathione modified quantum dots and nitrogen-doped carbon quantum dots complexes (CdTe-QDs @ N-CDs) with an internal filtration effect (IFE) was constructed to visual identify the origin of GB. The phenolic acid compounds in GB could quench the fluorescence of QDs and CDs through the photoinduced electron transfer (PET) and the aggregation-induced quenching (ACQ), respectively. Due to the different contents of phenolic acid in GB from different origins, the fluorescent sensor based on CdTe-QDs @ N-CDs complexes could produce distinct and different fluorescent colors, from orange to blue under the dual reaction. Finally, partial least squares discriminant analysis (PLS-DA) model was applied to establish classification models for identifying the geographical origin of GB based on the fluorescent colors. The results showed that the accuracy of GB visual recognition could be increased from 68.9% to 93.3%. This proven that the proposed strategy has excellent potentials for identification of the geographical origins of GB. [Display omitted] • A novel visual fluorescent sensing method was constructed for identified GB origins. • CdTe-QDs@N-CDs enables visual identification of GB origin through PET & ACQ effects. • The accuracy of GB origin identification based on RGB data was 93.3%. [ABSTRACT FROM AUTHOR]

• Thiomalic acid modified CDTE was utilized for visual detection of Ag+. • High sensitivity and selectivity for Ag+were achieved. • The detection limit of fluorescence spectrometry method for Ag+ was 13.16 nmol/L. • Paper-based sensors for Ag+ was carried out in a rapid, simple and effective way. • PLSR accurately quantified concentrations of Ag+ in matrices based on paper images. A fluorescence paper-based sensor method by simply using thiomalic acid modified CdTe (TMA-capped CdTe) was proposed for visual detection of silver ions (Ag+). Red-emission TMA-capped CdTe with a large amount of carboxyl groups on the surface could be combined with Ag+ by electrostatic interaction, thus leading to the fluorescence quenching. It was found that the adding of amino acids contributed to fluorescence recovery by the leaving of Ag+ on the surface of TMA-capped CdTe. Moreover, the more amino group, benzene and thiol group equipped in the structure of amino acid, the stronger fluorescence restoring of CdTe could be achieved. This fluorescence spectrometry method for Ag+ showed low detection of limit with the value of 13.16 nmol/L, with no response to other heavy metals, which demonstrating its high sensitivity and high selectivity for Ag+. More importantly, this paper-based sensor method combined with chemometrics could accurately identify and quantify different concentrations of Ag+ in different complex matrices. This fast, economical, accurate and effective approach exhibited a new idea for the on-site detection of Ag+, and was expected to be extended to the on-site detection of Ag+ in biological and environmental fields. [ABSTRACT FROM AUTHOR]

In this work, we constructed a machine learning-assisted dual-channel visual sensor array for identifying the origin of Lilium bulbs (BH). Nanogold clusters (AuNCs) and quantum dots (QDs) were selected and combined into sensor arrays. The amino acids existed in lilium bulbs could induce aggregation-induced fluorescence enhancement effect (AIEE) of AuNCs through hydrogen bonding. The hydrogen protons released from the amino acids and phenolic acids could interact with the COO- group of QDs, resulting in aggregation-caused quenching (ACQ) of QDs. Due to the different contents of amino acids and phenolic acids in BH from different origins, the sensor array can produce distinct and different fluorescent colors, such as red, blue, green and purple. In conjunction with pattern recognition by the RF model, the sensor array clearly identifies the origin of BH with 94.4% prediction accuracy. The visual sensor array constructed in this work exhibited the advantages of simplicity, speed, accuracy and portability, showing potential application prospects in identifying the origin of food and traditional Chinese medicine. [Display omitted] • A novel visual sensor array method was constructed for tracing BH origins. • The amino acids in BH could induce AIEE effect of AuNCs through hydrogen bonding. • The protonation and ET effect induced the ACQ of NAC-QDs. • The accuracy of BH origin identification based on dual-channel visual data was 94.4%. [ABSTRACT FROM AUTHOR]

Abstract A high-sensitivity fluorescence visualization paper-based sensor is developed and used to achieve specific detection and analysis of three organophosphorus pesticides (OPPs: dimethoate, dichlorvos, and demeton) in a "Turn-off-on" detection mode. The fluorescence visualization paper-based sensor is established through combining double quantum dots (QDs) with high-activity nanoporphyrins (QDs-nanoporphyrin), realizing double nanometer signal amplification and producing different color change responses to these three OPPs. In particular, this approach is based on Partial least squares discriminant analysis (PLSDA) for fingerprint spectrum analysis of three kinds of organophosphorus pesticides in complex matrix (apple and cabbage). Therefore, different concentrations of pesticide residues can be quickly identified at the same time with 100% accuracy for both training set and prediction set. In summary, this method has high selectivity and stability, and thus provides a new approach for the identification of organophosphorus residues in complex systems. Graphical abstract For a new method, not only the double nano signal amplification effect of dual QDs fluorescent color interval variability, but also nano-porphyrin high activity is employed to construct a high-sensitivity fluorescent visualization paper chip sensor, which is characterized in based on the "Turn-off-on" detection mode and producing different color change responses. fx1 Highlights • A paper sensor based on double quantum dots-nanoporphyrin is designed. • The high-sensitivity sensor is fluorescence-visualized based on "off-on" model. • Providing a new theoretical guidance for real-time monitoring of pesticide residues. [ABSTRACT FROM AUTHOR]

CQDs doped PVDF-HFP film with porous structure was firstly fabricated for self-powered flexible piezoelectric sensors. [Display omitted] • Carbon quantum dots (CQDs) doped PVDF-HFP film was firstly fabricated for self-powered flexible piezoelectric sensors (FPS). • The content of β phase in the PVDF-HFP/CQDs film is improved by 14.4 % compared with that in the PVDF-HFP film. • PVDF-HFP/CQDs based FPS exhibit better sensitivity (36.6 mV/g) than PVDF-HFP (25.7 mV/g) with good linearity (R2 > 99 %). • The FPS show excellent mechanical stability under repeated dynamic loading. • Some potential applications of the PVDF-HFP/CQDs based self-powered FPS were explored. Flexible piezoelectric sensors (FPS) have been widely applied to intelligent robot, human/machine interaction and human health measurement system, etc. To improve the piezoelectric performance of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), carbon quantum dots (CQDs) were introduced to form PVDF-HFP/CQDs piezoelectric film. Owing to their large specific surface area (96.3 m²/g) and abundant surface defects, CQDs provide mass potential induced active points for the formation of β phase in PVDF-HFP, and rich surface functional groups (COOH, OH and NH 2 , etc) which could promote chemical bond with PVDF-HFP. The content of β phase in the PVDF-HFP/CQDs film is increased by 14.4 % compared with that in the PVDF-HFP film. Thereby, PVDF-HFP/CQDs based FPS exhibit better sensitivity (36.6 mV/g) than PVDF-HFP based FPS (25.7 mV/g) with good linearity (R2 > 99 %). Besides, the FPS show excellent mechanical stability under repeated dynamic loading. On this basis, some potential applications of the PVDF-HFP/CQDs based self-powered FPS were explored, including anti-touch alarm system, finger bending detection, voice recognition and vibration monitoring. [ABSTRACT FROM AUTHOR]

• Colorimetric paper sensor array based on three color-emission QDs was established. • Production process and quality of basic liquors of Baijiu can be well monitored. • The sensor required neither special modification nor complex sample preparation. • The sensor only use a simple device and small amount of basic liquor samples. Process analysis of basic liquors of Baijiu is a great challenge in industry due to the complexity fermentation processes and tiny product differentiation of basic liquors. In this work, a new triple channel colorimetric paper sensor array based on quantum dots (QDs) with three color-emission was established for the rapid process monitoring of basic liquors of Baijiu. The fluorescence of QDs can be quenched to varying degrees by the ingredients in basic liquors with different production processes, batches and qualities. Through analyzing color change (RGB value) of QDs under the UV lamp, all the corresponding information that represents basic liquors of Baijiu was extracted and further processed by principal component analysis and partial least squares discriminant analysis. By utilizing this colorimetric paper sensor array, all the production processes, batches and qualities of basic liquors can be monitored quickly and accurately with a recognition rate of 100%. What's more, this paper sensor array required neither special modification nor complex sample preparation and can implement rapid and precise visualization analysis by the naked eye with the aid of a portable UV lamp using only a simple device and small amount of sample, showing its potential applications in the food industry. [ABSTRACT FROM AUTHOR]