A dual-signal fluorescent colorimetric tetracyclines sensor based on multicolor carbon dots as probes and smartphone-assisted visual assay

Nano-engineered eco-friendly materials for food safety: Chemistry, design and sustainability

The sensitive detection, extraction and analysis of organic compounds such as pharmaceuticals as contaminants in food is very crucial. For this purpose, the effective utilization of sustainable nanomaterials is a promising strategy that combines the benefits of sustainability principles with nanotechnology to ensure the quality and safety of food products. Eco-friendly nanomaterials are distinguished by their exceptional properties, including sustainable synthesis, minimized ecological impact, and production from renewable or waste resources (e.g., cellulose, chitosan, lignin). This review paper elucidates the latest advancements and emerging trends in the development of eco-friendly nanomaterial-based sensor and extraction platforms for the efficient detection and removal of antibiotics as organic contaminants from food samples. The introduction section briefly outlines the significance and benefits of nanomaterials in the construction of sensor platforms. Subsequently, green methodologies for the synthesis of nanomaterials are discussed. Then, the paper progresses with various applications of eco-friendly nanomaterial-based sensor platforms and separation systems towards antibiotic contaminants in food samples. The final section offers conclusions and future perspectives.

A smartphone-integrated bimetallic ratiometric fluorescent probe for specific visual detection of tetracycline antibiotics in food samples and latent fingerprinting

Designing and preparing highly sensitive and accurate fluorescent chemosensors for monitoring tetracycline antibiotics remains a challenge. Herein, a fluorescent chemosensor based on lanthanide metal-organic frameworks (Ln-MOFs) is proposed to realize high-precision monitoring by adjusting the ratio of lanthanide ions. Ln-MOFs with good aqueous stability were prepared by a solvothermal method using Eu3+, Tb3+ and the ligand 4,4',4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB) in DMF/NMP/H2O. The Ln-MOFs could recognize oxytetracycline (OTC) and doxycycline (DOX), and the detection limits of OTC and DOX were as low as 8.6 and 4.8 nM, respectively. In particular, Eu(1.4 μM)-Tb-MOF sensors were used for visual detection of OTC and DOX in combination with smartphones with detection lines as low as 9.8 nM and 14.2 nM, respectively. Meanwhile, Eu-MOF, Tb-MOF and Eu(1.4 μM)-Tb-MOF can be used for latent fingerprint (LFP) visualization, demonstrating their potential applications in the field of criminal case investigation. The developed probes were successfully applied to determining OTC and DOX in milk, beef and pork with recoveries ranging from 92.0 % to 109.63 % and relative standard deviations (RSDs) ranging from 1.83 % to 4.56 %. Eu(1.4 μM)-Tb-MOF is believed to utilize its lanthanide metal ion coordination and photoinduced electron transfer (PET) mechanism to achieve highly selective and accurate OTC and DOX detection, which is supported by experimental and density functional theory (DFT) calculations.

Portable real-time determination of Escherichia coli O157:H7 and Staphylococcus aureus based on smartphones and hydrogels

The aptamers functionalized orange-emission carbon dots (OCDs) and green-emission carbon dots (GCDs) had dual-emission peaks with single excitation. Tungsten disulfide nanosheets (WS2 NSs)-triggered fluorescence quenching achieved the ratiometric fluorescence determination of Escherichia coli O157:H7 (E. coli O157:H7) and Staphylococcus aureus (S. aureus) with wide ranges of 18-1.8 × 106 and 37-3.7 × 107 CFU/mL and low detection limits of 8 and 20 CFU/mL, respectively. The results in real sample with recoveries of 90-101 % and RSD < 4.12 % were no significant difference from standard plate counting method. Meanwhile, the dual-color CDs were further adopted in the smartphone-assisted hydrogel platform and achieved speedy, sensitive, portable and real-time determination of E. coli O157:H7 and S. aureus in real samples. This work has not only developed ratiometric fluorescence detection and constructed a portable hydrogel platform, but also provided a unique strategy in developing a time-efficient and easy-to-use portable device in food safety monitoring.

pH-regulated CQDs@Eu/GMP ICP sensor array and its fingerprinting on 96-well plates: Toward point-of-use/specific identification and quantitation of six tetracyclines in animal farm wastewater, milks and milk-derivative products

Herein, a "lab-on-an-AIE@Ln/ICP" sensor array was constructed by employing aggregation-induced emission carbon quantum dots (AIE-CQDs) as the guest and Eu/GMP ICP as the host. Based on the antenna effect (AE) and reductive photo-induced electron transfer (r-PET) between CQDs@Eu/GMP ICPs and tetracyclines (TCs), the as-constructed sensor produced satisfactorily dual-emitting fluorescence. By combining pH regulation with principal component analysis (PCA), the underlying fingerprinting patterns realized the specific identification and quantitation of six TCs in animal farm wastewater, milks and milk-derivative products. Through the aggregation-induced quenching of CQDs@Eu/GMP ICPs on test strips, the discernible fluorescence alterations were successfully utilized for developing smartphone-based visual assay. To sum up, the prominent novelty of this study lies in that based on the comprehensive principles of AE and r-PET along with combination of pH-adjustment and PCA, the pioneered sensor assay achieves specifically identifying and sensing individual TCs for their rapid and on-site detection in animal-derived matrices.

Smartphone-assisted fluorescent sensor for the visualization and quantitative detection of doxycycline and L-arginine

A novel smartphone-assisted fluorescent sensor based on europium/zirconium metal-organic framework (Eu0.5/Zr0.5-MOF) was developed for the fast and sensitive determination of doxycycline (DOX) and L-arginine (Arg). After the addition of DOX, the fluorescence of Eu0.5/Zr0.5-MOF was quenched owing to the inner filter effect (IFE). When Arg was introduced into the Eu0.5/Zr0.5-MOF@DOX complex system, the fluorescence was recovered because the interaction between Arg and Eu0.5/Zr0.5-MOF@DOX weakened the IFE. Moreover, the Eu0.5/Zr0.5-MOF produced continuous fluorescence color changes for the visual measurement of DOX and Arg. The fluorescent probe for DOX and Arg offered broad linear ranges of 0.05-80 and 0.1-60 μg/mL, respectively, with detection limits as low as 2.07 and 67.5 ng/mL. The proposed method was successfully applied to monitor DOX in eggs and Arg in human serum. This work provides a powerful platform for the real-time and visual analysis of DOX and Arg in food and biological samples.

Reliability of Multi-Emissive Carbon Quantum Dots for Multiplexing; Assessing the Figures of Merit

Incredible properties of quantum dots (QDs) have once again been acclaimed with this year's (2023) Nobel prize in chemistry. On the other hand, the invention of multicolour molecular imaging of cell surface receptors for tumour diagnosis by Koyama and group has opened up a new era in diagnostics. Among them carbon quantum dots (CQDs) are interesting class of fluorescent nanomaterials, superior in terms of low toxicity, high solubility and biocompatibility along with simple and cost-effective synthesis processes unlike the traditional metal chalcogenide or perovskite quantum dots. Multi emissive fluorescence property of these carbon quantum dots are very useful in multiplex sensing. Their excellent biocompatibility and low toxicity have attracted researchers to use them extensively for biosensing and imaging of multiple analytes at a time. Core state emission from π-domains and surface state emissions of functional groups surrounding CQDs play a major role in achieving the multicolour emissions and this review discusses the various strategies used to achieve desired multi colour emissions, yet preserving their stability, non-interactive emissive states and quantum yields. Their fine tuning via variation in temperature, pH, time, and heteroatom doping has been comprehensively discussed. A thorough history compared to a list of characteristics for creating effective multicolour CQDs will point us in the proper route. This minireview also assesses the electronic band structure of these multicolour CQDs, their stability with respect to multi emissions, photoluminescence quantum yields, approaches employed for tunability of their optical band gaps, and also enhancement of carrier lifetimes, to arrive at conclusions on the reliability of these materials for multiplexing. The mechanisms namely chemical coupling, FRET, On-Off, Ab-antigen interactions involved in sensing mechanisms involving these materials are analysed in depth. Ultimately, the present obstacles and future directions for the use of these CQDs in sensing applications are discussed.

Rapid Detection of Methyl Parathion Based on SiONPs-Eu3+ Dual-Emitting Fluoroprobe and Its On-Site Application

Herein, we pioneered an innovative methodology for the rapid identification and quantitation of methyl parathion (MP) residues, overcoming the drawbacks of existing methods such as poor selectivity, high costs, and intricate operational procedures. A dual-emitting fluoroprobe SiONPs-Eu3+ was engineered based on silica oxide nanoparticles (SiONPs) conjugated with Eu3+, and the synthetic conditions were meticulously optimized to ensure exceptional sensitivity and selectivity to 4-nitrophenol (4-NP), one of the MP hydrolytic products. Upon excitation at 317 nm, the blue fluorescence of SiONPs at 400 nm was quenched, while the red fluorescence of Eu3+ at 616 nm remained nearly unchanged, constituting a ratiometric fluorescent change that significantly enhanced the detection stability. The fluoroprobe rapidly detected 4-NP at concentrations below 80 μM within 10 s and gave a limit of detection (LOD) as low as 0.16 μM, markedly lower than the allowable residue limit of MP in China food safety standards. Also, it exhibited excellent anti-interference properties in complex matrices, remaining unaffected by common amino acids, cations, and pesticides. The underlying mechanism of the fluoroprobe was elucidated through time-dependent density functional theory (TD-DFT) calculations. Under optimized hydrolysis conditions, the detection of MP in real rice samples was successfully achieved. Furthermore, the self-developed and dual-channel portable device was conducive to on-site fluorescence detection of 4-NP, offering enhanced stability in contrast to traditional photography-based methods.

Luminol-Eu3+-Gd3+-functionalized mesoporous silica for ultrasensitive detection of tetracycline antibiotics and smartphone-assisted sensing analysis

An organic-inorganic hybrid nanoprobe, namely LML-D-SBA@Eu3+-Gd3+, was constructed, with SBA-15 acting as the carrier material, and luminol and Eu3+ acting as fluorescence channels to achieve ratiometric signals that eliminate external interference (accurate detection). Gd3+ was used as a sensitizer to amplify the red emission of Eu3+ (ultrasensitive detection). In TCs detection, the luminol emission at 428 nm was quenched due to the photoinduced electron transfer mechanism, and the Eu3+ emission at 617 nm was sensitized due to the synergistic energy transfer from TCs and Gd3+ to Eu3+. The fluorescence intensity at 617 and 428 nm showed ratiometric changes as indicated by notable color changes from blue to red. The detection limits for TC and OTC were 0.21 and 0.08 ng/mL, respectively. To realize a facile, rapid, and cost-effective detection, we constructed a portable intelligent sensing platform based on smartphones, and it demonstrated great potential for on-site detection of TCs.

Carbon dots-based dual-emission ratiometric fluorescent sensors for fluorescence and visual detection of hypochlorite and Cu2

Carbon dots (CDs) with blue emission were synthesized by solvothermal method using hydroquinone and 5-aminoisphthalic acid as precursors. The strong oxidation of ClO- caused the fluorescence quenching of CDs at 405 nm, and synchronously generated a new emission peak at 500 nm. Furthermore, upon the addition of Cu2+ to CDs-ClO- system, the green fluorescence at 500 nm was quenched, while the blue emission at 405 nm remained unchanged, due to the complexation between Cu2+ and the amino group on the CDs surface. Meanwhile, the fluorescence color of system changed from blue to bright green and then to dark blue by sequentially increasing the concentrations of ClO- and Cu2+. The fluorescence signal of F500/F405 exhibited a linear relationship with the concentration of ClO- and Cu2+ in a certain range, respectively. Thus, a ratiometric fluorescence sensor based on the obtained CDs were developed to sequentially detect ClO- and Cu2+ with detection limits of 0.40 μM and 0.31 μM, respectively. Additionally, the CDs were mixed with polyvinyl alcohol hydrogel to form test strips, which were successfully used for visual detection of ClO- and Cu2+. Satisfactory results were also obtained in the analysis of ClO- and Cu2+ in actual water samples.

A dual-response ratiometric fluorescent sensor for oxytetracycline determination in milk and mutton samples

Owing to the adverse effects of oxytetracycline (OTC) residues on human health, it is of great importance to construct a rapid and effective strategy for OTC detection. Herein, we developed a dual-response fluorescence sensing platform based on molybdenum sulfide quantum dots (MoS2 QDs) and europium ions (Eu3+) for ratiometric detection of OTC. The MoS2 QDs, synthesized through an uncomplicated one-step hydrothermal approach, upon OTC integration into the MoS2 QDs/Eu3+ sensing system, exhibit a significant quenching of blue fluorescence due to the inner filter effect (IFE), simultaneously enhancing the distinct red emission of Eu3+ at 624 nm, a phenomenon attributed to the antenna effect (AE). This sensor demonstrates exceptional selectivity and sensitivity towards OTC, characterized by a linear detection range of 0.2-10 μM and a notably low detection limit of 2.21 nM. Furthermore, we achieved a visual semi-quantitative assessment of OTC through the discernible fluorescence color transition from blue to red under a 365 nm ultraviolet lamp. The practical applicability of this sensor was validated through the successful detection of OTC in milk and mutton samples, underscoring its potential as a robust tool for OTC monitoring in foodstuffs to safeguard food safety.

Nitrogen-Doped Carbon Quantum Dots with Photoactivation Properties for Ultraviolet Ray Detection

Photoactivation is a phenomenon that could enhance the photoluminescence (PL) and photostability upon UV/vis light exposure, which is usually observed in CdSe/ZnS quantum dots (QDs). However, the photoactivation phenomenon has been scarcely reported in fluorescent carbon quantum dots (CQDs). Herein, the nitrogen-doped carbon quantum dots (N-CQDs) were prepared through a facile solvothermal approach with naphthalenetracarboxylic dianhydride and serine as precursors. Upon simple UV light irradiation for 10 min, the fluorescence quantum yield (QY) of N-CQDs could increase up to 10-fold. Based on this phenomenon, the N-CQDs were explored as an ultraviolet (UV) light sensor to assess the intensity of ultraviolet radiation in sunlight and indirectly evaluate the UV-blocking efficiency of various sunscreen products. Thus, this contribution not only provided an insight into developing a low-cost UV detector but also opened a door for the development of carbon quantum dots with converse-photobleaching properties.

Recent progress in lanthanide-based fluorescent nanomaterials for tetracycline detection and removal

Tetracycline (TC) has been widely used in clinical medicine and animal growth promotion due to its broad-spectrum antibacterial properties and affordable prices. Unfortunately, the high toxicity and difficult degradation rate of TC molecules make them easy to accumulate in the environment, which breaks the ecological balance and seriously threatens human health. Rapid and accurate detection of TC residue levels is important for ensuring water quality and food safety. Recently, fluorescence detection technology of TC residues has developed rapidly. Lanthanide nanomaterials, based on the high luminescence properties of lanthanide ions and the high matching with TC energy levels, are favored in the real-time trace detection of TC due to their advantages of high sensitivity, rapidity, and high selectivity. Therefore, they are considered potential substitutes for traditional detection methods. This review summarizes the synthesis strategy, TC response mechanism, removal mechanism, and applications in intelligent sensing. Finally, the development of lanthanide nanomaterials for TC fluorescence detection and removal is reasonably summarized and prospected. This review provides a reference for the establishment of a method for the accurate determination of TC content in complex food matrices.

A Highly Sensitive and Selective Fluorescent Sensor for Folic Acid Detection Based on D-penicillamine Stabilized Ag/Cu Alloy Nanoclusters

In this work, a highly sensitive and selective method for detecting folic acid (FA) was developed using D-penicillamine (DPA) stabilized Ag/Cu alloy nanoclusters (DPA@Ag/Cu NCs). The yellow emission of DPA@Ag/Cu NCs was found to be quenched upon the addition of FA to the system. The fluorescence intensity quenching value demonstrated a linear relationship with FA concentrations ranging from 0.01 to 1200 μM, with a limit of detection (LOD) of 5.3 nM. Furthermore, the detection mechanism was investigated through various characterization analyses, including high resolution transmission electron microscopy, fluorescence spectra, ultraviolet-visible absorption spectra, and fluorescence lifetime. The results indicated that the fluorescence quenching induced by FA was a result of electron transfer from FA to the ligands of DPA@Ag/Cu NCs. The selectivity of the FA sensor was also evaluated, showing that common amino acids and inorganic ions had minimal impact on the detection of FA. Moreover, the standard addition method was successfully applied to detect FA in human serum, chewable tablets and FA tablets with promising results. The use of DPA@Ag/Cu NCs demonstrates significant potential for detecting FA in complex biological samples.

Bimetallic Ag/Au nanoclusters encapsulated in ZIF-8 framework: A novel strategy for ratiometric fluorescence detection of doxycycline in food

This study successfully encapsulated the Ag+-doped Au nanoclusters (Ag/AuNCs) within the ZIF-8 framework to construct a novel Ag/AuNCs@ZIF-8 ratiometric fluorescent probe for the antibiotic doxycycline (DOX) detection. The incorporation of Ag+ contributed to the fluorescence enhancement of the nanoclusters through the "silver effect", consequently improving the stability of the developed bimetallic Ag/AuNCs. Furthermore, the encapsulation of bimetallic Ag/AuNCs within the ZIF-8 framework restricted their intramolecular vibrations, resulting in further amplification of fluorescence intensity at 595 nm. The ZIF-8 also sensitized the restoration of DOX green fluorescence at 515 nm. Within the concentration range of 0.001-20 μg mL-1, the ratio of fluorescence intensity (F515/F595) exhibited a favorable linearity for DOX concentration, with a detection limit of 36.8 ng mL-1. This ratiometric fluorescence approach had the promising potential for accurate and efficient quantitative detection of DOX residue in food and served as a valuable reference for rapid monitoring of food contaminants.

Ensuring food safety by artificial intelligence-enhanced nanosensor arrays

Current analytical methods utilized for food safety inspection requires improvement in terms of their cost-efficiency, speed of detection, and ease of use. Sensor array technology has emerged as a food safety assessment method that applies multiple cross-reactive sensors to identify specific targets via pattern recognition. When the sensor arrays are fabricated with nanomaterials, the binding affinity of analytes to the sensors and the response of sensor arrays can be remarkably enhanced, thereby making the detection process more rapid, sensitive, and accurate. Data analysis is vital in converting the signals from sensor arrays into meaningful information regarding the analytes. As the sensor arrays can generate complex, high-dimensional data in response to analytes, they require the use of machine learning algorithms to reduce the dimensionality of the data to gain more reliable outcomes. Moreover, the advances in handheld smart devices have made it easier to read and analyze the sensor array signals, with the advantages of convenience, portability, and efficiency. While facing some challenges, the integration of artificial intelligence with nanosensor arrays holds promise for enhancing food safety monitoring.

Metal-doped carbon dots for biomedical applications: From design to implementation

Carbon dots (CDs), as a new kind of fluorescent nanomaterials, show great potential for application in several fields due to their unique nano-size effect, easy surface functionalization, controllable photoluminescence, and excellent biocompatibility. Conventional preparation methods for CDs typically involve top-down and bottom-up approaches. Doping is a major step forward in CDs design methodology. Chemical doping includes both non-metal and metal doping, in which non-metal doping is an effective strategy for modulating the fluorescence properties of CDs and improving photocatalytic performance in several areas. In recent years, Metal-doped CDs have aroused the interest of academics as a promising nano-doping technique. This approach has led to improvements in the physicochemical and optical properties of CDs by altering their electron density distribution and bandgap capacity. Additionally, the issues of metal toxicity and utilization have been addressed to a large extent. In this review, we categorize metals into two major groups: transition group metals and rare-earth group metals, and an overview of recent advances in biomedical applications of these two categories, respectively. Meanwhile, the prospects and the challenges of metal-doped CDs for biomedical applications are reviewed and concluded. The aim of this paper is to break through the existing deficiencies of metal-doped CDs and fully exploit their potential. I believe that this review will broaden the insight into the synthesis and biomedical applications of metal-doped CDs.

Smartphone-integrated paper-based sensing platform for the visualization and quantitative detection of pymetrozine

Pymetrozine (PYM) is an effective pyridine insecticide for controlling aphids, while its residues pose a serious threat to human health. Herein, a europium complex (Eu-DBPA, DBPA represents deprotonated 2,5-dibromoterephthalic acid ligand) probe was prepared for the detection of PYM via fluorescence quenching. The detection process has the advantages of short response time (2 min), wide linear range (0-4 and 4-45 mg/kg) and low detection limit (2.2 μg/kg). Furthermore, a portable detection platform was designed by integrating Eu-DBPA-based paper strip with smartphone and applied for the visual detection of PYM in real cucumber, tomato, cabbage and apple samples, obtaining satisfactory recovery (99.00 %-107.00 %) and low standard deviation (RSD < 3.4 %). In addition, a logic gate device was designed to simplify the detection process. The smartphone-integrated paper-based probe detection platform provides a new strategy for intelligent and online identification of hazards in environmental and biological samples.

A dual-mode fluorometric/colorimetric sensor for sulfadimethoxine detection based on Prussian blue nanoparticles and carbon dots

A dual-mode (colorimetric/fluorescence) nanoenzyme-linked immunosorbent assay (NLISA) was developed based on Au-Cu nanocubes generating Prussian blue nanoparticles (PBNPs). It is expected that this method can be used to detect the residues of sulfonamides in the field, and solve the problem of long analysis time and high cost of the traditional method. Sulfadimethoxine (SDM) was selected as the proof-of-concept target analyte. The Au-Cu nanocubes were linked to the aptamer by amide interaction, and the Au-Cu nanocubes, SDM and antibody were immobilized on a 96-well plate using the sandwich method. The assay generates PBNPs by oxidising the Cu shells on the Au-Cu nanocubes in the presence of hydrochloric acid, Fe3+ and K3[Fe (CN)6]. In this process, the copper shell undergoes oxidation to Cu2+ and subsequently Cu2 + further quenches the fluorescence of the carbon point. PBNPs exhibit peroxidase-like activity, oxidising 3,3',5,5'-tetramethylbenzidine (TMB) to OX-TMB in the presence of H2O2, which alters the colorimetric signal. The dual-mode signals are directly proportional to the sulfadimethoxine concentration within the range 10- 3~10- 7 mg/mL. The limit of detection (LOD) of the assay is 0.023 ng/mL and 0.071 ng/mL for the fluorescent signal and the colorimetric signal, respectively. Moreover, the assay was successfully applied to determine sulfadimethoxine in silver carp, shrimp, and lamb samples with satisfactory results.

A paper-based ratiometric fluorescence sensor based on carbon dots modified with Eu3+ for the selective detection of tetracycline in seafood aquaculture water

Paper-based ratiometric fluorescence sensors are normally prepared using two or more types of fluorescent materials on a paper chip for simple, low-cost and fast detection. However, the choice of multi-step and one-step modifications on the paper chip affects the analytical performance. Herein, a novel paper-based dual-emission ratiometric fluorescence sensor was designed for the selective detection of tetracycline (TC). Carbon dots (CDs) modified with Eu3+ were combined with a sealed paper-based microfluidic chip by two methods: one-step grafting of CDs-Eu3+ on paper and step-by-step grafting of CDs and Eu3+ on paper. The analytical performance was studied and optimized respectively. The red fluorescence of Eu3+ at 450 nm is enhanced and the blue fluorescence of CDs at 617 nm is quenched by energy transfer in the presence of TC. Under optimal conditions, TC is selectively determined in the linear range from 0.1 μM to 100 μM with a detection limit of 0.03 μM by the step-by-step grafting method. In addition, the sealed paper chip could effectively prevent pollution and volatilization from the reagent. This technique has been used to analyze TC in seafood aquaculture water with satisfactory results.

Fluorimetric determination of tetracycline antibiotics in animal derived foods using boron and nitrogen co-doped ceria-based nanoparticles

An innovative synthesis of boron and nitrogen co-doped ceria-based nanoparticles (B/N-CeFNPs) with bright blue fluorescence emission is reported using the hydrothermal method. Based on the aggregation-induced emission enhancement (AIEE) effect between B/N-CeFNPs and chlortetracycline (CTC), a rapid detection method for CTC through fluorescence enhancement was developed. In addition, through the electron transfer process (ET), fluorescence resonance energy transfer (FRET) effect and static quenching between B/N-CeFNPs and oxytetracycline (OTC), a ratio fluorescence strategy for detecting OTC was generated. The fluorescence of B/N-CeFNPs at 410 nm can be effectively quenched by OTC, and new fluorescence emission appears at a wavelength of 500 nm. B/N-CeFNPs showed good linear responses with CTC and OTC in the range 0.1-1 µM and 1-40 µM, respectively. This system was used to simultaneously detect the CTC and OTC in milk and honey, realizing multi-residues detection of TCs in actual samples by using the same ceria-based fluorescence nanomaterial.

Fluorescence sensor based on optimized quantum yield manganese-carbon polymer dots and smartphone-integrated sensing platform for tetracycline detection

The one-step synthesis of Mn-doped carbon quantum dots (Mn-CPDs) with a high quantum yield (QY = 45%) is reported using the microwave-assisted method. Subsequently, Mn-CPDs were successfully combined with Eu3+ ions to construct an Eu3+@Mn-CPDs fluorescence sensor. The presence of tetracycline (TC) induced a transition of fluorescence emission from blue (434 nm) to red (618 nm), and a robust linear relationship was observed between the ratio of F618 nm / F434 nm and the TC concentration (5 - 50 nmol/L), with a limit of detection (LOD) of 5.76 nmol/L. The underlying mechanism of Eu3+@Mn-CPDs and TC sensing is unveiled as a synergistic effect involving inner filter effect (IFE) and concurrent interactions. Notably, the smartphone-integrated sensing platform based on Eu3+@Mn-CPDs enables rapid and quantitative TC detection within a short time (< 30 s) by monitoring fluorescence color changes, achieving high-detection sensitivities (with a LOD of 6.18 nmol/L). This versatile and efficient sensing platform demonstrates its potential for the determination of TC concentrations in milk, honey, and tap water samples.

Multi-component determination based on high quantum yield "on-off-on" carbon quantum dots sensor

The nitrogen(N)-sulfur(S)-sodium(Na(I)) co-doped carbon quantum dots (CQDs) were synthesized via a one-step hydrothermal method, which exhibited a remarkably high fluorescence quantum yield (24.58%) and exceptional optical properties. The fluorescence "on-off-on" sensor was constructed. The fluorescence of CQDs was rapidly quenched with Fe(III) and the fluorescence recovered by ascorbic acid (Asc) partially and arginine (Arg)/histidine (His) completely. The CQDs fluorescence sensor demonstrated rapid response, exceptional sensitivity, excellent stability, remarkable selectivity, and robust anti-interference performance, which was feasible to simultaneously determine the concentrations of multiple analytes in the sample with satisfactory recovery rates. The "on-off-on" fluorescence mechanism of CQDs was investigated, revealing the significant potential of carbon nano-functionalized materials in the field of drug detection through fluorescence sensing.

Machine learning integrated high quantum yield blue light carbon dots for real-time and on-site detection of Cr(VI) in groundwater and drinking water

The safety of groundwater and drinking water is directly related to the well-being of human beings and ecosystems. On-site monitoring and timely response to heavy metals in these water sources are crucial for water supply security. Fluorescent probes combined with machine learning technology have been applied to on-site detection of heavy metals. However, they were primarily focused on industrial-level detection and lacked the sensitivity required for detecting Cr(VI) in groundwater and drinking water. In this study, we developed an machine learning-integrated approach using high-quantum-yield (QY) N-doped blue-light carbon dots (N-BCDs) for instant detection of Cr(VI) in groundwater and drinking water. N-BCDs were synthesized within 3 min using a household microwave oven with citric acid and 1,2-diaminobenzene, resulting in a QY of approximately 90 %. The fluorescence of N-BCDs was quenched via the internal filter effect (IFE), enabling the detection of Cr(VI) within 1 min, with a detection limit of 0.1574 μg L-1 for Cr(VI) concentrations ranging from 0 to 60 μg L-1. We employed machine learning methods to determine Cr(VI) concentrations from simple shots, based on the red-green-blue (RGB) feature and Kmeans feature extraction. These features were input into four models (Ridge, XGB, SVR, and Linear), achieving a fitness of 95.2 %. Furthermore, the accuracies for Cr(VI) concentration identification in actual groundwater and drinking water were as high as 95.71 % and 96.81 %, respectively. Our work successfully extended the detection range of Cr(VI) to the μg level, significantly improving the practical applicability of the method and providing a new approach for on-site detection of Cr(VI) in groundwater and drinking water.

An intelligent smartphone-test strip detection platform for rapid and on-site sensing of benzoyl peroxide in flour samples

Benzoyl peroxide (BPO) is a commonly used flour whitener, but its excessive usage can have adverse effects on human health, such as nutrient loss, vitamin deficiencies and certain diseases. In this study, a europium metal organic framework (Eu-MOF) fluorescence probe was prepared, which exhibited a strong fluorescence emission at 614 nm upon excitation at 320 nm, with a high quantum yield of 8.11%. The red fluorescence of the probe could be effectively quenched by BPO through the inner filter effect (IFE) and photoinduced electron transfer (PET) mechanism. The detection process offered several advantages, including a wide linear range of 0-0.95 mM, a low detection limit of 66 nM and a fast fluorescence response of 2 min. Furthermore, an intelligent detection platform was designed to enhance the practical application of the detection method. This platform combined the portability and visuality of a traditional test strip with the color recognition capability of a smartphone, allowing for the visualization and quantitative detection of BPO in a convenient and user-friendly manner. The detection platform was successfully applied to the analysis of BPO in real flour samples with satisfactory recoveries (99.79%-103.94%), suggesting a promising strategy for the rapid and on-site detection of BPO in food samples.

A smartphone-integrated portable platform based on polychromatic ratiometric fluorescent paper sensors for visual quantitative determination of norfloxacin

The emergence of "superbugs" due to antibiotics overuse poses a significant threat to human health and security. The development of sensitive and effective antibiotics detection is undoubtedly a prerequisite for addressing antibiotics overuse-associated issues. However, current techniques for monitoring antibiotics typically require costly equipment and well-trained professionals. Hence, we developed herein a rapid, instrument-free, and on-site detection method for antibiotic residues such as norfloxacin (NOR) based on a ratiometric sensing platform utilizing "on-off-on" response properties of polychromatic fluorescence for direct visual quantitative NOR analysis. Specifically, this platform integrated iron ions (Fe3+)-chelated blue carbon dots (BCDs) for signal sensing and red carbon dots (RCDs) as an internal reference. The sensor mechanism is selective quenching of BCDs' blue fluorescence by Fe3+ via an inner filter effect with unaffected RCDs' red fluorescence. Further NOR addition led to competitive binding with BCDs due to Fe3+ shedding from the BCDs' surface for a recovered blue fluorescence signal. Notably, the ratiometric fluorescence sensor demonstrated rapid and highly sensitive NOR detection in a concentration range of 1-70 μM with an impressive detection limit of 6.84 nM. The ratiometric fluorescence sensing platform was constructed by integrating smartphone and paper-based strategies, which exhibited exceptional sensitivity, selectivity, and rapid response for portable, instrument-free, visual quantification of NOR in real samples.

Nitrogen-Doped Carbon Dots Encapsulated a Polyoxomolybdate-Based Coordination Polymer as a Sensitive Platform for Trace Tetracycline Determination in Water

The requirement of simple, efficient and accurate detection of tetracycline (TC) in water environments poses new challenges for sensing platform development. Here, we report a simple method for TC sensing via fluorescence detection based on metal-organic coordination polymers (MOCPs, (4-Hap)4(Mo8O26)) coated with nitrogen-doped carbon dots (NCDs). These NCDs@(4-Hap)4(Mo8O26) composites showed excellent luminescence features of NCDs with stable bright-blue emission under UV light. The results of the sensing experiment showed that the fluorescence of NCDs@(4-Hap)4(Mo8O26) can be quenched by TC (166 µM) with 94.1% quenching efficiency via the inner filter effect (IFE) in a short time (10 s), with a detection limit (LOD) of 33.9 nM in a linear range of 8-107 µM. More significantly, NCDs@(4-Hap)4(Mo8O26) showed a high selectivity for TC sensing in the presence of anions and metal cations commonly found in water environments and can be reused in at least six cycles after washing with alcohol. The potential practicality of NCDs@(4-Hap)4(Mo8O26) was verified by sensing TC in real water samples with the standard addition method, and satisfactory recoveries from 91.95% to 104.72% were obtained.