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[Display omitted] • A ratiometric probe with higher stability was prepared with natural substances. • Fluorescence inner filter effect was triggered between SCQDs and Cur in Fe-MOFs. • Fe2+ from MOFs was ably used to capture active sites of Cur to avoid interference. • The developed probe shows high sensitivity to SA with LOD as low as 0.14 μmol/L. Herein, a ratiometric fluorescent probe was developed for sensitive detection of salicylic acid (SA) in rice using silk-derived carbon quantum dots @ Curcumin @ iron-based metal organic framework (SCQDs@Cur@Fe-MOFs). Fe-MOFs with porous structure not only provided holes for SCQDs to evade self-aggregation of SCQDs, but Fe2+ ions from MOFs was ingeniously employed to capture active sites of Cur, solving the problem of lacking sufficient specificity of Cur to SA while converting weak response signal to amplified "turn on" mode. Upon exposed to SA, the probe interacted with SA to form Cur-Fe2+-SA ternary complex, which inhibited the internal filtration effect between Cur and SCQDs, and triggered a cascade of response signaling. With this strategy, the proposed probe achieved sensitive determination of salicylic acid in rice with detection limit as low as 0.14 μmol/L. This study provides unique insight into constructing economical and eco-friendly fluorescent sensor for SA detection with superior performance. [ABSTRACT FROM AUTHOR]

• MoS 2 QDs/CdTe-Apta ratiometric fluorescence sensor system was proposed for DEHP detection in pork. • Further validation of the fluorescence quenching mechanism. • MoS 2 QDs/CdTe-Apta has better detection stability than the single-emission CdTe-Apta. A ratiometric fluorescence sensor system is proposed for detecting bis(2-ethylhexyl) phthalate (DEHP) in pork, which is based on aptamer recognition with molybdenum disulfide quantum dots and cadmium telluride quantum dots (MoS 2 QDs/CdTe-Apta). Two signals exist in the system, among which the response signal is transmitted by CdTe-Apta. The amide condensation between aptamers and CdTe QDs shortens the distance between CdTe QDs and DEHP, thus quenching the fluorescence of CdTe QDs, possibly through a photoinduced electron transfer mechanism. The MoS 2 QDs deliver the self-calibration signal, and the fluorescence of MoS 2 QDs remains almost constant when co-existing with DEHP. Linearity (R2 = 0.9536) was established for the DEHP concentration range 0.005–3.0 mg·L−1, with a limit of detection of 0.21 μg·L−1. The system was successfully applied in the determination of DEHP in pork. The system has potential for the quantitative determination of DEHP in practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • CQDs@CCM probe with dual-emissive property was prepared using natural biomass. • CQDs constructed effective fluorescent inner filter channels with CCM through self-assembly. • Innovative application of the sensor in scenarios avoids interference from other metal ions. • Real-time monitoring of salt distribution in beef was achieved using smartphone assisted probe. Herein, a smartphone-assisted fluorescent sensor was proposed for real-time fluorescence imaging and monitoring of salt diffusion in beef curing process. The glutathione modified carbon quantum dots @ curcumin (CQDs@CCM) probe with dual-emissive properties was prepared using natural biomass materials. In the probe, the CQDs with blue fluorescence was quenched by CCM due to the inner filter effect (IFE). When the probe was exposed to highly saturated sodium salt, CCM formed a complex with sodium ions, interrupting the IFE behavior and resulting in the fluorescence recovery of CQDs. Significantly, the innovative application of CCM in curing scenarios effectively circumvents the interference of other metal ions. To our knowledge, this is the first report to apply smartphone-assisted fluorescent sensor to salt imaging of cured beef. Notably, the finite element analysis was performed to simulate the diffusion of salt in beef using COMSOL, and the simulation showed similar results to fluorescence analysis, indicating the established visualizing method and the simulated model can provide effective information for beef marination process. This study provide technical support for precise control of the beef curing degree and offer new insights into the fluorescence imaging in food flavor monitoring. [ABSTRACT FROM AUTHOR]

A novel fluorescence sensing platform was fabricated for visual detection of cadmium ions (Cd2+) with excellent stability and portability. In this protocol, dual-emission ratiometric fluorescence probe were constructed based on silicon oxide-coated copper nanoclusters (CuNCs@SiO 2) as a signal reference and cadmium telluride quantum dots (CdTe QDs) as signal response, thereby greatly improving the accuracy of test results. The level of Cd2+ can be reported within a wide linear range from 0.010 mg·L−1 to 2.0 mg·L−1 with a sensitive detection limit of 1.1 μg·L−1 (2.75 μg·kg−1) and a quick sample-to-answer monitoring time of 6 min, which was quite qualified for regularly monitoring Cd2+. Moreover, aiming to attain portable analysis, the smartphone as colorimetric reader and analyzer were also utilized for rapidly analyzing Cd2+ by capturing the change in fluorescence color. Additionally, benefiting from the strong combination of 1, 10-phenanthroline (Phen) and Cd2+, the fluorescence probe showed excellent anti-interference activities for Cd2+ assay in complex oyster matrix. Overall, the sensing platform had significant stability, specificity and sensitivity, offering a promising potential for conveniently evaluating the quality of marine bivalves polluted with Cd2+. ga1 • The fluorescence sensor with built-in reference probe improved detection selectivity and accuracy. • The limit of 1.1 μg·L−1 for Cd2+ detection is qualified for the safety inspection of Cd2+. • SiO 2 -coated CuNCs as reference was designed for further enhancing stability. • Smartphone-based colorimetry could achieve visual assay of Cd2+ in oyster. • The strategy offers a powerful solution for monitoring Cd2+ pollution in marine bivalves. [ABSTRACT FROM AUTHOR]

• CuNCs–CNQDs ratiometric fluorescence probe was proposed for Pb2+ detection. • The probe shows high sensitivity toward Pb2+ with a LOD of 0.0031 mg L−1. • The probe has better detection stability than the single-emission CuNCs. • The probe exhibits high precision (RSD < 5%) for Pb2+ in porphyra samples. A novel ratiometric fluorescence probe was proposed for detecting lead (II) ions (Pb2+) in porphyra, the approach was based on copper nanoclusters and nitrogen-doped carbon quantum dots (CuNCs-CNQDs). In this probe, the CuNCs delivered the response signal, the fluorescence of which was enhanced by Pb2+ due to the aggregation-induced emission enhancement (AIEE) between Pb2+ and CuNCs. The CNQDs provided the self-calibration signal, whose fluorescence remained almost unchanged in coexistence with Pb2+. According to the change of fluorescence intensity ratio between the fluorophores, CuNCs–CNQDs nanohybrid was used as ratiometric probes for the sensitive detection of Pb2+ in the range of 0.010–2.5 mg L−1, with a detection limit of 0.0031 mg L−1. Finally, the probe was successfully applied to detect Pb2+ in porphyra with relative standard deviations (RSDs) lower than 5%. This study provides a straightforward, stable, and sensitive approach for detecting Pb2+ in porphyra. [ABSTRACT FROM AUTHOR]

• A novel dual-signal fluorescent sensor was constructed for tetracycline (TET) detection. • MoS 2 quantum dots (QDs) and CdTe QDs were used to fabricate a dual-signal fluorescent sensor. • Dual-signal nanosensor significantly enhanced the reproducibility and stability. • The sensor exhibited strong application potential for TET detection in milk samples. A dual-signal fluorescent sensor was developed for tetracycline (TET) detection in milk with excellent reproducibility and stability. In this protocol, molybdenum disulfide quantum dots (MoS 2 QDs) with blue fluorescence and cadmium telluride quantum dots (CdTe QDs) with yellow fluorescence were synthesized to establish the MoS 2 /CdTe-based sensor with two fluorescence emission peaks at 433 nm and 573 nm. With the addition of TET, the fluorescence of MoS 2 /CdTe were quenched by photoinduced electron transfer (PET), and the fluorescence of CdTe QDs were quenched more obvious than MoS 2 QDs. With the strategy, a calibration curve was established between the TET concentration in the range of 0.1–1 μM and the ratio of fluorescence intensity at 573 nm and 433 nm (F 573 /F 433). Furthermore, the dual-signal sensor was applied for TET detection in milk samples with the recovery of 95.53–104.22% and the relative standard deviation (RSD) less than 5%, indicating the strong application potential. [ABSTRACT FROM AUTHOR]

The imbalance of Zn2+/Cd2+ in the human body can lead to many serious diseases due to the overuse of antibiotics and deposition in animal products. Developing a functional material for detecting is challenging and in demand. Herein, silicon quantum dots (SiQDs) are designed as a functional platform for the detection of tetracycline and Zn2+/Cd2+. The COOH functionalized SiQDs with the emission wavelength of 450 nm are chelated with Eu(NO3)3 to form SiQDs‐Eu3+ ratio fluorescent probes, which can be used to detect tetracycline (TCs) and Zn2+/Cd2+ by fluorescence resonance energy transfer (FRET) principle sequentially. The fluorescent probe showed good linearity between ion concentration and fluorescence enhancement. The detection limit of TCs and Zn2+/Cd2+ are 0.2 × 10−6 m and 3 × 10−6 m, respectively, when the pH of the solution is 7.4. In addition, the synthesized SiQDs‐Eu3+ exhibited good stability (from 94.9% to 103.1%). The relative standard deviations (RSD, n = 10) of human serum and urine were both less than 3%. Therefore, the SiQDs‐Eu3+ ratio fluorescence probe will provide a good application prospect in actual sample detection. [ABSTRACT FROM AUTHOR]

• CQDs and GNPs were synthesized as fluorescence and colorimetric nanomaterials, respectively. • CQDs-GNPs-based dual-mode nanosensor was applied for malathion detection. • Standard arrays were fabricated by a smartphone and used for visual detection of malathion. • Cabbages adulterated by malathion were detected by the established calibration curves and standard arrays. A dual-mode fluorescence/colorimetric sensor based on carbon quantum dots (CQDs) and gold nanoparticles (GNPs) was developed for visual detection of malathion in cabbage. The CQDs-GNPs nanocomposite exhibited emission wavelength at 527 nm and absorption wavelength at 524 nm. The fluorescence intensity increased and absorption decreased with addition of malathion. Fluorescence and colorimetric calibration curves were established based on fluorescence intensity (R2 = 0.9914) and absorbance (R2 = 0.9608) in the range of 1 × 10−9–1 × 10−2 M, respectively. Furthermore, fluorescence and colorimetric standard arrays were prepared for visual detection of malathion according to the change of fluorescence brightness and color. Finally, the approximate concentrations of malathion in cabbage samples were estimated by the standard arrays and naked eyes. The calibration curves were used for accurate detection in cabbage samples with recoveries of 89.9%–103.4% (fluorescence) and 88.7%–107.6% (colorimetric). The established sensor for visual malathion detection in cabbage was accurate with strong application potential, especially for rapid screening. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe based on the static quenching and the inner filter effect between boron nitrogen co-doped carbon quantum dots (B, N-CDs) and Cr(VI) was developed for the quantitative determination of Cr(VI) in real water samples. B, N-CDs were prepared using the hydrothermal method with ammonium citrate and bis(pinacolato) diboron as raw materials. Compared with undoped CDs, the fluorescence properties of the B, N-CDs were improved. The fluorescence quantum yield of the B, N-CDs was as high as 59.01%. After optimization of the experimental parameters, the B, N-CDs could be used as a fluorescence probe to detect Cr(VI). Strong linear correlation (R 2 = 0.9986) was established in the Cr(VI) concentration range 0.3–500 μM, and a detection limit of 0.24 μM was achieved. Moreover, the B, N-CDs successfully detected Cr(VI) in real water samples, indicating that they have broad application prospects in the sensitive detection of Cr(VI). The fluorescence of B, N-CD prepared by hydrothermal synthesis of ammonium citrate and bis(pinacolato) diboron can be quenched in a concentration-dependent manner by Cr(VI) based on the static quenching and the inner filter effect (IFE) mechanism. Unlabelled Image • The fluorescence quantum yield of B, N-CDs is as high as 59.01%. • Further validation of the fluorescence quenching mechanism • Use B, N-CDs for real river water and tap water detection [ABSTRACT FROM AUTHOR]

A fluorometric and electrochemical dual-mode method is described for sensitive and specific detection of tetracycline (Tc). A novel nanoprobe was designed that is making use of a Tc-specific aptamer (apta), carbon nitride quantum dots (CNQDs) and silver nanoparticles (AgNPs). The aptamer was linked to the CNQDs which then were used as templates to synthesize the apta-CNQD@AgNP nanocomposites. The blue fluorescence of the nanocomposites (with excitation/emission maxima at 365/440 nm) is quenched. The addition of Tc leads to fluorescence recovery and a decrease in the electroconductivity of a gold electrode modified with apta-CNQD@AgNPs. The fluorometric method has a linear response in the 0.1 μM - 10 mM Tc concentration range and a 15 nM detection limit. The amperometric method (best performed at a working voltage of 0.21 V vs. Ag/AgCl) has a linear response in the 1 nM to 0.1 mM Tc concentration range and a 0.26 nM detection limit. Recoveries of Tc from spiked milk samples were comparable to data obtained by HPLC. [ABSTRACT FROM AUTHOR]

Gold nanocluster@carbon nitride quantum dot nanocomposites protected by bovine serum albumin (BSA-AuNC@CNQDs) were designed as a ratiometric fluorescence nanosensor for ultra-sensitive detection of trypsin inhibitor (TI). CNQDs were prepared via thermal treatment of carbon nitride powder. BSA-CNQDs acted as templates to synthesize BSA-AuNC@CNQDs with dual-emission peaks at 450 and 650 nm. Trypsin can catalyze the hydrolysis of BSA and decompose BSA-AuNC@CNQDs resulting in fluorescence quenching. The fluorescence quenching at 650 nm was prevented by the addition of TI to inhibit the activity of trypsin. The nanosensor-trypsin system showed a satisfactory ability toward TI detection. The ratiometric responses (the ratio of intensity at 650 to 450 nm, I650/I450) had an excellent linearity (R2 = 0.981) with logarithmic values of TI concentrations in the broad range of 1–10,000 ng/mL. The limit of detection (LOD, 0.089 ng/mL) indicates ultra-sensitive detection of TI can be achieved. Additionally, TI in soybean flour was detected by the proposed ratiometric method with satisfactory recoveries (98.15–105.52%) and less than 6% of coefficient of variation. This study reveals that BSA-AuNC@CNQDs have potential applications in detection of TI in real samples. [ABSTRACT FROM AUTHOR]