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A multicolor fluorescent nanoprobe has been prepared by loading bovine serum albumin–stabilized copper nanoclusters (BSA-Cu NCs) onto amino clay (AC) and grafting Eu3+ with auxiliary ligand citric acid (Cit). Tetracycline (TC) can coordinate with Eu3+ by β-diketone structure and transfer energy to Eu3+ through antenna effect. When the concentration of TC is in the range 0 to 13 μM, the blue emission intensity of BSA-CuNCs is basically unchanged, and the red emission of Eu3+ is remarkably enhanced due to the coordination with TC. The emission color gradually changes from blue to red under UV lamp (λ = 365 nm). However, when the TC concentration is in the range 13 to 350 μΜ, the internal amino acid residues of BSA sensitize TC, and the emission color gradually changed from red to green. The nanoprobe has rich color, is simple to prepare, portable, and provide a wide detection range. The limit of detection (LOD) is 3.04 nM, which could be used for real-time visual analysis of trace TC in actual samples (lake water, milk, honey, and bovine serum albumin). In addition, a visual test paper has been designed and combined with the color scanning APP of a smartphone to complete the qualitative and semi-quantitative test of TC. BSA-Cu NCs were loaded on amino clay and graft Eu3+ to establish ratiometric fluorescent nanoprobe for TC detection. With the increase of TC concentration, the emission color under 365 nm UV lamp gradually changed from blue to red and then to green, and the color changed obviously and can be observed by the naked eye. The visual test paper and smartphone application detection sensor were developed to realize rapid, convenient, real-time, and visual detection of TC in actual samples. [ABSTRACT FROM AUTHOR]

Fluorescent probes with on-site visual detection function have received extensive attention in the detection of chlortetracycline (CTC), which was widely used in aquaculture and animal husbandry. Copper nanoclusters (Cu NCs) with excellent optical properties were prepared using bovine serum albumin (BSA) as a template, and a multicolor fluorescence strategy based on BSA-stabilized Cu NCs (BSA-Cu NCs) for detecting CTC was proposed. BSA-Cu NCs had a red emission at 640 nm. After the addition of CTC, the red emission of BSA-Cu NCs gradually decreased for internal filtering effect, while the green emission of CTC was significantly enhanced under the sensitization of BSA. This simple sensing process can be achieved in real time by directly mixing the target sample with BSA-Cu NCs, and the detection limit (LOD) of the system for CTC was 12.01 nM. Based on this sensing strategy, a fluorescence film sensing detection platform was constructed to achieve ultra-fast detection of CTC within 30 s. This work provided a fluorescent film sensor with the advantages of portability, ultra-fast and low cost, which provided a feasible alternative for on-site ultra-fast screening of CTC. [Display omitted] • A multicolor fluorescence nanoprobe for detection of CTC was constructed. • The fluorescence color changed from red to green under 365 nm UV lamp. • A fluorescent film intelligent detection strategy of CTC was developed. [ABSTRACT FROM AUTHOR]

A multicolor fluorescent nano-probe based on Tb3+-doped Au NCs was synthesized by one-pot method, and the red fluorescence of Au NCs was regarded as the internal standard. The green characteristic fluorescence peak of Tb3+ was enhanced significantly with the increase of DPA concentration, and the fluorescence color under UV lamp gradually changes from red to green. The smart phone test paper application program was developed, and the application of this method was more convenient and fast. [Display omitted] • The multicolor fluorescent nano-probe based on Tb3+-doped Au NCs was synthesized by one-pot method. • The fluorescence color under UV lamp gradually changed from red to green with the increase of DPA concentration. • Visual assay of DPA by test paper and color-scanning APP of smart phone was developed. A novel multicolor fluorescent nano-probe based on the hybridization of Tb3+ ion with gold nanoclusters (Au NCs) was synthesized to monitor and on-site visual assay of 2,6-pyridinedicarboxylic acid (DPA), a biomarker of bacterial spores. DPA can replace the water molecule in the center of Tb3+ and strongly coordinate with Tb3+ based on the analyte-triggered antenna effect. Simultaneously, the red fluorescence of Au NCs is not influenced after addition of DPA and can be used as steady inside fluorescence reference channel to measure background noise. On this basis, the multicolor fluorescence nano-probe based on Tb3+-doped Au NCs for fast analysis of DPA was fabricated. The linear range of this method is 0 to 12.5 μM and the limit of detection is 3.4 nM, which is well below the quantity of DPA concentration of 60 μM released by the spore transmission dose of anthrax infection. The proposed multicolor fluorescence nano-probe was successfully detecting DPA in actual sample with good sensitivity and specificity. In addition, the visual paper-based nano-probe is designed to detect DPA by using the color scanning application of smart phone. This developed platform possesses abroad application prospects with advantages of effective, convenient carrying, simple operation, good selectivity and repeatability. [ABSTRACT FROM AUTHOR]

Dipicolinic acid (DPA), as a biomarker for Bacillus anthracis , is highly toxic at trace levels. Rapid and on-site quantitative detection of DPA is essential for maintaining food safety and public health. This work develops a dual-channel self-calibrated fluorescence sensor constructed by the YVO 4 :Eu and Tb- β -diketone complex for rapid visual detection of DPA. This sensor exhibits high selectivity, fast response time, excellent detection sensitivity, and the detection limit is as low as 4.5 nM in the linear range of 0–16 μM. A smartphone APP and portable ultraviolet lamp can assemble a mobile fluorescence sensor for on-site analysis. Interestingly, adding Cu2+ ions can quench the fluorescence intensity of Tb3+. In contrast, the addition of cysteine can restore the fluorescence, allowing the accurate detection of Cu2+ ions and cysteine in environmental water and food samples. This work provides a portable sensor that facilitates real-time analysis of multiple targets in food and the environment. [Display omitted] • A self-calibrated YVO 4 :Eu@TTA-Si-Tb sensor. • The continuous detection of DPA, Cu2+ and Cys. • Smartphone-assisted mobile sensor for on-site rapid analysis. • Targets detection in environmental water and food samples. [ABSTRACT FROM AUTHOR]

With the rapid development of animal husbandry, animal food safety issues are increasingly exposed. Detecting pathogenic bacteria and residual antibiotics in animal food is of great significance for the early detection and regulation of harmful substances that threaten food safety. However, developing a fluorescent sensor that can detect both pathogenic bacteria and antibiotics is challenging. In this study, an interesting dual-channel ratiometric nanoprobe (CDs-Eu) based on europium-functionalized carbon dots was developed to realize the visual detection of Bacillus anthracis marker (DPA) and tetracycline antibiotics (TC) in a water environment under different excitation channels. This method had high sensitivity, comprehensive response range, anti-interference ability, and visualization for detecting DPA and TC. Combined with intelligent phone color scanning applications, a portable agarose gel nanosensor was designed to achieve multicolor on-site assessment of DPA and TC. In addition, an advanced three-to-six logic gate analysis method was also developed, which was expected to achieve intelligent sensing of DPA and TC in food safety. • A dual-channel ratiometric nanoprobe based on europium and carbon dots. • Realization of TC and DPA visual sensing through two channels. • Combined application of gelled detection device and intelligent APP. [ABSTRACT FROM AUTHOR]

A palygorskite (Pal)-based ratiometric fluorescent nanoprobe is designed in order to establish a real time, on-site visual, and highly sensitive detection method for tetracyclines (TCs). The nanoprobe comprises the green emissive dye molecules embedded in the natural Pal, which serve as the internal reference signal. The potential red-emissive seed-europium (Eu 3+ ) ions are covalently bound on the surface of modified Pal, and they can act as the specific recognition element. The emission intensity of Eu 3+ ions significantly increases upon TC addition. The nanoprobe fluorescence changes from green to yellow, orange, or red, thereby accomplishing the visual ratiometric fluorescent detection. This nanoprobe exhibits a high sensitivity with a detection limit of 7.1 nM and an excellent selectivity in monitoring the levels of TCs in milk samples. In addition, this nanoprobe is useful for quantitative determination of TCs, and it is not affected with intensity fluctuations due to instrumental or environmental factors. The nanoprobe-immobilized test paper realizes real-time TCs analysis by using a smartphone with an easy-to-access color-scanning APP as the detection platform. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea, that is, from nature, for nature, and into the nature. [ABSTRACT FROM AUTHOR]

Since the 2001 anthrax attacks, researchers have focused on the development of a bacterial spore biomarker detector with rapid response time and high sensitivity and selectivity. Hence, a ratiometric fluorescent nanosensor based on lanthanide-functionalized attapulgite (Atta) was designed and prepared using dye-doped Atta as an internal reference. Atta, which is famous because of Maya Blue, is a hydrated magnesium aluminum silicate present in nature, with pronounced adsorption and a large specific surface area rich in silicon hydroxyl. The adsorption of dye molecules benefits the formation of an internal reference with orange fluorescence. Meanwhile, silicon hydroxyl would be available for terbium (Tb 3+ ) complex grafting, which favors the sensitization of the bacterial spore biomarker. With increasing dipicolinic acid (DPA) concentrations, energy transfer from DPA to Tb 3+ gradually enhanced, thereby resulting in strong and predominant green fluorescence. The ratiometric fluorescence intensity is highly sensitive. It has a limit of detection of 9.8 nM, which is much lower than the infectious dosage of Bacillus anthracis spores (60 μM) for humans. The rapid response time (10s), high selectivity, and reliable and practical performances in actual applications make this ratiometric fluorescent nanosensor useful in the detection of biomarkers for various bacterial spores. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea of ‘‘from nature, for nature, into the nature’’ and promotes the use of naturally renewable resources to produce promising and eco-friendly functional materials for various applications. [ABSTRACT FROM AUTHOR]

• A novel multicolor probe based on Zif-8 and rare earth. • Realization of TC visual detection with high recognition. • Ultrafast POCT detection of TC in various water and food samples. • Combined application of gelled detection device and intelligent APP. In this work, a high-precision visual and point-of-care testing (POCT) ratiometric fluorescent nanosensor for TC was constructed by embedding fluorescein (FL) into l -histidine modified ZIF-8 (LZIF-8) and chelating with rare earth citrate complex. Upon exposure to TC, the coordination and energy transfer between Eu3+ and TC make Eu3+ sensitized emission characteristic red fluorescence, while without prejudice to the emission peak intensity of FL. This ratiometric fluorescent probe with stable reference signal had the characteristics of high sensitivity (ultralow LOD = 5.99 nM) and selectivity and fast response kinetics (within 20 s). The high-bright fluorescence emission was beneficial to human eye recognition and it can realize semi-quantitative detection of TC in eggs, meeting the requirements of household use. In addition, the color can be read and analyzed quickly with the help of smart phone color analysis APP, and the semi-quantitative concentration of TC can be determined more conveniently. [ABSTRACT FROM AUTHOR]

It is of vital significance to achieve accurate real-time detection of tetracycline (TC). In this research, the ratio fluorescence detection of tetracycline is realized by introducing europium-based aminoclay containing carbon dots with good sensitivity to tetracycline through subsequent surface modification. With the increase of tetracycline concentration, the fluorescence intensity of rare earth europium fluorophore increases continuously, while the fluorescence intensity of CDs is basically unchanged. The CIE chromaticity coordinate confirms that the luminous color of the probe can be adjusted continuously from blue to red. The results exhibit this approach owns the favourable linearity to TC within 0–12.5 μM and 10–25 μM, and the high sensitivity with a low detection limit of 3.133 nM. Moreover, it can entirely satisfy the requirements of field detection because the rapid monitoring time as short as 30 s. The multicolor fluorescence detection strategy is reliable and feasible in the field test of TC in various actual samples. In addition, a TC floating detector based on vertical float structure is designed to achieve the rapid visual detection of TC in simulated flow environment. The superiority of the sensing platform opens up a neo-pathway for point-of-care monitoring of TC residues. The aminoclay clay and carbon dots integrated visual fluorescence platform indicated point-of-care testing detection of tetracycline. [Display omitted] • Europium-based aminoclay nanoprobe containing carbon dots was prepared successfully. • This visual detection platform displayed point-of-care testing of TC. • Rapid visual detection of TC was realized by nanoprobe functionalized vertical float. • Smartphone-assisted detection platform for semi-quantitative TC analysis. [ABSTRACT FROM AUTHOR]

• The MOFs functionalized palygorskite hybrid as a novel multicolor fluorescence nanoprobe was manufactured. • The results indicated that the limit of detection (LOD) of this multicolor fluorescence nanoprobe was as low as 9.3 nM. • The nanoprobe can realize the real-time detection through the smartphone with a color-scanning application. • 4. The practicability of this nanoprobe was further verified by detecting DPA released by non-infectious Bacillus subtilis. The metal-organic frameworks (MOFs) functionalized palygorskite (Pal) hybrid as a novel multicolor fluorescence probe for the detection of bacterial spore biomarker-dipicolinic acid (DPA), had been prepared via in-situ growth. The MOFs can effectively encapsulate dye molecules on the surface of Pal, and the rich carboxyl groups on its surface can coordinate with europium ions (Eu3+), forming a highly sensitive recognition group. The results indicated that the limit of detection (LOD) of this multicolor fluorescence probe was as low as 9.3 nM and was obviously lower than the amount of anthrax spores infecting the human body (60 μM). Moreover, a wide linear range from 0 to 35 μM was obtained. The high specific surface area of Pal, as well as the permanent porosity and suitable binding sites of Eu3+-doped MOFs may play a major role in the sensitivity and linear detection range. The multicolor fluorescence strategy made full use of the diversity of fluorescence signals collected by dye molecules and lanthanide ions, which can realize the real-time and on-site detection through the smartphone with a color-scanning application (APP). The practicability of this probe was further verified by detecting DPA released by non-infectious Bacillus subtilis. [ABSTRACT FROM AUTHOR]

• Ag NPs were successfully loaded in the lumen of HNTs. • The MEF effect of the nanoprobe provided ultra-sensitive detection of TC. • The presence of Ag in the nanoprobe can also enhance the degradation of TC. The ultrasensitive detection and efficient degradation of tetracycline (TC) residues are important for improving food safety and protecting human health. In this paper, a smart silver-enhanced fluorescence platform for the ultrasensitive detection of TC was constructed via a simple and selective modification of the interior and external tubes of natural halloysite nanotubes. The thick pipe wall of this platform provides a natural defense and promotes metal-enhanced fluorescence effects, which subsequently accelerates the detection of TC. Moreover, the nanoplatform of the modified Ag nanoparticles can induce the separation of electrons and holes, thereby enhancing photocatalytic activity in TC degradation. This platform provides new opportunities for studying natural halloysite nanotubes and for simultaneously detecting and photodegrading other deleterious substances. [ABSTRACT FROM AUTHOR]