Surface enhanced FRET for sensitive and selective detection of doxycycline using organosilicon nanodots as donors

Ratiometric fluorescence sensing and discrimination of tetracycline analogs by using coumarin-embedded Eu-MOF nanosensor

As widely used antibiotics, tetracycline residues exist in food and environmental media, which pose certain hidden dangers and negative effects on public health. Therefore, the sensing and discrimination of tetracycline analogs (TCs) have great significance for improving food safety and preventing environmental pollution. Herein, a 7-hydroxycoumarin-3-carboxylic acid-embedded Eu-MOF (HC@Eu-MOF) material was constructed and then developed for the detection of TCs. Upon addition of TCs, the synthesized sensor displays opposite fluorescence changes at two different wavelengths due to the simultaneous presence of the inner filter effect (IFE) and the antenna effect (AE), and achieves a stable ratio signal response within 90 s. In addition, six important tetracycline analogs, including chlortetracycline (CTC), oxytetracycline (OTC), tetracycline (TC), metacycline (MC), doxycycline (DC) and demeclocycline (DMC) can be discriminated with 100 % accuracy through the principal component analysis even in extremely complicated mixtures. Further, a smartphone-assisted portable device was applied for visual sensing of TCs. The as-developed platform possessed the characteristics of simple synthesis, fast response, high sensitivity, and high stability, which further lays a further foundation for the on-site visual detection and discrimination of TCs in real samples.

A dual-response ratiometric fluorescent sensor by europium-doped silicon nanoparticles for fluorescent and smartphone imaging detection of tetracycline

Given the threat to human health posed by the abuse of tetracycline (TC), the development of a portable, on-site methods for highly sensitive and rapid TC detection is crucial. In this work, we initially synthesized europium-doped silicon nanoparticles (SiEuNPs) through a facile one-pot microwave-assisted method. Due to its blue-red dual fluorescence emission (465 nm/621 nm), which was respectively attributed to the silicon nanoparticles and Eu3+, SiEuNPs were designed as a ratiometric fluorescent sensor for TC detection. For the dual-signal reverse response mechanism: TC quenched the blue emission from silicon nanoparticles through inner filter effect (IFE), and enhanced the red emission through "antenna effect" (AE) between TC and Eu3+, the nanoprobe was able to detect TC within a range of 0.2-10 μM with a limit of detection (LOD) of 10.7 nM. Notably, the equilibrium detection time was only 1 min, achieving rapid TC detection. Furthermore, TC was also measured in real samples (tap water, milk and honey) with recoveries ranging from 95.7 % to 117.0 %. More importantly, a portable smartphone-assisted on-site detection platform was developed, enabling real-time qualitative identification and semi-quantitative analysis of TC based on fluorescence color changes. This work not only provided a novel doped silicon nanoparticles strategy, but also constructed a ratiometric sensing platform with dual-signal reverse response for intuitive and real-time TC detection.

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.

Molecular imprinting-based triple-emission ratiometric fluorescence sensor with aggregation-induced emission effect for visual detection of doxycycline

The development of high-performance sensors for doxycycline (DOX) detection is necessary because its residue accumulation will cause serious harm to human health and the environment. Here, a novel tri-emission ratiometric fluorescence sensor was proposed by using "post-mixing" strategy of different emissions fluorescence molecularly imprinted polymers with salicylamide as dummy template (DMIPs). BSA was chosen as assistant functional monomer, and also acted as sensitizers for the aggregation-induced emission (AIE) effect of DOX. The blue-emitting carbon dots and the red-emitting CdTe quantum dots were separately introduced into DMIPs as the response signals. Upon DOX recognition within 2 min, blue and red fluorescence of the tri-emission DMIPs sensor were quenched while green fluorescence of DOX was enhanced, resulting in a wide range of color variations observed over bluish violet-rosered-light pink-orange-yellow-green with a detection limit of 0.061 μM. The sensor possessed highly selective recognition and was successfully applied to detect DOX in complicated real samples. Moreover, with the fluorescent color collection and data processing, the smartphone-assisted visual detection of the sensors showed satisfied sensitivity with low detection limit. This work provides great potential applications for rapid and visual detection of antibiotics in complex substrates.

Smartphone-assisted colorimetric dual-mode sensing system based on europium-doped metal-organic frameworks for rapid on-site visual detection of Fe3+ and doxycycline

Exploring a rapid, sensitive, low-cost, in-situ intelligent monitoring multi-target fluorescence detection platform is important for food safety and environmental monitoring. A dual-mode ratiometric fluorescence sensing system integrated with a smartphone based on a luminescent metal-organic framework (NH2-MIL-53) and CdTe/Eu was developed for visual, in-situ analysis of Fe3+ and doxycycline (DOX) in this paper. Interestingly, with increasing Fe3+ concentration, the fluorescence sensing system exhibits dual-emission with CdTe QDs at 540 nM as the response signal and NH2-MIL-53 at 438 nm as the reference signal, resulting in a significant color shift of fluorescence color from blue-green to blue, with a linear range of 5--1550 nM and a detection limit of 1.08 nM. In the presence of DOX, the blue fluorescence of NH2-MIL-53 and the green fluorescence of CdTe QDs were quenched respectively by the internal filtering effect and the photoelectron transfer effect. While DOX enhances the red fluorescence of Eu3+ by the antenna effect, forming a triple-emission fluorescence sensor. The visual color of this fluorescent sensor shifted from blue green to grey to pink-white to pink to fuchsia to red as the DOX concentration increased with a detection limit of 0.11 nM. Furthermore, the developed intelligent sensing platform achieved real-time in-situ detection of Fe3+ and DOX with detection limit of 1.47 nM and 6.43 nM, respectively. The platform was applied to detection actual samples with satisfactory results, which proved a promising application for real-time on-site food safety monitoring and human health monitoring.

Synthesis of oil-soluble carbon dots via pyrolysis and their diverse applications in doxycycline detection, fluorescent ink and film

The overuse of doxycycline poses a risk for ecological environment. Advanced materials such as anti-counterfeiting and photovoltaic materials are urgently needed to develop innovative strategies for exploiting solar cells and protecting valuable products. Herein, oil-soluble CDs (o-CDs) were successfully fabricated from citric acid, tris-base and oleylamine as precursors via pyrolysis method. The o-CDs with uniform size distribution exhibited a high quantum yield of 0.48 and excellent photostability. The fluorescence of o-CDs was rapidly quenched by doxycycline at room temperature without further modification. Optimal conditions were selected to construct a fluorescence probe with high selectivity and good sensitivity to detect doxycycline. Interestingly, the probe achieved two linear ranges of 0.85--16.7 µM and 16.7--33.4 µM with a low detection limit of 0.26 µM. Furthermore, inner filter effect (IFE) was dominated in the process in which doxycycline interact with the oxygen-containing groups of o-CDs. This sensing platform has been further successfully applied to the detection of doxycycline in milk with recovery rates of 96.8%- 102.7% and relative standard deviations of 0.98%- 1.02%, suggesting that the novel probe has the potential to be applied in real samples. Moreover, o-CDs directly serve as fluorescence ink and work as fluorescence film using PVA as matrix because of strong fluorescence in the solid state, indicating that they have potential applications in anti-counterfeiting and photovoltaic materials. This is the first report that oil-soluble CDs via pyrolysis is applied in the detection of doxycycline in milk. Importantly, this work provides efficient strategies for the construction of anti-counterfeiting and photovoltaic materials.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 μM with a detection limit of 0.092 μΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

A novel nanostructured organic framework sensor for selective and sensitive detection of doxycycline based on fluorescence enhancement

It is critical for human health to develop sensitive and rapid analytical methods for detecting doxycycline (DOX) residues in food. This paper presents a novel metal-organic framework nanomaterial (Zn-MOF) based on dithiodiglycolic acid and its application in DOX detection by fluorescent probe method. Zn-MOF itself does not fluoresce. When DOX is added, the system exhibits strong fluorescence (100-fold) at 530 nm. The fluorescence intensity displayed an excellent linear relationship with DOX concentration with a detection limit of 2.7 nM. The reaction solution's fluorescence displayed a visible color shift from colorless to yellow that was concentration-dependent. A smartphone was used to detect DOX by recognizing the red, green, and blue values of the reaction solution and the corresponding test paper. The use of smartphones can speed up the detection process and streamline operations, offering a sensitive and visible method for the quantitative detection of DOX residues in actual samples. Interestingly, Zn-MOF can discriminate DOX from other tetracyclines with high selectivity. This material has been used successfully as a fluorescent probe to determine DOX in fish samples with an average spiked recovery of 94.6 % ∼ 95.1 %. The DOX levels in the measured perch samples were 1.25 ∼ 157 μg/kg. There are 2 batches of DOX exceeding the standard in 14 batches.

Ultra-small highly fluorescent zinc-based metal organic framework nanodots for ratiometric visual sensing of tetracycline based on aggregation induced emission

Color tonality by intrinsic fluorescent metal-organic frameworks (MOFs) is highly desirable in bioanalytical applications due to its stability, low-cost and robustness with no need for functionalization and/or encapsulation of fluorophores. In the present work, ultra-small and higly fluorescent zinc-based MOFs (FMOF-5) were synthesized. The prepared FMOFs were around 5 nm in size, and gave strong blue emission at 440 nm when excited at 350 nm. Interestingly, tetracycline (TC) selectively tuned the blue emission of FMOF-5 to greenish-yellow emission (520 nm) with dramatic enhancement through aggregation induced emission (AIE). The fluorimetric analysis of TC was carried out through the ratiometric peak intensities of F520/F440, with detection limit (LOD) of 5 nM. To realize quantitative point-of-care based on color tonality, a smartphone integrated with the ratiometric visual platform was thereby design. Hence, TC was visually detected with LOD of 10 nM. The prepared FMOF-5-based probe showed high stability (3 months) and reusability (∼10 times). The developed visual-based platform presents great promise for practical point of care testing due to its low-cost, robustness, ruggedness, simple operation, and excellent selectivity and repeatability.

Sulfur-Doped Organosilica Nanodots as a Universal Sensor for Ultrafast Live/Dead Cell Discrimination

Rapid and accurate differentiation between live and dead cells is highly desirable for the evaluation of cell viability. Here, we report the application of the orange-emitting sulfur-doped organosilica nanodots (S-OSiNDs) for ultrafast (30 s), ultrasensitive (1 μg/mL), and universal staining of the dead bacterial, fungal, and mammalian cells but not the live ones, which satisfies the requirements of a fluorescent probe that can specifically stain the dead cells. We further verify that the fluorescence distribution range of S-OSiNDs (which are distributed in cytoplasm and nucleus) is much larger than that of the commercial dead/fixed cell/tissue staining dye RedDot2 (which is distributed in the nucleus) in terms of dead mammalian cell staining, indicating that S-OSiNDs possess a better staining effect of dead cells than RedDot2. Overall, S-OSiNDs can be used as a robust fluorescent probe for ultrafast and accurate discrimination between dead and live cells at a single cell level, which may find a variety of applications in the biomedical field.

Reusable Ratiometric Fluorescent Probe for Detection and Removal of Doxycycline Antibiotic Demonstrated by Environmental Samples Investigations

Tetracycline antibiotics residue has attracted worldwide attention due to its serious damage to human health and environment. Herein, by taking the advantage of unique properties of zeolitic imidazolate framework (ZIF),...