Internal Filter Effect Research Articles

Construction of a Cd(II)-Based Metal-Organic Framework for Selective Luminescent Sensing of Chloramphenicol in Milk and Honey Samples

A new and water-stable metal-organic framework, [Cd2(L)2(tmd)]·3H2O (MOF 1), was successfully synthesized by mixed ligands of H2L and tmd under solvothermal condition (H2L= 5-acetamidoisophthalic acid, tmd= 4,4-trimethylenedipyridine). Single-crystal X-ray diffraction shows that the structural unit of MOF 1 is a tetranuclear [Cd4(L)6] primary building unit. Fluorescence sensing experiments revealed that MOF 1 exhibited selectivity and sensitivity detection of Chloramphenicol (CHL) antibiotic in aqueous solutions. The fluorescence quenching effect showed that MOF 1 had a very low detection limit for CHL (LOD= 0.11 μM). More importantly, MOF 1 can be used as a new fluorescence sensor for the detection of CHL in milk and honey samples with very good recoveries of 98.2-103.0 % and 97.0-98.9 %, respectively. Furthermore, the internal filtration effect (IFE) and photoelectron electron transfer (PET) may be responsible for the fluorescence quenching efficiency.

Phenylboronic acid functionalized high-crystallinity fluorescent covalent organic framework act as a sensing platform with dual performance for rifamycin antibiotics and water and adsorbent for rifamycin antibiotics

Phenylboronic acid functionalized high-crystallinity fluorescent covalent organic framework (BA@COF), which can be applied for rifamycin antibiotics and water sensing, and for rifamycin antibiotics adsorption, was synthesized for the first time. To effectively form BA@COF by post-synthetic modification, a fluorescent COF (COF–OMe) was prepared using deep-eutectic solvent as solvent without using catalyst. The BA@COF showed good fluorescence property and adsorption capacity, which owned superior effects in detecting and adsorbing rifampicin, rifapentine, and rifabutin. The results of fluorescence quenching mechanisms showed that internal filtration effect, dynamic quenching, and photoinduced electron transfer were the major mechanisms. Moreover, mainly due to the pore selectivity of BA@COF, hydrogen bonding, and π-π interaction, BA@COF showed good selectivity for three antibiotics. Finally, a dual-function platform based on BA@COF was successfully developed for sensing and adsorbing three antibiotics from various samples. Besides, BA@COF also showed good effect to detect water amount in ethanol (0.1−50%, v/v).

Phosphorescence, fluorescence, and colorimetric triple-mode sensor for the detection of acid phosphatase and corresponding inhibitor

Acid phosphatase (ACP) as a clinical diagnostic biomarker for several pathophysiological diseases has aroused widespread interest. Compared to commonly developed single-mode ACP detection technology, the multi-mode detection method with self-validation can provide more reliable results. Herein, we proposed a triple-mode phosphorescence, fluorescence, and colorimetric method for ACP detection in combination with CDs@SiO2. HAuCl4 with oxidase-like activity can catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to the blue oxide TMB (TMBox), offering absorption signals and quenching the phosphorescence and fluorescence of CDs@SiO2 based on the internal filtration effect (IFE). ACP can hydrolyze ascorbic acid 2-phosphate (AAP) to yield ascorbic acid (AA), thereby reducing TMBox to TMB, triggering solution fading and restoring phosphorescence and fluorescence signals. When the ACP inhibitor malathion is present, the reduction of TMBox is hindered, which successively led to the suppression of CDs@SiO2 phosphorescence and fluorescence signal recovery. According to these principles, triple-mode ACP (LOD = 0.0026 mU mL−1) and malathion detections (LOD = 0.039 μg mL−1) with favorable accuracy and sensitivity are realized. With simplicity, robustness, and versatility, the triple-mode sensor can be extended to the detection of the AAP hydrolase family and the screening of corresponding inhibitors.

Highly photoluminescent tryptophan-coated copper nanoclusters based turn-off fluorescent probe for determination of tetracyclines

Employing cheap Cu nanoclusters to design a novel fluorescent probe have promising opportunities in the field of optical sensors. Here, we fabricated a highly photoluminescent D-tryptophan (D-Trp)-coated Cu nanoclusters (Trp-Cu NCs) by rapid microwave-assisted method to achieve precise quantification of tetracyclines (TC). Due to protecting groups of Trp, the synthesized Trp-Cu NCs have remarkable fluorescence stability with a quantum yield reached 12.5%. A distinct fluorescence quenching with the incremental addition of TC via the internal filtration effect (IFE). Based on turn-off fluorescence within 1 min, a detection method for detecting TC was constructed with a linear range of 0.3–120 μM and a limit of detection (LOD) of 0.12 μM. Besides, the proposed fluorescent probe has been employed for the determination of practical samples such as water samples, milk and honey, and exhibited satisfactory recoveries of 96.1%–108.2%, with relative standard deviations (RSD) lower than 5.0%. This is a sensitive, rapid and easily recognizable Trp-Cu NCs based sensing platform for the determination of TC, which could offer a powerful tool for ensuring food safety.

Highly selective and sensitive determination of doxycycline integrating enrichment with thermosensitive magnetic molecular imprinting nanomaterial and carbon dots based fluorescence probe

Doxycycline (DOX), a typical tetracycline antibiotic, is widely used because of its excellent antibacterial activity. To develop effective method for DOX has attracted much more attention. Herein, a new detection technology integrating magnetic solid phase extraction (MSPE) based on thermosensitive magnetic molecularly imprinted polymers (T-MMIPs) and fluorescence spectrometry based on carbon dots (CDs) was established. Thermosensitive magnetic molecularly imprinted polymers (T-MMIPs) was designed for selective enrichment of trace DOX. The synthesized T-MMIPs showed excellent selectivity for DOX. The adsorption performance of T-MMIPs varied with temperature in different solvents, which could achieve the enrichment and rapid desorption of DOX. In addition, the synthesized CDs had stable fluorescent property and better water-solubility, and the fluorescence of CDs was significantly quenched by DOX due to the internal filtration effect (IFE). Under the optimized conditions, the method resulted in good linearity over the range from 0.5 to 30 μg L−1, and the limit of detection was 0.2 μg L−1. The constructed detection technology was validated with real water samples, and excellent spiked recoveries from 92.5 % to 105.2 % were achieved. These data clearly indicated that the proposed technology was rapid, highly selective, environmentally friendly, and possessed significant potential application and development prospects.

Sensitive fluorometric determination of picric acid and antioxidant stabilizers in propellant compositions using amine-rich nitrogen-doped carbon quantum dots

Determination of both trace explosives in soil samples and antioxidant stabilizers in propellant compositions using the same quantum dots is an important challenge in analytical chemistry. For this purpose, unmodified carbon quantum dots (CQDs) were prepared with surface heteroatom (nitrogen and oxygen) doped, water-soluble and highly fluorescent properties. The CQDs were synthesized by reflux method using citric acid (CA) and N-(4-methylpyridin-2-yl)ethane-1,2-diamine (NMPE) as carbon- and nitrogen-sources, respectively, and displayed a quantum yield as high as 48.30%. Surface morphology of CQDs was determined by STEM, IR, Raman and XPS techniques, and optical properties were determined by fluorescence spectroscopy, fluorescence lifetime measurement, and UV–vis spectroscopy. CQDs, excited at 310 nm, have a spherical structure with an average diameter of 2.0 nm, and emit strong blue fluorescence at a wavelength of 380 nm. With the static fluorescence quenching phenomenon based on the internal filter effect (IFE) mechanism, CQDs can precisely detect picric acid (PA), curcumin, and amine-type antioxidants used as stabilizers (i.e. N-phenyl-p-phenylenediamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, and diphenylamine). With detection limits of 0.5 nmol L−1 for picric acid, 70 nmol L−1 for curcumin, and 600 nmol L−1 for N-phenyl-p-phenylenediamine, CQDs can detect analytes with good recovery in the range of 95% to 105% in the presence of different explosives (i.e., tetryl, TNT, PETN, HMX, and RDX for picric acid), metal ions (Cd2+, Fe2+, Mg2+, Cu2+, Zn2+, Mn2+, and Ca2+ for picric acid and curcumin), anions (Cl−, NO3−, NO2−, SO42−, and CO32− for picric acid and curcumin), biomolecules (glucose, trypsin, lysine, l-phenylalanine, and DL-alanine for curcumin), and camouflage materials (i.e. paracetamol, glucose, detergent, aspartame, and acetyl salicylic acid for picric acid). The developed method was validated against LC-MS/MS (for picric acid) and spectrophotometric CUPRAC (for curcumin) by comparatively analyzing picric acid in contaminated sandy soil and curcumin in synthetically prepared propellant composition.

Construction of a laccase mimic enzyme with fluorescence properties for kanamycin multi-mode analysis

A copper-based dual-ligand biomimetic enzyme (Cu-BH) inspired by natural laccase was constructed, which had promising laccase-like activity and excellent fluorescence properties. More remarkably, Cu-BH can oxidize not only traditional phenolic substrates, but also catecholamines and amine substrates. As expected, OPD could be catalyzed by Cu-BH to produce the yellow fluorescent product DAP with absorbance and emission peaks at 426 nm and 566 nm, respectively. The generated DAP could quench the Cu-BH fluorescence at 440 nm by fluorescence internal filtration effect (IFE), thus constructing a ratiometric fluorescence signal(F566/F440). Kanamycin further promoted the catalytic activity of Cu-BH by accelerating electron transfer, resulting in a gradual increase in absorbance at 426 nm and fluorescence signal amplification at 566 nm. Based on this, a sensitive dual-mode sensing strategy was established to analyze kanamycin with the LOD of 0.033 and 0.26 nM, which was successfully applied to the monitoring of kanamycin in tap water, milk and honey. The visualization analysis was also achieved by RGB reading from a smartphone. In conclusion, this novel biomimetic enzyme (Cu-BH) had provided a new application path in bioanalysis and environmental monitoring.

Triarylamine-based polyamide containing adamantane group as Fe3+ probe and electrochromic smart devices

A new triarylamine-based polyamide was synthesized from 1,4-cyclohexanedicarboxylic acid and diamine monomer containing adamantane group (PA-CA), which exhibits high fluorescence quantum up to 46.1% and excellent electrochromic behaviors. The photoluminescence of PA-CA was quenched by coordination and internal filtration effect to realize Fe3+ response. Neutral colorless PA-CA film was converted to the oxidized blue in the electrochemical oxidation process and the maximum transmittance reached 80%, and the transmittance still exceeded 55% after 10,000 s. A Sandwich structure electrochromic device with PA-CA as the active layer was constructed with a simple strategy and different contents were displayed through patterned customization. Electrofluorochromic performance was regulated and decoding information was customized by applying voltage changes of the light and dark for PA-CA film. The applications of multifunctional integrated PA-CA responding to stimulus have broad prospects in the field of Fe3+ fluorescence sensors, photodetectors and multicolor electrochromic display devices.

Concentration-regulated multi-color fluorescent carbon dots for the detection of rifampicin, morin and Al3+

Carbon dots have many new and interesting phenomena, and the concentration dependent luminescence wavelength is an intriguing one. Herein, nitrogen-sulfur co-doped carbon dots (NSCDs) diluted to different concentrations, the high concentration of G-NSCDs (0.2 mg mL−1) with green fluorescence and the low-concentration of B-NSCDs (0.01 mg mL−1) with blue fluorescence were obtained. Further, it was found that the detection behaviors are different for different concentrations. The “turn-off” fluorescent sensor of G-NSCDs can specifically recognize rifampicin in a linear range of 0.2–20 μM with a detection limit of 56.6 nM employing the mutual effect of photo-induced electron transfer and dynamic quenching. Meanwhile, a “turn-off” B-NSCDs fluorescence sensor was constructed to effectively identify morin based on the internal filtration effect and static quenching, achieving a suitable linearity of 0.2–30 μM and a detection limit of 51.2 nM. Due to the strong chelation of morin and Al3+, a “turn-on” fluorescent probe for sequential detection Al3+ was fabricated based on B-NSCDs-morin system, obtaining a good linearity of 0.1–2.0 μM with a satisfactory detection limit of 45.8 nM. These interesting behaviors indicate that NSCDs are expected to become novel sensing materials for the monitoring of rifampicin, morin and Al3+ in organisms, which is beneficial for our health.

Novel dual-emission sulfur quantum dot sensing platform for quantitative monitoring of pesticide 2,4-dichlorophenoxyacetic acid

In this work, a novel environment-friendly dual-emission Rhodamine B modified sulfur quantum dots (RhB-SQDs) sensing platform was established to economically monitor organochlorine pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) through regulating the activity of alkaline phosphatase (ALP). This dual emission RhB-SQDs exhibited excellent fluorescence and high photostability with emission wavelengths of 455 nm and 580 nm. ALP catalyzed the hydrolysis of the substrate p-nitrophenyl phosphate to p-nitrophenol, which quenched RhB-SQDs fluorescence at 455 nm due to the internal filtration effect, but had no effect the fluorescence intensity of RhB-SQDs at 580 nm. When 2,4-D was present, the activity of ALP was specifically inhibited and enzymatic reaction was interrupted, leading to the reduction of p-nitrophenol production, so the fluorescence of RhB-SQDs at 455 nm was restored. It demonstrated a good linear relationship between the concentration of 2,4-D and F455/F580 in the range of 0.050–0.500 μg mL−1, with a detection limit of 17.3 ng mL−1. The dual-emission fluorescent probe was successfully realized in the identification of 2,4-D in natural water samples and vegetables with the advantages of exceptional accuracy, immunity to interference, and selectivity. The platform offers a fresh look at pesticide monitoring and has the potential to prevent pesticide-related health issues.

The synthesis of gold nanoclusters with high stability and their application in fluorometric detection for Hg2+ and cell imaging

Sensing Hg2+ is significant to protecting human health and environmental ecosystems, for its toxicity and genotoxicity. Here, highly stable fluorescent folic acid (FA)-protected Au nanoclusters (FA-AuNCs) were synthesized by optimizing the reactive parameters with high quantum yield of 34.7%. Main components of Au4L were confirmed by MALDI-TOF, and the electron-rich residues of FA shell enabled FA-AuNCs excellent photostability. FA-AuNCs exhibited sensitive response behavior to Hg2+ with a minimum detectability of 1.3 nM, and presented extreme effect to the detection of Hg2+ in real water. Notably, the cellular imaging and in-situ detection of Hg2+ in cells can be achieved visually. The high selectivity was attributed to the chemical bond formed between Au+ (4f145d10) and Hg2+ (4f145d10). And the internal filter effect and static quenching effect were proved triggering the quenching of FA-AuNCs. The ultra-stable FA-AuNCs provide a potential promising opportunity for the in-situ tracing Hg2+ from environmental and biological samples.

Development of a Dual Mode UCNPs-MB Biosensor in Combination with PCR for Sensitive Detection of Salmonella

In recent years, the high prevalence of Salmonella has emerged as a serious threat to public safety, prompting attempts to utilize accurate, rapid, and direct methods to ensure food safety. In this study, a multifunctional platform featuring dual-mode detection channels (colorimetric-fluorescence) combined with polymer chain reaction (PCR) was proposed for the sensitive and rapid detection of Salmonella. Additionally, the colorimetric measurements were achieved by color changes induced by methylene blue (MB) insertion into the double-stranded DNA, and the fluorescence measurements were performed by internal filter effect (IFE)-induced fluorescence quenching of upconversion nanoparticles (UCNPs) by MB. The results showed that the IFE and PCR amplification processes improved the sensitivity of the sensor towards Salmonella detection, with a limit of detection (LOD) of 21.8 CFU/mL. Moreover, this colorimetric-fluorescence dual-mode PCR biosensor was applied to determine Salmonella in food samples, such as chicken, egg, and fish, which produced satisfactory results. Overall, the present study results demonstrate the potential for combining PCR amplification with IFE to develop an efficient and reliable dual-mode analysis platform to safeguard food security.

Highly stable N-doped carbon dots as the sensitive probe for the detection of Fe3+

The nitrogen-doped carbon dots (NCDs) are facilely fabricated by a one-step hydrothermal strategy using citric acid and o-phenylenediamine as start ingredient. The as-synthesized NCDs with a high quantum yield of 38.63% at 370 nm excitation maintain significant fluorescence stability in various complex environments, indicating that NCDs have the possibility of application in harsh environments. Moreover, after adding the Fe3+ to this as-synthesized NCDs, the emission intensity at 446 nm is remarkably reduced and exhibits line-dependent relationship in the range of 0.5–90 μM with a detection limit of 0.37 μM. Meanwhile, the fluorescence lifetime and absorption characteristics are compared respectively, and Stern−Volmer is calculated. These results illustrate that the quenched fluorescence is attributed to the synergistic effect of internal filtration effect (IFE) and static quenching. Moreover, this carbon-based sensing material has elevated efficiency in detecting Fe3+ in practical samples, implying that the sensing probe provides a fast and accurate new technique for the detection of Fe3+.

A water-stable Zn (II) coordination polymer as a fluorescence sensor for multifunctional detection of Cefixime in milk, honey, beef and chicken

A new Zn (II) coordination polymer, {[Zn(dia)(bpeh)]·3H2O} (CP 1), was synthesized by solvothermal method by a mixed ligand of H2dia and bpeh (H2dia = 5-(dimethylamino)isophthalic acid, bpeh = (1E,2E)-1,2-bis(1-(pyridin-4-yl)ethylidene)hydrazine). CP 1 can be used as a fluorescence sensor with excellent fluorescence characteristics, which can selectively and sensitively identify Cefixime (CFM) antibiotic in aqueous solutions via luminescence quenching effects and has a low detection limit. In addition, CP 1 is the first example of a novel fluorescent probe material capable of sensitively detecting CFM antibiotic in multiple food samples. The possible fluorescence quenching mechanism has also been explored, which can be attributed to the internal filtration effect and photoelectron electron transfer.

Antimonene quantum dots as bifunctional fluorescent sensors for rapid detection of cation (Fe3+) and anions (CrO42−, Cr2O72−)

As an emerging bandgap material, antimonene quantum dots (AQDs) have attracted much attention due to their unique structure and outstanding physical and chemical properties. However, the research on the optical properties of AQDs is still in the initial stage and needs further exploration. Herein, the fluorescent AQDs were synthesized by ultrasonic liquid-phase exfoliation, combined with a hydrothermal treatment process. The as-prepared AQDs exhibit good fluorescence characteristics and have a fluorescence quantum yield value of 7.56%. Besides, the AQDs show good stability under different salt concentrations. Especially, the AQDs show high selectivity and rapid detection of Fe3+, CrO42−, and Cr2O72− ions in an aqueous solution with good anti-interference ability. The relatively low limit of detection for Fe3+ based on AQDs was 6.85 µM, and the limits of detection for CrO42−, and Cr2O72− were 23.0 and 5.91 µM, respectively. The mechanism for the fluorescence quenching of the AQDs can be attributed to the synergistic effect of the internal filter effect and the oxidation–reduction reaction between the AQDs and analytes. This work provided a simple synthesis method to easily prepare the AQDs with a larger yield, which can be applied to rapidly detect Fe3+ cation, and CrO42−, and Cr2O72− anions.

AIE-based cyclodextrin metal–organic frame material for fluorescence detection of nitrofuran and tetracycline antibiotics in aqueous solution

The problem of antibiotic residues is very serious and is harmful to the ecological environment and the human body. We have developed a method for the rapid detection of antibiotics in water samples. Firstly, we prepared a fluorescent material (TPE@CLMOF) with cyclodextrin cross-linked MOF (CLMOF) and tetraphenylethylene (TPE) using a simple way. Due to diphenyl carbonate cross-linking, the fluorescent MOF can glow stably in water. Compared with TPE (40.1%), the absolute quantum yield of TPE@CLMOF increases to 63.2%. The fluorescence of TPE@CLMOF can be selectively quenched by Nitrofurans (NFs) and Tetracyclines (TCs) antibiotics in water. The detection limits of nitrofurazone, nitrofurantoin and chlortetracycline are 0.11, 0.13 and 0.16 μM, respectively. We have studied the adsorption of nitrofurazone, nitrofurantoin and chlortetracycline in TPE@CLMOF and the Langmuir adsorption model and pseudo-second-order kinetic model were established. The maximum adsorption capacity is 223, 209 and 185 mg g−1, respectively. We also proposed a dual quenching mechanism of electron transfer and internal filtration effect, which is verified by quantum chemical calculations and experiments. Finally, the TPE@CLMOF was successfully used as a fluorescent sensor for the determination of antibiotic spiked honey samples.

A dual-channel and dual-signal microfluidic paper chip for simultaneous rapid detection of difenoconazole and mancozeb

Using L-cysteine (L-Cys) modified carbon quantum dots (CQDs) and CdTe quantum dots (CdTe QDs) as fluorescence signals, we developed a novel dual-channel and dual-signal microfluidic paper chip, which enables portable and rapid analysis of difenoconazole and mancozeb by internal filter effect (IFE) and photoinduced electron transfer (PET), respectively. The results indicate that the two single-fluorescence imprinted paper chips have great stability and fluorescence property, and the dual-channel microfluidic paper chip composed of them can achieve simultaneous rapid detection of difenoconazole and mancozeb in a mixed solution. The rapid quantitative detection of two templates was achieved under the same excitation wavelength (360 nm) within 5 min. The limits of detection of difenoconazole and mancozeb were 0.18 μg/mL and 2 μg/mL, respectively. Furthermore, the dual-channel microfluidic paper chip also had good specific recognition for their analogs. Moreover, its recoveries of the actual samples were 102.2–108.8% and 96.0–105.5%, respectively, and the relative standard deviations were all less than 5.6%. In conclusion, this work has successfully prepared a multi-template rapid quantitative pesticide residue detection sensor, which provides a useful exploration for the development of new universal rapid detection technologies and theories and is of great significance for the rapid detection of pesticide residues in export products.

Rapid and sensitive fluorescence determination of oxytocin using nitrogen-doped carbon dots as fluorophores

In this work, a novel nitrogen (N)-doped carbon dots (N-CDs) was prepared with quercetin as the carbon source and o-phenylenediamine as the nitrogen source by hydrothermal synthesis, and their application as fluorophores for selective and sensitive determination of oxytocin were reported. The fluorescence quantum yield of the as-prepared N-CDs, which exhibited good water solubility and photostability, was about 6.45 % using rhodamine 6 G as reference substance, and the maximum excitation (Ex) and emission (Em) wavelength were 460 nm and 542 nm, respectively. The results illustrated that the direct fluorescence quenching of N-CDs fluorophore for the detection of oxytocin achieved good linearity in the range of 0.2–5.0 IU/mL and 5.0–10.0 IU/mL, the correlation coefficients were 0.9954 and 0.9909, respectively, and the detection limit was 0.0196 IU/mL (S/N = 3). The recovery rates were 98.8∼103.8 % with RSD= 0.93 %. The interference experiments showed that common metal ions, possible impurities introduced in production and coexisting excipients in the preparation had little adverse influence on selective detection of oxytocin by the developed N-CDs based fluorescent detection method. The mechanism study on the fluorescence quenching of N-CDs by oxytocin concentrations under the given experimental conditions demonstrated that there were internal filtration effect and static quenching in the system. The developed fluorescence analysis platform for the detection of oxytocin had been proved to be rapid, sensitive, specific and accurate, and to be used for the quality inspection of oxytocin.

Insight into the Sensing Behavior of DNA Probes Based on MOF-Nucleic Acid Interaction for Bioanalysis.

Adsorption of DNA probes onto nanomaterials is a promising strategy for bioassay establishment typically using fluorescence or catalytic activities to generate signals. Albeit important, there is currently a lack of systematic understanding of the sensing behaviors building on nanomaterial-DNA interactions, which greatly limits the rational method design and their subsequent applications. Herein, the issue was investigated by employing multifunctional metal-organic frameworks (MOFs) (FeTCPP⊂UiO-66) as a model that was synthesized via integrating heme-like ligand FeTCPP into commonly used MOFs (UiO-66). Our results demonstrated that the fluorescently labeled DNA adsorbed onto FeTCPP⊂UiO-66 was quenched through photoinduced electron transfer, fluorescence resonance energy transfer, and the internal filtration effect. Among different DNA structures, double-stranded DNA and hybridization chain reaction products largely retained their fluorescence due to desorption and conformational variation, respectively. In addition, ssDNA could maximally inhibit the peroxidase activity of FeTCPP⊂UiO-66, and this inhibition was strongly dependent on the strand length but independent of base composition. On the basis of these discoveries, a fluorescence/colorimetric dual-modal detection was designed against aflatoxin B1 with satisfactory performances obtained to further verify our results. This study provided some new insights into the sensing behaviors based on MOF-DNA interactions, indicating promising applications for rational bioassay design and its performance improvement.

Epitaxial self-assembly of Bimetallic MOF heterostructure for fluorescent and colorimetric detection of tetracyclines

The irrational use of tetracycline antibiotics (TCs) leads to the pollution of environmental resources and finally threatens human health, which makes it urgent to develop a sensor for sensitively and selectively detecting the antibiotics. In this work, a Zn-based metal-organic framework (Zn-MOF) anchored on an amino-functionalized aluminum-based metal-organic framework (NH2-MIL-53(Al)) was constructed as a fluorescence sensor for TCs determination. The abundant –NH2 made NH2-MIL-53(Al) a self-assembly core, which facilitated the formation of MOF-on-MOF heterojunction by amide reaction with the exposed –COOH of Zn-MOF. The single characteristic emission peak of Zn-MOF-on–NH2–MIL-53(Al) at 402 nm could identify TCs by internal filtration effect. Upon introduction of TCs, Zn-MOF-on–NH2–MIL-53 (Al) enhanced the intrinsic fluorescence signal of TCs at 517 nm through the coordination via the metal active center (Zn (II)), forming a ratiometric fluorescent sensor with a reverse response. Zn-MOF-on–NH2–MIL-53(Al) sensor displayed excellent anti-interference capability with a broader linear range (0.1–80 μM), and a lower limit of detection (LOD) of 8.24 nM for tetracycline (TC), 2.77 nM for oxytetracycline (OTC), and 8.85 nM for doxycycline (DC), respectively. By merit of Zn-MOF-on–NH2–MIL-53(Al), a portable smartphone-integrated test hydrogel colorimetric platform was fabricated for visual colorimetric detecting TCs by incorporating the sensor with a smartphone. Additionally, the bimetal-organic framework smartphone sensing platform exhibited satisfactory recovery (95.66–107.65%) and reliability in beef, pork, and chicken. Accordingly, the tactics presented a new strategy for developing an integrated system for environmental pollutant detection.