Aptamers-functionalized nanoscale MOFs for saxitoxin and tetrodotoxin sensing in sea foods through FRET

Recognition and detection of histamine in foods using aptamer modified fluorescence polymer dots sensors

Histamine has been known as a momentous cause of biogenic amine poisoning. Therefore, the content of histamine in foods is strictly required to be controlled within a certain range. Here, an aptamer fluorescent sensor was developed for detection of histamine. Poly [(9, 9-di-n-octylfluorenyl-2, 7-diyl)-alt-(benzo [2,1,3] thiadia-zol-4, 8-diyl)] (PF8BT) and the styrene maleic anhydride copolymer (PSMA) were used for the preparation of PF8BT-Polymer dots (PF8BT-Pdots). PF8BT-Pdots and the cyanine3-phosphoramidite (Cy3) were linked through aptamer to achieve the ratiometric detection for histamine. PF8BT-Pdots were partly quenched by Cy3 due to the fluorescence resonance energy transfer (FRET), when the histamine molecule was recognized by aptamer on the surface of PF8BT-Pdots. A linear range (3-21 μmol/L) was obtained for histamine detection with a low limit of detection (LOD = 0.38 μmol/L). PF8BT aptamer Pdots (PF8BT-A) were used to detect histamine in simply treated aquaculture water and tuna. The cell imaging of HeLa cells presented a good biosecurity and outstanding fluorescent imaging capability of PF8BT-A. The aptamer fluorescent sensors provided a new platform for rapid and accurate detection of histamine in aquatic products and had great potential for the application in food safety and quality control.

Alizarin complexone modified UiO-66-NH2 as dual-mode colorimetric and fluorescence pH sensor for monitoring perishable food freshness

Food prone to spoilage has a huge food safety hazard, threatening people's health, so early detection of food spoilage is a continuous and urgent need. Herein, we developed a dual-mode response sensor, alizarin complexone@UiO-66-NH2, which can accurately detect pH. The sensor demonstrated significant changes in color from pale yellow to deep pink, while the fluorescence shifted from light blue to blue violet. Moreover, both UV absorption and fluorescence intensity showed a linear correlation with pH raging from 4.5 to 7.5. These results indicate that the sensor effectively responds to pH, making it suitable for detecting the freshness of perishable food. To put this into practice, we integrated the sensor with cellulose-based filter paper to determine the freshness of shrimp and beef, which was proved to be effective in assessing freshness. In the future, it can be combined with intelligent colorimetric and fluorescence instruments to achieve visual detection.

Dual-Mode Ce-MOF Nanozymes for Rapid and Selective Detection of Hydrogen Sulfide in Aquatic Products

Increasing concern over the safety of consumable products, particularly aquatic products, due to freshness issues, has become a pressing issue. Therefore, ensuring the quality and safety of aquatic products is paramount. To address this, a dual-mode colorimetric-fluorescence sensor utilizing Ce-MOF as a mimic peroxidase to detect H2S was developed. Ce-MOF was prepared by a conventional solvothermal synthesis method. Ce-MOF catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by hydrogen peroxide (H2O2) to produce blue oxidized TMB (oxTMB). When dissolved, hydrogen sulfide (H2S) was present in the solution, and it inhibited the catalytic effect of Ce-MOF and caused the color of the solution to fade from blue to colorless. This change provided an intuitive indication for the detection of H2S. Through steady-state dynamic analysis, the working mechanism of this sensor was elucidated. The sensor exhibited pronounced color changes from blue to colorless, accompanied by a shift in fluorescence from none to light blue. Additionally, UV-vis absorption demonstrated a linear correlation with the H2S concentration, ranging from 200 to 2300 µM, with high sensitivity (limit of detection, LOD = 0.262 μM). Fluorescence intensity also showed a linear correlation, ranging from 16 to 320 µM, with high selectivity and sensitivity (LOD = 0.156 μM). These results underscore the sensor's effectiveness in detecting H2S. Furthermore, the sensor enhanced the accuracy of H2S detection and fulfilled the requirements for assessing food freshness and safety.

MOFs as versatile scaffolds to explore environmental contaminants based on their luminescence bustle

Metal-Organic Frameworks (MOFs) with luminescent properties hold significant promise for environmental remediation. This review critically examines recent research on these materials design, synthesis, and applications, mainly focusing on their role in combating environmental pollutants. Through a comprehensive analysis of metal ions, ligands, and framework compositions, the review discusses the importance of tailored design and synthesis approaches in achieving desired luminescent characteristics. Key findings highlight the effectiveness of luminous MOFs as fluorescent sensors for a wide range of contaminants, including heavy metals, reactive species, antibiotics, and explosives. Considering all this, the review discusses future research needs and opportunities in the field of luminous MOFs. It emphasizes the importance of developing multifunctional materials, refining design methodologies, exploring sensing mechanisms, and ensuring environmental compatibility, scalability, and affordability. By providing insights into the current state of research and outlining future directions, this review is a valuable resource for researchers seeking to address environmental challenges using MOF-based solutions.

Ratiometric electrochemical aptasensor based on split aptamer and Au-rGO for detection of aflatoxin M1

A novel ratiometric electrochemical aptasensor based on split aptamer and Au-reduced graphene oxide (Au-rGO) nanomaterials was proposed to detect aflatoxin M1 (AFM1). In this work, Au-rGO nanomaterials were coated on the electrode through the electrodeposition method to increase the aptamer enrichment. We split the aptamer of AFM1 into 2 sequences (S1 and S2), where S1 was immobilized on the electrode due to the Au-S bond, and S2 was tagged with methylene blue (MB) and acted as a response signal. A complementary strand to S1 (CS1) labeled with ferrocene (Fc) was introduced as another reporter. In the presence of AFM1, CS1 was released from the electrode surface due to the formation of the S1-AFM1-S2 complex, leading to a decrease in Fc and an increase in the MB signal. The developed ratiometric aptasensor exhibited a linear range of 0.03 μg L-1 to 2.00 μg L-1, with a detection limit of 0.015 μg L-1 for AFM1 detection. The ratiometric aptasensor also showed a linear relationship from 0.2 μg L-1 to 1.00 μg L-1, with a detection limit of 0.05 μg L-1 in natural milk after sample pretreatment, indicating the successful application of the developed ratiometric aptasensor. Our proposed strategy provides a new way to construct aptasensors with high sensitivity and selectivity.

Development of magnetic fluorescence aptasensor for sensitive detection of saxitoxin based on Fe3O4@Au-Pt nanozymes

In this work, on the basis of Fe3O4@Au-Pt nanozymes (MAP NZs) and aptamer recognition, a magnetic fluorescent aptasensor (MFA) was developed for sensitive and accurate detection of saxitoxin (STX). With the bridge of STX aptamer (AptSTX) and complementary DNA (cDNA), AptSTX decorated MAP NZs (MAP/Apt) and cDNA modified green quantum dots (cDNA@g-QDs) were connected to form MAP/Apt-cDNA@g-QDs complex. As STX behaves a strong binding ability towards AptSTX, it will compete with cDNA and hybridize with Apt to release cDNA@g-QDs. With the addition of TMB, MAP will catalyze TMB to the oxidized TMB (ox-TMB), thereby quenching the fluorescence of g-QDs due to the inner filter effect. Based on this finding, the quantitative relationship between the change in fluorescence of gQDs and STX concentration was explored with a limit of detection (LOD, S/N = 3) of 0.6 nM. An internal standard signal of oxTMB was adopted and reduced the fluctuation of fluorescence signal output. Besides, the fluorescence probe can selectively recognize and detect STX among five marine toxins. Eventually, the MFA method behaved good performance in detecting seafood samples with recoveries of 82.0 % ∼ 102.6 % as well as coefficient of variations (CV) of 7.2 % ∼ 10.3 %. Therefore, the method with internal signal is hopeful to be a potential candidate for sensitive and accurate detection of STX in seafood.

A label-free ratiometric fluorescent aptasensor based on a peroxidase-mimetic multifunctional ZrFe-MOF for the determination of tetrodotoxin

A Fe/Zr bimetal-organic framework (ZrFe-MOF) is utilized to establish a ratiometric fluorescent aptasensor for the determination of tetrodotoxin (TTX). The multifunctional ZrFe-MOF possesses inherent fluorescence at 445 nm wavelength, peroxidase-mimetic activity, and specific recognition and adsorption capabilities for aptamers, owing to its organic ligand, and Fe and Zr nodes. The peroxidation of o-phenylenediamine (OPD) substrate generates fluorescent 2,3-diaminophenazine (OPDox) at 555 nm wavelength, thus quenching the inherent fluorescence of ZrFe-MOF because of the fluorescence resonance energy transfer (FRET) effect. TTX aptamers, which are absorbed on the material surface without immobilization or fluorescent labeling, inhibit the peroxidase-mimetic activity of ZrFe-MOF. It causes the decreased OPDox fluorescence at 555 nm wavelength and the inverse restoration of ZrFe-MOF fluorescence at 445 nm wavelength. With TTX, the aptamers specifically bind to TTX, triggering rigid complex release from ZrFe-MOF surface and reactivating its peroxidase-mimetic activity. Consequently, the two fluorescence signals exhibit opposite changes. Employing this ratiometric strategy, the determination of TTX is achieved with a detection limit of 0.027 ng/mL and a linear range of 0.05-500 ng/mL. This aptasensor also successfully determines TTX concentrations in puffer fish and clam samples, demonstrating its promising application for monitoring trace TTX in food safety.

Construction of a nanoscale metal-organic framework aptasensor for fluorescence ratiometric sensing of AFB1 in real samples

Aflatoxins B1 (AFB1) that could contaminate agricultural products has received sustained attention due to its high toxicity and wide distribution. Therefore, sensitive and facile detection method for AFB1 is significant for food safety and control. In this work, a ratiometric fluorescence NMOFs-Aptasensor was developed based on the combination of Cy3-modified aptamer and zirconium-based nanoscale metal-organic frameworks (NMOFs). NMOFs served as energy donors, and Cy3 labeled on the AFB1 aptamer was used as an acceptor. An energy donor-acceptor pair was fabricated in the NMOFs-Aptasensor. With AFB1 selectively caught by the AFB1 aptamer, the fluorescence of the NMOFs-Aptasensor changed via fluorescence resonance energy transfer (FRET), and the fluorescence spectra changed accordingly. The ratiometric fluorescence signal was utilized to quantitatively measure AFB1. The reported NMOFs-Aptasensor presented great detection performance from 0 to 3.33 ng mL^-1, with an LOD of 0.08 ng mL^-1. Moreover, the fluorescence sensor was successfully applied to detect AFB1 in real samples.

Detection of Ciguatoxins and Tetrodotoxins in Seafood with Biosensors and Other Smart Bioanalytical Systems

The emergence of marine toxins such as ciguatoxins (CTXs) and tetrodotoxins (TTXs) in non-endemic regions may pose a serious food safety threat and public health concern if proper control measures are not applied. This article provides an overview of the main biorecognition molecules used for the detection of CTXs and TTXs and the different assay configurations and transduction strategies explored in the development of biosensors and other biotechnological tools for these marine toxins. The advantages and limitations of the systems based on cells, receptors, antibodies, and aptamers are described, and new challenges in marine toxin detection are identified. The validation of these smart bioanalytical systems through analysis of samples and comparison with other techniques is also rationally discussed. These tools have already been demonstrated to be useful in the detection and quantification of CTXs and TTXs, and are, therefore, highly promising for their implementation in research activities and monitoring programs.

Nanoscale semiconducting polymer dots with rhodamine spirolactam as fluorescent sensor for mercury ions in living systems

Mercury ion (Hg²⁺), as one of the most poisonous heavy metal ions, could seriously damage mental and neurological functions thus causing severe diseases. A fluorescent ratiometric sensor based on semiconducting polymer dots (Pdots) and rhodamine spirolactam derivate was developed for the detection of Hg²⁺. The Pdots were prepared by Poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)] (PDDB) with emitting strong green fluorescence. The organic fluorescence dye N-(rhodamine-B) lactam-hydrazine (RhBH), as Hg²⁺-recognizing monomer, was conjugated to the surface of Pdots. Hg²⁺ could specifically trigger ring-opening process of RhBH and thus induce strong Förster resonance energy transfer (FRET) effect, resulting in the green fluorescence decrease of Pdots (energy donor) and red emission derived from the ring-opened RhBH (energy acceptor) increasing. PDDB@RhBH showed a sensitive and reversible response toward Hg²⁺ and had a great performance on resisting interferences from various biological analytes. Additionally, both fluorescent imaging in living cells and zebrafish, and systemic toxicity analysis in rats demonstrated that PDDB@RhBH was a great potential fluorescent sensor for quantitative Hg²⁺ imaging in living systems.