Novel sensing platform based on gold nanoparticle-aptamer and Fe-metal-organic framework for multiple antibiotic detection and signal amplification.

The development of a feasible antibiotic detection method is important in water quality analysis. In this study, we developed a metal-organic framework (MOF)-aptamer-3,3',5,5'-tetramethylbenzidine (TMB)-H2O2-based sensing platform composed of the reaction variable of TMB catalytic oxidation as the label (from colorless to blue) and aptamer as the target recognition element for antibiotic detection. The platform works by calculating the relation between the antibiotic concentration and the resultant decrease in MOF's catalytic activity. Basing from the comparison of typical iron-based MOF materials (Fe-MIL-53, Fe-MIL-88A, and Fe-MIL-100), we selected Fe-MIL-53 to obtain an improved signal amplification effect. The outstanding performance of the Fe-MIL-53-based sensing platform can be attributed to its topological flexibility and small electron transfer impedance. In addition, a signal increment of up to 86% was obtained with an intensified gold nanoparticle (AuNP)-supported aptamer. The inhibitory catalytic activity stemmed from the coating of antibiotic-(AuNP-aptamer) conjugates onto the outer surface of the MOF material, which increased the impedance and decreased the electron transfer efficiency. Validation results indicated that the platform showed high selectivity and sensitivity (i.e., wide linearity range of 50-200 nM, detection limit up to 8.1 ng/mL, and recovery rate of 106%-110%) for chloramphenicol detection and universal applicability for other antibiotics, including ampicillin, tetracycline, and oxytetracycline. In general, the detection reliability and easy operation of this platform render it a promising candidate for antibiotic detection in future water quality monitoring practices.

Identifying the tobacco related free radicals by UPCC-QTOF-MS with radical trapping method in mainstream cigarette smoke.

Tobacco related free radicals (TFRs) in the cigarette smoke are specific classes of hazardous compounds that merit concern. In this study, we developed a hybrid method to identify TFRs directly based on ultra-performance convergence chromatography with a quadrupole time-of-flight mass spectrometry (UPCC-QTOF MS) combined spin trapping technique. The short-lived TFRs were stabilized successfully in situ through spin trapping procedure and UPCC was applied to facilitate efficient separation of complex derivative products. Coupling of orthogonal partial least squares discriminant analysis (OPLS-DA), UPCC-QTOF MS system enabled us to identify specific potential TFRs with exact chemical formula. Moreover, computational stimulations have been carried out to evaluate the optimized stability of TFRs. This work is a successful demonstration for the application of an advanced hyphenated technique for separation of TFRs with short detection time (less than 7min) and high throughput.

Discovering the enzyme mimetic activity of metal-organic framework (MOF) for label-free and colorimetric sensing of biomolecules.

A label-free sensing strategy based on the enzyme-mimicking activity of MOF was demonstrated for colorimetric detection of biomolecules. Firstly obvious blue color was observed due to the high efficiency of peroxidase-like catalytic activity of Fe-MIL-88A (an ion-based MOF material) toward 3,3',5,5'-tetramethylbenzidine (TMB). Then in the presence of target biomolecule and corresponding aptamer, the mimetic activity of Fe-MIL-88A can be strongly inhibited and used directly to realize the colorimetric detection. On the basis of the interesting findings, we designed a straightforward, label-free and sensitive colorimetric method for biomolecule detection by using the enzyme mimetic property of MOF coupling with molecular recognition element. Compared with the existed publications, our work breaks the routine way by setting up an inorganic-organic MOF-aptamer hybrid platform for colorimetric determination of biomolecules, expanding the targets scope from H2O2 or glucose to biomolecules. As a proof of concept, thrombin and thrombin aptamer was used as a model analyte. The limit of detection of 10nM can be achieved with naked eyes and ultrahigh selectivity of thrombin toward numerous interfering substances with 10-fold concentration was demonstrated significantly. Of note, the method was further applied for the detection of thrombin in human serum samples, showing the results in agreement with those values obtained in an immobilization buffer by the colorimetric method. This inorganic-organic MOF-aptamer sensing strategy may in principle be universally applicable for the detection of a range of environmental or biomedical molecules of interests.