Ultrathin Two-Dimensional Covalent Organic Framework Nanosheets: Preparation and Application in Highly Sensitive and Selective DNA Detection

Abstract

The ability to prepare ultrathin two-dimensional (2D) covalent organic framework (COF) nanosheets (NSs) in high yield is of great importance for the further exploration of their unique properties and potential applications. Herein, by elaborately designing and choosing two flexible molecules with C molecular symmetry as building units, a novel imine-linked COF, namely, TPA-COF, with a hexagonal layered structure and sheet-like morphology, is synthesized. Since the flexible building units are integrated into the COF skeletons, the interlayer stacking becomes weak, resulting in the easy exfoliation of TPA-COF into ultrathin 2D NSs. Impressively, for the first time, the detailed structural information, i.e., the pore channels and individual building units in the NSs, is clearly visualized by using the recently developed low-dose imaging technique of transmission electron microscopy (TEM). As a proof-of-concept application, the obtained ultrathin COF NSs are used as a novel fluorescence sensing platform for the highly sensitive and selective detection of DNA.

2D Nanosheets and Their Composite Membranes for Water, Gas, and Ion Separation

“…[31] Thesynthesized 2D COFs are typically exfoliated nanosheets from layered COFs.Lietal. [33] TheC OFs with highly ordered hexagonal networks and sheet-like morphology were easily exfoliated by ultrasonication due to the weak interlayer stacking force between the flexible building blocks.Afacile synthesis of COFs or porous organic frameworks (POFs) is possible when polymer synthesis techniques such as interfacial polymerisation (IP) are applied. [32] The2 D COF-1 membranes exhibited decreased surface area, pore volume,a nd average pore size because of the loss of the original regular channels caused by the random stacking of the nanosheets.However,the nanosheets that were coated in an ultrathin film (thickness of 100 nm) had improved molecular transport properties.P eng et al prepared COF nanosheets from the synthetic monomer 1,3,5-tris(4-formylphenyl)benzene and the commercial monomers tris(4-aminophenyl)amine and tris(4-formylphenyl)amine;the COF nanosheets had 1.8 nm pores and an interlayer distance of 0.39 nm when stacked (Figure 8).…”

“…B) Crystal structure of the bulk TPA-COF material assuming the eclipsed stacking viewed along the [001] (left) and [100] (right) directions with the interlayer distance of 3.92 .C) SEM image of the bulk TPA-COF material with sheet-like morphology [33]. B) Crystal structure of the bulk TPA-COF material assuming the eclipsed stacking viewed along the [001] (left) and [100] (right) directions with the interlayer distance of 3.92 .C) SEM image of the bulk TPA-COF material with sheet-like morphology [33].…”

Kovalente organische Netzwerke und Käfigverbindungen: Design und Anwendungen von polymeren und diskreten organischen Gerüsten

“…Aufsätze sierte ionische COFs [232] oder COFs mit flexiblen C 3v -symmetrischen Eckpunkten, [233] die eine signifikante Abschwächung der Wechselwirkungen zwischen den Schichten bewirken, konnte eine Selbstabblätterung erreicht werden. Freistehende COF-Membranen wurden aus kolloidalen COF-Suspensionen, [234] durch mechanisches Pressen von COF-5-Volumenproben, [235] durch Backen der molekularen Vorstufen [236] oder Grenzflächenkristallisation [237] erhalten.…”

Metal‐Free Photoinduced Atom Transfer Radical Polymerization for Highly Sensitive Detection of Lung Cancer DNA

“…The morbidity and mortality of lung cancer has increased drastically in recent years and it is one of the most dangerous malignant tumor types. [6] Amongt hem, point-of-care testing of nucleic acids can be realized by directly introducing polymeric materials to nucleic acids.R eversible-de-activation radical polymerization (RDRP) has received extensive attention in the fields of polymer chemistry,m aterialss cience and biological applications, and has the benefits of predeterminedm olecular weights, well-defined polymers, narrow-molecular-weight distribution and tolerancet ofunctional groups. Thea chievement of nucleic acids detection at low concentrations can enhance the survival rate of patients.T raditional methodsa re the gold standard, for example,p olymerase chain reaction( PCR), Southernb lot and polyacrylamide gel electrophoresis, but usually have high cost, are time consuming and require skilled labor.…”

“…where i is the anodic current of [Fe(CN)6 ] 3À , n is the transferred electron number of [Fe(CN) 6 ] 3À , D is the diffusion coefficient of 5.0 mm [Fe(CN) 6 ] 3À in 0.1 m KNO 3 , u is scan rate of CV,a nd C represents the concentration of [Fe(CN) 6 ] 3À .A ss hown in Figure S2, the value of i was acquired from cyclic voltammograms (Figure S2 a), n is 1, the diffusion coefficiento f5 .0 mm [Fe(CN)6 ] 3À in 0.1 m KNO 3 was 2.4 10 À6 cm 2 s À1 [31]. The scan rate and the concentration of [Fe(CN) 6 ] 3À were, respectively, 1.0 Vs À1 and 5.0 mm.T he A eff was calculatedt ob ea bout 0.054 cm 2 .T he experiments were repeated five times.The surface coverage (G)o fP NA-modified Au electrode was determined according to [Eq.…”