Topics in current chemistry

Bioinspired smart asymmetric nanochannel membranes (BSANM) have been explored extensively to achieve the delicate ionic transport functions comparable to those of living organisms. The abiotic system exhibits superior stability and robustness, allowing for promising applications in many fields. In view of the abundance of research concerning BSANM in the past decade, herein, we present a systematic overview of the development of the state-of-the-art BSANM system. The discussion is focused on the construction methodologies based on raw materials with diverse dimensions (i.e. 0D, 1D, 2D, and bulk). A generic strategy for the design and construction of the BSANM system is proposed first and put into context with recent developments from homogeneous to heterogeneous nanochannel membranes. Then, the basic properties of the BSANM are introduced including selectivity, gating, and rectification, which are associated with the particular chemical and physical structures. Moreover, we summarized the practical applications of BSANM in energy conversion, biochemical sensing and other areas. In the end, some personal opinions on the future development of the BSANM are briefly illustrated. This review covers most of the related literature reported since 2010 and is intended to build up a broad and deep knowledge base that can provide a solid information source for the scientific community.

Bioinspired smart asymmetric nanochannel membranes

Towards sustainable ultrafast molecular-separation membranes: From conventional polymers to emerging materials

Smart gating membranes are important and promising in membrane science and technology. Rapid progress in developing smart membranes is transforming technology in many different fields, from energy and environmental to the life sciences. How a specific smart behavior for controllable gating of porous membranes can be obtained, especially for nano- and micrometer-sized multi-scale pore/channel-based membrane systems is addressed.

Smart Gating Multi-Scale Pore/Channel-Based Membranes.

The search of new-type membrane materials with ideal molecular sieving caused wide interest in both academia and industry. Covalent organic frameworks (COFs) are excellent candidates for efficient molecular separation because of their well-defined pore structure and fine-tuned pore size. However, existing synthetic approaches of COFs mainly result in an insoluble and unprocessable powder, which severely restricts their widespread applicability. In this work, a facile bottom-up interfacial crystallization approach to obtain a two-dimensional (2D) cationic COF, EB-COF:Br nanosheets, is reported. Then a layer-by-layer restacking process is performed to fabricate a continuous and dense 2D ionic COF membrane with a tunable thickness by simple vacuum filtration. The 2D COF membrane shows much higher solvent permeability than graphene-oxide membranes and commercial nanofiltration membranes because of its high porosity. Moreover, due to there being abundant positive charge sites in its pore walls, the EB-COF:Br membrane demonstrates highly selective sieving performance for dye molecules/ions with different charges and sizes. The EB-COF:Br membrane can efficiently reject ∼>98% of anionic dye molecules/ions, while maintaining high solvent permeability. The cationic 2D COF membrane far outperforms other nanofiltration membranes in terms of excellent selective molecular/ionic sieving and superior solvent permeability. The result suggested that the ionic COF membrane can offer a new avenue for separation technology.

A two-dimensional cationic covalent organic framework membrane for selective molecular sieving

Membranes with the ability of molecular/ionic separation offer potential in many processes ranging from molecular purification/sensing, to nanofluidics and to mimicking biological membranes. In this work, we report the preparation of a perforative free-standing ultrathin silica membrane consisting of straight and parallel nanochannels with a uniform size (∼2.3 nm) for precise and fast molecular separation. Due to its small and uniform channel size, the membrane exhibits a precise selectivity toward molecules based on size and charge, which can be tuned by ionic strength, pH or surface modification. Furthermore, the ultrasmall thickness (10-120 nm), vertically aligned channels, and high porosity (4.0 × 10(12) pores cm(-2)) give rise to a significantly high molecular transport rate. In addition, the membrane also displays excellent stability and can be consecutively reused for a month after washing or calcination. More importantly, the membrane fabrication is convenient, inexpensive, and does not rely on sophisticated facilities or conditions, providing potential applications in both separation science and micro/nanofluidic chip technologies.

Ultrathin Silica Membranes with Highly Ordered and Perpendicular Nanochannels for Precise and Fast Molecular Separation

Recent advances in polysaccharides stabilized emulsions for encapsulation and delivery of bioactive food ingredients: A review.

In this work, we report digital loop-mediated isothermal amplification (LAMP) or reverse-transcription LAMP (RT-LAMP) on a commercial membrane, without the need for complex chip fabrication or use of specialized equipment. Due to the pore size distribution, the theoretical error for digital LAMP on these membranes was analyzed, using a combination of Random Distribution Model and Multivolume Theory. A facile peel-off process was developed for effective droplet formation on the commercial track-etched polycarbonate (PCTE) membrane. Each pore functions as an individual nanoreactor for single DNA amplification. Absolute quantification of bacteria genomic DNA was realized with a dynamic range from 11 to 1.1 × 105 copies/μL. One-step digital RT-LAMP was also successfully performed on the membrane for the quantification of MS2 virus in wastewater. With the introduction of new probes, the positive pores can be easily distinguished from negative ones with 100 times difference in fluorescence intensities. Finally, the cost of a disposable membrane is less than $0.10/piece, which, to the best of our knowledge, is the most inexpensive way to perform digital LAMP. The membrane system offers opportunities for point-of-care users or common laboratories to perform digital quantification, single cell analysis, or other bioassays in an inexpensive, flexible, and simplified way.

Digital Loop-Mediated Isothermal Amplification on a Commercial Membrane.

Mesoporous silica films consisting of highly ordered and vertically aligned nanochannels (abbreviated as VMSFs) have received considerable attention because of their high surface area, long-range order, thermal and mechanical stability, controllable pore size and more importantly good molecular accessibility for rapid mass transport. These characteristics are ideal for electroanalytical chemistry and separation science. In this review, we firstly present briefly the strategies for the synthesis of VMSFs on the electrode surface, mainly the electrochemically assisted self-assembly and Stober-solution growth approaches, as well as the surface modification of channel walls with diverse terminal groups for various functionalities. In the next section, recent progress on the applications of VMSFs in electroanalytical chemistry and sensing is summarized, in terms of the spatial confinement and permselective effects (size, charge and lipophilicity selectivity of the mesochannels). We then present the preparation and application of perforated free-standing VMSFs for fast and precise molecular sieving/separation. The review ends with an outlook and perspective on the future applications of VMSFs.

Vertically ordered silica mesochannel films: electrochemistry and analytical applications.

Foodborne pathogen contamination has become a severe threat to human health. Traditional methods for foodborne pathogen detection have several disadvantages, including long detection time, low sensitivity, and low selectivity. The emergence of multiple excellent nanomaterials enables the construction of novel biosensors for foodborne pathogen detection. Based on the outstanding properties of nanomaterials, the novel biosensors possess the advantages of sensitivity, specificity, rapidity, accuracy, and simplicity. The present review comprehensively summarizes the advanced biosensors, including electrochemical, colorimetric, fluorescent, and surface enhanced Raman scattering biosensors for sensing key foodborne pathogens in recent decades. Furthermore, several issues are identified for further exploration, and possible directions for the development of biosensors are discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12576

Xingyu Lin

Papers

Ultrathin Silica Membranes with Highly Ordered and Perpendicular Nanochannels for Precise and Fast Molecular Separation

Recent advances in polysaccharides stabilized emulsions for encapsulation and delivery of bioactive food ingredients: A review.

Digital Loop-Mediated Isothermal Amplification on a Commercial Membrane.

Vertically ordered silica mesochannel films: electrochemistry and analytical applications.

Nanomaterial-based biosensors for sensing key foodborne pathogens: Advances from recent decades.