Isoporous membranes are versatile structures with numerous potential and realized applications in various fields of science such as micro/nanofiltration, cell separation and harvesting, controlled drug delivery, optics, gas separation, and chromatography. Recent advances in micro/nanofabrication techniques and material synthesis provide novel methods toward controlling the detailed microstructure of membrane materials, allowing fabrication of membranes with well-defined pore size and shape. This review summarizes the current state-of-the-art for isoporous membrane fabrication using different techniques, including microfabrication, anodization, and advanced material synthesis. Various applications of isoporous membranes, such as protein filtration, pathogen isolation, cell harvesting, biosensing, and drug delivery, are also presented.
Surface-enhanced
Raman scattering (SERS), owing to its high sensitivity
and rapid response, has been widely used in various fields. However,
it is still a challenge to prepare SERS substrates with high stability
and reproducibility. Metal–organic frameworks (MOFs), with
excellent enrichment capacity and stability, provide a new material
for high-performance SERS substrates. In this paper, we prepare a
MIL-101(Cr) film via a secondary growth method, and Ag+ is reduced to Ag NPs by UV irradiation and attach to the film to
synthesize the Ag@MIL-101(Cr) film SERS substrate. Then, we change
the time of UV light illumination and the amount of silver nitrate
in order to obtain the optimal substrate. The detection capability
of this sample can be up to 10–11 M for 4-ATP, and
the relative standard deviation (RSD) is only about 5%, which demonstrates
that the substrate has excellent SERS effect and reproducibility.
Finally, the prepared substrate has been applied for the determination
of nitrofurantoin, with its detection capability up to 10–7 M. This work proposes a simple method to synthesize MOF-based film
substrate with high SERS performance and uniformity and provides potential
for the sensitive detection of chemical or antibiotic residue.
A new model is presented to describe the quantum confinement and surface passivation effects of nanoclusters. The quantum well depth (ϕ) and the band gap width (Eg) of nanoclusters are independent concepts, because the ϕ depends on the surface electron density while the Eg is a function of the crystal field of the solid. The ϕ and Eg can be correlated with the joint physical and chemical effects, which are quite simple but have rarely been noticed. It is suggested that the bond contraction at the surface and the rise in the surface-to-volume ratio (γ), as well as the cluster interaction, enhance intrinsically the crystal field and hence the band gap Eg. Reaction with electronegative elements, such as oxygen and nitrogen, widens extrinsically the Eg by producing holes below the Fermi level [Appl. Phys. Lett.72, 1706 (1998)]. The formulation agrees well with experimental observations on the band gap enlargement by reducing particle size.
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