We report in this work the fabrication of a flow-through silica nanochannel membrane (SNM) for controlled drug release applications. The ultrathin SNM consists of parallel nanochannels with a uniform diameter of ∼2.3 nm and a density of 4 × 10 cm, which provide simultaneously high permeability and size selectivity toward small molecules. The track-etched porous polyethylene terephthalate film premodified with silane on its surface was used to support the ultrathin SNM via irreversible covalent bond formation, thus offering mechanical strength, flexibility, and stability to the ultrathin SNM for continuous and long-term use. Alkylamines were subsequently grafted onto the SNM surface to modulate the "on" and "off" state of nanochannels by medium pH for controlled drug release. Thiamphenicol glycinate hydrochloride (TPG), an intestinal drug, was studied as a model to permeate through an ultrathin SNM in both simulated gastric fluid (pH = 1.2) and simulated intestinal fluid (pH = 7.5). The release in the latter case was 178 times faster than that in the former. Moreover, a nearly zero-order constant release of TPG via single-file diffusion was achieved up to 24 h, demonstrating the feasibility of sustained and continuous release of small-molecule drugs in a pH-controlled manner.

Nonvolatile buffers and inorganic salts used for isolation and stabilization of biological samples are essential to be cleaned up prior to mass spectrometry (MS) analysis because of their deleterious effects such as ion suppression and instrumental pollution. In this work, a centimeter-scale continuous silica isoporous membrane (SIM) was prepared and integrated into a facile microfluidic chip for the desalting of protein samples based on dialysis principle. Thanks to the uniform pore size (∼2.3 nm in diameter), ultrasmall thickness (90 nm) and high pore density (4.0 × 10 12 pores cm −2 , corresponding to a porosity of 16.7%) of SIM, the device achieved ∼99% desalting efficiency for the sample with 154 mM NaCl (isotonic saline) at a flow rate of 1 μL min −1 , while protein loss was only 5%. High-quality electrospray ionization (ESI)-MS spectra of cytochrome c dissolved in isotonic saline was obtained after the desalting treatment. In addition, the SIM-based microfluidic device was successfully online-coupled with microchip ESI-MS for real-time desalting and characterization of proteins.

Public awareness of the toxicity of volatile organic compounds (VOCs) has led to increased requirements for direct measurement of these substances. This work reports the sensitive detection of VOCs at the ppb level by an interferometric sensor based on the multilayer silica-nanochannel membrane (MSNM). The MSNM is fabricated by layer-by-layer stacking of a free-standing ultrathin SNM composed of regularly ordered channels with an ultrasmall diameter of about 2.3 nm and an ultrahigh density of about 4 × 10 cm. Light reflected from parallel interfaces of the MSNM gives rise to the interferometric pattern with constructive and destructive fringes. The adsorption of VOCs to a highly porous MSNM varies the refractive index of the MSNM, resulting in the shift of the reflectometric interference spectrum (RIS) and thus yielding highly sensitive responses with a limit of detection (LOD) at the ppb level. Moreover, the sensor selectively responds to polar ethanol and acetone, as well as aromatic benzene, toluene, and chlorobenzene, but is insensitive to nonpolar ethane or hexane. The selectivity most likely arises from hydrogen bonding and dipole interaction of VOCs with silica surface.

Proton transport plays an important role in many biological and technological processes. Numerous experiments and molecular dynamics simulations have proved the increase of proton mobility in confined nanostructures. In this work, we studied the proton transport across flow-through silica nanochannel membranes (SNMs) with vertically aligned channels, uniform diameter (∼2.3 nm), high porosity (16.7%), and ultrasmall thickness (88 nm). Taking into account both the mutual interaction between nanochannels and the contribution of surface conductance, a new theoretical model of ion conductance for SNMs was derived by modifying the conductance model reported previously with a correction factor. The correction factor was estimated by closely matching the experimental conductance of SNMs in KCl and NaCl solutions with the theoretical one calculated by the model. Then the measured conductance of SNMs in HCl solutions was found to be at least four times higher than the calculated value by the model. Given the total conductance across SNMs is dominated by the access conductance instead of channel conductance, the difference between experimental and theoretical conductance values implies either that the theoretical model does not capture the real physics of access conductance or that the two-dimensional nanoconfinement effect exists at the nanochannel entrances. The latter effect likely arises from mutual interaction of neighboring nanochannel entrances.