Versatile ultrathin nanoporous silicon nitride membranes

Abstract

Single-and multiple-nanopore membranes are both highly interesting for biosensing and separation processes, as well as their ability to mimic biological membranes. The density of pores, their shape, and their surface chemistry are the key factors that determine membrane transport and separation capabilities. Here, we report silicon nitride (SiN) membranes with fully controlled porosity, pore geometry, and pore surface chemistry. An ultrathin freestanding SiN platform is described with conical or doubleconical nanopores of diameters as small as several nanometers, prepared by the track-etching technique. This technique allows the membrane porosity to be tuned from one to billions of pores per square centimeter. We demonstrate the separation capabilities of these membranes by discrimination of dye and protein molecules based on their charge and size. This separation process is based on an electrostatic mechanism and operates in physiological electrolyte conditions. As we have also shown, the separation capabilities can be tuned by chemically modifying the pore walls. Compared with typical membranes with cylindrical pores, the conical and double-conical pores reported here allow for higher fluxes, a critical advantage in separation applications. In addition, the conical pore shape results in a shorter effective length, which gives advantages for single biomolecule detection applications such as nanopore-based DNA analysis.ion track-etching ͉ nanofluidics ͉ filtration ͉ SiN

Rectification properties of conically shaped nanopores: consequences of miniaturization

“…There has been recent interest in the preparation of asymmetric pores in membranes of various thicknesses, thus we investigated the dependence of the current-voltage curves of conically shaped pores on the pore length 36,51,52 . The corresponding rectification degrees were calculated based on currents recorded at ± 1 V for 0.1 M KCl.…”

Coordination of the electrical and optical signals revealing nanochannels with an ‘onion-like’ gating mechanism and its sensing application

“…In recent years, researchers have made efforts to develop bioinspired smart nanochannels that mimic the function of gating property of biological ion channels for use in various applications, such as biosensors, 3-10 nanofluidic devices [11][12][13][14] and molecular filtration. 15,16 Monitoring the ionic current across a nanochannel is the conventional investigation method used to decode the properties of research subjects, such as size, structure, conformation and dynamic motion.…”

Milling a silicon nitride membrane by focused ion beam

“…A wide range of amorphous materials and composites can be suspended on a silicon wafer with thickness down to a few tens of nanometer and area up to mm 2 . However, because they are so inert and durable, it is tricky to pattern them into desired structures.…”