Fabrication of Solid State Nanopore in Thin Silicon Membrane Using Low Cost Multistep Chemical Etching

Fabrication of Taper Free Micro-Holes Utilizing a Combined Rotating Helical Electrode and Short Voltage Pulse by ECM

Fabrication of the injection nozzle micro-hole on the aero engine is a difficult problem in today’s manufacturing industry. In addition to the size requirements, the nozzle micro-hole also requires no burr, no taper and no heat-affected zone. To solve the above problem, an ultra-short voltage pulse and a high-speed rotating helical electrode were used in electrochemical drilling (ECD) process. Firstly, a theoretical model of ECD with ultra-short voltage pulse was established to investigate the effects of many predominant parameters on machining accuracy, and the effect of rotating helical electrode on the gap flow field was analyzed. Secondly, sets of experiments were carried out to investigate the effects of many key parameters on machining accuracy and efficiency. Finally, the optimized parameters were applied to machine micro holes on 500 μm thickness of GH4169 plate, and micro-holes with the diameter of 186 μm with no taper were machined at the feed rate of 1.2 μm/s. It is proved that the proposed ECD process for fabricating micro-holes with no taper has a huge potential and broad application prospects.

Microfluidic multiplexing of solid-state nanopores

Although solid-state nanopores enable electronic analysis of many clinically and biologically relevant molecular structures, there are few existing device architectures that enable high-throughput measurement of solid-state nanopores. Herein, we report a method for microfluidic integration of multiple solid-state nanopores at a high density of one nanopore per (35 µm²). By configuring microfluidic devices with microfluidic valves, the nanopores can be rinsed from a single fluid input while retaining compatibility for multichannel electrical measurements. The microfluidic valves serve the dual purpose of fluidic switching and electric switching, enabling serial multiplexing of the eight nanopores with a single pair of electrodes. Furthermore, the device architecture exhibits low noise and is compatible with electroporation-based in situ nanopore fabrication, providing a scalable platform for automated electronic measurement of a large number of integrated solid-state nanopores.

Electrophysiology of Epithelial Sodium Channel (ENaC) Embedded in Supported Lipid Bilayer Using a Single Nanopore Chip

Nanopore-based technologies are highly adaptable supports for developing label-free sensor chips to characterize lipid bilayers, membrane proteins, and nucleotides. We utilized a single nanopore chip to study the electrophysiology of the epithelial Na⁺ channel (ENaC) incorporated in supported lipid membrane (SLM). An isolated nanopore was developed inside the silicon cavity followed by fusing large unilamellar vesicles (LUVs) of DPPS (1,2-dipalmitoyl-sn-glycero-3-phosphoserine) and DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine) to produce a solvent-free SLM with giga-ohm (GΩ) sealed impedance. The presence and thickness of SLM on the nanopore chip were confirmed using atomic force spectroscopy. The functionality of SLM with and without ENaC was verified in terms of electrical impedance and capacitance by sweeping the frequency from 0.01 Hz to 100 kHz using electrochemical impedance spectroscopy. The nanopore chip exhibits long-term stability for the lipid bilayer before (144 h) and after (16 h) incorporation of ENaC. Amiloride, an inhibitor of ENaC, was utilized at different concentrations to test the integrity of fused ENaC in the lipid bilayer supported on a single nanopore chip. The developed model presents excellent electrical properties and improved mechanical stability of SLM, making this technology a reliable platform to study ion channel electrophysiology.

A Fluidic Interface with High Flow Uniformity for Reusable Large Area Resonant Biosensors

Resonant biosensors are known for their high accuracy and high level of miniaturization. However, their fabrication costs prevent them from being used as disposable sensors and their effective commercial success will depend on their ability to be reused repeatedly. Accordingly, all the parts of the sensor in contact with the fluid need to tolerate the regenerative process which uses different chemicals (H₃PO₄, H₂SO₄ based baths) without degrading the characteristics of the sensor. In this paper, we propose a fluidic interface that can meet these requirements, and control the liquid flow uniformity at the surface of the vibrating area. We study different inlet and outlet channel configurations, estimating their performance using numerical simulations based on finite element method (FEM). The interfaces were fabricated using wet chemical etching on Si, which has all the desirable characteristics for a reusable biosensor circuit. Using a glass cover, we could observe the circulation of liquid near the active surface, and by using micro-particle image velocimetry (μPIV) on large surface area we could verify experimentally the effectiveness of the different designs and compare with simulation results.

Lipid Bilayer Membrane in a Silicon Based Micron Sized Cavity Accessed by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy

Supported lipid bilayers (SLBs) are widely used in biophysical research to probe the functionality of biological membranes and to provide diagnoses in high throughput drug screening. Formation of SLBs at below phase transition temperature (Tm) has applications in nano-medicine research where low temperature profiles are required. Herein, we report the successful production of SLBs at above-as well as below-the Tm of the lipids in an anisotropically etched, silicon-based micro-cavity. The Si-based cavity walls exhibit controlled temperature which assist in the quick and stable formation of lipid bilayer membranes. Fusion of large unilamellar vesicles was monitored in real time in an aqueous environment inside the Si cavity using atomic force microscopy (AFM), and the lateral organization of the lipid molecules was characterized until the formation of the SLBs. The stability of SLBs produced was also characterized by recording the electrical resistance and the capacitance using electrochemical impedance spectroscopy (EIS). Analysis was done in the frequency regime of 10-2-10⁵ Hz at a signal voltage of 100 mV and giga-ohm sealed impedance was obtained continuously over four days. Finally, the cantilever tip in AFM was utilized to estimate the bilayer thickness and to calculate the rupture force at the interface of the tip and the SLB. We anticipate that a silicon-based, micron-sized cavity has the potential to produce highly-stable SLBs below their Tm. The membranes inside the Si cavity could last for several days and allow robust characterization using AFM or EIS. This could be an excellent platform for nanomedicine experiments that require low operating temperatures.

Simultaneous microfluidic spinning of multiple strands of submicron fiber for the production of free-standing porous membranes for biological application

Microfibers produced using electrospinning and microfluidics-based technologies have been developed as a powerful tool in tissue engineering applications such as drug delivery and scaffolds. The applications of these fibers, however, have been limited because of the hazardous solvents used to make them, difficulties in controlling the pore sizes of their membrane forms, and downscaling the size of the fiber. Nevertheless, extending the use of these fibers, for example in the production of a free-standing porous membrane appropriate for cell-based research, is highly needed for tissue engineering, organ-on-a-chip, and drug delivery research and applications. Here, we fabricated a free-standing porous membrane by using a novel method that involved simultaneously spinning multiple strands of submicron-thick 'noodle-like' fibers. In addition to the novelty of the single noodle fiber in overcoming the size-reducing limitations of conventional microfluidic spinning methods, these fibers can hence form the units of 'noodle membranes' whose pores have sizes that the convention electrospinning method cannot achieve. We confirmed the potential of the noodle membrane to serve as a free-standing porous membrane in two simple experiments. Also, we found that noodle membranes have an advantage in loading different amounts of different materials in itself that it was also shown to be of use as a new type of scaffold for complex tissue regeneration. Therefore, the proposed noodle membrane can be an effective tool in tissue engineering applications and biological studies.

Substrate Dependent Ad-Atom Migration on Graphene and the Impact on Electron-Beam Sculpting Functional Nanopores

The use of atomically thin graphene for molecular sensing has attracted tremendous attention over the years and, in some instances, could displace the use of classical thin films. For nanopore sensing, graphene must be suspended over an aperture so that a single pore can be formed in the free-standing region. Nanopores are typically drilled using an electron beam (e-beam) which is tightly focused until a desired pore size is obtained. E-beam sculpting of graphene however is not just dependent on the ability to displace atoms but also the ability to hinder the migration of ad-atoms on the surface of graphene. Using relatively lower e-beam fluxes from a thermionic electron source, the C-atom knockout rate seems to be comparable to the rate of carbon ad-atom attraction and accumulation at the e-beam/graphene interface (i.e., R_knockout ≈ R_accumulation). Working at this unique regime has allowed the study of carbon ad-atom migration as well as the influence of various substrate materials on e-beam sculpting of graphene. We also show that this information was pivotal to fabricating functional graphene nanopores for studying DNA with increased spatial resolution which is attributed to atomically thin membranes.