(Invited) Ultrasensitive Sensors Based on Solid State Nanopores
Authors: Chen Yun Fei , Si Wei , Tan Hong , Yu Jingwen 
Published: February 2020

Nanofluidics, the study of fluid, ion, and biomolecular behavior in highly confined nano-environments, shows great promise for single molecule sensing and manipulation, particularly for applications in biology. The ability to sequence DNA rapidly and inexpensively is essential to individualized medicine and scientific research, and has prompted the development of new sequencing techniques. Nanopore DNA sequencing is becoming one of the fastest and most effective methods of DNA sequencing technology. This talk covers the topics related with design, fabrication and test of the nano biomolecule sensors. In the design of a nanobio sensor, molecular dynamics (MD) simulation and multiscale simulation methods are used to mimic the crowed environment with DNA and protein molecules inside a nanochannel. We did molecular dynamics simulations to study the structure of DNA and protein molecules inside nanochannels under the interaction between the surface charge, the mobile ions in the solution, and the charges on the biomolecule itself. The molecular dynamics simulation is an integral research component of the nanofluidic sensor development since it will provide insights into charge distributions inside the nanochannel, and hence the resistance of the nanochannel, which is directly related to the sensor development. In addition to the MD model, multiscale simulation method is also employed to investigate the integration system of the nanochannel connecting with the microchannels at its two ends. Fabrication method is also discussed in my talk. Several novel type nanofluidic sensors are developed including a nanosensor integrating the nanochannel with the gate of a silicon field effect transistor, a graphene based nanopore sensor and a sensor that detects individual biomolecules through measuring the tunnel current instead of the ionic current. Several fabrication processes are also tried in our Lab. A typical fabrication process is based on the E-beam, in which the nanochannels were made by etching of 1 mm wide sacrificial lines of poly-silicon (30-40 nm thick) deposited by low pressure chemical vapor deposition (LPCVD), then, were covered by a SiO2 layer (600 nm thick) as the channel wall. Cr was then deposited and patterned as gate electrodes and a layer of PDMS was placed on the microchannels to form a nanofluidic device. Second type process is based on the dual beam, in which an atomic thick film such as graphene is exposed to the focused ion beam. A nanopore is drilled and will be used to detect biomolecules.

The sensing experiment after the device fabrication is to detect l-DNA translocation through the nanochannels. We have also performed the characterization experiment with different concentration solutions to explore the full capabilities of the device. As the l-DNA molecule enters the nanochannel, it may either increase or reduce the conductance of the part of the channel it resides, thus changes the resistance of the nanochannel, which will lead to a modulation of source-drain current of the FET. We also used the developed device to investigate the interactions between ions and proteins, and antigens and antibodies.