Thursday, August 6, 2015

Today I delivered my final presentation, "Fabrication of Novel Nanomaterial Tungsten Disulfide (WS2) Nanopores for Solid-State DNA Sequencing" for my REU fellowship at the Nano/Bio Interface Center (NBIC). 

My project abstract: Tungsten disulfide (WS2) is a novel nanomaterial that offers promise to create nanopores for easy and efficient detection of DNA translocation with high spatial resolution. In this work, nanopore membranes are fabricated, a method is designed for the transfer of WS2, WS2 flakes are characterized for nanopore application and transferred to membranes. Semiconductive properties of WS2 indicate promise for WS2  nanopores which will be drilled in the WS2 flakes. Silicon wafers were prepared using a standard method to form ~50 um x 50 um membranes for nanopore drilling. The created membranes were observed for uniformity and their size noted using optical microscopy. Scanning electron microscopy (SEM) was employed to visualize the membranes and focused ion beam (FIB) ~50 nm holes were sculpted. Flakes of WS2 were acquired and images were captured using optical microscopy, height profile characterized by atomic force microscopy (AFM), and Raman spectroscopy used to observe monolayer or multilayer flakes. A stamp transfer method was designed to achieve optimal alignment of one flake to a membrane. Testing of the stamp transfer indicated a touch, release set-up that provided visual observation using optical microscopy. This provided the ability to visually align WS2 flakes over membranes. Using minute motion, the flake was lowered to the microscope stage and contact is made with the membrane. The results of my contribution - wafer fabrication, SEM imaging, FIB drilled holes, designed stamp transfer, capturing optical microscopy images, atomic force microscopy (AFM) and Raman profiles for WS2  flakes, and transfer of WS2 to membrane indicate that the suspended WS2 is ready for nanopore drilling. Once a nanopore is drilled in the suspended WS2 flake, the Drndic group will conduct further experiments - Raman spectroscopy to check quality of 2D suspension,  atomic force microscopy (AFM) to observe the suspended thickness and height profile, and use methods to determine device noise and electronic frequency -  will assist in determining the viability of WS2 nanopores as gateways for DNA sequencing.   

I would like to give special thanks to Dr. Drndić and the University of Pennsylvania NBIC for hosting me this summer, my mentors Gopinath and Paul, and the Drndić lab for their support and encouragement. Through my 10 week research project, it was exciting to explore nanotechnology, learn cleanroom techniques, and become certified to use new equipment. The Drndić lab group became my summer science family. I will miss our lab's daily lunches together, the accompanied crazy idea sharing, David's bread baking, and the fun times we have shared. I'm looking forward to coming to PennApps in September to hack as a member of the Drndić lab coding team!

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