Title

Novel Approaches to Prepare and Utilize SERS Substrates: Multiplex Microfluidics and Nanotransfer Printing

Date of Award

5-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Michael J. Sepaniak

Committee Members

Ziling (Ben) Xue, Jimmy Mays, Elizabeth Howell

Abstract

Over the past few decades, surface enhanced Raman spectroscopy (SERS) has garnered respect as an analytical technique with significant chemical and biological applications. SERS is important for the life sciences because it can provide trace level detection and a high level of molecular structure information. The development of quantitative, highly sensitive substrates requires control over size, shape, and position of metal nanoparticles which function as the SERS active medium. Thus, creating and successfully implementing a sensitive, reproducible, and robust SERS active substrate continues to be a challenging ask. Its future development depends critically on techniques for lithography and nanofabrication. Herein, we report a novel method for SERS that is based upon using colloidal silver nanoparticles in a multiplexed microfluidics (MMFs) platform. The MMF is created in polydimethylsiloxane (PDMS) polymer material and used to perform parallel, high throughput, and sensitive detection/identification of single or various analytes under easily manipulated conditions. A facile passive pumping method is used to deliver samples into the channels under flowing conditions that are highly conducive for SERS measurments.

Also an unconventional nanofabrication approach is modified to produce efficient SERS substrates. Metallic nanopatterns of silver discs are transferred from a stamp onto PDMS to create nanocomposite substrates with regular periodic morphologies. The stamp with periodic arrays of square, triangular, and elliptical pillars is created via Electron Beam Lithography of ma-N 2403 resist. A modified cyclodextrin is thermally evaporated on the stamp to overcome the adhesive nature of the ebeam resist and to function as a releasing layer. Subsequently, the stamp is over coated with Ag by physical vapor deposition at a controlled rate and thickness and used directly for nanotransfer printing (nTP). Stamps, substrates, and the efficiency of the nTP process were explored by SEM. Ag nano-disc-PDMS substrates are studied by SERS using Rhodamine 6G as the probe analyte. The SERS response of metallic nano-discs of various shapes/sizes on the original stamp is compared to the corresponding nTP substrates. We demonstrate that physical manipulation of the PDMS post nTP can be used to alter morphology. Additionally, stamps are shown to be reusable after the nTP process.

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