Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique that can detect single molecules and simultaneously obtain structural information. When an analyte molecule binds to a nanostructured noble metal surface, the otherwise weak normal Raman signal is enhanced by as much as a factor of 108. This makes SERS the ideal technique to gain insights into challenging chemical problems, such as probing the how specific surface sites alter the dynamics of surface reactions, detecting ultralow concentrations of analytes in forensic samples, and monitoring biomolecules in vivo. In the first part of this thesis, we will examine the proof methodology for single molecule SERS. After an experimental comparison of the two leading statistical proof methods, we will rationalize the reason why one of the methods is prone to false positive results. The study will conclude with the first published guidelines for reliable single molecule proofs with SERS. We then turn to the next problem: the reliance of single molecule SERS on the resonance Raman enhancement of dye molecules. In the second part of the thesis, we elucidate the nonresonant chemical enhancement mechanism to provide new pathways to optimize the SER signal for successful single molecule detection of analytes other than dyes. In this study, we investigate 22 different substituted benzenethiols on Ag and Au substrates to determine the contribution of electron withdrawing and donating functional groups to the enhancement mechanism. We find that halogen-substituted benzenethiols yield the highest enhancements, and we demonstrate that the enhancement of certain vibrational modes is more strongly related to the functional group’s electronic properties. The third part of this thesis will examine the properties of SERS substrates and demonstrate the uses of low wavenumber Raman measurements to examine the structure of organometallic compounds. Overall, the work in this thesis highlights both the advances that SERS has made in probing new chemical systems and the challenges that remain in understanding the underlying mechanisms. The work presented paves new pathways for the successful implementation of SERS to study surface reactions at the single molecule level.

Creator

• Wong, Nolan Log-chi

DOI

• https://doi.org/10.21985/n2-8v3s-fc19

Subject

• Physical chemistry
• Nanoscience

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:14406
• etdadmin_upload_617842

Keyword

• Surface-Enhanced Raman Spectroscopy
• single molecule spectroscopy

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright