Department Chair

M. Scott Goodman

Date of Award

5-2023

Access Control

Campus-Only Access

Degree Name

Forensic Science, M.S.

Department

Chemistry Department

Advisor

Dr. Sujit Suwal

First Reader

Dr. Sujit Suwal

Second Reader

Dr. Jinseok Heo

Third Reader

Dr. Jamie Kim

Abstract

Near-infrared (NIR) surface-enhanced Raman scattering (SERS) is an emerging technique widely used in bioimaging due to its high-resolution output compared to other methods like MRI, CT, and PET imaging. Despite the high demand for ultrasensitive SERS probes in bioimaging, the development of new Raman-active dyes is necessary due to their limited availability, sensitivity, and reproducibility. This thesis describes the synthesis and characterization of a small library of NIR heptamethine indocyanine dyes containing various amino substituents for screening by SERS. IR-786, a known heptamethine indocyanine dye, was used as the parent compound for derivatization by different amines via nucleophilic substitutions of the meso-chloride. Subsequently, the secondary amine was further derivatized by introducing functionally diverse chemical substituents. This library of heptamethine indocyanine dyes was structurally analyzed using nuclear magnetic spectroscopy, electrospray mass spectrometry, and infrared spectroscopy. The UV-visible/near-infrared spectra were collected showing a relationship between the Raman signals produced and the UV-visible/near-infrared relative position to 780nm wavelength.

Furthermore, the heptamethine indocyanine dye molecules were individually coupled with citrate capped, quick-freezing induced AuNP aggregates (QFIAAs) prior to SERS analysis. The process of quick-freezing an AuNP solution followed by a thawing step result in increased “hot spots”, or area between closely spaced particles, which has been found to increase the SERS signal of an analyte. Quick-frozen AuNPs are advantageous in that they are easily reproducible and have a minimum stability of three months. My research suggests that the resonating effect of the functional substituent in the amine governs the QFIAA-enhanced NIR-SERS activity.

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