Raman-encoded nanoparticles for biomolecular detection and cancer diagnostics

Abstract

Optical assays to detect cancer-associated molecular biomarkers in biological substrates are commonly performed with antibody-targeted organic dye contrast agents but the potential for precise quantification, long-term imaging, and multiplexed readouts is limited by chemical and optical instability, non-optimal spectral characteristics, and complicated synthetic chemistry of the dyes. This dissertation tested the hypothesis that a novel class of optical contrast agents termed polymer-protected Raman-encoded nanoparticle tags (PRENTs) provides practical advantages over existing optical technologies for molecular diagnostic applications. First, PRENTs were developed through a modular design utilizing gold-nanoparticle-Raman reporter complexes protected and functionalized by polyethylene glycol derivatives. PRENTs produced optical readouts through surface enhanced Raman scattering (SERS) that were brighter and more photostable than the fluorescence of semiconductor quantum dots under identical experimental conditions. Unique spectral signatures were produced with a broader class of Raman reporters than is possible with silica coated Raman tags. Spectral signatures and colloidal stability of PRENTs were unaffected by harsh chemical conditions that cause spectral changes and aggregation of dyes, quantum dots, and protein coated Raman tags. Antibody-targeted PRENTs specifically tagged cell surface cancer biomarkers on living cells at reasonable integration times. PRENTs were non-toxic to cells under conditions exceeding those required for sensitive molecular detection. Next, PRENTs were efficiently optimized for excitation with near-infrared light through inclusion of near-infrared chromophores as Raman reporters and exploitation of the size-dependent optical enhancement of gold nanoparticles. Third, the development of a slide-based Raman-linked immunosorbent assay using antibody-conjugated PRENTs enabled quantification of protein biomarkers with a dynamic range of 3 to 4 logs. In summary, this dissertation establishes PRENTs as novel optical tags with unique features useful for biomedical applications and provides insights for further assay development.