Molecular Optical Diagnostic Probes: Rationally Designed Quinolines with Raman-Chiral-Fluorescent Activity

Molecular theranostic agents, due to their subnanometer size, have the advantage of long blood circulation times, leading to better targeting efficiency with minimal injected dosages. To that end, quinoline derivatives are attractive as drugs and are being explored for cancer therapy. Therefore, structurally adapting and repurposing them for use in diagnosis would improve disease-site targeting significantly. In this study, we report a strategic modification of the quinoline and “quinoline fragment” nicotinamide and demonstrate their diagnostic capabilities. The molecular design strategically incorporates a pyridine ring with cysteine functionalization specifically at position 3, along with thiol and carboxyl end groups. The synthesized molecules demonstrated strong fluorescence and chiroptical activities. When functionalized onto gold nanostructures, the surface-enhanced Raman scattering (SERS) of the synthesized molecules was similar to a commercial quinoline thiol Raman probe. The strong Raman-chiral-fluorescence optical activity of the molecules is promising for their use as multimodal diagnostic probes. In contrast to the commercially available quinoline thiol, the synthesized derivatives featured higher cell viability in both healthy and cancerous human cells and a potential to selectively kill cancer cells without negatively impacting the growth of the surrounding healthy ones. The reported work thus showcases custom-designed molecules with multimodal functionality of biocompatibility, fluorescence, chirality, Raman activity, and potential for cancer-selective therapy, enabling wider applicability in cancer theranostics.