Engineering Near‐Infrared SERS Contrast Agents for High‐Brightness In Vivo Spectroscopic Imaging

A significant hurdle for the clinical translation of in vivo surface‐enhanced Raman scattering (SERS) bioimaging is the scarcity of high‐brightness near‐infrared (NIR) contrast agents. To address this challenge, we develop such agents through the strategic optimization of gold nanorods (AuNRs) as plasmonic substrates and the selection of resonant Raman reporters. We quantitatively characterize the effective differential SERS cross‐section of nanoparticles comprising AuNRs spectrally encoded with various Raman reporters. Our findings establish that the spectral overlap between the AuNR plasmon resonance, reporter absorption, and laser excitation wavelength is a critical parameter for achieving high brightness. Guided by this principle, we engineer NIR‐I and NIR‐II SERS agents using optimized AuNRs and selected resonant reporters, encapsulated within cell membranes derived from 4T1 breast cancer cells. These agents exhibit superior brightness and specific homotypic targeting toward 4T1 cells. In vivo studies in mice demonstrate their capability for precise tumor margin delineation and sensitive detection of microtumors (<100 µm) via NIR‐I and NIR‐II SERS imaging. Furthermore, the agents enable image‐guided surgical resection of orthotopic 4T1 tumors, achieving complete tumor removal and significantly improving surgical outcomes. This work provides a foundational strategy for designing high‐brightness NIR SERS contrast agents for advanced in vivo molecular imaging applications.