Single-Injection Composite Tracer Achieves Intraoperative Dual-Tracing and Precise Localization of Sentinel Lymph Nodes

The use of dual-tracer contrast agents in clinical applications, such as sentinel lymph node (SLN) identification, offers significant advantages including enhanced accuracy, sensitivity, as well as comprehensive and multimodal visualization. In the current clinical practice, SLNs are typically marked prior to surgical resection by multiple and sequential injections of two tracers, the radioactive tracer and methylene blue (MB) dye. This imposes physical and psychological burden on patients and medical staff. Surface-enhanced Raman scattering (SERS) nanotags have emerged as promising SLN tracers due to their high sensitivity and specificity. In this study, we propose a novel single-injection composite tracer consisting of SERS nanotags and MB dye solution, to achieve the accurate intraoperative visualization and localization of SLNs. Laser excitation at the second near-infrared window (1064 nm) minimizes the MB fluorescence background interference, allowing the integration of SERS nanotags with MB solution to form the composite tracer, bridging two distinctive but complementary optical modalities. The feasibility of the composite tracer is demonstrated for SLN navigation on rabbit models. For the first time, we successfully visualize and localize multiple SLNs in the axilla of rhesus monkeys. Our study demonstrates the potential of combining MB with SERS nanotags for SLN navigation as the composite tracer, making a significant advancement toward the SLN biopsy in clinical applications.