Comparative SERS Analysis of Passive and Active Tumor Targeting in Single Cells, Spheroids, and Tissues

Nanoparticles (NPs) exhibit great promise in cancer diagnosis and treatment as drug carriers, imaging probes, and therapeutic agents. The surface ligands of NPs play a crucial role in determining their accumulation at the tumor site, thereby affecting the overall theranostic effectiveness. Here, we report a precise technique for the direct comparison of NP deposition within a singular tumor model by surface-enhanced Raman spectroscopy (SERS) encoding. We synthesized SERS-encoded NPs functionalized with diverse ligands (PEG for passive targeting and APT_MUC1 or iRGD for active targeting, respectively) and administered a 1:1:1 mixture of the NPs to monolayer-cultured T47D breast cancer cells, 3D multicellular spheroids, and xenograft tumor-bearing mice. Through simultaneous localization and quantification of different NPs in the same tumor cell/spheroid/tissue section, we found that APT_MUC1 incorporation could effectively enhance NP delivery in vitro (7.2× and 4.1× for T47D cells and spheroids, respectively, in comparison to the PEGylated NPs), albeit the active targeting efficacy was compromised for in vivo tumor delivery (1.4×). Modification with iRGD facilitated NP delivery with a lower efficiency (2.9×, 1.7×, and 1.1× for T47D cells, spheroids, and tumor tissue, respectively). The findings illustrate the effectiveness of employing the active targeting approach yet underscore the necessity for additional optimization of the NPs to surmount biological barriers in vivo despite successful active targeting observed in vitro. Moreover, this multicolor SERS-encoding technique can be further utilized to systematically explore the spatial distribution of NPs with diverse physiochemical attributes among different tissues and organs.