SIGNAL-Nano: a sequentially gated red light-activable silicon-rhodamine nanoplatform for mitochondria-targeted theranostics.

Precise control over drug activation within heterogeneous tumor microenvironments remains a central challenge in the design of next-generation therapeutic materials. Here, we report a sequentially gated theranostic nanoplatform based on a silicon-rhodamine (Si-Rhod) photocage that integrates endogenous reactive oxygen species (ROS) sensitivity with externally applied red light (≥680 nm) activation to achieve spatiotemporally programmable chemotherapy. The molecular design enables a two-stage activation process, wherein ROS-mediated oxidation generates a fluorescent intermediate that subsequently undergoes efficient single-photon red light-triggered photolysis, releasing the active drug chlorambucil with high fidelity. The photocaged system self-assembles into nanoscale architectures, facilitating cellular uptake and enabling controlled intracellular delivery. Importantly, the Si-Rhod scaffold provides intrinsic mitochondrial targeting, introducing an additional level of subcellular precision in therapeutic activation. Photophysical and chromatographic analyses confirm rapid and near-quantitative photoconversion under biologically relevant conditions, while mechanistic studies reveal the cooperative interplay between oxidative activation and photochemical release. Functionally, the platform exhibits minimal dark toxicity but demonstrates pronounced light-triggered cytotoxicity across multiple biological models. In three-dimensional tumor spheroids, the system overcomes diffusion-limited drug penetration, achieving efficient activation within hypoxic tumor-like architectures. In vivo evaluation in a melanoma model further reveals significant tumor suppression under red light irradiation, accompanied by negligible systemic toxicity. This work establishes a generalizable design paradigm for sequentially gated theranostic materials, wherein endogenous biochemical cues are integrated with external photonic triggers to enable programmable, on-demand drug activation. The presented strategy advances silicon-rhodamine-based systems as a versatile platform for precision oncology and highlights their potential in the broader development of stimuli-responsive functional materials.