Development of Far-Red Emitting Pt Nanocluster-Based Bio-Nanoprobes for In Vivo Tumor-Targeted Imaging.

Biomedical imaging has become an indispensable tool in the fields of cancer diagnosis and therapy. Fluorescent noble metal nanoclusters (NCs) are promising nanomaterials for biomedical applications. However, among the noble metal NCs, there is very little research on the biomedical application of platinum (Pt) NCs even though Pt NCs exhibit excellent optical properties. Our far-red emitting (Em/Ex = 680/580 nm) Pt NC-based bio-nanoprobes (Pt nanoprobes) possess ultrasmall size (0.8 ± 0.2 nm in diameter), high photostability, and biocompatibility, and these Pt nanoprobes are promising probes for in vivo imaging. Herein, we report the biomedical application of Pt nanoprobes and demonstrate that the far-red emitting Pt nanoprobes act as an in vivo contrast agent for precise fluorescence imaging of expressed marker protein (protease-activated receptor 1 (PAR1)) at metastatic breast cancer. The carboxylic acid-protected Pt NCs exhibit strong photostability and long colloidal stability over weeks in biological conditions, allowing us to prepare Pt nanoprobes by conjugating with antibodies of targeted biomolecules. Moreover, Pt nanoprobes have successfully been accumulated in MDA-MB-231 breast tumor tissues and further enable highly efficient in vivo tracking of the marker protein (PAR1). Therefore, the developed far-red emitting Pt nanoprobes can be utilized to monitor the physiological behavior of targeted biomolecules in living organisms.