Tumor Imaging: Tumor‐Responsive Fluorescent Light‐up Probe Based on a Gold Nanoparticle/Conjugated Polyelectrolyte Hybrid (Small 10/2014)

A tumor-responsive nanoprobe is reported on page 1967 by B. Liu and co-workers based on a conjugated polyelectrolyte and a gold nanoparticle (AuNP) hybrid is designed to fluoresce in response to the low pH extracellular microenvironment in tumors. AuNPs with positive surface charges are prepared by directly reducing Au salt with sodium borohydride and stabilization by cystamine. A pH-triggered, charge-reversible polymer and a water-soluble cationic conjugated polyelectrolyte (CPE) are sequentially deposited onto the AuNP surface through electrostatic interaction. Under physiological conditions (pH ≈ 7.4), the hybrid probe is almost non-fluorescent due to the quenching of CPE by AuNPs. When exposed to acidic extracellular microenvironments in tumors (pHe ≈ 6.5), the acid-labile amides hydrolyze into primary amines. The generated amine groups result in strong electrostatic repulsion between CPE and AuNPs, leading to recovered probe fluorescence. The fluorescence turnon is further utilized for extracellular acidic tumor microenvironment imaging in vivo, which provides new opportunities for easy tumor imaging and identification.