Ru(bpy)₃²⁺-Conjugated Magnetic Nanoparticle as Fluorescent-Electrochemiluminescent Biological Label

Electrochemiluminescence (ECL) has emerged as an ultrasensitive detection technique with zero background signal, and coupling of ECL with a commonly used fluorescence imaging technique can greatly advance the bioimaging/detection applications. However, molecular ECL luminophores have poor cellular uptake and cell-targeting properties. Here, we show that transforming a molecular ECL luminophore into a colloidal nanoprobe can increase its cellular uptake as well as enhance its application potential via both fluorescence and ECL. In particular, we have designed a colloidal magnetic nanoprobe that is composed of a 6-7 nm iron oxide core and surface terminated with a ruthenium complex that acts as both a fluorescent and ECL probe. The nanoparticles are functionalized with targeting ligands that enable the receptor-mediated uptake by specific cells. The designed nanoprobe has been used for imaging/detection of biotin/galactose overexpressed cells via both fluorescence and ECL, along with magnetic extraction of labeled cells for signal enhancement. Results demonstrate that molecular ECL luminophore can be transformed into a fluorescent-ECL nanoprobe with more advanced bioimaging and detection applications.