Single-particle characterization of theranostic liposomes with stimulus sensing and controlled drug release properties

Stimuli-responsive nanotheranostic systems, integrated with diagnosis and treatment features, have recently emerged and attracted much interest. However, most of the research mainly focuses on the novelty of nanomaterials, and undervalues the significance of single-particle characterization which can provide detailed physical and biochemical information for performance evaluation and heterogeneity assessment. Due to the small particle size and low content of functional modules, high throughput and multiparameter analysis of individual stimuli-responsive nanoparticles still remains challenging. Here, fabricating a reactive oxygen species (ROS)-responsive liposome (Lipo@BODIPY11) and taking it as an example, we report the development of a strategy for theranostic nanoparticle characterization by a laboratory-built nano-flow cytometer (nFCM). Coincident detection of light scatter and fluorescence intensity provided a measure for liposome quality assessment. Theranostic performance referred to stimuli-responsive capability and drug release behavior upon ROS treatment were obtained in minutes. Besides, the dissociation of functional modules from liposomes and the formation of aggregates under high modification degree were revealed, which was otherwise masked by ensemble-averaged methods. At last, consistent results were also observed in intracellular studies. This nFCM-based method provides a comprehensive approach for the proof-of-principle study, heterogeneity assessment and quality control of biochemical nanosensors and theranostic nanomaterials.