Recent advances in drug release monitoring

Monitoring drug release in vitro and in vivo is of paramount importance to accurately locate diseased tissues, avoid inappropriate drug dosage, and improve therapeutic efficiency. In this regard, it is promising to develop strategies for real-time monitoring of drug release inside targeted cells or even in living bodies. Thus far, many multi-functional drug delivery systems constructed by a variety of building blocks, such as organic molecules, polymeric nanoparticles, micelles, and inorganic nanoparticles, have been developed for drug release monitoring. Especially, with the advancements in imaging modalities relating to nanomaterials, there has been an increasing focus on the use of non-invasive imaging techniques for monitoring drug release and drug efficacy in recent years. In this review, we introduce the application of fluorescence imaging, magnetic resonance imaging (MRI), surface-enhanced Raman scattering (SERS), and multi-mode imaging in monitoring drug release, involving a variety of nanomaterials such as organic or inorganic nanoparticles as imaging agents; their design principles are also elaborated. Among these, a special emphasis is placed on fluorescence-based drug release monitoring strategies, followed by a brief overview of MRI, SERS, and multi-mode imaging-based strategies. In the end, the challenges and prospects of drug release monitoring are also discussed.