Characterisation of drug delivery vehicles using atomic force microscopy: current status.

INTRODUCTION: The field of nanomedicine, utilising nano-sized vehicles (nanoparticles and nanofibres) for targeted local drug delivery, has a promising future. This is dependent on the ability to analyse the chemical and physical properties of these drug carriers at the nanoscale and hence atomic force microscopy (AFM), a high-resolution imaging and local force-measurement technique, is ideally suited. Areas covered: Following a brief introduction to the technique, the review describes how AFM has been used in selected publications from 2015-2018 to characterise nanoparticles and nanofibers as drug delivery vehicles. These sections are ordered into areas of increasing AFM complexity: imaging/particle sizing, surface roughness/quantitative analysis of images and analysis of force curves (to extract nanoindentation and adhesion data). Expert opinion: AFM imaging/sizing is used extensively for the characterisation of nanoparticle and nanofibre drug delivery vehicles, with surface roughness and nanomechanical/adhesion data acquisition being less common. The field is progressing into combining AFM with other techniques, notably SEM, ToF-SIMS, Raman, Confocal and UV. Current limitations include a 50 nm resolution limit of nanoparticles imaged within live cells and AFM tip-induced activation of cytoskeleton proteins. Following drug release real-time with AFM-spectroscopic techniques and studying drug interactions on cell receptors appear to be on the horizon.