Advanced scattering techniques for characterisation of complex nanoparticles in solution

Nanoparticles are vital to a broad range of applications including commercial formulations, sensing and advanced material synthesis. Nanoparticles can come in a variety of shapes including cubes, polyhedra, rods, and prisms, and recent literature has demonstrated the importance of nanoparticle shape to downstream function (such as cellular uptake). While researchers routinely characterise nanoparticle shape using electron microscopy techniques, this generally requires drying of the samples. Many particles (e.g. lipid nanoparticles or polymer particles) change with drying, so complementary solution based techniques are needed. Scattering techniques can be used to characterise such nanoparticles in suspension, overcoming many of the limitations of other techniques. Here we review the current state of the art in the characterisation of complex nanoparticles (non- spherical and multi-layered) using advanced scattering techniques including light, X-ray, and neutron scattering. Recent improvements in instrument availability and data analysis makes these techniques much more accessible to researchers. This review provides an introduction to these techniques aimed at all researchers working with nanoparticles, in the hope that full characterisation of nanoparticles in solution becomes standard practice.