Aerosol optical tweezers (AOT) are a proven tool for measuring a selection of physicochemical properties of individual aerosol droplets within a controlled atmospheric environment. Radius, vapour pressure, mixing state and hygroscopicity can be measured routinely and with a high level of accuracy. However, until now, measurements of certain properties have remained inaccessible to AOT and other more conventional techniques. This presentation describes recent developments to the AOT technique to study fundamental bulk and surface properties of aerosol droplets including refractive index, viscosity and surface tension.