Soot particles derived from canola methyl ester (CME), soybean methyl ester (SME), a 50% mixture composed of soybean methyl ester (SME) and animal fats (AF), and diesel fuel have been studied using a wick-generated open-air laminar diffusion flame operating at atmospheric pressure. The particles were collected directly from inside the flame volume at different axial locations using the thermophoretic sampling technique and were analyzed using transmission electron microscopy (TEM) and high resolution TEM (HR-TEM). Interestingly, the results show that carbon particulates produced from several tested biodiesels have diameters significantly smaller than those produced in diesel fuel under the same experimental conditions. Within the tested biofuels, the soot from SME had the largest primary particle diameter followed by B50 SME/B50 AF, with CME having the smallest primary particle diameter. Further studies of the soot particle nanostructure were also conducted using a HR-TEM imaging technique. It was found that the soot derived from biodiesel has a highly graphitic shell-core arrangement compared to diesel soot which exhibits far less graphitic structure as it consists of short, disconnected and not concentrically oriented graphene segments. (C) 2012 Elsevier Ltd. All rights reserved.