Diffusion sensors for nano-sized materials dispersed in a solution are promising tools for investigating intermolecular interactions, which is an important task in a wide range of industrial and biomedical fields, such as the development of therapeutic products and diagnostic tools. For the development of the sensor applicable to point-of-care testing, an optofluidic sensor was proposed. The proposed sensor realizes a simple measurement in a short time using microscale manipulation by interferometrically-induced dielectrophoresis and optical detection. In this paper, the applicability of the proposed sensor to distinguish nanoscale differences in size was confirmed by measurements on a solution containing size-certified plain nano-beads (51 nm, 100 nm, 203 nm, 216 nm and 240 nm) with evaluating the uncertainties of the proposed sensor. Furthermore, measurements using 200-nm beads coated with functional groups (NH2 and biotin) and proteins (streptavidin and bovine serum albumin) demonstrated the applicability to the investigation of intermolecular interactions. (C) 2018 The Authors. Published by Elsevier Ltd.