Insightful understanding of size-dependent optical signatures and precise regularity of nanosensors is critical for developing applications of plasmonic sensing. This work presents a systematic study on localized surface plasmon resonance (LSPR)-based nanosensors of plasmonic silver nanocubes (AgNCs) with the edge lengths of 59.84 +/- 7.97 nm (no. 1 AgNCs), 75.70 +/- 9.05 nm (no. 2 AgNCs) and 110.32 +/- 14.63 nm (no. 3 AgNCs), respectively. The effects of different sizes on the scattering signatures and refractive index (RI) sensitivities of AgNCs were in situ determined using the multi-model co-localization approach of single AgNC by dark-field microscope (DFM), LSPR spectroscopy and scanning electron microscopy (SEM). The scattering light colour of single AgNC took place bathochromic shift from monocolour to multicolour with the growth of edge length of single AgNC. The LSPR scattering spectra of no. 1 and 2 AgNCs exhibited singlet and singlet with the shoulder peak from quadrupolar resonance mode, respectively. Compared with the scattering signatures of no. 1 and 2 AgNCs, the interesting LSPR effect of plasmon line shape with two distinct peaks was observed on single no. 3 AgNC. In situ studies on the scattering spectral response of single AgNC to the ambient solvents and probing the small-molecule adsorbates on the surface of single silver nanocube reveal that no. 2 AgNC is more suitable as nanosensor due to strong regularity and higher sensitivity. The mechanism involved in optical signatures was elaborated clearly by combining with the experiments and theoretical simulation. (C) 2020 Elsevier Inc. All rights reserved.