This paper aims to introduce a new nonlocal rod model for studying axial vibrations of hetero-junction CNTs (HJCNTs). The proposed model takes the connecting region of HJCNTs into account and is identically applicable to other carbon nanostructures such as uniform CNTs and nano cones. The equation of motions is derived based on the nonlocal elasticity theory and the frequencies and mode shapes are obtained by an analytical approach. The effects of the nonlocal parameter, the elastic ratios and the connecting region on the axial frequency are studied. Moreover, it is shown that, the axial vibration behavior of a cantilever HJCNT can be used in mass sensors. The effects of nonlocal parameter, the mass of attached particles and the length of structure on the frequency shift are investigated in detail. It is found that like the nonlocal parameter, the effect of connecting region on the frequency, especially for small lengths, is significant and cannot be ignored. Also, the results indicate that HJCNTs have higher axial frequencies than the uniform CNTs and due to having higher frequency shift, provide a higher sensitivity when used as nanomechanical mass sensors. Hence, HJCNTs can be used as novel mass nanosensors when they are in axial vibration.

Keywords