Carbon nanodots (CDs) with size dependent fluorescence are synthesized from multi-walled carbon nanotubes (MWCNTs) under continuous flow in a vortex fluidic device (VFD) when irradiated by a pulsed laser with a wavelength of 1064 nm, without subsequent passivation procedures. The CDs have a relatively narrow size distribution averaging ca. 6 nm in diameter, and have low cytotoxicity and high colloidal stability with the highest emission intensity of the solution at 450 nm under a 345 nm excitation wavelength. Further downstream processing on the as-processed CDs revealed tunability of the emission from 450 nm to 325 nm.