Rapid plasma-induced non-equilibrium electrochemistry (PiNE) at atmospheric pressure was used to prepare surfactant-free gold nanoparticles and copper oxide quantum dots. A suite of chemical and physical characterisation is carried out to assess the as-prepared materials. Nanofluids comprised of these nanoparticles in ethylene glycol have been prepared. The energy absorptive properties of the prepared nanofluids were investigated as a potential additive to the traditional working fluids used in solar thermal collectors. The application feasibility has been assessed by calculating a value of power which could be transferred to the thermal fluid. This work demonstrates an alternative and rapid method to produce nanofluids for solar thermal conversion.