In the suspension plasma spray, nanosized particles are suspended in a liquid and the suspension is injected into the plasma to deposit coatings. The structure of the highly branched solid aggregates has significant influence on the microstructure and performance of the coating. In this paper, we investigate the formation of branched nanoparticle aggregates resulting from the evaporation of nanofluid droplets. A kinetic Monte Carlo (KMC) approach is used to simulate the drying process of a nanofluid droplet in a circular domain. It is found that the two-dimensional lattice-gas-based Monte Carlo model can describe the self-assembly of nanoparticles into a highly branched solid aggregate. The results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The results also show that the initial chemical potential of boundary and the rate of chemical potential change have significant influence on the resulting patterns and the finger number.