Monolayer MoS2 has attracted extensive attention owing to its promising applications in optoelectronic devices. Recently, uniform and highly crystalline monolayer MoS2 was grown through chemical vapor deposition (CVD) using seed materials as a growth promoter. However, residual seed materials can remain on the surface of a monolayer MoS2 flake on a SiO2/Si substrate after growth. Here, we observe drastically increased photoluminescence (PL) intensity at the edge of MoS2 flake where residual particles are attached after repeated laser irradiation. On the other hand, the PL intensity of pure MoS2 remained almost the same. We attribute this to the effect of p-doping of the edge MoS2 by the adsorbed H2O and O-2 molecules in the residual particles. The p-doping effect of MoS2 is confirmed by the confocal PL and Raman spectroscopy analysis. (C) 2016 Elsevier B.V. All rights reserved.