Nanoparticle tracers(PbS and CdS) were prepared according to the literature (Ding et al.,
2009; Zhu et al., 2004) by using 3-mercaptoacetic acid as a stabilizer.
Briefly, 3-mercaptoacetic acid (9.22L) was added to 50mLof 0.4mMPb(NO3)2 solution; pH was adjusted to 7 with 0.5MNaOH.
The solution was bubbled with nitrogen for 30 min, then 1.34mM Na2S was dropwise added to the mixture.