Mercury detection due to harmful effects on the environment and human health is of importance. Among the reported methods, functionalized gold nanoparticles (AuNPs) due to their interesting ability for selective detection of Hg2+ have been considered. In this article, by employing full atomistic molecular dynamic (MD) simulations and quantum mechanic calculations, dynamical behavior and aggregation mechanism of the pure and 11-mecaptoundecanoic acid (MCA) functionalized gold nanoparticles (MCA-AuNPs) were investigated. MD simulation results indicate that pure AuNPs are not stable in water and aggregate due to van der Waals interactions. On the other hand, MCA groups increase the stability of AuNPs and their resistance against aggregation by elevating the repulsive interactions of the AuNPs. Moreover, MCA-AuNPs have the considerable ability for selective detection of Hg2+ in the presence of different metal ions, such as Zn2+ ,Cu2+,Ba2+,Ca2+,Cd2+,Fe2+,Mg2+,Ni2+and Pb2+. On the basis of the QM calculations, Hg2+ has a strong electrostatic interaction with the COO– groups of the MCA on the AuNPs surface. This metal ion acts as a linkage agent between the MCA-AuNPs, which facilitates the nanoparticle aggregation, through the elimination of the repulsive interactions. A good agreement between the theoretical results and experimental data indicates the importance of the theoretical methods for understanding the mechanism of ion sensing by the functionalized AuNPs, which is of great interest for designing new sensors based on gold nanoparticles.

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