Comparing with AChE and ATCh, only TCh can induce aggregation of the LA capped AuNPs. This feature makes the colorimetric measurement of inhibitor of AChE, i.e., OPs become possible. When OPs exist in this system, it can inactivate AChE via non reversible phosphorylation even in ultra-low concentration, and consequently block the generation of TCh, further suppress TCh induce AuNPs keep dispersing. The control experiments show that sole OPs exist in the LA capped AuNPs dispersions could not result in AuNPs aggregation or color alteration (see Fig. S7 in supplementary data). That is to say, the agglomeration status of AuNPs can be indirectly controlled by the concentration of OPs in the presence of AChE/ATCh system.