It is well-known that citrate capped AuNPs are generally not ideal structures for investigations and internalization studies because the weak interaction between citrate and AuNPs. They are susceptible to environmentally induced aggregation and can be quite difficult to work with (Giljohann et al., 2010). Therefore, colorimetric assay based on citrate capped AuNPs has been achieved only under critical conditions. To address this problem, LA is chosen here to displace citrate on the surface of AuNPs and a satisfied phenomenon is found as expected.