Optical investigations on ATP-induced aggregation of positive-charged gold nanoparticles

With the aids of localized plasmon resonance absorption and light-scattering measurements in this contribution, we investigated the aggregation of cetyltrimethylammonium bromide (CTAB) capped gold nanoparticles (AuNPs) in the presence of adenosine triphosphate (ATP). It was found that gradual aggregation of AuNPs occurs under physiological conditions with increasing ATP concentration from 200.0 to 400.0 μM, but the aggregates get dispersed again with much more increase of ATP concentration than 800.0 μM, corresponding with the color change from red to blue and to red again. Mechanism investigations showed that the aggregation of the AuNPs is likely induced by two interaction modes. One is the electrostatic interaction between the phosphate anions associated with the ATP and AuNPs owing to the cationic surfactant on the surfaces of AuNPs, and the other is the interaction between gold atom and nitrogen-containing bases. Further investigations showed that this aggregation mechanism could extend to the interactions between positively charged AuNPs with other analogs of ATP, such as guanosine triphosphate (GTP) and cytidine triphosphate (CTP).