Objective To study the photothermal killing effect on bacteria means of the strong photothermalproperties of gold nanoparticles system (GNPs system) after responsive aggregation. Methods Synthesized peptides A andB were modified at their surface by gold nanoparticles (GNPs) through the Au-S bond reaction, and then mixed at equal Acta Lab Anim Sci Sin,June 2019,Vol. 27, No. 3proportions to form the GNPs system. First, dynamic light scattering (DLS) and transmission electron microscopy (TEM)were used to assess the responsive aggregation under weakly acidic conditions. UV absorption changes under weakly acidicconditions were measured by a multifunction microplate reader. In order to understand the photothermal conversion of thenanoparticles in the bacterial suspension, their temperature curves in the solution under weakly acidic conditions and aftertreated with bacteria were measured, respectively. Finally, the antibacterial effect was tested in vitro. Results The particlesize of the synthesized GNPs system was increased from 16 nm to 900 nm as detected by DLS under weakly acidic conditions.Obvious aggregates were observed by TEM, and the UV absorption signal was significantly increased at 650~900 nm. Underthe weakly acidic conditions of simulated bacteria, the GNPs system achieved a rapid temperature rise of the solution withmixed bacterial under laser irradiation conditions. The highest temperature was 69. 8°C, significantly different from the controlgroup of GNPs-PEG2000. The result of antibacterial experiments in vitro showed that the GNP system had the strongest killingeffect against Staphylococcus aureus, which was 50% and 100% killing of the bacteria at concentration of 50 and 200 μg/ mL,respectively, showing a significant difference compared with the control group of GNPs-PEG2000. Conclusions This study provides a new approach for the design of GNPs and a new method to apply GNPs to photothermal therapy.