Preparation of carboxylated Ag nanoparticles as a coating material for medical devices and control of antibacterial activity

Carboxyl group-donated silver (Ag) nanoparticles for coating on medical devices were prepared by a two-phase reduction system in situ. AgNO₃ was the Ag ion source, tetraoctylammonium bromide [N(C₈H ₁₇)₄Br] the phase-transfer agent, sodium tetrahydroborate (NaBH₄) the reducing agent and 10-carboxy-1-decanthiol (C ₁₁H₂₂O₂S, CDT) the capping agent. The characterizations of the Ag nanoparticles were conducted by diffuse reflectance Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric differential thermal analysis (TG/DTA) and transmission electron microscope. With CDT capped on Ag nanoparticles, we found that the band around 3,100 cm^-1 was attributed to COO-H stretching vibration, two adsorptions at 2,928 and 2,856 cm^-1 to C-H symmetric/anti-symmetric stretching vibration, and at 1,718 cm^-1 to C=O stretching vibration in the FT-IR spectra. The organic components of the carboxylated Ag nanoparticles were 5.8-25.9 wt%, determined by TG/DTA. The particle sizes of the carboxylated Ag nanoparticles were well controlled by the addition of the capping agent, CDT, into the reaction system. The antimicrobial activity of the Ag nanoparticles covered with different contents of CDT against E. coli was evaluated. Smaller-size Ag nanoparticles showed higher antibacterial activity, which depended on a surface area that attached easily to a microorganism cell membrane.