Study On Dissolution Process Of Silver Nanoparticles In Different Cell Buffers By Raman Spectroscopy

Silver nanoparticles (AgNPs), due to their broad-spectrum antimicrobial effect, are widely used in daily consumer goods as well as the medical field. However, the medical application of AgNPs get stuck in China because there are studies and reports suggesting that AgNPs may cause adverse effects on humans and the environment. It is believed that the toxicity of AgNPs is majorly due to the ionic silver released from the oxidization and dissolution of AgNPs. Thus, it's in urgent need of a careful research on the dissolving process of AgNPs in aqueous solution.In view of this, we developed a new method to continuously detect the silver ion released from AgNPs based on Surface-enhanced Raman Spectroscopy (SERS). Main contents and results are as follows:(1) Based on our previous research, the quasi-spherical citrate-stabilized AgNPs with the average size of 28.5nm were synthesized via the seed-mediated growth method. In this method, citrate-stabilized AgNPs with tunable sizes were prepared through stepwise growth process using qualified spherical 4 nm AgNPs as starter seeds. The AgNPs with the average size of 28.5nm have the highest monodispersity among synthesized AgNPs of various size.(2) With the 28.5nm citrate-capped AgNPs as object of study, we developed a reliable and reproducible SERS-based method to continuously monitor the ion release in AgNPs colloids. The procedure of this method are quite simple. At first, the AgNPs were centrifuged and redissolved with Raman signal molecule (Nile Blue A, NBA), then the sample was laid in an airtight quartz cuvette for a 24 hours Raman measurement. The Raman intensity decreased as the dissolve process went on. During the 24 hours, ion release kinetics was closely related with the Raman intensity changes in detail. The result shows that about 10.64% of total silver were released from AgNPs after 24 h. The dissolving rate of AgNPs decreased against time and approached to zero at the end of test. Besides, ICP-MS was used to precisely measure the concentration changes of released ionic silver, and further validated the reliability of this SERS-based method.(3) We tried to apply the SERS-based method to continuous detect the silver ion released from AgNPs in cell buffers such as phosphate buffer saline and HEPES. Moreover, we studied citrate-capped AgNPs as well as PVP-capped AgNPs. The result showed the SERS-based method was unable to detect silver ion released from AgNPs in phosphate buffer saline as the ionic strength led to nanoparticle aggregation. On the other hand, the SERS-based method have the potential to detect silver ion released from AgNPs in HEPES.