Surface functionalization of graphite-encapsulated gold nanoparticles for multiple biomedical applications using RF plasma

Gold nanoparticle has attracted extensive attentions due to its special optical properties and less toxicity and multiple consequent biomedical applications such as biosensors, bioimaging, tumor treatment and immunoassays diagnosis. They are usually synthesized and capped in chemical ways. In the present work, we report a new convenient physical method as an alternative one to fabricate the graphite-encapsulated gold nanoparticles by employing the dc arc discharge. The discharge current and voltage was 100-120 A and 20-30 V, respectively. Several graphene layers covering the gold nanoparticles make the gold core more stable and through which bonding with various functionalities can be easily established due to the compatibility of carbon. To immobilize biomolecules onto the surface of nanoparticles, we performed the surface functionalization of nanoparticles by using the radio frequency inductively coupled ammonia plasma. A typical plasma condition was 50 Pa in gas pressure, and 80 W in RF power. HR-TEM, XRD, SEM, XPS and UV-Vis were performed to characterize the nanoparticles, part of the results as reported earlier showed the graphite-encapsulated gold nanoparticles have been fabricated successfully with a uniform size distribution ranging from 15 to 35 nm in diameter. Several gold and graphite crystallite structures were observed. Carbon, oxygen, gold and nitrogen chemical components were analyzed by the XPS measurement. Amino groups' introduction onto the surface of the particles has been demonstrated. Relationship between population of the amino groups and plasma exposure duration has been studied. The absolute population of amino groups grafted onto the surface of the nanoparticle has also been calculated recently using sulfosuccinimidyl 6-[3A(2-pyridyldithio)-propionamido] hexanoate(sulfo-LC-SPDP) reaction protocol. Other functionalities beside amino group, for instance, -COOH, are also in consideration by corresponding plasma treatment. It is considered that our robust graphite-encapsulated gold nanoparticles are promising to be used for different biomedical purposes, after being functionalized and immobilized by the biomolecules of interest.