Sandwich SERS-active Substrates For Immunoassays

Alpha fetoprotein (AFP) is an embryonic antigen tumor marker. Synthesis ofAFP occurs primarily in the liver and yolk sac of fetus. It is secreted into fetal serumand gradually declining thereafter. The normal level of AFP in adult body is lessthan20μg/L. AFP is a single polypeptide chain glycoprotein with a molecularweight of approximately70,000daltons. The physicochemical properties and aminoacid composition are similar to those of albumin. It is one of the most valuable tumormarkers of hepatocellular carcinoma and germ cell carcinoma. Therefore, thedetection of AFP has potential value for tumor prevention and clinical application.Interleukin (IL) is one kind of cytokines which is secreted by the cells to regulatecell growth, differentiation and immune activity. Interleukin-10(IL-10) is a type ofInterleukin and its molecular weight is35,000~40,000daltons. IL-10plays a veryimportant role in human bodys, such as restricting or terminating inflammation,inhibiting the inherent immunity and adaptive immunity caused by bacteria and fungi.The occurrence of many diseases are involves in IL-10. For example hepatitis c,systemic lupus erythematosus, rheumatoid arthritis and psoriasis. So it is important todevelop new methods to detect IL-10which is rapid, non-toxic and high sensitive. Inthis paper, we introduce a way based on SERS to detect IL-10and achived goodresults. (1)We prepared different size of gold and silver nanoparticles for the detection ofimmunoglobulin. By optimizing experimental conditions, we chose the proper size.After raman reporting compound mercaptobenzoic acid and antibody adsorbing ontothe surface of gold nanoparticles and bovine serum albumin blocking the residualvacant portion of the mercaptobenzoic acid-gold nanoparticles surface, we get theSERS biological tags. Then it will combine with the antigen adsorbed on to goldsubstrates by specific recognition. By this method, we detected the immunoglobulinsuccessfully.(2)“gold-proteins-gold” system used for detecting AFP and IL-10. This newsystem features a sandwich structure combining mercaptobenzoic acid-labeledimmunogold nanoparticles with the AFP or IL-10antigen and the AFP or IL-10antibody atop a pre-designed substrate made of a glass slide modified with goldnanoparticles. This SERS-based immunoassay can detect AFP concentrations as lowas100pg/ml and detect IL-10at a low level.