Functional gold nanoparticles for optical affinity biosensing.

Functional gold nanoparticles (AuNPs) are commonly used to enhance the response of optical affinity biosensors. In this work, we investigated the effect of preparation conditions on functional properties of AuNPs functionalized with antibody (Ab-AuNPs), specifically AuNPs with antibody against carcinoembryonic antigen (CEA) covalently attached via carboxy-terminated oligo-ethylene thiolate linker layer. The following parameters of preparation of Ab-AuNP have been found to have a significant effect on Ab-AuNP performance in affinity biosensors: the time of reaction of activated AuNPs with antibody, concentrations of antibody and amino-coupling reagents, and composition of immobilization buffer (molarity and salt content). In contrast, pH of immobilization buffer has been demonstrated to have only a minor influence. Our experiments showed that the Ab-AuNPs prepared under optimum conditions offered a binding efficiency of Ab-AuNPs to CEA as high as 63%, which is more than 4 times better than the best efficiencies reported for similar functional AuNPs so far. We employed these Ab-AuNPs with a surface plasmon resonance (SPR) biosensor for the detection of CEA and showed that the Ab-AuNPs enhanced the sensor response to CEA by a factor of 1000. We also demonstrated that the Ab-AuNPs allow the biosensor to detect CEA at concentrations as low as 12 and 40 pg/mL in buffer and 50% blood plasma, respectively.