Gold Nanorod Array Biochip for Label-Free, Multiplexed Biological Detection.

Gold nanorod (GNR) based label-free sensing has been attractive due to its unique property of localized surface plasmon resonance (LSPR). Compared to bulk gold, the SPR of GNRs is more sensitive to the refractive index change caused by biological binding in the close proximity. Numerous studies have reported biological detection in solution based GNR probes. However, the biosensing has the intrinsic problems of fluctuating readings and short storage time due to nanoparticle aggregation. In contrast, a chip-based nanorod biosensor is a more robust and reliable platform. We have developed a nanoplasmonic biosensor in a chip format by immobilizing functionalized GNRs on a (3-mercaptopropyl)trimethoxysilane modified glass substrate. The covalent Au-S bond ensures a strong GNR deposition on the substrate. This biochip exhibits a high sensitivity and stability when exposed to physiological buffer with high ionic strength. Another advantage of GNR as optical transducer is its LSPR peak dependence on the aspect ratio, which provides an ideal multiplexed detection mechanism. GNRs of different sizes that exhibit distinct SPR peaks are combined and deposited on designated spots of a glass substrate. The spectral shift of the respective peaks upon the biological binding are monitored for simultaneous detection of specific analytes. Coupled with a microplate reader, this spatially resolved GNR array biochip results in a high-throughput assay of samples as well as multiplexed detection in each sample. Since most biological molecules such as antibodies and DNA can be linked to GNR using previously reported surface chemistry protocol, the label-free nanosensor demonstrated here is an effective tool for protein/DNA array analysis, especially for detection of disease biomarkers.