Plasmonic Interferometric Biosensors for High-Performance Label-Free Biomolecular Detection

Compared to the conventional prism-based surface plasmon resonance (SPR) biosensor, plasmonic biosensors employ a significantly simpler collinear transmission geometry, and offer promising opportunities for system miniaturization and high-throughput multiplexing sensing. Here, we investigate a class of plasmonic interferometric biosensors that consist of arrays of circular aperture-groove nanostructures patterned on a gold film. The phase and amplitude of interfering surface plasmon polaritons (SPPs) in the proposed device can be effectively engineered by structural tuning, generating spectral fringes with high contrast, narrow linewidth, and large amplitude, which results in sensitive detection of protein surface coverage as low as 0.4 pg/mm². This sensor resolution compares favorably with commercial SPR systems (0.1 pg/mm²), but is achieved using a significantly simpler collinear transmission geometry, a miniaturized sensor footprint, and a low-cost compact spectrometer, showing great promise to develop fast, inexpensive, compact biomedical devices for personal healthcare.

Besides the enhanced sensor performance using a spectral measurement, the intensity-based sensing scheme can be easily combined with CCD imaging to advance our sensor platform for scalable high-throughput multiplexing detections. Therefore, we further demonstrate superior sensor performance of this plasmonic interferometric biosensor using intensity interrogation method, which incorporates CCD imaging for high-throughput multiplexing sensing. A novel low-background interferometric sensing scheme yields a record high sensing figure-of-merit of 146 in the visible region, surpassing previous plasmonic biosensors and facilitating ultrasensitive high-throughput detection.

On the other hand, detecting surface analyte binding in complex solutions remains challenging due to the difficulty of distinguishing the interaction of interest from background interfering effects, especially in the multi-component solutions commonly encountered in food safety, environmental, and medical applications. The background refractive index is unknown and time-varying due to changes in temperature and concentration of non-specific components. Therefore, it is highly desirable to differentiate the surface biomolecular binding from background changes. Thanks to different penetration depths of SPPs at multiple interference peaks and valleys, we present, for the first time, a plasmonic biosensor platform that can differentiate surface interactions from interfering bulk effects in a single sensing channel, finding solid applications in the measurement of a target analyte in complex unknown background media (e.g. blood samples).

fjb205@lehigh.edu