We report a plasmonic interferometer array (PIA) sensor and demonstrate its ability to detect circulating exosomal proteins in real-time with high sensitivity and low cost to enable the early detection of cancer. Specifically, a surface plasmon wave launched by the nano-groove rings interferes with the free-space light at the output of central nano-aperture and results in an intensity interference pattern. Under the single-wavelength illumination, when the target exosomal proteins are captured by antibodies bound on the surface, the biomediated change in the refractive index between the central aperture and groove rings causes the intensity change in transmitted light. By recording the intensity changes in real-time, one can effectively screen biomolecular binding events and analyze the binding kinetics. By integrating signals from multiple sensor pairs to enhance the signal-to-noise ratio, superior sensing resolutions of 1.63×10-6 refractive index unit (RIU) in refractive index change and 3.86×108 exosomes/mL in exosome detection were realized, respectively. Importantly, this PIA sensor can be imaged by a miniaturized microscope system coupled with a smart phone to realize a portable and highly sensitive healthcare device. The sensing resolution of 9.72×109 exosomes/mL in exosome detection was realized using the portable sensing system building upon a commercial smartphone.
Keywords: Plasmonic interferometer; cancer diagnosis; exosome; optical biosensor.