Study of optical phase transduction on localized surface plasmon resonance for ultrasensitive detection.

Localized surface plasmon resonance (LSPR) has shown its remarkable applications in biosensing, bioimaging, and nanophotonics. Unlike surface plasmon polariton (SPP), the current studies regarding LSPR as biosensor were restricted in probing the extinction spectra, and thus limit the performance in biosensing and bioimaging. Here, we reveal that optical phase of LSPR provides an acute change at resonance beyond extinction spectra, which permits an ultra-high sensitivity in phase interrogation. We found that optical phases of LSPR show two orders of magnitude higher sensing resolution than extinction spectra among the same nanostructures. For the first time, we demonstrated the feasibility of probing optical phase transduction in LSPR for biosensing, and the sensitivity is superior to not only the extinction spectra among the same metallic nanostructures, but also the LSPR sensors among the current literatures. In summary, the exploitation of LSPR by phase interrogation essentially complements the sensitivity insufficiency of LSPR, and provides new access to understanding and using the rich physics of LSPR.