Plasmonic Mach-Zehnder interferometer for ultrasensitive on-chip biosensing

Area of Science:

• Plasmonics
• Nanophotonics
• Biosensing

Background:

• Plasmonic sensors offer high sensitivity for biomolecular detection.
• Integrating plasmonic devices with microfluidics enables compact and efficient sensing platforms.
• Mach-Zehnder interferometers (MZIs) are sensitive to phase shifts, useful for detecting refractive index changes.

Purpose of the Study:

• To demonstrate a novel plasmonic Mach-Zehnder interferometer (MZI) integrated with a microfluidic chip.
• To achieve ultrasensitive, label-free optical biosensing using this integrated platform.
• To evaluate the performance of the device in terms of sensitivity and figure of merit.

Main Methods:

• Fabrication of a plasmonic MZI by patterning two parallel nanoslits in a thin metal film.
• Utilizing the phase difference between surface plasmon waves on the top and bottom surfaces of the metal film.
• Monitoring biomolecular adsorption events in real-time using optical interferometry.
• Integrating the plasmonic MZI with a microfluidic chip for sample delivery.

Main Results:

• Achieved enhanced refractive index sensitivities greater than 3500 nm/RIU.
• Obtained record high sensing figures of merit exceeding 200 in the visible region.
• Demonstrated real-time, label-free, quantitative monitoring of streptavidin-biotin binding.
• Exhibited a high signal-to-noise ratio in the biosensing experiments.

Conclusions:

• The integrated plasmonic MZI microfluidic chip is a simple, ultrasensitive, and miniaturized biosensor.
• The device significantly surpasses the performance of previous plasmonic sensors.
• The platform holds potential for further improvements through device structure optimization.