Spectrometer-Free Plasmonic Biosensing with Metal-Insulator-Metal Nanocup Arrays.

The development of high performing and accessible sensors is crucial to future point-of-care diagnostic sensing systems. Here, we report on a gold-titanium dioxide-gold metal-insulator-metal plasmonic nanocup array device for spectrometer-free refractometric sensing with a performance exceeding conventional surface plasmon resonance sensors. This device shows distinct spectral properties such that a superstrate refractive index increase causes a transmission intensity increase at the peak resonance wavelength. There is no spectral shift at this peak and there are spectral regions with no transmission intensity change, which can be used as internal device references. The sensing mechanism, plasmon-cavity coupling optimization, and material properties are studied using electromagnetic simulations. The optimal device structure is determined using simulation and experimental parameter sweeps to tune the cavity confinement and the resonance coupling. An experimental sensitivity of 800 ΔT%/RIU is demonstrated. Spectrometer-free, imaged-based detection is also carried out for the cancer biomarker carcinoembryonic antigen with a 10 ng/mL limit of detection. The high performance and distinct spectral features of this metal-insulator-metal plasmonic nanocup array make this device promising for future portable optical sensing systems with minimal instrumentation requirements.