Patterned plasmonic gradient for high-precision biosensing using a smartphone reader.

Smartphone-compatible biosensors are believed to be one of the key techniques for improving the quality of diagnosis in remote areas. However, to date, few smartphone-compatible biosensors can reach the specifications of their conventional counterparts due to the limitations of consumer-grade detectors carried by phones. To circumvent this issue, we reported a metasurface-inspired bio-sensor, patterned plasmonic gradient (PPG), which transduces local index information into 2D patterns. By harnessing the powerful imaging and computational capability of modern smartphones, the PPG is sensitive enough to detect tiny refractive index changes induced by a submonolayer of molecules with high precision (Δn < 0.001) in a large dynamic range. It allows us to monitor the conjugation process between biotin and a trace amount of streptavidin (15 nM, 20 μL) in real-time. With high sensitivity and accuracy, the PPG provides a high performance bio-sensing solution for the places where professional equipment is inaccessible.