C-Reaction Protein Detection in Human Saliva by Nanoplasmonic Color Imaging.

A label-free and highly sensitive imaging sensor based on plasmonic-photonic interaction in a gold-titanium dioxidegold metal-insulator-metal (MIM) plasmonic nanocup array is reported. The sensor can detect proteins and exhibits superior performance in visible light sensing. This device enables very sensitive detection of an increase in superstrate refractive index based on changes in the red channel intensity of color imaging. Compared to other conventional plasmonic sensors, our device achieves transmission imaging detection by using normal white light and minimizes instrumentation requirement. In this study, we used the device to detect C-reaction protein (CRP) level in saliva, which is widely tested to help make clinical decisions in different diseases and disorders. The intensity imaging showed a good linear response between CRP concentration (from 5 to 100 ng/mL) and relative intensity change in the device. The lowest concentration of CRP that could be detected was 5 ng/mL. Moreover, it could achieve a positive detection in saliva from patients when the CRP level in serum was 3.2 μg/mL. Owing to the high performance of the MIM plasmonic nanocup array, the proposed device is promising for future portable optical sensing with visible light illumination and imaging.