Color-sensitive and spectrometer-free plasmonic sensor for biosensing applications.

A color-sensitive and spectrometer-free sensing method using plasmonic nanohole arrays and the color components, L* , a* , and b* , of the CIELAB defined by the international commission on illumination (CIE) is introduced for the analysis of optically transparent materials in the visible range. Spectral analysis based on plasmonic nanoparticles or nanostructures can be applied to real-time bio-detection, but complex optical instrumentations and low spatial resolution have limited the sensing ability. Therefore, we take an advantage of color image processing instead of spectral analysis which induces the distinctive color information of plasmonic nanohole arrays with different transparent materials. It guarantees high spatial resolution which is essential to bio-detection such as living cells. To establish our sensing platform, the color components, L* , a* , and b* , were extracted from photo images by an image sensor, statistically processed using a JAVA program, and finally utilized as three individual sensing factors. Additionally, our study on a correlation between the spacing of plasmonic sensors and the color sensitivity to the refractive index reveals geometrically optimal conditions of nanohole arrays. The weighted mean calculation with the three individual sensing factors offers an enhanced distinction of the optical difference for transparent materials. In this work, a color sensitivity of 156.94 RIU-1 and a minimum mean absolute error of 1.298×10-4 RIU were achieved. The difference in the refractive index can be recognized up to 10-4 level with the suggested sensing platform and the signal process. This unique color-sensitive sensing method enables a simple, easy-to-control, and highly accurate analysis without complicated measurement systems including a spectrometer. Therefore, our sensing platform can be applied as a very powerful tool to in-situ label-free bio-detection fields.