Optimized miniature bio and chemical sensing system

A miniature surface plasmon resonance system for bio and chemical sensing is described based on several improvements in the substrates and the reading methodology. Recently we have developed several novel evanescent wave configurations that improve the performance of these sensors: (i) a self-referenced sensor based on enhanced optical transmission through metal nanoslits, (ii) a self-referenced ultra-large penetration depth SPR sensor, (iii) a TIR sensor in which the angular edge is converted into a dip with high figure of merit, (iv) a self-referenced SPR sensor based on thin dielectric grating on top of thin metal film, and (v) enahnced sensitivity by combining the metal film with high index dielectric layers. The self-referencing provides a more stable measurement compensated for thermal drifts and optomechanical instabilities, thus enabling a better detection limit. High penetration helps in detecting large bioentities more reliably such as bacteria and cells. Figure of merit is defined as the ratio between the sensitivity to the width of the resonance dip, hence its enhancement also improves the detection limit. Combining all these properties in one system together with a compact reading methodology using our diverging beam approach with unique image processing allows refractive index sensing limits down to 10^-8. The system is provided with a built in software that monitors the refractive index or concentration in solutions continuously with response time as short as 16msec.