Surface plasmon resonance biosensing via differential spectral phase interferometry

A novel surface plasmon resonance (SPR) sensor based on differential spectral phase interferometry is introduced. Our scheme incorporates a broadband white-light emitting diode (WLED) with double-pass Michelson interferometer for highly sensitive Kretschmann SPR phase detection over the visible spectrum. Superior to laser based SPR interferometer which is vulnerable to nonlinear phase saturation and conventional spectroscopic SPR sensor which only measures the spectral intensity, the proposed spectral phase interferometer directly acquires the optimal SPR phase response of every spectral component which is equivalent to having infinitely many SPR laser interferometers operating simultaneously at fixed angle of incidence. Therefore the inherent phase saturation problem due to monochromatic laser source could be readily addressed. As the result, our system prevail over existing phase detection schemes by (1) achieving comparable ultimate detection limit as good as 10^-7 refractive index unit (RIU), (2) extending the phase measurement range as far as 10^-2 RIU, (3) simplifying the phase modulation scheme by directly acquiring the spectral oscillation instead of adding a temporal carrier. Experimental verification with BSA-aBSA interaction demonstrates that our system is capable of achieving ultimate sensitivity of 0.5ng·ml^-1 (3.3pM) for ultra-sensitive aBSA detection which is among the best reported in literature. Yet such sensitivity is extended over a wide range of measurement as each wavelength specific SPR phase jump is monitored over the entire visible spectrum. Further biosensing application such as detection of cytochrome-c with aptamer immobilized on the SPR sensing surface is currently under investigation. We believe that by combination of high sensitivity, wide dynamic range and simplicity of operation, our SPR system would be truly applicable to complicated real-life biosensing. © 2011 SPIE.