Whispering gallery mode microresonators: results on aptasensors and on a new sensing approach

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We present results on the implementation of Whispering Gallery Modes (WGM) biosensors and on the demonstration of a new detection method for WGM based sensors. We first present a functionalization procedure based on the DNA-aptamer sequence immobilization on WGM resonators, able to recognize specifically thrombin protein. The protein binding was optically characterized in terms of specificity in buffer solution and in 10% diluted human serum. When performing the above measurements, we have used the typical detection scheme for WGM resonator based sensors, which relies on tracking the resonance shift − by scanning with a tunable laser − when a change of the refractive index in the region probed by the WGM takes place. In the second part of the presentation we propose a new sensing approach based instead on monitoring the position of the laser line of a fiber ring laser having a WGM microsphere in its loop. We demonstrate that the induced shift is the same for the ring laser line and for the microsphere resonance. The proposed method requires simpler and cheaper equipment and may also improve the sensor resolution because the ring laser line is narrower than the microsphere WGM resonance.