Utilizing a tunable photonic crystal resonant reflector as a mirror of an external cavity laser cavity, we demonstrate a new type of label-free optical biosensor that achieves a high quality factor through the process of stimulated emission, while at the same time providing high sensitivity and large dynamic range. The photonic crystal is fabricated inexpensively from plastic materials, and its resonant wavelength is tuned by adsorption of biomolecules on its surface. Gain for the lasing process is provided by a semiconductor optical amplifier, resulting in a simple detection instrument that operates by normally incident noncontact illumination of the photonic crystal and direct back-reflection into the amplifier. We demonstrate single-mode, biomolecule-induced tuning of the continuous-wave laser wavelength. Because the approach incorporates external optical gain that is separate from the transducer, the device represents a significant advance over previous passive optical resonator biosensors and laser-based biosensors.
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