A monolithic active optical resonator biosensor is fabricated for label-free sensing. The all-polymer sensor consists of a polymer distributed feedback (DFB) laser and a hydrogel recognition layer. Specific binding of analyte modulates the effective refractive index, shifting the laser emission wavelength. Real time detection of avidin–biotin interactions is demonstrated as a model for the new label-free biosensing principle. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.