A biosensor based upon a vertically emitting, distributed feedback (DFB) laser. The DFB laser comprises a replica-molded, one- or two-dimensional dielectric grating coated with a laser dye-doped-polymer as the gain medium. A sensor is also described in which the grating layer and the active layer are combined into a single layer. DFB lasers using an inorganic or organic thin film with alternating regions of high and low index of refraction as the active layer are also disclosed. The sensor actively generates its own narrowband high intensity light output without stringent requirements for coupling alignment, thereby resulting in a simple, robust illumination and detection configuration.