Optofluidic biolasers are an emerging tool for bio-sensing and diagnostics. However, in order to facilitate waveguiding, the most common optofluidic distributed feedback (DFB) laser design relies on high-refractive index gain materials which are usually not biocompatible. We report the realization and characterization of evanescently pumped optofluidic DFB lasers with biocompatible aqueous gain fluids. Record low pump thresholds were achieved by optimizing the mode shape in the waveguide structure. Measuring the photonic band dispersion permits to sense the refractive index of the fluidic gain material. Different biological gain materials were studied on our devices.