A novel spectroscopic sensor based on an optofluidic liquid jet waveguide is presented. In this device, a liquid jet waveguide is generated with the solution under analysis. This stream, exploiting total internal reflection, acts as an optical waveguide confining the autofluorescence light produced by chemical or biological samples when opportunely excited. Using a self-aligned configuration, the liquid jet is directly coupled with a multimode optical fiber collecting the fluorescence towards the detection system. Experimental measurements have been performed using an UV excitation source on water solutions containing representative water pollutants as aromatic hydrocarbons or bacteria showing very low limit of detection.