Fluorescent water soluble carbon nanoparticles, in short carbon dots (CDs), was synthesized from lactose by microwave assisted hydrochloric acid method. Characterized by TEM and DLS to obtain the morphology shape (average 10nm in size), with a higher negative surface charge supported by the composition was obtained by XPS spectroscopy. The maximum of the emission was centered at 450nm with a lifetime of 2.1ns. Without further functionalization of the CDs a nanosensor was obtained that responded exponentially to HAAs in the 0.35–0.45mgL−1 concentration range by fluorescence static quenching, demonstrated by the lifetime analysis of the CDs in presence of HAAs. Some amino compounds were selected as model for interferences to evaluate the selectivity of this method, showing a notorious added value, with recoveries around 98%. The accuracy of the method was in terms of RSD about 2.5%. The results suggest their promising applications in chemical sensing. Display omitted •Novel synthesis of fluorescent CDs from MW assisted HCl treatment.•CDs has been characterized and analyzed by DLS, XPS and fluorescence techniques.•The quenching caused by HAAs proposed analytical method.•The static mechanism was demonstrated by fluorescence lifetime analysis.•The wide range of interferences studied make suitable for sensor.