The electrosynthesis of a novel polyquinone film onto laser induced graphene (LIG) substrates is presented as a sensitive and scalable route to the production of thiol sensors. The one pot electroreduction of 5-nitro-1,4-naphthoquinone and subsequent electro-oxidation of the resulting amine was found to yield polymeric films consisting of repeating 1,4-naphthoquinone units. The resulting film exhibited electrochemically reversible behaviour (E^o = -0.1V at pH 7 (vs 3M NaCl Ag/AgCl) and found to exhibit a pH sensitivity of 61 mV / pH unit. The quinone groups within the film were found to react with cysteine (as a model thiol biomarker) through conventional 1,4-Michael addition resulting in the covalent modification of the film and the generation of new discrete redox entities. The voltammetric signature of the latter enabled interference free measurement of cysteine concentration at -0.42V with a detection limit of 5.2 mM. This contrasts the response to cysteine at unmodified LIG substrates where a detection potential of +0.55V was required and suffered inevitable interference from other species common to biofluids (i.e. tyrosine). The electrode mechanisms have been elucidated and the nature of the reaction with cysteine investigated using electrochemical and surface characterization techniques. The sensing performance of the polyquinone film towards cysteine is place in context with alternative electrode modifications.