This study reports the fabrication of flexible electrochemical sensors using a direct-write laser scribing process that transforms commercial polyimide sheet into graphitic carbon with self-standing porous 3D morphology, and abundant edge planes. The heterogeneous electron transfer rate (k0) of the laser scribed graphene (LSG) electrodes for both inner-sphere and outer-sphere redox mediators, ferrocyanide ([Fe(CN)6]4-) and hexaammineruthenium ([Ru(NH3)6]3+) are estimated to be 0.1150 and 0.0868 cm s-1, respectively. These values are significantly higher than those for similar carbon based materials, which this study ascribes to the binder free 3D porous network of LSG with enriched edge plane sites. Further, k0 is enhanced up to 0.2823 and 0.2312 cm s-1 for inner and outer-sphere redox mediators by selective anchoring of Pt nanoparticles over LSG. The LSG electrodes exhibit significantly improved electrocatalytic activity toward oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA). Consequently, the detection of these biomarkers is achieved with high sensitivity of 237.76 and 250.69 μA mm-1 cm-2 (AA), 2259.9 and 6995.6 μA mm-1 cm-2 (DA) and 5405 and 8289 μA mm-1 cm-2 (UA) for LSG and Pt/LSG electrodes, respectively, in a wide concentration range. These results outperform previously reported 2D/3D graphene based electrodes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.