3D printing is the most popular form of additive manufacturing, and conductive 3D-printed platforms have been recognized as an emerging class of devices with high potential for electrochemistry. Nevertheless, as-printed electrodes provide poor conductivity due to the presence of high amounts of insulating thermoplastic material, requiring surface post-treatments to enhance their electrochemical performance. Such treatments often employ non-eco-friendly, costly, and time-consuming protocols. In this regard, we propose, for the first time, a sub-minute (around 50 s) and reagentless surface treatment of carbon-black/PLA-based 3D-printed electrodes using a Photo-Thermal approach by a CO2 laser. After the proposed treatment (optimized conditions: the power of 6.2%, the scan rate of 20 mm s−1, and height of 10 mm), a marked improvement in the electrochemical electrode response (current increase and peak-to-peak separation) was achieved towards the detection of catechol, ascorbic and uric acids, paracetamol, hexaammineruthenium(III) chloride, and Ferri/ferrocyanide redox couple. The enhanced simultaneous determination of Cd2+, Pb2+, and Cu2+ was also demonstrated. As a proof-of-concept, the quantification of the adulterant paracetamol in a real seized cocaine sample was performed using a fully 3D-printed electrochemical system, and a good recovery value of 97.8% was acquired. To explain all the improved results, the electrode was carefully characterized by imaging, spectroscopic and electrochemical techniques. Additionally, the between-measurement % relative standard deviation (%RSD) was 6.8% (n = 12), while the between-device %RSD was 7.5% (n = 6) at the 1 µmol L-1 paracetamol, indicating adequate manufacturing reproducibility. Thus, the strategies developed here open up new possibilities for applications of carbon-based 3D-printed electrodes in analytical electrochemistry.