An intelligent microscale electrochemical device (iMED) for one-step quantitative and multiplexed electrochemical detection of biomarkers for infectious diseases and tumors is developed. A "plug-in-cartridge" technology is introduced and adapted for use in screen-printed electrodes (SPEs) in electrochemical devices. Using this iMED, biomarkers for two types of tumors and one infectious disease are detected at sub-ng/mL levels in less than 30 min.