An automated microfluidic bioreactor device and methods to rapidly detect drugs of abuse from human sweat are provided. The bioreactor can perform either single-plexed measurements (detecting only one target analyte at a time) or multiplexed measurement (detecting multiple analytes simultaneously). The bioreactor device has a cartridge comprising a capillary array that employs competitive enzyme-linked immunosorbent assay (ELISA) to detect the presence of various drugs or metabolite compounds. For example, four common drugs, methadone, methamphetamine, amphetamine, and tetrahydrocannabinol, were detected rapidly and quantitatively in about 16 minutes with a low sweat sample volume (about 4 μL per analyte) and a large dynamic range (methadone: 0.0016 ng/mL-1 ng/mL; METH: 0.016 ng/mL-25 ng/mL; amphetamine: 0.005 ng/mL-10 ng/mL; THC: 0.02 ng/mL-1000 ng/mL).