Abstract: A microfluidic device for on-site quantitative detection of marijuana in body fluids has a body fluid collecting reservoir for receiving a body fluid and an anti-THC antibody reservoir that retains anti-THC antibodies. A first micromixer receives the body fluid from the body fluid collecting reservoir and the anti-THC antibodies from the anti-THC antibody reservoir to form a sample mixture. The device further comprises a fluorescein-THC conjugate reservoir that fluorescein-THC conjugate; a second micromixer that receives the sample mixture and the fluorescein-THC conjugate to form a test mixture; and at least one light source to emit an excitation wavelength and at least one detector to receive an emission wavelength.