Systems and methods are provided for detecting and quantitating one or more compounds or molecules in a sample. An aptamer-based point-of-care device (such as a strip) is described for rapid detection of target molecules such as the cancer marker p-glycoprotein (Pgp). Fluorescent molecules or gold nanoparticles may be used to detect the binding between a target molecule and the aptamer. By way of example, fluorescence resonance energy transfer (FRET) or Dynamic Light Scattering (DLS) may be used for detecting the physical and/or chemical changes caused by the binding of the aptamers to the target molecules.