Control of monoclonal antibody (mAb) concentrations in serum is important for maintaining the safety and efficacy of these lifesaving therapeutics. Point-of-care (POC) quantification of therapeutic mAbs could ensure that patients have effective mAb levels without compromising safety. This work uses mimotope-functionalized microporous alumina affinity membranes in vertical flow assays for detection and quantitation of therapeutic mAbs. Selective capture of bevacizumab from 1000:1 diluted serum or plasma and binding of a fluorescently labelled anti-human IgG secondary antibody enable fluorescence-based analysis of bevacizumab at its therapeutically relevant concentration range of ～50-300?μg/mL. The assay results in a linear relationship between the fluorescence intensity of the antibody capture spot and the bevacizumab concentration. A simple prototype microfluidic device containing these membranes allows washing, reagent additions and visualization of signal within 15?min using a total of 5?mL of fluid. The prototype devices can monitor physiologically relevant bevacizumab levels in diluted serum, and future refinements might lead to a POC device for therapeutic drug monitoring.