The rapid, point-of-care detection of copper in plasma can greatly aid in a large number of diseases where copper has been implicated to be an important factor, such as cancer, Alzheimer's and Diabetes mellitus. Localized surface plasmon resonance (LSPR) technologies show promise in the inexpensive detection of copper, whereas previous platforms are plagued with selectivity and sensitivity issues. Herein, we have created a sensitive and selective on-chip copper sensor which can produce a colorimetric reading in 60 minutes. The selectivity of the assay is based on 'Click' chemistry and is shown to have little interference with other metal ions present in plasma. The sensitivity of the assay is generated from the coupling of the molecular resonance of a dye and the LSPR of the gold nanoparticles. The assay is capable of measuring copper concentrations in human plasma as low as 4 μM and the linear range of sensitivity, 4 to 20 μM, is in the physiologically relevant range. This robust, colorimetric assay should prove useful in a point-of-care setting.