A method for detecting albumin based on a colorimetric assay and a system thereof are disclosed. Gold nanoparticles are added into the sample preparing device having a sample without spectroscopic tags, wherein the sample without spectroscopic tags is formed as the alkaline solution to avoid the interference substances adhering on the gold nanoparticles. The gold nanoparticles are concentrated by using the microfluidic concentrator with the circular ion exchange membrane by applying an external electric field across two electrodes. The image of the concentrated gold nanoparticles is captured by the image capturing device for measuring the saturation intensities of the image, wherein there is a relation between the saturation intensities and the concentration of the albumin in the sample without spectroscopic tags. The concentration of the albumin of the sample without spectroscopic tags is obtained by the relation and the measured saturation intensities.
