[en] A colorimetric assay is described for acrylamide (AA). It is based on color changes induced by an increase in the distance between gold nanoparticles (AuNPs) that is caused by AA copolymerization. First, AuNPs were modified with a thiolated propylene amide poly(ethylene glycol) that also contains the AA functionality. The carbon-carbon double bonds on the modified AuNPs can be polymerized under the catalysis of a photoinitiator and under UV irradiation. This results in the aggregation of the AuNPs and in a color change from red to gray. In the presence of AA, the distance between the AuNPs increases due to copolymerization with AA, and the solution of AuNPs preserves its original red color. Under optimized conditions, the absorption ratio (A₅₂₅/A₇₄₀) of the solution increases linearly in the 1 nM to 10 μM free AA concentration range, with a 0.2 nM limit of detection. Hence, the method meets the need for rapid monitoring of trace AA in food. The method has a relative error (RSD) that is lower compared to the accepted HPLC method. .