Contamination of the environment with heavy metal ions has been an important worldwide concern for decades. Among them, mercury ion (Hg^2^+) is one of the heavy metal ion maintained in the detection because of its toxicity. In this study, we have designed the gold nanoparticle (AuNP) probes of carboxylic modified protein and employed the lateral flow assay to detect the Hg^2^+ without complicated instrumentations and technical expertise. The captured AuNP probes on the test zone and control zone of the sensor produced the characteristic red bands, enabling visual discrimination of Hg^2^+ concentrations. The demand of Hg^2^+ analysis in environmental applications requires parallel analytical strategies; such a method with simplicity and rapidity has enormous potential for the application of Hg^2^+ monitoring in environment, water, and food samples.
