This work describes a new class of gold nanoparticle-based liquid-phase colorimetric assay (GNP-LPCA) termed as two dimensional (2D) GNP-LPCA. Its utility is demonstrated with the development of an aptamer-based 2D GNP-LPCA for simple, low-cost, sensitive, specific, and quantitative detection of adenosine as a model analyte in buffer and human serum samples with the naked eye.