This article presents a survey of synthetic materials capable of reporting in real time by chromic transition the recognition event occurring between a specific ligand and a biomolecule such as a receptor or an antibody. The review focuses on conductive polymers and colloidal gold. Besides their mode of synthesis and coupling to biomolecules, it explores their physicochemical reactivity, emphasizing the mechanisms underlying the chromic transition occurring upon the biomolecular recognition event. The future prospects offered by composite materials based on these polymers and colloids are further discussed.