Proteins are central building blocks in living organisms. In diseases, they are frequently mutated, misfolded, truncated or their concentration is different. Accordingly, they present an important biomarker for diagnostic applications and basic research. Standard techniques for the detection of proteins use enzymatic reactions. Prominent examples are enzyme-linked immunosorbent assays (ELISA) or western blots . In both techniques, the protein analyte is bound on a surface by a capture antibody and subsequently visualized with a second antibody conjugated to an enzyme. The most common enzymes used in these reactions are horseradish peroxidase (HRP), alkaline phosphatase and β-galactosidase. They catalyze the reaction of a colorless substrate into a colored product with known absorption in the visible range of the spectrum.