Light induced pH cycle : a non invasive method to control biochemical reactions Background Many biochemical reactions depend on the pH of their environment and some are strongly accelerated in an acidic surrounding. A classical approach to control biochemical reactions non invasivly is by changing the temperature. However if the pH could be controlled by optical means using photo active chemicals this would mean to be able to accelerate suitable biochemical reactions. Optically switching the pH can be achieved by using photoacids. A photoacid is a molecule with a functional group that releases a proton upon irradiation with the suitable wavelength acidifying the environmental aqueous surrounding. A major goal of this work was to establish a non invasive method of optically controlling the pH in aqueous solutions offering the opportunity to enhance the known chemical reactions portfolio. To demonstrate the photo switchable pH cycling we chose an enzymatic assay using acid phosphatase which is an enzyme with a strong pH dependent activity. Results In this work we could demonstrate a light induced reversible ...