How to get bigger spectral responses to biochemical signals?
Despite the plethora of genetically encoded indicators for various biochemical signals, such as Ca2+, cyclic nucleotides, phosphorylation or protein protein associations, the maximal optical changes are often modest that is, typically 1050% changes in the ratio of intensities at two wavelengths. Larger responses are often obtainable from indicators in which fluorescent proteins have been split into two fragments and shuffled together with sensor domains21,22,23. However, these chimaeras are generally subject to pH interference and change their intensity in a wavelength-independent manner. Such wavelength-independent responses are subject to many more artefacts than responses in which signals at two wavelengths respond in opposite directions. The ‘glass ceiling’ on the dynamic range of the response might, in part, be because ratio changes of 1020% are enough to enable biological experiments to be carried out in cultured cells. Once this threshold is attained, junior scientists find them
