Abstract

The present invention comprises a genetically-encoded fluorescent nanosensor for detecting and quantifying lactate/pyruvate ratio in different types of samples, such as biological fluids, tissues, intra-cellular, and even in subcellular compartments, with high spatial and temporal resolution, and protocols to express this nanosensor in biological samples, and its use for the detection and quantification of intracellular lactate/pyruvate ratio in intact systems, evaluation of fermentative and oxidative metabolism in simultaneous fashion, detection of lactate/pyruvate ratio in biological samples and evaluation of monocarboxylate permeability, using a non-metabolized analogue.