Biosensors bring together the fields of protein engineering, fluorescence imaging and cell biology to offer a rich and colourful toolbox capable of probing complex biological systems in order to understand the mechanism(s) underlying complex processes such as learning and memory.  Synaptic plasticity, or the ability of neurons to alter  their sensitivity to a neurotransmitter/signal (Long Term Potentiation; LTP), is the process that is thought to govern learning and memory. Glutamate has been at the centre of biosensor development in the study of LTP; however, recent results suggest that LTP is closely regulated by the interplay between glutamate and other amino acid neurotransmitters, such as d-serine, glycine and arginine). The ultimate goal of this study is to use biosensors to observe, in vivo, the spatial and temporal distribution of these neurotransmitters during LTP. Using a combination of protein engineering techniques such as ancestral reconstruction, circular permutation and rational design with fluorescence imaging methods such as fluorescence intensity and FRET, a family of biosensors with specificity for the key amino acid neurotransmitters (Glu, D-Ser, Gly and Arg) is being constructed to allow monitoring of LTP. Deconvolution of the interplay of these neurotransmitters will allow for the construction of an accurate model, giving a platform to study and better interpret aberrant systems that could potentially occur in neurological disorders.