Tri-stable switch is a biological device that could perform three discrete, but alternating, steady states driven by three different repressible promoters. The presence of a transient pulse of inducer allows effective state shifting, while signal interference is prevented. In order to enhance the specificities towards inducers, improvements were made based on the Brown’s tri-stable switch model in 2006. This year, three well-characterized repressible promoters are used: phlFp, tetp, and lacp. The whole construct is divided into three parts, and each contains one functional system with two protein coding sequences (CDS), creating an interconnected tri-stable toggle switch. Moreover, mathematical modelling is applied to predict and verify the consistency of the experimental results. At present, it is by far possible and practical to apply the switch in biosensing which could be achieved by developing a combinatorial circuit of promoters and CDS. With its advantageous characteristics, it is foreseeable that the switch could be applied in a wider spectrum of fields in the near future, for example, biocomputational system and diseases diagnostic.
