2.1.4 CFPS component identification
In addition to the recognition mechanism mentioned above, there is another recognition mechanism that utilizes the cell-free translation system. So far, this mechanism has only been applied to amino acid detection. The design of a cell-free system selectively removes a specific amino acid, and it then adds the sample, which contains missing components from the system, such as amino acids in the patient’s plasma sample [40] (Fig. 2D). Aminoacyl-tRNA synthase can be used as a recognition element to identify the amino acid in the sample and then produce aminoacyl tRNA. After the CFPS system is complete, the translation machinery is activated to produce protein output. Janget al . [41] used this principle to design cell-free biosensors to detect amino acids. This cell-free biosensor not only can accurately detect the amino acid content in the sample but also has a high sensitivity.
In addition to using the recognition mechanism of the cell-free translation system, most of the recognition mechanisms are encoded in the genetic circuit and then added to the cell-free hybrid system for characterization. Because the CFPS system can regulate the complex genetic circuits, it is possible to design a variety of recognition mechanisms for the detection of cell-free biosensors. This extends the types, levels, and ranges of target analytes to be detected.