Figure 12.

Cell-free systems as field-deployable biosensors. (A) To make these biosensors, cells are processed to create a lysate containing the necessary biomolecules for transcription and translation. DNA coding for the biosensor is added to the lysate as well as biochemical fuel (nucleotides and amino acids). The reaction can be lyophilized in tubes or freeze-dried on paper to create stable, portable biosensors. (B) With paper assays (top), qualitative visual outputs (purple) are used as a yes/no reporter of a given environmental conditions, such as the presence of an analyte (red) above a threshold concentration. Control reactions are used to determine if other analytes (yellow) non-specifically activate the sensor. With liquid assays (bottom), a lyophilized reaction is hydrated and analyzed with similar controls. In this approach, the output can be quantified against standards using a fluorimeter or spectrophotometer.