Figure 4: Gas phase TNT detection using Phage litmus.

(a) Two thousand and seven hundred copies of the TNT-binding receptor (WHWQ) identified by directed evolution are genetically engineered onto the surface of M13 phage (TNT phage). (b) Using the iPhone-based analysis system, TNT is detectable down to 300 p.p.b. in the gas phase. The dashed redline indicates the sensitivity limit of the TNT–Phage litmus against TNT. (c) Photos and processed colour fingerprints from the TNT–Phage litmus after TNT, DNT and MNT exposure. The TNT–Phage litmus selectively detects the target TNT (20 p.p.m.) over other molecules with similar chemical structures, such as DNT (20 p.p.m.) and MNT (300 p.p.m.). (d) PCA plot of the colour changes resulting from the exposure of the Phage litmus to TNT, DNT and MNT.