Tryptophan based co-polymer as Fluorescence Turn-Off sensor for explosive detection

The highly sensitive and reliable detection of explosives is of paramount importance for civilian and military security.^1,2
Here, we report the synthesis and sensing applications of a highly emissive and electron-rich tryptophan based copolymer Poly[(N,N-dimethylacrylamide)-co-(Boc-Trp-EMA)] (RP)(Φ_f=35%) which exhibited high sensitivity and selectivity towards DNT, TNT and TNP with LOD 3.39, 2.55 and 0.7μM, respectively. In solution, PL signal from RP co-polymer gets quenched upon addition of aliquots of DNT, TNT and TNP caused by photo-induced electron-transfer i.e. quantified by plotting Stern–Volmer plot (K_SV=7.6×10³,1.1×10⁴ and 3.3×10⁴ M^-1 for DNT, TNT and TNP). The quenching mechanism was further established by time-resolved PL and steady state absorption spectroscopy which was found to be predominantly dynamic in nature as lifetime of RP (2.1 ns) is reduced to 0.9, 0.8 and 1.3 ns for DNT, TNT and TNP.
To explore the possibility of using the fluorescent co-polymer as sensor array, a prototype thin film polymer sensor was fabricated using drop-casted thin film of RP which was able to detect saturated nitroaromatic vapor in real time with high selectivity. The initial PL intensity of the 20 nm thin film of RP was quenched to 19% for DNT, 13% for TNT and 4% for TNP in just 2 min.