Quantum dot material for the detection of explosive-related chemicals

Abstract

Changes in the fluorescence of semiconductor nanocrystals were explored as a potential sensing mechanism for the detection of chemicals associated with landmines, IEDs and HME materials. A series of quantum dots (QDs) with fluorescence emissions spanning the visible spectrum was investigated using the Stern-Volmer relationship, specifically measuring the effect of quencher concentration on QD fluorescence intensity and photo-excited lifetime. The series of QDs was investigated with respect to their ability to donate excited-state electrons to an electronwithdrawing explosive related compound (ERC). Electron transfer was monitored by observing the steady-state fluorescence signal and the excited-state lifetimes of the QDs in the presence of ERC1. Increased sensitivities of QDs towards ERC1 were observed as the size and emission wavelength of the QDs decreased. As the QDs size decreased, the Stern-Volmer quenching constants increased. The larger QD exhibited the lowest Ksv and is thought to be quenched by a purely static quenching mechanism. As QD size decreased, an additional collisional quenching mechanism was introduced, denoted by a non-linearity in the quenching-vs-concentration Stern-Volmer plot. Increases in quenching efficiency were due to increased excited-state lifetimes, and the introduction of a collisional quenching mechanism. The quenching constant for the smallest QD was approximately an order of magnitude higher than those of similarly evaluated commercially available fluorescent polymers, suggesting that QDs could be exploited to develop sensitive detectors for electron-withdrawing compounds such as nitroaromatics.