Luminescent sensors for nitroaromatic compound detection: Investigation of mechanism and evaluation of suitability of using in screening test in forensics

Environmental and safety concerns have obliged efforts to detect nitroaromatic compounds (NACs), including the use of luminescent sensors. Photoinduced Electron Transfer (PET) has been generally accepted as the main sensing mechanism which would imply its use in highly selective sensors. However, the contribution of different mechanisms, such as the Inner Filter Effect (IFE), which can also play a very important role in these sensors, has been neglected. The proposal of this work is to provide a survey of some luminescent sensors, addressing their quenching mechanisms and the misconceptions related to them. In addition, these sensors were tested for forensic screening to see if they are suitable for primary detection of explosives in cases of suspicion of explosive handling. For this purpose, three luminescent sensors, which have been claimed to be selective and have PET, were tested and used as probes: amine capped CDot (1S), [Eu2(BDC)3(H2O)2]·(H2O)2 (2S), and [Tb(BTC)]n (3S). UV/vis and time-dependent measurements, as well as corrected Stern Volmer plots, were used to demonstrate that the PET is not the main quenching mechanism in the 1S. Besides, simple experiments (using a 1 mm cuvette and two cuvettes) proved that the IFE is the main mechanism responsible for quenches quenching the luminescence in all three sensors. Finally, the suitability of these sensors for use in a screening test to detect explosives was evaluated, where false positive results are not desirable. We observed that common products, such as cosmetics, may cause those false positives results. One interferer in particular reduced luminescence of all sensors by about 55%. Consequently, these systems cannot be considered suitable to be used as a screening test for explosive handling. [Display omitted] •Investigation of misconceptions about luminescent sensors for NAC detection•PET is one of the most cited mechanisms of luminescence decrease.•Three different sensors, supposedly presenting PET, were tested.•IFE was proved to be the main mechanism instead of PET.•In screening tests, sensors governed by IFE do not meet the selectivity requirements.