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Towards the Developmentof a Low-Cost Device for the Detection of Explosives Vapors by Fluorescence Quenching of Conjugated Polymers in Solid Matrices

Martelo, L. M. ; Pimentel das Neves, T. ; Figueiredo, J. ; Marques, L. ; Fedorov, A. ; Charas, A. ; Berberan-Santos, M. ; Burrows, H.

Sensors Vol. 17, Nº 11, pp. 2532 - 13 pages, November, 2017.

ISSN (print): 1424-3210
ISSN (online): 1424-8220

Journal Impact Factor: 2,033 (in 2015)

Digital Object Identifier: 10.3390/s17112532

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Abstract
Conjugated polymers (CPs) have proved to be promising chemosensory materials
for detecting nitroaromatic explosives vapors, as they quickly convert a chemical interaction
into an easily-measured high-sensitivity optical output. The nitroaromatic analytes are strongly
electron-deficient, whereas the conjugated polymer sensing materials are electron-rich. As a result,
the photoexcitation of the CP is followed by electron transfer to the nitroaromatic analyte, resulting
in a quenching of the light-emission from the conjugated polymer. The best CP in our studies was
found to be poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2). It is photostable, has a good
absorption between 400 and 450 nm, and a strong and structured fluorescence around 550 nm.
Our studies indicate up to 96% quenching of light-emission, accompanied by a marked decrease
in the fluorescence lifetime, upon exposure of the films of F8T2 in ethyl cellulose to nitrobenzene
(NB) and 1,3-dinitrobenzene (DNB) vapors at room temperature. The effects of the polymeric matrix,
plasticizer, and temperature have been studied, and the morphology of films determined by scanning
electron microscopy (SEM) and confocal fluorescence microscopy. We have used ink jet printing
to produce sensor films containing both sensor element and a fluorescence reference. In addition,
a high dynamic range, intensity-based fluorometer, using a laser diode and a filtered photodiode was
developed for use with this system.