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Low Dose Detection of γ Radiation via Solvent Assisted Fluorescence Quenching
journal contribution
posted on 2014-04-02, 00:00 authored by Ji-Min Han, Miao Xu, Brian Wang, Na Wu, Xiaomei Yang, Haori Yang, Bill J. Salter, Ling ZangDevelopment
of low cost, easy-to-use chemical sensor systems for
low dose detection of γ radiation remains highly desired for
medical radiation therapy and nuclear security monitoring. We report
herein on a new fluorescence sensor molecule, 4,4′-di(1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl
(DPI-BP), which can be dissolved into halogenated solvents (e.g.,
CHCl3, CH2Cl2) to enable instant
detection of γ radiation down to the 0.01 Gy level. The sensing
mechanism is primarily based on radiation induced fluorescence quenching
of DPI-BP. Pristine DPI-BP is strongly fluorescent in halogenated
solvents. When exposed to γ radiation, the halogenated solvents
decompose into various radicals, including hydrogen and chlorine,
which then combine to produce hydrochloric acid (HCl). This strong
acid interacts with the imidazole group of DPI-BP to convert it into
a DPI-BP/HCl adduct. The DPI-BP/HCl adduct possesses a more planar
configuration than DPI-BP, enhancing the π–π stacking
and thus molecular aggregation. The strong molecular fluorescence
of DPI-BP gets quenched upon aggregation, due to the π–π
stacking interaction (forming forbidden low-energy excitonic transition).
Interestingly the quenched fluorescence can be recovered simply by
adding base (e.g., NaOH) into the solution to dissociate the DPI-BP/HCl
adduct. Such sensing mechanism was supported by systematic investigations
based on HCl titration and dynamic light scattering measurements.
To further confirm that the aggregation caused fluorescence quenching,
a half size analogue of DPI-BP, 2-phenyl-1H-phenanthro[9,10-d]imidazole (PI-Ph), was synthesized and investigated in
comparison with the observations of DPI-BP. PI-Ph shares the same
imidazole conjugation structure with DPI-BP and is expected to bind
the same way with HCl. However, PI-Ph did not show fluorescence quenching
upon binding with HCl likely due to the smaller π-conjugation
structure, which can hardly enforce the π–π stacking
assembly. Combining the low detection limit, fast and reversible fluorescence
quenching response, and low cost of halogenated solvent composites,
the sensor system presented may lead to the development of new, simple
chemical dosimetry for low dose detection of γ radiation.
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half size analogueSolvent Assisted Fluorescence QuenchingDevelopmentfluorescence quenching responseaggregationfluorescence quenchingsolventLow Dose DetectionHCladductfluorescence sensor moleculechemical sensor systemsCH0.01 Gy leveldose detectionγ radiationshow fluorescence quenchingimidazole conjugation structure
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