The solvatochromic dye Nile Red dispersed in selected hydrogen bond acidic polymer matrixes demonstrated strong fluorescence enhancement at the presence of dimethyl methylphosphonate (DMMP) vapors. Two hydrogen bond acidic polymers were examined as dye matrixes, one with fluorinated alcohol groups on a polystyrene backbone (PSFA) and the other with fluorinated bisphenol groups alternating with oligo(dimethylsiloxane) segments (BSP3). The combination of hydrogen bond acidic polymer (a strong sorbent for DMMP) with the solvatochromic dye led to initial depression of the dye fluorescence and a significant red shift in the absorbance and fluorescence spectra. DMMP sorption changed the dye environment and dramatically altered the fluorescence spectrum and intensity, resulting in a strong fluorescence enhancement. It is proposed that this fluorescence enhancement is due to the competition set up between the dye and the sorbed vapor for polymeric hydrogen-bonding sites. The highest responses were obtained with BSP3. DMMP detection has been demonstrated at sub-ppm DMMP concentrations, indicating very low detection limits compared to previous Nile Red/polymer matrix fluorescence vapor sensors. Nile Red/poly(methyl methacrylate) films prepared for comparisons exhibited substantially lower response to DMMP. Rational selection of polymers providing high sorption for DMMP and competition for hydrogen-bonding interactions with Nile Red yielded flourescent films with high sensitivity.

A method for signal amplification in the detection of vapors with luminescence-based sensors is described. Amplification involves energy transfer between two or more fluorescent chromophores in a carefully selected polymer matrix. A quantitative model has been derived that can be applied to any luminescence sensor comprising donor−acceptor pairs, and it can be generalized to multichromophore systems with n chromophores leading to n-fold signal amplification. Signal amplification has been demonstrated experimentally in the fluorescent sensing of dimethyl methylphosphonate (DMMP) using two dyes, 3-aminofluoranten (AM) and Nile Red (NR), in a hydrogen-bond acidic polymer matrix. The selected polymer matrix quenches the fluorescence of both dyes and shifts dye emission and absorption spectra relative to those of more inert matrixes. Upon DMMP sorption, the AM fluorescence shifts to the red at the same time that the NR absorption shifts to the blue, resulting in more band overlap and increased energy transfer between chromophores. In addition, the emission of both chromophores is enhanced. Using an excitation wavelength tuned to the AM dye, we found that the absolute signal magnitude observed upon DMMP exposure in the two-dye film was an order of magnitude greater than that observed when using a single-dye NR-containing film. The ratio of the response signal under vapor exposure to the signal prior to exposure was 250 for the two-dye film compared to 15 for single-dye films. The two-dye approach to signal amplification also significantly increases the selectivity relative to the potentially interfering vapors. Experimental results to date favor a reabsorption mechanism over a Förster radiationless direct energy-transfer mechanism.

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