Luminescent Silole Nanoparticles as Chemoselective Sensors for Cr(VI)

Abstract

Colloidal suspensions of 3-aminopropylmethyl(tetraphenyl)silole nanoparticles can be used as selective chemosensors for carcinogenic chromium(VI) analyte. Methylhydrosilole is functionalized by hydrosilation of allylamine, and the colloid is prepared by the rapid addition of water to a THF solution of the silole. The method of detection is through electron-transfer quenching of the fluorescence of the silole colloid (λ_em = 485 nm at 360 nm excitation) by the analytes, with hundred parts per billion detection limits. Stern−Volmer plots are linear up to 10 ppm in the case of chromium, but exhibit saturation behavior near 5−10 ppm for arsenic. Dynamic light scattering experiments and AFM measurements show the particle sizes to be around 100 nm in diameter and dependent on solvent composition, with a particle size dispersity of ±25%. The fluorescence lifetimes of the silole in solution and colloid are ∼31 ps and ∼4.3 ns, respectively, while the silole has a lifetime of 6 ns in the bulk solid. A minimum volume fraction of 80% water is necessary to precipitate the colloid from THF, and the luminescence continues to rise with higher water fractions. Colloids in a pH 7 phosphate-buffered suspension show both higher sensitivity and greater selectivity (100-fold) for CrO₄^2- detection than for other oxoanion interferents, NO₃^-, NO₂^-, SO₄^2-, and ClO₄^-.