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Fluorescence of Cascade Blue™ inside nano-sized porous shells of silicate

2002; Elsevier BV; Volume: 57; Issue: 1 Linguagem: Inglês

10.1016/s1387-1811(02)00502-4

1873-3093

Agnes Ostafin, Matthew Siegel, Q Wang, Hiroshi Mizukami,

Analytical chemistry methods development

Cascade Blue™ (CB) dye at a concentration as high as 0.227 M was encapsulated within nano-sized porous silicate shells, and its relative fluorescence yield determined over the pH range of 1.8–12.3, using 380 nm as the excitation wavelength. The results were compared with those obtained in aqueous solution using similar pH and total dye concentration. Near neutral pH, the relative fluorescence yields of CB inside the shells exhibited little fluorescence quenching, even though a high concentration of the dye was trapped inside the particles, while the peak wavelength of fluorescence was shifted from 420 nm in solution to 430 nm in shells. Both in shells and solution, the relative fluorescence intensity decreased as the solution pH was raised from 2 to 4, and in shells it nearly disappeared at about pH 3–4. As the pH was further increased, the red shift of fluorescence peak in the shell-trapped dyes was evident at pH 5 and its fluorescence intensity regained equal to that in acid. In the neutral pH range, the fluorescence intensity of CB in the shells was similar to that of the equivalent total concentration of the CB in solution. In solution, a similar red shift of the fluorescence maximum of CB to 430 nm was observed only above pH 9. These observations suggest that the fluorescence intensities of dyes trapped inside nano-sized porous silicate shells can be equal to or higher than that observed in solution under comparable conditions, leading to several hundreds times more fluorescent intensity when it is measured per single shell rather than per unit fluorophore.