The effect of L-alanine concentration with anionic Erythrosin B (EryB) and cationic Rhodamine 6G (R6G) dye in water and nano-confined water was studied by absorption, fluorescence and Z-Scan instruments. The nano-confined water was prepared with a mixture of water and n-decane and Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) that the size of nanoconfined water can change with molar ratio of water to AOT (X). By the change of L-alanine concentration up to 1.5M, absorption spectra do not change and the peak position of absorption spectra is constant. The fluorescence spectra of AOT/n-Decane/Water/EryB with W=40, shows a peak at 555 nm that shifts to 553 nm by increasing of L-alanine concentration. The fluorescence intensity of mixed with AOT/n-Decane/Water/EryB with W=40 quenches by increasing of Lalanine concentration that this behavior was not observed in other samples. The nonlinear absorption (β) of EryB and also R6G nano-confined water is enhanced compared to bulk water. Moreover, the slope of β as function L-alanine concentration of for both of dyes in nano-confined water is higher than that of in bulk water. Therefore, the nano-confined water and the nonlinear absorption are suitable medium and parameter to detection of the L-alanine concentration.

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