Figure 2.
(A) Fiber probe response as a function of time at 565 nm, arrows indicates the addition of TB solution. (B) Signal change at 565 nm for increasing TB concentration.
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3.2. Toluidine blue adsorption on nanoparticulated titanium dioxide NPTiO2(s)
The aim of the optical sensor studied is the detection of dyes in high turbidity media. With this purpose the detection of TB was followed after the addition of NPTiO2(s). Once a steady optical signal was reached at a TB concentration of 10 μМ, 20 mg of anatase NPTiO2(s) nanoparticles were added to the solution; a clear decrease in the signal was observed (See Supp. Info Figure S1) due to a decrease of TB concentration in solution after the adsorption of the dye on TiO2. Noticeably the spectral shape did not change (See Supp. Info Figure S2) after the addition of nanoparticles, indicating the capability of the sensor of detecting TB even in a medium with high turbidity. Considering these two evidences, it can be concluded that the optical sensor output is correlated with the amount of dye in solution and it is not affected by the presence of TiO2 nanoparticles. Furthermore the signal change can be used to quantify the amount of dye adsorbed on TiO2; consequently the optical sensor was used to characterize the adsorption of TB on TiO2 nanoparticles. Figure 3.A shows the analytical responses of the sensor towards TB in presence and absence of 100 mg of TiO2(s) dispersed in the buffer solution.