Carboxylate-modified squaraine dye doped silica fluorescent pH nanosensors

Novel carboxylate-modified fluorescent silica pH nanosensors were synthesized using a reverse microemulsion method with a pH sensitive squaraine dye used as pH indicator. This pH sensitive squaraine dye was simply doped inside SiNPs without any complicated procedures. To avoid aggregation among the particles and to increase the water solubility of the pH nanosensors, the SiNPs were surface modified with a carboxyl group. This pH probe exhibits a good linear dynamic response between pH 3.01 and 5.72. Many alkali, alkaline earth, and transitional metal ions including Li⁺, Na⁺, K ⁺, Rb⁺, Cs⁺, Mg^{2 +}, Ca ^{2 +}, Sr^{2 +}, Al^{3 +}, V^{5 +}, Cr ^{3 +}, Cr^{6 +}, Mn^{2 +}, Fe^{2 +}, Fe ^{3 +}, Co^{2 +}, Ni^{3 +}, Cu^{2 +}, Zn ^{2 +}, As^{3 +}, Se^{4 +}, Mo^{6 +}, Ag ⁺, Cd^{2 +}, La^{3 +}, Er^{3 +}, Ir ^{3 +}, Hg⁺, Hg^{2 +}, and Pb^{2 +} had no significant interference on pH value determination. Artificial sample determination showed that the pH nanosensors developed in this work possess a very promising applicability in biological and biomedical fields.