Facile preparation of FITC-modified silicon nanodots for ratiometric pH sensing and imaging.

A ratiometric fluorescent pH sensor was facilely constructed by covalent modification of amino-terminated silicon nanodots (SiND) with pH-sensitive fluorescein isothiocyanate (FITC). After optimization, the SiND-FITC(40:1) material with a SiND:FITC initial mass ratio of 40:1 was selected for the sensing of hydrogen ions. It was observed that the material inherits the unique features of SiND and FITC, and there is significant improvement of SiND acid−base stability, which is a favorable factor in terms of providing fluorescence reference signal. The SiND-FITC(40:1) material displays not only high pH sensitivity, but also good stability and anti-interference ability, and the response process is highly reversible. Deploying the SiND-FITC(40:1) material, we have made available a simple, sensitive, and precise approach for pH sensing. In aqueous solutions, the I517/I466 fluorescence intensity ratio of SiND-FITC(40:1) increases linearly in the pH range of 5.40–7.76. This dual emission nanosensor was successfully applied for pH sensing and cellular fluorescence imaging.