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.

Silicon nanodot-based aptasensor for fluorescence turn-on detection of mucin 1 and targeted cancer cell imaging

We report herein a new dual-color fluorescent aptasensor for detection of tumor marker mucin 1 (MUC1) and targeted imaging of MCF-7 cancer cells based on the specific interaction between MUC1 and its aptamer S2.2. The aptasensor was prepared by covalent attachment of the cyanine (Cy5)-tagged aptamer S2.2 to fluorescent silicon nanodot (SiND). The fluorescence of S2.2-Cy5 could be quenched by the SiND carrier in the absence of MUC1, and its fluorescence was restored in the presence of MUC1 due to structure switching of S2.2. This aptasensor exhibits specificity for MUC1-possitive MCF-7 cells rather than MUC1-negative MCF-10A cells and Vero cells. The SiND plays multiple roles in this fluorescence assay, making the method easier compared with other approaches. The limit of detection and precision of this method for MUC1 was 1.52 nM and 3.6% (10 nM, n = 7), respectively. The linear range was 3.33-250 nM, and the recoveries in spiked human serum were in the range of 87-108%. This is a simple, selective, sensitive and reliable method, which can well achieve not only quantitative analysis of tumor marker but also dual-color visualization of single cancer cells.