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A facile, one-pot synthetic approach has been developed for the preparation of BSA-Ce/Au NCs. The fluorescence intensities of BSA-Ce/Au NCs at 410 and 650 nm are pH dependent and independent, respectively. The fluorescence intensity ratio (I410/I650) is linear against pH values from 6.0 to 9.0. These stable and biocompatible BSA-Ce/Au NCs have been used as ratiometric probes for monitoring local pH values inside HeLa cells.

We have developed a simple, sensitive, and rapid fluorescence assay for the detection of cancer cells, based on "turn-on" retro-self-quenched fluorescence inside the cells. 1,3-Phenylenediamine resin (DAR) nanoparticles (NPs) containing rhodamine 6G (R6G) are conjugated with aptamer (apt) sgc8c to prepare sgc8c-R6GDAR NPs, while that containing rhodamine 101 (R101) are conjugated with TD05 for the preparation of TD05-R101DAR NPs. The sgc8c-R6GDAR and TD05-R101DAR NPs separately recognize CCRF-CEM and Ramos cells. The fluorescence intensities of the two apt-DAR NPs are both weak due to self-quenching, but they increase inside the cells as a result of release of the fluorophores from the apt-DAR NPs. The apt-DAR NPs' structure becomes less compact at low pH value, leading to the release of the fluorophores. The sgc8c-R6GDAR and TD05-R101DAR NPs allow detection of as low as 44 CCRF-CEM cells and 79 Ramos cells mL(-1), respectively, using a commercial reader within 10 min. Practicality of the two probes have been validated by the quantitation and identification of CCRF-CEM and Ramos cells spiked in blood samples through conventional fluorescence and flow cytometry analysis, with advantages of sensitivity, selectivity, and rapidity.

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