Abstract
Polymer dots (Pdots) represent newly developed semiconductor polymer nanoparticles and exhibit excellent characteristics as fluorescent probes. To improve the sensitivity and biocompatibility of Pdots ratiometric pH biosensors, we synthesized 3 types of water-soluble Pdots: Pdots-PF, Pdots-PP, and Pdots-PPF by different combinations of fluorescent dyes poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly[(9,9-dioctyl-fluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′,3}-thiadazole)] (PFBT), and fluorescein isothiocyanate (FITC). We found that Pdots-PPF exhibits optimal performance on pH sensing. PFO and FITC in Pdots-PPF produce pH-insensitive (λ = 439 nm) and pH-sensitive (λ = 517 nm) fluorescence respectively upon a single excitation at 380 nm wavelength, which enables Pdots-PPF ratiometric pH sensing ability. Förster resonance energy transfer (FRET) together with the use of PFBT amplify the FITC signal, which enables Pdots-PPF robust sensitivity to pH. The emission intensity ratio (I517/I439) of Pdots-PPF changes linearly as a function of pH within the range of pH 3.0 to 8.0. Pdots-PPF also possesses desirable reversibility and stability in pH measurement. More importantly, Pdots-PPF was successfully used for cell imaging in Hela cells, exhibiting effective cellular uptake and low cytotoxicity. Our study suggests the promising potential of Pdots-PPF as an in vivo biomarker.
Highlights
Intracellular pH is closely related to cellular behavior and pathological processes, including many types of cancer and neurodegenerative diseases [1]
Our study suggests the promising potential of Polymer dots (Pdots)-PPF as an in vivo biomarker
In order to improve currently available pH-sensitive ratiometric Pdots for better performance on pH sensing and biocompatibility, we first chose pH-insensitive dye PFO and pH-sensitive dye fluorescein isothiocyanate (FITC) cross-linked by PMSA to prepare dual-emission semiconductor Pdots (Pdots-PF, Scheme 1)
Summary
Intracellular pH is closely related to cellular behavior and pathological processes, including many types of cancer and neurodegenerative diseases [1]. PH sensors have a wide range of applications such as food, beverages, environmental monitoring, chemical processing, biomedical applications, and laboratory pH measurements [2,3]. These applications typically require highly reliable and accurate pH sensors. The most common one is based on glass electrodes, which have been recognized as commercial products with high stability and accuracy They still have some drawbacks, such as the high brittleness of glass membrane electrodes, which create a strong incentive to develop new pH sensors [4,5]
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