Ratiometric pH Sensing and Imaging in Living Cells with Dual-Emission Semiconductor Polymer Dots

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.

Recent progress in 0D optical nanoprobes for applications in the sensing of (bio)analytes with the prospect of global health monitoring and detailed mechanistic insights

“…To improve the biocompatibility and sensitivity of Pdots, Jin and Huang et al proposed semiconductor water-soluble fluorescent Pdots via selective reprecipitation methods, which exhibited ratiometric fluorogenic pH sensing in the pH range of 3.0 to 8.0. 264 This probe could also be used for in vivo bioimaging in HeLa cells due to its effective cellular uptake and low cytotoxicity. Alternatively, Wang et al designed robust two-photon excitable semiconducting polymer nanoparticles (PFV/PSMA-DA NPs) (PFV= poly(9,9′-dihexylfluorene-2,7-ylene-vinylene- co -alt-1,4-phenylene), PSMA= poly(styrene- co -maleic anhydride) and DA = dopamine) via the reprecipitation method, which were functionalized with the redox-active and pH-sensitive DA for the highly sensitive and reversible fluorogenic detection of pH over the range of 5.0 to 9.0 (Fig.…”

“…These polymer dots can be easily coupled with small organic molecules or biomolecules to tune the energy transfer process to be applied for target-specific detection in complex biological matrices. Nowadays, Pdots have emerged as flexible probes for the detection of numerous biomolecules such as ascorbic acid, quercetin, glutathione, intracellular pH, and alkaline phosphatase, etc., [259][260][261][262][263][264][265][266][267][268][269] via the chromogenic and/or fluorogenic strategy through tunable IFE, FRET, PET, static and dynamic quenching mechanism (Table 6).…”

Nanomaterial-Based Dual-Emission Ratiometric Fluorescent Sensors for Biosensing and Cell Imaging

“…Fluorescent PNPs possess excellent optical properties, diverse structures, controllable functionalization, and good biocompatibility, and hold great promise for fluorescence detection and bioimaging [ 69 , 70 ]. Wu et al found that Pdot-bioconjugates are much brighter (~30×) than QD-bioconjugates [ 71 ].…”

Development of Fluorescent Carbon Nanoparticle-Based Probes for Intracellular pH and Hypochlorite Sensing

“…Chen et al designed another fluorescent probe based on Förster resonance energy transfer (FRET) between a pH-insensitive fluorophore [poly(9,9-dioctylfluorenyl-2,7-diyl), λ em = 439 nm] and a pH-sensitive fluorescent dye (fluorescein isothiocyanate, λ em = 517 nm) in the semiconducting polymer dots (Pdots-PPF). Upon a single excitation at 380 nm, the Pdots-PPF exhibit ratiometric pH sensing ability within a wide range of pH value ranging from 3.0 to 8.0 [10]. Recently, fluorescent carbon based-nanoparticles have received great interest due to their low chemical/cytotoxicity, good biocompatibility, multicolor luminescence tunability, and resistance to photobleaching [11][12][13].…”