Dually Fluorescent Sensing of pH and Dissolved Oxygen Using a Membrane Made from Polymerizable Sensing Monomers

Using a thermal polymerization approach and polymerizable pH and oxygen sensing monomers with green and red emission spectra, respectively, new pH, oxygen, and their dual sensing membranes were prepared using poly(2-hydroxyethyl methacrylate)-co-poly(acrylamide) as a matrix. The sensors were grafted on acrylate-modified quartz glass and characterized under different pH values, oxygen concentrations, ion strengths, temperatures and cell culture media. The pH and oxygen sensors were excited using the same excitation wavelength and exhibited well-separated emission spectra. The pH-sensing films showed good response over the pH range 5.5 to 8.5, corresponding to pK(a) values in the biologically-relevant range between 6.9 and 7.1. The oxygen-sensing films exhibited linear Stern-Volmer quenching responses to dissolved oxygen. As the sensing membranes were prepared using thermally initiated polymerization of sensing moiety-containing monomers, no leaching of the sensors from the membranes to buffers or medium was observed. This advantageous characteristic accounts in part for the sensors' biocompatibility without apparent toxicity to HeLa cells after 40 hours incubation. The dual-sensing membrane was used to measure pH and dissolved oxygen simultaneously. The measured results correlated with the set-point values.

Utilization of micelles formed from poly(ethylene glycol)-block-poly(epsilon-caprolactone) block copolymers as nanocarriers to enable hydrophobic red two-photon absorbing emitters for cells imaging

A hydrophobic two-photon absorbing (2PA) red emitter (R) was successfully incorporated into micelles formed from two block copolymers, poly(epsilon-caprolactone)-block-poly(ethylene glycol)s, for imaging and toxicity studies. In micelles, the chromophore R exhibits a 2PA cross-section of 400 GM (1 GM = 1 x 10(-50) cm(4) s photon(-1) molecule(-1)) at 820 nm, which is among the highest values reported for red 2PA emitters. The micelles with a cationic amino moiety-containing poly(ethylene glycol) corona showed an enhancement of cell internalization and delivered the dye into the cytoplasmic regions of the mouse macrophage RAW 264.7 cells. In comparison, the dye in micelles with neutral poly(ethylene glycol) as corona could not be delivered into the cells. Cytotoxicity of the micelle-R constructs was studied using a 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. More than 90% of the cells were viable after they were stained with the dye-containing micelles at different concentrations (dye concentrations of 2-6 muM and polymer concentrations of 0.05-0.15 mg/mL) for 16 h. This is the first reported application of a hydrophobic 2,1,3-benzothiadiazole-containing 2PA red emitter delivered into the cytoplasm of cells for bioimaging and toxicity assessment.

2,1,3-Benzothiadiazole (BTD)-moiety-containing red emitter conjugated amphiphilic poly(ethylene glycol)-block-poly(epsilon-caprolactone) copolymers for bioimaging

2,1,3-Benzothiadiazole (BTD)-containing red emitter was chemically conjugated onto amphiphilic poly(ethylene glycol)-block-poly(epsilon-caprolactone) (PEG-b-PCL) copolymers to form two new fluorophore-conjugated block copolymers (P5 and P7). P5 is a cationic amino group-containing polymer, whereas, P7 is a neutral polymer. The polymers formed micelles in aqueous solution with average diameters of 45 nm (P7) and 78 nm (P5), which were characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM). Cell internalization of the micelles using mouse macrophage RAW 264.7 was investigated. The micelles formed from P5 were endocytosed into the cell's cytoplasm through a non-specific endocytosis process, which was affected by temperature and calcium ions. Micelles formed from P7 could not be endocytosed. The dramatic difference of cell uptake between P5 and P7 indicated the cationic amino groups had a strong influence on the cell internalization to enhance the endocytosis pathway. 3-(4,5-Dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) viability assay was used to evaluate the cytotoxicity of the P5 micelle and no significant toxicity was observed. This study is the first report regarding the synthesis of BTD-conjugated block copolymers and the application of the biomacromolecules for bioimaging.