Neutral red (NR), a eurhodin dye, is often used for staining living cells, but we demonstrated for the first time that NR can also serve as a CO2 sensor, because of NR's unique pH dependent optical properties, which change with dissolved carbon dioxide (dCO2) concentrations. In the present study, the optical sensitivity of NR was quantified as a function of changes in absorption and emission spectra to dCO2 in a pH 7.3 buffer medium at eight different dCO2 concentrations. NR exhibited a response time of two minutes for equilibration under pure N2 to 100% CO2 with an ~200% percent change (%∆) in emission intensity and >400%∆ in absorbance, both with full reversibility. Important to its application to biological systems, NR exhibited zero sensitivity to dissolved oxygen, which has routinely caused interference with CO2 measurements. NR exhibited pH sensitive emission and excitation energies with dual excitation maxima at 455 nm and 540 nm, and a single emission maximum at 640 nm. The CO2 sensing properties of NR were benchmarked by a comparison to pyranine = 8-hydroxypyrene-1, 3,6-trisulfonic acid trisodium salt) = HPTS. Future studies will evaluate the feasibility of NR as an intracellular in vivo pCO2 sensor in aquatic organisms critically impacted by increasing global CO2 levels. Stabilization of a well-known green emission phosphor, Pt-POP = diplatinum(II) tetrakispyrophosphite, was carried out using various protocols including polymerization, encapsulation within a polymer matrix and by varying other parameters, such as the solvent, pH, and concentration of the phosphor. A slight modification to the novel microwaveassisted synthesis protocol that our group has pioneered vs conventional reflux heating has yielded stabilized Pt-POP with a simultaneous doubling of the synthetic yield obtained. Heating to 260 °C produced a different form of PtPOP (exhibiting red/663 nm instead of green/515 nm phosphorescence and red-shifted spin-forbidden excitation maximum of 556 nm instead of 450 nm in both the solid-state and solution). This finding gives rise to additional broadening of the technological applications of this phosphor in terms of sensing under variable temperature, gaseous environment, pH and solvent.

Phosphorescent transition metal complexes make up an important group of compounds that continues to attract intense research owing to their intrinsic bioimaging applications that arise from bright emissions, relatively long excited state lifetimes, and large stokes shifts. Now for biomaging assay a model organism is required which must meet certain criteria for practical applications. The organism needs to be small, with a high turn-over of progeny (high fecundity), a short lifecycle, and low maintenance and assay costs. Our model organism C. elegans met all the criteria. The ideal phosphor has low toxicity in the model organism. In this work the strongly phosphorescent platinum (II) pyrophosphito-complex was tested for biological applications as a potential in vivo hypoxia sensor. The suitability of the phosphor was derived from its water solubility, bright phosphorescence at room temperature, and long excited state lifetime (~ 10 µs). The applications branched off to include testing of C. elegans survival when treated with the phosphor, which included lifespan and fecundity assays, toxicity assays including the determination of the LC50, and recovery after paraquat poisoning. Quenching experiments were performed using some well knows oxygen derivatives, and the quenching mechanisms were derived from Stern-Volmer plots. Reaction stoichiometries were derived from Job plots, while percent scavenging (or antioxidant) activities were determined graphically. The high photochemical reactivity of the complex was clearly manifested in these reactions.