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The novel sensing scheme, unlike previous ones that are based on the use of pH indicator probes, is making use of solvatochromic probe Nile Red (NR). Dissolved in a matrix of ethyl cellulose, it can report the polarity of its microenvironment that is modulated by an additive (a hydrophobic amidine) that is capable of reversibly binding carbon dioxide. The spectra of NR undergo a strong solvatochromic shift both in color (from brick-red to magenta) and in fluorescence (from orange to red) if the respective sensor layer is exposed to gaseous CO(2) (gCO(2)) or dissolved CO(2) (dCO(2)). Both visual and instrumental readouts are possible. The sensor layer responds to gCO(2) in the range from 0 to 100% and to dCO(2) in the range from 0 to 1 M solutions of bicarbonate (equivalent to a CO(2) partial pressure of up to 255 hPa). The detection limits are around 0.23% for gCO(2) and 1.53 hPa for dCO(2). The response time is in the order of 10 min in the forward direction and 3 min in the reverse direction for gCO(2) but up to 25 min in the case of dCO(2). The optical response also was quantified using a digital camera by extracting the spectral information using the blue and green color channels (in reflectometry) and the green and red channels (in fluorescence), respectively, and by generating pseudocolor pictures.

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We report that the luminescence of upconverting luminescent nanoparticles (UCLNPs) is quenched by heavy metal ions and halide ions in aqueous solution. The UCLNPs consist of hexagonal NaYF(4) nanocrystals doped with trivalent rare earth ions and were synthesized by both the oleic acid (solvothermal) method and the ethylenediaminetetraacetic acid (co-precipitation) method. Quenching was studied for the Cu(II), Hg(II), Pb(II), Cd(II), Co(II), Ag(I), Fe(III), Zn(II), bromide, and iodide ions and is found to be particularly strong for Hg(II). Stern-Volmer plots are virtually linear up to quencher concentrations of 10-25 mM, but deviate from linearity at higher quencher concentrations, because static quenching causes an additional effect. The UCLNPs display two main emission bands (blue, green, red or near-infrared), and the quenching efficiencies for these are found to be different. The effect seems to be generally associated with UCLNPs because it was observed for all UCLNPs doped with trivalent lanthanide ions including Yb(III), Er(III), Ho(III), and Tm(III). The results are discussed in terms of quenching mechanisms and with respect to potential applications such as optical sensing.

We report on the preparation of fluorescent silica nanoparticles (NPs). They have been prepared by (a) modification of the NPs by amino groups and subsequent introduction of amino-reactive fluorophores of various color and (b) by modification of the NPs by either azido groups or alkyne groups and subsequent conjugation to fluorophores by so-called click chemistry, which is a novel approach toward modifying silica NPs. The new NPs were characterized in terms of size and spectral properties.

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