Ion-detecting microspheres and methods of use thereof

A method of detecting nanomolar or sub-nanomolar levels of lead ions in a sample, comprising;

• (a) providing ion-detecting polymeric microspheres comprising an ionophore selective for said lead ions, a reference dye, a chromoionophore selective for hydrogen ions, and a fluorescent dye, wherein said chromoionophore is a chromoionophore that becomes deprotonated when said lead ions are present in said sample, and wherein said deprotonated form of said chromoionophore is absorbent at the frequency of the fluorescence emission of said dye, wherein said polymeric microspheres comprise a copolymer having a glass transitional temperature (Tg) of about or below 0° C., wherein said copolymer comprises polymerized units of methacrylate monomers, wherein said methacrylate monomers comprise a monomer having an R1 pendant alkyl group and a monomer having an R2 pendant alkyl group, wherein R1 is any of C1-3 alkyl groups and R2 is any of C4-12 alkyl groups;
• (b) contacting said microspheres with a flowing stream of said sample under conditions that allow the ion-selective ionophores to bind and form complexes with the lead ions, if present in the sample, and to cause deprotonation of the chromoionophore, wherein the ionophore/ion complex causes deprotonation of the chromoionophore, and the lead ions are extracted into the bulk of the microsphere where they are complexed by the ion-selective ionophores;
• (c) exposing the dye in microspheres containing said complexes, if formed, to an excitation wavelength light source suitable for exciting the dye to emit a fluorescence signal pattern;
• and
• (d) detecting the fluorescence signal pattern emitted by the dye by a detection means for detecting the fluorescence signal pattern, wherein said fluorescence signal pattern is inversely proportional to the amount of said lead ions in said sample.