Multiplexed sensing of ions with barcoded polyelectrolyte capsules.

Multiplexed detection of analytes is a challenge for numerous medical and biochemical applications. Many fluorescent particulate devices are being developed as ratiometric optical sensors to measure the concentration of intracellular analytes. The response of these sensors is based on changes of the emission intensity of analyte-sensitive probes, entrapped into the carrier system, which depends on the concentration of a specific analyte. However, there are a series of technical limits that prevent their use for quantitative detection of several analytes in parallel (e.g., emission crosstalk between different sensor molecules). Here we demonstrate that double-wall barcoded sensor capsules can be used for multiplexed analysis of proton, sodium, and potassium ions. The sensor detection methodology is based on porous microcapsules which carry ion-sensitive probes in their inner cavity for ion detection and a unique QD barcode in their outermost wall as tag for identification of individual sensors. The engineering of QD barcodes to capsules walls represents a promising strategy for optical multianalyte determination.