Optode sensor design revolves around the choice of functional components embedded in a hydrophobic polymer matrix. The ionophore, acting as the recognition unit, extracts and stabilizes the ion of choice into the nanoparticle core. At the same time, the non-fluorescent pH indicator, blueberry-C6-ester-652 (blueberry) is deprotonated and increases in absorbance, gating the PLNP emission. An ionic additive, Na + TFPB -, is incorporated into the sensor core to balance the positive charge on the protonated blueberry. Combining blueberry and Na + TFPB -, with either potassium ionophore I, sodium ionophore X, or calcium ionophore II into the FNP solvent stream yielded K + , Na + , or Ca 2+ PLNs, respectively. The ion PLN emission decreases as a function of analyte concentration and blueberry absorbance (Figure and). As expected, the addition of optode components still allowed for ZGO:Cr 3+ @TMOS incorporation into the PLN core (Figure ). Using a 100µs delay time, the K + PLNs in Figure are 100-times more selective for K + than Na + (logKK,Na = -2.1) and have a dynamic range that overlaps with concentrations found in serum . Importantly, the K + PLN response stays consistent as the delay time is increased out to 1 ms which could allow K + quantification in systems with fluorescent sources of variable luminescent lifetimes (e.g., when multiplexing) (Figure ). The K + PLNs are also reversible (corroborating the expected equilibrium-based ion exchange mechanism) and have a functional lifetime of at least 8 days (Figure &). Likewise, using a 100µs delay, the Na + PLNs shown in Figure have a selectivity coefficient that compares to other Na + sensors using the same ionophore and PEG-based surfactants (logKNa,K = -1.1), which are known to impact K + partitioning and selectivity . The Na + PLNs have a dynamic range sufficient for serum quantification and a functional lifetime between 4 and 8 days (Figure ). The Ca 2+ PLNs (Figure , 100µs delay) are ~1000times more selective over the major competing ion Mg 2+ (logKCa,Mg = -3.2) and have a functional lifetime of less than 4 days (Figure ). The size and selectivity coefficients of all ion PLNs can be seen in Tables and, respectively. To further confirm the ion exchange mechanism of the ion PLNs, the ionophores were excluded from formulations, and the time-resolved response to ions was tested. As expected, without an ionophore, the sensors respond according to ion lipophilicity (Hofmeister series) (Figure ). Additionally, there is no response to pH or ions when the optode components are excluded from the formulation, indicating the modulation of ZGO:Cr 3+ emission is a function of the dye's protonation degree and selective partitioning (Figure ).