LAUSR

Typical ionophore-based nanosensors use nile blue-derived indicators called chromoionophores which must contend with strong background absorption, autofluorescence, and scattering in biological samples that limit their usefulness. Here, we demonstrate potassium-selective nanosensors that utilize triplet-triplet annihilation upconversion to minimize potential optical interference in biological media and a pH-sensitive quencher molecule to modulate upconversion intensity in response to changes in analyte concentration. A triplet-triplet annihilation dye pair (platinum (II) octaethylporphyrin and 9,10-diphenylanthracene) was integrated into nanosensors containing an analyte binding ligand (ionophore), charge-balancing additive, and a pH indicator quencher. Nanosensor response to potassium was shown to be reversible and stable for three days. In addition, the nanosensors are selective against sodium, calcium, and magnesium (selectivity coefficient in log10 units of -2.2 for calcium, -2.0 for sodium, and -2.4 for magnesium), three interfering ions found in biological samples. The lack of signal overlap between the upconversion nanosensors and GFP, a common biological fluorescent indicator, is demonstrated in confocal microscope images of sensors embedded in a bacterial biofilm.