To fabricate O2-sensitive PLNs, we used the phosphorescent PdTPTBP (em: 800 nm, t0 = 356 µs( )) as the O2 indicator and the ZGO:Cr 3+ emission as the O2 insensitive reference (Figure ) for time-resolved, ratiometric measurements. Exciting the Pd-chelate results in an electronic transition to S1 and intersystem crossing to an excited triplet state (T1) causing spin inversion and a forbidden transition back to S0 -the mechanism of phosphorescence . Molecular O2 can collide with the dye and quench it, resulting in a lower emission intensity and luminescence lifetime . This collisional quenching process is characterized by the Stern-Volmer relationship (equation S3A). Ratiometric O2 measurements are described by a pseudo-Stern Volmer relationship (equation S3B) by instead plotting the quotient of the ratiometric signal (PdTPTBP/ZGO:Cr 3+ ) at 0 mg/L O2 by the same ratio at prevailing [O2], giving a linear response (Figure , black) . As expected, the pseudo-Ksv increases over the measured O2 range by increasing the delay timea function of the variable luminescence lifetime of PdTPTBP (Figure and S20). While spectral separation approaches have been used to overcome autofluorescence in microbial systems , this work achieves this with ratiometric sensors that are compatible with a time-resolved measurement approach. O2 consumption of Saccharomyces cerevisiae (Kolsch I) was monitored over 65 hours with the O2 PLNs (plate setup in Figure ). Without a delay, yeast autofluorescence interferes with ZGO:Cr 3+ emission and precludes ratiometric O2 measurements (Figure ) but using a 500 µs delay eliminates the autofluorescence and shows an increasing ratiometric signal at 20hrs (Figure and). Figure shows that metabolic activity is inhibited upon the addition of an antimicrobial agent (potassium metabisulfite) and the O2 concentration is brought back to baseline after 10 hrs.