Attachment system.

(Left) Close-up rendering of the attachment system for a 250 mL medium bottle. Two vertical rod magnets are used to align the sensor patch. Plastic parts are rendered as partially transparent. (Right) The full set of designed attachments.</p

Raw data acquired during the growth of <i>E</i>. <i>coli</i>.

The data were not filtered or smoothed. The two insets show the behavior of the sensor at intervals outlined by the two rectangles and share the same units on the x- and y-axes. The zero point was re-calibrated by flushing the chamber with oxygen-free nitrogen after the end of the experiment.</p

Electrical schematics of the main components of the analog board.

A) LED driver circuit. B) Transimpedance amplifier with a programmable gain amplifier. Full schematics are available in the S1 File. Temperature coefficients (in ppm) and dielectric specifications for critical resistors and capacitors are listed in the S1 File as well.</p

Comparison between oxygen sensors talked about in this article.

Comparison between oxygen sensors talked about in this article.</p

Chemical structure of 5,10,15,20-Tetrakis(pentafluorophenyl)-21H,23H-porphyrin palladium(II) [10], the dye used in our sensor patches.

Image generated from PubChem data using OpenBabel [12].</p

Finished sensor system design attached to a serum bottle.

Right part shows the screen and highlights the most important information shown. A highly degraded sensor patch was used to make the background clearly visible. The background is negligible compared to the luminescence for a non-degraded sensor patch.</p

A graph illustrating the calibration procedure.

(A) Behavior of luminescence lifetime during calibration (blue). The total volume of liquid injected is shown as red dots, orange crosses indicate injection points on the lifetime graph. After injections, the bottle was flushed with 75 ppm oxygen reference gas and equilibrated with the ambient pressure (green rectangle). (B) The luminescence lifetime of the dye as a function of the effective injected reference liquid volume. Red line is the initial approximation and blue line is the final approximation that compensates for the unintentional inflow of oxygen. (C) Effective amount of oxygen in the gas phase in the units of the injected volume of the reference solution. Red line shows the initial approximation and blue the final one. (D) Calibration curves for the luminescence lifetime as a function of the partial pressure of oxygen with 75 ppm oxygen reference gas in N2 used a calibration point. Red is the initial approximation and blue the final one.</p

General operating principle of luminescence lifetime sensors based on sine wave attenuation.

General operating principle of luminescence lifetime sensors based on sine wave attenuation.</p

Calibration data at higher oxygen concentrations.

Red circles show calibration points, with two independent calibrations overlaid to test repeatability. The solid red line shows the regression function. Blue circles are the standard deviation of measurements and show the sensor noise.</p

General operating principle of luminescence lifetime sensors based on the sine wave phase shift.

DAC is the digital to analog converter, PGA is the programmable gain amplifier and ADC is the analog to digital converter.</p