Simple, photoluminescence standard for fluorometer calibration in low-resource settings

The proposed photoluminescence calibration standard comprises a solid-state phosphor film, neutral density gel filter(s), and a 3D-printed optomechanical cartridge. The proposed standard demonstrated exceptional photostability; photoluminescence did not deviate from the baseline more than 1.27% under 5 minutes of continuous illumination. Remarkably, there was no measurable degradation over a 3-year study. Precise photoluminescence intensity modulation was accomplished with neutral density gel filters (R² > 0.9982) and optical apertures (R² > 0.9970). A model for photoluminescence intensity as a function of neutral-density filter and optical aperture parameters yielded a mean percentage error (MPE) of 2.79%, indicating high precision. Inter-sample variability was low, with a mean coefficient of variation (CV) of 1.32%. Mean CV across 24 channels decreased from 11.88% to 1.51% following multi-point calibration of multichannel point-of-care (POC) fluorometers. Cost analysis revealed a per-unit cost between $0.49 to $1.80. This work suggests that the proposed calibration standards provide a cost-effective, highly stable solution for reliable fluorometer calibration in low-resource settings.