Bimodal persistent luminescence for autofluorescence-free ratiometric biosensing.

In optical biosensing, analyte-independent factors such as autofluorescence interference and excitation source fluctuation decrease the sensitivity and accuracy. Herein, we reported a bimodal persistent luminescence strategy to design dual-emissive persistent luminescence nanoparticles (PLNPs) with built-in self-calibration to preclude interference from analyte-independent factors in biosensing. As a proof of concept, ZnGaO:Cr PLNPs with emissions at both 490 nm and 695 nm were designed. The I/I ratio of ZnGaO:Cr was readily adjusted by simply changing the doping concentration of Cr. The ZnGaO:Cr PLNPs were employed for the ratiometric detection of urinary mesna. A good linear relationship between the I/I ratio of ZnGaO:Cr-based nanoprobe and the concentration of mesna was obtained in the range of 0-40 μM. The limit of detection was about 0.40 μM. Results showed that autofluorescence interference from urine was totally eliminated by collecting the persistent luminescence signal of ZnGaO:Cr after excitation ceased. Moreover, the built-in self-calibration feature of the ratiometric ZnGaO:Cr PLNPs efficiently suppressed the interference from fluctuations in instrumental parameters during urinary mesna detection. The recovery rates of mesna in the spiked urine samples are in the range of 99.1~109.0%, showing the reliability of the ratiometric ZnGaO:Cr PLNPs in urinary mesna detection. ZnGaO:Cr can further be expanded to the detection of other analytes in complex matrices. This study may open new opportunities for the design of dual-emissive PLNPs with tunable ratios of emission intensity, and it can further promote the applications of optical biosensing in disease diagnosis, food safety, and environmental monitoring.