Time-gated and lifetime-unmixed imaging of near- and short wave infrared photoluminescence from rare-earth ion doped nanoparticles

Continuously increasing demand for biomedical diagnostics requires advanced imaging techniques. Time-gated imaging (TGI) of photoluminent bioprobes has a number of unique features, such as possibility to cut-off the excitation and autofluorescence and provide photoluminescence (PL) lifetime information in every pixel. However, as the other bioimaging techniques, TGI itself is not able to overcome the problem of high attenuation of light in the biological tissues. In recent years, imaging in the biological windows of optical transparency in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges is being actively developed, providing an opportunity for the excitation and detection of PL signal in deeper biological tissues with higher resolution. In order to combine both advantages of NIR-SWIR imaging and TGI, we have built a time-gated imaging system performing in NIR-SWIR (900-1700nm) spectral range. Synchronizing setup has been developed in order to control delay between pulsed excitation source and NIR-SWIR camera. Through manipulation of the delay between the PL excitation source and imaging camera, stack of time-resolved PL images is obtained, which can be processed by the unmixing software. In summary, the developed technique allows us to distinguish and map regions of different NIR-SWIR PL lifetimes. An application of this method for spatial discrimination of rareearth ion doped nanoparticles emitting in NIR-SWIR range has been demonstrated.