Auto-phase-locked time-gated luminescence detection for background-free upconversion spectra measurement and true-color biological imaging

Time-resolved technique is widely used in biological detection and imaging, since this technique can eliminate the background signals from scattering and short-lived autofluorescence and greatly increase the signal-to-noise ratio. However, the relative apparatus always require pulse source, gated detector and electronic phase matching circuitry, which are expensive to implement and maintain. Herein, a simple method for time-gated upconversion luminescence spectra measurement and biological imaging was developed. By adjusting the exciting and detecting optical paths to pass through the same chopper wheel, only one mechanical chopper was needed, which simultaneously acted as pulse generator and detecting shutter. The phases of each excitation and time gate were synchronized and locked automatically as the optical paths fixed. Therefore, no complex electronic phase matching circuitry or control system was needed. By equipping with a 980 nm CW laser as exciting source, the time-gated spectra of upconversion lanthanide luminescence free from the scattering light was measured. Moreover, smart phones or the human eyes could easily detect the delayed luminescence of these materials, promising the true-color biological imaging with common cameras. This approach could be used in many other time-gated luminescence detection for long-lived luminescence materials and probes excited by other light sources.