Time-resolved spectroscopy at 19,000 lines per second using a CMOS SPAD line array enables advanced biophotonics applications

A SPAD-based line sensor fabricated in 130 nm CMOS technology capable of acquiring time-resolved fluorescence spectra (TRFS) in 8.3 milliseconds is presented. To the best of our knowledge, this is the fastest time correlated single photon counting (TCSPC) TRFS acquisition reported to date. The line sensor is an upgrade to our prior work and incorporates: i) parallelized interface from sensor to surrounding circuitry enabling high line rate to the PC (19,000 lines/s) and ii) novel time-gating architecture where detected photons in the OFF region are rejected digitally after the output stage of the SPAD. The time-gating architecture was chosen to avoid electrical transients on the SPAD high voltage supplies when gating is achieved by excess bias modulation. The time-gate has an adjustable location and time window width allowing the user to focus on time-events of interest. On-chip integrated center-of-mass (CMM) calculations provide efficient acquisition of photon arrivals and direct lifetime estimation of fluorescence decays. Furthermore, any of the SPC, TCSPC and on-chip CMM modes can be used in conjunction with the time-gating. The higher readout rate and versatile architecture greatly empower the user and will allow widespread applications across many techniques and disciplines. Here we focused on 3 examples of TRFS and time-gated Raman spectroscopy: i) kinetics of chlorophyll A fluorescence from an intact leaf; ii) kinetics of a thrombin biosensor FRET probe from quenched to fluorescence states; iii) ex vivo mouse lung tissue autofluorescence TRFS; iv) time-gated Raman spectroscopy of toluene at 3056 cm-1peak. To the best of our knowledge, we detect spectrally for the first time the fast rise in fluorescence lifetime of chlorophyll A in a measurement over single fluorescent transient.