title: 256 × 2 SPAD line sensor for time resolved fluorescence spectroscopy.
abstract: We present a CMOS chip 256 × 2 single photon avalanche diode (SPAD) line sensor, 23.78 µm pitch, 43.7% fill factor, custom designed for time resolved emission spectroscopy (TRES). Integrating time-to-digital converters (TDCs) implement on-chip mono-exponential fluorescence lifetime pre-calculation allowing timing of 65k photons/pixel at 200 Hz line rate at 40 ps resolution using centre-of-mass method (CMM). Per pixel time-correlated single-photon counting (TCSPC) histograms can also be generated with 320 ps bin resolution. We characterize performance in terms of dark count rate, instrument response function and lifetime uniformity for a set of fluorophores with lifetimes ranging from 4 ns to 6 ns. Lastly, we present fluorescence lifetime spectra of multicolor microspheres and skin autofluorescence acquired using a custom built spectrometer. In TCSPC mode, time-resolved spectra are acquired within 5 minutes whilst in CMM mode spectral lifetime signatures are acquired within 2 ms for fluorophore in cuvette and 200 ms for skin autofluorescence. We demonstrate CMOS line sensors to be a versatile tool for time-resolved fluorescence spectroscopy by providing parallelized and flexible spectral detection of fluorescence decay.
authors.forename: Nikola
authors.initials: N
authors.lastname: Krstajić
authors.forename: James
authors.initials: J
authors.lastname: Levitt
authors.forename: Simon
authors.initials: S
authors.lastname: Poland
authors.forename: Simon
authors.initials: S
authors.lastname: Ameer-Beg
authors.forename: Robert
authors.initials: R
authors.lastname: Henderson
mesh_terms: D016477:Artifacts; D019793:Fluorescein; D006801:Humans; D008863:Microspheres; D055095:Optics and Photonics; D017785:Photons; D012867:Skin; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013997:Time Factors
chemical_list: D019793:Fluorescein