In this paper, we report on SwissSPAD2, an image sensor with 512 × 512 photon-counting pixels, each comprising a single-photon avalanche diode (SPAD), a 1-b memory, and a gating mechanism capable of turning the SPAD on and off, with a skew of 250 and 344 ps, respectively, for a minimum duration of 5.75 ns. The sensor is designed to achieve a frame rate of up to 97 700 binary frames per second and sub-40 ps gate shifts. By synchronizing it with a pulsed laser and using multiple successive overlapping gates, one can reconstruct a molecule's fluorescent response with picosecond temporal resolution. Thanks to the sensor's number of pixels (the largest to date) and the fully integrated gated operation, SwissSPAD2 enables widefield fluorescence lifetime imaging microscopy with an all-solid-state solution and at relatively high frame rates. This was demonstrated with preliminary results on organic dyes and semiconductor quantum dots using both decay fitting and phasor analysis. Furthermore, pixels with an exceptionally low dark count rate and high photon detection probability enable uniform and high-quality imaging of biologically relevant fluorescent samples stained with multiple dyes. While future versions will feature the addition of microlenses and optimize firmware speed, our results open the way for low-cost alternatives to commercially available scientific time-resolved imagers.
|Journal||IEEE Journal of Selected Topics in Quantum Electronics|
|State||Published - 1 Jan 2019|
Bibliographical noteFunding Information:
Manuscript received April 7, 2018; revised July 1, 2018 and August 21, 2018; accepted August 21, 2018. Date of publication August 28, 2018; date of current version December 21, 2018. This work was supported in part by the Swiss National Science Foundation Grant 166289, in part by the Netherlands Organization for Scientific Research Project 13916, in part by the HFSP Grant RGP0061/2015, and in part by the NIH Grant GM 095904 and CRCC Grant CRR-18-523872 (UCLA). The work of R. Ankri was supported by an Excelling Post-Doctoral Students Scholarship from the Council of Higher Education, Israel. (Corresponding author: Arin Can Ulku.) A. C. Ulku, C. Bruschini, I. M. Antolović, and E. Charbon are with the School of Engineering, École Polytechnique Fédérale de Lausanne, Neuchâtel 2002, Switzerland (e-mail:, email@example.com; firstname.lastname@example.org; michel. email@example.com; firstname.lastname@example.org).
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- fluorescence lifetime imaging microscopy
- image sensor
- phasor analysis
- single-photon avalanche diodes
- time gating