Fluorescence lifetime imagers
Traditional Fluorescence Lifetime Imaging Microscopy systems use laser
scanning techniques in concert with a single photon detector, such as
a photomultiplier tube or avalanche photodiode, to construct lifetime
based images using Time Correlated Single Photon Counting (TCSPC). In
order to acquire enough data within each pixel to determine the
lifetime, thousands of samples must be taken. As a result, the time
required to capture a single frame can be several to tens of seconds,
which presents a limit to the types of biological processes that can
be monitored using FLIM. The focus of this project is creating a
CMOS-based Single Photon Avalanche Diode (SPAD) array that is capable
of acquiring multiple frames per second, which would make real-time
FLIM imaging of biological processes possible.
Our most recent array design was capable of a maximum frame rate of 3.9 Hz and consisted of a 64 x 64 SPAD array with integrated timing and pixel control circuitry in 0.35μm technology. The image on this page below shows a FLIM image of quantum dots (in color) next to a CCD image showing the location of the quantum dots on the array.
Our recent efforts are focused on developing a SPAD array in a standard CMOS process flow for a more advanced technology node. We have developed a low-noise SPAD in 0.13μm technology that will enable higher imaging rates through improved circuit performance. A full imaging array based on this SPAD design is currently under development.
- R. M. Field, J. Lary, J. Cohn, L. Paninski, and K. L. Shepard, "A low-noise, single-photon avalanche diode in standard 0.13 μm complementary metal-oxide-semiconductor process," Applied Physcis Letters, 97, 211111 (2010)
- D. E. Schwartz, E. Charbon, and K. L. Shepard, "A single-photon
avalanche diode imager for fluorescence lifetime applications,"
Symposium on VLSI Circuits, 2007, pp. 144-245.