CMOS system for high throughput fluorescence lifetime sensing using time correlated single photon counting
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Date
26/11/2015Author
Tyndall, David
Metadata
Abstract
Fluorescence lifetime sensing using time correlated single photon counting (TCSPC) is a key
analytical tool for molecular and cell biology research, medical diagnosis and pharmacological
development. However, commercially available TCSPC equipment is bulky, expensive
and power hungry, typically requiring iterative software post-processing to calculate the
fluorescence lifetime. Furthermore, the technique is restrictively slow due to a low photon
throughput limit which is necessary to avoid distortions caused by TCSPC pile-up.
An investigation into CMOS compatible multimodule architectures to miniaturise the standard
TCSPC set up, allow an increase in photon throughput by overcoming the TCSPC pile-up
limit, and provide fluorescence lifetime calculations in real-time is presented. The investigation
verifies the operation of the architectures and leads to the selection of optimal parameters for
the number of detectors and timing channels required to overcome the TCSPC pile-up limit by
at least an order of magnitude.
The parameters are used to implement a low power miniaturised sensor in a 130 nm
CMOS process, combining single photon detection, multiple channel timing and embedded
pre-processing of the fluorescence lifetime, all within a silicon area of < 2 mm2. Single
photon detection is achieved using an array of single photon avalanche diodes (SPADs)
arranged in a digital silicon photomultiplier (SiPM) architecture with a 10 % fill-factor and
a compressed 250 ps output pulse, which provides a photon throughput of > 700 MHz. An
array of time-interleaved time-to-digital converters (TI-TDCs) with 50 ps resolution and
no processing dead-time records up to eight photon events during each excitation period,
significantly reducing the effect of TCSPC pile-up. The TCSPC data is then processed using
an embedded centre-of-mass method (CMM) pre-calculation to produce single exponential
fluorescence lifetime estimations in real-time.
The combination of high photon throughput and real-time calculation enables advances in
applications such as fluorescence lifetime imaging microscopy (FLIM) and time domain
fluorescence lifetime activated cell sorting. To demonstrate this, the device is validated in
practical bulk sample fluorescence lifetime, FLIM and simulated flow based experiments.
Photon throughputs in excess of the excitation frequency are demonstrated for a range of
organic and inorganic fluorophores for minimal error in lifetime calculation by CMM (< 5 %).