Time-resolved spectroscopy at 19,000 lines per second using a CMOS SPAD line array enables advanced biophotonics applications
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A. Kufcsák, A. Erdogan, R. Walker, K. Ehrlich, M. Tanner, A. Megia-Fernandez, E. Scholefield, P. Emanuel, K. Dhaliwal, M. Bradley, R. K. Henderson, and N. Krstajić
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University of Edinburgh / Heriot-Watt University

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This paper shows the unique properties of light detectors designed in our group, and the improved performance they provide in various different biomedical applications. Our main focus was using time-resolved fluorescence spectroscopy and Raman spectroscopy to demonstrate the detector capabilities.

Introduction:

In many biomedical applications, we gather information on the examined specimen by exciting its molecules with light of a certain wavelength. Fluorescence light is released from the specimen, typically nanoseconds later during the relaxation process. The wavelength of this fluorescence light and the distribution of its intensity in time are indicative measures of the molecules in question and their environment.

Another technique to measure the ‘fingerprint’ of the molecules under investigation is Raman spectroscopy. In Raman spectroscopy, we measure the light that is scattered on the molecules during excitation, and also the shift in wavelength with respect to the wavelength of the excitation light.

Aim:

We intended to show that the versatile architecture of our detector, with its surrounding circuitry, provides a powerful tool for improving various spectroscopic applications. We also wanted to show that the speed of the sensor allows real-time measurement of changes in the fluorescent signals and the ability to fingerprint fast chemical reactions in a cost-effective system.

Method:

Our detector has the sensitivity to detect single photons whilst measuring the exact point in time when the photon is detected. The detector has 256 pixels that allows parallel measurements of several wavelengths of light as they fall on the detector. Timing circuitry at each of the pixels allows efficient timestamping of photon arrivals to measure the lifetime of exponential fluorescent decays. The capability of restricting the detection to a certain time interval (time-gating) can be used for enhanced detection of light signals and suppressing noise of the measurements.

Results:

We have shown that, to date, our system is the fastest at measuring time-resolved spectral fluorescence signals based on single photon counting and using low cost instruments. We also showed the potential use of our detector for improved detection of Raman signals.

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This paper was published in Optics Express Vol. 25, Issue 10, pp. 11103-11123 (2017)