MHz LED source for nanosecond fluorescence sensing

Abstract

An inexpensive and portable pulsed light emitting diode (LED) source with variable repetition rate up to 10 MHz suitable for time-resolved fluorescence sensing in medical, environmental and industrial applications is described. The pocket-sized battery-driven source is pulsed by signals from a simple logic circuit, giving measured optical pulse widths of ~1.9 ns at 525 nm as recorded using time-correlated single-photon counting. Pulses are presented for three LEDs with peak emissions at 525, 560 and 590 nm. The measurement performance is illustrated by the fluorescence lifetime and anisotropy decay of rhodamine 6G in various solvents and a fluorescence resonance energy transfer (FRET) sensor for detecting metal ions in water which uses a new measurand, namely the site distribution function ρ(r) of metal ion acceptors accumulating in an anionic porous polymer with respect to the donor fluorophores. The ρ(r) dependence reveals a minimum fluorophore-metal ion separation of ~7 Å which explains the selectivity of such FRET sensors in discriminating against other quenching mechanisms.

Compact, non-invasive frequency domain lifetime differentiation of collagens and elastin

“…A single exponential model was used to fit for the fluorescent standards. The fitting showed results of 2.57, 3.94, and 11.75 ns for FAD, FITC, and 9CA, respectively, which are comparable to results in [58,64,69]. Protein samples were fitted to a two-exponential model, with a longer lifetime component and a shorter one around 1 ns, consistent with reported values [56,57,69].…”

“…Respective standard deviations from their measurements were used to represent these uncertainties. A single exponential model was used for fluorescence standard FAD, FITC, and 9CA, to be consistent with other reported studies [58,64,69]. A two-exponential model was used for protein and tissue samples, where fractional ˛1, ˛2, and their respective 1 and 2 were calculated by minimizing the 2 function describing deviations of their ω and m ω values.…”

“…Optimum modulation frequencies for tissue fluorophores-e.g. collagen, elastin, NADH-range from 10 to 100 MHz [62], lowering the requirements for the LED modulation electronics, photodetector temporal response, as well as signal digitization and recording speed [63,64]. Moreover, a single multichannel oscilloscope can perform the timing and acquisitions for both the excitation and emissions signals.…”

Microscopic imaging of the initial stage of diesel spray formation

“…The relatively long and random jitter associated with the timing of the spark can also lead to a significant proportion of 'missed' acquisitions which, combined with the long recharge time of the high-voltage electronics, may significantly lengthen the experimental work. The LED technology has advanced rapidly, and can now provide low-jitter sub-nanosecond [14] and high-frequency light pulses [15]. However, the energy output of high-power LEDs is still insufficient to enable blur-free microscopic imaging of high-speed sprays.…”

LED-based Vis-NIR spectrally tunable light source - the optimization algorithm

“…This approach allows for the generating a broad range of different output spectral distributions of almost arbitrary shape. This in turn, enables various applications such as calibration of light-measuring instruments, ambient lighting, applications in forensic science, fluorescence applications [8][9][10], etc.…”