In vitro and in vivo NIR Fluorescence Lifetime Imaging with a time-gated SPAD camera

Near-infrared (NIR) fluorescence lifetime imaging (FLI) provides a unique contrast mechanism to monitor biological parameters and molecular events in vivo. Single-photon avalanche photodiode (SPAD) cameras have been recently demonstrated in FLI microscopy (FLIM) applications, but their suitability for in vivo macroscopic FLI (MFLI) in deep tissues remains to be demonstrated. Herein, we report in vivo NIR MFLI measurement with SwissSPAD2, a large time-gated SPAD camera. We first benchmark its performance in well-controlled in vitro experiments, ranging from monitoring environmental effects on fluorescence lifetime, to quantifying Förster Resonant Energy Transfer (FRET) between dyes. Next, we use it for in vivo studies of target-drug engagement in live and intact tumor xenografts using FRET. Information obtained with SwissSPAD2 was successfully compared to that obtained with a gated-ICCD camera, using two different approaches. Our results demonstrate that SPAD cameras offer a powerful technology for in vivo preclinical applications in the NIR window.

Spatiotemporal Characteristics of Radio Frequency Dielectric Barrier Glow Discharge at Atmospheric Pressure

In this paper, argon was used in radio frequency (13.56 MHz) dielectric barrier discharge (rf-DBD) at atmospheric pressure. The IV curve was recorded after gas breakdown, and discharge photos were captured by ICCD camera. Discharges of α mode and γ mode were observed based on IV curve and ICCD photos. As the existence of negative glow in γ mode, the luminescence intensity of different position of the discharge gap was analyzed. It was found that in the α mode, the electron avalanche occurs from negative to positive and negative glow appeared after the discharge changed into γ mode. In every half cycle, the peak position of negative glow is 13 ± 1 ns later than that of electron avalanche on cathode surface.

Acceleration characteristics of laser ablation Cu plasma in the electrostatic field

As a new concept of space propulsion system, laser-ablation propulsion has attracted more and more attention due to its characteristics of low power consumption, high specific impulse, variable and controllable thrust. With an aim to further raise up the movement velocity of plasma, we combine the laser with high-voltage electrostatic field to accelerate the Cu plasma induced by laser ablation. To demonstrate the acceleration characteristics of plasma under different electric field intensity, the plasma conductivity, plasma shockwave intensity and plasma plume movement process were tested using parallel electrode plate device, self-made torsion pendulum impulse test bench and high-speed ICCD camera. The results showed that the conductive current and impulse formed by the plasma obviously increased under the applied electric field. The images captured by high-speed ICCD camera showed the plasma cross-sectional area was 0.194 mm2 at 900 ns and 0.217 mm2 at 1600 ns when the electric field intensity was 0 V/mm. With the electric field intensity increased to 30 V/mm, the plasma cross-sectional area elevated to 0.280 mm2 at 900 ns and 0.288 mm2 at 1600 ns. The acquisitions prove that the idea of this paper is feasible and favorable, which provide a theoretical basis for the combination of laser ablation propulsion and electric field.

On the formation of a bead structure of spark channels during a discharge in air at atmospheric pressure

The conditions for the formation of spark channels with a bead structure in an inhomogeneous electric field at different polarities of voltage pulses are studied. Voltage pulses with an amplitude of up to 150 kV and a rise time of ≈1.5 µs were applied across a 45-mm point-to-plane gap. Under these conditions, spark channels consisting of bright and dim regions (bead structure) were observed. It is shown that when current is limited, an increase in the rise time and the gap length does not affect the formation of the bead structure. It was found that an increase in the amplitude of voltage pulses leads to an increase in the length of beads. The appearance of the bead structure is more likely at negative polarity of the pointed electrode. The formation of spark channels was studied with a four-channel ICCD camera.

New Insights into the Reaction Paths of Hydroxyl Radicals with Purine Moieties in DNA and Double-Stranded Oligodeoxynucleotides

The reaction of hydroxyl radical (HO•) with DNA produces many primary reactive species and many lesions as final products. In this study, we have examined the optical spectra of intermediate species derived from the reaction of HO• with a variety of single- and double-stranded oligodeoxynucleotides and ct-DNA in the range of 1 μs to 1 ms by pulse radiolysis using an Intensified Charged Coupled Device (ICCD) camera. Moreover, we applied our published analytical protocol based on an LC-MS/MS system with isotopomeric internal standards to enable accurate and precise measurements of purine lesion formation. In particular, the simultaneous measurement of the four purine 5′,8-cyclo-2′-deoxynucleosides (cPu) and two 8-oxo-7,8-dihydro-2′-deoxypurine (8-oxo-Pu) was obtained upon reaction of genetic material with HO• radicals generated either by γ-radiolysis or Fenton-type reactions. Our results contributed to the debate in the literature regarding absolute level of lesions, method of HO• radical generation, 5′R/5′S diastereomeric ratio in cPu, and relative abundance between cPu and 8-oxo-Pu.

Time-of-Flight Imaging at 10 ps Resolution with an ICCD Camera

ICCD cameras can record low light events with extreme temporal resolution. Thus, they are used in a variety of bio-medical applications for single photon time of flight measurements and LIDAR measurements. In this paper, we present a method which allows improvement of the temporal resolution of ICCD cameras down to 10 ps (from the native 200 ps of our model), thus placing ICCD cameras at a better temporal resolution than SPAD cameras and in direct competition with streak cameras. The higher temporal resolution can serve for better tracking and visualization of the information carried in time-of-flight measurements.

Analysis of C2 Swan Bands in Ablation-Dominated Arcs in CO2 Atmosphere

A model circuit breaker in a high-pressure chamber filled with CO₂ atmosphere is used to operate a wall-stabilized arc of several kilo-amperes between tungsten-copper electrodes surrounded by polytetrafluoroethylene nozzles. Optical emission spectroscopy (OES) is carried out via quartz plates inserted into the nozzles using a combination of an imaging spectrometer either with a high-speed video camera or with an ICCD camera. Depending on the nozzle geometry and the current, continuum from C₂ Swan bands was detected as absorption as well as emission pattern. After current zero, optical absorption spectroscopy (OAS) using a xenon flashlamp as broadband background radiator was applied. An absorption around 493 nm was detected and attributed to CuF molecules. The study proofs the existence of C₂ in the active phase and the formation of CuF near to current zero.

Application of The Chain Code and Fourier Analysis Techniques for The Investigation of Wrinkles and Distortions on Early Flames

The study of flame commencement and growth in SI engine has attracted the attention of many researchers due to its strong dependence to the in-cylinder flow and its capability to influence flame propagation characteristics in SI engines. Optical visualisation has been one of the prominent techniques utilized in this study of the early flame properties. This work shows the application of Elliptic Fourier analysis (EFA) and image processing tools for the investigation of the early flame details from its shape features. An endoscopic ICCD camera was used to capture the flame images, at an interval of 2° CA starting from ignition onset for a period of 30° CAs (about 3 ms), from a CNG DI single cylinder SI engine operation in stratified and homogeneous charge conditions. The intake configuration was adjusted to acquire tumble or swirl induction, and engine speed was made to vary between 1500 and 2100 rpm. The sequences of collected images were processed to investigate wrinkles, distortion and growth rate of the early flame within the 3 ms combustion duration. Some tools of image processing, such as intensity enhancement, filtering, thresholding and boundary tracing, were applied. Once the flame boundary identified, it was chain coded, and elliptic Fourier function was utilised to characterise the contour. For this purpose, a computer programming code was proposed by the authors for automatic processing of the flame image data. The application of the elliptic Fourier analysis was found useful in the investigation of the early flame characteristics from its shape features; led to the portrayal of wrinkles and distortion levels quantitatively in a simpler way.