Multiplexed near infrared fluorescence lifetime imaging in turbid media.

Significance: Fluorescence lifetime imaging (FLI) plays a pivotal role in enhancing our understanding of biological systems, providing a valuable tool for non-invasive exploration of biomolecular and cellular dynamics, both in vitro and in vivo. Its ability to selectively target and multiplex various entities, alongside heightened sensitivity and specificity, offers rapid and cost-effective insights. Aim: Our aim is to investigate the multiplexing capabilities of near-infrared (NIR) FLI within a scattering medium that mimics biological tissues. We strive to develop a comprehensive understanding of FLI's potential for multiplexing diverse targets within a complex, tissue-like environment. Approach: We introduce an innovative Monte Carlo (MC) simulation approach that accurately describes the scattering behavior of fluorescent photons within turbid media. Applying phasor analyses, we enable the multiplexing of distinct targets within a single FLI image. Leveraging the state-of-the-art single-photon avalanche diode (SPAD) time-gated camera, SPAD512S, we conduct experimental wide-field FLI in the NIR regime. Results: Our study demonstrates the successful multiplexing of dual targets within a single FLI image, reaching a depth of 1 cm within tissue-like phantoms. Through our novel MC simulation approach and phasor analyses, we showcase the effectiveness of our methodology in overcoming the challenges posed by scattering media. Conclusions: This research underscores the potential of NIR FLI for multiplexing applications in complex biological environments. By combining advanced simulation techniques with cutting-edge experimental tools, we introduce significant results in the non-invasive exploration of biomolecular dynamics, to advance the field of FLI research.

Non-monotonic dynamics of thin film spreading.

The phenomenon of a precursor spreading in front of an advancing droplet is still not fully understood. We recently used a driven lattice-gas model to study the microscopic dynamics of thin film spreading. We found that the scaling exponents describing the dynamics of both the precursor and the bulk layers are not universal, and strongly depend on the parameters describing the various interactions in the system. In this paper we show yet another nontrivial and rich behavior of the system. This is the non-monotonicity of the exponents, which reflects the competition between the various mechanisms that drive the system. In particular, we study the dependence of the scaling exponents on the ratio of the external substrate potential and the internal short-range interactions that drive the spreading in both layers.

Effect of temperature on the dynamics and geometry of reactive-wetting interfaces around room temperature.

The temperature effect on the dynamics and geometry of a mercury droplet (∼150 µm) spreading on a silver substrate (4000 Å) was studied. The system temperature was controlled by a heating stage in the temperature range of -15 °C < T < 25 °C, and the spreading process was monitored using an optical microscope. We studied the wetting dynamics (droplet radius and velocity) as a function of temperature. We found that for all studied temperatures, the spreading radius R(t) grows linearly with time, with a velocity value depending on temperature. We also studied the temperature effect on the kinetic roughening properties of the advancing interface (growth (ß) and roughness (α) exponents). Our results show that the growth exponent increases with temperature while the roughness exponent is relatively constant. In addition, we obtained the system's activation energy at this temperature range.