Diffusion of Methylene Blue in Phantoms of Agar Using a Photoacoustic Technique

Abstract

In this work, the kinetics of diffusion of methylene blue in agar aqueous solution is studied using a photoacoustic technique. Two agar phantoms solutions in water with a relation of mass/volume of 0.01 % and 0.05 % were analyzed. The study was performed using a modified Rosencwaig photoacoustic cell that is enclosed by transparent windows, on both sides. The sample is deposited directly on top of the upper window. A red light beam, at a fixed modulation frequency, is sent through the lower window illuminating the sample and inducing the photoacoustic effect inside the closed chamber of the cell. At the beginning of the experiment, a droplet of 100 µL of agar solution is deposited; afterwards, the signal stabilizes, and 10 µL of methylene blue aqueous solution (0.0125 g · mL −1 ) is added to the surface of the agar. During the first seconds of the experiment, the photoacoustic signal amplitude increases followed by a gradual and long decay. Results for modulation frequencies in the range from 10 Hz to 80 Hz for both agar concentrations are presented. A simple theoretical approach is presented to analyze the experimental data. It is demonstrated that the kinetics of the process can be parameterized as a function of the changes of an effective optical absorption coefficient. From these results, the characteristic time, in which the dye diffusion process stabilizes, is obtained. It is found that this time is larger for samples with a higher agar concentration. These differences provide important results for biomedical sciences in which agar gels are used as phantoms resembling some of the properties of living organs and tissues.

Molecular Photoacoustic Contrast Agents: Design Principles & Applications

“…In recent years, with a growing interest in PAI for biological applications, there has been a resurgence PA studies of MB. These studies have ranged from PAI in tissue phantoms to in vivo PAI of sentinel lymph nodes , to PA lifetime studies for aggregate and in vivo dissolved oxygen quantification, US/PA dual modality imaging of MB/perfluorocarbon microbubbles (Fig. ) and theranostic PAI/PTT studies of polypyrrole‐methylene blue nanoparticles .…”

Diffusion of Methylene Blue in Phantoms of Agar Using Optical Absorption Techniques

“…In order to get data independent of the microphone characteristics, the PA signal amplitude at any time was normalized dividing it by the maximum value of the PA signal amplitude for a given experiment. In order to understand the evolution of the PA signal, a theoretical methodology is used, in which it is considered that the system has homogeneous optical and thermal properties at any given time (Vilca et al, 2010). The formalism consists in finding the temperature of the layered system shown in Fig.…”

“…Also, the low frequency option provides a better measurement due to a higher thermal diffusion length of the PA system. These effects have been studied for different frequencies indicating that thermal wave phenomena, is more sensitive when the thermal wave monitors the changes occurring through the column detector that contains the sample (Vilca et al, 2010). In Figs.…”

Implementation of Polyvynil-Alcohol Mixed With Nano-Particles as a Near Representation of Biological Tissue: Ultrasonic and Photo- Thermal Study

“…These are made with the aid of dummy samples (phantoms). Among the most frequent types of phantoms are those manufactured with agar, polyester, epoxy -resins and natural rubber [9]. In each case, the model is tailormade for a specific purpose since the optical, the mass density, the elasto-mechanical and the thermal properties are not easy to manipulate [10].…”