Optical and electrical breakdown of materials, which describe material modification in the presence of extreme optical or electrical fields, have been studied since the 1950s. However, simultaneous application of optical and electrical fields, especially, to biologically relevant systems hasn't been explored before. Prof. Vladislav V. Yakovlev from Texas A&M University said by investigating the synergistic action of electrical and optical pulses, they were able to promote highly localized breakdown, while reducing the threshold for such breakdown.

The newly discovered synergistic effect is particularly important if there is a need to selectively disrupt cellular membrane in a highly localized manner. Typically, an electroporation, a technique that applies an electrical field to cells to increase the permeability of the cell membrane, is used. Alternatively, an optoporation, which uses ultrashort laser pulses to form a small hole in the cell membrane, can be employed. A powerful combination of electroporation and optoporation can provide the benefits of both of approaches, leading to new ways drugs and vaccines can be delivered to cells and tissues.

The cooperative team's recent publication in Photonics Research vol. 9 No. 3 (Zachary N. Coker, Xiao-Xuan Liang, Allen S. Kiester, Gary D. Noojin, Joel N. Bixler, Bennett L. Ibey, Alfred Vogel, Vladislav V. Yakovlev. Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions[J]. Photonics Research, 2021, 9(3): 03000416) demonstrated that upon simultaneous excitation by nanosecond electrical pulse and picosecond optical pulse, a synergetic effect occurs, leading to reduced threshold for such breakdown.

Figure 1. (a) A theoretical model, which predicts the synergistic effect of electrical and optical pulses on the threshold of dielectric breakdown; (b) a schematic of experimental setup which used for initiating and monitoring dielectric breakdown in a medium; (c) experimental results demonstrating the probability of breakdown on the input laser energy.

The research was completed with the joint efforts of three different teams. The German team led by Prof. Alfred Vogel, the leading expert in the optical breakdown studies of biological materials, developed a theoretical model (Fig. 1a) which provided Texas A&M University and Air Force Research Laboratory researchers with guidelines for experimental realization of the proposed synergistic interactions. An experimental setup, which included both the nanosecond electrical pulser and a focused beam picosecond optical pulse excitation, was constructed (Fig. 1b), and the proposed effect was experimentally demonstrated for a number of biologically relevant media (Fig. 1c).

Figure 2. Preliminary results for cell-based studies. Fluorescent images showing YO-PRO-1 dye uptake under (a) control, (b) nanosecond electrical pulse alone, (c) picosecond optical pulses alone, and (d) combined picosecond optical and nanosecond electrical exposure conditions. Yellow dashed circle in c indicates where cells were removed from culture layer by breakdown event. Orange dashed circle in d indicates where picosecond optical pulse was focused and the reduced YO-PRO dye uptake in targeted cells, compared to surrounding cells exposed to nanosecond electrical pulse.

One of the impacts of paramount significance of this effect, which can be of great interest to a general audience, is improved accuracy of vaccine delivery for COVID-19. In preliminary data, the team performed cellular exposure to both electrical and optical pulses (Fig. 2) monitoring the integrity of the cellular membrane using a well-established dye, YO-PRO-1, which upon membrane disruption penetrates the cell.

While this technology would be a new addition to a laboratory, the research team noted that creating the effect doesn't require sophisticated equipment, allowing it to be used in a broad range of facilities.

As the research team states, a unique combination of a new fundamental science and a broad range of high-impact applications ranging from extreme light-matter interactions to nano- and biotechnology would be of great interest for a broad audience.