Effect of Gel–Solution Interface on Femtosecond Laser-Induced Nucleation of Protein

Abstract

The effect of gel–solution interfaces on the femtosecond laser-induced nucleation of proteins was investigated. Using hen egg white lysozyme, we found that the nucleation efficiency could be modulated by the distance between the laser focus and agarose gel surfaces (h) and the gel concentration (c). In particular, laser irradiation near the soft gel surface (h = 50 μm, c = 0.5%) could induce nucleation at very low supersaturation, where no nucleation could be induced in the bulk solutions even with femtosecond laser irradiation. Such enhancement of the nucleation was also confirmed for the membrane protein, acriflavine resistance protein B (AcrB), and an organic compound, N-(4-hydroxyphenyl)acetamide (paracetamol). To gain further insights into the role of gel–solution interfaces, we conducted fast imaging of cavitation bubbles, which are known to locally concentrate supersaturated solutions and thus act as a trigger for laser-induced nucleation. We found that the cavitation bubbles shrank asymmetrically near the soft gel surfaces and then finally collapsed toward the solution side. This is in contrast to the symmetric collapse in bulk solutions, which generates a large amount heat and chemical decomposition at the focus. In addition, cavitation bubbles generated near stiff gel surfaces (c ≥ 2%) caused an axial liquid jet toward the gel surfaces, which would disturb the formation of locally concentrated regions. These results suggest that gel–solution interfaces significantly modulate cavitation bubble dynamics and can be cues to achieve effective nucleation.