Compartmentalization inside cells is essential to provide confined reaction spaces for multistep enzyme reactions¹. So far, several artificial systems such as liposomes, vesicles, polymersomes, etc. have been developed to mimic such phenomenon^2-4. Our group’s strong interest in expanding the scope of audible sound led us to an exciting journey of exploring spatiotemporal regulation of enzymatic cascade reactions within region-specific domains in the same solution!

We noticed the creation of transient domains well-separated by an invisible wall at the nodal regions of the surface waves while dealing with liquid vibrations caused by sound. These spatiotemporal domains behave as “pseudo-compartments” while the invisible walls act as “pseudo-barriers”. The domains can be utilized to control enzyme-based cascade reactions in a region-specific fashion. We took advantage of the fact that oxygen in the air gets dissolved faster in the antinodal regions below the surface waves (Figure 1).

_{Figure 1. Audible sound-induced generation of transient domains and spatiotemporally controlled cascade reaction networks.}

 To test this hypothesis, we first studied a multistep enzyme process including glucose oxidase (GOx) and horseradish peroxidase (HRP). The enzyme GOx catalyzes the oxidation of glucose (with the help of aerial oxygen) and creates hydrogen peroxide in the first step. The enzyme HRP uses this peroxide to power the second phase, which includes converting a colorless dye (ABTS) into its cyan-colored (radical) state. As shown in Figure 2, the appearance of cyan hue within specific domains of the solution verified our claim that multistep enzyme cascade reactions can indeed be controlled utilizing this approach.

_{Figure 2. Audible sound-mediated spatiotemporal control over glucose/GOx/HRP/ABTS cascade reaction. (A) Schematic representation of glucose/GOx/HRP/ABTS cascade reaction. (B) The random shaped pattern generated without applying audible sound (C) Time-dependent changes of a concentric ring pattern obtained by applying an audible sound input (40 Hz).}

 We further extended this concept to control the redox-driven in situ growth and self-assembly of gold nanoparticles within spatiotemporal domains present in the solution, as shown in Figure 3A. Thereafter, we arrested this nanoparticle pattern within a hydrogel matrix, which contained self-assembled gold nanoparticles (blue) only in the selected regions of the hydrogel. As illustrated in Figure 3B, this hydrogel was employed as a scaffold for the region-specific growth of HeLa cells.

_{Figure 3. (A) Audible sound and enzyme-mediated spatiotemporal control of gold nanoparticle assembly. Colored concentric patterns and TEM images were taken from each region of the pattern. (B) A photograph of nanoparticle patterned hydrogel (left) and its utilization for selective HeLa cell growth on the hydrogel (right).}

 “This new approach using audible sound will provide a totally new and reliable strategy to control chemical processes within predictable yet transiently generated pseudo-compartments within a solution”, explains Director Kim.

 For more information read the full paper under this link:

https://www.nature.com/articles/s41467-022-30124-x

References

1. Szostak, J. W., Bartel, D. P. & P., L. Synthesizing life. Nature 409, 387–390 (2001).
2. Marguet, M., Bonduelle, C. & Lecommandoux, S. Multicompartmentalized polymeric systems: towards biomimetic cellular structure and function. Chem. Soc. Rev. 42, 512–529 (2013).
3. Küchler, A., Yoshimoto, M., Luginbühl, S., Mavelli, F. & Walde, P. Enzymatic reactions in confined environments. Nat. Nanotechnol. 11, 409–420 (2016).
4. Rideau, E., Dimova, R., Schwille, P., Wurm, F. R. & Landfester, K. Liposomes and polymersomes: a comparative review towards cell mimicking. Chem. Soc. Rev. 47, 8572–8610 (2018).