Autonomous molecularly crowded confinement in inkjet printed femtoliter-scale aqueous compartments

Natural evolution has chosen the localization of biomolecular processes into crowded sub-cellular femtoliter (fL) scale compartments for organizing complex biological processes. [1] Many synthetic biology platforms with life-like activities have been able to mimic these systems under different compartment sizes regimes. [2] However, the fabrication of crowded compartments down to sub-cellular scales is challenging, mainly because of high surface-volume ratio of these systems, finally compromising the stability of the encapsulated biomolecules. In this regard, we here bridge this gap by showing the possibility to produce femtoliter-scale aqueous droplets using a novel inkjet printing approach reproducing a theoretical model from Eggers et al. [3] The fL-scale droplets are spiked with non-ionic surfactants to stabilize the water/oil interface whilst not compromising ink viscosity and surface tension. [4] When injected into nL-scale mineral oil droplets, the fL-droplets form an almost-regular circular pattern at the border of mineral oil drops due to Marangoni flows (see Figure). Remarkably, downscaling at the fL-size induces the spontaneous formation of molecularly crowded shell structures at the water/oil interface, as observed by fluorescence microscopy, showing typical thickness in order of hundreds of nanometers, in accordance with previously reported models. [5] Molecular crowding effects are tested by using fluorescence lifetime imaging under the convenient phasor plot approach, [6] revealing different characteristic lifetimes of specific probe molecules in the confined volumes with respect to macroscopic solutions. The fL-scale compartments autonomously trigger the formation of unique features (e.g., spatial heterogeneity, up-concentration, molecular proximity) that are mediated by the intermolecular interactions in these novel environments. Remarkably, the crowding conditions are observed not to affect the conformation variation of a model DNA hairpin in presence of molecular triggers and of a CYP2E1-catalyzed enzymatic reaction. Our results can be a first step towards the fabrication of lab-on-a-chip compartments for molecularly crowded confinement mimicking sub-cellular environments. Bibliography 1. S. F. Banani et al., Nat. Rev. Mol. Cell Biol. 2017, 18, 285. 2. B. C. Buddingh’, J. C. M. Van Hest, Acc. Chem. Res. 2017, 50, 769. 3. G. Arrabito, F. Cavaleri et al. Adv. Biosys. 2019, 1900023 4. J. Eggers, Phys. Rev. Lett. 1993, 71, 3458. 5. M. Staszak, J. Surfactants Deterg. 2016, 19, 297. 6. C. Stringari et al. Proc. Natl. Acad. Sci. USA 2011, 108, 13582.