Studying biological processes and mechanics in living cells is challenging but highly rewarding. Recent advances in experimental techniques have provided numerous ways to investigate cellular processes and mechanics of living cells. However, most of existing techniques for biomechanics are limited to experiments outside or on the membrane of cells, due to the difficulties in physically accessing the interior of living cells. On the other hand, nanomaterials, such as fluorescent quantum dots (QDs) and magnetic nanoparticles, have shown great promise to overcome such limitations due to their small sizes and excellent functionalities, including bright and stable fluorescence and remote manipulability. However, except a few systems, the use of nanoparticles has been limited to the study of biological studies on cell membranes or related to endocytosis, because of the difficulty of delivering dispersed and single nanoparticles into living cells. Various strategies have been explored, but delivered nanoparticles are often trapped in the endocytic pathway or form aggregates in the cytoplasm, limiting their further use. Here we show a nanoscale direct delivery method, named nanomechanochemical delivery, where we manipulate a nanotube-based nanoneedle, carrying “cargo” (QDs in this study), to mechanically penetrate the cell membrane, access specific areas inside cells, and release the cargo [1]. We selectively delivered well-dispersed QDs into either the cytoplasm or the nucleus of living cells. We quantified the dynamics of the delivered QDs by single-molecule tracking and demonstrated the applicability of the QDs as a nanoscale probe for studying nanomechanics inside living cells (by using the biomicrorhology method), revealing the biomechanical heterogeneity of the cellular environment. This method may allow new strategies for studying biological processes and mechanics in living cells with spatial and temporal precision, potentially at the single-molecule level.
Using bespoke fluorescence microscopy to study the soft condensed matter of living cells at the single molecule level
