Nonlinearity of electroosmotic flows (EOFs) is ubiquitous and plays a crucial role in ion transport, specimen mixing, electrochemistry reaction, and electric energy storage and utilization. When and how the transition from a linear regime to a nonlinear one occurs is essential for understanding, prohibiting, or utilizing nonlinear EOF. However, due to the lack of reliable experimental instruments with high spatial and temporal resolutions, the investigation of the onset of nonlinear EOF still remains in theory. Herein, we experimentally studied the velocity fluctuations of EOFs driven by an alternating current (AC) electric field via ultrasensitive fluorescent blinking tricks. The linear and nonlinear AC EOFs are successfully identified from both the time trace and energy spectra of velocity fluctuations. The transitional electric field (E A,C ) is determined by both the convection velocity (U) and AC frequency (f f ) as E A,C ∼ f f 0.48−0.027U . We hope the current investigation could be essential in the development of both theory and applications of nonlinear EOFs.

Mechanically induced chromosome reorganization plays important roles in transcriptional regulation. However, the interplay between chromosome reorganization and transcription activities is complicated, such that it is difficult to decipher the regulatory effects of intranuclear geometrical cues. Here, we simplify the system by introducing DNA, packaging proteins (i.e., histone and protamine), and transcription factor NF-κB into a well-defined fluidic chip with changing spatical confinement ranging from 100 to 500 nm. It is uncovered that strong nanoconfinement suppresses higher-order folding of histone-and protamine-DNA complexes, the fracture of which exposes buried DNA segments and causes increased quantities of NF-κB binding to the DNA chain. Overall, these results reveal a pathway of how intranuclear geometrical cues alter the open/closed state of a DNAprotein complex and therefore affect transcription activities: i.e., NF-κB binding.

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In situ, real-time, and non-destructive monitoring of the synthesis of nanomaterials is essence crucial for the development and prospective applications of nanoscience and nanotechnology. Reflection interference spectroscopy technology was used to systematically monitor the synthesis process of a transparent (ZnCl2-ZnO)/NpAA composite film which consists of ZnCl2-ZnO nanosheets formed by ZnCl2 precursor solution on the top surface of the substrate layer of nanoporous anodic alumina. Some significant results are found, e.g., the curve of effective optical thickness with time can be divided into three stages, corresponding to the synthesis process of ZnCl2-ZnO; and more, these films generated from ZnCl2 precursor solution with different concentrations, such as 0.05 M, 0.07 M, 0.085 M, or 0.1 M, can be directly distinguished according to the characteristics of the three stages.