Nanoscale detection of carbon dots-induced changes in actin skeleton of neural cells.

Understanding the cytotoxicity of fluorescent carbon dots (CDs) is crucial for their applications, and various biochemical assays have been used to study the effects of CDs on cells. Knowledge on the effects of CDs from a biophysical perspective is integral to the recognition of their cytotoxicity, however the related information is very limited. Here, we report that atomic force microscopy (AFM) can be used as an effective tool for studying the effects of CDs on cells from the biophysical perspective. We achieve this by integrating AFM-based nanomechanics with AFM-based imaging. We demonstrate the performance of this method by measuring the influence of CDs on living human neuroblastoma (SH-SY5Y) cells at the single-cell level. We find that high-dose CDs can mechanically induce elevated normalized hysteresis (energy dissipation during the cell deformation) and structurally impair actin skeleton. The nanomechanical change highly correlates with the alteration of actin filaments, indicating that CDs-induced changes in SH-SY5Y cells are revealed in-depth from the AFM-based biophysical aspect. We validate the reliability of the biophysical observations using conventional biological methods including cell viability test, fluorescent microscopy, and western blot assay. Our work contributes new and significant information on the cytotoxicity of CDs from the biophysical perspective.

Considerable Piezochromism in All-Inorganic Zero-Dimensional Perovskite Nanocrystals via Pressure-Modulated Self-Trapped Exciton Emission.

Piezochromic materials refer to a class of matters that alter their photoluminescence (PL) colors in response to the external stimuli, which exhibit promising smart applications in anti-counterfeiting, optoelectronic memory and pressure-sensing. However, so far, most reported piezochromic materials have been confined to organic materials or hybrid materials containing organic moieties with limited piezochromic range of less than 100 nm in visible region. Here, we achieved an intriguing piezochromism in all-inorganic zero-dimensional (0D) Cs3Cu2Cl5 nanocrystals (NCs) with a considerable piezochromic range of 232 nm because of their unique inorganic rigid structure. The PL energy shifted from the lowest-energy red fluorescence (1.85 eV) to the highest-energy blue fluorescence (2.83 eV), covering almost the entire visible wavelength range. Pressure-modulated self-trapped exciton emission between different energy levels of self-trapped states within Cs3Cu2Cl5 NCs was the main reason for this piezochromism property. Note that the quenched emission, which is over five times more intense than that in the initial state, is retained under ambient conditions upon decompression. This work provides a promising pressure indicating material, particularly used in pressure stability monitoring for equipment working at extreme environments.

Exceptional point protected robust on-chip optical logic gates.

Optical logic gates are crucial components for information processing and communication using photons. Current optical logic gates typically rely on the light interference principle which requires an accurate manipulation of the dynamical phase of light, making the device quite sensitive to system disturbances such as fabrication errors. Here we introduce non-Hermitian principles into the design of optical logic gates that work in the signal transmission process. We propose an exclusive-or gate for silicon-on-insulator platform by employing the physics in the exceptional point (EP) encirclement process. The EP induced mode switching behavior is applied to manipulate the phase of light which is topologically protected by the energy surface around the EP. As a result, the performance of the device is found to be extremely robust to structural parameter disturbances. The proposed non-Hermitian principle is expected to find applications for other on-chip photonic devices toward high robust performance.

Design of a non-Hermitian on-chip mode converter using phase change materials.

The introduction of non-Hermiticity into photonics has enabled new design principles for photonic devices. Here we propose the design of a tunable non-Hermitian on-chip mode converter working at telecommunication wavelengths. The key component of the converter is a phase change material, and switching its working state can enable a topological change in the energy surface of the system. The conversion functionality can be realized by dynamically encircling an exceptional point in the parameter space of the device. The device based on this non-Hermitian principle is robust to perturbations of structural parameters and works in broadband. The non-Hermitian principle can be applied for the design of more complex on-chip photonic devices.