Facile Synthesis of pH-sensitive Germanium Nanocrystals with High Quantum Yield for Intracellular Acidic Compartment Imaging

Excessive STAU1 condensate drives mTOR translation and autophagy dysfunction in neurodegeneration

The double-stranded RNA-binding protein Staufen1 (STAU1) regulates a variety of physiological and pathological events via mediating RNA metabolism. STAU1 overabundance was observed in tissues from mouse models and fibroblasts from patients with neurodegenerative diseases, accompanied by enhanced mTOR signaling and impaired autophagic flux, while the underlying mechanism remains elusive. Here, we find that endogenous STAU1 forms dynamic cytoplasmic condensate in normal and tumor cell lines, as well as in mouse Huntington's disease knockin striatal cells. STAU1 condensate recruits target mRNA MTOR at its 5'UTR and promotes its translation both in vitro and in vivo, and thus enhanced formation of STAU1 condensate leads to mTOR hyperactivation and autophagy-lysosome dysfunction. Interference of STAU1 condensate normalizes mTOR levels, ameliorates autophagy-lysosome function, and reduces aggregation of pathological proteins in cellular models of neurodegenerative diseases. These findings highlight the importance of balanced phase separation in physiological processes, suggesting that modulating STAU1 condensate may be a strategy to mitigate the progression of neurodegenerative diseases with STAU1 overabundance.

Insight into the Effect of Ligands on the Optical Properties of Germanium Quantum Dots and Their Applications in Persistent Cell Imaging

Germanium quantum dots (GeQDs) show unique advantages in fluorescence applications due to their large quantum confinement effect and excellent biocompatibility. However, GeQDs are confronted with difficulty in accurately controlling the fluorescence emission. This defect brings challenges to understanding the fluorescence mechanism and limits the potential applications of GeQDs. In this paper, a series of GeQDs with the average diameter of about 2.6 nm modified with different ligands were synthesized by the chemical reduction method. The fluorescence emission of GeQDs can be changed from blue to yellow-green through adjusting the surface ligands. The influence of surface ligands on the fluorescence emission of GeQDs was thoroughly investigated by experimental and theoretical calculations. Furthermore, the synthesized GeQDs exhibit good biocompatibility and photostability and can act as high-performance fluorescence probes for long-term fluorescent bioimaging. This work provides a good and deep understanding of the fluorescence mechanism of GeQDs and will facilitate diverse promising applications of GeQDs in the near future.

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12-14 and 14-16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

Effect of temperature on B(C6F5)3-catalysed reduction of germanium alkoxides by hydrosilanes - a new route to germanium nanoparticles

Reduction of Ge(OBu)4 with PhMe2SiH catalyzed by B(C6F5)3 at ambient temperature leads to GeH4. We discovered that a higher temperature (above 100 °C) completely changes the reaction course by producing germanium nanoparticles (Ge NPs) in high yield. This process provides a simple one-pot method for Ge NPs synthesis from readily available substrates under mild conditions.

Surface coordination chemistry of germanium nanocrystals synthesized by microwave-assisted reduction in oleylamine

As surface ligands play a critical role in the colloidal stability and optoelectronic properties of semiconductor nanocrystals, we used solution NMR experiments to investigate the surface coordination chemistry of Ge nanocrystals synthesized by a microwave-assisted reduction of GeI2 in oleylamine. The as-synthesized Ge nanocrystals are coordinated to a fraction of strongly bound oleylamide ligands (with covalent X-type Ge-NHR bonds) and a fraction of more weakly bound (or physisorbed) oleylamine, which readily exchanges with free oleylamine in solution. The fraction of strongly bound oleylamide ligands increases with increasing synthesis temperature, which also correlates with better colloidal stability. Thiol and carboxylic acid ligands bind to the Ge nanocrystal surface only upon heating, suggesting a high kinetic barrier to surface binding. These incoming ligands do not displace native oleylamide ligands but instead appear to coordinate to open surface sites, confirming that the as-prepared nanocrystals are not fully passivated. These findings will allow for a better understanding of the surface chemistry of main group nanocrystals and the conditions necessary for ligand exchange to ultimately maximize their functionality.

Intracellular Trafficking Network and Autophagy of PHBHHx Nanoparticles and their Implications for Drug Delivery

3-hydroxybutyrate-co-3-hydroxyhexanoate (PHBHHx), which is naturally generated by biodegradable polyhydroxyalkanoates synthesized by bacteria, is an attractive material for drug delivery due to its controllable physical properties, non-toxicity, environmental friendliness, degradable properties and good biocompatibility. However, the intracellular trafficking network pathways, especially the autophagy mechanism of PHBHHx nanoparticles (NPs), have rarely been investigated. In this paper, we successfully prepared the NPs used solvent displacement method and investigated the autophagy pathways and other intracellular trafficking mechanisms based on NPs with the assistance of Rab proteins. We found that NPs were internalized in cells mainly via clathrin endocytosis and caveolin endocytosis. Beside the classical pathways, we discovered two new pathways: the micropinocytosis early endosome (EEs)-micropinocytosis-lysosome pathway and the EEs-liposome-lysosome pathway. NPs were delivered to cells through endocytosis recycling vesicles and GLUT4 exocytosis vesicles. Similar to other nanoparticles, NPs also induced intracellular autophagy and were then degraded via endolysosomal pathways. 3-MA and CQ were used as autophagy inhibitors to avoid the degradation of NPs through lysosomes by blocking endolysosomal pathways. Tumor volumes and weights were significantly decreased when autophagy inhibitors and chemical drugs packaged in NPs were cooperatively used.

Inhibition of CaMKIIα Activity Enhances Antitumor Effect of Fullerene C60 Nanocrystals by Suppression of Autophagic Degradation

Fullerene C60 nanocrystals (nano-C60) possess various attractive bioactivities, including autophagy induction and calcium/calmodulin-dependent protein kinase IIα (CaMKIIα) activation. CaMKIIα is a multifunctional protein kinase involved in many cellular processes including tumor progression; however, the biological effects of CaMKIIα activity modulated by nano-C60 in tumors have not been reported, and the relationship between CaMKIIα activity and autophagic degradation remains unclear. Herein, nano-C60 is demonstrated to elicit reactive oxygen species (ROS)-dependent cytotoxicity and persistent activation of CaMKIIα in osteosarcoma (OS) cells. CaMKIIα activation, in turn, produces a protective effect against cytotoxicity from nano-C60 itself. Inhibition of CaMKIIα activity by either the chemical inhibitor KN-93 or CaMKIIα knockdown dramatically promotes the anti-OS effect of nano-C60. Moreover, inhibition of CaMKIIα activity causes lysosomal alkalinization and enlargement, and impairs the degradation function of lysosomes, leading to autophagosome accumulation. Importantly, excessive autophagosome accumulation and autophagic degradation blocking are shown to play an important role in KN-93-enhanced-OS cell death. The synergistic anti-OS efficacy of KN-93 and nano-C60 is further revealed in an OS-xenografted murine model. The results demonstrate that CaMKIIα inhibition, along with the suppression of autophagic degradation, presents a promising strategy for improving the antitumor efficacy of nano-C60.

Versatile Hydrogel Ensembles with Macroscopic Multidimensions

Methods allowing construction of macroscopic programmed materials in a flexible and efficient fashion are highly desirable. However, the existing approaches are far removed from such materials. A new self-healing-driven assembly (SHDA) strategy to fabricate various programmed materials by using uniform gel beads (microsize of 212 µm or millimeter size of 4 mm) as building blocks is described here. In virtue of hydrogen bonds and host-guest interactions between gel beads, a series of linear, planar, and 3D beaded assemblies are fabricated via SHDA in microfluidic channels in a continuous and controlled manner. From the perspective of practical applications, the use of gel assemblies is exploited for tissue engineering with controlled cells coculture, as well as light conversion materials toward white-light-emitting diodes (WLEDs). The SHDA strategy developed in this study gives a new insight into the facile and rapid fabrication of various programmed materials toward biological tissue and optoelectronic device.

Non-Metal-Heteroatom-Doped Carbon Dots: Synthesis and Properties

Carbon dots (CDs) are new materials with applications in bioimaging, optical devices, catalysis, and many other fields. Their advantages, such as ease of large-scale preparation, low-costing precursors, highly tunable photoluminescence, satisfactory biocompatibility, and photostability against photobleaching, make them competitive alternatives to conventional semiconductor-based quantum dots and organic dyes. To overwhelm other luminescent materials in applications, their functionalities still need to be improved in spite of the abovementioned advantages. In recent years, it has been proven that heteroatom doping is an effective approach to improve the optical and electronic performance of CDs by tuning their carbon skeleton matrices and chemical structures. In this review, the development of non-metal-heteroatom-doped CDs, including heteroatom categories, preparation methods, and physicochemical properties, are discussed. Progressive trends in heteroatom-doped CDs are also discussed at the end of this review.

Graphene oxide induces p62/SQSTM-dependent apoptosis through the impairment of autophagic flux and lysosomal dysfunction in PC12 cells

Graphene oxide (GO), as a two-dimensional carbon nanosheet, has been extensively studied for potential biomedical applications due to its notable properties. Although a growing number of studies have investigated the adverse effects of GO nanosheets, the available toxicity data concerning GO's effect on the neuronal cells remain highly limited. In this work, we systematically investigated the toxic responses of commercially available GO on a rat pheochromocytoma-derived PC12 cell line, which was an ideal in vitro model to study the neurotoxicity of GO. GO exerted a significant toxic effect on PC12 cells in a dose- and time-dependent manner. GO treatments under doses of 40, 50, and 60 μg/mL triggered an autophagic response and the blockade of autophagic flux via disrupting lysosome degradation capability. Caspase 9-mediated apoptosis was also observed in GO-treated cells. Moreover, GO-induced apoptosis was relevant to the aberrant accumulation of autophagy substrate p62/SQSTM. Inhibitionofthe accumulation of autophagic substrate alleviated GO-caused apoptotic cell death. Our findings raise a concern for the putative biomedical applications of GO in the form of diagnostic and therapeutic tools, where its systematic biocompatibility should be thoroughly explored. STATEMENT OF SIGNIFICANCE: Graphene oxide (GO) has attracted considerable interests in biomedical fields, which also resulted in numerous safety risks to human bodies. It is urgently required to establish a paradigm for accurately evaluating their adverse effects in biological systems. This study thoroughly explored the neurotoxicity of GO in PC12 cells. We found GO triggered an increased autophagic response and the impairment of autophagic flux, which was functionally involved in cell apoptosis. Inhibitionofexcessive accumulation of autophagic cargo attenuated apoptotic cell death. Our findings highlight deep considerations on the regulation mechanism of autophagy-lysosomes-apotosis-axis, which will contribute to a better understanding of the neurotoxicity of graphene-family nanomaterials, and provide a new insight in the treatment of cancer cells at nanoscale levels.

Transcription factor E3 protects against cadmium-induced apoptosis by maintaining the lysosomal-mitochondrial axis but not autophagic flux in Neuro-2a cells

Cadmium (Cd), is a well-known environmental and occupational hazard with a potent neurotoxic action. However, the mechanism underlying cadmium-induced neurotoxicity remains unclear. Herein, we exposed Neuro-2a cells to different concentrations of cadmium chloride (CdCl₂) (12.5, 25 and 50 μM) for 24 h and found that Cd significantly induced lysosomal membrane permeabilization (LMP) with the release of cathepsin B (CTSB) to the cytosol, which in turn caused the release of mitochondrial cytochrome c (Cyt c) and eventually triggered caspase-dependent apoptosis. Interestingly, Cd decreased TFE3 expression but induced the nuclear translocation of TFE3 and TFE3 target-gene expression, which might be associated with lysosomal stress mediated by Cd. Notably, Tfe3 overexpression protected against Cd-induced neurotoxicity by maintaining the lysosomal-mitochondrial axis, and the protective effect of TFE3 is not dependent on the restoration of autophagic flux. In conclusion, our study demonstrated for the first time that lysosomal-mitochondrial axis dependent apoptosis, a neglected mechanism, may be the most important reason for Cd-induced neurotoxicity and that manipulation of TFE3 signaling may be a potential therapeutic approach for treatment of Cd-induced neurotoxicity.

A fullerene-rhodamine B photosensitizer with pH-activated visible-light absorbance/fluorescence/photodynamic therapy

A heavy-atom-free photosensitizer (C₆₀-RB) with pH-activable visible-light absorbance enhancement, fluorescence turn-on and triplet excited state generation was designed for tumor bioimaging and photodynamic therapy.

Dual-spectra encoded suspension array using reversed-phase microemulsion UV curing and electrostatic self-assembling

The rapid growth of demand for high-throughput multiplexed biochips from modern biotechnology has led to growing interest in suspension array based on multi-channel encoded microbeads. We prepare dual-spectra encoded PEGDA microbeads (DSEPM) by reversed-phase microemulsion UV curing method and layer-by-layer electrostatic self-assembly method. Excitation of the synthesized DSEPM results in two spectra, including fluorescence spectra from quantum dots and laser induced breakdown spectra from nanoparticles with specific elements. With further surface modification and bio-probes grafting, we use DSEPM to carry a series of detection experiments of biomolecules. The adsorption experiment to two types of anti-IgG in mixture sample has demonstrated the availability of DSEPM in multiplexing. Then, the contrast experiment has verified the specificity of DSEPM in detection. Finally, we carry out the concentration gradient experiment and obtain the response curve to show the performance of DSEPM in quantitative analysis. The results indicate our method provide an effective way to improve multiplexed biochips with more coding capacity, accuracy and stability.

The rapid growth of demand for high-throughput multiplexed biochips from modern biotechnology has led to growing interest in suspension array based on multi-channel encoded microbeads.

Transition metal dichalcogenide quantum dots: synthesis, photoluminescence and biological applications

We introduce the synthesis strategy, photoluminescence features and biological applications of TMD QDs.

Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties

Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO₂. Crystalline Ge nanoparticles were directly formed during co-deposition of SiO₂ and Ge on substrates at 300, 400 and 500 °C. Using this approach, effects related to Ge-Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO₂/ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW^-1), fast response time (0.5 µs at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO₂ matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO₂ matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.

Assembly of hepatitis E vaccine by 'in situ' growth of gold clusters as nano-adjuvants: an efficient way to enhance the immune responses of vaccination

Vaccine-based immunotherapy plays an integral role in the development of present and future clinical therapies. Despite the success, there is still a great need to improve the efficiency and safety of vaccines. Nanoparticles have been widely used for improving the efficacy of vaccines by encapsulating the vaccines or using nanoparticles as immune adjuvants. However, the methods for the preparation of nanoparticles are complex with a relatively low encapsulation efficiency of protein vaccine inside the nanocarriers and/or undefined physiochemical properties. Here, we report a new method of preparation of a vaccine by the "in situ" growth of gold clusters in the hepatitis E vaccine (HEVA). The gold cluster grafted HEVA (HEVA/Au) can be easily obtained and there is no loss of HEVA during the preparation process. More importantly, the "in situ" prepared HEVA/Au can not only enhance its immune responses in vivo, but also reduce the potential toxicity of HEVA. Furthermore, the intrinsic fluorescence of gold clusters enables the HEVA to be traceable, which may open a way to track the dynamic behavior of vaccines and further help to optimize an individual therapeutic regimen for immunotherapy.

Microfluidic synthesis of QD-encoded PEGDA microspheres for suspension assay

A simple microfluidic device is designed to generate monodispersed QD-encoded PEGDA microbeads. PEGDA/PDA composite microspheres are prepared to easily couple protein on their surface. A sandwich immunoassay of rabbit IgG is performed to indicate that PDA on the bead surface facilitates efficient attachment of biomacromolecules.

Probing Bio-Nano Interactions between Blood Proteins and Monolayer-Stabilized Graphene Sheets

Meeting proteins is regarded as the starting event for nanostructures to enter biological systems. Understanding their interactions is thus essential for a newly emerging field, nanomedicine. Chemically converted graphene (CCG) is a wonderful two-dimensional (2D) material for nanomedicine, but its stability in biological environments is limited. Systematic probing on the binding of proteins to CCG is currently lacking. Herein, we report a comprehensive study on the interactions between blood proteins and stabilized CCG (sCCG). CCG nanosheets are functionalized by monolayers of perylene leading to significant improvement in their resistance to electrolyte salts and long-term stability, but retain their core structural characteristics. Five types of model human blood proteins including human fibrinogen, γ-globulin, bovine serum albumin (BSA), insulin, and histone are tested. The main driving forces for blood protein binding involve the π-π interacations between the π-plane of sCCG and surface aromatic amonic acid (sAA) residues of proteins. Several key binding parameters including the binding amount, Hill coefficient, and binding constant are determined. Through a detailed analysis of key controlling factors, we conclude that the protein binding to sCCG is determined mainly by the protein size, the number, and the density of the sAA.

Microfluidic generation of uniform quantum dot-encoded microbeads by gelation of alginate

A facile method was reported to generate monodispersed QD encoded alginate microbeads by employing a simple microfluidic device using an internal gelation approach. The application of the as-prepared microbeads for a suspension assay was demonstrated.