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ZnO, as an important semiconductor, has been extensively studied for a wide range of applications. To date, with the development of micro/nano manufacturing technology, various hierarchical ZnO nanostructures have been fabricated and explored, showing encouraging success in advanced photodetectors. ZnO nanotube structure has a high surface-to-volume ratio, and versatile hollow channels, which are promising for sensing applications. Typical nanotube arrays primarily rely on advanced nanofabrication technologies. Simple and low-cost fabrication strategies are still lacking. Herein, we report a simple template fabrication method to obtain vertically aligned ZnO nanotube arrays. Using flexible, etched polyimide membranes as the template, ZnO nanotube arrays can be prepared in situ by dip-coating the sample into a zinc acetate solution followed by heating. Different hierarchical ZnO nanotube structures were obtained with the nanotube arrays when the method was combined with hydrothermal growth. We have demonstrated that the structures may be used in flexible and transparent photodetectors. Our work provides a facile approach for fabricating ZnO nanotube arrays and expands the application of ZnO nanotube structures to flexible and transparent photodetectors. [ABSTRACT FROM AUTHOR]

Nano-electroporation technology allows external biomolecules to cross the cell membrane and enter cells. Nanostraws (NSs) with hollow channels are promising nanostructures to provide nano-electroporation for intracellular delivery, yet the preparation processes of NSs usually require intricated nanofabrication instruments and possess high requirements for operations. Here, a straightforward spin-coating processing technique was developed to prepare oxide NS arrays without relying on delicate instruments, which could be further integrated with microfluidic devices for effective cell nano-electroporation. The fabrication procedures of these NSs were simpler than the reported method relying on atomic layer deposition and Cl2 reactive ion etching. By this spin-coating method, SiO2 and TiO2 NSs were successfully prepared with controllable NS diameters and spacing. SiO2 and TiO2 NSs were further integrated with a microfluidic system to build a nano-electroporation system, which realized efficient intracellular drug delivery of cell membrane-impermeable molecules into both HeLa cells and MCF-7 cells. This strategy provides a unique solution for batch fabrication of NSs with a low-cost process, which could serve as the essential module of a nano-electroporation platform for various biomedical studies. [ABSTRACT FROM AUTHOR]

Copper species were incorporated into SBA-15 by solid-state grinding precursor with as-prepared mesoporous silica (SPA). The obtained materials (CuAS) were well-characterized by XRD, TEM, N2adsorption, H2-TPR, IR, and TG and compared with the material derived from calcined SBA-15 (CuCS). Surprisingly, CuO up to 6.7 mmol·g−1can be highly dispersed on SBA-15 by use of SPA strategy. Such CuO forms a smooth layer coated on the internal walls of SBA-15, which contributes to the spatial order and results in less-blocked mesopores. However, the aggregation of CuO takes place in CuCS material containing 6.7 mmol·g−1copper, which generates large CuO particles of 21.4 nm outside the mesopores. We reveal that the high dispersion extent of CuO is ascribed to the abundant silanols, as well as the confined space between template and silica walls provided by as-prepared SBA-15. The SPA strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in conventional modification process, and saves time and energy. We also demonstrate that the CuAS material after autoreduction exhibits much better adsorptive desulfurization capacity than CuCS. Moreover, the adsorption capacity of regenerated adsorbent can be recovered completely. [ABSTRACT FROM AUTHOR]

Techniques used to understand the dynamic expression of intracellular proteins are critical in both fundamental biological research and biomedical engineering. Various methods for analyzing proteins have been developed, but these methods require the extraction of intracellular proteins from the cells resulting in cell lysis and subsequent protein purifications from the lysate, which limits the potential of repetitive extraction from the same set of viable cells to track dynamic intracellular protein expression. Therefore, it is crucial to develop novel methods that enable nondestructive and repeated extraction of intracellular proteins. This work reports a hollow nanoneedle-electroporation system for the repeated extraction of intracellular proteins from living cells. Hollow nanoneedles with ∼450 nm diameter were fabricated by a material deposition and etching process, followed by integration with a microfluidic device. Long-lasting electrical pulses were coupled with the nanoneedles to permeate the cell membrane, allowing intracellular contents to diffuse into the microfluidic channels located below the cells via hollow nanoneedles. Using lactate dehydrogenase B (LDHB) as the model intracellular protein, the nanoneedle-electroporation system effectively and repeatedly extracted LDHB from the same set of cells at different time points, followed by quantitative analysis of LDHB via standard enzyme-linked immunosorbent assay. Our work demonstrated an efficient method to nondestructively probe intracellular protein levels and monitor the dynamic protein expression, with great potential to help understanding cell behaviors and functions.

Implantable sensors that detect biomarkers in vivo are critical for early disease diagnostics. Although many colloidal nanomaterials have been developed into optical sensors to detect biomolecules in vitro, their application in vivo as implantable sensors is hindered by potential migration or clearance from the implantation site. One potential solution is incorporating colloidal nanosensors in hydrogel scaffold prior to implantation. However, direct contact between the nanosensors and hydrogel matrix has the potential to disrupt sensor performance. Here, we develop a hollow-microcapsule-based sensing platform that protects colloidal nanosensors from direct contact with hydrogel matrix. Using microfluidics, colloidal nanosensors were encapsulated in polyethylene glycol microcapsules with liquid cores. The microcapsules selectively trap the nanosensors within the core while allowing free diffusion of smaller molecules such as glucose and heparin. Glucose-responsive quantum dots or gold nanorods or heparin-responsive gold nanorods were each encapsulated. Microcapsules loaded with these sensors showed responsive optical signals in the presence of target biomolecules (glucose or heparin). Furthermore, these microcapsules can be immobilized into biocompatible hydrogel as implantable devices for biomolecular sensing. This technique offers new opportunities to extend the utility of colloidal nanosensors from solution-based detection to implantable device-based detection.

We demonstrate here that the electrochemical generation of hydroxyl ions and hydrogen bubbles can be used to induce the synthesis of enzyme- or protein-encapsulated 3D porous silica structure on the surface of noble metal electrodes. In the present work, the one-step synthesis of a glucose oxidase (GOD)-encapsulated silica matrix on a platinum electrode is presented. In this process, glucose oxidase was mixed with ethanol and TEOS to form a doped precursory sol solution. The electrochemically generated hydrogen bubbles at negative potentials assisted the formation of the porous structure of a GOD-encapsulated silica gel, and then the one-step immobilization of enzyme into the silica matrix was achieved. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) characterizations showed that the GOD-encapsulated silica matrix adhered to the electrode surface effectively and had an interconnected porous structure. Because the pores started at the electrode surface, their sizes increased gradually along the distance away from the electrode and reached maximum at the solution side, and effective mass transport to the electrode surface could be achieved. The entrapped enzyme in the silica matrix retained its activity. The present glucose biosensor had a short response time of 2 s and showed a linear response to glucose from 0 to 10 mM with a correlation coefficient of 0.9932. The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3. The apparent Michaelis-Menten constant (K m app) and the maximum current density were determined to be 20.3 mM and 112.4 microA cm-2, respectively. The present method offers a facile way to fabricate biosensors and bioelectronic devices in situ.