Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.
This study demonstrates a fluorescence method for in vivo sensing of the dynamic change of Zn(2+) concentration in auditory cortex microdialysates induced by salicylate with N'-(7-nitro-2,1,3-benzoxadiazole-4-yl)-N,N,N'-tris(pyridine-2-ylmethyl) ethane-1,2-diamine (NBD-TPEA) as a probe. The excellent properties of the NBD-TPEA probe make it possible to achieve a high selectivity for Zn(2+) sensing with the co-existence of amino acids and other metal ions as well as the species commonly existing in the cerebral system. To validate the method for in vivo fluorescence sensing of Zn(2+) in the rat brain, we pre-mix the microdialysates in vivo sampled from the auditory cortex with the NBD-TPEA probe and then perfuse the mixtures into a fluorescent cuvette for continuous-flow fluorescence detection. The method demonstrated here shows a linear relationship between the signal output and Zn(2+) concentration within the concentration range from 0.5 μM to 4 μM, with a detection limit of 156 nM (S/N = 3). The basal level of extracellular Zn(2+) in auditory cortex microdialysates is determined to be 0.52 ± 0.082 μM (n = 4). This value is increased by the injection of 100 mg mL(-1) of salicylate (1 μL min(-1), 5 min, i.p.), reaches a peak at the time point of 90 min, and levels off with time. Such an increase is attenuated by the injection of MK-801, a potent and specific NMDA receptor antagonist, after the pre-injection of 100 mg mL(-1) salicylate for 5 min. This study offers a fluorescence method for in vivo sensing of Zn(2+) in the rat brain that could be useful for the investigations of chemical processes involved in brain functions.
A gold-based assay: By taking advantage of the unique optical properties of gold nanoparticles (AuNPs) and the cascade reactions of glucose, a simple but effective method has been successfully developed for the direct colorimetric visualization of glucose in the rat brain. GOD=glucose oxidase. Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Probing chemical information in the central nervous system is essential for understanding the molecular mechanism of brain function. Electrochemistry with tissue-implantable carbon fiber electrodes (CFEs) provides a powerful tool for monitoring the dynamics of neurochemicals in a subsecond time scale; however, the implantation of CFEs into brain tissue immediately causes the nonspecific adsorption of proteins on electrode surfaces. This process can dramatically impact the performance of the electrochemical method in terms of reduced sensitivity and accuracy. Herein, we report a strategy to minimize the electrode biofouling by masking CFEs with leukocyte membranes (LMs). We find that the LM masking endows CFEs with a highly hydrophilic surface that gains a high resistance to nonspecific protein adsorption. The electrode reactivity to target molecules decreases by a small degree due to the membrane coating, but the sensitivity loss of the LM-masked CFEs is greatly lessened even after in vivo implantation for 8 h. This study offers a new method of microelectrode modification by natural cell membranes for sustained sensing performance during long-term in vivo analysis.
The discovery of ionic current rectification (ICR) phenomena in synthetic nanofluidic systems elicits broad interest from interdisciplinary fields of chemistry, physics, materials science, and nanotechnology; and thus, boosts their applications in, for example, chemical sensing, fluidic pumping, and energy related aspects. So far, it is generally accepted that the ICR effect stems from the broken symmetry either in the nanofluidic structures, or in the environmental conditions. Although this empirical regularity is supported by numerous experimental and theoretical results, great challenge still remains to precisely figure out the correlation between the asymmetric ion transport properties and the degree of symmetry breaking. An appropriate and quantified measure is therefore highly demanded. Herein, taking DNA-stuffed nanopores as a model system, we systematically investigate the evolution of dynamic ICR in between two symmetric states. The fully stuffed and fully opened nanopores are symmetric; therefore, they exhibit linear ion transport behaviors. Once the stuffed DNA superstructures are asymmetrically removed from one end of the nanopore via aptamer-target interaction, the nanofluidic system becomes asymmetric and starts to rectify ionic current. The peak of ICR is found right before the breakthrough of the stuffed DNA forest. After that, the nanofluidic system gradually retrieves symmetry, and becomes non-rectified. Theoretical results by both the coarse-grained Poisson-Nernst–Planck model and the 1D statistic model excellently support the experimental observations, and further establish a quantified correlation between the ICR effect and the degree of asymmetry for different molecular filling configurations. Based on the ICR properties, we develop a proof-of-concept demonstration for sensing ATP, termed the ATP balance. These findings help to clarify the origin of ICR, and show implications to other asymmetric transport phenomena for future innovative nanofluidic devices and materials.
In vivo electrochemistry is one powerful strategy for probing brain chemistry. However, the decreases in sensitivity mainly caused by the adsorption of proteins onto electrode surface in short-term in vivo measurements unfortunately render great challenges in both electrode calibration and selectivity against the alternation of proteins. In this study, we observe that the pretreatment of carbon fiber microelectrodes (CFEs) with bovine serum albumin (BSA) would offer a simple but effective strategy to the challenges mentioned above. We verify our strategy for dopamine (DA) with conventionally used CFEs and for ascorbate with our previously developed carbon nanotube-modified CFEs. We find that, in artificial cerebral spinal fluid (aCSF) solution containing BSA, the current responses of the microelectrodes equilibrate shortly and the results for precalibration carried out in this solution are found to be almost the same as those for the postcalibration in pure aCSF. This observation offers a new solution to electrode calibration for in vivo measurements with a technical simplicity. Furthermore, we find that the use of BSA pretreated CFEs to replace bare CFEs would minimize the interference from the alternation of proteins in the brain. This study offers a new general and effective approach to in vivo electrochemistry with a high reliability and a simplified procedure.
Real-time tracking of respiratory patterns provides noninvasive and quick access for evaluating pathophysiological conditions yet remains challenging due to limited temporal resolution and poor sensitivity to dig out fingerprints of respiratory waveforms. Here, we report an electrochemical sensor for accurately tracing respiratory patterns of small animal models based on the electrochemical impedance mechanism for wireless coupling of a graphdiyne oxide (GYDO)-modified sensing coil chip and a reader coil chip via near-field magnetic induction. In the electrochemical impedance measurement mode, an alternating current is applied through the reader coil chip to perturb proton transport at the GYDO interface of the sensing coil chip. As demonstrated, a high-frequency perturbing condition significantly reduces the interfacial resistance for proton transport by 5 orders of magnitude under 95% relative humidity (RH) and improves the low-humidity responses with a limit of detection down to 0.2% RH, enabling in vivo accurate profiling of respiratory patterns on epileptic rats. The electrochemical impedance coupling system holds great potential for new wireless bioelectronics.
Bioorthogonal catalysis provides a powerful tool to perform non-natural chemical reactions in living systems to dissect complex intracellular processes. Its potency to precisely regulate cellular function, however, is limited by the lack of bioorthogonal catalysts with cell selectivity. Herein, we report that palladium nanoparticles deposited on metal-organic frameworks, Pd@UiO-66, are highly efficient for intracellular bioorthogonal catalysis. In addition, introducing a cancer cell-targeting aptamer, AS1411, onto Pd@UiO-66 enables a threefold enhancement of catalysis efficiency in cancer cells. Moreover, AS1411@Pd@UiO-66 is effective in activating chemically caged 4-hydroxytamoxifen to regulate the activity of a protein destabilizing domain, ER50, and therefore protein function selectively in cancer cells. We show that the control over the activity of a bacterial effector, OspF, using AS1411@Pd@UiO-66 inactivates mitogen-activated protein kinase (MAPK) signaling of cancer cells to selectively prohibit tumor cell growth. We believe that the strategy developed herein for cell-selective bioorthogonal catalysis can expand the chemical biology toolbox for spatiotemporal control of protein function for advanced therapeutic applications.
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