A new ionic current rectification device responsive to a broad range of pH stimuli is established using highly ordered nanochannels of porous anodic alumina membrane with abrupt surface charge discontinuity. The asymmetric surface charge distribution is achieved by patterning the nanochannels with surface amine functional groups at designed positions using a two‐step anodization process. Due to the protonation/deprotonation of the patterned amine and the remaining intrinsic hydroxyl groups upon solution pH variation, the nanochannel‐array‐based device is able to regulate ion transport selectivity and has ionic current rectification properties. The rectification ratio of the device is mainly determined by the nanochannel size, and the rectification ratio is less sensitive to the patterned length of the amine groups when the nanochannels size is defined. Thus, the isoelectric point of nanochannels can be easily estimated to be the pH value with a unit rectification ratio. The present ionic device is promising for biosensing, molecular transport and separation, and drug delivery in confined environments.

Noble metal nanoparticles are promising catalysts in electrochemical reactions, while understanding the relationship between the structure and reactivity of the particles is important to achieve higher efficiency of electrocatalysis, and promote the development of single-molecule electrochemistry. Electrogenerated chemiluminescence (ECL) was employed to image the catalytic oxidation of luminophore at single Au, Pt, and Au-Pt Janus nanoparticles. Compared to the monometal nanoparticles, the Janus particle structure exhibited enhanced ECL intensity and stability, indicating better catalytic efficiency. On the basis of the experimental results and digital simulation, it was concluded that a concentration difference arose at the asymmetric bimetallic interface according to different heterogeneous electron-transfer rate constants at Au and Pt. The fluid slip around the Janus particle enhanced local redox reactions and protected the particle surface from passivation.

Confined and free diffusion of phenol occur in the electric double layer (EDL) and extra‐EDL region in the nanochannels of porous anodic alumina (see picture). The inductive effect of the EDL electric field on the phenol molecules slows their diffusion, but it is negligible in the free‐diffusion region. The extent of the two regions depends on EDL thickness, and hence the diffusion flux increases with increasing ionic strength of the electrolyte.

Materials and reagents. A Sylgard 184 poly(dimethylsiloxane) (PDMS) kit was purchased from Dow Corning Co. (Midland, MI, USA). Glass plates coated with chromium and photoresist for chip fabrication were obtained from Shaoguang Microelectronics Corp. (Hunan, China). All the other chemicals were of analytical grade and used without further purification. Milli-Q grade water (Millipore Inc., Bedford, MA, USA) was used for preparing all solutions and cleaning microchannels. 10 mM phosphate-buffered saline (PBS, pH 7.4) containing 137 mmol/L NaCl, 2.7 mmol/L KCl, 8.72 mmol/L Na 2 HPO 4 , and 1.41 mmol/L KH 2 PO 4 . Glass capillary (1.0 mm id, 10 cm length) was purchased from Sichuan University Inc. (Chengdu, China). Free hemoglobin test kit was acquired from Jiancheng Bioengineering Institute (Nanjing, China). Silicone tube was from Nuoyawei Inc. (Shenzhen, China). Theophylline was from National Institutes for Food and Drug Control (Beijing, China). Other chemicals were of analytical grade and used without purification.

The effective capture and release of circulating tumor cells (CTCs) is of significant importance in cancer prognose and treatment. Here we report a highly efficient method to capture and release human leukemic lymphoblasts (CCRF-CEM) using aptamers modified gold nanowire arrays (AuNWs). The gold nanowires, showing tunable morphologies from relatively random pillar deposit to relatively uniform arrays, were fabricated by electrochemical deposition using anodic aluminum oxide (AAO) as template. Upon simply being modified with aptamers by Au-S chemistry, the AuNWs exhibit higher specificity to target cells. Also compared to flat gold substrate, the AuNWs with nanostructure can capture target cells with much higher capture yield. Moreover, the captured CCRF-CEM cells can be released from AuNWs efficiently with little damage through an electrochemical desorption process. We predict that our strategy has great potential in providing a simple and economical platform for CTCs isolation, cancer diagnosis, and therapy.