A simple and rapid two-step anodic oxidization method, including annealing- and polishing-free pretreatment and electrochemical membrane detachment, has been used to prepare ordered and through-hole porous alumina membrane.

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.

With the growing demands of the early, accurate, and sensitive diagnosis for cancers, the development of new diagnostic technologies becomes increasingly important. In this study, we proposed a strategy for efficient capture and sensitive detection of circulating tumor cells (CTCs) using an array nanochannel-ion channel hybrid coupled with an electrochemical detection technique. The aptamer probe was immobilized on the ion channel surface to couple with the protein overexpressed on the CTCs membrane. Through this special molecular recognition, CTCs can be selectively captured. The trapped CTCs cover the ion channel entrance efficiently, which will dramatically block the ionic flow through channels, resulting in a varied mass-transfer property of the nanochannel-ion channel hybrid. On the basis of the changed mass-transfer properties, the captured CTCs can be sensitively detected using the electrochemical linear sweep voltammetry technique. Furthermore, due to the amplified response of array channels compared to that of a single channel, the detection sensitivity can be enhanced greatly. The results showed that acute leukemia CCRF-CEM (a type of CTC) concentration as low as 100 cells mL can be successfully captured and detected. The present method provides a simple, sensitive, and label-free technique for CTCs capture, detection, and release, which would hold great potential in the early clinical diagnosis and treatment of cancers.

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.

A crack-free sub-nanometer composite structure for the study of ion transfer was constructed by in situ growth of ZIF-90 [Zn(ICA) , ICA=Imidazole-2-carboxaldehyde] on the tip of a glass nanopipette. The potential-driven ion transfer through the sub-nanometer channels in ZIF-90 is strongly influenced by the pH of the solution. A rectification ratio over 500 is observed in 1 m KCl solution under alkaline conditions (pH 11.58), which is the highest value reported under such a high salt concentration. Fluorescence experiments show the super-high rectification ratio under alkaline conditions results from the strong electrostatic interaction between ions and the sub-nanometer channels of ZIF-90. In addition to providing a general pathway for further study of mass-transfer process through sub-nanometer channels, the approach enable all kinds of metal-organic frameworks (MOFs) to be used as ionic permselectivity materials in nanopore-based analysis.