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.

We explored the application of two-dimensional covalent organic frameworks (2D COFs) in single molecule DNA analysis. Two ultrathin COF nanosheets were exfoliated with pore sizes of 1.1 nm (COF-1.1) and 1.3 nm (COF-1.3) and covered closely on a quartz nanopipette with an orifice of 20 ± 5 nm. COF nanopores exhibited high size selectivity for fluorescent dyes and DNA molecules. The transport of long (calf thymus DNA) and short (DNA-80) DNA molecules through the COF nanopores was studied. Because of the strong interaction between DNA bases and the organic backbones of COFs, the DNA-80 was transported through the COF-1.1 nanopore at a speed of 270 μs/base, which is the slowest speed ever observed compared with 2D inorganic nanomaterials. This study shows that the COF nanosheet can work individually as a nanopore monomer with controllable pore size like its biological counterparts.

It is challenging to develop a robust nanoprobe for real-time operational and accurate detection of heavy metals in single cells. Fe-CN coordination chemistry has been well studied to determine the structural characteristics of hemeproteins by different techniques. However, the frequently used cyanide ligands are inorganic molecules that release cyanide anion under particular conditions and cause cyanide poisoning. In the present study, organic cyanide (4-mercaptobenzonitrile, MBN) was utilized for the first time in developing a facile nanoprobe based on surface-enhanced Raman scattering (SERS) for quantitative detection of hemeproteins (oxy-Hb) and trivalent iron (Fe) ions. The nanoprobe prepared by coating the glass capillary tip (100 nm) with a thin gold film, which enables highly localized study in living cell system. The cyanide stretching vibration in MBN was highly sensitive and selective to Fe and oxy-Hb with excellent binding affinity (K 0.4 pM and 0.1 nM, respectively). The high sensitivity of the nanoprobe to analyte (Fe) was attributed to the two adsorption conformations (-SH and -CN) of MBN to the gold surface. Therefore, MBN showed an exceptional dual-peak (2126 and 2225 cm) behavior. Furthermore, the special Raman peaks of cyanide in 2100-2300 cm (silent region of SERS spectra) are distinguishable from other biomolecules characteristic peaks. The selective detection of Fe in both free and protein-bound states in aqueous solution is achieved with 0.1 pM and 0.08 μM levels of detection limits, respectively. Furthermore, practical applicability of fabricated nanoprobe was validated by detection of free Fe in pretreated living HeLa cells by direct insertion of a SERS active nanoprobe. Regarding the appropriate precision, good reproducibility (relative standard deviation, RSD 7.2-7.6%), and recyclability (retain good Raman intensity even after three renewing cycles) of the method, the developed sensing strategy on a nanopipette has potential benefits for label-free, qualitative and quantitative recognition of heavy metal ions within nanoliter volumes.

A single gold nanopore with high surface enhanced Raman spectroscopy (SERS) activity is fabricated on the tip of a glass nanopipette.

Methanol extracts of the dried leaves and seeds of Amaranthus viridis were collected and used for phytochemicals and antibacterial analysis. By detecting the MIC and zone inhibition, the antibacterial activity was determined against different bacterial and fungal strains. The extract yields from the leaves and seeds ranged 5.5 -6.1 and 2.42% -3.72% w/w, respectively. Phytochemical investigation of this plant determines that tanins (6.07% -5.96%), saponins (53% -32%), alkaloids (13.14% -11.42%), protiens (16.76% -24.51%) and glycosides (63.2% -32.3%) were rich in leaves. The extracts also contained appreciable levels of total phenolic contents (2.81 -3.61 GAE, g/100 g), total flavanoid contents (18.4 -5.42 QE, g/100 g) and DPPH free radical scavenging activity, showing IC 50 (83.45 -75.95 µg/mL) along with reducing power was calculated. The MIC of extracts ranged 178 -645 µg/mL. The results of this study suggest the possibility of using the methanolic extracts in treating the diseases caused by the test organisms.