Nanopore-based single-molecule biosensors have been extensively studied. Protein pores that have receptors attached to them are target-selective, but their real-time applications are limited by the fragility of the lipid membrane into which the protein pores are embedded. Synthetic nanopores are more stable and provide flexible pore sizes, but the selectivity is low when detecting in the translocation mode. In spite of modifications with probing molecules, such as antibodies, to potentiate specific targeting, these nanopores fail to bind individual target molecules. Distinguishing between binding and translocation blocks remains unsolved. Here, we propose an aptamer-encoded nanopore that overcomes these challenges. Aptamers are well-known probing oligonucleotides that have high sensitivity and selectivity. In contrast to antibodies, aptamers are much smaller than their targets, rendering target blockades in the nanopore much more distinguishable. We used aptamer-encoded nanopores to detect single molecules of immunoglobulin E and the bioterrorist agent ricin, sequentially captured by the immobilized aptamer in the sensing zone of the pore. The functional nanopore also probed sequence-dependent aptamer-protein interactions. These findings will facilitate the development of a universal nanopore for multitarget detection.
Nanopores are increasingly utilized as tools for single-molecule detection in biotechnology. Many nanopores are fabricated through procedures that require special materials, expensive facilities and experienced operators, which limiting their usefulness on a wide-scale. We have developed a simple method of fabricating a robust, low-noise nanopore by externally penetrating a nanocavity enclosed in the terminal of a capillary pipette. The nanocavity was shown to have a pore size on the scale of a single molecule, verified by translocation of molecules of known sizes, including double-stranded DNA (2 nm), gold nanoparticles (10 nm) and ring-shaped cyclodextrin (1.5 nm). The small pore size allows entrapment of a single cyclodextrin molecule. Cyclodextrin in the nanopore may prove useful as a molecular adapter for chiral enantiomer discrimination.
With potassium acetate as an intercalation agent, kaolinite-potassium acetate(KAc) intercalation complexes was prepared. Afterwards, nano-kaolinite was successfully made through exfoliated intercalation complexes using power ultrasonic. The intermediate and final products were characterized by X-ray diffraction(XRD), infrared spectroscopy(IR), laser particle size analyzer, and scanning electron microscope (SEM). The results show that intercalation of KAc into kaolinite resulted in a crystal space expansion, from a basal spacing of 7.14Ǻ to 14.20 Ǻ, and the intercalation rate was about 80%. KAc intercalation causes the weakening of interlayer stability. It was shown that the particles of nano-kaolinite is very thin lamellar in shape, whose average thickness, average particle size, are 50 nm and 450 nm respectively.
A novel polyacrylic acid /xanthan gum/bentonite superabsorbent polymer (SAP) was prepared through chemical crosslinking by a polymerization technique in a complete aqueous environment. This SAP was fabricated effectively by dispersing xanthan gum (XG) and bentonite in a monomeric solution, using N,N’-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. Fourier transform infrared (FTIR) spectral analysis showed that graft copolymerization reaction took place between acrylic acid (AA), XG and bentonite. The optimal process conditions of preparing SAP were investigated. Results showed that the relevant SAP had maximal salt-water absorption (98g/g) when mass ratio of m (bentonite):m (AA) was 5:1, m (ammonium persulfate):m (AA) was 1.75×10-4, m (N,N’-methylenebisacrylamide):m (AA) was 3×10-4, m (XG) :m (AA) was 1:5, the neutralization degree of AA was 75%. Bentonite can not only effectively increase water absorbency, but also improve water retention ability.
This article presents the optimization of process parameters in chitosan-gelatin composite microcarriers preparation based on multi-index test breakdown formula evaluation combined with orthogonal array. In this study, the concentration of crosslinker solution, the concentration of water phase and stirring speed were considered as controllable factors, and three levels for each of these factors were selected, in an L9 orthogonal array. The optimal levels of the process parameters were determined through the range analysis and the relative importance among the process parameters were identified through analysis of variance. According to the evaluations of particle size, morphological analysis, compressibility, and equilibrium swelling from the nine different sets, the optimum combinations for microcarriers preparation were showed as: the concentration of crosslinker solution:0.5% (wt/v), the concentration of water phase:5% (wt/v) and stirring speed:240 rpm.
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