Nanopore detection of double stranded DNA using a track-etched polycarbonate membrane.

We investigate the resistive-pulse sensing of 50-bp DNA using track-etched polycarbonate (PC) nanopores and show the translocation dynamics originating from the electrophoretic transport of DNAs. Conically shaped PC nanopore membranes have been prepared with asymmetric chemical etching technique. We show the potential and concentration dependence of DNA translocation through a PC nanopore. We find that the translocation of DNA scales linearly with both potential and concentration. Additionally, the threshold potential is determined to complete the translocation. Finally, by investigating the current-pulse amplitudes of nanopores with different tip sizes, we show that the nanopore size can be successfully used to distinguish the DNA molecules. These results suggest great promise for the sensing of short DNAs and understanding the dynamics of the translocation process using chemically-etched PC nanopores.

Resistive-pulse measurements with nanopipettes: detection of Au nanoparticles and nanoparticle-bound anti-peanut IgY.

Solid-state nanopores have been widely employed in sensing applications from Coulter counters to DNA sequencing devices. The analytical signal in such experiments is the change in ionic current flowing through the orifice caused by the large molecule or nanoparticle translocation through the pore. Conceptually similar nanopipette-based sensors can offer several advantages including the ease of fabrication and small physical size essential for local measurements and experiments in small spaces. This paper describes the first evaluation of nanopipettes with well characterized geometry for resistive-pulse sensing of Au nanoparticles (AuNP), nanoparticles coated with an allergen epitope peptide layer, and AuNP-peptide particles with bound antipeanut antibodies (IgY) on the peptide layer. The label-free signal produced by IgY-conjugated particles was strikingly different from those obtained with other analytes, thus suggesting the possibility of selective and sensitive resistive-pulse sensing of antibodies.

Label-free detection of proteins in ternary mixtures using surface-enhanced Raman scattering and protein melting profiles.

ABSTRACT. The multiplex detection of biologically important molecules such as proteins in complex mixtures has critical importance not only in disease diagnosis but also in other fields such as proteomics and biotechnology. Surface-enhanced Raman scattering (SERS) is a powerful technique for multiplex identification of molecular components in a mixture. We combined the multiplexing power of SERS and heat denaturation of proteins to identify proteins in ternary protein mixtures. The heat denaturation profiles of four model blood proteins, transferrin, human serum albumin, fibrinogen, and hemoglobin, were studied with SERS. Then, two ternary mixtures of these four proteins were used to test the feasibility of the approach. It was demonstrated that unique denaturation profiles of each protein could be used for their identification in the mixture.

Laser desorption ionization mass spectrometry on silicon nanowell arrays.

This paper describes a new technique for fabrication of nanostructured porous silicon (pSi) for laser desorption ionization mass spectrometry. Porous silicon nanowell arrays were prepared by argon plasma etching through an alumina mask. Porous silicon prepared in this way proved to be an excellent substrate for desorption/ionization on silicon (DIOS) mass spectrometry (MS) using adenosine, Pro-Leu-Gly tripeptide, and [Des-Arg(9)]-bradykinin as the model compounds. It also allows the analyses of complex biological samples such as a tryptic digest of bovine serum albumin and a carnitine standard mixture. Nanowell array surfaces were also used for direct quantification of the illicit drug fentanyl in red blood cell extracts. This method also allows full control of the surface features. MS results suggested that the pore depth has a significant effect on the ion signals. Significant improvement in the ionization was observed by increasing the pore depth from 10 to 50 nm. These substrates are useful for laser desorption ionization in both the atmospheric pressure and vacuum regimes.

Resistive-pulse detection of short dsDNAs using a chemically functionalized conical nanopore sensor.

AIMS: To develop nanopore resistive-pulse sensors for the detection of short (50 base-pair [bp] and 100 bp) DNAs. MATERIALS & METHODS: Conically shaped nanopores were chemical etched into polyethylene terphthalate membranes. The as-etched membrane had anionic carboxylate sites on the pore walls. Neutral and hydrophilic ethanolamine functional groups were attached to these carboxylate sites using well-established EDC (1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride) chemistry. RESULTS & DISCUSSION: The ethanolamine-functionalized pores were used to detect 50 and 100 bp DNAs via the resistive-pulse method. The resistive-pulse signature produced by the 50 bp DNA could be distinguished from that of the 100 bp DNA with these sensors. CONCLUSIONS: Attachment of ethanolamine to the carboxylate groups on the pore wall lowered the anionic charge density on the wall. This mitigated the problem of electrostatic rejection of the anionic DNAs from the pore and enabled the detection of these DNA analytes.

Antibody-functionalized nano test tubes target breast cancer cells.

AIM: To develop nano test tubes that will deliver a biomedical payload to a specific cell type. METHODS: The template-synthesis method was used to prepare silica nano test tubes. An antibody that is specific for breast cancer cells was attached to the outer tube surfaces. A fluorophore was attached to the inner surfaces of the nano test tubes. The tubes were incubated with the breast cancer cells and the extent of attachment to the cell surfaces was investigated by fluorescence microscopy. RESULTS: Tubes modified on their outer surfaces with the target antibody showed enhanced attachment to breast-cancer cells, relative to tubes modified on their outer surfaces with a species and isotype-matched control antibody. CONCLUSIONS: This work is a first step toward demonstrating that nano test tubes can be used as cell-specific delivery vehicles.

Norfloxacin-loaded chitosan sponges as wound dressing material.

The aim of this study was the preparation and characterization of chitosan sponges including a model antibiotic (i.e., norfloxacin). The chitosan sponges were prepared by a solvent evaporation method. The matrix was also cross-linked during the preparation. The results indicated that the chitosan sponges were in the fibrillar structure. The swelling behavior, norfloxacin loading, in vitro release characteristics, and antibacterial activity were determined. The effects of cross-linker concentration, norfloxacin/chitosan ratio, chitosan molecular weight, and base concentration were investigated. The most effective parameter was found to be the degree of neutralization. It was also observed that the equilibrium swelling ratio decreased with increasing cross-linking density. The norfloxacin release was found to be swelling controlled initially and diffusion controlled at the extended release periods. It was also found that the antibacterial activity was directly proportional to the release rate.