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.

Corking nano test tubes by chemical self-assembly.

There is tremendous current interest in using nanoparticles to deliver biomolecules and macromolecules (e.g., drugs and DNA) to specific sites in living systems. Release of the biomedical payload from the nanoparticle can be accomplished by chemical or enzymatic degradation of the nanoparticle or of the link between the payload and the nanoparticle. We are exploring an alternative payload-release strategy that builds on our work on template-synthesized nano test tubes. These are hollow nanotubes that are closed on one end and open on the other, and the dimensions can be controlled at will. If these nano test tubes could be filled with a payload and then the open end corked with a chemically labile cap, they might function as a universal delivery vehicle. We show here that silica nano test tubes can be covalently corked by chemical self-assembly of nanoparticles to the tubes. We also show that the nanoparticle corks remain attached to the mouths of the nano test tubes after liberation from the alumina template. For this proof-of-principle study, we used simple imine linkages to attach the corks to the test tubes. Schiff's bases are thermodynamically unstable in the presence of water; however, the multiple points of contact between the nano test tubes and nanoparticles allow the assembled structure to be metastable under our experimental conditions. Other chemical linkages-either more or less stable-may be more appropriate for other applications, and these are currently under development.

Protein capture in silica nanotube membrane 3-D microwell arrays.

The microarray format has allowed for rapid and sensitive detection of thousands of analyte DNAs in a single sample, and there is considerable interest in extending this technology to protein biosensing. While glass is the most common substrate for microarrays, its binding capacity is limited because the glass surface is flat. One way to overcome this limitation is to develop arrays based on porous materials. Such "3-D" arrays can provide greater sensitivity because both the capture molecules and the analyte species they bind are immobilized throughout the thickness of the porous material. We describe here 3-D protein microarrays based on nanopore alumina membranes that contain silica nanotubes within the pores. These microarrays are prepared via a plasma-etch method using a TEM grid as the etch mask and consist of individual nanotube-containing microwells imbedded in a Ag film that coats the alumina membrane surface. We show that the microwells can be functionalized with antibodies and that these antibodies can capture their antigen proteins, which serve as prototype analytes. The analyte proteins are fluorescently tagged, which allows for fluorescence microscopy-based imaging of the array. The Ag surrounding the microwells shows very low background fluorescence, thus improving the signal-background ratio obtained from these arrays.

Effect of crown ether on ion currents through synthetic membranes containing a single conically shaped nanopore.

Ion-current measurements were made on synthetic polymer membranes that contained a single conically shaped nanopore. This entailed placing an electrolyte solution on either side of the membrane, using an electrode placed in each solution to control the transmembrane potential, and measuring the resulting transmembrane ion current. The effect of the crown ether commonly called 18-crown-6 (18C6) on the measured ion current was investigated. Adding 18C6 to the electrolyte solution on one side of a conical nanopore membrane provides a way to rectify the ion current flowing through the nanopore. This chemical rectification is observed only when the cation of the electrolyte is complexed by 18C6 (e.g., K+), and when the mouth diameter of the conical nanopore is of molecular dimensions, in this case approximately 1.5 nm. This chemical rectification can either augment or diminish the inherent electrostatic rectification observed with these small mouth-diameter nanopores. We have interpreted these results using a model based on the formation of a junction potential at the membrane-solution interface. This junction potential arises because the transference number for the K+-18C6 complex in bulk solution is larger than its transference number in the mouth of the conical nanopore.