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.

A new mode of the scanning electrochemical microscope (SECM) operation was developed that combines reagent delivery from the nanopipette with electron transfer at the conductive substrate and ion transfer across the liquid/liquid interface supported at the nanopipette tip. This approach offers potential advantages for measurements of heterogeneous electron transfer kinetics and reaction rate imaging by enabling straightforward separation of the contributions of surface topography and reactivity features to the tip current. It addresses some other long-standing technical issues, including sensitive probing of low signal sources (e.g., immobilized enzymes or catalyst particles) without diffusional broadening and the elimination of the elevated background signal in generation/collection-type experiments. The high spatial resolution attainable in electron transfer/ion transfer mode experiments and the absence of redox mediator species in the bulk solution are advantageous for studies of biological cells.

The need to fabricate a nanoporous sensor that can be utilized for the resistive-pulse sensing of particles without labeling them has generated extensive research and led to various methods for nanopore fabrication on several materials. Since the first development of track-etching method and its use on polymer membranes, there has been an ongoing interest in their applications. In this review, we look at the background on tracking technology, chemical etching of these tracks for the fabrication of nanopores with varying geometries and we discuss their applications as electrochemical sensors for biomolecules (i.e. DNA and protein), nanoparticles and others. The main emphasis is on resistive-pulse sensing using single nanopores fabricated by track-etching on polymer membranes. We also discuss sensing based on the specific current – potential (I–V) behavior of asymmetric nanopores as the sensing element.

ABSTRACT:The aim of this study is preparation and characterization of alginate/chitosan sponges including a model antibiotic (i.e., ciprofloxacin) to use in wound and/or burn treatment. Sponges were prepared firstly by the gelation of sodium alginate followed by lyophilization, crosslinking with calcium chloride, and finally coating with chitosan. Sponges were characterized with respect to morphology, water uptake, in vitro drug release behavior, and antimicrobial activity. Investigated and evaluated parameters in all of these studies were selected as the concentration of calcium chloride, alginate viscosity, drug content, and molecular weight of chitosan. Drug release and water uptake were found to be greatly influenced by these parameters. Water uptake and drug release rate were decreased by increasing the crosslinking density, chitosan molecular weight, and alginate viscosity. In the antimicrobial tests, it was obtained that the antimicrobial activity is directly proportional with the release rates and water uptake. Morphological studies showed a highly porous structure with interconnected pores.

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.