Ion current rectification with quartz nanopipette electrodes was investigated through the control of the surface charge. The presence and absence of a positively charged poly-L-lysine (PLL) coating resulted in the rectified current with opposite polarity. The results agreed with the theories developed for current-rectifying conical nanopores, suggesting the similar underlying mechanism among asymmetric nanostructure in general. This surface condition dependence can be used as the fundamental principle of multi-purpose real-time in vivo biosensors. Nanomaterials are being widely exploited by recent technologies because of their extraordinary properties. Although the development of fabrication processes for particular nanostructures poses great challenges by itself, the practical use of these nanomaterials is also of great interest for biology and medicine. 1 Because of their structural diversity, these materials are often categorized and referred to as nanoparticles, 2 nanowires, 3 nanotubes, 4 nanopores, 5 or nanopatterned surfaces. 6 Nanopipettes are among these; a nanopipette is defined as a pipette with a very fine tip that has a nanoscale opening. Nanolithography is one of the typical applications of nanopipettes as a delivery tool of a tiny amount of chemicals. 7,8 Nanopipettes are versatile enough to be used as a tool for sensitive detection in biomedical applications. Optical detection of fluorescently labeled macromolecules such as DNA or proteins with nanopipettes has been reported. 9,10 Fully electrical detection has also been shown with similarly sized nanoparticles, whose flow through the nanopipette opening creates temporal current blockades. 11 The ultimate goal of these efforts, the label-free real-time electrical detection of single molecules, could be achieved eventually by a deeper understanding of the fundamental characteristics of nanopipette electrodes under an external electric field. It not only helps to unveil the dynamics of biological systems but can also have a remarkable impact on drug screening and pathogen detection. Interestingly, although a general understanding of nanopipette electrodes can be based on the understanding of microelectrodes, the unique nanoscale geometry often causes characteristic behavior that requires further focused studies. For example, related studies have examined the physicochemical properties of nanopipettes under varying conditions such as electrolyte concentrations and pH, 12 or polyethylene glycol polymer coatings. 13 Similarly shaped goldplated conical nanopores have been studied in a more detailed manner, involving observations of the role of surface charge in the ionic current. 14 Our target here is the effect of cationic polymer coating on a glass nanopipette surface, providing the basis for functionalized nanopipettes that will be used as sensitive biosensors. By understanding how ions flow through the nanometer-sized opening, how these ions interact with the surface inside and outside the tip, and what happens if the surface is modified by...

Nanopipette technology can uniquely identify biomolecules such as proteins based on differences in size, shape, and electrical charge. These differences are determined by the detection of changes in ionic current as the proteins interact with the nanopipette tip coated with probe molecules. Here we show that electrostatic, biotin-streptavidin, and antibody-antigen interactions on the nanopipette tip surface affect ionic current flowing through a 50-nm pore. Highly charged polymers interacting with the glass surface modulated the rectification property of the nanopipette electrode. Affinity-based binding between the probes tethered to the surface and their target proteins caused a change in the ionic current due to a partial blockade or an altered surface charge. These findings suggest that nanopipettes functionalized with appropriate molecular recognition elements can be used as nanosensors in biomedical and biological research.biomolecules ͉ biosensor ͉ immunoassay ͉ current rectification ͉ nanopore N anopipettes, characterized by the submicron to nanoscale size of the pore at the tip, are of great interest because of their unique physicochemical properties and potential for various biomedical and biological applications. By pulling a single glass capillary, one can easily and cost-effectively create a pair of nanopipettes that can be used for molecular deposition onto a solid surface (1, 2), for delivery to the surface of a single cell (3) and its inner compartments (4, 5), or for biomolecular sensing as described hereafter. These applications can be optimized by an enhanced understanding of the physical and chemical interactions at the pore region, which has been a subject of theoretical studies (6). Advances in both technical and theoretical fronts will further demonstrate the utility of nanopipettebased devices for many purposes.Biomolecule sensing with a nanopipette probe has been performed with and without the aid of optical methods. Fluorescence-based pH sensing (7) shows the submicron spatial resolution and millisecond time resolution of such sensors. Fully-electrical detection of DNA-conjugated gold nanoparticles (8) uses resistive pulses caused by the translocation of fairly large (10 nm) particles, the underlying principle identical to that of nanopore biosensors (9) and DNA sequencers (10). Unlike other nanostructure-based chemical sensors (11), which often require access to semiconductor facilities, nanopipette biosensors can be created and tailored at the bench, thereby reducing turnaround time. Nanopipettes also have enormous potential for detecting a small number of molecules from a tiny amount of clinical samples or live single cells, a feature useful for medical diagnostics and molecular and cellular biology research.A key challenge for nanopipette biosensors is adapting to applications where specific molecules can be targeted. One approach would be to separate the sensing and actuating functions, an idea embodied by an engineered ion channel fused with a surface receptor protein responsible f...

Japan has been facing challenges relating to specifically defined rare diseases, called Nan-Byo in Japanese (literally ‘difficult’+‘illness’), and has already taken measures for them since 1972. This governmental support has surely benefited Nan-Byo patients; however, those suffering from medically unidentified conditions do not fall into this scheme and thus still confront difficulty in obtaining an examination, a diagnosis, and a treatment. To identify such rare and often undiagnosed diseases, we must integrate systematic diagnosis by medical experts with phenotypic and genetic data matching. Thus, in collaboration with Nan-Byo researchers and the Japanese universal healthcare system, the Japan Agency for Medical Research and Development launched the Initiative on Rare and Undiagnosed Diseases (IRUD) in 2015. IRUD is an ambitious challenge to construct a comprehensive medical network and an internationally compatible data-sharing framework. Synergizing with existing next-generation sequencing capabilities and other infrastructure, the nationwide medical research consortium has successfully grown to accept more than 2000 undiagnosed registrants by December 2016. We also aim at expanding the concept of microattribution throughout the initiative; that is, proper credit as collaborators shall be given to local primary care physicians, nurses and paramedics, patients, their family members, and those supporting the affected individuals whenever appropriate. As it shares many challenges among similar global efforts, IRUD’s future successes and lessons learned will significantly contribute to ongoing international endeavors, involving players in basic research, applied research, and societal implementation.