Macroscopic Quantum Tunneling in Superconducting Junctions of ß-Ag2Se Topological Insulator Nanowire.

We report on the fabrication and electrical transport properties of superconducting junctions made of ß-Ag2Se topological insulator (TI) nanowires in contact with Al superconducting electrodes. The temperature dependence of the critical current indicates that the superconducting junction belongs to a short and diffusive junction regime. As a characteristic feature of the narrow junction, the critical current decreases monotonously with increasing magnetic field. The stochastic distribution of the switching current exhibits the macroscopic quantum tunneling behavior, which is robust up to T = 0.8 K. Our observations indicate that the TI nanowire-based Josephson junctions can be a promising building block for the development of nanohybrid superconducting quantum bits.

Simple and rapid detection of bacteria using a nuclease-responsive DNA probe.

We demonstrate simple and rapid bacterial detection using a nuclease-responsive DNA probe. The probe consisting of a fluorescent dye and a quencher at the 5' and 3' termini, respectively, was designed to be cleaved by nucleases such as endonucleases, exonucleases, and DNases, which are released from bacteria using an optimized lysis buffer. The fluorescence signal of the cleaved DNA probe correlates with the number of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, and the detection limit was 103 CFU for E. coli and 104 CFU for S. aureus. Moreover, this method is specific for live bacteria and takes just one minute to get the signal including sample collection. These features make the present bacterial detection method a powerful on-site bacterial contamination assay which is simple, rapid, and quantitative.

A Multivalent Structure-Specific RNA Binder with Extremely Stable Target Binding but Reduced Interaction with Nonspecific RNAs.

By greatly enhancing binding affinities against target biomolecules, multivalent interactions provide an attractive strategy for biosensing. However, there is also a major concern for increased binding to nonspecific targets by multivalent binding. A range of charge-engineered probes of a structure-specific RNA binding protein PAZ as well as multivalent forms of these PAZ probes were constructed by using diverse multivalent avidin proteins (2-mer, 4-mer, and 24-mer). Increased valency vastly enhanced the binding stability of PAZ to structured target RNA. Surprisingly, nonspecific RNA binding of multivalent PAZ can be reduced even below that of the PAZ monomer by controlling negative charges on both PAZ and multivalent avidin scaffolds. The optimized 24-meric PAZ showed nearly irreversible binding to target RNA with negligible binding to nonspecific RNA, and this ultra-specific 24-meric PAZ probe allowed SERS detection of intact microRNAs at an attomolar level.

Composition-selective fabrication of ordered intermetallic Au-Cu nanowires and their application to nano-size electrochemical glucose detection.

Bimetallic nanostructures can provide distinct and improved physicochemical properties by the coupling effect of the two metal components, making them promising materials for a variety of applications. Herein, we report composition-selective fabrication of ordered intermetallic Au-Cu nanowires (NWs) by two-step chemical vapor transport method and their application to nano-electrocatalytic glucose detection. Ordered intermetallic Au3Cu and AuCu3 NWs are topotaxially fabricated by supplying Cu-containing chemicals to pre-synthesized single-crystalline Au NW arrays. The composition of fabricated Au-Cu NWs can be selected by changing the concentration of Cu-containing species. Interestingly, Au3Cu NW electrodes show unique electrocatalytic activity for glucose oxidation, allowing us to detect glucose without interference from ascorbic acid. Such interference-free detection of glucose is attributed to the synergistic effect, induced by incorporation of Cu in Au. We anticipate that Au3Cu NWs could show possibility as efficient nano-size electrochemical glucose sensors and the present fabrication method can be employed to fabricate valuable ordered intermetallic nanostructures.

Ciliary Neurotrophic Factor Derived From Astrocytes Protects Retinal Ganglion Cells Through PI3K/AKT, JAK/STAT, and MAPK/ERK Pathways.

Purpose: The purpose of this study was to investigate the roles of ciliary neurotrophic factor (CNTF) on the protective effects of astrocytes on retinal ganglion cells (RGCs). Methods: Primary RGCs were isolated from neonatal rats. Oxidative stress was induced, and the effects of co-culture with astrocytes and CNTF treatment on RGCs were evaluated. The pathways commonly altered by astrocytes and CNTF were investigated. Effects of each pathway were investigated using pathway inhibitors against PI3K/AKT, JAK/STAT, and MAPK/ERK. RNA sequencing was performed to identify the genes upregulated and downregulated by CNTF treatment. Results: Astrocytes improved the viability and increased ß3-tubulin expression in RGCs. The concentration of CNTF increased in the RGC-astrocyte co-culture medium. The protective effects of astrocytes were abolished by neutralization with the anti-CNTF antibody; thus, CNTF may play an important role in the effects mediated by astrocytes. Furthermore, CNTF treatment alone enhanced the viability and ß3-tubulin expression of RGCs and increased the population of viable RGCs under oxidative stress. The PI3K/AKT pathway was associated with both RGC viability and ß3-tubulin expression. However, the JAK/STAT pathway increased the viability of RGCs, whereas the MAPK/ERK pathway was associated with ß3-tubulin expression. RNA sequencing revealed the CNTF-upregulated genes associated with response to DNA damage and downregulated genes associated with photoreceptor cell differentiation. Conclusions: Our data revealed protective effects of astrocyte-derived CNTF on RGCs. In addition, we showed that multiple pathways exert these protective effects and identified the novel genes involved. These results may be helpful in developing treatments for RGC injury.

3D Hierarchical Nanotopography for On-Site Rapid Capture and Sensitive Detection of Infectious Microbial Pathogens.

Effective capture and rapid detection of pathogenic bacteria causing pandemic/epidemic diseases is an important task for global surveillance and prevention of human health threats. Here, we present an advanced approach for the on-site capture and detection of pathogenic bacteria through the combination of hierarchical nanostructures and a nuclease-responsive DNA probe. The specially designed hierarchical nanocilia and network structures on the pillar arrays, termed 3D bacterial capturing nanotopographical trap, exhibit excellent mechanical reliability and rapid (<30 s) and irreversible bacterial capturability. Moreover, the nuclease-responsive DNA probe enables the highly sensitive and extremely fast (<1 min) detection of bacteria. The bacterial capturing nanotopographical trap (b-CNT) facilitates the on-site capture and detection of notorious infectious pathogens (Escherichia coli O157:H7, Salmonella enteritidis, Staphylococcus aureus, and Bacillus cereus) from kitchen tools and food samples. Accordingly, the usefulness of the b-CNT is confirmed as a simple, fast, sensitive, portable, and robust on-site capture and detection tool for point-of-care testing.

Troponin Aptamer on an Atomically Flat Au Nanoplate Platform for Detection of Cardiac Troponin I.

Well-ordered bioreceptors on atomically flat Au surfaces can be a high-performance biosensor. Cardiac troponin I proteins (cTnIs) have been regarded as a specific biomarker for acute myocardial infarction (AMI). Here, we report the accurate detection of cTnIs using an aptamer-immobilized Au nanoplate platform. The single-crystalline and atomically flat Au nanoplate was characterized by atomic force microscopy. For the precise detection of cTnI, we immobilized an aptamer that can strongly bind to cTnI onto an atomically flat Au nanoplate. Using the aptamer-immobilized Au nanoplate, cTnIs were successfully detected at a concentration of 100 aM (2.4 fg/mL) in buffer solution. Furthermore, cTnIs in serum could be identified at a concentration of 100 fM (2.4 pg/mL). The total assay time was ~7 h. Importantly, the aptamer-immobilized Au nanoplate enabled us to diagnose AMI patients accurately, suggesting the potential of the present method in the diagnosis of AMI.

Superb Specific, Ultrasensitive, and Rapid Identification of the Oseltamivir-Resistant H1N1 Virus: Naked-Eye and SERS Dual-Mode Assay Using Functional Gold Nanoparticles.

To prevent the global transmission of mutant viruses and minimize the damage caused by mutant virus infection, the accurate identification of newly emerged mutant viruses should be a priority. The key problem in mutant virus identification is that the selective detection of a mutant virus in the biological environment, where small amounts of mutant virus and copious amounts of wild-type virus coexist, is difficult. Herein, we report specific and ultrasensitive detection of oseltamivir-resistant (pH1N1/H275Y mutant) virus using functional Au nanoparticles (NPs). The functional Au NPs were prepared by modifying the surfaces of Au NPs with oseltamivir hexylthiol (OHT) and malachite green isothiocyanate (MGITC) simultaneously. OHT is an excellent receptor for the pH1N1/H275Y mutant virus because it has a 250-fold higher binding affinity for the pH1N1/H275Y mutant virus than for the wild-type virus. MGITC is a Raman reporter that provides a distinctive surface-enhanced Raman scattering (SERS) signal. The SERS signal of MGITC on Au NPs allows us to detect pH1N1/H275Y mutant viruses sensitively and quantitatively. The functional Au NPs enable naked-eye and SERS dual-mode detection of mutant viruses. Only in the presence of the pH1N1/H275Y mutant virus, the functional Au NPs aggregate, and the color of the NPs changes from red to purple. This allows us to detect mutant viruses with the naked eye. Furthermore, the aggregated Au NPs can provide strong SERS signals of MGITC. By measuring the SERS signals, we could detect the pH1N1/H275Y mutant virus with a detection limit of 10 PFU. Importantly, the pH1N1/H275Y mutant virus could be detected by using the functional Au NPs even in a mixture of mutant and wild-type viruses with a ratio of 1/100. This result suggests that the present method might be employed for the diagnosis of oseltamivir-resistant virus and for further research, including mutant virus analysis and drug development.

Diagnosis of Tamiflu-Resistant Influenza Virus in Human Nasal Fluid and Saliva Using Surface-Enhanced Raman Scattering.

Influenza viruses cause respiratory infection, spread through respiratory secretions, and are shed into the nasal secretion and saliva specimens. Therefore, nasal fluid and saliva are effective clinical samples for the diagnosis of influenza virus-infected patients. Although several methods have been developed to detect various types of influenza viruses, approaches for detecting mutant influenza viruses in clinical samples are rarely reported. Herein, we report for the first time a surface-enhanced Raman scattering (SERS)-based sensing platform for oseltamivir-resistant pandemic H1N1 (pH1N1) virus detection in human nasal fluid and saliva. By combining SERS-active urchin Au nanoparticles and oseltamivir hexylthiol, an excellent receptor for the pH1N1/H275Y mutant virus, we detected the pH1N1/H275Y virus specifically and sensitively in human saliva and nasal fluid samples. Considering that the current influenza virus infection testing methods do not provide information on the antiviral drug resistance of the virus, the proposed SERS-based diagnostic test for the oseltamivir-resistant virus will inform clinical decisions about the treatment of influenza virus infections, avoiding the unnecessary prescription of ineffective drugs and greatly improving therapy.

Atomically Flat Au Nanoplate Platforms Enable Ultraspecific Attomolar Detection of Protein Biomarkers.

Atomically flat surfaces of single-crystalline Au nanoplates can maximize the functionality of biomolecules, thus realizing extremely high-performance biosensors. Here, we report both highly specific and supersensitive detection of C-reactive protein (CRP) by employing atomically flat Au nanoplates. CRP is a protein biomarker for inflammation and infection and can be used as a predictive or prognostic marker for various cardiovascular diseases. To maximize the binding capacity for CRP, we carefully optimized the Au nanoplate-Cys3-protein G-anti-CRP structure by observing atomic force microscopy (AFM) images. The optimally anti-CRP-immobilized Au nanoplates allowed extremely specific detection of CRP at the attomolar level. To confirm the binding of CRP onto the Au nanoplate, we assembled Au nanoparticles (NPs) onto the CRP-captured Au nanoplate by sandwich immunoreaction and obtained surface-enhanced Raman scattering (SERS) spectra and scanning electron microscopy (SEM) images. Both the SERS and SEM results showed that we completely eliminated the nonspecific binding of Au NPs onto the optimally anti-CRP-immobilized Au nanoplate. Compared with the anti-CRP-immobilized rough Au film and the randomly anti-CRP-attached Au nanoplate, the optimally anti-CRP-immobilized Au nanoplate provided a highly improved detection limit of 10-17 M. In this study, it was validated that ultraclean and ultraflat Au nanoplates can maximize the sensing capability of CRP. We expect that these Au nanoplates will enable the feasible detection of many important biomarkers with high specificity and high sensitivity.

Quantum Electronic Transport of Topological Surface States in ß-Ag2Se Nanowire.

Single-crystalline ß-Ag2Se nanostructures, a new class of 3D topological insulators (TIs), were synthesized using the chemical vapor transport method. The topological surface states were verified by measuring electronic transport properties including the weak antilocalization effect, Aharonov-Bohm oscillations, and Shubnikov-de Haas oscillations. First-principles band calculations revealed that the band inversion in ß-Ag2Se is caused by strong spin-orbit coupling and Ag-Se bonding hybridization. These investigations provide evidence of nontrivial surface state about ß-Ag2Se TIs that have anisotropic Dirac cones.