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Herein, we report a simple non-enzymatic electrochemical sensor for the detection of serotonin (5-HT) in blood serum using ZnO oxide nanoparticles-copper metal-organic framework (MOF) composite on 3D porous nickel foam, namely, ZnO-Cu MOF/NF. The x-ray diffraction analysis reveals the crystalline nature of synthesized Cu MOF and Wurtzite structure of ZnO nanoparticles, whereas SEM characterization confirms the high surface area of the composite nanostructures. Differential pulse voltammetry analysis under optimal conditions yields a wide linear detection range of 1 ng ml−1 to 1 mg ml−1 to 5-HT concentrations and a LOD (signal to noise ratio = 3.3) of 0.49 ng ml−1, which is well below the lowest physiological concentration of 5-HT. The sensitivity of the fabricated sensor is found to be 0.0606 mA ng−1 ml−1.cm2, and it exhibited remarkable selectivity towards serotonin in the presence of various interferants, including dopamine and AA, which coexist in the real biological matrix. Further, successful determination of 5-HT is achieved in the simulated blood serum sample with a good recovery percentage from ∼102.5% to ∼99.25%. The synergistic combination of the excellent electrocatalytic properties and surface area of the constituent nanomaterials proves the overall efficacy of this novel platform and shows immense potential to be used in developing versatile electrochemical sensors. [ABSTRACT FROM AUTHOR]

Telomerase plays an important role in maintaining the length of telomere during cell division and is recognized as a new kind of biomarkers for cancer diagnosis. In this work, we present a brand new telomerase detection strategy based on a DNA points accumulation for imaging in nanoscale topography (DNA-PAINT) like strategy. With an extraordinary spatial resolution (∼10 nm), the DNA-PAINT based strategy offers several advantages. First, it avoids complicated polymerase chain reaction and electrophoresis procedures. Second, it enables super resolution imaging of the reaction products with a high signal-to-noise ratio and facilitates the location of telomeric elongation sites on the single particle level, which results in a high sensitivity. Third, the detection scheme of the DNA-PAINT strategy allows direct in situ visualization of the telomeric elongation process, which has never been achieved before. All these advantages make the DNA-PAINT telomerase detection strategy significant for dynamic investigation of telomerase related physiological processes as well as cancer diagnosis. [ABSTRACT FROM AUTHOR]

This paper reports an IC-compatible method for fabricating a PDMS-based resistive pulse sensing (RPS) device with embedded nanochannel (nanochannel-RPS) for label-free analysis of biomolecules and bionanoparticles, such as plasmid DNAs and exosomes. Here, a multilayer lithography process was proposed to fabricate the PDMS mold for the microfluidic device, comprising a bridging nanochannel, as the sensing gate. RPS was performed by placing the sensing and excitation electrodes symmetrically upstream and downstream of the sensing gate. In order to reduce the noise level, a reference electrode was designed and placed beside the excitation electrode. To demonstrate the feasibility of the proposed nanochannel-RPS device and sensing system, polystyrene micro- and nanoparticles with diameters of 1 μm and 300 nm were tested by the proposed device with signal-to-noise ratios (SNR) ranging from 9.1–30.5 and 2.2–5.9, respectively. Furthermore, a nanochannel with height of 300 nm was applied for 4 kb plasmid DNA detection, implying the potential of the proposed method for label-free quantification of nanoscale biomolecules. Moreover, HeLa cell exosomes, known as a well-studied subtype of extracellular vesicles, were measured and analyzed by their size distribution. The result of the resistive pulse amplitude corresponded well to that of nanoparticle tracking analysis (NTA). The proposed nanochannel-RPS device and the sensing strategy are not only capable of label-free analysis for nanoscale biomolecules and bionanoparticles, but are also cost-effective for large-scale manufacturing. [ABSTRACT FROM AUTHOR]

Herein, Ti3C2Tx MXene/N-doped reduced graphene oxide (MXene/N-rGO) composite was employed as the electrocatalyst to construct a new electrochemical sensing platform for the determination of adrenaline (AD). The MXene/N-rGO was synthesized via a facile one-step hydrothermal method, where ethylenediamine acted as a reducing agent and N source. The doped N in rGO served as a bridge between MXene and rGO through tight hydrogen bonds. Scanning electron microscopy showed that large numbers of MXenes with accordion-like morphology were distributed on the surface of the N-rGO. The MXene/N-rGO composite displayed a synergetic catalytic effect for oxidizing AD, originating from the unique catalytic activity of N-rGO and the large surface area and satisfactory conductivity of MXene. These characteristics of composite material led to a remarkable effect on signal amplification for the detection of AD, with a wide linear range from 10.0 nM to 90.0 μM and a low detection limit of 3.0 nM based on a signal to noise ratio of 3. Moreover, the MXene/N-rGO electrode displayed good stability, repeatability, and reproducibility. Additionally, the proposed sensor was successfully applied for voltammetric sensing of AD in urine with recoveries from 97.75% to 103.0%. [ABSTRACT FROM AUTHOR]

High-performance ultraviolet (UV) detectors with both high responses and fast speeds are hard to make on homogeneous crystal semiconductor materials. Here, the UV response characteristics of mixed-phase MgZnO thin films with different internal structure distributions are studied. The mixed-phase MgZnO-based detector with the given crystal composition has a high response at both deep UV light (96 A W−1 at 240 nm) and near UV light (80 A W−1 at 335 nm). Meanwhile, because of the quasi-tunneling breakdown mechanism within the device, the high-response UV detector also shows a fast response speed (tr = 0.11 μs) and recovery speed (td1 = 26 μs) at deep UV light, which is much faster than both low-response mixed-phase MgZnO-based UV detectors with other structure constitutions and reported high-response UV devices on homogenous crystal materials. The Idark of the device is just 4.27 pA under a 5 V bias voltage, so the signal-to-noise ratio of the device reached 23852 at 5.5 uW cm−2 235 nm UV light. The new quasi-tunneling breakdown mechanism is observed in some mixed-phase MgZnO thin films that contain both c-MgZnO and h-MgZnO parts, which introduce a high response, signal-to-noise ratio, and fast speed into mixed-phase MgZnO-based UV detectors at weak deep UV light. [ABSTRACT FROM AUTHOR]

This work presents a H2S selective resistive gas sensor design based on a chemical field effect transistor (ChemFET) with open gate formed by hundreds of high temperature chemical vapour deposition (CVD) grown zinc oxide nanowires (ZnO NW). The sensing ability of pristine ZnO NWs and surface functionalized ZnO NWs for H2S is analysed systematically. ZnO NWs are functionalized by deposition of discontinuous gold (Au) nanoparticle films of different thicknesses of catalyst layer ranging from 1 to 10 nm and are compared in their gas sensing properties. All experiments were performed in a temperature stabilized small volume compartment with adjustable gas mixture at room temperature. The results allow for a well-founded understanding of signal-to-noise ratio, enhanced response, and improved limit of detection due to the Au functionalisation. Comprehension and controlled application of the beneficial effects of Au catalyst on ZnO NWs allow for the detection of very low H2S concentrations down to 10 ppb, and a theoretically estimated 500 ppt in synthetic air at room temperature. [ABSTRACT FROM AUTHOR]

As an emerging field in the discipline of optics, plasmonics and metasurfaces have been demonstrated to enable a new degree of freedom to manipulate light for arbitrary beam steering, spectral splitting as well as precise wavefront shaping. However, it has been mostly studied in parallel with the field of diffractive optics, and awaits the unveiling of how the hybridizations between plasmonic effect and diffraction effect interact and impact. Here, we have theoretically proposed a new type of polarization-insensitive meta-grating structure across the broadband visible regime. The structure design combines the width gradient (critical resonant length) from a trapezoid-nanoantenna with the height gradient from a blazed grating profile. The hybridized meta-grating creates both plasmonic effect and grating effect, which enables all the optical incident photons to be directed to the same orientation regardless of the light polarization. As we know, both metasurfaces and diffractive optical elements (such as gratings) are, more often than not, quite sensitive to the incident light polarization. Moreover, if placing our meta-grating on a flexible/stretchable substrate (such as polydimethylsiloxane), the outgoing angle can be effectively adjusted by tuning the period or density of meta-grating arrays. Such meta-grating architectures can be potentially manufactured by existing photolithography and nanoimprint techniques, and can easily find a wide range of practical polarization-insensitive applications, including broadband deflector and emitter, tunable display and imaging device, high signal-to-noise ratio spectrometer, polarization-insensitive plasmonic coupler, etc. [ABSTRACT FROM AUTHOR]

We present a method by which multi-harmonic signals acquired during a normal tapping mode (amplitude modulated) AFM scan of a sample in air or vacuum with standard microcantilevers can be used to map quantitatively the local mechanical properties of the sample such as elastic modulus, adhesion, and indentation. The approach is based on the observation that during the tapping mode operation in air or vacuum, the 0th and 2nd harmonic signals of microcantilever vibration are encountered under most operating conditions and can be mapped with sufficient signal to noise ratio. By measuring the amplitude and phase of the driven harmonic as well as the 0th and 2nd harmonic observables, we find analytical/semi-analytical formulas that relate these multi-harmonic observables to local mechanical properties for several classical tip-sample interaction models. Least squares estimation of the local mechanical properties is performed pixel by pixel. The method is validated through computations as well as experimental data acquired on a polymer blend made of Polystyrene and Polyolefin elastomer. [ABSTRACT FROM AUTHOR]

Red emitting (~612 nm) CaTiO3:Pr3+ long afterglow nanocrystals with a persistence time ~20 min (dark adapted human eyes) have been synthesised for developing high contrast latent fingerprints using the sol-gel process. Due to the persistent emission, CaTiO3:Pr3+ nanophosphor does not require a continuous source for excitation, thereby eliminating the background information even from multi-colour substrates, resulting in a high signal to noise ratio. As a consequence of which, minute features of level- I, II and III can be clearly studied in high contrast fingerprints. Considerable blue shift (~20 nm) was recorded in photoluminescence excitation due to the quantum confinement properties of CaTiO3:Pr3+ nanocrystals. Powder x-ray diffraction confirms the formation of a single phase orthorhombic structure of CaTiO3:Pr3+ with average crystallite size ~40 nm. Spectral parameters indicate a very high color purity of 99% with CIE coordinates (0.62, 0.37) which are very close to NTSC standards for an ideal red-emission. Transmission electron microscopy studies confirm the formation of spherical particles with narrow size distribution which makes them suitable to combine with fingerprint development methods such as powder dusting and cyanoacrylate fuming methods. [ABSTRACT FROM AUTHOR]

We present a systematic investigation on the enhancement of the quality (Q) factors for guided-mode resonance (GMR) sensors with shallow subwavelength grating structures. By introducing the coupled-mode model, a theoretical high-Q factor can be achieved by choosing the proper geometric structure. Based on this method, a GMR sensor with a Q factor up to 8000, which is an order of magnitude larger than those of typical GMR sensors with Q factors within 100 ∼ 300, was demonstrated experimentally. Besides, the approached GMR sensor achieved a bulk sensitivity of 135 nm RIU−1 with a high signal to noise ratio, which supports a detection limit of 1 ng ml−1 for bovine serum albumin detection. This high performance GMR sensor paves the way towards high-throughput industrial mass production, and shows great potential for other applications, such as optical filters, spectrometer, and bio-imaging. [ABSTRACT FROM AUTHOR]

Nanopore-based sequencing has demonstrated a significant potential for the development of fast, accurate, and cost-efficient fingerprinting techniques for next generation molecular detection and sequencing. We propose a specific multilayered graphene-based nanopore device architecture for the recognition of single biomolecules. Molecular detection and analysis can be accomplished through the detection of transverse currents as the molecule or DNA base translocates through the nanopore. To increase the overall signal-to-noise ratio and the accuracy, we implement a new ‘multi-point cross-correlation’ technique for identification of DNA bases or other molecules on the single molecular level. We demonstrate that the cross-correlations between each nanopore will greatly enhance the transverse current signal for each molecule. We implement first-principles transport calculations for DNA bases surveyed across a multilayered graphene nanopore system to illustrate the advantages of the proposed geometry. A time-series analysis of the cross-correlation functions illustrates the potential of this method for enhancing the signal-to-noise ratio. This work constitutes a significant step forward in facilitating fingerprinting of single biomolecules using solid state technology. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) is a noninvasive imaging technique capable of obtaining high-resolution anatomical images of the body. Major drawbacks of MRI are the low contrast agent sensitivity and inability to distinguish healthy tissue from diseased tissue, making early detection challenging. To address this technological hurdle, paramagnetic contrast agents have been developed to increase the longitudinal relaxivity, leading to an increased signal-to-noise ratio. This review focuses on methods and principles that enabled the design and engineering of nanoparticles to deliver contrast agents with enhanced ionic relaxivities. Different engineering strategies and nanoparticle platforms will be compared in terms of their manufacturability, biocompatibility properties, and their overall potential to make an impact in clinical MR imaging. [ABSTRACT FROM AUTHOR]

Atomic force microscope infrared spectroscopy (AFM-IR) can perform IR spectroscopic chemical identification with sub-100 nm spatial resolution, but is relatively slow due to its low signal-to-noise ratio (SNR). In AFM-IR, tunable IR laser light is incident upon a sample, which results in a rise in temperature and thermomechanical expansion of the sample. An AFM tip in contact with the sample senses this nanometer-scale photothermal expansion. The tip motion induces cantilever vibrations, which are measured either in terms of the peak-to-peak amplitude of time-domain data or the integrated magnitude of frequency-domain data. Using a continuous Morlet wavelet transform to the cantilever dynamic response, we show that the cantilever dynamics during AFM-IR vary as a function of both time and frequency. Based on the observed cantilever response, we tailor a time–frequency-domain filter to identify the region of highest vibrational energy. This approach can increase the SNR of the AFM cantilever signal, such that the throughput is increased 32-fold compared to state-of-the art procedures. We further demonstrate significant increases in AFM-IR imaging speed and chemical identification of nanometer-scale domains in polymer films. [ABSTRACT FROM AUTHOR]

Bismuth sulpho iodide (BiSI) belongs to the family of chalcohalides, which present several attractive electro-optic properties. In particular, BiSI is a semiconductor which could be used in X and gamma ray detection due to a band gap of 1.6 eV, density of 6.4 g cm−3, and absorption coefficient for 60 keV radiation of 5.6 cm2 g−1. This work presents a facile synthesis under solvothermal conditions of a nanocomposite consisting of BiSI nanorods and amorphous carbon structures. Furthermore, it studies its ionising radiation detection properties at room temperature, when prototype detectors were built from pellets. The construction conditions of pellets were also studied, varying the applied pressure and heat treatment to the nanocomposite. Dark current density and response to different exposure rates of a 241Am source were measured for the prototype detectors built. It was found that heat treatment of pellets considerably improves detectors performance. Dark current density was one order of magnitude lower than for the pellets without heat treatment, and its response to the 241Am source, linear, with a signal to noise ratio of 7 for 20 V. Finally, the resistivity for the heat treated detector was in the order of 1011 Ω cm, comparable to other materials studied for this application. [ABSTRACT FROM AUTHOR]

We proposed the integration of metasurfaces on atomic force microscopy (AFM) cantilevers to improve the optical lever sensitivity. The metasurface positioned at the back of an AFM cantilever enables anomalous reflection of the laser beam and provides a nonlinear relationship between the incidence and reflection angles following the generalized Snell’s law. Therefore, the displacement of the reflected laser spot at the photodetector can be amplified. The metasurface was composed of 30 nm thick Au nano-discs with different diameters in an array of 1500 nm × 300 nm super cells. Using the fabricated metasurface mounted on a precise angle dial and a macroscale cantilever as prototypes, the concept of a metasurface-enhanced cantilever was experimentally ascertained. Results proved that the optical lever sensitivity can be easily increased. Finite element analysis showed that integration of the thin metasurface does not have a significant impact on the cantilever’s mechanical properties including stiffness and eigenfrequencies. The proposed metasurface-enhanced optical lever sensitivity may have potential applications in improving functional performances of AFM instruments and cantilever-based sensors, such as allowing much smaller imaging forces and boosting the signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Hollow-structured carbon materials play a crucial role in research of biosensors, energy storage and nanomedicine as a kind of material with advantages like high surface area, tunable pore volume, excellent mechanical properties, and good biocompatibility. Herein, we developed a simple, facile and controllable method for synthesis of Fe3O4 nanoparticles encapsulated in hollow carbon nanocages (FNHCs) with SiO2 nanospheres as a sacrificial template. Owing to the unique structure of multiple Fe3O4 nanoparticles cores integrated with N-doped carbon nanocages, the as-synthesized FNHCs exhibited greatly enhanced peroxidase mimicking activity with extremely high signal-to-noise ratio of ∼91 fold. Also, it was found that the FNHCs possessed a higher peroxidase-like activity than that of other similar-structured Fe3O4 architectures (e.g. Fe3O4@C NPs). The resulting steady-state kinetic curve demonstrated the enzymatic activity of FNHCs with classic Michaelis–Menton kinetics following a ping-pong mechanism. On the basis of the superior enzymatic activity, the FNHCs performed as a high-efficiency peroxidase mimic, realizing facile, label-free, highly sensitive/selective colorimetric detection of H2O2 and glucose. Furthermore, the colorimetric sensor successfully determined glucose in patients’ serum samples with high accuracy and precision, suggesting great potential for real applications. [ABSTRACT FROM AUTHOR]

An electrochemical sensor based on core–shell nanostructured copper sulfide@Prussian blue composites (CuS@PB) was investigated for ascorbic acid (AA) detection. CuS nanoparticles (NPs) were prepared by a hydrothermal method, then core–shell CuS@PB nanohybrid was fabricated through in situ synthesis of PB on CuS NPs. Taking advantage of their enhanced properties, a novel electrochemical AA sensor was developed by drop-coating of CuS@PB nanohybrid on glassy carbon electrode (GCE). As expected, electrochemical observations showed that CuS@PB/GCE presented higher electrocatalytic performance of AA than PB/GCE, with a wide linear range (5–3875 μM, R = 0.9997), fast response time (<3 s), high sensitivity (256.91 μAmM−1cm−2), as well as a low limit of detection (0.24 μM at a signal-to-noise ratio of 3). Additionally, the CuS@PB/GCE showed excellent reproducibility, storage stability, anti-interference, and selectivity. The application of a CuS@PB/GCE sensor for an AA assay in beverage samples achieved satisfactory results, demonstrating great prospects for the quantitative detection of AA in various fields. [ABSTRACT FROM AUTHOR]

We theoretically demonstrate that pure magnetic quadrupole (MQ) scattering is achieved via the excitation of anapole modes and Fano resonance in noble metal (Au or Ag) and high refractive index dielectric (AlGaAs) hybrid nano-antennas. In Au-AlGaAs hybrid nano-antennas, electric anapole and magnetic anapole modes are observed, leading to the suppressions of electric and magnetic dipoles. Introducing gain material to AlGaAs nanodisk to increase the strength of electric quadrupole (EQ) Fano resonance leads to the suppression of EQ scattering. Then, ideal MQ scattering is achieved at the wavelength of total scattering cross-section dip. The increase of signal-to-noise ratio of MQ results in the great enhancement of near-field inside AlGaAs nanodisk. Additionally, the strong MQ resonance exhibits great capability for boosting second-harmonic generation by proper mode matching. These findings achieved in subwavelength geometries have important implications for functional metamaterials and nonlinear photonic nanodevices. [ABSTRACT FROM AUTHOR]

Orthorhombic molybdenum oxide (α-MoO3) nanostructures were deposited on the surface of carbon cloth (CC) as a flexible and high conductive scaffold by reactive RF magnetron sputtering technique. Structure and morphology of the as prepared molybdenum coated carbon cloth (MoO3CC) were thoroughly characterized with field emission scanning electron microscopy, x-ray diffraction, energy dispersive x-ray and Raman spectroscopy. Benefiting from high surface area and superior conductivity of CC as well as electrocatalytic activity of α-MoO3 nanostructures, an electrochemical sensor was fabricated. The electrochemical behavior of this new sensor toward determination of dopamine was studied in detail by cyclic voltammetry, amperometry (AM) and square wave voltammetry (SWV). Results reported here reveal that using SWV not only enhances the sensitivity of sensors to dopamine by more than 14 times compared to AM, but also offers higher linear dynamic range (1–700 μM compared to 5–550 μM). Limit of detection, for signal to noise ratio 3, was calculated to be 0.48 μM. Applicability of the proposed sensor for measurement of dopamine in real samples, like urine and pharmaceutical formulation, was also evaluated that concluded to satisfactory results. [ABSTRACT FROM AUTHOR]

This paper presents a maskless method to manufacture fused silica chips for low-noise resistive-pulse sensing. The fabrication includes wafer-scale density modification of fused silica with a femtosecond-pulsed laser, low-pressure chemical vapor deposition (LPVCD) of silicon nitride (SiNx) and accelerated chemical wet etching of the laser-exposed regions. This procedure leads to a freestanding SiNx window, which is permanently attached to a fused silica support chip and the resulting chips are robust towards Piranha cleaning at ∼80 °C. After parallel chip manufacturing, we created a single nanopore in each chip by focused helium-ion beam or by controlled breakdown. Compared to silicon chips, the resulting fused silica nanopore chips resulted in a four-fold improvement of both the signal-to-noise ratio and the capture rate for signals from the translocation of IgG1 proteins at a recording bandwidth of 50 kHz. At a bandwidth of ∼1 MHz, the noise from the fused silica nanopore chips was three- to six-fold reduced compared to silicon chips. In contrast to silicon chips, fused silica chips showed no laser-induced current noise—a significant benefit for experiments that strive to combine nanopore-based electrical and optical measurements. [ABSTRACT FROM AUTHOR]

An ideal microelectrode array (MEA) design should include materials and structures which exhibit biocompatibility, low electrode polarization, low impedance/noise, and structural durability. Here, the fabrication of MEAs with indium tin oxide (ITO) electrodes deposited with self-similar gold nanostructures (GNS) is described. We show that fern leaf fractal-like GNS deposited on ITO electrodes are conducive for neural cell attachment and viability while reducing the interfacial impedance more than two orders of magnitude at low frequencies (100–1000 Hz) versus bare ITO. GNS MEAs, with low interfacial impedance, allowed the detection of extracellular action potentials with excellent signal-to-noise ratios (SNR, 20.26 ± 2.14). Additionally, the modified electrodes demonstrated electrochemical and mechanical stability over 29 d in vitro. [ABSTRACT FROM AUTHOR]

Plasmon based field effect transistors (FETs) can be used to convert energy induced by incident optical radiation to electrical energy. Plasmonic FETs can efficiently detect incident light and amplify it by coupling to resonant plasmonic modes thus improving selectivity and signal to noise ratio. The spectral responses can be tailored both through optimization of nanostructure geometry as well as constitutive materials. In this paper, we studied various plasmonic nanostructures using gold for a wideband spectral response from visible to near-infrared. We show, using empirical data and simulation results, that detection loss exponentially increases as the volume of metal nanostructure increases and also a limited spectral response is possible using gold nanostructures in a plasmon to electric conversion device. Finally, we demonstrate a plasmon FET that offers a broadband spectral response from visible to telecommunication wavelengths. [ABSTRACT FROM AUTHOR]

Exploring and making predictions based on single-molecule data can be challenging, not only due to the sheer size of the datasets, but also because a priori knowledge about the signal characteristics is typically limited and poor signal-to-noise ratio. For example, hypothesis-driven data exploration, informed by an expectation of the signal characteristics, can lead to interpretation bias or loss of information. Equally, even when the different data categories are known, e.g., the four bases in DNA sequencing, it is often difficult to know how to make best use of the available information content. The latest developments in machine learning (ML), so-called deep learning (DL) offer interesting, new avenues to address such challenges. In some applications, such as speech and image recognition, DL has been able to outperform conventional ML strategies and even human performance. However, to date DL has not been applied much in single-molecule science, presumably in part because relatively little is known about the ‘internal workings’ of such DL tools within single-molecule science as a field. In this Tutorial, we make an attempt to illustrate in a step-by-step guide how one of those, a convolutional neural network (CNN), may be used for base calling in DNA sequencing applications. We compare it with a SVM as a more conventional ML method, and discuss some of the strengths and weaknesses of the approach. In particular, a ‘deep’ neural network has many features of a ‘black box’, which has important implications on how we look at and interpret data. [ABSTRACT FROM AUTHOR]

During dynamic atomic force microscopy (AFM), the deflection of a scanning cantilever generates multiple frequency terms due to the nonlinear nature of AFM tip–sample interactions. Even though each frequency term is reasonably expected to encode information about the sample, only the fundamental frequency term is typically decoded to provide topographic mapping of the measured surface. One of main reasons for discarding higher harmonic signals is their low signal-to-noise ratio. Here, we introduce a new design concept for multi-harmonic AFM, exploiting intentional nonlinear internal resonance for the enhancement of higher harmonics. The nonlinear internal resonance, triggered by the non-smooth tip–sample dynamic interactions, results in nonlinear energy transfers from the directly excited fundamental bending mode to the higher-frequency mode and, hence, enhancement of the higher harmonic of the measured response. It is verified through detailed theoretical and experimental study that this AFM design can robustly incorporate the required internal resonance and enable high-frequency AFM measurements. Measurements on an inhomogeneous polymer specimen demonstrate the efficacy of the proposed design, namely that the higher harmonic of the measured response is capable of enhanced simultaneous topography imaging and compositional mapping, exhibiting less crosstalk with an abrupt height change. [ABSTRACT FROM AUTHOR]

Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including the use of nanopores in DNA sequencing, the potential application of silicene on nanopore sequencing, and the low-frequency noise on the ionic currents.

The operation of solid-state qubits often relies on single-shot readout using a nanoelectronic charge sensor, and the detection of events in a noisy sensor signal is crucial for high fidelity readout of such qubits. The most common detection scheme, comparing the signal to a threshold value, is accurate at low noise levels but is not robust to low-frequency noise and signal drift. We describe an alternative method for identifying charge sensor events using wavelet edge detection. The technique is convenient to use and we show that, with realistic signals and a single tunable parameter, wavelet detection can outperform thresholding and is significantly more tolerant to and low-frequency noise. [ABSTRACT FROM AUTHOR]

In this work, we calculate the effect of the binding and unbinding of molecules at the surface of a nanowire biosensor on the signal-to-noise ratio of the sensor. We model the fluctuations induced by association and dissociation of target molecules by a stochastic differential equation and extend this approach to a coupled diffusion-reaction system. Where possible, analytic solutions for the signal-to-noise ratio are given. Stochastic simulations are performed wherever closed forms of the solutions cannot be derived. Starting from parameters obtained from experimental data, we simulate DNA hybridization at the sensor surface for different target molecule concentrations in order to optimize the sensor design. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid–liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments. [ABSTRACT FROM AUTHOR]

Recently, pulsed magneto-motive ultrasound (pMMUS) imaging augmented with ultra-small magnetic nanoparticles has been introduced as a tool capable of imaging events at molecular and cellular levels. The sensitivity of a pMMUS system depends on several parameters, including the size, geometry and magnetic properties of the nanoparticles. Under the same magnetic field, larger magnetic nanostructures experience a stronger magnetic force and produce larger displacement, thus improving the sensitivity and signal-to-noise ratio (SNR) of pMMUS imaging. Unfortunately, large magnetic iron-oxide nanoparticles are typically ferromagnetic and thus are very difficult to stabilize against colloidal aggregation. In the current study we demonstrate improvement of pMMUS image quality by using large size superparamagnetic nanoclusters characterized by strong magnetization per particle. Water-soluble magnetic nanoclusters of two sizes (15 and 55 nm average size) were synthesized from 3 nm iron precursors in the presence of citrate capping ligand. The size distribution of synthesized nanoclusters and individual nanoparticles was characterized using dynamic light scattering (DLS) analysis and transmission electron microscopy (TEM). Tissue mimicking phantoms containing single nanoparticles and two sizes of nanoclusters were imaged using a custom-built pMMUS imaging system. While the magnetic properties of citrate-coated nanoclusters are identical to those of superparamagnetic nanoparticles, the magneto-motive signal detected from nanoclusters is larger, i.e. the same magnetic field produced larger magnetically induced displacement. Therefore, our study demonstrates that clusters of superparamagnetic nanoparticles result in pMMUS images with higher contrast and SNR. [ABSTRACT FROM AUTHOR]

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern. [ABSTRACT FROM AUTHOR]

Contact mode atomic force microscopy (AFM) is the most frequently used AFM imaging mode in biology. It is about 5-10 times faster than oscillating mode imaging (in conventional AFM setups), and provides topographs of biological samples with sub-molecular resolution and at a high signal-to-noise ratio. Unfortunately, contact mode imaging is sensitive to the applied force and intrinsic force drift: inappropriate force applied by the AFM tip damages the soft biological samples. We present a methodology that automatically searches for and maintains high resolution imaging forces. We found that the vertical and lateral vibrations of the probe during scanning are valuable signals for the characterization of the actual applied force by the tip. This allows automated adjustment and correction of the setpoint force during an experiment. A system that permanently performs this methodology steered the AFM towards high resolution imaging forces and imaged purple membrane at molecular resolution and live cells at high signal-to-noise ratio for hours without an operator. [ABSTRACT FROM AUTHOR]

In this paper, we report on a process to prepare gold nanoparticle stripes on SiO2 by convective/capillary assembly without any patterning of the substrate. Electrical devices were then fabricated using stencil lithography in order to avoid any contamination. I(V) measurements at room temperature show that these stripes have an ohmic behavior between +- 0.5 V with a resistivity ranging from one to two orders higher than the gold bulk value. Furthermore, I(V) and I(t) measurements reveal current fluctuations that were interpreted in terms of charging and discharging of nanoparticle islands leading to a very large electrostatic perturbation of current conduction paths. Unconventional relative amplitudes of up to 99% RTS fluctuations were observed. [ABSTRACT FROM AUTHOR]

Nanoelectrodes are fabricated from individual carbon nanotubes (CNTs) connected to tungsten probes or carbon fibers. The whole electrode was covered by an insulating HfO2 layer except for a section of conducting CNT at the apex. The fabrication process includes mounting individual CNTs to the conductive support through nanomanipulation, coating the whole probe by a dielectric layer using atomic layer deposition and removing the dielectric layer at the apex through a nanomanipulation process. Differential pulse voltammetry and cyclic voltammetry measurements show the CNT nanoelectrode has similar electrochemical behavior to the widely used carbon fiber probe, but has a much smaller active electrode area and can provide much higher spatial resolution and signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) attached to type I collagen-modified glassy carbon (GC) electrodes were successfully synthesized by the electrodepositing method. Atomic force microscopy images showed that many Ag NPs with homogeneous size were formed and uniformly distributed on the type I collagen/GC electrode. The amount, size and distribution of Ag NPs could be controlled by the collagen. The results of electrochemical experiments showed that Ag NPs had an excellent catalytic ability for the reduction of hydrogen peroxide (H2O2), suggesting that they could be used as a sensor to determine H2O2. The good catalytic activity of the Ag NPs was ascribed to the type I collagen that resulted in the homogeneous distribution of Ag NPs with small size. The effects of type I collagen concentration and electrodeposition time on Ag NPs were investigated. When the Ag NPs were used as a sensor to determine H2O2, the sensor could achieve 95% of the steady-state current in less than 2 s and had a linear range of 5.0 uM to 40.6 mM and a 0.7 uM detection limit of H2O2 at a signal-to-noise ratio of 3. [ABSTRACT FROM AUTHOR]