Sensors, which are transducer-type devices, are indispensable to today’s advanced information society. A huge number of sensors are used not only in everyday devices but also in advanced industrial systems. They are used in Internet of things (IoT) services to gather external information, intelligent robots to recognize the world around them and control their movements, and all advanced vehicle technologies to operate safely and automatically. Sensors detect light, motion, force, fluid flow, electric/magnetic fields, and other physical, chemical, and biological aspects of the external environment.
To improve the performances of these sensors, such as their sensitivity, sensing resolution, and power consumption, extensive R&D is conducted in industry and academia. Recent technological progress in MEMS technology has allowed sensors to be manufactured on scales that are increasingly microscopic. More recently, the extreme downsizing of structures to nanometer scale has led to innovative sensing devices called NEMS.
This special issue addresses the latest research advances in nanosensing and microsensing science and engineering. It covers a wide range of topics, including novel sensing devices and technologies; small structures fabrication technologies for sensors; MEMS/NEMS sensing devices; physical, chemical, optical and biological sensing devices; and nanoscale science and engineering for sensors.
All papers were refereed through careful peer reviews. We would like to express our sincere thanks to the authors for their submissions and to the reviewers for their invaluable efforts. Lastly, we hope this special issue provides valuable and useful information to our interested readers and researchers.
We have engaged in researching and developing a large number of sensor devices using piezo-resistive cantilevers. The important technical features of our sensor devices lie in their very high detection sensitivity that has been achieved by the use of cantilevers of a very thin structure: as a typical example, force-detection sensitivity of about 10 pN has been achieved by using cantilevers of 300-nm thickness. This paper presents our developed sensor devices and applications and their respective features: more specifically, devices to directly measure object-contacting forces, devices embedded in an elastic body to measure its deformations, devices to measure air flows and vibrations, devices to measure differential air pressure, devices to measure differential pressure between cavities and external environment, and devices with cantilevers arranged on the liquid interface.
Microelectromechanical systems (MEMS) and micrototal analysis systems (μTAS) have been developed using microfabrication technologies. As MEMS and μTAS contribute to smaller, higher-performance, less expensive, and integrated sensing techniques, they have been applied in many fields. In this paper, we focus on microfabricated thermal detection devices, including a microthermistor fabricated using vanadium oxide (VOx) and a resonant thermal sensor integrated into a microfluidic chip, and we present the research work we have done into biological applications, applications using a unique material and detection method for liquid samples. The VOx thermistor, which has a high temperature coefficient of resistance at –1.3%/K, is mounted onto a thermally insulated membrane in the microfluidic chip. This device is used to detect glucose and cholesterol concentrations in solutions. The resonant thermal sensor is another candidate for obtaining highly sensitive thermal measurements; however, this sensor is difficult to use with liquids because of vibration damping and thermal loss. To solve these problems, we propose a partial vacuum packaging system for the sensor in the microfluidic chip. This technique, which involves silicon resonators, was used to successfully detect the heat from a single brown fat cell. Moreover, the possibility of using a VOx resonant thermal sensor is discussed. The future prospects for MEMS and automation technology are described, with a focus on the Internet of Things/big data for medical and healthcare applications.
We report the local top-gated graphene resonator inertial mass sensing of mixed H2/Ar gas. The graphene resonator is fabricated with monolayer graphene. The fabricated resonator dimensions are 900 nm in length and 500 nm in width. Measurements of the fabricated resonator are performed using a co-planar structure probe and radio-frequency (RF) connectors. At the vacuum condition of the chamber, the resonant frequency of the doubly clamped graphene resonator is measured as 94.3 MHz with the quality factor of 42.2, based on transmission S-parameter characterization. The measured resonant frequency is consistent with the theoretical calculation based on the continuum model for the graphene resonator. When the chamber pressure is increased to 1.1×10-1 Pa by injecting mixed H2/Ar gas, the resonant frequency of the device is downshifted by 4.32 MHz to 89.98 MHz and the quality factor is reduced to 22.5. As the mass of the graphene resonator is increased by the adsorption of mixed gas molecules adsorption, the resonant frequency is downshifted further. The detected mass of the adsorbed gas molecules is calculated as ∼15 attograms.
A high-yield, bridged assembly of single-walled carbon nanotubes (SWCNT) was demonstrated using single-strand DNA (ssDNA) modification, dielectrophoresis (DEP), and electroless deposition of gold. ssDNA modification is used for the mono-dispersion of an SWCNT solution for DEP. Gold deposition after DEP was used for the electrical and mechanical clamping of assembled SWCNTs. DEP conditions were investigated, and the best conditions, namely, 2 Vpp, 1 kHz, 1 min for 200-nm gap electrodes, resulted in 8 single-assembly and 19 multiple-assembly SWCNTs between 33 pairs of electrode gaps. The electrical properties of the assembled ssDNA-modified SWCNTs were measured as a back-gate type of FET, and both metallic and semiconducting properties were observed.
We review the recent advances in the use of our originally developed on-chip graphene aptasensor to detect biologically important proteins, such as cancer markers. The detection mechanism, based on fluorescence resonance energy transfer (FRET), occurs at a graphene–biomolecule interface. In our system, the graphene surface is modified with a pyrene–aptamer–dye probe. Pyrene functions as a linker to the graphene surface, the aptamer as a probe for selective protein recognition, and the dye as a fluorescence detection tag. Here, graphene behaves simultaneously as both an efficient acceptor for FRET over the entire visible region and as a strong adsorbate for single-stranded DNA (ssDNA), such as aptamers, via π-π interactions in the sp2 domain. The system allows us to perform molecular detection on a solid surface, which is advantageous for realizing on-chip sensors. Such on-chip sensors allow parallel analysis systems, such as array sensors. This enables the quantitative comparison of different samples by forming a multichannel configuration and/or a micropattern with different probes. Moreover, detecting the target protein is possible simply by adding a sample of less than 1 μL to the on-chip sensor; detection is completed in approximately 1 min. Aptasensors can be used for the detection of many different targets simply by replacing the aptamers. The simultaneous detection of multiple target molecules on a single chip using a 2 × 3 linear-array aptasensor was demonstrated here. Improved sensitivity was observed when a DNA spacer was incorporated into the aptamer, demonstrating that the probe can be modified in interesting ways.
In this study, we report a simple and rapid biosensing method for the analysis and in vitro monitoring of biological processes, including DNAbinding events, antigen-antibody interactions, and cellular functions, using a semiconductor device. Most biological phenomena involve cell-cell communication processes that are mediated by the transport of sodium or potassium ions and other charged biomolecules, such as DNA, across ion channels in the cell membrane. Therefore, our approach focused on the direct detection of changes in ion concentrations by utilizing a semiconductor-based biosensor device. Our results demonstrated that our semiconductor-based biosensor platform achieves label-free and noninvasive biosensing that is suitable for in vitro diagnosis.
In this paper, we introduce semiconductor biosensors for detecting or monitoring various biological substances and for surface chemical technologies tailored to target molecules. To fabricate the semiconductor biosensor best suited to the target biomolecules, the gate electrodes for extended-gate type field-effect transistors (EGFETs), which are separated from semiconductor part, must be constructed by interfacial chemical modification. First, ion-sensitive EGFET was developed by self-assembled monolayer (SAM) modification on gold gate electrode. Polar functional-group-terminated alkanethiol SAM-coated-gate FET showed pH dependency. In particular, carboxy-terminated alkanethiol SAM-coated gate FET showed higher sensitivities from 42 to 56 mV/pH, which was close to the Nernstian response, in a wide range of biological environments. By using the ion-sensitive EGFET, the hydroxyapatite biomineralization process was successfully monitored by increasing the gate surface potential. Furthermore, saccharides were quantified using EGFET by changing the functional group of SAM, with phenylboronic acid as a functional molecule. In conclusion, target-specific surface modification on gate electrodes makes it possible for semiconductor devices to be applied as biosensors.
More than two decades have passed since the initial clinical trial of noninvasive glucose sensing using optical absorption spectroscopy. Today, noninvasive sensing technologies are expected to meet the increasing demand for high-quality diabetes management. Here, we review the latest advances in noninvasive glucose sensing research, focusing on how photonics-, acoustic- and electronics-based sensing technologies have played key roles in the development of the first noninvasive glucose sensors. We also present our recent work on multiphysics-based glucose sensing using near-infrared photoacoustic spectroscopy and broadband dielectric spectroscopy and a comparison with other competitive technologies.
A V-trench biosensor is a sensitive biosensing platform utilizing fluorescence enhancement induced by surface plasmon resonance (SPR). Instruments for the SPR-assisted fluorescence assays, which were complicated and bulky, are drastically simplified and miniaturized by employing sensor chips equipped with prism-integrated microfluidic channels. In this review, the working principle, sensor design, and examples of virus detection of the V-trench biosensor are presented.
This paper presents a high-precision and high-yield nanotemplate-guided self-assembly process for spherical gold nanoparticles. This process enables us to arrange particles in designated patterns on a substrate with nanotemplates. These particles are trapped on the nanotemplate by liquid-air interfacial force during drying of the colloidal solution. In this method, particle concentration and electrostatic interaction between particles have a considerable effect on the assembly yield. The particle concentration should be optimized based on the template pattern. A nanogap-controlled particle arrangement with a high yield is achieved by controlling the electrostatic interaction, which is accomplished by adding an electrolyte. This technique enables control of the plasmonic resonance properties of metal nanoparticles on substrates for many emerging applications. Among them, this paper discusses the application of nanotemplate-guided self-assembly to an ultrasensitive nanostructure for surface-enhanced Raman spectroscopy. The gold nanoparticle dimer, which has been reported as the highest Raman enhancing structure, is directionally arrayed on a substrate. The highest enhancement can be achieved when the direction of a particle connection for a dimer is matched to the polarization direction of incident light. A considerable enhancement can be achieved at all dimers. The fabricated structures are evaluated by focusing on the polarization angle. The 10-11-M limit of detection and a 0.05-s rapid detection are achieved by using 4,4-bipyridine molecules with single-molecule sensitivity.
Sensing and imaging with THz waves is an active area of modern research in optical science and technology. There have been a number of studies for enhancing THz sensing technologies. In this paper, we review our recent development of THz plasmonic structures and carbon-based THz imagers. The plasmonic structures have strong possibilities of largely increasing detector sensitivity because of their outstanding properties of high transmission enhancement at a subwavelength aperture and local field concentration. We introduce novel plasmonic structures and their performance, including a Si-immersed bull’s-eye antenna and multi-frequency bull’s-eye antennas. The latter part of this paper explains carbon-based THz detectors and their applications in omni-directional flexible imaging. The use of carbon nanotube films has led to a room-temperature, flexible THz detector and has facilitated the visualization of samples with three-dimensional curvatures. The techniques described in this paper can be used effectively for THz sensing and imaging on a micro- and nano-scale.
This study designs and develops a new material measure with a chirp form. Material measures are measurement standards for calibration, verification, and inspection. Since material measures are essential for ensuring the traceability of surface texture instruments, we have been developing a manufacturing system to provide them. ISO 5436-1:2000 contains material measures with sinusoidal wave forms, random wave forms, triangular wave forms, trapezoidal wave forms, cusp forms, rectangular forms, etc. However, ISO 5436-1:2000 does not contain a material measure with a chirp (sweep) form. Therefore, we propose a material measure with a chirp form. Chirp signals are frequently used for various analyses in the fields of mechanical engineering, electrical engineering, physics, and others. The primary purpose of the proposed material measure with a chirp form is to rapidly and simply examine the characteristics and capabilities of implemented Gaussian filters. We designed the surface form of the material measure as a logarithmic chirp form to maximize the utility of the primary purpose in this study. The wavelength of the manufactured chirp form varies logarithmically in the lateral (x) direction. This paper presents the following five points: 1) the design and development of the material measure with a chirp form, 2) the application of the proposed material measure to the examination of the attenuation characteristics of implemented Gaussian filters, 3) the application of the proposed material measure to obtain the deformation of the roughness form due to the implemented Gaussian filters, 4) the application of the proposed material measure to specify the algorithm of the implemented Gaussian filters, and 5) the possibility of another application of the material measure with a chirp form.
The objective of this study is to utilize measured temperatures for process monitoring in precision end-milling. Thermal expansion of machining workpiece deteriorates machining accuracy and is considered as an important phenomenon to achieve accurate end-milling process. Thermo-couples are typically employed to measure the temperatures of machining workpiece. This study proposes a method to select appropriate temperature measurement positions based on variations in conscious machining evaluation. The variations in the conscious evaluation of temperature distributions on the workpiece are calculated by extending a conventional nominal machining simulation. Variations in the machining process are generated by using different combinations of model parameters for process simulations. An orthogonal array is employed to assign the parameters to reduce the combination number. An evaluation criterion to select measuring points is calculated given the temperature distributions corresponding to the parameter combinations. Feasibility of the proposed criterion is investigated by evaluating a reported temperature estimation case study. Furthermore, an adaptability of the proposed criterion to different machining situations is evaluated by comparing selected measuring points corresponding to different cutter paths.
For structure analysis with the finite element method (FEM), the hexahedral element is preferable to the tetrahedral one from the viewpoint of accuracy. Previously, we had introduced a label-driven subdivision method for a two-dimensional mesh and showed that the meshes generated by our method were useful for structural analyses. In this study, we extend our two-dimensional algorithm to three-dimensions and verify that the meshes generated by the proposed mesh-subdivision algorithm are useful for structural analyses.
In this paper, a novel application of a robust controller for an electronic governor of a small gas engine generator is presented. There are a few studies regarding the fluctuations in the concentration of bio-methane fuel and load fluctuation of a generator using an approximately 1-kW small gas engine generator. For a relatively small-scale local-production-type energy circulation system, such as the gas energy from a Tambo (GET) system, it is necessary to develop a small gas engine generator that can use the generated unpurified bio-methane gas to accommodate the load fluctuation. The GET system is a bio-methane gas production system, utilizing the sustainable resources from a paddy field, without requiring any distinct auxiliary facilities. We have examined the bio-methane gas produced from the GET system as the fuel of a small gas engine generator, which can supply electric energy and thermal energy to a greenhouse. We have studied the application of a robust engine controller by combining a model matching controller and an optimal observer (MM_OBSV controller) with the electronic governor of the small gas engine generator. The results indicate that the control system is adapted for the input disturbance (load fluctuation and modeling error), with the MM_OBSV controller embedded in the electronic governor of the small gas engine generator.