Shengbo Sang

Progress of new label-free techniques for biosensors: a review

Abstract The detection techniques used in biosensors can be broadly classified into label-based and label-free. Label-based detection relies on the specific properties of labels for detecting a particular target. In contrast, label-free detection is suitable for the target molecules that are not labeled or the screening of analytes which are not easy to tag. Also, more types of label-free biosensors have emerged with developments in biotechnology. The latest developed techniques in label-free biosensors, such as field-effect transistors-based biosensors including carbon nanotube field-effect transistor biosensors, graphene field-effect transistor biosensors and silicon nanowire field-effect transistor biosensors, magnetoelastic biosensors, optical-based biosensors, surface stress-based biosensors and other type of biosensors based on the nanotechnology are discussed. The sensing principles, configurations, sensing performance, applications, advantages and restriction of different label-free based biosensors are considered and discussed in this review. Most concepts included in this survey could certainly be applied to the development of this kind of biosensor in the future.

Surface stress-based biosensors.

Surface stress-based biosensors, as one kind of label-free biosensors, have attracted lots of attention in the process of information gathering and measurement for the biological, chemical and medical application with the development of technology and society. This kind of biosensors offers many advantages such as short response time (less than milliseconds) and a typical sensitivity at nanogram, picoliter, femtojoule and attomolar level. Furthermore, it simplifies sample preparation and testing procedures. In this work, progress made towards the use of surface stress-based biosensors for achieving better performance is critically reviewed, including our recent achievement, the optimally circular membrane-based biosensors and biosensor array. The further scientific and technological challenges in this field are also summarized. Critical remark and future steps towards the ultimate surface stress-based biosensors are addressed.

One‐Dimensional Nano‐Interconnection Formation

Interconnection of one-dimensional nanomaterials such as nanowires and carbon nanotubes with other parts or components is crucial for nanodevices to realize electrical contacts and mechanical fixings. Interconnection has been being gradually paid great attention since it is as significant as nanomaterials properties, and determines nanodevices performance in some cases. This paper provides an overview of recent progress on techniques that are commonly used for one-dimensional interconnection formation. In this review, these techniques could be categorized into two different types: two-step and one-step methods according to their established process. The two-step method is constituted by assembly and pinning processes, while the one-step method is a direct formation process of nano-interconnections. In both methods, the electrodeposition approach is illustrated in detail, and its potential mechanism is emphasized.

Investigation of Charge Injection and Relaxation in Multilayer Dielectric Stacks for Capacitive RF MEMS Switch Application

This paper proposes a new approach to the problem of irreversible stiction of capacitive radio frequency (RF) microelectromechanical (MEMS) switch attributed to the dielectric charging. We investigate how charge accumulates in multi- and single-layer dielectric structures for a capacitive RF MEMS switch using metal-insulator-semiconductor (MIS) capacitor structure. Two multidielectric-layers are structured, which are SiO2+Si3N4 and SiO2+Si3N4+SiO2 stack films. Meanwhile, Si3N4 single-layer dielectric structure is also fabricated for comparison. In the experiments, the space charges are first injected into the dielectric layers by stressing MIS devices with a dc bias; then the injected charge kinetics are monitored by capacitance-voltage measurement before and after charge injection. We found that the polarity of charge accumulated in the dielectric is strongly influenced by the dielectric structure. When the metal electrode is positively biased, a negative charge accumulates in the single and triple-layer devices, while a positive charge accumulates in the double-layer devices. Furthermore, the experiment results also show that the lowest charge accumulation can be achieved using double-layer dielectric structure even though the fastest relaxation process takes place in triple-layer dielectric structure.

Fabrication and characterization of silicon nanostructures based on metal-assisted chemical etching

We present a facile method to fabricate one-dimensional Si nanostructures based on Ag-induced selective etching of silicon wafers. To obtain evenly distributed Si nanowires (SiNWs), the fabrication parameters have been optimized. As a result, a maximum of average growth rate of 0.15 μm/min could be reached. Then, the fabricated samples were characterized by water contact angle (CA) experiments. As expected, the as-etched silicon samples exhibited a contact angle in the range of 132°–136.5°, whereas a higher contact angle (145°) could be obtained by chemical modification of the SiNWs with octadecyltrichlorosilane (OTS). Additionally, Raman spectra experiments have been carried out on as-prepared nanostructures, showing a typical decreasing from 520.9 cm−1 to 512.4 cm−1 and an asymmetric broadening, which might be associated with the phonon quantum confinement effect of Si nanostructures.

Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and UV–vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA) models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electric field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO) flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS) activity, using 4-mercaptopyridine (4-MP) as model molecules.

A highly sensitive electrochemical sensor based on Cu/Cu2O@carbon nanocomposite structures for hydrazine detection

We report a simple and large-scale fabrication of carbon-coated Cu/Cu2O nanocomposite materials (Cu/Cu2O@carbon) and their application as sensing materials for hydrazine detection in a neutral medium. The Cu/Cu2O@carbon nanocomposite structures were successfully synthesized using a facile, cost-effective calcination method. The morphology, crystalline structure, and composition of the prepared Cu/Cu2O@carbon were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and high-resolution transmission electron microscopy. The hydrazine electrochemical sensor was fabricated by painting Cu/Cu2O@carbon on a glassy carbon electrode and immobilized using Nafion. By optimizing the Cu/Cu2O@carbon modified quantity and evaluating the performance using cyclic voltammetry and amperometry techniques, we demonstrated an optimal hydrazine electrochemical sensor with a high sensitivity of 2.37 μA μM−1 cm−2, an excellent linear concentration range of 0.25 μM to 800 μM, and a low detection limit of 0.022 μM.

The Design of Burglar Alarm Circuit Based on the Magnetic Field Sensor

This paper introduces a design method and a hardware circuit of burglar alarm circuit based on the magnetic field sensor, which can be used to achieve the protection of valuables. The circuit design is ingenious, and has the characteristics of simple structure, light weight, small size, timeliness, high sensitivity and low cost. It has been proved to have a stable and reliable performance by experiment.

Synthesis of p-Co3O4/n-TiO2 Nanoparticles for Overall Water Splitting under Visible Light Irradiation

p-Co3O4/n-TiO2 nanoparticles (~400 nm) for photocatalysis were prepared via carbon assisted method and sol-gel method in this work. The paper also studied the application of visible light illuminated p-Co3O4/n-TiO2 nanocomposites cocatalyst to the overall pure water splitting into H2 and O2. In addition, the H2 evolution rate of the p-Co3O4/n-TiO2 nanocomposites is 25% higher than that of the pure Co3O4 nanoparticles. Besides, according to the results of the characterizations, the scheme of visible light photocatalytic water splitting is proposed, the Co3O4 of the nanocomposites is excited by visible light, and the photo-generated electrons and holes existing on the conduction band of Co3O4 and valence band of TiO2 have endowed the photocatalytic evolution of H2 and O2 with higher efficiency. The optimal evolution rate of H2 and O2 is 8.16 μmol/h·g and 4.0 μmol/h·g, respectively.

A self-developed indoor three-dimensional pedestrian localization platform based on MEMS sensors

Purpose – This study aims to design a new low-cost localization platform for estimating the location and orientation of a pedestrian in a building. The micro-electro-mechanical systems (MEMS) sensor error compensation and the algorithm were improved to realize the localization and altitude accuracy. Design/methodology/approach – The platform hardware was designed with common low-performance and inexpensive MEMS sensors, and with a barometric altimeter employed to augment altitude measurement. The inertial navigation system (INS) – extended Kalman filter (EKF) – zero-velocity updating (ZUPT) (INS-EKF-ZUPT [IEZ])-extended methods and pedestrian dead reckoning (PDR) (IEZ + PDR) algorithm were modified and improved with altitude determined by acceleration integration height and pressure altitude. The “AND” logic with acceleration and angular rate data were presented to update the stance phases. Findings – The new platform was tested in real three-dimensional (3D) in-building scenarios, achieved with position ...