anlong Ji

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.

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.

α-Fe2O3 concave and hollow nanocrystals: top-down etching synthesis and their comparative photocatalytic activities

In this work, uniform single-crystalline α-Fe2O3 concave and hollow nanocrystals have been synthesized by a facile top-down etching method. Phosphate ions were employed as an etching agent to etch pristine icositetrahedra along their [006] direction in a top-down manner. The etched Fe2O3 concave and hollow nanocrystals exhibit a much larger specific surface area (SSA) and more edges, corners and rough structures (hot spots) on the crystal surface compared to their mother crystal, thus serving as the possible origin of their comparative photocatalytic activities in the degradation of cationic dye Rhodamine B. These characteristics make them promising candidates as catalysts and sensing materials.

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.

Fe2O3 icositetrahedra: evolution and their comparative photocatalytic activities

Single crystal Fe2O3 icositetrahedra have been synthesized by a facile hydrothermal synthesis method in the presence of dihydrogen phosphate ions. The icositetrahedron particles are of hexagonal shape and enclosed by 24 quadrilaterals. It could be seen as a particle with six equivalent {110} facets added to the truncated hexagonal bipyramidal structure, that is, it is enclosed by six {110} planes, six {104} planes and twelve {113} planes. Dihydrogen phosphate ions play an important role in the formation of α-Fe2O3 icositetrahedron particles, because high concentration of [H2PO4]− drives the ferric oxide nanocrystals growth along the [006] zone axis. Furthermore, the as-synthesized Fe2O3 icositetrahedron single crystals show comparative photocatalytic activities on the degradation of cationic dye Rhodamine B, which make them promising candidates for catalysts and sensing materials.

Monocrystalline hematite nanostructures: three-dimensionally oriented aggregation synthesis and their comparative visible-light photocatalytic activities

Intelligent three-dimensionally oriented aggregation of nanobuilding blocks during the formation of α-Fe2O3 single crystals with a nano-saucer structure has been studied. The hematite truncated hexagonal bipyramids assembled together with the aid of dihydrogen phosphate ions and grew along the direction to form a slice structure, then the slices piled up layer by layer along the [006] zone axis to form the brand-new geometry of saucer-like nanoparticles. On the basis of the small size, rough surface and loose, zigzag edge characteristics of the 3D assembly structure, the novel saucer nanoparticles exhibited distinguishable absorption and specific surface area (SSA) properties, thus serving as the possible origin of their comparative visible-light photocatalytic activities on the degradation of cationic dye rhodamine B. These characteristics make them promising candidates for catalysts and sensing materials.

Portable microsystem integrates multifunctional dielectrophoresis manipulations and a surface stress biosensor to detect red blood cells for hemolytic anemia

Hemolytic anemia intensity has been suggested as a vital factor for the growth of certain clinical complications of sickle cell disease. However, there is no effective and rapid diagnostic method. As a powerful platform for bio-particles testing, biosensors integrated with microfluidics offer great potential for a new generation of portable point of care systems. In this paper, we describe a novel portable microsystem consisting of a multifunctional dielectrophoresis manipulations (MDM) device and a surface stress biosensor to separate and detect red blood cells (RBCs) for diagnosis of hemolytic anemia. The peripheral circuit to power the interdigitated electrode array of the MDM device and the surface stress biosensor test platform were integrated into a portable signal system. The MDM includes a preparing region, a focusing region, and a sorting region. Simulation and experimental results show the RBCs trajectories when they are subjected to the positive DEP force, allowing the successful sorting of living/dead RBCs. Separated RBCs are then transported to the biosensor and the capacitance values resulting from the variation of surface stress were measured. The diagnosis of hemolytic anemia can be realized by detecting RBCs and the portable microsystem provides the assessment to the hemolytic anemia patient.

Highly Sensitive and Stretchable Strain Sensor Based on Ag@CNTs

Due to the rapid development and superb performance of electronic skin, we propose a highly sensitive and stretchable temperature and strain sensor. Silver nanoparticles coated carbon nanowires (Ag@CNT) nanomaterials with different Ag concentrations were synthesized. After the morphology and components of the nanomaterials were demonstrated, the sensors composed of Polydimethylsiloxane (PDMS) and CNTs or Ag@CNTs were prepared via a simple template method. Then, the electronic properties and piezoresistive effects of the sensors were tested. Characterization results present excellent performance of the sensors for the highest gauge factor (GF) of the linear region between 0–17.3% of the sensor with Ag@CNTs1 was 137.6, the sensor with Ag@CNTs2 under the strain in the range of 0–54.8% exhibiting a perfect linearity and the GF of the sensor with Ag@CNTs2 was 14.9.

Detection system based on magnetoelastic sensor for classical swine fever virus

In this paper, a magnetoelastic (ME) sensing system for the detection of classical swine fever virus (CSFV) is presented. The detection system comprises a test paper and a measurement circuit. The test paper consists mainly of an ME biosensor to detect the CSFV. Based on the impedance analysis technique, the measurement circuit is designed to measure the resonance frequency of the ME biosensor. The anti-CSFV IgG is immobilized onto the ME sensor surface to form the ME biosensor through a physical absorption approach. The experimental results show that the shift in the resonance frequency of the ME biosensor increases with the augmentation of the CSFV concentration. The effectiveness of the combination between the anti-CSFV IgG and CSFV is confirmed by the scanning electron microscopy (SEM) images, the sandwich-based enzyme-linked immunosorbent assay (ELISA) analysis, the interference study and the reference biosensor test method. The resonance frequency shift is linearly proportional to the concentration in the range from 0 to 2.5μg/ml, and becomes sub-linear at higher concentrations. The ME biosensor for CSFV detection has a sensitivity of about 95Hz/μg·ml(-1), with a detection limit of 0.6μg/ml.

A magnetoelastic biosensor based on E2 glycoprotein for wireless detection of classical swine fever virus E2 antibody

A wireless magnetoelastic (ME) biosensor immobilized with E2 glycoprotein was first developed to detect classical swine fever virus (CSFV) E2 antibody. The detection principle is that a sandwich complex of CSFV E2 – rabbit anti-CSFV E2 antibody – alkaline phosphatase (AP) conjugated goat anti-rabbit IgG formed on the ME sensor surface, with biocatalytic precipitation used to amplify the mass change of antigen–antibody specific binding reaction, induces a significant change in resonance frequency of the biosensor. Due to its magnetostrictive feature, the resonance vibrations and resonance frequency can be actuated and wirelessly monitored through magnetic fields. The experimental results show that resonance frequency shift increases with the augmentation of the CSFV E2 antibody concentration. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and fluorescence microscopy analysis proved that the modification and detection process were successful. The biosensor shows a linear response to the logarithm of CSFV E2 antibody concentrations ranging from 5 ng/mL to 10 μg/mL, with a detection limit (LOD) of 2.466 ng/mL and the sensitivity of 56.2 Hz/μg·mL−1. The study provides a low-cost yet highly-sensitive and wireless method for selective detection of CSFV E2 antibody.