Hanbin Ma

An impedance-based integrated biosensor for suspended DNA characterization

Herein, we describe a novel integrated biosensor for performing dielectric spectroscopy to analyze biological samples. We analyzed biomolecule samples with different concentrations and demonstrated that the solutions impedance is highly correlated with the concentration, indicating that it may be possible to use this sensor as a concentration sensor. In contrast with standard spectrophotometers, this sensor offers a low-cost and purely electrical solution for the quantitative analysis of biomolecule solutions. In addition to determining concentrations, we found that the sample solution impedance is highly correlated with the length of the DNA fragments, indicating that the sizes of PCR products could be validated with an integrated chip-based, sample-friendly system within a few minutes. The system could be the basis of a rapid, low-cost platform for DNA characterization with broad applications in cancer and genetic disease research.

Controlling Surface Termination and Facet Orientation in Cu2O Nanoparticles for High Photocatalytic Activity: A Combined Experimental and Density Functional Theory Study

Cu2O nanoparticles with controllable facets are of great significance for photocatalysis. In this work, the surface termination and facet orientation of Cu2O nanoparticles are accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu2O nanoparticles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. Density functional theory simulations confirm that sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increase the density of exposed Cu atoms at the surfaces and thus benefit the photocatalytic activity. It also shows that the poor reactivity of the Cu-terminated Cu2O (100) surface is due to the high energy barrier of holes at the surface region.

Ultrathin Multifunctional Graphene-PVDF Layers for Multidimensional Touch Interactivity for Flexible Displays

This paper presents a flexible graphene/polyvinylidene difluoride (PVDF)/graphene sandwich for three-dimensional touch interactivity. Here, x-y plane touch is sensed using graphene capacitive elements, while force sensing in the z-direction is by a piezoelectric PVDF/graphene sandwich. By employing different frequency bands for the capacitive- and force-induced electrical signals, the two stimuli are detected simultaneously, achieving three-dimensional touch sensing. Static force sensing and elimination of propagated stress are achieved by augmenting the transient piezo output with the capacitive touch, thus overcoming the intrinsic inability of the piezoelectric material in detecting nontransient force signals and avoiding force touch mis-registration by propagated stress.

Precise control of Cu2O nanostructures and LED-assisted photocatalysis

We describe the synthesis and characterization of a high-efficiency visible light Cu2O photocatalyst. Uniform cubic, octahedral and rhombic dodecahedral Cu2O nanocrystals with a size of 300–600 nm were synthesized using a simple hydrothermal method. Photocatalytic experiments performed for different water samples (methyl orange solution, toluene solution and industrial wastewater) demonstrate that the rhombic dodecahedral Cu2O nanocrystals were highly active when driven by low-power white LEDs as a light source. In comparison with other reported photocatalysts, the Cu2O nanocrystals reported here show a much higher reaction rate and lower electrical energy per order. The reaction rate and photoefficiency were found to be highly correlated with the irradiated photon flux, and the Cu2O nanocrystals displayed high efficiency in the degradation of aromatic organics. The Cu2O photocatalyst in this work has the potential to be used for a low-cost and high-efficiency green technology for wastewater treatment.

Surface/Interface Carrier-Transport Modulation for Constructing Photon-Alternative Ultraviolet Detectors Based on Self-Bending-Assembled ZnO Nanowires

Surface/interface charge-carrier generation, diffusion, and recombination/transport modulation are especially important in the construction of photodetectors with high efficiency in the field of nanoscience. In the paper, a kind of ultraviolet (UV) detector is designed based on ZnO nanostructures considering photon-trapping, surface plasmonic resonance (SPR), piezophototronic effects, interface carrier-trapping/transport control, and collection. Through carefully optimized surface/interface carrier-transport modulation, a designed device with detectivity as high as 1.69 × 1016/1.71 × 1016 cm·Hz1/2/W irradiating with 380 nm photons under ultralow bias of 0.2 V is realized by alternating nanoparticle/nanowire active layers, respectively, and the designed UV photodetectors show fast and slow recovery processes of 0.27 and 4.52 ms, respectively, which well-satisfy practical needs. Further, it is observed that UV photodetection could be performed within an alternative response by varying correlated key parameters, through efficient surface/interface carrier-transport modulation, spectrally resolved photoresponse of the detector revealing controlled detection in the UV region based on the ZnO nanomaterial, photodetection allowed or limited by varying the active layers, irradiation distance from one of the electrodes, standing states, or electric field. The detailed carrier generation, diffusion, and recombination/transport processes are well illustrated to explain charge-carrier dynamics contributing to the photoresponse behavior.

Inkjet-printed Ag electrodes on paper for high sensitivity impedance measurements

Low-cost electrodes were fabricated by a standard office inkjet printer with commercial silver ink on glossy paper. Compared to conventional thin-film metal thermal evaporated gold electrodes, the paper-based ones show a two-order enhanced sensitivity for impedance measurement over a low frequency range. The high surface roughness of paper electrodes increases the effective area of the electrolyte–electrode double layer capacitance, and therefore reduces the measured impedance at low frequency range. A passivation layer on the top of the paper electrodes is used to mimic the behaviour of the double layer capacitance. The surface roughness was characterized by optical microscopy and atomic force microscopy. Finite element analysis and impedance equivalent model analysis were also performed for different thin-film electrode devices.

Influence of polarization on contact angle saturation during electrowetting

Electrowetting is widely used to manipulate liquids on a dielectric surface by changing the wettability of the solid-liquid interface using an externally applied electric field. While the contact angle can be adequately predicted at low fields using Lippmanns model, there is a large disagreement with experimental behavior at high fields, where the contact angle saturates. Previous attempts to explain this saturation effect (by considering a range of different mechanisms) have led to models that are applicable only to limited field ranges. Here, we use a model for the solid-liquid interfacial surface energy (based on a dipole-dipole interaction) to describe electrowetting and find that this explains the contact angle change at both low (continuous change) and high (saturation) fields. The model is compared with measured contact angle changes for both water and ethylene glycol liquids, with good agreement over the whole field range.

Impedance-based sensor for potassium ions

A conductometric sensor for potassium ions in solution is presented. Interdigitated, planar gold electrodes were coated with a potassium-selective polymer membrane composed of a poly(vinyl chloride) matrix with about 65 wt% of plasticiser and 2-5 wt% of a potassium-selective ionophore. The impedance of the membrane was measured, using the electrodes as a transducer, and related to the concentration of potassium in a sample solution in contact with the membrane. Sensitivity was optimised by varying the sensor components, and selectivity for potassium over sodium was also shown. The resulting devices are compact, miniature, robust sensors which, by means of impedance measurements, eliminate the need for a reference electrode. The sensor was tested for potassium concentration changes of 2 mM across the clinically relevant range of 2.7-18.7 mM.

Amorphous silicon thin film transistor biosensing system

Electronic systems are a very good platform for sensing biological signals for fast point-of-care diagnostics or threat detection. One of the solutions is the lab-on-a-chip integrated circuit (IC), which is low cost and high reliability, offering the possibility for label-free detection. In recent years, similar integrated biosensors based on the conventional complementary metal oxide semiconductor (CMOS) technology have been reported. However, post-fabrication processes are essential for all classes of CMOS biochips, requiring biocompatible electrode deposition and circuit encapsulation. In this work, we present an amorphous silicon (a-Si) thin film transistor (TFT) array based sensing approach, which greatly simplifies the fabrication procedures and even decreases the cost of the biosensor. The device contains several identical sensor pixels with amplifiers to boost the sensitivity. Ring oscillator and logic circuits are also integrated to achieve different measurement methodologies, including electro-analytical methods such as amperometric and cyclic voltammetric modes. The system also supports different operational modes. For example, depending on the required detection arrangement, a sample droplet could be placed on the sensing pads or the device could be immersed into the sample solution for real time in-situ measurement. The entire system is designed and fabricated using a low temperature TFT process that is compatible to plastic substrates. No additional processing is required prior to biological measurement. A Cr/Au double layer is used for the biological-electronic interface. The success of the TFT-based system used in this work will open new avenues for flexible label-free or low-cost disposable biosensors.