Aoqun Jian

Laser-induced thermal bubbles for microfluidic applications

We present a unique bubble generation technique in microfluidic chips using continuous-wave laser-induced heat and demonstrate its application by creating micro-valves and micro-pumps. In this work, efficient generation of thermal bubbles of controllable sizes has been achieved using different geometries of chromium pads immersed in various types of fluid. Effective blocking of microfluidic channels (cross-section 500 × 40 μm(2)) and direct pumping of fluid at a flow rate of 7.2-28.8 μl h(-1) with selectable direction have also been demonstrated. A particular advantage of this technique is that it allows the generation of bubbles at almost any location in the microchannel and thus enables microfluidic control at any point of interest. It can be readily integrated into lab-on-a-chip systems to improve functionality.

Resonant Optical Tunneling Effect: Recent Progress in Modeling and Applications

A resonant optical tunneling effect (ROTE) is a special phenomenon that bridges the wave optics and the quantum physics, and has attracted continuous research efforts for many years. This paper aims to summarize the latest progress of the ROTE in theoretical modeling and application studies. As the background, the analogies of photon tunneling and electron tunneling are first discussed using different optical structures and their corresponding quantum configurations. Then, two theoretical models are presented based on the optics interpretation and the quantum interpretation, respectively. Next, the applications of the ROTE are explored for optical switches and refractive index sensors. Finally, brief discussions are presented to distinguish the ROTE from some other similar phenomena.

Optofluidic refractometer using resonant optical tunneling effect

This paper presents the design and analysis of a liquid refractive index sensor that utilizes a unique physical mechanism of resonant optical tunneling effect (ROTE). The sensor consists of two hemicylindrical prisms, two air gaps, and a microfluidic channel. All parts can be microfabricated using an optical resin NOA81. Theoretical study shows that this ROTE sensor has extremely sharp transmission peak and achieves a sensitivity of 760 nm∕refractive index unit (RIU) and a detectivity of 85 000 RIU(-1). Although the sensitivity is smaller than that of a typical surface plasmon resonance (SPR) sensor (3200 nm∕RIU) and is comparable to a 95% reflectivity Fabry-Pérot (FP) etalon (440 nm∕RIU), the detectivity is 17 000 times larger than that of the SPR sensor and 85 times larger than that of the FP etalon. Such ROTE sensor could potentially achieve an ultrahigh sensitivity of 10(-9) RIU, two orders higher than the best results of current methods.

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.

Facile synthesis of AgNPs on reduced graphene oxide for highly sensitive simultaneous detection of heavy metal ions

Silver nanoparticles grown on reduced graphene oxide (AgNPs/RGO) were successfully synthesized via a facile in situ method. The samples were characterized by scanning electron microscopy (SEM), Raman spectroscopy, field emission transmission electron microscopy (FETEM) and X-ray diffraction (XRD). The results show that silver ions distribute extensively on the RGO sheets. In order to prepare an electrochemical sensor, the AgNPs/RGO nanocomposite was used to modify the surface of a magnetic glassy carbon electrode. The device was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The as-prepared AgNPs/RGO nanocomposite was measured with square wave anodic stripping voltammetry (SWASV), and exhibited excellent electrochemical activity and sensitivity towards the detection of heavy metal ions, including Pb(II), Cd(II), Cu(II) and Hg(II). The sensitivities were respectively 48.69, 40.06, 15.66 and 43.18 μA μM−1 and the limits of detection (LOD) were respectively 0.141, 0.254, 0.178 and 0.285 μM. Compared to the bare RGO film, the AgNPs/RGO nanocomposite showed a significantly higher activity for anodic stripping analysis of the four considered heavy metal ions; in particular, the peak current enhancement was about 1.5 times higher for Pb(II). Experiments also show that the AgNPs/RGO-modified electrode displays good anti-interference properties. Moreover, this study provides a potential material for electrochemical detection of heavy metal ions, individually or simultaneously.

Resonance modes of freestanding magnetoelastic resonator and the application in viscosity measurement

The magnetoelastic material possesses several resonance modes, but the magnetoelastic sensors operate in basically the fundamental resonant frequency. This paper investigates the resonance modes of a freestanding ME resonator, tests these modes in liquids with different viscosity and measures the viscosity of human blood. Five resonance modes with different amplitudes appear in the frequency range of 30–280 kHz. The resonance modes are affected by the direction and strength of the DC bias magnetic field. Compared with the width of the resonance peak, the quality factor cannot correctly reflect the sharpness of the resonance peak of different resonance modes. The five modes are affected by liquid. The first mode has better resolution in determining the resonant frequency, but the higher mode is more sensitive to viscosity. The ME resonator can be used to quickly distinguish the viscosity of blood.

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.

Theoretical study on sensing performance of hydrogen annealed silicon waveguides

Due to the surface diffusion movement of Si atom in hydrogen annealing process, the sharply formed corners of waveguides will be rounded and its sidewall profile could be reformed. In this paper, the performances of microring sensors based on three different gradual annealed structures, strip with large/small round corners and cylinder waveguide, are investigated theoretically. Characteristic parameters of sensors based on cylinder waveguide, sensitivity, Q factor, and measuring range are analyzed and compared with that of sensors based on the widely-used strip and slot waveguides. Simulation results demonstrate that the sensitivity of microring is significantly increased after annealing with comparable Q factor and measuring range. The hydrogen annealing process promises a feasible and effective method to improve the performance of biosensors in the future.

Theoretical Analysis of an Optical Accelerometer Based on Resonant Optical Tunneling Effect

Acceleration is a significant parameter for monitoring the status of a given objects. This paper presents a novel linear acceleration sensor that functions via a unique physical mechanism, the resonant optical tunneling effect (ROTE). The accelerometer consists of a fixed frame, two elastic cantilevers, and a major cylindrical mass comprised of a resonant cavity that is separated by two air tunneling gaps in the middle. The performance of the proposed sensor was analyzed with a simplified mathematical model, and simulated using finite element modeling. The simulation results showed that the optical Q factor and the sensitivity of the accelerometer reach up to 8.857 × 107 and 9 pm/g, respectively. The linear measurement range of the device is ±130 g. The work bandwidth obtained is located in 10–1500 Hz. The results of this study provide useful guidelines to improve measurement range and resolution of integrated optical acceleration sensors.

Modeling and simulation of the effect of surface roughness on properties of silicon-on-insulator optical ring resonator coupled with a straight waveguide

Abstract. This paper describes a relatively general method based on finite-difference time-domain for modeling the scattering loss of silicon nano-optical waveguides as well as quality factor Q of the waveguide resonators. This paper explains how the surface roughness affects the performance of silicon-on-insulator optical ring resonators. Furthermore, the model we built in this paper was also employed to design and optimize the structure of an optical resonator and a good match was found between calculated and measured data. Also, our results were compared with those obtained by other approaches, again proving that the model worked well.