Teng Cheng

Mechanism and enhancement of the surface stress caused by a small-molecule antigen and antibody binding.

Generation of microcantilever bending from biochemical interactions can have wide applications, ranging from high-throughput molecular detection to bioactuation. However, the origin of the biochemically induced surface stress causing the bending is a subject of much scientific debate and interest. Unlike a compressive surface stress caused by biomacromolecule antigen and antibody binding, here we show that a small molecule antigen and antibody binding on the surface gives rise to a tensile stress. We propose that the tensile stress is induced by antibody conformational change which manifests itself as Fab arm motion that exposes the C1q binding site of the antibody due to antigen binding. A microcantilever immunosensor was developed for the detection of Chlorimuron-ethyl (CE). We found that antibodies with oriented immobilization induce a greater resultant surface stress than those with random immobilization. The length of linker between the surface and the antibody plays an important role on the stress transmission. The shorter the length, the greater the surface stress. These mechanism and principles will underpin the design of devices and coatings to significantly lower the small molecule detection limit and may also have an impact on our understanding of antigen and antibody binding.

Photophoretic trapping of multiple particles in tapered-ring optical field

We demonstrate the photophoretic trapping of more than several hundreds of absorbing particles by tapered-ring optical traps diffracted from a circular aperture. The experiments with different laser powers show the influence of air flow acting on particles. Three kinds of particles with different densities (about 1~7 g/cm(3)) and different shapes (spherical, non-spherical) can be trapped. The non-spherical particles (toner particles) disperse in optical field, while the spherical particles (ink droplets and iron particles) arrange as a straight line. More importantly, in the experiments of two counter-propagating tapered-ring beams, the agglomeration of particles is achieved and can help research the dynamics of aerosols.

Nano-fabricated pixelated micropolarizer array for visible imaging polarimetry

Pixelated micropolarizer array (PMA) is a novel concept for real-time visible imaging polarimetry. A 320 × 240 aluminum PMA fabricated by electron beam lithography is described in this paper. The period, duty ratio, and depth of the grating are 140 nm, 0.5, and 100 nm, respectively. The units are standard square structures and the metal nanowires of the grating are collimating and uniformly thick. The extinction ratio of 75 and the maximum polarization transmittance of 78.8% demonstrate that the PMA is suitable for polarization imaging. When the PMA is applied to real-time polarization imaging, the degree of linear polarization image and the angle of linear polarization image are calculated from a single frame image. The polarized target object is highlighted from the unpolarized background, and the surface contour of the target object can be reflected by the polarization angle.

Uncooled Infrared Imaging Using a Substrate-Free Focal-Plane Array

A substrate-free 160 times 160 focal-plane array (FPA) with a 60-mum times 60-mum pitch has been developed and used for an optical readout uncooled infrared (IR) detector. The supporting frame of the FPA is a temperature-variable one due to its large decreases in both heat capacity and thermal conductance. This thermal characteristic significantly increases the temperature change of the microcantilever, which depends on both the temperature change induced by its absorption of IR radiation and the linear superposition of the temperature prechange induced by other microcantilevers, and therefore improves the performance of the substrate-free FPA. In the proposed IR detector, the fabricated FPA had an average noise equivalent temperature difference (NETD) and a response time of 330 mK and 16 ms, respectively. Its performance increased by about 4.3 times compared with that of the substrate FPA that consists of the same microcantilevers.

Optical readout sensitivity of deformed microreflector for uncooled infrared detector: theoretical model and experimental validation

The authorss group proposed an optical-readout uncooled infrared detector. Primarily because of the bilayer structure of the usual such detector, deformation of the reflector is often unavoidable and seriously degrades the optical readout sensitivity. According to the theoretical analysis and experimental validation, an optical solution to this problem was established, and it was found that for the specific curvature radius, there are many characteristic reflector lengths and filter positions corresponding to the sensitivity peaks. When employing this solution, the sensitivity loss induced by the deformed reflector would be reduced to a minimum level. The strategy of this solution may also be suitable for other micromechanical devices that experience the same problem.

Optical sensitivity analysis of deformed mirrors for microcantilever array IR imaging

Optical sensitivity is a major issue to improve the sensor responsivity and the spatial resolution of uncooled optomechanical focal plane arrays (FPA). The optical sensitivity is closely related to the mirror length and the undesired mirror deformation induced from the imbalanced residual stresses in different layers. In this paper, the influences of mirror length and deformation on the optical sensitivity are discussed by Fourier Optics. Theoretical analysis and experiments demonstrate that the optical sensitivity is seriously degraded by undesired mirror deformation, and that there exists an optimal mirror length which makes the optical sensitivity achieve its maximum under a certain mirror deformation. Based on the results, an optimized mirror configuration is presented to increase the optical sensitivity of substrate-free bi-material microcantilever array (SFBMA).

Manipulation of aerosols revolving in taper-ring optical traps.

We designed taper-ring optical traps by a weakly focused laser beam through a circular aperture. By railing-like potential barriers, these optical traps are partitioned into enclosed rings, in which irregular light-absorbing microparticles can be driven by photophoretic force to revolve around optical axis in air. The diameter of revolution can reach about 700 μm, which is much larger than that in traditional optical traps based on radiation pressure and gradient force. More importantly, multiple particles were driven to revolve simultaneously in different planes in air for the first reported time to the best of our knowledge.

Highly sensitive nanomechanical assay for the stress transmission of carbon chain

Abstract Here, we report the first quantitative experimental study into the molecular basis of the transmission of mechanical signal that originates from biochemical reaction focusing on the length of carbon chain. We designed an experiment by using n-alkanethiols with a same carboxyl group and different chain lengths (n =1, 5, 10 and 15) to immobilize a same receptor molecule on the gold surface of a microcantilever, and detected the nanomechanical response of biochemical reaction. The sensitivity of the microcantilever was found to be greatly influenced by the chain length of linker that is between the receptor molecule and the microcantilever surface. The efficiency of stress transmission increases significantly with decreasing length of carbon chain. At the same time, we develop a label-free microcantilever sensor for highly sensitive detection of Glycyrrhizic acid (GL). The detection limit of the microcantilever sensor for GL is found to be as low as 20pg/mL for the shortest linker (n =1), which is 500 times lower than the longest linker (n =15) and 50 times lower than that of the corresponding icELISA. These findings will provide new insights into the fundamental mechanisms of stress transmission, which may be exploited for biochemical sensor and nanoactuation applications.

Performance of an optimized substrate-free focal plane array for optical readout uncooled infrared detector

This note presents an optimized substrate-free focal plane array (FPA), which is implemented in an optical readout uncooled infrared (IR) detector. The supporting frame of such FPA is a temperature-variable one due to the large decreases in both the heat capacity and the thermal conductance. This brings a unique thermal characteristic: the supporting frame functions as a “thermal isolation” frame which reduces the thermal conductance and therefore increases the temperature change and also functions as a “thermal diffusion” frame which certainly results in the temperature prechange in the ones not absorbing IR radiation. This characterization could significantly increase the temperature change of microcantilevers and therefore improve the performance of the substrate-free FPA. In the proposed IR detector, the fabricated 160×160 FPA has an average noise equivalent temperature difference (NETD) and a response time of 330 mK and 16 ms, respectively. The performance of the IR detector theoretically increases b...

Wave-plate phase shifting method

Abstract. This paper proposes a new phase shifting method: wave-plate phase shifting method. By different combinations of a quarter-wave-plate, a half-wave-plate, and an analyzer, phase delays are introduced in the interference light path in order to achieve the phase shifting digital holography. Theoretical analysis, numerical simulation, and experiments are conducted to verify the validity of this method. The numerical simulation shows that the result of the wave-plate phase shifting method is consistent with that of the traditional four-step phase shifting method. The experimental results successfully reconstruct the object light intensity in the image plane. Based on the wave-plate phase shifting method, a pixelated wave-plate array structure is designed to achieve real-time phase shifting digital holography. The wave-plate array phase shifting method not only can reconstruct object image of high quality, but also can be used in dynamic phase measurement. Therefore, pixelated wave-plate array structure and wave-plate array phase shifting method could be widely used in practical applications.