Shangquan Wu

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.

Highly Sensitive Nanomechanical Immunosensor Using Half Antibody Fragments

The improvement of sensitivity is of great significance to the application of biochemical sensor. In this study, we propose a micocantilever-based immunosensor in surface stress mode using half antibody fragments as receptor molecules. The thiol-containing half antibody fragment was obtained with a low loss of antibody biological activity and then was covalently and orientedly immobilized on the gold surface of microcantilevers via two native thiol groups. Such a one-step reaction and immobilization of receptor molecule simplify the preparation process of micocantilever immunosensor. Using shortened and highly oriented half antibody fragments as receptor molecules, the generation of surface stress and the transmission of stress from the interaction region of molecules to the surface of the microcantilever have been elevated significantly. The limit of detection (LOD) of the presented sensor has been significantly lowered to 1 pg/mL, or 1.1 pM in equivalence, which is a 500-fold improvement when compared with intact full antibody coated conventional micocantilever sensors. The results indicate that the half antibody fragment is well suited for the functionalization of the microcantilever surface and is generally applicable to all microcantilever immunosensor development, and this principle will help to design a functional film of devices with significantly lower LOD.

Quantification of cell viability and rapid screening anti-cancer drug utilizing nanomechanical fluctuation.

Cancer is a serious threat to human health. Although numerous anti-cancer drugs are available clinically, many have shown toxic side effects due to poor tumor-selectivity, and reduced effectiveness due to cancers rapid development of resistance to treatment. The development of new highly efficient and practical methods to quantify cell viability and its change under drug treatment is thus of significant importance in both understanding of anti-cancer mechanism and anti-cancer drug screening. Here, we present an approach of utilizing a nanomechanical fluctuation based highly sensitive microcantilever sensor, which is capable of characterizing the viability of cells and quantitatively screening (within tens of minutes) their responses to a drug with the obvious advantages of a rapid, label-free, quantitative, noninvasive, real-time and in-situ assay. The microcantilever sensor operated in fluctuation mode was used in evaluating the paclitaxel effectiveness on breast cancer cell line MCF-7. This study demonstrated that the nanomechanical fluctuations of the microcantilever sensor are sensitive enough to detect the dynamic variation in cellular force which is provided by the cytoskeleton, using cell metabolism as its energy source, and the dynamic instability of microtubules plays an important role in the generation of the force. We propose that cell viability consists of two parts: biological viability and mechanical viability. Our experimental results suggest that paclitaxel has little effect on biological viability, but has a significant effect on mechanical viability. This new method provides a new concept and strategy for the evaluation of cell viability and the screening of anti-cancer drugs.

Development of a Secondary Antibody Thio-Functionalized Microcantilever Immunosensor and an ELISA for Measuring Ginsenoside Re Content in the Herb Ginseng

Ginsenoside Re (GRe) is a major active component of the Chinese medicinal herb ginseng, Panax ginseng . A sensitive and specific monoclonal antibody (mAb), designated as mAb3D6, was generated with a GRe-bovine serum albumin conjugate as an immunogen. Microcantilever immunosensors (MCS), one modified with thiolated anti-GRe antibody and one modified with thiolated goat antimouse immunoglobulin G (IgG), were developed to detect the content of ginsenoside. The MCS immobilized with thiolated goat antimouse IgG had a better sensitivity than the MCS modified with thiolated anti-GRe antibody. The advantage of a secondary antibody thio-functionalized MCS was verified with the anti-paclitaxel mAb. An indirect competitive enzyme-linked immunosorbent assay (icELISA) was also established with mAb3D6. The concentration of analyte producing 50% inhibition and the working range of icELISA were 1.20 and 0.15-16.1 ng/mL, respectively. The icELISA had a cross-reactivity of 89% with ginsenoside Rg1 and less than 3% with other ginsenosides. The icELISA and MCS with thiolated secondary antibody were applied for the determination of GRe in ginseng samples, and the results agreed well with those determined by high-performance liquid chromatography.

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.

Microcantilever array instrument based on optical fiber and performance analysis

We developed a microcantilever array biosensor instrument based on optical readout from a microcantilever array in fluid environment. The microcantilever signals were read out sequentially by laser beams emitted from eight optical fibers. The optical fibers were coupled to lasers, while the other ends of the fibers were embedded in eight V-grooves with 250 μm pitch microfabricated from a Si wafer. Aspherical lens was used to keep the distance between lasers. A programmable logic controller was used to make the system work stably. To make sure that the output of lasers was stable, a temperature controller was set up for each laser. When the deflection signal was collected, lasers used here were set to be on for at least 400 ms in each scanning cycle to get high signal-to-noise ratio deflection curves. A test was performed by changing the temperature of the liquid cell holding a microcantilever array to verify the consistent response of the instrument to the cantilever deflections. The stability and conformance of the instrument were demonstrated by quantitative detection of mercury ions in aqueous solution and comparison detection of clenbuterol by setting test and reference cantilevers. This microcantilever array detection instrument can be applied to highly sensitive detection of chemical and biological molecules in fluid environment.

Measurement of Airy-vortex beam topological charges based on a pixelated micropolarizer array

In this paper, we numerically studied the intensity patterns and screw phases of an embedded optical vortex in an Airy beam generated by a 3/2 phase pattern imposed on a spatial light modulator. It is found that the optical vortex and the Airy beams main lobe approach each other during propagation, which means the energy of the Airy beams intensity peaks can be taken advantage of by the imposed vortices. Based on a pixelated micropolarizer array in the interference path, we succeeded in measuring the integer topological charges up to -10 according to the phase jump. In addition, fractional topological charges were also obtained in the experiment. Both of the experimental results are acquired in a high-precision and robust way. This work will promote potential application of Airy-vortex beams in fields such as optical manipulation, laser processing, and photon entanglement.

Aptamer-based microcantilever-array biosensor for profenofos detection

Profenofos, a highly poisonous organophosphorus pesticide, has been widely used in agricultural production. These pesticide residues have seriously influenced food security and threatened human health, and new methods with high sensitivity are greatly needed to detect profenofos. Here, we developed an aptamer-based microcantilever-array sensor operated in stress mode to detect profenofos, with advantages of being a label-free, highly sensitive, one-step immobilization method capable of quantitative and real-time detection. The microcantilevers were functionalized with a profenofos-specific aptamer (SS2-55), and then the specific binding of profenofos to aptamer induced a deflection of the microcantilever, which was monitored using an optical method in a real-time manner. The microcantilever deflection showed a positive relationship with profenofos concentration, and the detection limit was low to 1.3 ng mL-1 (3.5 nM) for profenofos, which was much lower than other aptamer-based detection methods. The selectivity of the sensor was verified with another organophosphorus pesticide. Additionally, we successfully detected profenofos dissolved in vegetable-soak solution. Our results showed that this aptamer-based microcantilever-array sensor is a convenient and label-free method for detecting profenofos in small amounts and has great potential for food-security applications.