Zaili Dong

Atomic force microscopy study of the antigen-antibody binding force on patient cancer cells based on ROR1 fluorescence recognition

Knowledge of drug–target interaction is critical to our understanding of drug action and can help design better drugs. Due to the lack of adequate single‐molecule techniques, the information of individual interactions between ligand‐receptors is scarce until the advent of atomic force microscopy (AFM) that can be used to directly measure the individual ligand‐receptor forces under near‐physiological conditions by linking ligands onto the surface of the AFM tip and then obtaining force curves on cells. Most of the current AFM single‐molecule force spectroscopy experiments were performed on cells grown in vitro (cell lines) that are quite different from the human cells in vivo. From the view of clinical practice, investigating the drug–target interactions directly on the patient cancer cells will bring more valuable knowledge that may potentially serve as an important parameter in personalized treatment. Here, we demonstrate the capability of AFM to measure the binding force between target (CD20) and drug (rituximab, an anti‐CD20 monoclonal antibody targeted drug) directly on lymphoma patient cancer cells under the assistance of ROR1 fluorescence recognition. ROR1 is a receptor expressed on some B‐cell lymphomas but not on normal cells. First, B‐cell lymphoma Raji cells (a cell line) were used for ROR1 fluorescence labeling and subsequent measurement of CD20‐rituximab binding force. The results showed that Raji cells expressed ROR1, and the labeling of ROR1 did not influence the measurement of CD20‐rituximab binding force. Then the established experimental procedures were performed on the pathological samples prepared from the bone marrow of a follicular lymphoma patient. Cancer cells were recognized by ROR1 fluorescence. Under the guidance of fluorescence, with the use of a rituximab‐conjugated tip, the cellular topography was visualized by using AFM imaging and the CD20‐Rituximab binding force was measured by single‐molecule force spectroscopy. Copyright

Optical Spectrum and Electric Field Waveform Dependent Optically-Induced Dielectrophoretic (ODEP)Micro-Manipulation

In the last seven years, optoelectronic tweezers using optically-induced dielectrophoretic (ODEP) force have been explored experimentally with much success in manipulating micro/nano objects. However, not much has been done in terms of in-depth understanding of the ODEP-based manipulation process or optimizing the input physical parameters to maximize ODEP force. We present our work on analyzing two significant influencing factors in generating ODEP force on a-Si:H based ODEP chips: (1) the waveforms of the AC electric potential across the fluidic medium in an ODEP chip based microfluidic platform; and (2) optical spectrum of the light image projected onto the ODEP chip. Theoretical and simulation results indicate that when square waves are used as the AC electric potential instead of sine waves, ODEP force can double. Moreover, numerical results show that ODEP force increases with increasing optical frequency of the projected light on an ODEP chip following the Fermi-Dirac function, validating that the optically-induced dielectrophoresis force depends strongly on the electron-hole carrier generation phenomena in optoelectronic materials. Qualitative experimental results that validate the numerical results are also presented in this paper.

AFM-Based Robotic Nano-Hand for Stable Manipulation at Nanoscale

One of the major limitations for Atomic Force Microscopy (AFM)-based nanomanipulation is that AFM only has one sharp tip as the end-effector, and can only apply a point force to the nanoobject, which makes it extremely difficult to achieve a stable manipulation. For example, the AFM tip tends to slip-away during nanoparticle manipulation due to its small touch area, and there is no available strategy to manipulate a nanorod in a constant posture with a single tip since the applied point force can make the nanorod rotate more easily. In this paper, a robotic nano-hand method is proposed to solve these problems. The basic idea is using a single tip to mimic the manipulation effect that multi-AFM tip can achieve through the planned high speed sequential tip pushing. The theoretical behavior models of nanoparticle and nanorod are developed, based on which the moving speed and trajectory of the AFM tip are planned artfully to form a nano-hand. In this way, the slip-away problem during nanoparticle manipulation can be get rid of efficiently, and a posture constant manipulation for nanorod can be achieved. The simulation and experimental results demonstrate the effectiveness and advantages of the proposed method.

Fabrication of CNT-based MEMS piezoresistive pressure sensors using DEP nanoassembly

This paper reports the fabrication technique of a novel carbon nanotubes (CNTs) based MEMS pressure sensor with piezoresistive gauge factor potentially much greater than polysilicon based sensors. By using the dielectrophoretic (DEP) nanoassembly of CNTs and a MEMS-compatible process, we have successfully integrated bundled strands of CNT sensing elements on arrays of polymethylmethacrylate (PMMA) diaphragms. The piezoresistive effects of CNT were preliminarily investigated by measuring the pressure-resistance dependency of the sensors and preliminary results indicated that the CNT-based microsensors were capable of sensing input pressure variations. Moreover, the mechanical properties of the diaphragms were studied experimentally and theoretically, which showed the deflection and strain distribution of the diaphragms with different input pressures, in order to conclusively determine the piezoresistivity of bundled CNTs. Based on these experimental evidences, we propose that carbon nanotubes is a novel material for fabricating micropressure sensors on polymer substrates-which may serve as alternative sensors for silicon based pressure sensors when biocompatibility and low-cost applications arc required.

Nanoscale mapping and organization analysis of target proteins on cancer cells from B-cell lymphoma patients

CD20, a membrane protein highly expressed on most B-cell lymphomas, is an effective target demonstrated in clinical practice for treating B-cell non-Hodgkins lymphoma (NHL). Rituximab is a monoclonal antibody against CD20. In this work, we applied atomic force microscopy (AFM) to map the nanoscale distribution of CD20 molecules on the surface of cancer cells from clinical B-cell NHL patients under the assistance of ROR1 fluorescence recognition (ROR1 is a specific cell surface marker exclusively expressed on cancer cells). First, the ROR1 fluorescence labeling experiments showed that ROR1 was expressed on cancer cells from B-cell lymphoma patients, but not on normal cells from healthy volunteers. Next, under the guidance of ROR1 fluorescence, the rituximab-conjugated AFM tips were moved to cancer cells to image the cellular morphologies and detect the CD20-rituximab interactions on the cell surfaces. The distribution maps of CD20 on cancer cells were constructed by obtaining arrays of (16×16) force curves in local areas (500 × 500 nm(2)) on the cell surfaces. The experimental results provide a new approach to directly investigate the nanoscale distribution of target protein on single clinical cancer cells.

Cutting forces related with lattice orientations of graphene using an atomic force microscopy based nanorobot

The relationship between cutting forces and lattice orientations of monolayer graphene is investigated by using an atomic force microscopy (AFM) based nanorobot. In the beginning, the atomic resolution image of the graphene lattice is obtained by using an AFM. Then, graphene cutting experiments are performed with sample rotation method, which gets rid of the tip effect completely. The experimental results show that the cutting force along the armchair orientation is larger than the force along the zigzag orientation, and the cutting forces are almost identical every 60 degrees, which corresponds well with the 60 degrees symmetry in graphene honeycomb lattice structure. By using Poisson analysis method, the single cutting force along zigzag orientation is 3.9 nN, and the force along armchair is 20.5 nN. This work lays the experimental foundation to build a close-loop fabrication strategy with real-time force as a feedback sensor to control the cutting direction

A programmable AFM-based nanomanipulation method using vibration-mode operation

A novel method is developed to effectively manipulating nano-entities to predefined positions and orientations autonomously. In this method, the nanomanipulation process is programmed by planning and executing the AFM tips movement, and the amplitude of probe-tips vibration is measured in real-time to detect the boundary of the nano-entities under manipulation - which will change as a function of the distance between the probe-tip and a nano-entity due to their inter-molecular force interactions. After the start- position and destination are defined by the user interface software, the nanomanipulation process is operated automatically. The result from each manipulation step is detected and used as the information for feedback control on the subsequent operating step. Using this method, CNTs can be manipulated to any position and orientation. Experimental results show that this manipulation method is effective and more efficient (reduce operation time by >50%) than nanomanipulation processes with a human operator in the feedback loop.

Fabrication of Micrometer- and Nanometer-Scale Polymer Structures by Visible Light Induced Dielectrophoresis (DEP) Force

We report in this paper a novel, inexpensive and flexible method for fabricating micrometer- and nanometer-scale three-dimensional (3D) polymer structures using visible light sources instead of ultra-violet (UV) light sources or lasers. This method also does not require the conventional micro-photolithographic technique (i.e., photolithographic masks) for patterning and fabricating polymer structures such as hydrogels. The major materials and methods required for this novel fabrication technology are: (1) any cross-linked network of photoactive polymers (examples of fabricated poly(ethylene glycol) (PEG)-diacrylate hydrogel structures are shown in this paper); (2) an Optically-induced Dielectrophoresis (ODEP) System which includes an “ODEP chip” (i.e., any chip that changes its surface conductivity when exposed to visible light), an optical microscope, a projector, and a computer; and (3) an animator software hosted on a computer that can generate virtual or dynamic patterns which can be projected onto the “ODEP chip” through the use of a projector and a condenser lens. Essentially, by placing a photosensitive polymer solution inside the microfluidic platform formed by the “ODEP chip” bonded to another substrate, and applying an alternating current (a.c.) electrical potential across the polymer solution (typically ~20 Vp-p at 10 kHz), solid polymer micro/nano structures can then be formed on the “ODEP chip” surface when visible-light is projected onto the chip. The 2D lateral geometry (x and y dimensions) and the thickness (height) of the micro/nano structures are dictated by the image geometry of the visible light projected onto the “ODEP chip” and also the time duration of projection. Typically, after an image projection with intensity ranging from ~0.2 to 0.4 mW/cm2 for 10 s, ~200 nm high structures can be formed. In our current system, the thickness of these polymer structures can be controlled to form from ~200 nanometers to ~3 micrometers structures. However, in the in-plane dimensions, only ~7 μm resolution can be achieved now, due to the optical diffraction limit and the physical dimensions of DMD mirrors in the projector. Nevertheless, with higher quality optical components, the in-plane resolution is expected to be sub-micron.

Carbon nanotube-sensor-integrated microfluidic platform for real-time chemical concentration detection

This paper presents the development of a chemical sensor employing electronic‐grade carbon nanotubes (EG‐CNTs) as the active sensing element for sodium hypochlorite detection. The sensor, integrated in a PDMS‐glass microfluidic chamber, was fabricated by bulk aligning of EG‐CNTs between gold microelectrode pairs using dielectrophoretic technique. Upon exposure to sodium hypochlorite solution, the characteristics of the carbon nanotube chemical sensor were investigated at room temperature under constant current mode. The sensor exhibited responsivity, which fits a linear logarithmic dependence on concentration in the range of 1/32 to 8 ppm, a detection limit lower than 5 ppb, while saturating at 16 ppm. The typical response time of the sensor at room temperature is on the order of minutes and the recovery time is a few hours. In particular, the sensor showed an obvious sensitivity to the volume of detected solution. It was found that the activation power of the sensor was extremely low, i.e. in the range of nanowatts. These results indicate great potential of EG‐CNT for advanced nanosensors with superior sensitivity, ultra‐low power consumption, and less fabrication complexity.

Limitations of Au Particle Nanoassembly Using Dielectrophoretic Force—A Parametric Experimental and Theoretical Study

When a gold colloidal suspension is subjected to ac electric field, ldquogold pearl chainsrdquo will form due to the dielectrophoretic (DEP) force. Our latest experiments show that the formation rate of gold pearl chains, which tends to zero at high and low frequency limits and has a maximum at a narrow mid range of frequency, is dependent on the applied field frequency. This letter analyzes the frequency-dependent DEP manipulation of gold colloid suspensions using the protoplast model. Simulated results show that the relationship curve between the frequency of applied field and the velocity of gold colloids motion due to DEP agrees with our experimental observations. In addition, the orders of magnitude of the velocity due to various effects in our experimental system, such as DEP force, Brownian motion, gravity, and fluid flows induced by electric field, were also estimated. The result implies that the DEP-based manipulation of less than 2 nm gold colloids is extremely difficult to be controlled.