Integrated Assembly and Photopreservation of Topographical Micropatterns.

Micromanipulation techniques that are capable of assembling nano/micromaterials into usable structures such as topographical micropatterns (TMPs) have proliferated rapidly in recent years, holding great promise in building artificial electronic and photonic microstructures. Here, a method is reported for forming TMPs based on optoelectronic tweezers in either "bottom-up" or "top-down" modes, combined with in situ photopolymerization to form permanent structures. This work demonstrates that the assembled/cured TMPs can be harvested and transferred to alternate substrates, and illustrates that how permanent conductive traces and capacitive circuits can be formed, paving the way toward applications in microelectronics. The integrated, optical assembly/preservation method described here is accessible, versatile, and applicable for a wide range of materials and structures, suggesting utility for myriad microassembly and microfabrication applications in the future.

Size-scaling effects for microparticles and cells manipulated by optoelectronic tweezers.

In this work, we investigated the use of optoelectronic tweezers (OET) to manipulate objects that are larger than those commonly positioned with standard optical tweezers. We studied the forces that could be produced on differently sized polystyrene microbeads and MCF-7 breast cancer cells with light-induced dielectrophoresis (DEP). It was found that the DEP force imposed on the bead/cell did not increase linearly with the volume of the bead/cell, primarily because of the non-uniform distribution of the electric field above the OET bottom plate. Although this size-scaling work focuses on microparticles and cells, we propose that the physical mechanism elucidated in this research will be insightful for other micro-objects, biological samples, and micro-actuators undergoing OET manipulation.

Escape from an Optoelectronic Tweezer Trap: experimental results and simulations.

Optoelectronic tweezers (OET) are a microsystem actuation technology capable of moving microparticles at mm s-1 velocities with nN forces. In this work, we analyze the behavior of particles manipulated by negative dielectrophoresis (DEP) forces in an OET trap. A user-friendly computer interface was developed to generate a circular rotating light pattern to control the movement of the particles, allowing their force profiles to be conveniently measured. Three-dimensional simulations were carried out to clarify the experimental results, and the DEP forces acting on the particles were simulated by integrating the Maxwell stress tensor. The simulations matched the experimental results and enabled the determination of a new "hopping" mechanism for particle-escape from the trap. As indicated by the simulations, there exists a vertical DEP force at the edge of the light pattern that pushes up particles to a region with a smaller horizontal DEP force. We propose that this phenomenon will be important to consider for the design of OET micromanipulation experiments for a wide range of applications.

Micromanipulation of InP lasers with optoelectronic tweezers for integration on a photonic platform.

The integration of light sources on a photonic platform is a key aspect of the fabrication of self-contained photonic circuits with a small footprint that does not have a definitive solution yet. Several approaches are being actively researched for this purpose. In this work we propose optoelectronic tweezers for the manipulation and integration of light sources on a photonic platform and report the positional and angular accuracy of the micromanipulation of standard Fabry-Pérot InP semiconductor laser die. These lasers are over three orders of magnitude bigger in volume than any previously assembled with optofluidic techniques and the fact that they are industry standard lasers makes them significantly more useful than previously assembled microdisk lasers. We measure the accuracy to be 2.5 ± 1.4 µm and 1.4 ± 0.4° and conclude that optoelectronic tweezers are a promising technique for the micromanipulation and integration of optoelectronic components in general and semiconductor lasers in particular.

Spatially selecting a single cell for lysis using light-induced electric fields.

An optoelectronic tweezing (OET) device, within an integrated microfluidic channel, is used to precisely select single cells for lysis among dense populations. Cells to be lysed are exposed to higher electrical fields than their neighbours by illuminating a photoconductive film underneath them. Using beam spot sizes as low as 2.5 µm, 100% lysis efficiency is reached in <1 min allowing the targeted lysis of cells.

Optoelectronic tweezers system for single cell manipulation and fluorescence imaging of live immune cells.

A compact optoelectronic tweezers system for combined cell manipulation and analysis is presented. CMOS-controlled gallium nitride micro-LED arrays are used to provide simultaneous spatio-temporal control of dielectrophoresis traps within an optoelectronic tweezers device and fluorescence imaging of contrasting dye labelled cells. This capability provides direct identification, selection and controlled interaction of single T-lymphocytes and dendritic cells. The trap strength and profile for two emission wavelengths of micro-LED array have been measured and a maximum trapping force of 13.1 and 7.6 pN was achieved for projected micro-LED devices emitting at λmax 520 and 450 nm, respectively. A potential application in biological research is demonstrated through the controlled interaction of live immune cells where there is potential for this method of OET to be implemented as a compact device.

Shape-dependent optoelectronic cell lysis.

We show an electrical method to break open living cells amongst a population of different cell types, where cell selection is based upon their shape. We implement the technique on an optoelectronic platform, where light, focused onto a semiconductor surface from a video projector creates a reconfigurable pattern of electrodes. One can choose the area of cells to be lysed in real-time, from single cells to large areas, simply by redrawing the projected pattern. We show that the method, based on the "electrical shadow" that the cell casts, allows the detection of rare cell types in blood (including sleeping sickness parasites), and has the potential to enable single cell studies for advanced molecular diagnostics, as well as wider applications in analytical chemistry.

Realtime monitoring of thrombus formation in vivo using a self-reporting vascular access graft.

BACKGROUND: Chronic kidney disease (CKD) affects 10% of the global population costing over a hundred billion dollars per annum and leading to increased risk of cardiovascular disease. Many patients with CKD require regular haemodialyses. Synthetic arteriovenous grafts (AVG) are increasingly used to provide rapid vascular connection for dialysis. Initially, they have excellent patency rates but are critically limited by neointimal hyperplasia at the venous anastomosis, which drives subsequent thrombosis, graft failure and death. METHODS: Here, we describe a system in which electrical impedance spectroscopy sensors are incorporated circumferentially into the wall of a synthetic arteriovenous graft. This is combined with an implantable radiotelemetry system for data transmission outside the patient. The system was tested using monolayers of endothelial and smooth muscle cells as well as swine blood and clots with explanted human carotid artery plaques. Sensor testing was then performed in vitro and the device was implanted in vivo in female swine. RESULTS: The device can wirelessly report the accumulation of biological material, both cells and blood. Differences are also detected when comparing controls with pathological atheroma. In swine differences between blockage formation in a graft were remotely obtained and wireless reported. CONCLUSIONS: Combining electrical impedance spectroscopy and an implantable radiotelemetry system enables graft surveillance. This has the potential to be used for early detection of venous stenosis and blood clot formation in real-time in vivo. In principle, the concept could apply to other cardiovascular diseases and vascular implantable devices.

Chronic kidney disease is common throughout the world and required treatments are expensive. People with chronic kidney disease require frequent blood dialysis treatment to filter their blood and remove waste products and toxic substances circulating in the blood. For some patients, implantable tubular structures called AV grafts are used for providing access to dialysis. These grafts frequently block sometimes without warning leading to patients not being able to undergo dialysis. Through a series of laboratory experiments looking at cells that block the graft, fatty deposits and blood clots, we evaluated whether sensors could detect blockages in an AV graft. We also tested the device in an animal model. From these results we were able to show that our device could detect blockages within a graft. In the future we hope that introduction to the clinic of an optimized version of our device will reduce costs to healthcare systems and improve patient outcomes.

Cell Electrokinetic Fingerprint: A Novel Approach Based on Optically Induced Dielectrophoresis (ODEP) for In-Flow Identification of Single Cells.

A novel optically induced dielectrophoresis (ODEP) system that can operate under flow conditions is designed for automatic trapping of cells and subsequent induction of 2D multi-frequency cell trajectories. Like in a "ping-pong" match, two virtual electrode barriers operate in an alternate mode with varying frequencies of the input voltage. The so-derived cell motions are characterized via time-lapse microscopy, cell tracking, and state-of-the-art machine learning algorithms, like the wavelet scattering transform (WST). As a cell-electrokinetic fingerprint, the dynamic of variation of the cell displacements happening, over time, is quantified in response to different frequency values of the induced electric field. When tested on two biological scenarios in the cancer domain, the proposed approach discriminates cellular dielectric phenotypes obtained, respectively, at different early phases of drug-induced apoptosis in prostate cancer (PC3) cells and for differential expression of the lectine-like oxidized low-density lipoprotein receptor-1 (LOX-1) transcript levels in human colorectal adenocarcinoma (DLD-1) cells. The results demonstrate increased discrimination of the proposed system and pose an additional basis for making ODEP-based assays addressing cancer heterogeneity for precision medicine and pharmacological research.

Predicting Cardiovascular Stent Complications Using Self-Reporting Biosensors for Noninvasive Detection of Disease.

Self-reporting implantable medical devices are the future of cardiovascular healthcare. Cardiovascular complications such as blocked arteries that lead to the majority of heart attacks and strokes are frequently treated with inert metal stents that reopen affected vessels. Stents frequently re-block after deployment due to a wound response called in-stent restenosis (ISR). Herein, an implantable miniaturized sensor and telemetry system are developed that can detect this process, discern the different cell types associated with ISR, distinguish sub plaque components as demonstrated with ex vivo samples, and differentiate blood from blood clot, all on a silicon substrate making it suitable for integration onto a vascular stent. This work shows that microfabricated sensors can provide clinically relevant information in settings closer to physiological conditions than previous work with cultured cells.

Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays.

A novel, miniaturized optoelectronic tweezers (OET) system has been developed using a CMOS-controlled GaN micro-pixelated light emitting diode (LED) array as an integrated micro-light source. The micro-LED array offers spatio-temporal and intensity control of the emission pattern, enabling the creation of reconfigurable virtual electrodes to achieve OET. In order to analyse the mechanism responsible for particle manipulation in this OET system, the average particle velocity, electrical field and forces applied to the particles were characterized and simulated. The capability of this miniaturized OET system for manipulating and trapping multiple particles including polystyrene beads and live cells has been successfully demonstrated.

Reconfigurable multi-component micromachines driven by optoelectronic tweezers.

There is great interest in the development of micromotors which can convert energy to motion in sub-millimeter dimensions. Micromachines take the micromotor concept a step further, comprising complex systems in which multiple components work in concert to effectively realize complex mechanical tasks. Here we introduce light-driven micromotors and micromachines that rely on optoelectronic tweezers (OET). Using a circular micro-gear as a unit component, we demonstrate a range of new functionalities, including a touchless micro-feed-roller that allows the programming of precise three-dimensional particle trajectories, multi-component micro-gear trains that serve as torque- or velocity-amplifiers, and micro-rack-and-pinion systems that serve as microfluidic valves. These sophisticated systems suggest great potential for complex micromachines in the future, for application in microrobotics, micromanipulation, microfluidics, and beyond.

Phototransistor-based optoelectronic tweezers for dynamic cell manipulation in cell culture media.

Optoelectronic tweezers (OET), based on light-induced dielectrophoresis, has been shown as a versatile tool for parallel manipulation of micro-particles and cells (P. Y. Chiou, A. T. Ohta and M. C. Wu, Nature, 2005, 436, 370-372). However, the conventional OET device cannot operate in cell culture media or other high-conductivity physiological buffers due to the limited photoconductivity of amorphous silicon. In this paper, we report a new phototransistor-based OET (Ph-OET). Consisting of single-crystalline bipolar junction transistors, the Ph-OET has more than 500x higher photoconductivity than amorphous silicon. Efficient cell trapping of live HeLa and Jurkat cells in Phosphate Buffered Saline (PBS) and Dulbecco's Modified Eagle's Medium (DMEM) has been demonstrated using a digital light projector, with a cell transport speed of 33 microm/sec, indicating a force of 14.5 pN. Optical concentration of cells and real-time control of individually addressable cell arrays have also been realized. Precise control of separation between two cells has also been demonstrated. We envision a new platform for single cell studies using Ph-OET.

Motile and non-motile sperm diagnostic manipulation using optoelectronic tweezers.

Optoelectronic tweezers was used to manipulate human spermatozoa to determine whether their response to OET predicts sperm viability among non-motile sperm. We review the electro-physical basis for how live and dead human spermatozoa respond to OET. The maximal velocity that non-motile spermatozoa could be induced to move by attraction or repulsion to a moving OET field was measured. Viable sperm are attracted to OET fields and can be induced to move at an average maximal velocity of 8.8 ± 4.2 µm s(-1), while non-viable sperm are repelled to OET, and are induced to move at an average maximal velocity of -0.8 ± 1.0 µm s(-1). Manipulation of the sperm using OET does not appear to result in increased DNA fragmentation, making this a potential method by which to identify viable non-motile sperm for assisted reproductive technologies.

NanoPen: dynamic, low-power, and light-actuated patterning of nanoparticles.

We introduce NanoPen, a novel technique for low optical power intensity, flexible, real-time reconfigurable, and large-scale light-actuated patterning of single or multiple nanoparticles, such as metallic spherical nanocrystals, and one-dimensional nanostructures, such as carbon nanotubes. NanoPen is capable of dynamically patterning nanoparticles over an area of thousands of square micrometers with light intensities <10 W/cm(2) (using a commercial projector) within seconds. Various arbitrary nanoparticle patterns and arrays (including a 10 x 10 array covering a 0.025 mm(2) area) are demonstrated using this capability. One application of NanoPen is presented through the creation of surface-enhanced Raman spectroscopy hot-spots by patterning gold nanoparticles of 90 nm diameter with enhancement factors exceeding 10(7) and picomolar concentration sensitivities.

Microparticle manipulation using laser-induced thermophoresis and thermal convection flow.

We demonstrate manipulation of microbeads with diameters from 1.5 to 10 µm and Jurkat cells within a thin fluidic device using the combined effect of thermophoresis and thermal convection. The heat flow is induced by localized absorption of laser light by a cluster of single walled carbon nanotubes, with no requirement for a treated substrate. Characterization of the system shows the speed of particle motion increases with optical power absorption and is also affected by particle size and corresponding particle suspension height within the fluid. Further analysis shows that the thermophoretic mobility (DT) is thermophobic in sign and increases linearly with particle diameter, reaching a value of 8 µm2 s-1 K-1 for a 10 µm polystyrene bead.

Trap profiles of projector based optoelectronic tweezers (OET) with HeLa cells.

In this paper we present trap profile measurements for HeLa cells in Optoelectronic Tweezers (OET) based on a data projector. The data projector is used as a light source to illuminate amorphous Si creating virtual electrodes which are used to trap particles through dielectrophoresis. We show that although the trap stiffness is typically greater at the edges of the optical spot it is possible to create a trap with constant trap stiffness by reducing the trap's size until it is similar to the object being trapped. We have successfully created a trap for HeLa cells with a constant trap stiffness of 3 x 10(-6) Nm-1 (capable of moving the cell up to 50 microms-1) with a 12 microm diameter trap. We also calculate the depth of the potential well that the cell will experience due to the trap and find that it to be 1.6 x 10(-16)J (4 x 10(4) kBT).

Whisky tasting using a bimetallic nanoplasmonic tongue.

Metallic nanostructures are ideal candidates for optical tongue devices thanks to their chemical stability, the sensitivity of their plasmonic resonance to environmental changes, and their ease of chemical-functionalization. Here, we describe a reusable optical tongue comprising multiplexed gold and aluminum nano-arrays: a bimetallic device which produces two distinct resonance peaks for each sensing region. Through specific modification of these plasmonic arrays with orthogonal surface chemistries, we demonstrate that a dual-resonance device allows us to halve sensor sizes and data-acquisition times when compared to single-resonance, monometallic devices. We applied our bimetallic tongue to differentiate off-the-shelf whiskies with >99.7% accuracy by means of linear discriminant analysis (LDA). This advance in device miniaturization, functionalization, and multiplexed readout indicates nanoplasmonic tongues will have future applications in chemical mixture identification in applications where portability, reusability, and measurement speed are key.

Multilayered Nanoplasmonic Arrays for Self-Referenced Biosensing.

Nanostructured sensors based on localized surface plasmon resonance (LSPR) offer a number of advantages over other optical sensing technologies, making them excellent candidates for miniaturized, label-free chemical and biological detection. Highly sensitive to local refractive index changes, the resonance peaks of the nanosensors shift by different amounts when subject to different biological and chemical environments. Modifications to the nanostructure surface allow for the detection of specific molecules and chemicals with shifts so sensitive that the presence of single molecules can be detected. However, this extreme sensitivity has its drawbacks. Resonance shifts also occur because of temperature shifts, light-intensity fluctuations, and other environmental factors. To distinguish detection from drift, a secondary sensor region is often required. This often doubles the size of the device, requires two light sources and detectors (or complex optics), doubles the sample volume required (which may be expensive, or may not be possible if the sample quantity is limited), and subjects the reference to potential biofouling. Here, we present a new proof-of-concept multilayered LSPR sensor design that incorporates both a sensing layer and an encapsulated reference layer within the same region. By doing so, we are able to monitor and correct for sensor drift without the need for a secondary reference channel. We demonstrate the suitability of this sensor for sucrose concentration measurements and for the detection of biotin-avidin interactions, while also showing that the sensor can self-correct for drift. We believe that this multilayer sensor design holds promise for point-of-care diagnostics.

Bridging the Gap: Rewritable Electronics Using Real-Time Light-Induced Dielectrophoresis on Lithium Niobate.

In the context of micro-electronics, the real-time manipulation and placement of components using optics alone promises a route towards increasingly dynamic systems, where the geometry and function of the device is not fixed at the point of fabrication. Here, we demonstrate physically reconfigurable circuitry through light-induced dielectrophoresis on lithium niobate. Using virtual electrodes, patterned by light, to trap, move, and chain individual micro-solder-beads in real-time via dielectrophoresis, we demonstrate rewritable electrical contacts which can make electrical connections between surface-bound components. The completed micro-solder-bead bridges were found to have relatively low resistances that were not solely dominated by the number of interfaces, or the number of discrete beads, in the connection. Significantly, these connections are formed without any melting/fusing of the beads, a key feature of this technique that enables reconfigurability. Requiring only a low-power (~3.5 mW) laser source to activate, and without the need for external power supply or signal generation, the all-optical simplicity of virtual-electrodes may prove significant for the future development of reconfigurable electronic systems.