Optoelectronic tweezers: a versatile toolbox for nano-/micro-manipulation

This review covers the fundamentals, recent progress and state-of-the-art applications of optoelectronic tweezers technology, and demonstrates that optoelectronic tweezers technology is a versatile and powerful toolbox for nano-/micro-manipulation.

High-throughput optofluidic screening for improved microbial cell factories via real-time micron-scale productivity monitoring

The industrial synthetic biology sector has made huge investments to achieve relevant miniaturized screening systems for scalable fermentation. Here we present the first example of a high-throughput (>10³ genotypes per week) perfusion-based screening system to improve small-molecule secretion from microbial strains. Using the Berkeley Lights Beacon® system, the productivity of each strain could be directly monitored in real time during continuous culture, yielding phenotypes that correlated strongly (r² > 0.8, p < 0.0005) with behavior in industrially relevant bioreactor processes. This method allows a much closer approximation of a typical fed-batch fermentation than conventional batch-like droplet or microplate culture models, in addition to rich time-dependent data on growth and productivity. We demonstrate these advantages by application to the improvement of high-productivity strains using whole-genome random mutagenesis, yielding mutants with substantially improved (by up to 85%) peak specific productivities in bioreactors. Each screen of ∼5 × 10³ mutants could be completed in under 8 days (including 5 days involving user intervention), saving ∼50-75% of the time required for conventional microplate-based screening methods.

A unified platform for optoelectrowetting and optoelectronic tweezers

A platform capable of seamlessly unifying both optoelectrowetting and optoelectronic tweezers is presented. This enables the user to manipulate aqueous droplets (with electrowetting) as well as individual particles within those droplets (with dielectrophoresis). The device requires no photolithography and droplet/particle manipulation can occur continuously over the entire surface of the device. Droplet and 10 µm polystyrene particle speeds of up to 8 mm s(-1) and 60 µm s(-1), respectively, are demonstrated. Particle concentration within, and subsequent splitting of, a droplet is performed resulting in average concentration efficiencies of 93%. Serial concentration is also demonstrated resulting in exponentially increasing particle concentrations and a 10× concentration increase. Finally, the platform is used to select a single cell out of a cohort and subsequently encapsulate it in its own aqueous droplet.

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.

Preimplantation mouse embryo selection guided by light-induced dielectrophoresis

Selection of optimal quality embryos for in vitro fertilization (IVF) transfer is critical to successful live birth outcomes. Currently, embryos are chosen based on subjective assessment of morphologic developmental maturity. A non-invasive means to quantitatively measure an embryo's developmental maturity would reduce the variability introduced by the current standard. We present a method that exploits the scaling electrical properties of pre-transfer embryos to quantitatively discern embryo developmental maturity using light-induced dielectrophoresis (DEP). We show that an embryo's DEP response is highly correlated with its developmental stage. Uniquely, this technique allows one to select, in sequence and under blinded conditions, the most developmentally mature embryos among a mixed cohort of morphologically indistinguishable embryos cultured in optimized and sub-optimal culture media. Following assay, embryos continue to develop normally in vitro. Light-induced dielectrophoresis provides a non-invasive, quantitative, and reproducible means to select embryos for applications including IVF transfer and embryonic stem cell harvest.

Optoelectronic tweezers as a tool for parallel single-cell manipulation and stimulation

Optoelectronic tweezers (OET) is a promising approach for the parallel manipulation of single cells for a variety of biological applications. By combining the manipulation capabilities of OET with other relevant biological techniques (such as cell lysis and electroporation), one can realize a true parallel, single-cell diagnostic and stimulation tool. Here, we demonstrate the utility of the OET device by integrating it onto single-chip systems capable of performing in-situ, electrode-based electroporation/lysis, individual cell, light-induced lysis, and light-induced electroporation.

Parallel trapping of multiwalled carbon nanotubes with optoelectronic tweezers

Here we report the use of optoelectronic tweezers and dynamic virtual electrodes to address multiwalled carbon nanotubes (MWCNTs) with trap stiffness values of approximately 50 fNmum. Both high-speed translation (>200 mums) of individual-MWCNTs and two-dimensional trapping of MWCNT ensembles are achieved using 100,000 times less optical power density than single beam laser tweezers. Modulating the virtual electrode's intensity enables tuning of the MWCNT ensemble's number density by an order of magnitude on the time scale of seconds promising a broad range of applications in MWCNT science and technology.

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.

Parallel single-cell light-induced electroporation and dielectrophoretic manipulation

Electroporation is a common technique for the introduction of exogenous molecules across the, otherwise, impermeant cell membrane. Conventional techniques are limited by either low throughput or limited selectivity. Here we present a novel technique whereby we use patterned light to create virtual electrodes which can induce the parallel electroporation of single cells. This technique seamlessly integrates with optoelectronic tweezers to provide a single cell manipulation platform as well. We present evidence of parallel, single cell electroporation using this method through use of fluorescent dyes and dielectrophoretic responses. Additionally, through the use of integrated microfluidic channels, we show that cells remain viable following treatment in the device. Finally, we determine the optimal field dosage to inject propidium iodide into a HeLa cell and maintain cellular viability.

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).

Operational Regimes and Physics Present in Optoelectronic Tweezers

Optoelectronic tweezers (OET) are a powerful light-based technique for the manipulation of micro- and nanoscopic particles. In addition to an optically patterned dielectrophoresis (DEP) force, other light-induced electrokinetic and thermal effects occur in the OET device. In this paper, we present a comprehensive theoretical and experimental investigation of various fluidic, optical, and electrical effects present during OET operation. These effects include DEP, light-induced ac electroosmosis, electrothermal flow, and buoyancy-driven flow. We present finite-element modeling of these effects to establish the dominant mode for a given set of device parameters and bias conditions. These results are confirmed experimentally and present a comprehensive outline of the operational regimes of the OET device.

Optically actuated thermocapillary movement of gas bubbles on an absorbing substrate

The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.