Expanding CAR-T cell immunotherapy horizons through microfluidics

Chimeric antigen receptor (CAR)-T cell therapies have revolutionized cancer treatment, particularly in hematological malignancies. However, their application to solid tumors is limited, and they face challenges in safety, scalability, and cost. To enhance current CAR-T cell therapies, the integration of microfluidic technologies, harnessing their inherent advantages, such as reduced sample consumption, simplicity in operation, cost-effectiveness, automation, and high scalability, has emerged as a powerful solution. This review provides a comprehensive overview of the step-by-step manufacturing process of CAR-T cells, identifies existing difficulties at each production stage, and discusses the successful implementation of microfluidics and related technologies in addressing these challenges. Furthermore, this review investigates the potential of microfluidics-based methodologies in advancing cell-based therapy across various applications, including solid tumors, next-generation CAR constructs, T-cell receptors, and the development of allogeneic "off-the-shelf" CAR products.

Genetically Stable and Scalable Nanoengineering of Human Primary T Cells via Cell Mechanoporation

Effective tumor regression has been observed with chimeric antigen receptor (CAR) T cells; however, the development of an affordable, safe, and effective CAR-T cell treatment remains a challenge. One of the major obstacles is that the suboptimal genetic modification of T cells reduces their yield and antitumor activity, necessitating the development of a next-generation T cell engineering approach. In this study, we developed a nonviral T cell nanoengineering system that allows highly efficient delivery of diverse functional nanomaterials into primary human T cells in a genetically stable and scalable manner. Our platform leverages the unique cell deformation and restoration process induced by the intrinsic inertial flow in a microchannel to create nanopores in the cellular membrane for macromolecule internalization, leading to effective transfection with high scalability and viability. The proposed approach demonstrates considerable potential as a practical alternative technique for improving the current CAR-T cell manufacturing process.

Highly efficient mRNA delivery with nonlinear microfluidic cell stretching for cellular engineering

In the past few years, messenger RNA (mRNA) has emerged as a promising therapeutic agent for the treatment and prevention of various diseases. Clinically, mRNA-based drugs have been used for cancer immunotherapy, infectious diseases, and genomic disorders. To maximize the therapeutic efficacy of mRNA, the exact amount of mRNAs must be delivered to the target locations without degradation; however, traditional delivery modalities, such as lipid carriers and electroporation, are suboptimal because of their high cost, cell-type sensitivity, low scalability, transfection/delivery inconsistency, and/or loss of cell functionality. Therefore, new effective and stable delivery methods are required. Accordingly, we present a novel nonlinear microfluidic cell stretching (μ-cell stretcher) platform that leverages viscoelastic fluids, i.e., methylcellulose (MC) solutions, and cell mechanoporation for highly efficient and robust intracellular mRNA delivery. In the proposed platform, cells suspended in MC solutions with mRNAs were injected into a microchannel where they rapidly passed through a single constriction. Owing to the use of viscoelastic MC solutions, a high shear force was applied to the cells, effectively creating transient nanopores. This feature allows mRNAs to be effectively internalized through generated membrane discontinuities. Using this platform, high delivery efficiency (∼97%), high throughput (∼3.5 × 10⁵ cells per min), cell-type-/cargo-size-insensitive delivery, simple operation (single-step), low analyte consumption, low-cost operation (<$1), and nearly clogging-free operation were demonstrated, demonstrating the high potential of the proposed platform for application in mRNA-based cellular engineering research.

Microfluidic Impedance-Deformability Cytometry for Label-Free Single Neutrophil Mechanophenotyping

The intrinsic biophysical states of neutrophils are associated with immune dysfunctions in diseases. While advanced image-based biophysical flow cytometers can probe cell deformability at high throughput, it is nontrivial to couple different sensing modalities (e.g., electrical) to measure other critical cell attributes including cell viability and membrane integrity. Herein, an "optics-free" impedance-deformability cytometer for multiparametric single cell mechanophenotyping is reported. The microfluidic platform integrates hydrodynamic cell pinching, and multifrequency impedance quantification of cell size, deformability, and membrane impedance (indicative of cell viability and activation). A newly-defined "electrical deformability index" is validated by numerical simulations, and shows strong correlations with the optical cell deformability index of HL-60 experimentally. Human neutrophils treated with various biochemical stimul are further profiled, and distinct differences in multimodal impedance signatures and UMAP analysis are observed. Overall, the integrated cytometer enables label-free cell profiling at throughput of >1000 cells min^-1 without any antibodies labeling to facilitate clinical diagnostics.

Development of a Photonic Switch via Electro-Capillarity-Induced Water Penetration Across a 10-nm Gap

With narrow and dense nanoarchitectures increasingly adopted to improve optical functionality, achieving the complete wetting of photonic devices is required when aiming at underwater molecule detection over the water-repellent optical materials. Despite continuous advances in photonic applications, real-time monitoring of nanoscale wetting transitions across nanostructures with 10-nm gaps, the distance at which photonic performance is maximized, remains a chronic hurdle when attempting to quantify the water influx and molecules therein. For this reason, the present study develops a photonic switch that transforms the wetting transition into perceivable color changes using a liquid-permeable Fabry-Perot resonator. Electro-capillary-induced Cassie-to-Wenzel transitions produce an optical memory effect in the photonic switch, as confirmed by surface-energy analysis, simulations, and an experimental demonstration. The results show that controlling the wetting behavior using the proposed photonic switch is a promising strategy for the integration of aqueous media with photonic hotspots in plasmonic nanostructures such as biochemical sensors.

Melanoma cells adopt features of both mesenchymal and amoeboid migration within confining channels

For metastasis to occur, cancer cells must traverse a range of tissue environments. In part, this is accomplished by cells adjusting their migration mode to one that is best suited to the environment. Melanoma cells have been shown to be particularly plastic, frequently using both mesenchymal and amoeboid (bleb-based) modes of migration. It has been demonstrated that 2D confinement will promote the transition from mesenchymal to bleb-based migration. However, if melanoma cells similarly transition to bleb-based migration in response to 3D confinement, such as within narrow channels, is unknown. Here, using micro-fabricated channels, we demonstrate that metastatic, A375-M2, melanoma cells adopt features of both mesenchymal and bleb-based migration. In narrow (8 µm; height and width) channels coated with fibronectin, ~ 50% of melanoma cells were found to use either mesenchymal or bleb-based migration modes. In contrast, the inhibition of Src family kinases or coating channels with BSA, completely eliminated any features of mesenchymal migration. Detailed comparisons of migration parameters revealed that blebbing cells, particularly in the absence of adhesions, were faster than mesenchymal cells. In contrast to what has been previously shown under conditions of 2D confinement, pharmacologically inhibiting Arp2/3 promoted a fast filopodial-based mode of migration. Accordingly, we report that melanoma cells adopt a unique range of phenotypes under conditions of 3D confinement.

Highly Efficient Transfection of Human Primary T Lymphocytes Using Droplet-Enabled Mechanoporation

Whole-cell-based therapy has been extensively used as an effective disease treatment approach, and it has rapidly changed the therapeutic paradigm. To fully accommodate this shift, advances in genome modification and cell reprogramming methodologies are critical. Traditionally, molecular tools such as viral and polymer nanocarriers and electroporation have been the norm for internalizing external biomolecules into cells for cellular engineering. However, these approaches are not fully satisfactory considering their cytotoxicity, high cost, low scalability, and/or inconsistent and ineffective delivery and transfection. To address these challenges, we present an approach that leverages droplet microfluidics with cell mechanoporation, bringing intracellular delivery to the next level. In our approach, cells and external cargos such as mRNAs and plasmid DNAs are coencapsulated into droplets, and as they pass through a series of narrow constrictions, the cell membrane is mechanically permeabilized where the cargos in the vicinity are internalized via convective solution exchange enhanced by recirculation flows developed in the droplets. Using this principle, we demonstrated a high level of functional macromolecule delivery into various immune cells, including human primary T cells. By utilizing droplets, the cargo consumption was drastically reduced, and near-zero clogging was realized. Furthermore, high scalability without sacrificing cell viability and superior delivery over state-of-the-art methods and benchtop techniques were demonstrated. Notably, the droplet-based intracellular delivery strategy presented here can be further applied to other mechanoporation microfluidic techniques, highlighting its potential for cellular engineering and cell-based therapies.

Microfluidic and Nanofluidic Intracellular Delivery

Innate cell function can be artificially engineered and reprogrammed by introducing biomolecules, such as DNAs, RNAs, plasmid DNAs, proteins, or nanomaterials, into the cytosol or nucleus. This process of delivering exogenous cargos into living cells is referred to as intracellular delivery. For instance, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing begins with internalizing Cas9 protein and guide RNA into cells, and chimeric antigen receptor-T (CAR-T) cells are prepared by delivering CAR genes into T lymphocytes for cancer immunotherapies. To deliver external biomolecules into cells, tools, including viral vectors, and electroporation have been traditionally used; however, they are suboptimal for achieving high levels of intracellular delivery while preserving cell viability, phenotype, and function. Notably, as emerging solutions, microfluidic and nanofluidic approaches have shown remarkable potential for addressing this open challenge. This review provides an overview of recent advances in microfluidic and nanofluidic intracellular delivery strategies and discusses new opportunities and challenges for clinical applications. Furthermore, key considerations for future efforts to develop microfluidics- and nanofluidics-enabled next-generation intracellular delivery platforms are outlined.

Nanoscale Terahertz Monitoring on Multiphase Dynamic Assembly of Nanoparticles under Aqueous Environment

Probing the kinetic evolution of nanoparticle (NP) growth in liquids is essential for understanding complex nano-phases and their corresponding functions. Terahertz (THz) sensing, an emerging technology for next-generation laser photonics, has been developed with unique photonic features, including label-free, non-destructive, and molecular-specific spectral characteristics. Recently, metasurface-based sensing platforms have helped trace biomolecules by overcoming low THz absorption cross-sectional limits. However, the direct probing of THz signals in aqueous environments remains difficult. Here, the authors report that vertically aligned nanogap-hybridized metasurfaces can efficiently trap traveling NPs in the sensing region, thus enabling us to monitor the real-time kinetic evolution of NP assemblies in liquids. The THz photonics approach, together with an electric tweezing technique via spatially matching optical hotspots to particle trapping sites with a nanoscale spatial resolution, is highly promising for underwater THz analysis, forging a route toward unraveling the physicochemical events of nature within an ultra-broadband wavelength regime.

Microfluidic Cell Stretching for Highly Effective Gene Delivery into Hard-to-Transfect Primary Cells

Cell therapy and cellular engineering begin with internalizing synthetic biomolecules and functional nanomaterials into primary cells. Conventionally, electroporation, lipofection, or viral transduction has been used; however, these are limited by their cytotoxicity, low scalability, cost, and/or preparation complexity, especially in primary cells. Thus, a universal intracellular delivery method that outperforms the existing methods must be established. Here, we present a versatile intracellular delivery platform that leverages intrinsic inertial flow developed in a T-junction microchannel with a cavity. The elongational recirculating flows exerted in the channel substantially stretch the cells, creating discontinuities on cell membranes, thereby enabling highly effective internalization of nanomaterials, such as plasmid DNA (7.9 kbp), mRNA, siRNA, quantum dots, and large nanoparticles (300 nm), into different cell types, including hard-to-transfect primary stem and immune cells. We identified that the internalization mechanism of external cargos during the cell elongation-restoration process is achieved by both passive diffusion and convection-based rapid solution exchange across the cell membrane. Using fluidic cell mechanoporation, we demonstrated a transfection yield superior to that of other state-of-the-art microfluidic platforms as well as current benchtop techniques, including lipofectamine and electroporation. In summary, the intracellular delivery platform developed in the present study enables a high delivery efficiency (up to 98%), easy operation (single-step), low material cost (<$1), high scalability (1 × 10⁶ cells/min), minimal cell perturbation (up to 90%), and cell type/cargo insensitive delivery, providing a practical and robust approach anticipated to critically impact cell-based research.

Intracellular Nanomaterial Delivery via Spiral Hydroporation

In recent nanobiotechnology developments, a wide variety of functional nanomaterials and engineered biomolecules have been created, and these have numerous applications in cell biology. For these nanomaterials to fulfill their promises completely, they must be able to reach their biological targets at the subcellular level and with a high level of specificity. Traditionally, either nanocarrier- or membrane disruption-based method has been used to deliver nanomaterials inside cells; however, these methods are suboptimal due to their toxicity, inconsistent delivery, and low throughput, and they are also labor intensive and time-consuming, highlighting the need for development of a next-generation, intracellular delivery system. This study reports on the development of an intracellular nanomaterial delivery platform, based on unexpected cell-deformation phenomena via spiral vortex and vortex breakdown exerted in the cross- and T-junctions at moderate Reynolds numbers. These vortex-induced cell deformation and sequential restoration processes open cell membranes transiently, allowing effective and robust intracellular delivery of nanomaterials in a single step without the aid of carriers or external apparatus. By using the platform described here (termed spiral hydroporator), we demonstrate the delivery of different nanomaterials, including gold nanoparticles (200 nm diameter), functional mesoporous silica nanoparticles (150 nm diameter), dextran (hydrodynamic diameters between 2-55 nm), and mRNA, into different cell types. We demonstrate here that the system is highly efficient (up to 96.5%) with high throughput (up to 1 × 10⁶ cells/min) and rapid delivery (∼1 min) while maintaining high levels of cell viability (up to 94%).

Hydroporator: a hydrodynamic cell membrane perforator for high-throughput vector-free nanomaterial intracellular delivery and DNA origami biostability evaluation

The successful intracellular delivery of exogenous macromolecules is crucial for a variety of applications ranging from basic biology to the clinic. However, traditional intracellular delivery methods such as those relying on viral/non-viral nanocarriers or physical membrane disruptions suffer from low throughput, toxicity, and inconsistent delivery performance and are time-consuming and/or labor-intensive. In this study, we developed a single-step hydrodynamic cell deformation-induced intracellular delivery platform named "hydroporator" without the aid of vectors or a complicated/costly external apparatus. By utilizing only fluid inertia, the platform focuses, guides, and stretches cells robustly without clogging. This rapid hydrodynamic cell deformation leads to both convective and diffusive delivery of external (macro)molecules into the cell through transient plasma membrane discontinuities. Using this hydroporation approach, highly efficient (∼90%), high-throughput (>1 600 000 cells per min), and rapid delivery (∼1 min) of different (macro)molecules into a wide range of cell types was achieved while maintaining high cell viability. Taking advantage of the ability of this platform to rapidly deliver large molecules, we also systematically investigated the temporal biostability of vanilla DNA origami nanostructures in living cells for the first time. Experiments using two DNA origami (tube- and donut-shaped) nanostructures revealed that these nanostructures can maintain their structural integrity in living cells for approximately 1 h after delivery, providing new opportunities for the rapid characterization of intracellular DNA biostability.

Microfluidics-enabled orientation and microstructure control of macroscopic graphene fibres

Macroscopic graphene structures such as graphene papers and fibres can be manufactured from individual two-dimensional graphene oxide sheets by a fluidics-enabled assembling process. However, achieving high thermal-mechanical and electrical properties is still challenging due to non-optimized microstructures and morphology. Here, we report graphene structures with tunable graphene sheet alignment and orientation, obtained via microfluidic design, enabling strong size and geometry confinements and control over flow patterns. Thin flat channels can be used to fabricate macroscopic graphene structures with perfectly stacked sheets that exhibit superior thermal and electrical conductivities and improved mechanical strength. We attribute the observed shape and size confinements to the flat distribution of shear stress from the anisotropic microchannel walls and the enhanced shear thinning degree of large graphene oxide sheets in solution. Elongational and step expansion flows are created to produce large-scale graphene tubes and rods with horizontally and perpendicularly aligned graphene sheets by tuning the elongational and extensional shear rates, respectively.

DIY 3D Microparticle Generation from Next Generation Optofluidic Fabrication

Complex-shaped microparticles can enhance applications in drug delivery, tissue engineering, and structural materials, although techniques to fabricate these particles remain limited. A microfluidics-based process called optofluidic fabrication that utilizes inertial flows and ultraviolet polymerization has shown great potential for creating highly 3D-shaped particles in a high-throughput manner, but the particle dimensions are mainly at the millimeter scale. Here, a next generation optofluidic fabrication process is presented that utilizes on-the-fly fabricated multiscale fluidic channels producing customized sub-100 µm 3D-shaped microparticles. This flexible design scheme offers a user-friendly platform for rapid prototyping of new 3D particle shapes, providing greater potential for creating impactful engineered microparticles.

Intracellular Delivery of Nanomaterials via an Inertial Microfluidic Cell Hydroporator

The introduction of nanomaterials into cells is an indispensable process for studies ranging from basic biology to clinical applications. To deliver foreign nanomaterials into living cells, traditionally endocytosis, viral and lipid nanocarriers or electroporation are mainly employed; however, they critically suffer from toxicity, inconsistent delivery, and low throughput and are time-consuming and labor-intensive processes. Here, we present a novel inertial microfluidic cell hydroporator capable of delivering a wide range of nanomaterials to various cell types in a single-step without the aid of carriers or external apparatus. The platform inertially focuses cells into the channel center and guides cells to collide at a T-junction. Controlled compression and shear forces generate transient membrane discontinuities that facilitate passive diffusion of external nanomaterials into the cell cytoplasm while maintaining high cell viability. This hydroporation method shows superior delivery efficiency, is high-throughput, and has high controllability; moreover, its extremely simple and low-cost operation provides a powerful and practical strategy in the applications of cellular imaging, biomanufacturing, cell-based therapies, regenerative medicine, and disease diagnosis.

Inertial Microfluidic Cell Stretcher (iMCS): Fully Automated, High-Throughput, and Near Real-Time Cell Mechanotyping

Mechanical biomarkers associated with cytoskeletal structures have been reported as powerful label-free cell state identifiers. In order to measure cell mechanical properties, traditional biophysical (e.g., atomic force microscopy, micropipette aspiration, optical stretchers) and microfluidic approaches were mainly employed; however, they critically suffer from low-throughput, low-sensitivity, and/or time-consuming and labor-intensive processes, not allowing techniques to be practically used for cell biology research applications. Here, a novel inertial microfluidic cell stretcher (iMCS) capable of characterizing large populations of single-cell deformability near real-time is presented. The platform inertially controls cell positions in microchannels and deforms cells upon collision at a T-junction with large strain. The cell elongation motions are recorded, and thousands of cell deformability information is visualized near real-time similar to traditional flow cytometry. With a full automation, the entire cell mechanotyping process runs without any human intervention, realizing a user friendly and robust operation. Through iMCS, distinct cell stiffness changes in breast cancer progression and epithelial mesenchymal transition are reported, and the use of the platform for rapid cancer drug discovery is shown as well. The platform returns large populations of single-cell quantitative mechanical properties (e.g., shear modulus) on-the-fly with high statistical significances, enabling actual usages in clinical and biophysical studies.

Non-spherical particle generation from 4D optofluidic fabrication

Particles with non-spherical shapes can exhibit properties which are not available from spherical shaped particles. Complex shaped particles can provide unique benefits for areas such as drug delivery, tissue engineering, structural materials, and self-assembly building blocks. Current methods of creating complex shaped particles such as 3D printing, photolithography, and imprint lithography are limited by either slow speeds, shape limitations, or expensive processes. Previously, we presented a novel microfluidic flow lithography fabrication scheme combined with fluid inertia called optofluidic fabrication for the creation of complex shaped three-dimensional (3D) particles. This process was able to address the aforementioned limits and overcome two-dimensional shape limitations faced by traditional flow lithography methods; however, all of the created 3D particle shapes displayed top-down symmetry. Here, by introducing the time dimension into our existing optofluidic fabrication process, we break this top-down symmetry, generating fully asymmetric 3D particles where we termed the process: four-dimensional (4D) optofluidic fabrication. This 4D optofluidic fabrication is comprised of three sequential procedures. First, density mismatched precursor fluids flow past pillars within fluidic channels to manipulate the flow cross sections via fluid inertia. Next, the time dimension is incorporated by stopping the flow and allowing the denser fluids to settle by gravity to create asymmetric flow cross sections. Finally, the fluids are exposed to patterned ultraviolet (UV) light in order to polymerize fully asymmetric 3D-shaped particles. By varying inertial flow shaping, gravity-induced flow shaping, and UV light patterns, 4D optofluidic fabrication can create an infinite set of complex shaped asymmetric particles.

Correction: Continuous inertial microparticle and blood cell separation in straight channels with local microstructures

Correction for 'Continuous inertial microparticle and blood cell separation in straight channels with local microstructures' by Zhenlong Wu et al., Lab Chip, 2016, 16, 532-542.

Continuous inertial microparticle and blood cell separation in straight channels with local microstructures

Fluid inertia which has conventionally been neglected in microfluidics has been gaining much attention for particle and cell manipulation because inertia-based methods inherently provide simple, passive, precise and high-throughput characteristics. Particularly, the inertial approach has been applied to blood separation for various biomedical research studies mainly using spiral microchannels. For higher throughput, parallelization is essential; however, it is difficult to realize using spiral channels because of their large two dimensional layouts. In this work, we present a novel inertial platform for continuous sheathless particle and blood cell separation in straight microchannels containing microstructures. Microstructures within straight channels exert secondary flows to manipulate particle positions similar to Dean flow in curved channels but with higher controllability. Through a balance between inertial lift force and microstructure-induced secondary flow, we deterministically position microspheres and cells based on their sizes to be separated downstream. Using our inertial platform, we successfully sorted microparticles and fractionized blood cells with high separation efficiencies, high purities and high throughputs. The inertial separation platform developed here can be operated to process diluted blood with a throughput of 10.8 mL min(-1)via radially arrayed single channels with one inlet and two rings of outlets.

Sugar additives improve signal fidelity for implementing two-phase resorufin-based enzyme immunoassays

Enzymatic signal amplification based on fluorogenic substrates is commonly used for immunoassays; however, when transitioning these assays to a digital format in water-in-mineral oil emulsions, such amplification methods have been limited by the leakage of small reporting fluorescent probes. In the present study, we used a microfluidic system to study leakage from aqueous droplets in a controlled manner and confirmed that the leakage of fluorescent resorufin derivatives is mostly due to the presence of the lipophilic surfactant Span80, which is commonly used to preserve emulsion stability. This leakage can be overcome by the addition of specific sugars that most strongly interfered with the surfactants ability to form micelles in water. The application of the microfluidic system to the quantitative analysis of droplets and the implementation of the described sugar additives would allow for alternatives to fluorinated surfactant-based platforms and improve the signal fidelity in enzyme immunoassays implemented through multiphase microfluidics.

Advances in high-throughput single-cell microtechnologies

Micro-scale biological tools that have allowed probing of individual cells--from the genetic, to proteomic, to phenotypic level--have revealed important contributions of single cells to direct normal and diseased body processes. In analyzing single cells, sample heterogeneity between and within specific cell types drives the need for high-throughput and quantitative measurement of cellular parameters. In recent years, high-throughput single-cell analysis platforms have revealed rare genetic subpopulations in growing tumors, begun to uncover the mechanisms of antibiotic resistance in bacteria, and described the cell-to-cell variations in stem cell differentiation and immune cell response to activation by pathogens. This review surveys these recent technologies, presenting their strengths and contributions to the field, and identifies needs still unmet toward the development of high-throughput single-cell analysis tools to benefit life science research and clinical diagnostics.

Microstructure-induced helical vortices allow single-stream and long-term inertial focusing

Fluid inertia has been used to position microparticles in confined channels because it leads to precise and predictable particle migration across streamlines in a high-throughput manner. To focus particles, typically two inertial effects have been employed: inertial migration of particles in combination with geometry-induced secondary flows. Still, the strong scaling of inertial effects with fluid velocity or channel flow rate have made it challenging to design inertial focusing systems for single-stream focusing using large-scale microchannels. Use of large-scale microchannels (≥100 μm) reduces clogging over long durations and could be suitable for non-single-use flow cells in cytometry systems. Here, we show that microstructure-induced helical vortices yield single-stream focusing of microparticles with continuous and robust operation. Numerical and experimental results demonstrate how structures contribute to improve focusing in these larger channels, through controllable cross-stream particle migration, aided by locally-tuned secondary flows from sequential obstacles that act to bring particles closer to a single focusing equilibrium position. The large-scale inertial focuser developed here can be operated in a high-throughput manner with a maximum throughput of approximately 13,000 particles per s.

Three dimensional, sheathless, and high-throughput microparticle inertial focusing through geometry-induced secondary flows

A novel inertial focusing platform creates a single-stream microparticle train in a single-focal plane without sheath fluids and external forces, all in a high-throughput manner. The proposed design consists of a low-aspect-ratio straight channel interspersed with a series of constrictions in height arranged orthogonally, making use of inertial focusing and geometry-induced secondary flows. Focusing efficiency as high as 99.77% is demonstrated with throughput as high as 36 000 particles s(-1) for a variety of different sized particles and cells.

Large area flexible SERS active substrates using engineered nanostructures

Surface enhanced Raman scattering (SERS) is an analytical sensing method that provides label-free detection, molecularly specific information, and extremely high sensitivity. The Raman enhancement that makes this method attractive is mainly attributed to the local amplification of the incident electromagnetic field that occurs when a surface plasmon mode is excited at a metallic nanostructure. Here, we present a simple, cost effective method for creating flexible, large area SERS-active substrates using a new technique we call shadow mask assisted evaporation (SMAE). The advantage of large, flexible SERS substrates such as these is they have more area for multiplexing and can be incorporated into irregular surfaces such as clothing. We demonstrate the formation of four different types of nanostructure arrays (pillar, nib, ellipsoidal cylinder, and triangular tip) by controlling the evaporation angle, substrate rotation, and deposition rate of metals onto anodized alumina nanoporous membranes as large as 27 mm. In addition, we present experimental results showing how a hybrid structure comprising of gold nanospheres embedded in a silver nano-pillar structure can be used to obtain a 50× SERS enhancement over the raw nanoparticles themselves.

Optofluidic waveguides for reconfigurable photonic systems

We report the development of two liquid waveguide based photonic elements for use in reconfigurable photonic systems. This work demonstrates the ability to couple light from a conventional optical fiber to an adaptable liquid-core/liquid-cladding waveguide and back again to an optical fiber(s) enabling us to take advantage of both liquid- and solid-state photonic modalities. We demonstrate and characterize the use of this fiber-in and fiber-out system as either an optical switch or signal attenuator. Microscale flow control enables the adaptive morphology and tunable position of the liquid waveguide yielding an attenuation range of 3.1-10.7 dB, operability over a broad bandwidth spanning the range of wavelengths from visible to telecommunication, and a 1x2 sub-second switching system with a cross-talk as low as 20 dB and maximum coupling efficiency of 3.87 dB.

Analysis of liquid-to-solid coupling and other performance parameters for microfluidically reconfigurable photonic systems

In this paper, we analytically investigate the coupling of light from liquid-core waveguides to conventional solid-core waveguides and a series of other optical properties of liquid waveguides in order to gauge the practicality of such a system for use in microfluidically reconfigurable photonic systems. A finite element model of the system was constructed and relevant properties such as mode field diameter, attenuation, bending loss, and efficiency of evanescent and end-fire coupling were investigated as a function of the liquid waveguide Peclet number and the relative difference in refractive index. For pure liquid systems we show that the mode field diameter decreases monotonically with increasing Peclet number and that bending losses could be significantly reduced by increasing the Peclet number. More critically, we observed irreversible evanescent coupling, in which the light coupled in the solid waveguide is entrapped within the solid rather than coupled back into the liquid waveguide. This effect was caused by the lengthwise variation in the propagation constant of the liquid core due to downstream diffusion. We demonstrate that coupling efficiencies as high as 84% can be obtained for fluid based end-fire coupling by taking advantage of the tunable mode field diameter. By developing techniques for coupling light between liquid and solid states we hope to be able to overcome the drawbacks of solid waveguide systems (e.g. unchangeable structure and properties) and liquid waveguide systems (e.g. diversion and attenuation) yielding a new paradigm for reconfigurable photonics.

Engineering insect flight metabolics using immature stage implanted microfluidics

Small-scale insect inspired aircraft represent a promising approach to downscaling traditional aircraft designs. Despite advancements in microfabrication, however, it has proven difficult to fully replicate the mechanical complexities that enable these natural systems. As an alternative, recent efforts have used implanted electrical, optical or acoustic microsystems to exert direct control over insect flight. Here we demonstrate, for the first time, a method of directly and reversibly engineering insect flight metabolics using immature stage implanted microfluidics. We present our technique and device for on-command modulation of the internal levels of l-glutamic and l-aspartate acids and quantify the resulting changes in metabolic activity by monitoring respiratory CO(2) output. Microfluidic devices implanted 1 to 2 days prior to insects' emergence achieved survivability and flight-capable rates of 96% and 36%, respectively. Behavior ranging from retarded motion to complete, reversible paralysis, over timescales ranging from minutes to hours is demonstrated.

Enhanced on-chip SERS based biomolecular detection using electrokinetically active microwells

Here we present a novel microfluidic technique for on-chip surface enhanced Raman spectroscopy (SERS) based biomolecular detection, exploiting the use of electrokinetically active microwells. Briefly, the chip comprises of a series of microfluidic channels containing embedded microwells that, when electrically actuated, either locally attract or repulse species from solution through a combination of electrokinetic effects. We demonstrate that the approach combines the advantages of existing homogeneous (solution phase) and heterogeneous (surface phase) on-chip techniques by enabling active mixing to enhance the rate of binding between the SERS enhancers and the biomolecular targets as well as rapid concentration of the product for surface phase optical interrogation. This paper describes the chip design and fabrication procedure, experimental results illustrating the optimal conditions for our concentration and mixing processes, and a numerical analysis of the flow pattern. To demonstrate the usefulness of the device we apply it to the quantitative detection of nucleic acid sequences associated with Dengue virus serotype 2. We report a limit of detection for Dengue sequences of 30 pM and show excellent specificity against other serotypes.

Electrokinetic microfluidic devices for rapid, low power drug delivery in autonomous microsystems

In this work, a low power and robust electroactive microwell-based implantable drug delivery system, intended for use with autonomous microsystems, is presented. The device comprises of an upper silicon based structure in which the drug storage sites are defined and a lower electrically functionalized PDMS (polydimethylsiloxane) backing. The drug ejection mechanism developed here exploits localized electrokinetic effects to control both the release time and release rate of chemicals stored in independent well sites. It is shown how this can reduce the dosage time from hours to seconds over previous diffusion based approaches, using as little as 20 mJ of energy per dose. This paper focuses on presenting the design and characterizing the electrokinetic transport mechanics which govern the release time and dispersal pattern of the well contents using a series of experimental and numerical techniques.