Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms

Polymerization in living organisms

Vital biomacromolecules, such as RNA, DNA, polysaccharides and proteins, are synthesized inside cells via the polymerization of small biomolecules to support and multiply life. The study of polymerization reactions in living organisms is an emerging field in which the high diversity and efficiency of chemistry as well as the flexibility and ingeniousness of physiological environment are incisively and vividly embodied. Efforts have been made to design and develop in situ intra/extracellular polymerization reactions. Many important research areas, including cell surface engineering, biocompatible polymerization, cell behavior regulation, living cell imaging, targeted bacteriostasis and precise tumor therapy, have witnessed the elegant demeanour of polymerization reactions in living organisms. In this review, recent advances in polymerization in living organisms are summarized and presented according to different polymerization methods. The inspiration from biomacromolecule synthesis in nature highlights the feasibility and uniqueness of triggering living polymerization for cell-based biological applications. A series of examples of polymerization reactions in living organisms are discussed, along with their designs, mechanisms of action, and corresponding applications. The current challenges and prospects in this lifeful field are also proposed.

New Dimension in Magnetism and Superconductivity: 3D and Curvilinear Nanoarchitectures

Traditionally, the primary field, where curvature has been at the heart of research, is the theory of general relativity. In recent studies, however, the impact of curvilinear geometry enters various disciplines, ranging from solid-state physics over soft-matter physics, chemistry, and biology to mathematics, giving rise to a plethora of emerging domains such as curvilinear nematics, curvilinear studies of cell biology, curvilinear semiconductors, superfluidity, optics, 2D van der Waals materials, plasmonics, magnetism, and superconductivity. Here, the state of the art is summarized and prospects for future research in curvilinear solid-state systems exhibiting such fundamental cooperative phenomena as ferromagnetism, antiferromagnetism, and superconductivity are outlined. Highlighting the recent developments and current challenges in theory, fabrication, and characterization of curvilinear micro- and nanostructures, special attention is paid to perspective research directions entailing new physics and to their strong application potential. Overall, the perspective is aimed at crossing the boundaries between the magnetism and superconductivity communities and drawing attention to the conceptual aspects of how extension of structures into the third dimension and curvilinear geometry can modify existing and aid launching novel functionalities. In addition, the perspective should stimulate the development and dissemination of research and development oriented techniques to facilitate rapid transitions from laboratory demonstrations to industry-ready prototypes and eventual products.

Wavefront Control with Nanohole Array-Based Out-of-Plane Metasurfaces

Planar metasurfaces provide exceptional wavefront manipulation at the subwavelength scale by controlling the phase of the light. Here, we introduce an out-of-plane nanohole-based metasurface design with the implementation of a unique self-rolling technique. The photoresist-based technique enables the fabrication of the metasurface formed by nanohole arrays on gold (Au) and silicon dioxide (SiO₂) rolled-up microtubes. The curved nature of the tube allows the fabrication of an out-of-plane metasurface that can effectively control the wavefront compared to the common planar counterparts. This effect is verified by the spectral measurements of the fabricated samples. In addition, we analytically calculated the dispersion relation to identify the resonance wavelength of the structure and numerically calculate the phase of the transmitted light through the holes with different sizes. Our work forms the basis for the unique platform to introduce a new feature to the metasurfaces, which may find many applications from stacked metasurface layers to optical trapping particles inside the tube.

Evolution of Plant Virus Diagnostics Used in Australian Post Entry Quarantine

As part of a special edition for MDPI on plant virology in Australia, this review provides a brief high-level overview on the evolution of diagnostic techniques used in Australian government Post-Entry Quarantine (PEQ) facilities for testing imported plants for viruses. A comprehensive range of traditional and modern diagnostic approaches have historically been employed in PEQ facilities using bioassays, serological, and molecular techniques. Whilst these techniques have been effective, they are time consuming, resource intensive and expensive. The review highlights the importance of ensuring the best available science and diagnostic developments are constantly tested, evaluated, and implemented by regulators to ensure primary producers have rapid and safe access to new genetics to remain productive, sustainable and competitive.

Fighting COVID-19: Integrated Micro- and Nanosystems for Viral Infection Diagnostics

The pandemic of coronavirus disease 2019 (COVID-19) highlights the importance of rapid and sensitive diagnostics of viral infection that enables the efficient tracing of cases and the implementation of public health measures for disease containment. The immediate actions from both academia and industry have led to the development of many COVID-19 diagnostic systems that have secured fast-track regulatory approvals and have been serving our healthcare frontlines since the early stage of the pandemic. On diagnostic technologies, many of these clinically validated systems have significantly benefited from the recent advances in micro- and nanotechnologies in terms of platform design, analytical method, and system integration and miniaturization. The continued development of new diagnostic platforms integrating micro- and nanocomponents will address some of the shortcomings we have witnessed in the existing COVID-19 diagnostic systems. This Perspective reviews the previous and ongoing research efforts on developing integrated micro- and nanosystems for nucleic acid-based virus detection, and highlights promising technologies that could provide better solutions for the diagnosis of COVID-19 and other viral infectious diseases. With the summary and outlook of this rapidly evolving research field, we hope to inspire more research and development activities to better prepare our society for future public health crises.

Sensitivity enhancement of a fiber-based interferometric optofluidic sensor

Optofluidic sensors, which tightly bridge photonics and micro/nanofluidics, are superior candidates in point-of-care testing. A fiber-based interferometric optofluidic (FIO) sensor can detect molecular biomarkers by fusing an optical microfiber and a microfluidic tube in parallel. Light from the microfiber side coupled to the microtube leads to lateral localized light-fluid evanescent interaction with analytes, facilitating sensitive detection of biomolecules with good stability and excellent portability. The determination of the sensitivity with respect to the interplay between light and fluidics, however, still needs to be understood quantitatively. Here, we theoretically and experimentally investigate the relationship between refractive index (RI) sensitivity and individual geometrical parameters to determine the lateral localized light-fluid evanescent interaction. Theoretical analysis predicted a sensitive maximum, which could be realized by synergically tuning the fiber diameter d and the tube wall thickness t at an abrupt dispersion transition region. As a result, an extremely high RI sensitivity of 1.6×10⁴ nm/RIU (σ=4074 nm/RIU), an order of magnitude higher than our previous results, with detection limit of 3.0×10^-6 RIU, is recorded by precisely governing the transverse geometry of the setup. The scientific findings will guide future exploration of both new light-fluid interaction devices and biomedical sensors.

Holographic femtosecond laser integration of microtube arrays inside a hollow needle as a lab-in-a-needle device

In this Letter, the femtosecond laser holographic two-photon polymerization (HTPP) method is adopted to rapidly realize a unique lab-in-a-needle (LIN) device by manufacturing microtube arrays inside a needle. The HTPP method is to modulate a Gaussian beam into a ring Bessel beam by a spatial light modulator (SLM) loaded with a Bessel hologram, and can fabricate microtube arrays with controllable inside diameter (1-10 μm) and designable patterns on such complex three-dimensional (3D) substrates by optimizing experimental parameters. A single LIN device can be processed by this method in about 4 min, which is not possible with traditional micronano technology and is much faster than the traditional two-photon polymerization method (at least several hours). To further demonstrate the functionality of this LIN device, a particle separation experiment is carried out. For the purpose of achieving greater functionality and integration of the on-chip system, this HTPP method provides a powerful processing method for integrating 3D functional microstructures on 3D nonplanar substrates.

Thermal-controlled releasing and assembling of functional nanomembranes through polymer pyrolysis

Pyrolysis, which involves thermal decomposition of materials at elevated temperatures, has been commonly applied in the chemical industry. Here we explored the pyrolysis process for 3D nanofabrication. By strain engineering of nanomembranes on a thermal responsive polymer as the sacrificial layer, we demonstrated that diverse 3D rolled-up microstructures with different functions could be achieved without any additional solution and drying process. We carefully studied the effect of molecular weight of the polymer in the pyrolysis process and identified that the rapid breakdown of molecular backbone to a monomer is the key for nanomembrane releasing and rolling. Preferential rolling direction and corresponding dynamics were studied by analyzing the real-time video of the rolling process. We further demonstrated the versatile functions of the fabricated 3D structures as catalytic microengines and optical resonators. The simple fabrication methodology developed here may have great potential in producing functional 3D tubular micro-/nanostructures.

Three-Dimensional Microtubular Devices for Lab-on-a-Chip Sensing Applications

The rapid advance of micro-/nanofabrication technologies opens up new opportunities for miniaturized sensing devices based on novel three-dimensional (3D) architectures. Notably, microtubular geometry exhibits natural advantages for sensing applications due to its unique properties including the hollow sensing channel, high surface-volume ratio, well-controlled shape parameters and compatibility to on-chip integration. Here the state-of-the-art sensing techniques based on microtubular devices are reviewed. The developed microtubular sensors cover microcapillaries, rolled-up nanomembranes, chemically synthesized tubular arrays, and photoresist-based tubular structures via 3D printing. Various types of microtubular sensors working in optical, electrical, and magnetic principles exhibit an extremely broad scope of sensing targets including liquids, biomolecules, micrometer-sized/nanosized objects, and gases. Moreover, they have also been applied for the detection of mechanical, acoustic, and magnetic fields as well as fluorescence signals in labeling-based analyses. At last, a comprehensive outlook of future research on microtubular sensors is discussed on pushing the detection limit, extending the functionality, and taking a step forward to a compact and integrable core module in a lab-on-a-chip analytical system for understanding fundamental biological events or performing accurate point-of-care diagnostics.

Overlooked? Underestimated? Effects of Substrate Curvature on Cell Behavior

In biological systems, form and function are inherently correlated. Despite this strong interdependence, the biological effect of curvature has been largely overlooked or underestimated, and consequently it has rarely been considered in the design of new cell-material interfaces. This review summarizes current understanding of the interplay between the curvature of a cell substrate and the related morphological and functional cellular response. In this context, we also discuss what is currently known about how, in the process of such a response, cells recognize curvature and accordingly reshape their membrane. Beyond this, we highlight state-of-the-art microtechnologies for engineering curved biomaterials at cell-scale, and describe aspects that impair or improve readouts of the pure effect of curvature on cells.

Catalytic Janus Colloids: Controlling Trajectories of Chemical Microswimmers

Catalytic Janus colloids produce rapid motion in fluids by decomposing dissolved fuel. There is great potential to exploit these "autonomous chemical swimmers" in applications currently performed by diffusion limited passive colloids. Key application areas for colloids include transporting active ingredients for drug delivery, gathering analytes for medical diagnostics, and self-assembling into regular structures used for photonic materials and lithographic templating. For drug delivery and medical diagnostics, controlling colloidal motion is key in order to target therapies, and transport analytes through lab-on-a-chip devices. Here, the autonomous motion of catalytic Janus colloids can remove the current requirements to induce and control colloid motion using external fields, thereby reducing the technological complexity required for medical therapies and diagnostics. For materials applications exploiting colloidal self-assembly, the additional interactions introduced by catalytic activity and rapid motion are predicted to allow access to new reconfigurable and responsive structures. In order to realize these goals, it is vital to develop methods to control both individual colloidal paths and collective behavior in motile catalytic colloidal systems. However, catalytic Janus colloids' trajectories are randomized by Brownian effects, and so require new strategies in order to be harnessed for transport. This is achievable using a variety of different approaches. For example, self-assembly and control of catalyst geometry can introduce controlled amounts of rotary motion, or "spin" into chemical swimmer trajectories. Furthermore, rotary motion combined with gravity, produces well-defined orientated helical trajectories. In addition, when catalytic colloids interact with topographical features, such as edges and trenches, they are steered. This gives rise to a new approach for autonomous colloidal microfluidic transport that could be deployed in future lab-on-a-chip devices. Chemical gradients can also influence the motion of catalytic Janus colloids, for example, to cause collective accumulations at specific locations. However, at present, the predicted theoretical degree of control over this phenomenon has not been fully verified in experimental systems. Collective behavior control for chemical swimmers is also possible by exploiting the potential for the complex interactions in these systems to allow access to self-assembled, dynamic and reconfigurable ordered structures. Again, current experiments have not yet accessed the breadth of possible behavior. Consequently, continued efforts are required to understand and control these interaction mechanisms in real world systems. Ultimately, this will help realize the use of catalytic Janus colloids for tasks that require well-controlled motion and structural organization, enabling functions such as analyte capture and concentration, or targeted drug delivery.

Effect of topological patterning on self-rolling of nanomembranes

The effects of topological patterning (i.e., grating and rectangular patterns) on the self-rolling behaviors of heteroepitaxial strained nanomembranes have been systematically studied. An analytical modeling framework, validated through finite-element simulations, has been formulated to predict the resultant curvature of the patterned nanomembrane as the pattern thickness and density vary. The effectiveness of the grating pattern in regulating the rolling direction of the nanomembrane has been demonstrated and quantitatively assessed. Further to the rolling of nanomembranes, a route to achieve predictive design of helical structures has been proposed and showcased. The present study provides new knowledge and mechanistic guidance towards predictive control and tuning of roll-up nanostructures via topological patterning.

Assembly and Self-Assembly of Nanomembrane Materials-From 2D to 3D

Nanoscience and nanotechnology offer great opportunities and challenges in both fundamental research and practical applications, which require precise control of building blocks with micro/nanoscale resolution in both individual and mass-production ways. The recent and intensive nanotechnology development gives birth to a new focus on nanomembrane materials, which are defined as structures with thickness limited to about one to several hundred nanometers and with much larger (typically at least two orders of magnitude larger, or even macroscopic scale) lateral dimensions. Nanomembranes can be readily processed in an accurate manner and integrated into functional devices and systems. In this Review, a nanotechnology perspective of nanomembranes is provided, with examples of science and applications in semiconductor, metal, insulator, polymer, and composite materials. Assisted assembly of nanomembranes leads to wrinkled/buckled geometries for flexible electronics and stacked structures for applications in photonics and thermoelectrics. Inspired by kirigami/origami, self-assembled 3D structures are constructed via strain engineering. Many advanced materials have begun to be explored in the format of nanomembranes and extend to biomimetic and 2D materials for various applications. Nanomembranes, as a new type of nanomaterials, allow nanotechnology in a controllable and precise way for practical applications and promise great potential for future nanorelated products.

Advances of Optofluidic Microcavities for Microlasers and Biosensors

Optofluidic microcavities with high Q factor have made rapid progress in recent years by using various micro-structures. On one hand, they are applied to microfluidic lasers with low excitation thresholds. On the other hand, they inspire the innovation of new biosensing devices with excellent performance. In this article, the recent advances in the microlaser research and the biochemical sensing field will be reviewed. The former will be categorized based on the structures of optical resonant cavities such as the Fabry⁻Pérot cavity and whispering gallery mode, and the latter will be classified based on the working principles into active sensors and passive sensors. Moreover, the difficulty of single-chip integration and recent endeavors will be briefly discussed.

Magnetic sensing platform technologies for biomedical applications

Detection and quantification of a variety of micro- and nanoscale entities, e.g. molecules, cells, and particles, are crucial components of modern biomedical research, in which biosensing platform technologies play a vital role. Confronted with the drastic global demographic changes, future biomedical research entails continuous development of new-generation biosensing platforms targeting even lower costs, more compactness, and higher throughput, sensitivity and selectivity. Among a wide choice of fundamental biosensing principles, magnetic sensing technologies enabled by magnetic field sensors and magnetic particles offer attractive advantages. The key features of a magnetic sensing format include the use of commercially available magnetic field sensing elements, e.g. magnetoresistive sensors which bear huge potential for compact integration, a magnetic field sensing mechanism which is free from interference by complex biomedical samples, and an additional degree of freedom for the on-chip handling of biochemical species rendered by magnetic labels. In this review, we highlight the historical basis, routes, recent advances and applications of magnetic biosensing platform technologies based on magnetoresistive sensors.

Deterministic Self-Rolling of Ultrathin Nanocrystalline Diamond Nanomembranes for 3D Tubular/Helical Architecture

Nanocrystalline diamond nanomembranes with thinning-reduced flexural rigidities can be shaped into various 3D mesostructures, such as tubes, jagged ribbons, nested tubes, helices, and nested rings. Microscale helical diamond architectures are formed by controlled debonding in agreement with finite-element simulation results. Rolled-up diamond tubular microcavities exhibit pronounced defect-related photoluminescence with whispering-gallery-mode resonance.

Optical microtube cavities monolithically integrated on photonic chips for optofluidic sensing

Microtubular optical resonators are monolithically integrated on photonic chips to demonstrate optofluidic functionality. Due to the compact subwavelength-thin tube wall and a well-defined nanogap between polymer photonic waveguides and the microtube, excellent optical coupling with extinction ratios up to 32 dB are observed in the telecommunication relevant wavelength range. For the first time, optofluidic applications of fully on-chip integrated microtubular systems are investigated both by filling the core of the microtube and by the microtube being covered by a liquid droplet. Total shifts over the full free spectral range are observed in response to the presence of the liquid medium in the vicinity of the microtube resonators. This work provides a vertical coupling scheme for optofluidic applications in monolithically integrated so-called "lab-in-a-tube" systems.

Integrative optofluidic microcavity with tubular channels and coupled waveguides via two-photon polymerization

Miniaturization of functional devices and systems demands new design and fabrication approaches for lab-on-a-chip application and optical integrative systems. By using a direct laser writing (DLW) technique based on two-photon polymerization (TPP), a highly integrative optofluidic refractometer is fabricated and demonstrated based on tubular optical microcavities coupled with waveguides. Such tubular devices can support high quality factor (Q-factor) up to 3600 via fiber taper coupling. Microtubes with various diameters and wall thicknesses are constructed with optimized writing direction and conditions. Under a liquid-in-tube sensing configuration, a maximal sensitivity of 390 nm per refractive index unit (RIU) is achieved with subwavelength wall thickness (0.5 μm), which offers a detection limit of the devices in the order of 10^-5 RIU. Such tubular microcavities with coupled waveguides underneath present excellent optofluidic sensing performance, which proves that TPP technology can integrate more functions or devices on a chip in one-step formation.

Magnetically Patterned Rolled-Up Exchange Bias Tubes: A Paternoster for Superparamagnetic Beads

We realized a deterministic transport system for superparamagnetic microbeads through micrometer-sized tubes acting as channels. Beads are moved stepwise in a paternoster-like manner through the tube and back on top of it by weak magnetic field pulses without changing the field pulse polarity and taking advantage of the magnetic stray field emerging from the tubular structures. The microtubes are engineered by rolling up exchange bias layer systems, magnetically patterned into parallel stripe magnetic domains. In this way, the tubes possess distinct azimuthally aligned magnetic domain patterns. This transport mechanism features high step velocities and remote control of not only the direction and trajectory but also the velocity of the transport without the need of fuel or catalytic material. Therefore, this approach has the potential to impact several fields of 3D applications in biotechnology, including particle transport related phenomena in lab-on-a-chip and lab-in-a-tube devices.

High-Performance Three-Dimensional Tubular Nanomembrane Sensor for DNA Detection

We report an ultrasensitive label-free DNA biosensor with fully on-chip integrated rolled-up nanomembrane electrodes. The hybridization of complementary DNA strands (avian influenza virus subtype H1N1) is selectively detected down to attomolar concentrations, an unprecedented level for miniaturized sensors without amplification. Impedimetric DNA detection with such a rolled-up biosensor shows 4 orders of magnitude sensitivity improvement over its planar counterpart. Furthermore, it is observed that the impedance response of the proposed device is contrary to the expected behavior due to its particular geometry. To further investigate this difference, a thorough model analysis of the measured signal and the electric field calculation is performed, revealing enhanced electron hopping/tunneling along the DNA chains due to an enriched electric field inside the tube. Likewise, conformational changes of DNA might also contribute to this effect. Accordingly, these highly integrated three-dimensional sensors provide a tool to study electrical properties of DNA under versatile experimental conditions and open a new avenue for novel biosensing applications (i.e., for protein, enzyme detection, or monitoring of cell behavior under in vivo like conditions).

Molecular Insights into Division of Single Human Cancer Cells in On-Chip Transparent Microtubes

In vivo, mammalian cells proliferate within 3D environments consisting of numerous microcavities and channels, which contain a variety of chemical and physical cues. External environments often differ between normal and pathological states, such as the unique spatial constraints that metastasizing cancer cells experience as they circulate the vasculature through arterioles and narrow capillaries, where they can divide and acquire elongated cylindrical shapes. While metastatic tumors cause most cancer deaths, factors impacting early cancer cell proliferation inside the vasculature and those that can promote the formation of secondary tumors remain largely unknown. Prior studies investigating confined mitosis have mainly used 2D cell culture systems. Here, we mimic aspects of metastasizing tumor cells dividing inside blood capillaries by investigating single-cell divisions of living human cancer cells, trapped inside 3D rolled-up, transparent nanomembranes. We assess the molecular effects of tubular confinement on key mitotic features, using optical high- and super-resolution microscopy. Our experiments show that tubular confinement affects the morphology and dynamics of the mitotic spindle, chromosome arrangements, and the organization of the cell cortex. Moreover, we reveal that membrane blebbing and/or associated processes act as a potential genome-safety mechanism, limiting the extent of genomic instability caused by mitosis in confined circumstances, especially in tubular 3D microenvironments. Collectively, our study demonstrates the potential of rolled-up nanomembranes for gaining molecular insights into key cellular events occurring in tubular 3D microenvironments in vivo.

Luminescent nanoparticles embedded in TiO2 microtube cavities for the activation of whispering-gallery-modes extending from the visible to the near infrared

Luminescent nanoparticles (NPs) are deposited onto two dimensional (2D) pre-strained TiO2 nanomembranes by spin-coating. After rolling up the 2D differentially strained TiO2 nanomembranes into 3D microtube structures, the NPs are embedded within the tube windings. The embedded NPs serve as a light source for optical whispering-gallery-mode resonances under laser excitation, and therefore allow the TiO2 microtube to work as an active microcavity operating in emission mode. The spectral range of resonant modes can be tuned from the visible to the near infrared by embedding the proper NPs in the TiO2 tube wall. Rolled-up TiO2 microcavities combined with luminescent NPs could offer interesting opportunities in a variety of research fields, such as bio- and nanophotonics, optoelectronics, and optofluidics.

Polydimethylsiloxane bilayer films with an embedded spontaneous curvature

Elastomer polydimethylsiloxane (PDMS) films with embedded in-plane gradient stress are created by making PDMS/(PDMS + silicone oil) crosslinked bilayers and extracting the oil in a suitable organic solvent bath. The collapse of the elastomer after oil extraction generates differential stress in the films that is manifested through their out-of-plane deformation. The curvature κ of narrow stripes of the bilayer, which is composed of layers of approximately equal thicknesses and elasticity moduli, is satisfactorily described by the simple relationship κ = 1.5δH(-1), where δ is the mechanical strain, and H is the total thickness of the bilayer. Curvature mapping of triangular PDMS plates reveals the existence of spherical and cylindrical types of deformation at different locations of the plates. Various 3D-shaped objects can be formed by the self-folding of appropriately designed 2D patterns that are cut from the films, or by nonuniform distribution of the collapsing layer. Thin PDMS bilayers with embedded stress roll up into microtubes of almost perfect cylindrical shape when released in a controlled manner from a substrate.

Engineered nanomembranes for smart energy storage devices

This review presents recent progress in engineered tubular and planar nanomembranes for smart energy storage applications, especially related to the investigation of fundamental electrochemical kinetics.

Vertical optical ring resonators fully integrated with nanophotonic waveguides on silicon-on-insulator substrates

We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step toward 3D photonic integration. The on-chip integration is realized by rolling up 2D differentially strained TiO(2) nanomembranes into 3D microtube cavities on a nanophotonic microchip. The integration configuration allows for out-of-plane optical coupling between the in-plane nanowaveguides and the vertical microtube cavities as a compact and mechanically stable optical unit, which could enable refined vertical light transfer in 3D stacks of multiple photonic layers. In this vertical transmission scheme, resonant filtering of optical signals at telecommunication wavelengths is demonstrated based on subwavelength thick-walled microcavities. Moreover, an array of microtube cavities is prepared, and each microtube cavity is integrated with multiple waveguides, which opens up interesting perspectives toward parallel and multi-routing through a single-cavity device as well as high-throughput optofluidic sensing schemes.

Dimensionality of Rolled-up Nanomembranes Controls Neural Stem Cell Migration Mechanism

We employ glass microtube structures fabricated by rolled-up nanotechnology to infer the influence of scaffold dimensionality and cell confinement on neural stem cell (NSC) migration. Thereby, we observe a pronounced morphology change that marks a reversible mesenchymal to amoeboid migration mode transition. Space restrictions preset by the diameter of nanomembrane topography modify the cell shape toward characteristics found in living tissue. We demonstrate the importance of substrate dimensionality for the migration mode of NSCs and thereby define rolled-up nanomembranes as the ultimate tool for single-cell migration studies.

Tailoring three-dimensional architectures by rolled-up nanotechnology for mimicking microvasculatures

Artificial microvasculature, particularly as part of the blood-brain barrier, has a high benefit for pharmacological drug discovery and uptake regulation. We demonstrate the fabrication of tubular structures with patterns of holes, which are capable of mimicking microvasculatures. By using photolithography, the dimensions of the cylindrical scaffolds can be precisely tuned as well as the alignment and size of holes. Overlapping holes can be tailored to create diverse three-dimensional configurations, for example, periodic nanoscaled apertures. The porous tubes, which can be made from diverse materials for differential functionalization, are biocompatible and can be modified to be biodegradable in the culture medium. As a proof of concept, endothelial cells (ECs) as well as astrocytes were cultured on these scaffolds. They form monolayers along the scaffolds, are guided by the array of holes and express tight junctions. Nanoscaled filaments of cells on these scaffolds were visualized by scanning electron microscopy (SEM). This work provides the basic concept mainly for an in vitro model of microvasculature which could also be possibly implanted in vivo due to its biodegradability.

Lab-in-a-tube systems as ultra-compact devices

In this Focus article, I will give an overview on the current and future interests of our multidisciplinary research group. One of our main interests is to develop highly integrated on-chip components towards ultra-compact devices for biosensing technologies (lab-in-a-tube). Our other activities are focused in developing self-powered devices that can generate either motion of a fluid or autonomous propulsion. We are particularly interested in three-dimensional (3D) nanofabrication technologies and stimuli responsive soft materials.

Magnetofluidic platform for multidimensional magnetic and optical barcoding of droplets

We present a concept of multidimensional magnetic and optical barcoding of droplets based on a magnetofluidic platform. The platform comprises multiple functional areas, such as an encoding area, an encoded droplet pool and a magnetic decoding area with integrated giant magnetoresistive (GMR) sensors. To prove this concept, penicillin functionalized with fluorescent dyes is coencapsulated with magnetic nanoparticles into droplets. While fluorescent dyes are used as conventional optical barcodes which are decoded with an optical decoding setup, an additional dimensionality of barcodes is created by using magnetic nanoparticles as magnetic barcodes for individual droplets and integrated micro-patterned GMR sensors as the corresponding magnetic decoding devices. The strategy of incorporating a magnetic encoding scheme provides a dynamic range of ~40 dB in addition to that of the optical method. When combined with magnetic barcodes, the encoding capacity can be increased by more than 1 order of magnitude compared with using only optical barcodes, that is, the magnetic platform provides more than 10 unique magnetic codes in addition to each optical barcode. Besides being a unique magnetic functional element for droplet microfluidics, the platform is capable of on-demand facile magnetic encoding and real-time decoding of droplets which paves the way for the development of novel non-optical encoding schemes for highly multiplexed droplet-based biological assays.

All-optical tuning of a magnetic-fluid-filled optofluidic ring resonator

An all-optical tunable optofluidic ring resonator (OFRR) is proposed and experimentally demonstrated. The all-optical control of a silica microresonator is highly attractive, but it is difficult to realize because of the relatively weak Kerr effect and the absence of a plasma dispersion effect of silica. Here, we infuse a silica microcapillary-based optofluidic ring resonator with a magnetic fluid, into which pump light is injected by a fiber taper. Iron oxide nanoparticles dispersed in the magnetic fluid produce a strong pump light absorption, and this leads to a resonance shift of the silica microresonator due to the photothermal effect. To the best of our knowledge, this is the first scheme for all-optical tuning of an OFRR. A tuning sensitivity of up to 0.15 nm mW(-1) and a tuning range of 3.3 nm are achieved. With such excellent performance, the magnetic-fluid-filled OFRR has great potential in filtering, sensing, and signal processing applications.

Rolled-up functionalized nanomembranes as three-dimensional cavities for single cell studies

We use micropatterning and strain engineering to encapsulate single living mammalian cells into transparent tubular architectures consisting of three-dimensional (3D) rolled-up nanomembranes. By using optical microscopy, we demonstrate that these structures are suitable for the scrutiny of cellular dynamics within confined 3D-microenvironments. We show that spatial confinement of mitotic mammalian cells inside tubular architectures can perturb metaphase plate formation, delay mitotic progression, and cause chromosomal instability in both a transformed and nontransformed human cell line. These findings could provide important clues into how spatial constraints dictate cellular behavior and function.

Photoactive rolled-up TiO2 microtubes: fabrication, characterization and applications†Electronic supplementary information (ESI) available. See DOI: 10.1039/c4tc00796dClick here for additional data file

Because of its unique properties, titania (TiO2) represents a promising candidate in a wide variety of research fields. In this paper, some of the properties and potential applications of titania within rolled-up nanotechnology are explored. It is shown how the structural and optical properties of rolled titania microtubes can be controlled by properly tuning the microfabrication parameters. The rolling up of titania films on different sacrificial layers and containing different shapes, achieving a control on the diameter of the fabricated titania microtubes, is presented. In order to obtain the more photoactive crystalline form of titania, one during-fabrication and two post-fabrication methods are demonstrated. Interesting applications in the fields of photocatalysis and photonics are suggested: the use of titania rolled-up microtubes as micromotors and optical microresonators is presented.

Imaging of buried 3D magnetic rolled-up nanomembranes

Increasing performance and enabling novel functionalities of microelectronic devices, such as three-dimensional (3D) on-chip architectures in optics, electronics, and magnetics, calls for new approaches in both fabrication and characterization. Up to now, 3D magnetic architectures had mainly been studied by integral means without providing insight into local magnetic microstructures that determine the device performance. We prove a concept that allows for imaging magnetic domain patterns in buried 3D objects, for example, magnetic tubular architectures with multiple windings. The approach is based on utilizing the shadow contrast in transmission X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy and correlating the observed 2D projection of the 3D magnetic domains with simulated XMCD patterns. That way, we are not only able to assess magnetic states but also monitor the field-driven evolution of the magnetic domain patterns in individual windings of buried magnetic rolled-up nanomembranes.

Self-folding single cell grippers

Given the heterogeneous nature of cultures, tumors, and tissues, the ability to capture, contain, and analyze single cells is important for genomics, proteomics, diagnostics, therapeutics, and surgery. Moreover, for surgical applications in small conduits in the body such as in the cardiovascular system, there is a need for tiny tools that approach the size of the single red blood cells that traverse the blood vessels and capillaries. We describe the fabrication of arrayed or untethered single cell grippers composed of biocompatible and bioresorbable silicon monoxide and silicon dioxide. The energy required to actuate these grippers is derived from the release of residual stress in 3-27 nm thick films, did not require any wires, tethers, or batteries, and resulted in folding angles over 100° with folding radii as small as 765 nm. We developed and applied a finite element model to predict these folding angles. Finally, we demonstrated the capture of live mouse fibroblast cells in an array of grippers and individual red blood cells in untethered grippers which could be released from the substrate to illustrate the potential utility for in vivo operations.

Bacteria-instructed synthesis of polymers for self-selective microbial binding and labelling

The detection and inactivation of pathogenic strains of bacteria continues to be an important therapeutic goal. Hence, there is a need for materials that can bind selectively to specific microorganisms for diagnostic or anti-infective applications, but that can be formed from simple and inexpensive building blocks. Here, we exploit bacterial redox systems to induce a copper-mediated radical polymerization of synthetic monomers at cell surfaces, generating polymers in situ that bind strongly to the microorganisms that produced them. This 'bacteria-instructed synthesis' can be carried out with a variety of microbial strains, and we show that the polymers produced are self-selective binding agents for the 'instructing' cell types. We further expand on the bacterial redox chemistries to 'click' fluorescent reporters onto polymers directly at the surfaces of a range of clinical isolate strains, allowing rapid, facile and simultaneous binding and visualization of pathogens.

Ultracompact three-dimensional tubular conductivity microsensors for ionic and biosensing applications

We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection = 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.

Vapour processed self-rolled poly(dimethylsiloxane) microcapillaries form microfluidic devices with engineered inner surface

We propose a microfluidics device whose main functional part consists of a microcapillary produced by the self-rolling of a thin poly(dimethylsiloxane) film. Rolling is caused by inhomogeneous swelling of the film, pre-treated by oxygen plasma, in the vapour of chloroform. The capillaries are integrated with external electrical circuits by co-rolling electrodes and micro-resistors. The local control of temperature in the tubes by Joule heating is illustrated via the rate of an intra-tubular chemiluminescent reaction. The novel tubes with engineered inner structure can find numerous advanced applications such as functional elements of integrated microfluidics circuits.

Continuous flowing micro-reactor for aqueous reaction at temperature higher than 100 °C

Some aqueous reactions in biological or chemical fields are accomplished at a high temperature. When the reaction temperature is higher than 100 °C, an autoclave reactor is usually required to elevate the boiling point of the water by creating a high-pressure environment in a closed system. This work presented an alternative continuous flowing microfluidic solution for aqueous reaction with a reaction temperature higher than 100 °C. The pressure regulating function was successfully fulfilled by a small microchannel based on a delicate hydrodynamic design. Combined with micro heater and temperature sensor that integrated in a single chip by utilizing silicon-based microfabrication techniques, this pressure regulating microchannel generated a high-pressure/high-temperature environment in the upstream reaction zone when the reagents continuously flow through the chip. As a preliminary demonstration, thermal digestion of aqueous total phosphorus sample was achieved in this continuous flowing micro-reactor at a working pressure of 990 kPa (under the working flow rate of 20 nl/s) along with a reaction temperature of 145 °C. This continuous flowing microfluidic solution for high-temperature reaction may find applications in various micro total analysis systems.

Rolled-up nanomembranes as compact 3D architectures for field effect transistors and fluidic sensing applications

We fabricate inorganic thin film transistors with bending radii of less than 5 μm maintaining their high electronic performance with on-off ratios of more than 10(5) and subthreshold swings of 160 mV/dec. The fabrication technology relies on the roll-up of highly strained semiconducting nanomembranes, which compacts planar transistors into three-dimensional tubular architectures opening intriguing potential for microfluidic applications. Our technique probes the ultimate limit for the bending radius of high performance thin film transistors.