Integrated Microfluidic-Electromagnetic System to Probe Single-Cell Magnetotaxis in Microconfinement

Magnetotactic bacteria have great potential for use in biomedical and environmental applications due to the ability to direct their navigation with a magnetic field. Applying and accurately controlling a magnetic field within a microscopic region during bacterial magnetotaxis studies at the single-cell level is challenging due to bulky microscope components and the inherent curvilinear field lines produced by commonly used bar magnets. In this paper, a system that integrates microfluidics and electromagnetic coils is presented for generating a linear magnetic field within a microenvironment compatible with microfluidics, enabling magnetotaxis analysis of groups or single microorganisms on-chip. The platform, designed and optimised via finite element analysis, is integrated into an inverted fluorescent microscope, enabling visualisation of bacteria at the single-cell level in microfluidic devices. The electromagnetic coils produce a linear magnetic field throughout a central volume where the microfluidic device containing the magnetotactic bacteria is located. The magnetic field, at this central position, can be accurately controlled from 1 to 10 mT, which is suitable for directing the navigation of magnetotactic bacteria. Potential heating of the microfluidic device from the operating coils was evaluated up to 2.5 A, corresponding to a magnetic field of 7.8 mT, for 10 min. The maximum measured heating was 8.4 °C, which enables analysis without altering the magnetotaxis behaviour or the average swimming speed of the bacteria. Altogether, this work provides a design, characterisation and experimental test of an integrated platform that enables the study of individual bacteria confined in microfluidics, under linear and predictable magnetic fields that can be easily and accurately applied and controlled.

Hybrid plasmonic metasurface as enhanced Raman hot-spots for pesticide detection at ultralow concentrations

A surface-enhanced Raman scattering (SERS) active metasurface composed of metallic nanohole arrays and metallic nanoparticles is developed. The metasurface can operate in aqueous environments, achieves an enhancement factor of 1.83 × 10⁹ for Rhodamine 6G, and enables the detection of malachite green at a concentation of 0.46 ppb.

Biomimetic macroscopic hierarchical moire gratings

Large-scale hierarchical macroscopic moire gratings resembling the surface structure of Peruvian lily flower petals are fabricated on azobenzene molecular glass thin films using a Lloyd's mirror interferometer. It is shown that nanostructured linear and crossed moire gratings can be made with pitch values reaching a few millimeters. Also, using atomic force microscopy, scanning electron microscopy, optical microscopy, and surface profilometry techniques, it is shown that the obtained moire gratings have two-fold or three-fold hierarchical structures fabricated using a simple all optical technique.

FDTD Analysis of Hotspot-Enabling Hybrid Nanohole-Nanoparticle Structures for SERS Detection

Metallic nanoparticles (MNPs) and metallic nanostructures are both commonly used, independently, as SERS substrates due to their enhanced plasmonic activity. In this work, we introduce and investigate a hybrid nanostructure with strong SERS activity that benefits from the collective plasmonic response of the combination of MNPs and flow-through nanohole arrays (NHAs). The electric field distribution and electromagnetic enhancement factor of hybrid structures composed of silver NPs on both silver and gold NHAs are investigated via finite-difference time-domain (FDTD) analyses. This computational approach is used to find optimal spatial configurations of the nanoparticle positions relative to the nanoapertures and investigate the difference between Ag-NP-on-Ag-NHAs and Ag-NP-on-Au-NHAs hybrid structures. A maximum G_SERS value of 6.8 × 10⁹ is achieved with the all-silver structure when the NP is located 0.5 nm away from the rim of the NHA, while the maximum of 4.7 × 10¹⁰ is obtained when the nanoparticle is in full contact with the NHA for the gold-silver hybrid structure. These results demonstrate that the hybrid nanostructures enable hotspot formation with strong SERS activity and plasmonic enhancement compatible with SERS-based sensing applications.

Cicada Wing Inspired Template-Stripped SERS Active 3D Metallic Nanostructures for the Detection of Toxic Substances

This article introduces a bioinspired, cicada wing-like surface-enhanced Raman scattering (SERS) substrate based on template-stripped crossed surface relief grating (TS-CSRG). The substrate is polarization-independent, has tunable nanofeatures and can be fabricated in a cleanroom-free environment via holographic exposure followed by template-stripping using a UV-curable resin. The bioinspired nanostructures in the substrate are strategically designed to minimize the reflection of light for wavelengths shorter than their periodicity, promoting enhanced plasmonic regions for the Raman excitation wavelength at 632.8 nm over a large area. The grating pitch that enables an effective SERS signal is studied using Rhodamine 6G, with enhancement factors of the order of 1 × 10⁴. Water contact angle measurements reveal that the TS-CSRGs are equally hydrophobic to cicada wings, providing them with potential self-cleaning and bactericidal properties. Finite-difference time-domain simulations are used to validate the nanofabrication parameters and to further confirm the polarization-independent electromagnetic field enhancement of the nanostructures. As a real-world application, label-free detection of melamine up to 1 ppm, the maximum concentration of the contaminant in food permitted by the World Health Organization, is demonstrated. The new bioinspired functional TS-CSRG SERS substrate holds great potential as a large-area, label-free SERS-active substrate for medical and biochemical sensing applications.

Electrokinetically-Driven Assembly of Gold Colloids into Nanostructures for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) enables the highly sensitive detection of (bio)chemical analytes in fluid samples; however, its application requires nanostructured gold/silver substrates, which presents a significant technical challenge. Here, we develop and apply a novel method for producing gold nanostructures for SERS application via the alternating current (AC) electrokinetic assembly of gold nanoparticles into two intricate and frequency-dependent structures: (1) nanowires, and (2) branched "nanotrees", that create extended sensing surfaces. We find that the growth of these nanostructures depends strongly on the parameters of the applied AC electric field (frequency and voltage) and ionic composition, specifically the electrical conductivity of the fluid. We demonstrate the sensing capabilities of these gold nanostructures via the chemical detection of rhodamine 6G, a Raman dye, and thiram, a toxic pesticide. Finally, we demonstrate how these SERS-active nanostructures can also be used as a concentration amplification device that can electrokinetically attract and specifically capture an analyte (here, streptavidin) onto the detection site.

Structural Stability of Optofluidic Nanostructures in Flow-Through Operation

Optofluidic sensors based on periodic arrays of subwavelength apertures that support surface plasmon resonance can be employed as both optical sensors and nanofluidic structures. In flow-through operation, the nanoapertures experience pressure differences across the substrate in which they are fabricated, which imposes the risk for structural failure. This work presents an investigation of the deflection and structural stability of nanohole array-based optofluidic sensors operating in flow-through mode. The analysis was approached using experiments, simulations via finite element method, and established theoretical models. The results depict that certain areas of the sensor deflect under pressure, with some regions suffering high mechanical stress. The offset in the deflection values between theoretical models and actual experimental values is overturned when only the effective area of the substrate, of 450 µm, is considered. Experimental, theoretical, and simulation results suggest that the periodic nanostructures can safely operate under trans-membrane pressures of up to 20 psi, which induce deflections of up to ~20 μm.

Rapid label-free detection of intact pathogenic bacteria in situ via surface plasmon resonance imaging enabled by crossed surface relief gratings

The unique plasmonic energy exchange occurring within metallic crossed surface relief gratings (CSRGs) has recently motivated their use as biosensors. However, CSRG-based biosensing has been limited to spectroscopic techniques, failing to harness their potential for integration with ubiquitous portable electronics. Here, we introduce biosensing via surface plasmon resonance imaging (SPRi) enabled by CSRGs. The SPRi platform is fully integrated including optics and electronics, has bulk sensitivity of 613 Pixel Intensity Unit (PIU)/Refractive Index Unit (RIU), a resolution of 10^-6 RIU and a signal-to-noise ratio of ∼33 dB. Finite-Difference Time-Domain (FDTD) simulations confirm that CSRG-enabled SPRi is supported by an electric field intensity enhancement of ∼30 times, due to plasmon resonance at the metal-dielectric interface. In the context of real-world biosensing applications, we demonstrate the rapid (<35 min) and label-free detection of uropathogenic E. coli (UPEC) in PBS and human urine samples for concentrations ranging from 10³ to 10⁹ CFU mL^-1. The detection limit of the platform is ∼100 CFU mL^-1, three orders of magnitude lower than the clinical detection limit for diagnosis of urinary tract infection. This work presents a new avenue for CSRGs as SPRi-based biosensing platforms and their great potential for integration with portable electronics for applications requiring in situ detection.

Facile actuation of aqueous droplets on a superhydrophobic surface using magnetotactic bacteria for digital microfluidic applications

Magnetic actuation provides a low-cost, simple method for droplet manipulation on a digital microfluidic platform. The impetus to move the droplets on a low friction surface can come from internal superparamagnetic particles or paramagnetic salts. Recently, the use of microbes for bio-actuation has been established, where the thrust produced by the microbes can be exploited to exert the force required for droplet movement. This study presents biologically-driven magnetic actuation of droplets on a superhydrophobic surface using magnetotactic bacteria (MTB). MTB-droplets were impelled along various trajectories such as rectangular and figure-of-eight-shaped paths. Droplets were reproducibly actuated with speeds up of to 30 mm s^-1. We demonstrated the ability to sequentially merge and mix multiple droplets by merging a 10 μL MTB droplet with two 4 μL colored droplets. The reorientation of MTB in the droplet enhanced mixing rate of the merged fluids by ∼40% compared with the control experiment where no actuation was used. Biologically-driven magnetic actuation was compared with actuation by superparamagnetic particles and paramagnetic salts, in terms of controllability and speed. MTB droplet was moved with the same average speed as other two methods and showed higher response time as the magnet acceleration increased. Lastly, MTB were used to perform a phosphatase assay using endogenous enzyme. The relative absorbance at 405 nm, indicating the production of the yellow product, increased over time and levels off after 75 min.

Wavelength-selective plasmonic sensor based on chirped-pitch crossed surface relief gratings

Two-dimensional chirped-pitch crossed surface relief gratings (CP-CSRGs) were fabricated on azobenzene-functionalized thin films using a simple two-step procedure. The resulting gratings had a constant pitch in one direction and a varying (chirped) pitch in the orthogonal direction. They were coated with silver and tested for their ability to change the polarization of surface plasmon resonance (SPR) signals, when placed between crossed polarizers. It was observed that several different bandwidths of SPR wavelengths are excitable using a single device, making CP-CSRGs suitable as next generation SPR-based sensors. The SPR wavelengths shifted as much as 10.5 nm/mm along the chirped grating, and a maximum sensitivity of 778.6 nm/RIU was obtained when detecting the refractive index change of various concentrations of aqueous sucrose solutions.

Direct Detection of Toxic Contaminants in Minimally Processed Food Products Using Dendritic Surface-Enhanced Raman Scattering Substrates

We present a method for the surface-enhanced Raman scattering (SERS)-based detection of toxic contaminants in minimally processed liquid food products, through the use of a dendritic silver nanostructure, produced through electrokinetic assembly of nanoparticles from solution. The dendritic nanostructure is produced on the surface of a microelectrode chip, connected to an AC field with an imposed DC bias. We apply this chip for the detection of thiram, a toxic fruit pesticide, in apple juice, to a limit of detection of 115 ppb, with no sample preprocessing. We also apply the chip for the detection of melamine, a toxic contaminant/food additive, to a limit of detection of 1.5 ppm in milk and 105 ppb in infant formula. All the reported limits of detection are below the recommended safe limits in food products, rendering this technique useful as a screening method to identify liquid food with hazardous amounts of toxic contaminants.

Erratum: Publisher's Note: "Migration of magnetotactic bacteria in porous media" [Biomicrofluidics , 011101 (2018)]

[This corrects the article DOI: 10.1063/1.5024508.].

Magnetotaxis Enables Magnetotactic Bacteria to Navigate in Flow

Magnetotactic bacteria (MTB) play an important role in Earth's biogeochemical cycles by transporting minerals in aquatic ecosystems, and have shown promise for controlled transport of microscale objects in flow conditions. However, how MTB traverse complex flow environments is not clear. Here, using microfluidics and high-speed imaging, it is revealed that magnetotaxis enables directed motion of Magnetospirillum magneticum over long distances in flow velocities ranging from 2 to 1260 µm s^-1 , corresponding to shear rates ranging from 0.2 to 142 s^-1 -a range relevant to both aquatic environments and biomedical applications. The ability of MTB to overcome a current is influenced by the flow, the magnetic field, and their relative orientation. MTB can overcome 2.3-fold higher flow velocities when directed to swim perpendicular to the flow as compared to upstream, as the latter orientation induces higher drag. The results indicate a threshold drag of 9.5 pN, corresponding to a flow velocity of 550 µm s^-1 , where magnetotaxis enables MTB to overcome counterdirectional flow. These findings bring new insights into the interactions of MTB with complex flow environments relevant to aquatic ecosystems, while suggesting opportunities for in vivo applications of MTB in microbiorobotics and targeted drug delivery.

Cost-effective flow-through nanohole array-based biosensing platform for the label-free detection of uropathogenic E. coli in real time

Rapid, inexpensive and sensitive detection of uropathogenic Escherichia coli (UPEC), a common cause of ascending urinary tract infections (UTIs) including cystitis and pyelonephritis, is critical given the increasing number of cases and its recurrence worldwide. In this paper, we present a label-free nanoplasmonic sensing platform, built with off-the-shelf optical and electronic components, which can detect intact UPEC at concentrations lower than the physiological limit for UTI diagnosis, in real time. The sensing platform consists of a red LED light source, lens assembly, CMOS detector, Raspberry Pi interface in conjugation with a metallic flow-through nanohole array-based sensor. Detection is achieved exploiting nanoplasmonic phenomena from the nanohole arrays through surface plasmon resonance imaging (SPRi) technique. The platform has a bulk sensitivity of 212 pixel intensity unit (PIU)/refractive index unit (RIU), and a resolution in the order of 10^-6 RIU. We demonstrate capture and detection of UPEC with a detection limit of ~100 CFU/ml - a concentration well below the threshold limit for UTI diagnosis in clinical samples. We also demonstrate detection of UPEC in spiked human urine samples for two different concentrations of bacteria. This work is particularly relevant for point-of-care applications, especially for regions around the world where accessibility to medical facilities is heavily dependent upon economy, and availability.

Migration of magnetotactic bacteria in porous media

Magnetotactic bacteria (MTB) migrate in complex porous sediments where fluid flow is ubiquitous. Here, we demonstrate that magnetotaxis enables MTB to migrate effectively through porous micromodels. Directed MTB can circumvent curved obstacles by traveling along the boundaries and pass flat obstacles by repeatedly switching between forward and backward runs. Magnetotaxis enables directed motion of MTB through heterogeneous porous media, overcoming tortuous flow fields with local velocities as high as 250 μm s-1. Our findings bring new insights into the migration behaviour of MTB in their natural habitats and their potential in vivo applications as microbiorobots.

Structure of a 1.5-MDa adhesin that binds its Antarctic bacterium to diatoms and ice

Bacterial adhesins are modular cell-surface proteins that mediate adherence to other cells, surfaces, and ligands. The Antarctic bacterium Marinomonas primoryensis uses a 1.5-MDa adhesin comprising over 130 domains to position it on ice at the top of the water column for better access to oxygen and nutrients. We have reconstructed this 0.6-μm-long adhesin using a "dissect and build" structural biology approach and have established complementary roles for its five distinct regions. Domains in region I (RI) tether the adhesin to the type I secretion machinery in the periplasm of the bacterium and pass it through the outer membrane. RII comprises ~120 identical immunoglobulin-like β-sandwich domains that rigidify on binding Ca²⁺ to project the adhesion regions RIII and RIV into the medium. RIII contains ligand-binding domains that join diatoms and bacteria together in a mixed-species community on the underside of sea ice where incident light is maximal. RIV is the ice-binding domain, and the terminal RV domain contains several "repeats-in-toxin" motifs and a noncleavable signal sequence that target proteins for export via the type I secretion system. Similar structural architecture is present in the adhesins of many pathogenic bacteria and provides a guide to finding and blocking binding domains to weaken infectivity.

In situ assembly of active surface-enhanced Raman scattering substrates via electric field-guided growth of dendritic nanoparticle structures

Surface-enhanced Raman scattering (SERS) can provide ultrasensitive detection of chemical and biological analytes down to the level of a single molecule. The need for costly, nanostructured, noble-metal substrates, however, poses a major obstacle in the widespread application of the method. Here we present for the first time a novel type of metallic nanostructured substrates that, not only exhibit a remarkable SERS activity, but are also produced in a facile, cost-effective and nanofabrication-free manner. The substrates are formed through an electric field-guided assembly process of silver nanocolloids, which results in extended and interconnected dendritic nanoparticle structures with a high density of "hot spots". A unique and significant performance attribute of these nanostructures is their ability to also function as concentration amplification devices, thereby further enhancing their analyte detection efficiency. This major advantage against conventional SERS substrates is illustrated experimentally here with the concentration and detection of proteins from solution. Low limits of detection for illicit drugs, food contaminants and pesticides in relevant matrices are also demonstrated. The SERS-active dendrites are reusable and can be removed and replaced in a few minutes. The SERS substrates presented herein constitute a significant advance towards more effective and less expensive diagnostic tools.

Polycaprolactone- and polycaprolactone/ceramic-based 3D-bioplotted porous scaffolds for bone regeneration: A comparative study

One of the critical challenges that scaffolding faces in the organ and tissue regeneration field lies in mimicking the structure, and the chemical and biological properties of natural tissue. A high-level control over the architecture, mechanical properties and composition of the materials in contact with cells is essential to overcome such challenge. Therefore, definition of the method, materials and parameters for the production of scaffolds during the fabrication stage is critical. With the recent emergence of rapid prototyping (RP), it is now possible to create three-dimensional (3D) scaffolds with the essential characteristics for the proliferation and regeneration of tissues, such as porosity, mechanical strength, pore size and pore interconnectivity, and biocompatibility. In this study, we employed 3D bioplotting, a RP technology, to fabricate scaffolds made from (i) pure polycaprolactone (PCL) and (ii) a composite based on PCL and ceramic micro-powder. The ceramics used for the composite were bovine bone filling Nukbone® (NKB), and hydroxyapatite (HA) with 5%, 10% or 20% wt.

CONTENT

The scaffolds were fabricated in a cellular lattice structure (i.e. meshing mode) using a 0/90° lay down pattern with a continuous contour filament in order to achieve interconnected porous reticular structures. We varied the temperature, as well as injection speed and pressure during the bioplotting process to achieve scaffolds with pore size ranging between 200 and 400μm and adequate mechanical stability. The resulting scaffolds had an average pore size of 323μm and an average porosity of 32%. Characterization through ATR-FTIR revealed the presence of the characteristic bands of hydroxyapatite in the PCL matrix, and presented an increase of the intensity of the phosphate and carbonyl bands as the ceramic content increased. The bioplotted 3D scaffolds have a Young's modulus (E) in the range between 0.121 and 0.171GPa, which is compatible with the modulus of natural bone. PCL/NKB scaffolds, particularly 10NKBP (10% NKB wt.) exhibited the highest proliferation optical density, demonstrating an evident osteoconductive effect when cultured in Dulbecco's Modified Eagle Medium (DMEM). Scanning electron microscopy (SEM) confirmed osteoblast anchorage to all composite scaffolds, but a low adhesion to the all-PCL scaffold, as well as cell proliferation. The results from this study demonstrate the potential of PCL/NKB 3D bioplotted scaffolds as viable platforms to enable osseous tissue formation, which can be used in several tissue engineering applications, including improvement of bone tissue regeneration.

Crossed Surface Relief Gratings as Nanoplasmonic Biosensors

We present an original, low-cost nanoplasmonic (bio)sensor based on crossed surface relief gratings (CSRGs) generated from orthogonally superimposed surface relief gratings (SRGs) on gold-coated azo-glass substrate. This surface plasmon resonance (SPR)-based sensing approach is unique, since the light transmitted through a CSRG is zero except in the narrow bandwidth where the SPR conversion occurs, enabling quantitative monitoring of only the plasmonic signal from biomolecular interactions in real time. We validated the individual SRG plasmonic signature of CSRGs by observing their respective SPR excitation peaks, and tested them to detect both bulk and near-surface refractive index (RI) changes. Compared to simple SRGs, CSRGs portray a much-improved sensitivity of 647.8 nm/RIU, a resolution on the order of 10^-5 RIU, and a figure of merit (FOM) of 14 for bulk RI-change sensing. We also demonstrate their ability to perform as biosensors, through the detection and monitoring of near-surface biomolecular interactions in real time, a first for CSRGs. The minimum detectable concentration of biotin-streptavidin binding events was 8.3 nM. Due to their sensing abilities, low cost (<10 cents/unit), ease of fabrication, and inherent suitability for integration with microfluidics, we anticipate that CSRGs will stand as strong candidates in the portable diagnostics arena.

A Versatile Bonding Method for PDMS and SU-8 and Its Application towards a Multifunctional Microfluidic Device

This paper reports a versatile and irreversible bonding method for poly(dimethylsiloxane) (PDMS) and SU-8. The method is based on epoxide opening and dehydration reactions between surface-modified PDMS and SU-8. A PDMS replica is first activated via the low-cost lab equipment, i.e., the oxygen plasma cleaner or the corona treater. Then both SU-8 and plasma-treated PDMS samples are functionalized using hydrolyzed (3-aminopropyl)triethoxysilane (APTES). Ultimately, the samples are simply brought into contact and heated to enable covalent bonding. The molecular coupling and chemical reactions behind the bonding occurring at the surfaces were characterized by water contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis. The reliability of bonded PDMS-SU-8 samples was examined by using tensile strength and leakage tests, which revealed a bonding strength of over 1.4 MPa. The presented bonding method was also applied to create a metal-SU-8-PDMS hybrid device, which integrated SU-8 microfluidic structures and microelectrodes. This hybrid system was used for the effective trapping of microparticles on-chip, and the selective releasing and identification of predefined trapped microparticles. The hybrid fabrication approach presented here, based on the PDMS-SU-8 bonding, enables multifunctional integration in complex microfluidic devices.

On-chip lysis of mammalian cells through a handheld corona device

On-chip lysis is required in many lab-on-chip applications involving cell studies. In these applications, the complete disruption of the cellular membrane and a high lysis yield is essential. Here, we present a novel approach to lyse cells on-chip through the application of electric discharges from a corona handheld device. The method only requires a microfluidic chip and a low-cost corona device. We demonstrate the effective lysis of BHK and eGFP HCT 116 cells in the sub-second time range using an embedded microelectrode. We also show cell lysis of non-adherent K562 leukemia cells without the use of an electrode in the chip. Cell lysis has been assessed through the use of bright-field microscopy, high-speed imaging and cell-viability fluorescence probes. The experimental results show effective cell lysis without any bubble formation or significant heating. Due to the simplicity of both the components involved and the lysis procedure, this technique offers an inexpensive lysis option with the potential for integration into lab-on-a-chip devices.

Quantification of ovarian cancer markers with integrated microfluidic concentration gradient and imaging nanohole surface plasmon resonance

Nanohole array-based biosensors integrated with a microfluidic concentration gradient generator were used for imaging detection and quantification of ovarian cancer markers. Calibration curves based on controlled concentrations of the analyte were created using a microfluidic stepped diffusive mixing scheme. Quantification of samples with unknown concentration of analyte was achieved by image-intensity comparison with the calibration curves. The biosensors were first used to detect the immobilization of ovarian cancer marker antibodies, and subsequently applied for the quantification of the ovarian cancer marker r-PAX8 (with a limit of detection of about 5 nM and a dynamic range from 0.25 to 9.0 μg.mL(-1)). The proposed biosensor demonstrated the ability of self-generating calibration curves on-chip in an integrated microfluidic platform, representing a further step towards the development of comprehensive lab-on-chip biomedical diagnostics based on nanohole array technology.

On-chip nanohole array based sensing: a review

The integration of nanohole array based plasmonic sensors into microfluidic systems has enabled the emergence of platforms with unique capabilities and a diversified palette of applications. Recent advances in fabrication techniques together with novel implementation schemes have influenced the progress of these optofluidic platforms. Here, we review the advances that nanohole array based sensors have experienced since they were first merged with microfluidics. We examine established and new fabrication methodologies that have enabled both the fabrication of nanohole arrays with improved optical attributes and a reduction in manufacturing costs. The achievements of several platforms developed to date and the significant benefits obtained from operating the nanoholes as nanochannels are also reviewed herein. Finally, we discuss future opportunities for on-chip nanohole array sensors by outlining potential applications and the use of the abilities of the nanostructures beyond the optical context.

Single-cell lysis for visual analysis by electron microscopy

The stochastic nature of biological systems makes the study of individual cells a necessity in systems biology. Yet, handling and disruption of single cells and the analysis of the relatively low concentrations of their protein components still challenges available techniques. Transmission electron microscopy (TEM) allows for the analysis of proteins at the single-molecule level. Here, we present a system for single-cell lysis under light microscopy observation, followed by rapid uptake of the cell lysate. Eukaryotic cells were grown on conductively coated glass slides and observed by light microscopy. A custom-designed microcapillary electrode was used to target and lyse individual cells with electrical pulses. Nanoliter volumes were subsequently aspirated into the microcapillary and dispensed onto an electron microscopy grid for TEM inspection. We show, that the cell lysis and preparation method conserves protein structures well and is suitable for visual analysis by TEM.

Surface-enhanced Raman scattering (SERS) optrodes for multiplexed on-chip sensing of nile blue A and oxazine 720

The fabrication and on-chip integration of surface-enhanced Raman scattering (SERS) optrodes are presented. In the optrode configuration, both the laser excitation and the back-scattered Raman signal are transmitted through the same optical fiber. The SERS-active component of the optrode was fabricated through the self-assembly of silver nanoparticles on the tip of optical fibers. The application of SERS optrodes to detect dyes in aqueous solution indicated a limit of quantification below 1 nM, using nile blue A as a molecular probe. Using the optrode-integrated microfluidic chip, it was possible to detect several different dyes from solutions sequentially injected into the same channel. This approach for sequential detection of different analytes is applicable to monitoring on-chip chemical processes. The narrow bandwidth of the vibrational information generated by SERS allowed solutions of different compositions of two chemically similar dyes to be distinguished using a dilution microfluidic chip. These results demonstrate the advantages of the SERS-optrode for microfluidics applications by illustrating the potential of this vibrational method to quantify components in a mixture.

Optofluidic concentration: plasmonic nanostructure as concentrator and sensor

The integration of fluidics and optics, as in flow-through nanohole arrays, has enabled increased transport of analytes to sensing surfaces. Limits of detection, however, are fundamentally limited by local analyte concentration. We employ the nanohole array geometry and the conducting nature of the film to actively concentrate analyte within the sensor. We achieve 180-fold enrichment of a dye, and 100-fold enrichment and simultaneous sensing of a protein in less than 1 min. The method presents opportunities for an order of magnitude increase in sensing speed and 2 orders of magnitude improvement in limit of detection.

Radial sample preconcentration

In this paper we present a radial sample preconcentration strategy enabled by axisymmetric concentration polarization in a microfluidic chamber on a uniform nanoporous film. Sample analytes are focused into the centre, creating a concentrated plug that is injected vertically into the microfluidic analysis layer. No balancing pressure driven flows or tangential fields are required, and the process has essentially zero footprint on the analysis layer. An electrokinetic loading scheme enables repeat loading/concentration cycles, and a finned radial chamber geometry dampens instabilities and accommodates larger volumes. Modelling results indicate over 1800-fold concentration increases are possible in 10 s, for high mobility buffers and high applied field strength. At moderate field strength and buffer mobility, experiments demonstrate a 168-fold increase in concentration of FITC-BSA protein in 36 s.

Flow-through vs flow-over: analysis of transport and binding in nanohole array plasmonic biosensors

We quantify the efficacy of flow-through nanohole sensing, as compared to the established flow-over format, through scaling analysis and numerical simulation. Nanohole arrays represent a growing niche within surface plasmon resonance-based sensing methods, and employing the nanoholes as nanochannels can enhance transport and analytical response. The additional benefit offered by flow-through operation is, however, a complex function of operating parameters and application-specific binding chemistry. Compared here are flow-over sensors and flow-through nanohole array sensors with equivalent sensing area, where the nanohole array sensing area is taken as the inner-walls of the nanoholes. The footprints of the sensors are similar (e.g., a square 20 μm wide flow-over sensor has an equivalent sensing area as a square 30 μm wide array of 300 nm diameter nanoholes with 450 nm periodicity in a 100 nm thick gold film). Considering transport alone, an analysis here shows that given equivalent sensing area and flow rate the flow-through nanohole format enables greatly increased flux of analytes to the sensing surface (e.g., 40-fold for the case of Q = 10 nL/min). Including both transport and binding kinetics, a computational model, validated by experimental data, provides guidelines for performance as a function of binding time constant, analyte diffusivity, and running parameters. For common binding kinetics and analytes, flow-through nanohole arrays offer ∼10-fold improvement in response time, with a maximum of 20-fold improvement for small biomolecules with rapid kinetics.

Structural performance and hydrodynamic resistance of a new silicone auricular cannula tip

Development of a new generation pneumatic of Ventricular Assist Device (VAD) required the design of cannulae to improve its optimal performance. In this case, a relevant restrictive design parameter was the material of the cannulae. Silicone was the best choice in a hemocompatible focus, but this is a material with very low stiffness. If the material is flexible, the most important parameter that affects either the structural performance or the hydrodynamic resistance is the amount of side holes on the cannulae tip, known as the effective drainage area. In order to obtain an estimation of the structural performance and of the hydrodynamic resistance, a study based on two independent analysis is needed: the structural and the in vitro drop pressure analysis. Structural analyses based on computer simulations were made in order to estimate the bending behavior of four silicone prototypes of cannulae tips. On the other hand, experiments under hydrostatic conditions were made to test and compare the pressure loss and flow rate relationship. A cannula tip with six side holes showed good hydrostatic performance, having almost the same as the one with nine side holes. Plus, it presented and a satisfactory structural behavior. This study assisted the design process of an auricular silicone cannula, recommending the use of cannulae with six side holes for a specific VAD.

Experimental and Computer-Based Performance Analysis of Two Elastomer VAD Valve Designs

The development of a new generation pneumatic Ventricular Assist Device (VAD) required the design of valves for the optimization of its performance. Experiments and computer-based simulations under hydrostatic conditions were analyzed in order to test and compare two low-cost elastomer valve designs. The trileaflet valve design showed a superior hydrostatic performance, having almost a ratio of 1:2 hydraulic resistance than the bileaflet valve design in agreement with both, the experimental and the simulation evidences. This study will address the use of a trileaflet valve designs in the future VAD redesign.

Hemodynamic performance in-vivo of a new ventricular assist device

Nowadays, circulatory support has become a common practice in medicine and a standard in the treatments of Cardio Vascular Disease (CVD). A new Pneumatic Ventricular Assist Device (VAD) has been developed in México City. This paper shows the first results of acute in-vivo trials, intended to verify the new system for providing physiological flows and pressures. Two VADs were implanted to as right (RVAD), left (LVAD) support in a 65 kg pig. The support time was 20 minutes with RVAD, 20 minutes with LVAD and 20 minutes with Biventricular (BiVAD). The VAD proved its capability to maintain physiological parameters during the support time. We are satisfied with the results of this trial, and we believe this study will ascertain the first step on the next phase of invivo trials.

Hydrodynamic effects of the partial opening of a trileaflet valve

Manufacturing process of medical grade silicon rubber trileaflet valves for VADs could propitiate important leaflet thickness variations which could result in partial opening of the valve and affect its hydrodynamic performance. The leaflets of a total of 10 valves were measured to assess its thickness variability. Two experiments were performed to asses the impact of the leaflets thickness variation under hypothetical situations. The first experiment was divided into three hypothetical cases. In each case either none, one or two leaflets of different valves were mechanically blocked, resembling possible critical working circumstances. The second experiment was intended to know how the variation on the leaflets thickness affects the hydrodynamic performance of the valves. The results demonstrated a significant variation on the leaflets thickness was found. As for the first experiment, a small variation on the hydrodynamic performance was found above 4 L/min flow rates and a slightly higher energy loss was found in one of the cases. As for the second experiment, the results showed that the variation of the leaflet thickness does not affect the general hydrodynamic performance of the valves. No relationship between the thickness variability and the hydrostatic performance of the valves was found.

Premenstrual symptomatology: role of prior knowledge about premenstrual syndrome

OBJECTIVE

Most women have some premenstrual symptoms that may be influenced by diverse environmental factors. The aim of this study was to determine the influence of knowledge about premenstrual syndrome (PMS) in the reports of women and their symptoms.

METHOD

We studied 86 healthy Mexican women whose highest level of education was sixth grade. Participants were assigned to one of two groups. The experimental group watched a videotape describing PMS and its negative consequences in daily life. The control group watched a videotape describing the menstrual cycle. The Menstrual Distress Questionnaire was administered to all women during the first week after menstruation, after which they were shown their designated videotape, and the questionnaire was administered again after the next menstruation.

RESULTS

In the control group, there were no significant differences in premenstrual symptoms reported both before and after the women watched the videotape. However, women in the experimental group reported more severe premenstrual symptoms after watching the videotape.

CONCLUSIONS

These results suggest that after observing the videotape, women's expectancies of negative symptoms in the premenstrual phase increased. Thus, the symptoms reported by these women were enhanced.