Dries Kil

Single-Step Imprinting of Femtoliter Microwell Arrays Allows Digital Bioassays with Attomolar Limit of Detection

Bead-based microwell array technology is growing as an ultrasensitive analysis tool as exemplified by the successful commercial applications from Illumina and Quanterix for nucleic acid analysis and ultrasensitive protein measurements, respectively. High-efficiency seeding of magnetic beads is key for these applications and is enhanced by hydrophilic-in-hydrophobic microwell arrays, which are unfortunately often expensive or labor-intensive to manufacture. Here, we demonstrate a new single-step manufacturing approach for imprinting cheap and disposable hydrophilic-in-hydrophobic microwell arrays suitable for digital bioassays. Imprinting of arrays with hydrophilic-in-hydrophobic microwells is made possible using an innovative surface energy replication approach by means of a hydrophobic thiol-ene polymer formulation. In this polymer, hydrophobic-moiety-containing monomers self-assemble at the hydrophobic surface of the imprinting stamp, which results in a hydrophobic replica surface after polymerization. After removing the stamp, microwells with hydrophobic walls and a hydrophilic bottom are obtained. We demonstrate that the hydrophilic-in-hydrophobic imprinted microwell arrays enable successful and efficient self-assembly of individual water droplets and seeding of magnetic beads with loading efficiencies up to 96%. We also demonstrate the suitability of the microwell arrays for the isolation and digital counting of single molecules achieving a limit of detection of 17.4 aM when performing a streptavidin-biotin binding assay as model system. Since this approach is up-scalable through reaction injection molding, we expect it will contribute substantially to the translation of ultrasensitive digital microwell array technology toward diagnostic applications.

Extracellular matrix proteins as temporary coating for thin-film neural implants

OBJECTIVE This study investigates the suitability of a thin sheet of extracellular matrix (ECM) proteins as a resorbable coating for temporarily reinforcing fragile or ultra-low stiffness thin-film neural implants to be placed on the brain, i.e. microelectrocorticographic (µECOG) implants. APPROACH Thin-film polyimide-based electrode arrays were fabricated using lithographic methods. ECM was harvested from porcine tissue by a decellularization method and coated around the arrays. Mechanical tests and an in vivo experiment on rats were conducted, followed by a histological tissue study combined with a statistical equivalence test (confidence interval approach, 0.05 significance level) to compare the test group with an uncoated control group. MAIN RESULTS After 3 months, no significant damage was found based on GFAP and NeuN staining of the relevant brain areas. SIGNIFICANCE The study shows that ECM sheets are a suitable temporary coating for thin µECOG neural implants.

A foldable electrode array for 3D recording of deep-seated abnormal brain cavities

OBJECTIVE This study describes the design and microfabrication of a foldable thin-film neural implant and investigates its suitability for electrical recording of deep-lying brain cavity walls. APPROACH A new type of foldable neural electrode array is presented, which can be inserted through a cannula. The microfabricated electrode is specifically designed for electrical recording of the cavity wall of thalamic lesions resulting from stroke. The proof-of-concept is demonstrated by measurements in rat brain cavities. On implantation, the electrode array unfolds in the brain cavity, contacting the cavity walls and allowing recording at multiple anatomical locations. A three-layer microfabrication process based on UV-lithography and Reactive Ion Etching is described. Electrochemical characterization of the electrode is performed in addition to an in vivo experiment in which the implantation procedure and the unfolding of the electrode are tested and visualized. MAIN RESULTS Electrochemical characterization validated the suitability of the electrode for in vivo use. CT imaging confirmed the unfolding of the electrode in the brain cavity and analysis of recorded local field potentials showed the ability to record neural signals of biological origin. SIGNIFICANCE The conducted research confirms that it is possible to record neural activity from the inside wall of brain cavities at various anatomical locations after a single implantation procedure. This opens up possibilities towards research of abnormal brain cavities and the clinical conditions associated with them, such as central post-stroke pain.

Uniplanar microwave heater for digital microfluidics

This paper reports on a 4 GHz microwave droplet heater for digital microfluidics. The uniplanar device was fabricated using a gold-on-quartz process and was optimized for uniform heating within a 1 μL droplet. Microwave measurements show excellent agreement with COMSOL simulations. The uniformity of the induced temperature within the droplet was experimentally validated using fluorescence microscopy using a temperature sensitive fluorophore.

Investigation of thermal effect caused by different input power of biosensor using a novel microwave and optical sensing system for biological liquids

In this paper, we present a novel measurement system combining microwave vector network analysis with high-speed multi-channel fluorescence microscopy. Microwave and fluorescent measurement of 1 mM rhodamine B water solution was accomplished simultaneously with our system. No thermal effect was observed using the temperature dependent fluorescence of rhodamine B when the input power of the device varies from −21.99 dBm to 4.90 dBm. This novel system will enable us to correlate microwave and optical methods for biological characterization.

Liquid measurements at microliter volumes using 1-port coplanar interdigital capacitor

A coplanar waveguide based 1-port interdigital capacitor is presented as 0.1 μΕ dielectric liquid sensor for frequencies up to 1 GHz. An equivalent circuit circuit of the sensor is given, from which capacitance C and conductance G are used to compute the complex permittivity of the material under test (MUT). 3D FEM simulations show a linear relationship between real and imaginary parts of the complex permittivity of the MUT and the C and G of the equivalent circuit, respectively, which has been validated by measurements on water-isopropanol mixtures. Time-resolved spectral measurements on bakers yeast cells were also conducted and are analysed in this paper.