Hans L. de Boer

Electrokinetic label-free screening chip: a marriage of multiplexing and high throughput analysis using surface plasmon resonance imaging

We present an electrokinetic label-free biomolecular screening chip (Glass/PDMS) to screen up to 10 samples simultaneously using surface plasmon resonance imaging (iSPR). This approach reduces the duration of an experiment when compared to conventional experimental methods. This new device offers a high degree of parallelization not only for analyte samples, but also for multiplex analyte interactions where up to 90 ligands are immobilized on the sensing surface. The proof of concept has been demonstrated with well-known biomolecular interactant pairs. The new chip can be used for high throughput screening applications and kinetics parameter extraction, simultaneously, of interactant-protein complex formation.

Microstamped Petri dishes for scanning electrochemical microscopy analysis of arrays of microtissues.

While scanning electrochemical microscopy (SECM) is a powerful technique for non-invasive analysis of cells, SECM-based assays remain scarce and have been mainly limited so far to single cells, which is mostly due to the absence of suitable platform for experimentation on 3D cellular aggregates or microtissues. Here, we report stamping of a Petri dish with a microwell array for large-scale production of microtissues followed by their in situ analysis using SECM. The platform is realized by hot embossing arrays of microwells (200 μm depth; 400 μm diameter) in commercially available Petri dishes, using a PDMS stamp. Microtissues form spontaneously in the microwells, which is demonstrated here using various cell lines (e.g., HeLa, C2C12, HepG2 and MCF-7). Next, the respiratory activity of live HeLa microtissues is assessed by monitoring the oxygen reduction current in constant height mode and at various distances above the platform surface. Typically, at a 40 μm distance from the microtissue, a 30% decrease in the oxygen reduction current is measured, while above 250 μm, no influence of the presence of the microtissues is detected. After exposure to a model drug (50% ethanol), no such changes in oxygen concentration are found at any height in solution, which reflects that microtissues are not viable anymore. This is furthermore confirmed using conventional live/dead fluorescent stains. This live/dead assay demonstrates the capability of the proposed approach combining SECM and microtissue arrays formed in a stamped Petri dish for conducting cellular assays in a non-invasive way on 3D cellular models.

Electrokinetic lab-on-a-biochip for multi-ligand/multi-analyte biosensing.

We present a simple electrokinetic lab-on-a-biochip (EKLB) with four microchannels integrated with a surface plasmon resonance imaging (iSPR) label-free biosensor that is operated using a single electrical voltage for the simultaneous transport of reagents in all microchannels without conventional fluidic plumbing. We demonstrate the utility of the simple approach with various biosensing experiments, including single injection kinetics (multiple varied ligand densities and single analyte concentration), one shot kinetics (single ligand densities and multiple varied analyte concentrations), and multi-ligand/multianalyte detection. In all cases, the binding kinetics and affinity were extracted using a conventional 1:1 interaction model. Since the reagent transport is done with a single electrical voltage source, scaling up to hundreds to thousands of simultaneous experiments is straightforward.

Spermometer: electrical characterization of single boar sperm motility

OBJECTIVE To study single sperm boar motility using electrical impedance measurements in a microfluidic system. DESIGN Comparison of the optical data and electrical impedance data. SETTING Research laboratory at a university. ANIMAL(S) Boar semen sample were used. INTERVENTION(S) A microfluidic system is developed that is able to spatially confine single boar sperm cells and allows noninvasive analysis of their motility on the single cell level. Using this system, the single sperm motility was affected by changing the temperature or adding chemical stimuli (caffeine). The retrieved electrical impedance and video data were processed using Matlab. MAIN OUTCOME MEASURE(S) The sperm beat frequency and amplitude determined from the electrical impedance and video data. RESULT(S) The electrically measured sperm beat frequency was verified by optical analysis and in correspondence. Furthermore the microfluidic platform allowed single sperm analysis by altering the sperm by temperature and chemical stimuli. CONCLUSION(S) This platform could be exploited as a potential tool to study sperm cells on the single cell level and to perform advanced sperm selection for intracytoplasmic sperm injection (ICSI) applications.

Integrated microfluidic biosensing platform for simultaneous confocal microscopy and electrophysiological measurements on bilayer lipid membranes and ion channels

Combining high‐resolution imaging and electrophysiological recordings is key for various types of experimentation on lipid bilayers and ion channels. Here, we propose an integrated biosensing platform consisting of a microfluidic cartridge and a dedicated chip‐holder to conduct such dual measurements on suspended lipid bilayers, in a user‐friendly manner. To illustrate the potential of the integrated platform, we characterize lipid bilayers in terms of thickness and fluidity while simultaneously monitoring single ion channel currents. For that purpose, POPC lipid bilayers are supplemented with a fluorescently‐tagged phospholipid (NBD‐PE, 1% mol) for Fluorescence Recovery After Photobleaching (FRAP) measurements and a model ion channel (gramicidin, 1 nM). These combined measurements reveal that NBD‐PE has no effect on the lipid bilayer thickness while gramicidin induces thinning of the membrane. Furthermore, the presence of gramicidin does not alter the lipid bilayer fluidity. Surprisingly, in lipid bilayers supplemented with both probes, a reduction in gramicidin open probability and lifetime is observed compared to lipid bilayers with gramicidin only, suggesting an influence of NBD‐PE on the gramicidin ion function. Altogether, our proposed microfluidic biosensing platform in combination with the herein presented multi‐parametric measurement scheme paves the way to explore the interdependent relationship between lipid bilayer properties and ion channel function.