Wolfgang Streule

PipeJet: A Simple Disposable Dispenser for the Nano- and Microliter Range

This paper reports on a simple, disposable non-contact dispenser for the nano- and microliter range. In contrast to other known dispensers manufactured by silicon micromachining1-4 the new device simply consists of an elastic polymer tube with a circular cross section. Actuation is done by a piezostack driven piston, squeezing the tube at a defined position near the open end by a significant fraction of the cross section. In contrast to drop-on-demand devices based on an acoustic actuation principle,5 the squeezing of the tube leads to a significant mechanical displacement of the liquid. Our experiments tested a large number of media in the viscosity range from 1 to 27 mPas. Some of our experiments tested up to approximately 2,000 mPas. Frequency characteristics showed an independent dosage volume for water up to a frequency of 15 Hz for tubes with an inner diameter of approximately 200 um. Standard deviation within 1,000 shots resulted in an excellent CV (standard deviation/dosage volume) of less than 2% of the dosage volume. Using tubes with an inner diameter of approximately 1,000 um and a print frequency of 340 Hz, a flow rate of less than or equal to 143 μL/s could be reached. Beyond the possibility to dispense pure liquids, emulsion paints with particles that have a diameter of approximately 40 μm have also been printed successfully.

Single-Cell Printer: Automated, On Demand, and Label Free

Within the past years, single-cell analysis has developed into a key topic in cell biology to study cellular functions that are not accessible by investigation of larger cell populations. Engineering approaches aiming to access single cells to extract information about their physiology, phenotype, and genotype at the single-cell level are going manifold ways, meanwhile allowing separation, sorting, culturing, and analysis of individual cells. Based on our earlier research toward inkjet-like printing of single cells, this article presents further characterization results obtained with a fully automated prototype instrument for printing of single living cells in a noncontact inkjet-like manner. The presented technology is based on a transparent microfluidic drop-on-demand dispenser chip coupled with a camera-assisted automatic detection system. Cells inside the chip are detected and classified with this detection system before they are expelled from the nozzle confined in microdroplets, thus enabling a “one cell per droplet” printing mode. To demonstrate the prototype instrument’s suitability for biological and biomedical applications, basic experiments such as printing of single-bead and cell arrays as well as deposition and culture of single cells in microwell plates are presented. Printing efficiencies greater than 80% and viability rates about 90% were achieved.

Quantitative volume determination of dispensed nanoliter droplets on the fly

In this paper we present a sensor for non-contact monitoring of dispensed micro-droplets on the fly. In extension to our previous work [1], the sensor now allows for a direct, quantitative volume determination of single liquid droplets in the volume range from 20 to 100 nl. The improved electronic transducer enables to measure the droplet volume with an accuracy of ΔV ± 3 nl. The sensor signal provides a variety of information about the monitored droplet like for examples droplet velocity. This paper considers in particular the influence of the droplet velocity on the volume measurement. It turned out that the velocity effect can be fully compensated, if the signals are interpreted correctly.

Teflon-carbon black as new material for the hydrophobic patterning of polymer labs-on-a-chip

We provide a new method for the selective surface patterning of microfluidic chips with hydrophobic fluoropolymers which is demonstrated by the fabrication of hydrophobic valves. It enables efficient optical quality control for the surface patterning thus permitting the low-cost production of highly reproducible hydrophobic valves. Specifically, a fluoropolymer-solvent-dye solution based on carbon black (CB) is presented which creates superhydrophobic surfaces (contact angle = 157.9°) on chips made from cyclic olefin copolymer (COC). It further provides good visibility for the quality control (QC) in polymer labs-on-a-chip and increases the burst pressure of hydrophobic valves. Finally, an application which aims for the amplification of mRNA on-chip and relies on the defined flow control by hydrophobic valves is presented. Here, the QC in combination with the Teflon-CB coating improves the average standard deviation of the burst pressures from 14.5% down to 6.1 % compared to solely Teflon-coated valves.