Publications by authors named "John-Alexander Preuss"

7 Publications

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3D Printed Microfluidic Spiral Separation Device for Continuous, Pulsation-Free and Controllable CHO Cell Retention.

Micromachines (Basel) 2021 Aug 31;12(9). Epub 2021 Aug 31.

Institute of Technical Chemistry, Leibniz University Hannover, 30167 Hannover, Germany.

The development of continuous bioprocesses-which require cell retention systems in order to enable longer cultivation durations-is a primary focus in the field of modern process development. The flow environment of microfluidic systems enables the granular manipulation of particles (to allow for greater focusing in specific channel regions), which in turn facilitates the development of small continuous cell separation systems. However, previously published systems did not allow for separation control. Additionally, the focusing effect of these systems requires constant, pulsation-free flow for optimal operation, which cannot be achieved using ordinary peristaltic pumps. As described in this paper, a 3D printed cell separation spiral for CHO-K1 (Chinese hamster ovary) cells was developed and evaluated optically and with cell experiments. It demonstrated a high separation efficiency of over 95% at up to 20 × 10 cells mL. Control over inlet and outlet flow rates allowed the operator to adjust the separation efficiency of the device while in use-thereby enabling fine control over cell concentration in the attached bioreactors. In addition, miniaturized 3D printed buffer devices were developed that can be easily attached directly to the separation unit for usage with peristaltic pumps while simultaneously almost eradicating pump pulsations. These custom pulsation dampeners were closely integrated with the separator spiral lowering the overall dead volume of the system. The entire device can be flexibly connected directly to bioreactors, allowing continuous, pulsation-free cell retention and process operation.
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http://dx.doi.org/10.3390/mi12091060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8470376PMC
August 2021

3D printed microfluidic lab-on-a-chip device for fiber-based dual beam optical manipulation.

Sci Rep 2021 07 16;11(1):14584. Epub 2021 Jul 16.

Institute of Quantum Optics, Gottfried Wilhelm Leibniz University Hannover, Welfengarten 1, 30167, Hannover, Germany.

3D printing of microfluidic lab-on-a-chip devices enables rapid prototyping of robust and complex structures. In this work, we designed and fabricated a 3D printed lab-on-a-chip device for fiber-based dual beam optical manipulation. The final 3D printed chip offers three key features, such as (1) an optimized fiber channel design for precise alignment of optical fibers, (2) an optically clear window to visualize the trapping region, and (3) a sample channel which facilitates hydrodynamic focusing of samples. A square zig-zag structure incorporated in the sample channel increases the number of particles at the trapping site and focuses the cells and particles during experiments when operating the chip at low Reynolds number. To evaluate the performance of the device for optical manipulation, we implemented on-chip, fiber-based optical trapping of different-sized microscopic particles and performed trap stiffness measurements. In addition, optical stretching of MCF-7 cells was successfully accomplished for the purpose of studying the effects of a cytochalasin metabolite, pyrichalasin H, on cell elasticity. We observed distinct changes in the deformability of single cells treated with pyrichalasin H compared to untreated cells. These results demonstrate that 3D printed microfluidic lab-on-a-chip devices offer a cost-effective and customizable platform for applications in optical manipulation.
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http://dx.doi.org/10.1038/s41598-021-93205-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8285473PMC
July 2021

Miniaturized free-flow electrophoresis: production, optimization, and application using 3D printing technology.

Electrophoresis 2021 02 22;42(3):305-314. Epub 2020 Nov 22.

Institute of Technical Chemistry, Leibniz University Hannover, Callinstraße 5, Hannover, 30167, Germany.

The increasing resolution of three-dimensional (3D) printing offers simplified access to, and development of, microfluidic devices with complex 3D structures. Therefore, this technology is increasingly used for rapid prototyping in laboratories and industry. Microfluidic free flow electrophoresis (μFFE) is a versatile tool to separate and concentrate different samples (such as DNA, proteins, and cells) to different outlets in a time range measured in mere tens of seconds and offers great potential for use in downstream processing, for example. However, the production of μFFE devices is usually rather elaborate. Many designs are based on chemical pretreatment or manual alignment for the setup. Especially for the separation chamber of a μFFE device, this is a crucial step which should be automatized. We have developed a smart 3D design of a μFFE to pave the way for a simpler production. This study presents (1) a robust and reproducible way to build up critical parts of a μFFE device based on high-resolution MultiJet 3D printing; (2) a simplified insertion of commercial polycarbonate membranes to segregate separation and electrode chambers; and (3) integrated, 3D-printed wells that enable a defined sample fractionation (chip-to-world interface). In proof of concept experiments both a mixture of fluorescence dyes and a mixture of amino acids were successfully separated in our 3D-printed μFFE device.
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http://dx.doi.org/10.1002/elps.202000149DOI Listing
February 2021

3D-Printed Flow Cells for Aptamer-Based Impedimetric Detection of Crooks Strain.

Sensors (Basel) 2020 Aug 7;20(16). Epub 2020 Aug 7.

Institute of Technical Chemistry, Leibniz University Hannover, Callinstraße 5, 30167 Hannover, Germany.

Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of () Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications.
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http://dx.doi.org/10.3390/s20164421DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7472219PMC
August 2020

Impedimetric Aptamer-Based Biosensors: Principles and Techniques.

Adv Biochem Eng Biotechnol 2020 ;174:17-41

Institute of Technical Chemistry, Leibniz Universität Hannover, Hanover, Germany.

Aptamers are a specific class of ligands with high affinities comparable to antibodies, which are selected and synthesized in vitro. In combination with impedance spectroscopy as sensitive measurement method, we gain a class of biosensors with high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors. Besides giving a short summary of electrochemical measurement techniques, the most exciting innovative developments of detection strategies in the last decades are reviewed. Finally, important criteria for the comparison of aptamer-based biosensors are discussed.
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http://dx.doi.org/10.1007/10_2019_113DOI Listing
August 2020

Impedimetric Aptamer-Based Biosensors: Applications.

Adv Biochem Eng Biotechnol 2020 ;174:43-91

Institute of Technical Chemistry, Leibniz Universität Hannover, Hannover, Germany.

Impedimetric aptamer-based biosensors show high potential for handheld devices and point-of-care tests. In this review, we report on recent advances in aptamer-based impedimetric biosensors for applications in biotechnology. We detail on analytes relevant in medical and environmental biotechnology as well as food control, for which aptamer-based impedimetric biosensors were developed. The reviewed biosensors are examined for their performance, including sensitivity, selectivity, response time, and real sample validation. Additionally, the benefits and challenges of impedimetric aptasensors are summarized.
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http://dx.doi.org/10.1007/10_2020_125DOI Listing
August 2020

The Impact of Photobleaching on Microarray Analysis.

Biology (Basel) 2015 Sep 11;4(3):556-72. Epub 2015 Sep 11.

Institute of Technical Chemistry, Leibniz University Hanover, Callinstr. 5, 30167 Hanover, Germany.

DNA-Microarrays have become a potent technology for high-throughput analysis of genetic regulation. However, the wide dynamic range of signal intensities of fluorophore-based microarrays exceeds the dynamic range of a single array scan by far, thus limiting the key benefit of microarray technology: parallelization. The implementation of multi-scan techniques represents a promising approach to overcome these limitations. These techniques are, in turn, limited by the fluorophores' susceptibility to photobleaching when exposed to the scanner's laser light. In this paper the photobleaching characteristics of cyanine-3 and cyanine-5 as part of solid state DNA microarrays are studied. The effects of initial fluorophore intensity as well as laser scanner dependent variables such as the photomultiplier tube's voltage on bleaching and imaging are investigated. The resulting data is used to develop a model capable of simulating the expected degree of signal intensity reduction caused by photobleaching for each fluorophore individually, allowing for the removal of photobleaching-induced, systematic bias in multi-scan procedures. Single-scan applications also benefit as they rely on pre-scans to determine the optimal scanner settings. These findings constitute a step towards standardization of microarray experiments and analysis and may help to increase the lab-to-lab comparability of microarray experiment results.
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http://dx.doi.org/10.3390/biology4030556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4588150PMC
September 2015
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