The Belder Group's research focuses on lab-on-a-chip technology as a fundamental science in chemistry. A broad field of research and application of lab-on-a-chip technology is carried out in the Belder laboratories at the University of Leipzig. The Belder group is known for miniaturized separation techniques such as chip electrophoresis and chip HPLC.

Vergrößerte Aufnahme eines Mikrofluidik Chips
Mikrofluidik Chip, Foto: Universität Leipzig, AK Konzentrationsanalytik

The Belder Group is known for miniaturized separation techniques such as chip electrophoresis and chip HPLC. The Belder lab also works on detection techniques such as coupling microfluidic chips with mass spectrometry or ion mobility spectrometry, and optical techniques such as fluorescence and Raman microscopy. A particular focus in recent years has been on integrated chip laboratories, which combine chemical reactors and analysis units on a single chip.

Our research topics

Chromatography offers a wide range of different separation modes. The use of commercially available particulate phases promises the greatest possible potential as stationary phases due to their wide range of applications and constant further development in industry and science.

The technical challenge lies in the immobilization of the particles within the microfluidic separation channel. For this purpose, we introduce frits in a size range of a few micrometers in a spatially resolved manner. With the help of a high-pressure-tight connection technology ("world-to-chip-interface") and a specially developed injection technique, we obtain the highest separation efficiency coupled with very fast separations.

Selected publications

Microchip electrophoresis (MCE) is a further development of capillary electrophoresis (CE). The heart of MCE is a microchip of a few cm in size, made of glass, quartz or polymer, with integrated microfluidic channels of a few micrometers in diameter. By generating electric fields, migration currents can be generated in these channels, which can be used to inject and separate a sample zone comprising a few nL (see figure). Different separation principles of CE are used for separation.

One of the most fascinating features of microchip electrophoresis is its unsurpassed separation speed. Thus, chemical analyses can be performed in seconds or even ms, with the perspective of developing fast, portable analytical instruments for field analysis or point-of-care diagnostics.

In numerous projects, we have been able to apply this new technique to real-world analytical problems in chemical synthesis, bioanalytics as well as diagnostics. Among other things, sophisticated chiral separations have been achieved in ms.

Selected publications

The use of mass spectrometry (MS) in microchip electrophoresis (MCE) is an interesting alternative to conventional fluorescence detection. Not only does it eliminate the need for problematic fluorescence derivatization, but MS also allows analytes to be identified by their mass spectrum. In order to ensure efficient coupling of the MCE with the MS, we presented and patented a method for producing a glass chip with an integrated nanospray emitter. With the help of this chip, dead volume-free MCE-MS coupling could thus be realized for the first time.

Selected publications

Free-flow electrophoresis (FFE) is a continuous separation method that is particularly suitable for the pre-fractionation and purification of complex chemical and biological samples.

In its miniaturized form, it enables not only significantly faster separations and greatly reduced chemical consumption, but also the purification and analysis of very small sample volumes. Due to the possibility of using the miniaturized FFE for continuous separations, it is also suitable for monitoring purposes in the form of "online monitoring".

Our research in the field of µFFE includes design and chip development with a focus on efficient manufacturing processes and adaptations to different applications, the implementation of alternative analyte detection strategies as well as couplings with further detection options.

Selected publications

One goal of miniaturizing chemical reaction and analysis systems is to combine all the steps of a chemical process into a lab-on-a-chip (LOC) or micro-total analysis system (µ-TAS). This is complemented by the integration of reaction and detection on a so-called microchip.

First, the integration of a microfluidic reactor for enantioselective synthesis of organic compounds on an electrophoresis chip was successful, and later on other analytical chips, such as chips with integrated nanospray emitter for MS detection. In addition to conventional metal catalysts, enzymes and whole cells can also be used. For example, one publication shows the determination of the enantioselectivity of enzyme mutants in cells. In addition to determining optimal reaction conditions, such reactor analysis units also enable high-throughput screening of enantioselective catalysts.

Selected publications

The fluorescence lifetime is an attractive measurement parameter. It is molecule-specific, sensitive with respect to the environment, and insensitive to many sources of interference from common fluorescence measurements. For example, lifetime is independent of variations in excitation light intensity and detector efficiency, stray light, and other optical background.

We pursue fluorescence lifetime measurements in various microfluidic analysis platforms in both the time and frequency domains. The two methods allow a wide measurement range of luminescence lifetime from nanoseconds to microseconds. On the one hand, the study of lifetime is used to determine changes in the molecular environment (e.g., pH, O2 concentration, temperature) and develop sensitive sensors. On the other hand, the potential of fluorescence lifetime measurement is shown in peak identification in microfluidic separations.

Selected publications

Continuous online monitoring of process parameters and detection of chemical and biological anlays in microfluidic analysis systems requires the integration of sensors.

This is realized using optical chemical sensors. The combination of miniaturized analytical systems and fluorescent probes eliminates additional costly as well as time-consuming subsequent analytical methods.
For this purpose, sensitive indicator molecules are immobilized in micrometer-thick layers or also in the form of sensor arrays in microfluidic systems.
Visualization of the presence of analytes or changes in environmental parameters such as pH or temperature can thus be realized. Further research is aimed at coupling microfluidic chemical sensing with other chip-integrated processes such as chemical syntheses, analytical separations and biological applications.

Selected publications

Chemical modification of channel surfaces in microchips is essential, especially for complex protein separations as performed in proteomics research.

For this purpose, surface coating methods are used and validated in our group. For example, we developed a method for coating glass substrates with polyvinyl alcohol (PVA), which enabled the highly efficient electrophoretic separation of protein proteins in less than 2 min.

Selected publications

 

Laser-induced fluorescence detection is one of the most important detection methods in microanalysis due to its outstanding sensitivity, selectivity and versatility. Fluorescence measurements can be used to detect even the smallest traces of analytes in the microchip channels, which are only a few micrometers in size.

By exploiting the native molecular fluorescence often present in the deep UV spectral range, the cumbersome derivatization of analytes can be dispensed with prior to measurement. Using a quartz microchip electrophoresis system developed by us, label-free detection of proteins and small molecules was thus achieved. To avoid the use of expensive quartz materials, a two-photon excitation was implemented.

Selected publications

 

Microfluidic droplets represent an extremely versatile tool in synthesis and high-throughput analysis in microchip laboratories. Droplets are self-contained microreaction vessels surrounded by a non-miscible medium, with volumes down to the nano- and picoliter range.

We use the combination of time-resolved fluorescence detection with microdroplet technology to clarify bioanalytical questions, for example the determination of protein concentrations in aqueous matrices via Förster resonance energy transfer (FRET).

Selected publications

Surface-enhanced Raman spectroscopy (SERS) is an excellent method for label-free detection of analytes even in trace amounts. Thus, it is a good alternative to the established fluorescence spectroscopy, especially for substances that do not show their own fluorescence.
Furthermore, similar to infrared spectroscopy, Raman spectroscopy provides structural information of the investigated substances. Thus, especially in microfluidics, it represents an advantageous tool for substance screening or as a detection method for a wide variety of separation processes.

Selected publications

Third-party funded large-scale equipment since 2018

Thanks to an infrastructure measure funded by the Free State of Saxony, a novel tuneable quantum cascade laser IR microscope will be made available to the Belder working group in 2021. The use of this QCL-IR microscope is expected to enable for the first time IR-based label-free, real-time chemical imaging of dynamic processes in microfluidic IR-transparent microfluidic chips.

Quantum Cascade Laser IR Microscope, Foto: Universität Leipzig, AK Konzentrationsanalytik

Aims of the project

Current scientific activities include the microfluidic chip / QCL-IR microscope setup as well as microsynthetic research for the first label-free, real-time IR tracking of chemical processes in chip-based microsystems. For this purpose, organocatalytic model reactions from the research group FOR 2177 are initially investigated, supported by our coorperation partners from the synthetic chemistry working groups. Among the most important aspects of this research are the development of chip designs such as microflow reactors and the 3D microfabrication of the corresponding chips in IR-transparent materials using SLE technology. This synergistic interplay of the two cutting-edge technologies SLE and quantum cascade laser IR microscopy is currently unique, opening up completely new possibilities and, in the long term, a significant innovation boost for basic research in micro-chemistry.

As part of an ERDF infrastructure measure, the instrumental infrastructure of the university will be strengthened and the AK Belder will be enabled to use a high-speed triple quadrupole mass spectrometer. This instrument can detect multiple target analytes over a wide range of masses and concentrations with unsurpassed speed and sensitivity. Triple quadrupole mass spectrometry is therefore the undisputed method of choice today in application fields where high speed and excellent detection limits are equally decisive criteria.

High-Sensitive High-speed Mass Spectrometer, Image: Agilent
High-Sensitive High-speed Mass Spectrometer, Image: Agilent

Aims of the project

With the financed instrumental upgrade, an ideal basic technical prerequisite has been created to perform mass spectrometric analyses in microsystems with previously unattained sensitivity and speed. Thus, multiple target analytes will now be detected and analyzed simultaneously with unsurpassed speed and sensitivity. The use of the funded instrument in combination with the microlaboratories developed to date now offers the possibility of a real breakthrough for research in the field of single-cell and single-particle catalysis as well as ultrafast chip chromatography.

Within the scope of this ERDF infrastructure measure, a novel 3D laser structuring system based on the selective laser etching (SLE) process is being established. This is a hybrid technique consisting of pre-structuring by an ultrashort pulse laser, in which the layout designed in CAD is transferred to the glass substrate. The laser-treated material has a significantly increased etch rate, so that etching (e.g. with KOH) is favored at these points. This makes it possible to produce complex 3D structures in glass, as shown in the following figure.

Fotocollage eines Laserstrukturierungssystems zur Erzeugung von Mikro- und Nanostrukturen in Glas und Polymeren (LasMino).
Laserstrukturierungssystem zur Erzeugung von Mikro- und Nanostrukturen in Glas und Polymeren (LasMino). Fotocollage: Universität Leipzig, AK Konzentrationsanalytik

Aims of the project

The 3D laser structuring system is intended to expand the technical-instrumental infrastructure at the Leipzig academic site in the field of chip clean room process technology for microfluidic lab-on-chip systems. The novel process for micro-nano-laser structuring of glass and polymers will be used in all current research areas around the topic of complex, integrated micro-laboratories to overcome current technical limitations and to open up new research and development opportunities, e.g. for coordinated programs like the DFG research group "InChem". This includes research topics such as the development of optically fully transparent microcavity electrode arrays for tissue-based drug testing or the miniaturization and seamless integration of chemical flow synthesis, analytical separation techniques and high-performance detection methods in complex microlaboratories.

As part of an infrastructure measure funded by the German Research Foundation (DFG) and the Free State of Saxony, a laser spectroscopy microscope for studying chemical processes in chip-based microlaboratories was procured in 2019 and installed in the laboratory facilities of the Belder working group at the University of Leipzig. This system features a custom-built dual-microscope setup, multiple laser excitation sources including a tuneable TiSa laser, and a wide variety of options for sensitive detection. The versatility of the equipment setup now available enables simultaneous detection of chemical species at different locations on a chip by fluorescence and Raman spectroscopic methods, allowing significant advances in the research and development of miniaturized analytical and synthesis platforms to be realized.

Photo of a Fluorescence / Raman microscope for the development of miniaturized analysis and synthesis platforms. Photo: University of Leipzig, AK Concentration Analytics
Fluorescence / Raman microscope for the development of miniaturized analysis and synthesis platforms. Photo: University of Leipzig, AK Concentration Analytics

Aims of the project

In addition to the sensitive and selective analysis of diverse species, processes and materials will also be studied and visualized in more detail at the micrometer scale. The system opens up previously unavailable opportunities for research and development of miniaturized analytical systems of high complexity and functionality. Furthermore, the dual microscope will be used across faculties for research on a wide variety of microspectroscopy topics. In addition to intensive research activities, the system will also be used in advanced teaching in the master's degree program in chemistry, providing scientific staff and students with novel opportunities in spectroscopic analysis.

Large equipment before 2018

Of the large-scale equipment acquired prior to 2018, the following are being used in current research projects:

  • Various mass spectrometers
  • An ion mobility spectrometer
  • A time-resolved fluorescence microscope
  • One Raman microscope

Vacancies

At the Institute of Analytical Chemistry of the University of Leipzig in the professorship Concentration Analytics we offer temporary positions within the framework of externally funded projects.
In addition to the supervision of doctoral theses, bachelor, advanced or master theses on various topics are offered in our working group.

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