TY - JOUR A1 - van Wasen, S. A1 - You, Yi A1 - Beck, S. A1 - Riedel, Jens A1 - Volmer, D. A. T1 - Miniaturized Protein Digestion Using Acoustic Levitation with Online High Resolution Mass Spectrometry N2 - The combination of acoustically levitated droplets, mid-IR laser evaporation, and subsequent post-ionization by secondary electrospray ionization was applied for monitoring the enzymatic digestion of various proteins. Acoustically levitated droplets are an ideal, wall-free model reactor, readily allowing compartmentalized microfluidic trypsin digestions. Time-resolved interrogation of the droplets yielded real-time information on the progress of the reaction and thus provided insights into reaction kinetics. After 30 min of digestion in the acoustic levitator, the obtained protein sequence coverages were identical to the reference overnight digestions. Importantly, our results clearly demonstrate that the applied experimental setup can be used for the real-time investigation of chemical reactions. Furthermore, the described methodology only uses a fraction of the typically applied amounts of solvent, analyte, and trypsin. Thus, the results exemplify the use of acoustic levitation as a green analytical chemistry alternative to the currently used batch reactions. KW - Acoustic levitation KW - Protein analysis KW - Mass spectrometry PY - 2023 DO - https://doi.org/10.1021/acs.analchem.2c05334 VL - 95 SP - 4190 EP - 4195 PB - ACS Publications AN - OPUS4-57053 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stindt, Arne A1 - Andrade, M. A. B. A1 - Buurman, Merwe A1 - Adamowski, J. C. A1 - Panne, Ulrich A1 - Riedel, Jens T1 - Experimental and numerical characterization of the sound pressure in standing wave acoustic levitators N2 - A novel method for predictions of the sound pressure distribution in acoustic levitators is based on a matrix representation of the Rayleigh integral. This method allows for a fast calculation of the acoustic field within the resonator. To make sure that the underlying assumptions and simplifications are justified, this approach was tested by a direct comparison to experimental data. The experimental sound pressure distributions were recorded by high spatially resolved frequency selective microphone scanning. To emphasize the general applicability of the two approaches, the comparative studies were conducted for four different resonator geometries. In all cases, the results show an excellent agreement, demonstrating the accuracy of the matrix method. KW - Acoustic levitation KW - Matrix calculation KW - Microphony KW - Noncontact ultrasonic transportation KW - Small objects KW - Matrix-method KW - Droplets KW - Air KW - Manipulation KW - Simulation KW - Fields KW - Water PY - 2014 DO - https://doi.org/10.1063/1.4861197 SN - 0034-6748 SN - 1089-7623 N1 - Geburtsname von Buurman, Merwe: Albrecht, M. - Birth name of Buurman, Merwe: Albrecht, M. VL - 85 IS - 015110 SP - 1 EP - 6 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-30405 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Andrade, M. A. B. A1 - Stindt, Arne A1 - Panne, Ulrich A1 - Riedel, Jens A1 - Adamowski, J. C. T1 - Numerical and experimental determination of the sound pressure distribution in single-axis acoustic levitators N2 - This paper presents a numerical and an experimental procedure to obtain the pressure field in single-axis acoustic levitators. Numerically, the pressure field is determined by a matrix method based on the Rayleigh integral that take into account the multiple wave reflections that occur between the transducer and the reflector. The numerical pressure field is compared with the acoustic pressure measured by an earplug microphone, that is connected to a hollow needle. The tip of the needle is moved by a µm translation stage through the field and the signal is recorded using a lock-in amplifier locked to the levitator frequency. The pressure field obtained numerically show good agreement with that obtained experimentally. T2 - 2012 IEEE International Ultrasonics Symposium (IUS) CY - Dresden, Germany DA - 07.10.2012 KW - Acoustic levitation KW - Matrix method KW - Pressure field PY - 2012 SN - 978-1-4673-4562-0 DO - https://doi.org/10.1109/ULTSYM.2012.0690 SP - 2754 EP - 2757 PB - Institute of Electrical and Electronics Engineers (IEEE) CY - Piscataway, NJ AN - OPUS4-32587 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Michalik-Onichimowska, Aleksandra A1 - Beitz, T. A1 - Panne, Ulrich A1 - Löhmannsröben, H.-G. A1 - Riedel, Jens T1 - Laser ionization ion mobility spectrometric interrogation of acoustically levitated droplets N2 - Acoustically levitated droplets have been suggested as compartmentalized, yet wall-less microreactors for high-throughput reaction optimization purposes. The absence of walls is envisioned to simplify up-scaling of the optimized reaction conditions found in the microliter volumes. A consequent pursuance of high-throughput chemistry calls for a fast, robust and sensitive analysis suited for online interrogation. For reaction optimization, targeted Analysis with relatively low sensitivity suffices, while a fast, robust and automated sampling is paramount. To follow this approach, in this contribution, a direct coupling of levitated droplets to a homebuilt ion mobility spectrometer (IMS) is presented. The sampling, Transfer to the gas phase, as well as the ionization are all performed by a single exposure of the sampling volume to the resonant output of a mid-IR laser. Once formed, the nascent spatially and temporally evolving analyte ion cloud needs to be guided out of the acoustically confined trap into the inlet of the ion mobility spectrometer. Since the IMS is operated at ambient pressure, no fluid dynamic along a pressure Gradient can be employed. Instead, the transfer is achieved by the electrostatic potential gradient inside a dual ring electrode ion optics, guiding the analyte ion cloud into the first stage of the IMS linear drift tube accelerator. The design of the appropriate atmospheric pressure ion optics is based on the original vacuum ion optics design of Wiley and McLaren. The obtained experimental results nicely coincide with ion trajectory calculations based on a collisional model. KW - Ambient pressure laser ionization KW - Ionmobility spectrometry KW - Acoustic levitation KW - ion optics PY - 2019 DO - https://doi.org/10.1007/s00216-019-02167-5 VL - 411 IS - 30 SP - 8053 EP - 8061 PB - Springer CY - Heidelberg AN - OPUS4-50132 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - van Wasen, S. A1 - You, Yi A1 - Beck, S. A1 - Riedel, Jens A1 - Volmer, D. A. T1 - Laser Ablation Secondary Electrospray Ionization for In Situ Mass Spectrometric Interrogation of Acoustically-Levitated Droplets N2 - The composition of acoustically levitated droplets was probed by a novel combination of mid-IR laser evaporation and subsequent postionization via secondary electrospray ionization. The combination of microliter samples and subnanoliter sampling provided time-resolved interrogation of droplets and allowed for a kinetic investigation of the laser-induced release of the analyte, which was found to strongly depend on the analytes. The observed substancespecific delayed release of the analytes permitted baseline-separated discrimination of the analytes, ideal for the study of complex samples. The additionally applied postionization scheme was found to enable efficient detection of small volatile compounds as well as peptides. The detection of small molecules and peptides occurred under very different sampling geometries, pointing to two distinct underlying ionization mechanisms. Overall, our results suggest that the experimental setup presented in this study can serve as a widely applicable platform to study chemical reactions in acoustically levitated droplets as model reactors. KW - Acoustic levitation KW - Mass spectrometry KW - Electrospray KW - Laser ablation PY - 2022 DO - https://doi.org/10.1021/acs.analchem.2c03800 SN - 0003-2700 VL - 2022 SP - 1 EP - 5 PB - ACS Publications CY - Washington AN - OPUS4-56531 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -