@article{StankeWengerBieretal.2022,
  author    = {Stanke, Sandra and Wenger, Christian and Bier, Frank Fabian and H{\"o}lzel, Ralph},
  title     = {AC electrokinetic immobilization of influenza virus},
  series = {Electrophoresis : microfluids \& proteomics},
  volume    = {43},
  journal   = {Electrophoresis : microfluids \& proteomics},
  number    = {12},
  publisher = {Wiley-Blackwell},
  address   = {Weinheim},
  issn      = {0173-0835},
  doi       = {10.1002/elps.202100324},
  pages     = {1309 -- 1321},
  year      = {2022},
  abstract  = {The use of alternating current (AC) electrokinetic forces, like dielectrophoresis and AC electroosmosis, as a simple and fast method to immobilize sub-micrometer objects onto nanoelectrode arrays is presented. Due to its medical relevance, the influenza virus is chosen as a model organism. One of the outstanding features is that the immobilization of viral material to the electrodes can be achieved permanently, allowing subsequent handling independently from the electrical setup. Thus, by using merely electric fields, we demonstrate that the need of prior chemical surface modification could become obsolete. The accumulation of viral material over time is observed by fluorescence microscopy. The influences of side effects like electrothermal fluid flow, causing a fluid motion above the electrodes and causing an intensity gradient within the electrode array, are discussed. Due to the improved resolution by combining fluorescence microscopy with deconvolution, it is shown that the viral material is mainly drawn to the electrode edge and to a lesser extent to the electrode surface. Finally, areas of application for this functionalization technique are presented.},
  language  = {en}
}
@article{PrueferWengerBieretal.2022,
  author    = {Pr{\"u}fer, Mareike and Wenger, Christian and Bier, Frank Fabian and Laux, Eva-Maria and H{\"o}lzel, Ralph},
  title     = {Activity of AC electrokinetically immobilized horseradish peroxidase},
  series = {Electrophoresis : microfluidics, nanoanalysis \& proteomics},
  journal   = {Electrophoresis : microfluidics, nanoanalysis \& proteomics},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0173-0835},
  doi       = {10.1002/elps.202200073},
  pages     = {1920 -- 1933},
  year      = {2022},
  abstract  = {Dielectrophoresis (DEP) is an AC electrokinetic effect mainly used to manipulate cells. Smaller particles, like virions, antibodies, enzymes, and even dye molecules can be immobilized by DEP as well. In principle, it was shown that enzymes are active after immobilization by DEP, but no quantification of the retained activity was reported so far. In this study, the activity of the enzyme horseradish peroxidase (HRP) is quantified after immobilization by DEP. For this, HRP is immobilized on regular arrays of titanium nitride ring electrodes of 500 nm diameter and 20 nm widths. The activity of HRP on the electrode chip is measured with a limit of detection of 60 fg HRP by observing the enzymatic turnover of Amplex Red and H2O2 to fluorescent resorufin by fluorescence microscopy. The initial activity of the permanently immobilized HRP equals up to 45\% of the activity that can be expected for an ideal monolayer of HRP molecules on all electrodes of the array. Localization of the immobilizate on the electrodes is accomplished by staining with the fluorescent product of the enzyme reaction. The high residual activity of enzymes after AC field induced immobilization shows the method's suitability for biosensing and research applications.},
  language  = {en}
}