TY  - JOUR
A1  - Prüfer, Mareike
A1  - Wenger, Christian
A1  - Bier, Frank Fabian
A1  - Laux, Eva-Maria
A1  - Hölzel, Ralph
T1  - Activity of AC electrokinetically immobilized horseradish peroxidase
JF  - Electrophoresis : microfluidics, nanoanalysis & proteomics
N2  - 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.
KW  - AC electrokinetics
KW  - dielectrophoresis
KW  - enzyme activity
KW  - immobilization;
KW  - nanoelectrodes
Y1  - 2022
U6  - https://doi.org/10.1002/elps.202200073
SN  - 0173-0835
SN  - 1522-2683
SP  - 1920
EP  - 1933
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Laux, Eva-Maria
A1  - Bier, Frank Fabian
A1  - Hölzel, Ralph
T1  - Electrode-based AC electrokinetics of proteins
BT  - a mini-review
JF  - Bioelectrochemistry : official journal of the Bioelectrochemical Society ; an international journal devoted to electrochemical aspects of biology and biological aspects of electrochemistry
N2  - Employing electric phenomena for the spatial manipulation of bioparticles from whole cells down to dissolved molecules has become a useful tool in biotechnology and analytics. AC electrokinetic effects like dielectrophoresis and AC electroosmosis are increasingly used to concentrate, separate and immobilize DNA and proteins. With the advance of photolithographical micro- and nanofabrication methods, novel or improved bioanalytical applications benefit from concentrating analytes, signal enhancement and locally controlled immobilization by AC electrokinetic effects. In this review of AC electrokinetics of proteins, the respective studies are classified according to their different electrode geometries: individual electrode pairs, interdigitated electrodes, quadrupole electrodes, and 3D configurations of electrode arrays. Known advantages and disadvantages of each layout are discussed.
KW  - AC electrokinetics
KW  - Dielectrophoresis
KW  - Electrodes
KW  - Electroosmosis
KW  - Proteins
Y1  - 2017
U6  - https://doi.org/10.1016/j.bioelechem.2017.11.010
SN  - 1567-5394
SN  - 1878-562X
VL  - 120
SP  - 76
EP  - 82
PB  - Elsevier B.V.
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Stanke, Sandra
A1  - Wenger, Christian
A1  - Bier, Frank Fabian
A1  - Hölzel, Ralph
T1  - AC electrokinetic immobilization of influenza virus
JF  - Electrophoresis : microfluids & proteomics
N2  - 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.
KW  - AC electrokinetics
KW  - AC electroosmosis
KW  - dielectrophoresis
KW  - influenza virus
KW  - nanoelectrodes
Y1  - 2022
U6  - https://doi.org/10.1002/elps.202100324
SN  - 0173-0835
SN  - 1522-2683
VL  - 43
IS  - 12
SP  - 1309
EP  - 1321
PB  - Wiley-Blackwell
CY  - Weinheim
ER  -