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Label-free electrical quantification of the dielectrophoretic response of DNA.

Henning A, Henkel J, Bier FF, Hölzel R - PMC Biophys (2008)

Bottom Line: The method has been applied to the characterisation of the dielectrophoretic response of DNA without the need for any chemical modifications.The results are in good agreement with data from dielectrophoretic studies on fluorescently labelled DNA.Extension of the method down to the single molecule level appears feasible.PACS: 87.50.ch, 87.80.Fe, 87.85.fK.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fraunhofer Institute for Biomedical Engineering, Am Mühlenberg 13, 14476 Potsdam-Golm, Germany. ralph.hoelzel@ibmt.fraunhofer.de.

ABSTRACT
A purely electrical sensing scheme is presented that determines the concentration of macromolecules in solution by measuring the capacitance between planar microelectrodes. Concentrations of DNA in the ng/mL range have been used in samples of 1 muL volume. The method has been applied to the characterisation of the dielectrophoretic response of DNA without the need for any chemical modifications. The influence of electrical parameters like duty cycle, voltage and frequency has been investigated. The results are in good agreement with data from dielectrophoretic studies on fluorescently labelled DNA. Extension of the method down to the single molecule level appears feasible.PACS: 87.50.ch, 87.80.Fe, 87.85.fK.

No MeSH data available.


Electrical setup for combined dielectrophoresis and impedance measurement. Electrodes are alternately connected by relays either to the capacitance bridge for measurement or to the DEP signal supply for dielectrophoretic action. A personal computer controls relays, capacitance bridge and RF synthesizer.
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Figure 2: Electrical setup for combined dielectrophoresis and impedance measurement. Electrodes are alternately connected by relays either to the capacitance bridge for measurement or to the DEP signal supply for dielectrophoretic action. A personal computer controls relays, capacitance bridge and RF synthesizer.

Mentions: Usually transformers were used limiting the accessible frequency range as well as the amplitude range. Recently Beck et al. [26] introduced an operational amplifier for this purpose with, however, similar restrictions. Subsequently both signals had to be separated for impedance determination calling for additional low-pass filters [23,26] or a properly balanced bridge [25]. Hölzel and Bier [27] introduced a somewhat different approach by separating DEP and measurement temporally by switching. They used a frequency variable RLC-meter rendering any additional circuitry unnecessary. However, sensitivity and DEP amplitude were limited. For a significant improvement, in particular of the sensitivity, in this work the measurement was performed with an ultra-precision capacitance bridge (Andeen-Hagerling AH 2550A). It was connected to the micro-electrodes through relays (Fig. 2) and was controlled by a personal computer using purpose-built software. The reed relays (Meder) also were computer controlled via the capacitance bridge. The measuring signal of 1 kHz was kept at or below 30 mVRMS to minimise impact on the measurement itself. The dielectrophoresis signal was supplied by an RF synthesizer (Hameg HM 8133-2) and raised to up to 17 VRMS by a power amplifier (Toellner Toe 7606). The synthesizer output could be modulated or gated by a DDS generator (TTi TG 1010 A) giving a variable duty cycle of the DEP field between 0.1% and 100%. DEP field amplitude and duty cycle were monitored by a digital oscilloscope (Agilent MSO 6104 A). All electrical connections were shielded. The input cables to the capacitance bridge were double shielded and arranged close to each other to minimise loop area and, hence, magnetically induced pickup.


Label-free electrical quantification of the dielectrophoretic response of DNA.

Henning A, Henkel J, Bier FF, Hölzel R - PMC Biophys (2008)

Electrical setup for combined dielectrophoresis and impedance measurement. Electrodes are alternately connected by relays either to the capacitance bridge for measurement or to the DEP signal supply for dielectrophoretic action. A personal computer controls relays, capacitance bridge and RF synthesizer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2666632&req=5

Figure 2: Electrical setup for combined dielectrophoresis and impedance measurement. Electrodes are alternately connected by relays either to the capacitance bridge for measurement or to the DEP signal supply for dielectrophoretic action. A personal computer controls relays, capacitance bridge and RF synthesizer.
Mentions: Usually transformers were used limiting the accessible frequency range as well as the amplitude range. Recently Beck et al. [26] introduced an operational amplifier for this purpose with, however, similar restrictions. Subsequently both signals had to be separated for impedance determination calling for additional low-pass filters [23,26] or a properly balanced bridge [25]. Hölzel and Bier [27] introduced a somewhat different approach by separating DEP and measurement temporally by switching. They used a frequency variable RLC-meter rendering any additional circuitry unnecessary. However, sensitivity and DEP amplitude were limited. For a significant improvement, in particular of the sensitivity, in this work the measurement was performed with an ultra-precision capacitance bridge (Andeen-Hagerling AH 2550A). It was connected to the micro-electrodes through relays (Fig. 2) and was controlled by a personal computer using purpose-built software. The reed relays (Meder) also were computer controlled via the capacitance bridge. The measuring signal of 1 kHz was kept at or below 30 mVRMS to minimise impact on the measurement itself. The dielectrophoresis signal was supplied by an RF synthesizer (Hameg HM 8133-2) and raised to up to 17 VRMS by a power amplifier (Toellner Toe 7606). The synthesizer output could be modulated or gated by a DDS generator (TTi TG 1010 A) giving a variable duty cycle of the DEP field between 0.1% and 100%. DEP field amplitude and duty cycle were monitored by a digital oscilloscope (Agilent MSO 6104 A). All electrical connections were shielded. The input cables to the capacitance bridge were double shielded and arranged close to each other to minimise loop area and, hence, magnetically induced pickup.

Bottom Line: The method has been applied to the characterisation of the dielectrophoretic response of DNA without the need for any chemical modifications.The results are in good agreement with data from dielectrophoretic studies on fluorescently labelled DNA.Extension of the method down to the single molecule level appears feasible.PACS: 87.50.ch, 87.80.Fe, 87.85.fK.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fraunhofer Institute for Biomedical Engineering, Am Mühlenberg 13, 14476 Potsdam-Golm, Germany. ralph.hoelzel@ibmt.fraunhofer.de.

ABSTRACT
A purely electrical sensing scheme is presented that determines the concentration of macromolecules in solution by measuring the capacitance between planar microelectrodes. Concentrations of DNA in the ng/mL range have been used in samples of 1 muL volume. The method has been applied to the characterisation of the dielectrophoretic response of DNA without the need for any chemical modifications. The influence of electrical parameters like duty cycle, voltage and frequency has been investigated. The results are in good agreement with data from dielectrophoretic studies on fluorescently labelled DNA. Extension of the method down to the single molecule level appears feasible.PACS: 87.50.ch, 87.80.Fe, 87.85.fK.

No MeSH data available.