Probing Interactions at the Nanoscale: Sensing Protein Molecules

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Introduction We have developed a high-frequency electronic biosensor of parallel-plate geometry that is embedded within a microfluidic device. This novel biosensor allows us to perform dielectric spectroscopy on a variety of biological samples—from cells to molecules—in solution. Because it is purely electronic, the sensor allows for rapid characterization with no sample preparation or chemical alteration. In addition, it is capable of probing length scales from millimeters to microns over a frequency range 50 MHz to 40 GHz, and sample volumes as small as picoliters [1,2]. Our high-frequency biosensor has evolved from previous device designs based on a coplanar waveguide (CPW) ... continued below

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Sohn, Lydia; Weiss, Ron & Tavazoie, Saeed September 15, 2003.

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Introduction We have developed a high-frequency electronic biosensor of parallel-plate geometry that is embedded within a microfluidic device. This novel biosensor allows us to perform dielectric spectroscopy on a variety of biological samples—from cells to molecules—in solution. Because it is purely electronic, the sensor allows for rapid characterization with no sample preparation or chemical alteration. In addition, it is capable of probing length scales from millimeters to microns over a frequency range 50 MHz to 40 GHz, and sample volumes as small as picoliters [1,2]. Our high-frequency biosensor has evolved from previous device designs based on a coplanar waveguide (CPW) geometry [2]. For our current device, we employ microfluidic tectonics (µFT) [3] to embed two microstrip conductors within a microfluidic channel. The electronic coupling between the two conductors is greater than in our previous CPW design and more importantly, leads to an enhanced sensitivity. Our utilization of µFT allows us to incorporate easily this high-frequency electronic biosensor with a variety of lab-on-a-chip architectures. Device Description Figure 1 is a schematic of our high-frequency electronic biosensor. We fabricate this sensor by first depositing a 500 Å seed layer of gold onto two glass microscope slides. We then use photolithography to pattern the gold that is subsequently electroplated to a thickness of 4-6 µm. After reactive-ion etching the photoresist and removing the unplated gold with a standard iodine-based gold etchant, we align the two slides under a microscope such that the microstrip conductors overlap one another in a parallel-plate geometry (80 µm x 500 µm). We control the separation between the microstrip conductors using gold foil spacers 3–25 µm thick. The foil additionally ensures coupling between the grounds on each slide. Following alignment, we employ µFT to bond the two glass slides together and to create a microfluidic channel running perpendicular to the microstrip conductors (see Figure 1). We complete the device by inserting 0.02” ID vinyl tubing through predrilled input and output holes of the device [3]. All of our devices are designed to have a 50 Ω matched impedance and minimal insertion loss for 0.05 – 40 GHz. With these characteristics, we expect a sensitivity of 0.05 dB. Results By accessing frequencies > 20 GHz with our device, we can probe unique low-frequency vibrational or rotational modes of bio-macromolecules, since at these frequencies the counterions have fully relaxed, the dipole moment of water is rapidly decreasing, and the macroscopic distortions of macromolecules become important and are reflected in the obtained spectra. As a first demonstration, we have measured PCR products. We are able to distinguish between non-reacted primers for PCR amplification and reacted PCR products (24 amplification cycles). Figure 2 shows representative spectra of the two different DNA solutions obtained from a single device and scaled to DI water. We have obtained similar spectral features from additional devices and are currently developing a quantitative model to explain our results. This initial demonstration of molecular differentiation using a high-frequency electronic biosensor shows the great promise of electronic biosensing.

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  • Report No.: DOE/ER/15355-1
  • Grant Number: FG02-02ER15355
  • DOI: 10.2172/940829 | External Link
  • Office of Scientific & Technical Information Report Number: 940829
  • Archival Resource Key: ark:/67531/metadc896815

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  • September 15, 2003

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  • Sept. 27, 2016, 1:39 a.m.

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  • Jan. 9, 2018, 6:04 p.m.

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Sohn, Lydia; Weiss, Ron & Tavazoie, Saeed. Probing Interactions at the Nanoscale: Sensing Protein Molecules, report, September 15, 2003; United States. (digital.library.unt.edu/ark:/67531/metadc896815/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.