Name: terahertz microfluidic sensing using a parallel-plate waveguide sensor
Uploaded: 2012-08-30T13:00:00
Description: Watch this Scientific Journal Video about Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor at JoVE.com

This project was supported in part by the National Science Foundation and by the Air Force Research Laboratory through the CONTACT program.

1. Sensor Design and Fabrication
<ol>
 <li>Design a parallel-plate waveguide with one or more integrated cavities (or "grooves"). See Figures 1 and 2. Geometry may be based on that given in our previous publications 8,9 or specially designed for the particular application. The following general guiding principles are suggested:
 <ol>
 <li>Plate Spacing: In this experiment a plate spacing of 1mm is used for effective coupling to the TE1 mode without the need for special opti...

<ol>
	<li>Kuswandi, B., Nuriman, ., Huskens, J., Verboom, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+sensing+systems+for+microfluidic+devices:+A+review.">Optical sensing systems for microfluidic devices: A review.</a> Ana. Chim. Acta. 601, 141-155 (2007).</li><li>Zhu, H., White, I. M., Suter, J. D., Zourob, M., Fan, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrated+refractive+index+optical+ring+resonator+detector+for+capillary+electrophoresis.">Integrated refractive index optical ring resonator detector for capillary electrophoresis.</a> Anal. Chem. 79, 930-937 (2007).</li><li>Kurt, H., Citrin, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coupled-resonator+optical+waveguides+for+biochemical+sensing+of+nanoliter+volumes+of+analyte+in+the+terahertz+region.">Coupled-resonator optical waveguides for biochemical sensing of nanoliter volumes of analyte in the terahertz region.</a> Appl. Phys. Lett. 87, 241119 (2005).</li><li>Debus, C., Bolivar, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Frequency+selective+surfaces+for+high+sensitivity+terahertz+sensing.">Frequency selective surfaces for high sensitivity terahertz sensing.</a> Appl. Phys. Lett. 91, 184102 (2007).</li><li>Harsha, S. S., Laman, N., Grischkowsky, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Q+terahertz+Bragg+rsonances+within+a+metal+parallel+plate+waveguide.">High-Q terahertz Bragg rsonances within a metal parallel plate waveguide.</a> Appl. Phys. Lett. 94, 091118 (2009).</li><li>Mendis, R., Mittleman, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+the+lowest-order+transverse-electric+(TE1)+and+transverse-magnetic+(TEM)+modes+of+the+parallel-plate+waveguide+for+terahertz+pulse+applications.">Comparison of the lowest-order transverse-electric (TE1) and transverse-magnetic (TEM) modes of the parallel-plate waveguide for terahertz pulse applications.</a> Optics Express. 17, 14839-14850 (2009).</li><li>Mendis, R., Mittleman, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+investigation+of+the+lowest-order+transverse-electric+(TE1)+mode+of+the+parallel-plate+waveguide+for+THz+pulse+propagation.">An investigation of the lowest-order transverse-electric (TE1) mode of the parallel-plate waveguide for THz pulse propagation.</a> JOSA B. 26, A6-A13 (2009).</li><li>Astley, V., McCracken, B., Mendis, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+rectangular+resonant+cavities+in+terahertz+parallel-plate+waveguides.">Analysis of rectangular resonant cavities in terahertz parallel-plate waveguides.</a> Opt. Lett. 36, 1452 (2011).</li><li>Mendis, R., Astley, V., Liu, J., Mittleman, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Terahertz+microfluidic+sensor+based+on+a+parallel-plate-waveguide+resonant+cavity.">Terahertz microfluidic sensor based on a parallel-plate-waveguide resonant cavity.</a> Appl. Phys. Lett. 95, 171113 (2009).</li><li>Astley, V., Reichel, K., Jones, J., Mendis, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Terahertz+multichannel+microfluidic+sensor+based+on+parallel-plate+waveguide+resonant+cavities.">Terahertz multichannel microfluidic sensor based on parallel-plate waveguide resonant cavities.</a> Appl. Phys. Lett. , (2012).</li></ol>

It should be noted that the refractive index of the liquid under test is determined only at the frequency of the cavity resonance, not over a broad bandwidth. This has a few distinct advantages. First, although our measurements have made use of a broadband terahertz source for characterization purposes, one could also build an equivalent sensing system with a single-frequency THz source with only a limited degree of frequency tunability, an approach that could be much less expensive and more compact. Second, the ...

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 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments (optional)</td>
 </tr>
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 <td>10 &mu;l syringe</td>
 <td>Hamilton</td>
 <td>80314</td>
 <td>High precision syringe</td>
 </tr>
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 <td>Liquid alkanes </td>
 <td>Acros Organics</td>
 <td></td>
 <td>Samples for calibration and testing</td>
 </tr>
<tr>
 <td></td>
<td></td>
<td></td>
<td>No specific equipment is required. Suitable test materials and solvents are left to the experimenter's discretion. The high-precision syringes used in this procedure are listed in the table below, but the experimenter may wish to use syringes of a different volume or design, including digital syringes for improved accuracy. The test alkanes used in this experiment are also listed.
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 </tbody>
</table>

terahertz microfluidic sensing using a parallel-plate waveguide sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators 1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.
Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides 3, asymmetric split-ring resonators 4, and photonic band gap structures integrated into parallel-plate waveguides 5. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.
The sensor design we use here is based on a simple parallel-plate waveguide 6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE1) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove 6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index 9.
Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves 10. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.

Watch this Scientific Journal Video about Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor at JoVE.com

Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

The procedure for implementing a refractive index sensor for terahertz frequencies based on a grooved parallel-plate waveguide geometry is described here. The method yields a measurement of the refractive index of a small volume of liquid through monitoring of the shift in the resonant frequency of the waveguide structure

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic ...

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