Silicon based microfluidic cell for terahertz frequencies

Abstract

We present a detailed analysis of the design, fabrication and testing of a silicon based, microfluidic cell, for transmission terahertz time-domain spectroscopy. The sensitivity of the device is tested through a range of experiments involving primary alcohol/water mixtures. The dielectric properties of these solutions are subsequently extracted using a Nelder–Mead search algorithm, and are in good agreement with literature values obtained via alternative techniques. Quantities in the order of 2 μmol can be easily distinguished for primary alcohols in solution, even with the subwavelength optical path lengths used. A further display of the device sensitivity is shown through the analysis of commercial whiskeys, where there are clear, detectable differences between samples. Slight absorption variations were identified between samples of the same commercial brand, owing to a 2.5% difference in their alcoholic content. Results from data taken on subsequent days after system realignment are also presented, confirming the robustness of the technique, and the data extraction algorithm used. One final experiment, showing the possible use of this device to analyze aqueous biological samples is detailed; where biotin, a molecule known for its specific terahertz absorptions, is analyzed in solution. The device sensitivity is once again displayed, where quantities of 3 nmol can be clearly detected between samples.

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

“…76 In addition, microfluidic devices for liquid spectroscopy have also been demonstrated. 77 As soon as other molecules, such as carbohydrates or proteins, are dissolved in water, it is possible to distinguish between different populations of water molecules based on the change in the relaxational dynamics because the water molecules that are part of the solvation shell exhibit a significantly different dynamics than the bulk water molecules. This concept was applied to study a wide range of molecular interactions of biomolecules during solvation: lactose; 78 threhalose, lactose, and glucose; 79 among others.…”

Nanofluidic terahertz metasensor for sensing in aqueous environment

“…This is extremely critical for sensing of biological molecules in aqueous solution, since THz absorption by water is significantly large and has been a challenge to THz spectroscopy for biological sensing. 34 Earlier reports using the THz metamaterial for sensing of sugars, 35 yeast, 36 virus, 37,38 and other biomaterials 39,40 have been carried out under dehydrated conditions. 41 Few studies have demonstrated sensing with THz metamaterial in aqueous environment by confining aqueous solution at the microscale level.…”

“…41 Few studies have demonstrated sensing with THz metamaterial in aqueous environment by confining aqueous solution at the microscale level. 34,[42][43][44][45] However, further reduction of the analyte volume to the nanoscale level would aid in much higher sensitivity of detection as the absorption from water could be greatly reduced. More interestingly, confinement of liquid in extremely small space also allows for efficient delivery of molecules to the sensing area, and the recent effort in the field of microfluidics has scaled down the interaction space to nanometer size.…”

Integrated On-Chip THz Sensors for Fluidic Systems Fabricated Using Flexible Polyimide Films

“…Free-space THz measurements typically employ a transmission geometry, using a suitably thin sample cell to minimise attenuation [2]. However, the closely-spaced material interfaces of the cell introduce etalons into the measured time-domain signal, arising from interfacial reflections, which can adversely affect subsequent data analysis.…”