A high-sensitivity THz-sensing technology for DNA detection with split-ring resonator based biochips

The detection and characterization of dielectric thin-films and biomolecules are of great interest for THz-research due to characteristic material properties at these frequencies. The detection of films much thinner than wavelength or material amounts in femtomol range requires specialized sensors. The sensors identify a material’s permittivity, or refractive index, respectively, by a signal delay in the time domain or the detuning of a resonator in the frequency domain. A biochip in particular aims at the detection of sub-μm-size molecules, such as DNA or proteins. This work begins with a review of the state-of-the-art THz-thin-film sensing approaches evolving towards lower film thicknesses. These indicate that more promising results are achieved with high-Q resonators due to their more efficient sample/E-field interaction. The asymmetric double-split ring resonator (aDSR) is researched, exhibiting a sharp resonance feature and a strong concentration of the electric field. In a two-dimensional array, corresponding to a frequency selective surface, the aDSR qualifies as the basic element for a biochip with a high sensitivity. For the biochip development material properties as well as practical and commercial aspects are taken into account. The result is a glass chip with a structured three-layer metal surface and undercut edges. With regard to practical aspects, a biochip reader is developed being compact, easy to use, of low-maintenance and affordable, to find application in biomedical laboratories. The reader is essentially a fully-electronic spectrometer for 240 – 320 GHz, reading a single measurement spot in 110 Milliseconds. Compared to a classical network analyzer, the setup has reduced complexity and cost. It generates the high frequencies from a single voltage controlled oscillator by upconverting in diode-based mixers. Heterodyne detection is realized by utilizing the time delay of the signal sweeping through the frequency band. The functionality of biochip and reader is compared to TDS measurements proving good results. The detection of dielectric thin-films is successfully applied with dye, photo-resist and gelatin. Hybridized DNA, deposited locally by a functionalization process, is detected. However, the DNA detection could not be confirmed by additional measurements. Causes for this failure are investigated and discussed.