Fast and accurate tools for detection and analysis of biomolecules are essential for modern medicine and healthcare. One example over all is DNA detection, where high sensitivity and high specificity are main keywords. What is typically done in conventional approaches is to employ amplification techniques to improve the limit of detection as well as fluorescence labelling to target specific DNA strands. Not only are these techniques time-consuming, but even worse they may alter the DNA itself. On paper, Terahertz radiation offers good alternatives, because biomolecular interactions exhibit resonances in this frequency range, but the sensitivity of THz biosensors reported so far has been rather poor.

This work by C. Weisenstein and co-workers sounds as a dramatic step forward in the field. They exploited resonance-enhanced interaction of THz radiation with DNA samples in an array of asymmetric double split ring resonators (aDSRRs), which are selectively functionalized to interact with specific DNA strands. The aDSRR design was optimized in order to exhibit a sharp resonance around a frequency of 0.28 THz, and an all-electronic spectroscopic system was employed to detect resonant frequency shifts as low as 6 MHz when the device is loaded with DNA. Results demonstrate a detection limit as low as 1.55 × 10^-12 mol/l (that is only 4.64 × 10^-18 mol of molecules) without any amplification process. In other words, this device performs one million times better than state-of-the-art THz biosensors. An impressive leap forward indeed and clear evidence of what we could do with THz radiation in the near future.  

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