Since several subtypes of Avian Influenza (AI) viruses, frequently causing worldwide outbreaks, are extremely pathogenic, a development of quick and accurate diagnostic methods has been highly demanded (see details in Supplementary Information). In order to investigate fundamental optical characteristics of targeted virus samples, THz transmission measurements without any assistive sensing chip were performed firstly. The targeted three virus samples are: A/NWS/33 (H1N1), A/wild bird/Korea/K09-652/2009 (H5N2), and A/Korean native chicken/Korea/K040110/2010 (H9N2), as shown in Table 1. Among three different virus samples, we chose the H9N2 subtype virus and control (without inoculation of any virus) in pellet forms after freeze-drying process. An absorbance was extracted from the transmission measurement through a pallet type sample in a same way described in ref. 10. The H9N2 and control samples have no recognizable absorption features in the THz spectrum (Fig. 1a) due to superposition of many protein vibration modes and inhomogeneous broadening of absorption features17. In contrast to earlier works10–12, it is not easy to define fundamental resonance frequency to design nano-antenna based sensing chip for the target bio sample in this case without unique spectral features from their intrinsic modes. In this experiment, therefore, multi-resonance nano-antenna was suggested which is based on the concept of THz nano-antennas with a log-periodic alignment18. For an optically unknown target molecules, the multi-resonance nano-antenna is very useful, since it maintains very high sensitivity in ultrabroadband THz regime.Table 1The strain names with subtype and total protein concentration of each virus samples are represented.Subtype-strain nameTotal protein concentration (mg/ml)A/NWS/33 (H1N1)0.54A/wild bird/Korea/K09-652/2009 (H5N2)0.2A/Korean native chicken/Korea/k040110/2010 (H9N2)0.28 Figure 1THz detection of virus samples. (a) Absorption spectra for pallet types of virus included a protein sample (H9N2) and a control sample without virus in it. (b) A conceptual schematic of THz detection of virus samples in liquid state using a nano slot-antenna array based sensing chip. (c) Optical images of dropped virus solutions onto the multi-resonance nano-antenna array before (top) and after (down) THz excitation. (d) Transmittance spectra through multi-resonance nano-antenna that have three resonance peaks, with and without H9N2 sample onto the antenna. (e) The difference in transmitted intensity (ΔT) and shifted resonance frequency from each fundamental resonance peak of multi-resonance nano-antenna (Δf) for H9N2 sample are represented.