Supplementary Information for
Detection of microorganisms using terahertz
metamaterials
S. J. Park,1 J. T. Hong,1 S. J. Choi,2 H. S. Kim,2 W. K. Park,3 S. T. Han,3 J. Y. Park,1 S. Lee,1
D. S. Kim,4 and Y. H. Ahn1
1
Department of Physics and Division of Energy Systems Research, Ajou University, Suwon
443-749, Korea
2
Department of Biological Science, Ajou University, Suwon 443-749, Korea
3
Advanced Medical Device Research Center, Korea Electrotechnology Research Institute,
Ansan 426-170, Korea
4
Center for Subwavelength Optics and Department of Physics and Astronomy, Seoul National
University, Seoul 151-747, Korea
1
Figure S1. THz transmission on a plain substrate with deposition of yeasts and E. coli:
(a) THz transmission amplitudes, for transmission through a plain Si substrate, with (red
solid line) and without (black dashed line) deposition of yeasts. (inset) A microscopic image
of yeasts deposited on a Si substrate with a density of 0.048/µm2. (b) THz transmission
before (black line) and after (red line) the deposition of E. coli (inset) in aqueous environment.
No noticeable change in transmission amplitude was found following the deposition of the
yeasts and E. coli compared to the bare substrate case.
2
Figure S2. Metamaterials sensing on different kinds of fungi such as yeasts, neurospora,
and niger: (a) Microscopic image of metamaterials patterns on Si substrate with the
deposition of yeasts (left) and the corresponding THz transmission amplitudes measured
before (blue line) and after (red line) the deposition. (b) and (c) Those of (a) for the
deposition of Neurospora sitophila (KACC 40972; neurospora) and Aspergillus niger
(KACC 40280; niger), respectively. All the fungi were obtained from the Korean Agricultural
Culture Collection (KACC) and were grown by a streaking on medium method followed by
the incubation at 37 °C for 2 days. The culture media used for the neurospora and niger were
potato dextrose agar and malt extract agar, respectively.
3
Figure S3. Sensing with different types of metamaterial patterns: (a) Microscopic image
of metamaterials with single split ring resonators (S-SRR) on a Si substrate with the
deposition of yeasts (left) and the corresponding THz transmission amplitudes measured
before (blue line) and after (red line) the deposition. The S-SRR pattern has a linewidth of 4
μm, gap size of 3 μm, and a periodicity of 50 μm. (b) Same with (a) but with different
metamaterials of double split ring resonator (D-SRR) for the detection of yeasts. The D-SRR
pattern has a linewidth of 4 μm, and gap size of 4 μm, and a periodicity of 50 μm.
4
Figure S4. Dielectric constant measurements of E. coli and sensing in ambient
condition: (a) Plots of frequency-dependent, complex dielectric constants of the E. coli films,
extracted from the THz transmission experiments. Films’ thickness was 280 μm. (b) The
dielectric constants of the individual E. coli, extracted from (a) by using a Maxwell-Garnet
theory with the fill factor of 0.72–0.9, assuming that it consists of the closely packed
cylinders (Li et al., Chin. Sci. Bull. 55, 114 (2010).) (c) Microscopic image of functionalized
metamaterials on Si substrate with the deposition of E. coli (d) Corresponding THz
transmission amplitudes measured before (blue line) and after (red line) the deposition. The
resonant peak shows a red-shift in ambient condition, whereas it shows a blue-shift in a liquid
environment as shown in the main text.
5
Figure S5. Resonant frequency of metamaterials as a function of the substrate index:
Finite-difference time-domain (FDTD) simulation results for the effective index ( neff ) as a
function of substrate index ( nsub ), where the substrate dependent resonant frequency f res is
expressed as f res  f air / neff , with f air the resonant frequency for nsub  nair  1 . The
geometrical parameters used for the simulation is depicted in the inset. By fitting the data, we
found the relation of neff  0.672nsub  0.265nair , in other words, the effective index in the
case of the silicon substrate ( nSi  3.38 ) is determined at neff  2.53 (  eff  6.40 ).
6
Figure S6. FDTD simulation results for the resonant peak shift as a function of the
dielectric constants: (a) 2D cross-sectional plots of the electric field strength at the resonant
frequency, extracted from the FDTD simulation for THz transmission through the
metamaterials with the gap size of 2 μm and 3 μm. The diameter of the sphere was 2 μm with
the dielectric constant of εf = 8. (b) Resonant frequency shifts as a function of εf for the gapsizes of 2 μm (red circles) and 3 μm (blue boxes), respectively. Note that the frequency shift
is higher (i.e., more sensitive) when the gap size is small.
7
Figure S7. FDTD simulation results for different locations of fungi: (a) Image of
metamaterials pattern used for FDTD simulations with a series of dielectric spheres
positioned in the gap-area (with a diameter of 2 μm and a dielectric constant of  f  8 ). (b)
Image of metamaterial patterns with ten dielectric spheres scattered outside the gap area. (c)
FDTD simulations for THz transmission amplitude for (a) (blue solid line) and (b) (red solid
line), respectively. Shown together with black dashed line is the data without the dielectric
spheres. This shows that the resonant frequency shift of the inductive-capacitive resonance is
governed by the fungi located in the gap area.
8