Page 20 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 3 – Internet of Bio-Nano Things for health applications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 3

Therefore, there is still a need for a bottom-up physical kinetics of DNA
modeling approach originating from irst principles, cap‑ hybridization.
turing all interactions in practical transmitter, channel Biological MC testbeds have also been reported by many
and receiver architectures, causing nonlinear and research groups. For example, in [73] and [74],
authors implement a micro luidic MC testbed with
time‑varying behavior and unconventional noise and
genetically en‑ gineered Escherichia coli (E. coli)
interference that may have decisive impacts on the
bacteria acting as receiver nanomachines. The
development of MC techniques for IoBNT.
bacteria in these studies have been engineered to
c) Experimental MC System Testbeds and respond to certain biomolecules, e.g., N‑(3‑Oxyhe-
xanoyl)‑L‑homoserine lactone (C6‑HSL) and N‑Acyl
Practical Demonstrations: Testbeds are crucial for
homoserine lactone (AHL), by expressing green
validating theoretical models, and practically
luorescent proteins (GFP), which can later be detected
evaluating the performance of new communication
via luorescent microscopy upon excitation with light
techniques. However, research for building expe-
of certain wavelengths. Both studies report extremely
rimental MC systems has just recently gained
low communication rates on the order of 1 bit/hour
momentum. Few studies in MC literature have focused
due to the lengthy process of gene expression required
on ‘macroscale’ implementation of MC systems with
for each bit transmission. In [75], the authors prefer
off‑the‑shelf components. For example, in [66, 70], the
a different approach by exploiting the
isopropyl alcohol (IPA) is used as airborne in‑
light‑responsive proton pump gloeorhodopsin (GR)
formation carriers, and commercially available metal
located in the bacterial membrane to obtain
oxide semiconductor alcohol sensors are used as the
an optically controlled MC transmitter that can
MC receiver. The transmission of molecules is
export protons into the luidic channel upon the
realized by electrically‑controlled spray nozzles. In
application of external light stimuli. Accordingly,
[71], the information is encoded in pH level of the
protons are used as information carriers, which
transmitted luid instead of molecular concentration or
propagate through structural diffusion in water, and
type. The acidic and basic luids are injected into
are detected by a pH sensor acting as the receiver.
off‑the‑shelf lexible tubes via peristaltic pumps, and a
Using this testbed, the authors report commu-
macroscale pH meter is used as the MC receiver. In
nication rates on the order of 1 bit/
another testbed [67], magnetic nanoparticles (MNs)
minute. Although biological designs have been
are employed as information carriers, which are
demonstrated individually for both MC transmitter
injected into off‑the‑shelf mm‑scale lexible tubes by
and receiver, there is yet to be any practical
low pumps, and propagate through convection and
implementation of an entirely biological testbed
diffusion. In this study, for the detection of messages
for end‑to‑end MC.
encoded into MN concentration, the authors designed
bulky detector coils placed around the tubes coupled d) Development of MC Techniques: The unconven‑
with capacitors to form a resonator circuit, which tional characteristics of MC, such as discrete nature of
informs about the concentration through a change in in‑ information carriers and slow nature of propagation
ductance and shift in resonance frequency. In this imple‑ mechanisms, which bear no similarity to conventional
mentation, the designed receiver acts only as an EM communications, lead to various challenges, such as
observer, and does not physically interact with the high channel memory causing severe ISI, non‑Gaussian
information carrier molecules. The focus of the noise sources, time‑variance, and very low communica‑
aforementioned studies is on macroscale MC using tion rates, as revealed by several theoretical investiga‑
commercially available channels, and off‑the‑shelf tions [62, 13]. The initial experimental studies performed
sensors or bulky detectors as receivers that are not on both macro‑ and micro‑scales also demonstrated the
physically relevant for the application domain of MC and high level of nonlinearity mainly resulting from the cha-
IoBNT. racteristics of sensors utilized as receivers [66, 70,
72]. One can expect that practical MC system
Recently, the irst micro/nanoscale demonstration of an
implementations for IoBNT applications may face many
MC system is reported in [72]. In this study, the au‑
more challenges, such as molecular interference due to
thors provide the results of MC experiments using a
existence of different types of molecules in the channel,
custom‑made micro luidic testbed with a graphene FET
environmental luctuations, such as those in low
DNA biosensor‑based MC receiver integrated into a mi‑
velocity and temperature, ionic screening in
cro luidic channel. A commercially available micro luidic
physiologically relevant environments preventing the
low control system is used to pump single‑stranded
receiver from detecting the electrical charges of
DNA (ssDNA) molecules of different molecular
information molecules, and new noise sources such as
concentrations into the micro luidic channel. Graphene
electronic 1/f noise in nanomaterial‑based MC
transducer chan‑ nel of the receiver functionalized with
receivers. Therefore, MC requires new com‑
complementary ss‑ DNAs transduces the real‑time
munication methods that account for these peculiarities,
concentration of the propagating DNA molecules into
and overcome their detrimental effects on the communi‑
electrical signals, which are then used for detection.
cation performance. Considering physical limitations of
The authors of the study report nM‑level sensitivity and
the envisioned BNTs, these techniques should be also low‑
single‑base‑pair‑mismatch selec‑ tivity for the receiver.
complexity and low‑energy, i.e., low‑molecule‑use.
However, they also note the very low communication
We summarize some of the major problems stemming
rates on the order of 1 bit/minute, mainly resulting
from the limitations associated with the physical proper‑
8 © International Telecommunication Union, 2021