Page 18 - 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

Example MC scenarios between pairs of nanomachines a) Transmitter and Receiver Architectures for MC:
are depicted in Fig. 2, where the messages are encoded There are mainly two design approaches considered for
into the concentration of molecules, and then transmit‑ icial nanomachines that can perform MC and form
ted to the receiver via molecular propagation in a luidic MC nanonetworks within the IoBNT framework. The
channel. The information can also be encoded into the irst approach is to build the components of nanoma‑
type, release time, or the electronic state of the molecules chines using newly discovered nanomaterials, such as
[8]. Different kinds of propagation methods for mole- two‑dimensional graphene, and one‑dimensional silicon
cular messages are investigated in the literature, such nanowire (SiNW) and carbon nanotube (CNT), which all
manifest extraordinary characteristics at the interface of
as passive diffusion, active transport with molecular
biology and electronics [55]. The other approach re‑
mo‑ tors [49], convection, and transport through gap
lies on synthetic biology, and envisions the use of en‑
junctions [50]. Among these, passive diffusion is the
gineered, i.e., genetically ied, bacteria as arti icial
most promis‑ ing, as it does not require energy
nanomachines with communication functionalities wired
consumption, and thus perfectly suits the energy
into their intracellular signaling networks [24].
limitations of the envisioned nanomachines.
The physical nature of the BNTs determines the potential
transmitter and receiver architectures. The MC transmit‑
Engineered Bacteria-based ter of a BNT should perform the modulation of MC signals,
Biological MC-Transceivers
and the release of molecules into the channel upon a sti-
mulation by an external source, or as a result of an
internal biochemical or electrical process. The receiver
of a BNT is responsible for detecting the incoming
molecular mes‑ sages, transducing them into a
Information
Molecules processable signal, and extracting the encoded
information through signal processing. The decoded
Transmitter MC Channel Receiver information can then be used by the BNT to perform a
Transmitted Received
Signal Signal prescribed operation, e.g., modulation of gene
Information expression or translocation. Therefore, the per‑
Molecules formance of the transmitter and receiver is critical for the
proper operation of a BNT within an IoBNT application.
Nanomaterial‑based design approaches for MC transmit‑
ter mainly draw on the existing drug delivery technolo‑
gies, such as stimuli‑responsive hydrogels, molecule re‑
lease rate of which is controlled by an electrical or
chemical stimuli. Synthetic biology‑based approaches,
Electrical Stimuli-responsive Graphene Biosensor-based on the other hand, rely on making use of the already
Hydrogel/Graphene MC Transmitter MC Receiver existing molecule release mechanisms of living cells,
and tailoring these functionalities through genetic
Fig. 2 – Components of an MC system with biological and nanomaterial‑ modi ications to realize the desired MC modulation
based MC transmitter and receiver design approaches. schemes. There are also theoretical MC transmitter
designs that exploit stimuli‑responsive ion channels to
trigger the release of molecules in an externally
MC channel has many peculiar characteristics. For
controllable fashion [56]. Nanomaterial‑based receiver
example, the discrete nature of information carriers,
designs are widely inspired by nanobiosensors, which
i.e., molecules, results in molecular counting noise, which
share a common objective with MC receivers, that is to
is of similar nature with the shot noise occurring in
transduce biomolecular signals into a signal form
photonic devices [51]. The stochastic nature of the suitable for processing. Although there are many
ligand‑receptor binding process occurring at the receiver
nanobiosensor designs differing in their transducing
gives rise to colored noise, also leading to a strong mechanisms and the resulting signal form at the output,
correlation between molecular propagation process and ield‑effect‑transistor (FET)‑based nanobiosensors
reception [52]. The slow nature of diffusion leads to a have attracted the most attention for MC receiver
substantial amount of channel memory, which in turn, design due to their scalability, simple design similar to
causes severe inter-symbol interference (ISI), and limits conventional FETs, internal signal ampli ication by elec‑
the achievable data transmission rates [53]. The same trical ield‑effect, label‑free operation, and the electri‑
reason also causes a signi icant delay in the cal output signals that allow fast processing of received
transmission [54]. signals. More importantly, FET‑based nanobiosensors
provide a wide range of design options. For example,
Deviations from the conventional means of communica‑
they can accommodate different types of nanomaterials,
tions necessitate radically different ideas for the design
e.g., graphene, SiNW, CNT, as the transducer channel,
of transmitter and receiver architectures, and communi‑
the conductivity of which is modulated by the molecu‑
cation techniques for MC, and new approaches to channel
lar concentration in its proximity through the alteration
modeling.
of the surface potential and electrical ield‑effect. FET‑

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