Microsystems for Bioelectronics

L – A logic unit that processes information collected from A and that provides summary

information for transmission by C.

E – An energy source that powers operations of all units. The energy can be supplied to the system

from an external energy source (Fig. 1.2a) or/and the system can have an internal energy source

(Fig. 1.2b). In the former case, an energy converter must be embedded into the system. In the

latter case a finite supply of energy is implied.

Each of the above essential system units occupies certain volume in space and, taken together, they

determine the scaling limits of an electronic system. Investigation of these limits is the primary

purpose of this text.

1.3 NANOMORPHIC CELL

The nanomorphic cell concept refers to an atomic-level, integrated, self-sustaining microsystem with

six primary components: energy supply, sensing, actuation, computation, memory, and communica-

tion. It is a model system, designed to analyze the physical scaling limits of electronic systems, which

for future reference is postulated to be confined within a 10

m

m  10

m

m  10

m

m cube [3]. A cartoon

for the hypothetical nanomorphic cell is shown in Figure 1.3.

Volume is one of the primary design constraints for the nanomorphic cells and it will be shown in

the subsequent chapters that this resource should be very carefully allocated among all functional

units. Literally every atom must play a role when one needs to fit all functional units into the 10

m

m 

10

m

m  10

m

m cube (Fig. 1.4). From an application point of view, the nanomorphic cell can be

considered as an extreme example of a class of systems known generically as autonomous micro-

systems, for example WIMS (wireless integrated microsystems) [4], PicoNode [5], Lab-on-a-Pill [6],

and Smart Dust [7]. A brief disc ussion of these will be given at the end of the chapter.

1.3.1 The nanomorphic cell vis-a

`

-vis the living cell

The living cell is a marvelous machine that is the cornerstone of all living things and that has

embedded mechanisms for (i) staying alive and for (ii) reproducing itself. It is not an exaggeration to

M

L

C

S

E

F

I

A

M

L

S

F

I

A

E

C

(b)(a)

FIGURE 1.2

Block diagrams for arbitrary electronic system: (a) with external energy supply; (b) with internal energy source

4 CHAPTER 1 The nanomorphic cell

say that the living cell is purposeful [8]. In order to achieve the goal of staying alive, cells need to

acquire information about their environment. Next, the cell needs to appropriately respond to the

information, e.g., about changes in temperature, water availability, nutrients supply, dangerous species,

and many other factors. Th e ability to acquire and use such information is critical for organism survival

[9]. As was recently stated by A. Kinkhabwale and P. Bastiaens (Max Planck Institute of Molecular

Physiology), ‘to live is to compute’ [8].

The second goal of reproduction itself involves a series of precise tasks which requires

controlled flows of information and matter ensuring that all atoms forming the cell are positioned in

a specific place within the cell. Recently, Antoine Danchine at the Institut Pasteur in Paris, France

suggested that a living cell (e.g. a bacterium) can be considered a computer making computers [10].

The author argues that a cell has all essential attributes of a computer, i.e. a machine expressing

a program.

The studies of the living cell as a functional microsystem may help engineers to understand the

physical limits of scaling for functional electronic systems. Or, vice versa, lessons from extremely

scaled electronic systems may help biologists to gain new insights into the fundamental questions of

theoretical biology, such as ‘What is the minimum size of Life?’ [11], or ‘What is the minimum energy

needed to support Life?’ [12].

In this section, a brief overview of unicellular organisms is presented with an emphasis on syst em

size and energy. Other system-level parameters such as ‘speed of operation’, informational complexity,

etc. will be discussed in Chapter 6.

Energy

Communication

~10 mm

Control

Sensor

Sensor

FIGURE 1.3

Cartoon for the nanomorphic cell showing essential components and physical scale

1.3 Nanomorphic cell 5