Biomedical Engineering Reference
In-Depth Information
Depending on the purpose of its use, a device can be very big or very small. In the
last 50 years, progressive miniaturization of the components employed for the con-
struction of devices and machines has resulted in outstanding technological achieve-
ments, particularly in the fi eld of information processing. A common prediction is
that further progress in miniaturization will not only decrease the size and increase
the power of computers, but could also open the way to new technologies in the fi elds
of medicine, environment, energy, and materials.
Until now, miniaturization has been pursued by a large-downward (top-down)
approach, which is reaching practical and fundamental limits (Keyes
2001
) .
Miniaturization, however, can be pushed further on since “there is plenty of room at
the bottom,” as Richard Feynman stated in a famous talk to the American Physical
Society in 1959 (Feynman
1960a,
b
). The key sentence of Feynman's talk was the
following: “The principles of physics do not speak against the possibility of manoeu-
vring things atom by atom.” The idea of the “atom-by-atom,” bottom-up approach to
the construction of nanoscale devices and machines, however, which was so much
appealing to some physicists (Drexler
1986,
1992
), did not convince chemists who are
well-aware of the high reactivity of most atomic species and of the subtle aspects of
chemical bond. Chemists know (Smalley
2001
) that atoms are not simple spheres that
can be moved from a place to another place at will. Atoms do not stay isolated; they
bond strongly to their neighbors and it is diffi cult to imagine that the atoms can be
taken from a starting material and transferred to another material.
In the late 1970s, a new branch of chemistry, called
supramolecular chemistry
,
emerged and expanded very rapidly. In the frame of research on supramolecular
chemistry, the idea began to arise in a few laboratories (Joachim and Launay
1984
;
Lehn
1990
; Balzani and Scandola
1991
) that molecules are much more convenient
building blocks than atoms to construct nanoscale devices and machines (Fig.
1
, bot-
tom). The main reasons at the basis of this idea are: (1) molecules are stable species,
whereas atoms are diffi cult to handle; (2) nature starts from molecules, not from
atoms, to construct the great number and variety of nanodevices and nanomachines
that sustain life; (3) most of the laboratory chemical processes deal with molecules,
not with atoms; (4) molecules are objects that exhibit distinct shapes and carry
device-related properties (e.g., properties that can be manipulated by photochemical
and electrochemical inputs); (5) molecules can self-assemble or can be connected to
make larger structures. In the same period, research on molecular electronic devices
began to fl ourish (Aviram and Ratner
1974
; Carter
1982
; Metzger
2003
) .
In the following years, supramolecular chemistry grew very rapidly (Lehn
1995,
1996
; Steed and Atwood
2000,
2004
) and it became clear that the bottom-up
approach based on molecules opens virtually unlimited possibilities concerning
design and construction of artifi cial molecular devices and machines. More recently,
the concept of molecules as nanoscale objects exhibiting their own shape, size, and
properties has been confi rmed by new, very powerful techniques, such as single-
molecule fl uorescence spectroscopy and the various types of probe microscopies,
capable of visualizing (Rigler et al.
2001
; Moerner
2002
; Zander et al.
2002
) or
manipulating (Gimzewski and Joachim
1999
; Hlavina et al.
2001
; Samori et al.
2004
) single molecules, and even to investigate bimolecular chemical reactions at
the single-molecule level (Christ et al.
2001
) .
