Nanoelectrochemistry: Fundamentals and Applications in Biology and Medicine - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 35

and Rohrer introduced Scanning Tunneling Miscroscopy (STM) 131
and Atomic Force Microscopy (AFM) 132 - techniques which used
sharp nanoscale tip probes to investigate surfaces on the atomic
scale. Below we consider advances made in the studies of individ-
ual molecules using electrochemical methods either alone or in
conjunction with other techniques. We have divided the treatment
into two categories, one dealing with immobilized molecules and
the other with freely diffusing molecules.
1. ImmobilizedMolecules
Immobilization of molecules and nanoparticles on electrode sur-
faces has several important advantages. When redox-active mole-
cules are in permanent direct contact with the electrode, all mole-
cules are rapidly synchronized to the applied potential, and are
relatively easy to find and track. When electrochemistry is com-
bined with spectroscopy (e.g., fluorescence, surface-enhanced
Raman) or scanning probe microscopy, and the spacing is compat-
ible with the lateral resolution (which requires dilute sub-
monolayer surface coverage), this allows for detailed thermody-
namic and kinetic analysis of individual molecules. Statistical
analysis of many individual molecules and of time-dependent fluc-
tuations is pivotal for the interpretation of single-molecule data.
Surface confinement greatly facilitates long-time data accumula-
tion on individual features, and repeated addressing of many indi-
vidual molecules (scanning with a confocal spot or a thin optical
fiber, or by scanning probe microscopy) as well as many mole-
cules in parallel (wide-field or total internal reflection imaging).
Single-molecule spectro-electrochemistry requires a spectro-
scopic method that amplifies a single electron-transfer event into a
multi-photon signal. Notably, laser-induced fluorescence and sur-
face-enhanced (resonant) Raman spectroscopy, and electrogener-
ated chemiluminescence (ECL) can be applied to probe the redox
state of individual molecules
A pioneering example of combining spectroscopic and elec-
trochemical detection was the work of Bard, Barbara and cowork-
ers. 133 In this study of a luminescent polymer widely used in solar
cells and organic light emitting diodes (OLEDs), poly(9,9-
dioctylfluorene- co -benzothiadiazole) (F8BT), the fluorophore was
immobilized on a transparent (ITO) electrode, embedded in a pol-