Biomedical Engineering Reference
In-Depth Information
self-assembled nanostructures thereby giving rise to an increase in electrical current
conductivity. After the functionalization step, the functionalized nanostructures can be
integrated with transducers and used for the detection of compounds of biomedical
relevance. Following changes in current, potential or capacitance as a result of the
interaction between the analyte and the biorecognition element the presence and quantity of
these samples can be confirmed.
Scheibel et al. fabricated conducting nanowires thanks to a controlled self-assembly of
amyloid fibers and selective metal deposition (Scheibel et al., 2003). Nanowires containing
cysteine residues were used to covalently link colloidal gold nanoparticles on the surface of
these nanostructures. And additional metal was then deposited by chemical enhancement of
the colloidal gold by reductive deposition of metallic silver and gold from salts. The final
biotemplated metal wires showed an increase in conductivity from the pA- to the mA-range,
figure 11.
Fig. 11. Electrical behavior of NM-templated metallic fibers. (a) Gold nanowires not bridging
the gap between two electrodes did not conduct. (b) Gold nanowires bridging the gap
between two electrodes (
Left
) exhibited linear I-V curves (
Right
), demonstrating ohmic
conductivity with a low resistance of
R
=86 Ω (the same for each). Such an ohmic response is
indicative of continuous, metallic connections across the sample. Reprinted from Scheibel, T.
et al. PNAS, 100, 2003, 4527-4532. Copyright (2003) National Academy of Sciences, U.S.A.
In a different approach, Sasso et al. used a conductive polymer, polypyrrole, in order to
increase the conductivity of self-assembled peptide nanofibers. The presence of the
conductive polymer on the surface of the nanofibers increased their conductivity and
rendered possible their use as the biorecognition element in a dopamine biosensor. By
employing this sensor, dopamine detection was possible with a detection limit of 3.1 µM; a
value close to the dopamine concentration in in-vivo systems (Sasso et al., 2011).
Enzyme-modified peptide nanotubes have been utilized for the detection of compounds of
biomedical relevance such as glucose, ethanol, or hydrogen peroxide as demonstrated by
several groups. The enzymes were connected to the self-assembled peptide nanostructures
through different matrices such as poly(allylamine hydrochloride) (Cipriano et al., 2010) or
glutaraldehyde (Yemini et al., 2005, Yemini et al., 2005). Finally the modified peptide
nanotubes were immobilized on the surface of metallic electrodes using polymer matrices
like polyethyleneimine. Amperometric detection was used to detect and quantify the
presence of the previously mentioned compounds. Based on a similar approach, Yang and
co-workers developed a glucose sensor using glucose oxidase functionalized peptide
