Chemistry Reference
In-Depth Information
syringe tip containing a mixture of a diacetylene lipid, poly(ethylene oxide), and
tetraethyl orthosilicate to a high voltage, resulting in the formation of a mat of thin
silica fibers containing PDA assemblies within them. Subsequent irradiation produces
the blue form of the mat. Addition of various organic solvents to a panel of four mats,
each containing a different diacetylene, results in the formation of a slightly different
color in each mat, generating a diagnostic fingerprint for the identification of these
volatile organic materials (Fig. 12.7).
Polymerized PDA/phospholipid vesicles embedded in agar were used to detect
bacterial growth in the agar plate (Silbert et al. 2006). Zones of the liposome-
doped agar that were closer to the site of bacterial growth turned red, while the
rest of the agar remained blue. Control experiments using solutions of liposomes indi-
cated that the trigger for the chromatic transition was not the bacteria themselves.
Instead, it was suggested that the color change was attributable to interactions of
the liposomes with molecules shed from bacterial cell surfaces, such as secreted
membrane-binding peptides and LPSs (Fig. 12.8).
Although the agar assay permits the detection of bacteria, it does not allow one to
distinguish between different bacterial species. A subsequent version of this assay
reported the use of Langmuir-Blodgett monolayers of mixed phospholipid/PDA
films for bacterial detection and identification (Scindia et al. 2007). Four different
slides, each coated with a monolayer of PDA and different phospholipids, were
prepared. As a result of the different surface charges and lipid compositions, each
monolayer afforded a slightly different CR value when exposed to different species
of bacteria. Consequently, each species generated a distinct pattern of CRs, which
could be used diagnostically (Fig. 12.9).
A variety of methods for immobilizing polymerized liposomes have been reported.
Multiple layers of vesicles were deposited on quartz slides by layer-by-layer assembly
(Su 2005). The slides were first coated with a layer of poly(ethylene imine), a
Figure 12.7 Photographs of electrospun fiber mats embedded with 1 (a) before and (b) after
254-nm UV irradiation (1 mW/cm
2
) for 3 min. (c) Scanning electron microscopy image of the
microfibers containing polymerized 1. (c) Photographs of the polydiacetylene-embedded
electrospun fiber mats prepared with various diacetylene monomers after exposure to
organic solvent. Reprinted from Yoon et al. (2007). Copyright 2007 American Chemical
Society. (See color insert.)
