Structure, Emissive Properties, and Reporting Abilities of Conjugated Polymers - Advanced Fluorescence Reporters in Chemistry and Biology - page 365

PPEs in water and prevent aggregation and self-quenching [ 53 ]. Heeger and
co-workers paired anionic PPV with a nonconjugated cationic polymer to form a
charge-neutral complex and saw both reduction of nonspecific effects and some loss
in sensitivity in protein detection [ 54 ]. Polyelectrolytes may be best used in assay
schemes, such as DNA hybridization assays or drug discovery screens, where the
assay conditions are well controlled and nonspecific interactions reduced or avoided.
Another approach for biological sensing materials is to prepare the conjugated
polymer in biomimetic forms, such a liposomes (vesicles) or films that imitate cell
membranes. PDA is particularly well known for being suitable for forming biomi-
metic materials [ 5 ]. Amphiphilic diacetylene monomers with a variety of head
groups are dispersed in water or buffer by sonication where they self-assemble into
liposomes, tubules, fibers, etc.; these are photopolymerized to form the polymer in
situ (Fig. 5 ). PDA liposomes have been patterned on glass [ 55 , 56 ] and attached to
fiber membranes [ 57 , 58 ] for fluorescence assay applications where liposomes tend
to aggregate [ 5 , 59 ]. Diacetylene films have been prepared by Langmuir techniques
and photopolymerized; PDA coatings on filters have been prepared by the capture
of diacetylene liposomes on filter membranes followed by polymerization [ 47 , 59 ,
60 ]. Non-diacetylene species such as phospholipids can be incorporated at high
percentages in diacetylene precursor materials without preventing the PDA forma-
tion [ 61 ]; domains form separating the monomers (and hence the polymers) from
the added lipids [ 62 ]. Peptides and proteins can be inserted into the membranes or
conjugated to the surfaces either before or after polymerization. The PDA domains
are rigid unlike cell membranes; however, the lipid domains can incorporate

PDA Material Form Examples:

Immobilized Liposomes

polar head group

UV

Multilayer Coatings

UV

Liposomes

UV

Diacetylene
Amphiphile

PDA/Phospholipid Domains:

UV

+

diacetylene

phospholipid

R 1 R 1

R 1

R 1 R 1

R 1

R 2

R 2

R 2 R 2

R 2

R 2

Fig. 5 Polydiacetylene self-assembled sensing material examples. PDA materials with phospho-
lipids (or other natural lipids) may have separate domains