There
is an urgent need to develop a rapid and selective method
for the detection of bacteria because delayed diagnosis and the overuse
of antibiotics have triggered drug resistance in bacteria. To this
end, we prepared boronic acid-modified poly(amidoamine) generation
4 (B-PAMAM(G4)) dendrimer as cross-linking molecules that form aggregates
with bacteria. Within 5 min of adding B-PAMAM(G4) dendrimer solution
to a bacterial suspension, large aggregates were observed. Interestingly,
the aggregate formation with various bacteria was pH-dependent. In
basic pH, both Gram-positive and Gram-negative bacteria formed aggregates,
but in neutral pH, only Gram-positive bacteria formed aggregates.
We revealed that this bacteria-selective aggregation involved the
bacterial surface recognition of the phenylboronic acid moiety of
B-PAMAM(G4) dendrimer. In addition, we demonstrated that the spherical
structure of B-PAMAM(G4) was one of the important factors for the
formation of large aggregates. The aggregation was also observed in
the presence of ≤10 mM fructose. B-PAMAM(G4) dendrimer is expected
to be a powerful tool for the rapid and selective discrimination between
Gram-positive and Gram-negative bacteria.
Cyclodextrins (CDs) are water-soluble host compounds having nano-size hydrophobic cavities that enable them to incorporate organic molecules in water. Optically inert CDs can be efficiently combined with various types of chromoionophores and fluoroionophores. In this study, using diverse combinations of phenylboronic acid fluorescent sensors and azoprobes with CDs, the unique saccharide recognition functions of CD, chemically modified CD, and CD gel complexes based on their synergistic function are clarified, thereby confirming their use as supramolecular saccharide sensors. To realize novel supramolecular chirality, the twisted structure of two ditopic azoprobes inside the γ-CD chiral cavity is controlled by multi-point recognition of guest ions in water. As different types of supramolecular saccharide sensors, phenylboronic acidbased self-assembling systems are also reviewed.
We have developed a convenient and selective method for the detection of Gram-positive bacteria using a ditopic poly(amidoamine) (PAMAM) dendrimer probe. The dendrimer that was modified with dipicolylamine (dpa) and phenylboronic acid groups showed selectivity toward Staphylococcus aureus. The ditopic dendrimer system had higher sensitivity and better pH tolerance than the monotopic PAMAM dendrimer probe. We also investigated the mechanisms of various ditopic PAMAM dendrimer probes and found that the selectivity toward Gram-positive bacteria was dependent on a variety of interactions. Supramolecular interactions, such as electrostatic interaction and hydrophobic interaction, per se, did not contribute to the bacterial recognition ability, nor did they improve the selectivity of the ditopic dendrimer system. In contrast, the ditopic PAMAM dendrimer probe that had a phosphate-sensing dpa group and formed a chelate with metal ions showed improved selectivity toward S. aureus. The results suggested that the targeted ditopic PAMAM dendrimer probe showed selectivity toward Gram-positive bacteria. This study is expected to contribute to the elucidation of the interaction between synthetic molecules and bacterial surface. Moreover, our novel method showed potential for the rapid and species-specific recognition of various bacteria.
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