Antibiotics are used for treatment of human and animal diseases, but they are also added to animal feed to improve growth rates and feed efficiency. These contribute to the rising number of multi-resistant bacteria. Thus, there is need in the detection of antibiotics appearing in environmental fluids. Penicillins and cephalosporins are two of the most widely used antibiotic classes for both humans and animals. They are also structurally similar, with a β-lactam ring and at least one carboxylate group, similarities that make them hard to differentiate from each other.  Our group has had success in using poly(amidoamine) (PAMAM) dendrimers as supramolecular hosts in carboxylate sensing applications. Such hosts can establish electrostatic and H-bonding interactions with a variety of anionic species, among which organic carboxylates, in addition to weaker hydrophobic interactions which may be relevant in binding antibiotics.  We became interested in exploiting these interactions for the detection of antibiotic analytes in water through optical spectroscopy. However, such interactions are hard to use analytically because neither the antibiotics nor the PAMAM receptors have detectable signals in the non-interfering visible region of the spectrum. We circumvented this problem by utilizing a dye-displacement assay based on PAMAM-calcein complexes. Analytical data was interpreted using pattern recognition algorithms to recover discriminatory power. In neutral aqueous HEPES buffer, we first formed a complex between a G5 PAMAM dendrimer and calcein, an organic dye. Then, an antibiotic was introduced, which caused dye displacement from its complex with PAMAM. The displacement was monitored through absorbance and fluorescence techniques. Linear discriminant analysis (LDA) was then used for data interpretation, to discriminate among these carboxylate analytes.

Sensing of penicillins and cephalosporins in neutral aqueous solution using a calcein-PAMAM complex

2019 Fall National Meeting

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