Abstract
Carboxylate anions are analytical targets with environmental and biological relevance, whose detection is often challenging in aqueous solutions. We describe a method for discrimination and quantitation of carboxylates in water buffered to pH 7.4 based on their differential interaction with a supramolecular fluorescent sensor, self-assembled from readily available building blocks. A fifth-generation poly(amidoamine) dendrimer (PAMAM G5), bound to organic fluorophores (calcein or pyranine) through noncovalent interactions, forms a [dye•PAMAM] complex responsive to interaction with carboxylates. The observed changes in absorbance, and in fluorescence emission and anisotropy, were interpreted through linear discriminant analysis (LDA) and principal component analysis (PCA) to differentiate 10 structurally similar carboxylates with a limit of discrimination around 100 μM. The relationship between the analytes’ chemical structures and the system’s response was also elucidated. This insight allowed us to extend the system’s capabilities to the simultaneous identification of the nature and concentration of unknown analytes, with excellent structural identification results and good concentration recovery, an uncommon feat for a pattern-based sensing system.
Highlights
Carboxylates can be recognized using complex biomolecules as sensors with high selectivity [1,2], but synthetic chromogenic or fluorogenic chemosensors have garnered interest for their high sensitivity, ruggedness, and fast operation [3]
The carboxylates studied showed differential behavior on binding to PAMAM G5, but the differences were too subtle for direct interpretation, so binding to PAMAM G5, but the differences were too subtle for direct interpretation, so we set up a pattern-based chemical recognition system, using the two [PAMAMdye]
The [pyraninePAMAM] sensor was exposed to samples of the carboxylate analytes (Scheme 1) at the optimal discrimination concentration identified for pyranine (2.04 mM); 38 instrumental measurements were acquired
Summary
Carboxylates can be recognized using complex biomolecules as sensors with high selectivity [1,2], but synthetic chromogenic or fluorogenic chemosensors have garnered interest for their high sensitivity, ruggedness, and fast operation [3]. As a proof of viability, we selected seven carboxylates involved in the citric acid cycle as analytes (shown in red in Scheme 1), as well as three structurally similar carboxylates (shown in blue) commonly found in physiological media that may act as interferents. Are these anions involved in the energy machinery of aerobic cells; some of them participate in biological signaling [9,10], and mis-regulation of their metabolism is linked to multiple diseases [11].
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