Lactate monitoring using fluorescence with stable boronic acid-functionalized nanoparticles from Polymerization-Induced Self-Assembly (PISA)

L-Lactate is elevated in various disease states, and monitoring is important to the food industry and to the performance management of high-endurance athletes. Commercial monitors are enzyme-based with low upper limits of detection (<50 mM) and are less robust than synthetic sensors using L-lactate binding to boronic acid (BA). The fluorescence indicator displacement assay (FIDA) for lactate has not been investigated and is convenient since BA is known to bind to catechol dyes, including Alizarin Red S (ARS) with large increases in fluorescence intensity. Herein, reversible addition–fragmentation chain transfer (RAFT) dispersion PISA of N-phenylacrylamide (PhA) in water/ethanol using BA-containing polyacrylamide macroRAFT gave stable spherical core–shell nanoparticles (NPs) functionalized with BA at the surface. It is demonstrated that the degree of polymerization (DP) of the BA-containing block of NPs can be acquired from the fluorescence-derived binding constant (KARS) using the Benesi–Hildebrand approach. FIDA involved the displacement of ARS by the L-lactate quencher from the fluorescent NP complex and allows the detection of higher L-lactate concentrations (4.0–625 mM) than current commercial monitors. The derived Stern–Volmer constant (Ksv) is independent of DP of the BA-containing block and increased by ∼2.5 times by addition of ethanol to the pH 7.4 aqueous dispersion. When using D-glucose and D-fructose as quenchers, Ksv is about 4-fold smaller and 13-fold greater, respectively, than L-lactate.