4-Mercaptophenylboronic acid-induced in situ formation of silver nanoparticle aggregates as labels on an electrode surface

Abstract This work presented a general way for in situ formation of citrate-capped silver nanoparticle (AgNP) aggregates as labels on an electrode surface. When the electrode surface was functionalised with a member of the o -diphenol family, 4-mercaptophenylboronic acid (MPBA) was anchored onto the electrode surface via a boronate ester covalent bond. The anchored MPBA captured AgNPs through Ag S interaction. The resulting surface-tethered AgNPs could recruit more MPBA molecules and AgNPs through the formation of an Ag S bond and the covalent interaction between the α-hydroxycarboxylate of the citrate and the boronate of the MPBA. This led to in situ formation of a network of AgNPs. The complexes formed between MBPA and citrate acid, as well as dopamine (a member of the o -diphenol family), were characterized by mass spectrometry. The MBPA-induced aggregation of citrate-capped AgNPs in solution was confirmed by UV–Vis spectrophotometry and transmission electron microscopy. The network of AgNPs formed on the diphenol-covered electrode surface was characterized by scanning electron microscopy. The electrochemical signal was measured based on the solid-state Ag/AgCl reaction of the AgNPs. To demonstrate the applications and analytical merits of our design, tyrosinase and protease (thrombin) were measured as model analytes. The proposed strategy is likely to lead to the development of sensors for the detection of other biomolecules.