Localized surface plasmon resonance coupled single-particle galactose assay with dark-field optical microscopy

•A sensitive single-particle detection method is established for galactose assay.•The specific boronate affinity is utilized for galactose recognition.•A lower detection limit of 0.83 nM is attained for galactose determination.•The potential practicality is evaluated by analyzing galactose in urine samples. Galactosemia as a metabolic disease is associated with the increase of galactose concentration in blood. Hence, it is important to detect the amount of galactose for the early discovery of diseases. In this study, we demonstrate a convenient and sensitive localized surface plasmon resonance (LSPR) coupled method for the quantification of galactose by single- particle detection (SPD) with dark-field optical microscopy (DFM). The design is based on the specific boronate affinity interaction between the boronic acid ligands and cis-diol groups. The mercaptophenylboronic acid (MPBA) functionalized gold nanoparticles (MPBA-GNPs) served as the signal probe were prepared. In the presence of galactose, MPBA can react with the cis-diol groups of the galactose, resulting in the occurrence of MPBA-GNPs plasmon oscillations coupling and the apparent change of particle scattering color from green to yellow. By quantifying the ratio of yellow particles by SPD with DFM, the trace amount of galactose in solution can be accurately detected. Limit-of-detection (LOD) as low as 0.83 nM is achieved in the linear range of 1–75 nM, which is more sensitive than that of the previous reported ensemble measurement methods. The satisfactory spike recoveries in human urine sample are successfully obtained, which indicates the potential applications of this proposed method in practical sample. As a consequence, this study provides a prospect platform for the ultra-sensitive biomolecules detection in the future.