Photothermal and colorimetric detection of cholesterol using hollow ruthenium nanoparticles

Abstract

Nanozyme, an artificial enzyme with some advantages that compensate for the inherent shortcomings of natural enzymes have been explored. Among the various nanoparticles, those with a hollow structure have the advantage of enabling facile transfer of reactants and exhibiting a high surface-to-volume ratio. Herein, we synthesized hollow ruthenium nanoparticles (HRNs) by the galvanic replacement reaction. Transmission electron microscopy confirmed an average size of 32 nm and a shell thickness of about 2.5 nm. HRNs showed superior catalytic activity compared to natural enzymes due to the advantages of their hollow structure. Based on enhanced catalytic activity, HRNs were applied to cholesterol detection using 2,2′-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid) (ABTS) and 3,3′,5,5′-tetramethylbenzidine (TMB). These common chromogenic substrates in colorimetric methods have strong absorbance in the UV–visible and near-infrared (NIR) regions in their oxidized forms. Therefore, both substrates can serve as probes in photothermal and colorimetric assays. Two oxidized substrates absorbed the NIR laser (808 nm) and released energy in the form of heat. Consequently, the temperature of the reaction solution increased in proportion to the cholesterol concentration. In the cholesterol detection assay using ABTS, linear ranges were ranged from 0.08 to 10 mM (R2 = 0.998) for the colorimetric assay and from 0.08 to 2.5 mM (R2 = 0.996) for the photothermal assay, respectively. The limits of detection were determined to be 12.3 μM in the colorimetric method and 43.5 μM in the photothermal method. These results demonstrate that HRN is an excellent substitute for natural enzymes and a promising material for analytical applications. © 2024 Elsevier B.V.