Ultrabright silicon nanoparticle fluorescence probe for sensitive detection of cholesterol in human serum

A highly sensitive fluorescence-based assay for cholesterol detection was developed using water-dispersible green-emitting silicon nanoparticles (SiNPs) as a fluorescence indicator and enzyme-catalyzed oxidation product PPDox (Bandrowski's base) as a quencher. The SiNPs were facilely synthesized via a simple, one-step hydrothermal treatment using 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) as the silicon source, which has ultrahigh quantum yield and low phototoxicity. Under the catalysis of cholesterol oxidase (ChOx), hydrogen peroxide (H₂O₂) was generated as a result of cholesterol oxidation. Utilizing p-phenylenediamine (PPD) as the substrate for horseradish peroxidase (HRP) in the presence of H₂O₂ led to the production of PPDox. Based upon the inner filter effect (IFE), the established ultrasensitive fluorescent assay could accurately measure cholesterol. The limit of detection (LOD) of the assay was 0.018 μM with a linear range of 0.025-10 μM. The results for the detection of real serum samples by the proposed assay were comparable to those by a commercial reagent kit, demonstrating that our proposed strategy has high application potential in disease diagnosis and other related biological studies.