A hybrid catalyst-triggered cascade reaction for cholesterol detection using a smartphone-based miniature fluorescent...

A new hybrid biological-chemical catalyst, magnetic nanoparticles functionalized with cholesterol oxidase (Fe₃O₄/APTES/ChOx), was developed for cholesterol detection. In the presence of cholesterol, the enzyme produced H₂O₂, which facilitated the generation of fluorescent molecules from the fluorogenic substrate with the assistance of Fe₃O₄ nanoparticles. A smartphone camera with a miniature fluorescent apparatus was used to assess fluorescence emission. Then, a smartphone application was employed to translate the fluorescence intensity to the red, green, and blue (RGB) domain. The developed approach achieved excellent selectivity and acceptable performances while supporting an onsite analysis approach. The practical operational range spanned from 5 to 100 nM, with a detection limit of 0.85 nM. Fe₃O₄/APTES/ChOx was applied for up to four replicates of reuse and demonstrated stability for at least 30 days. The applicability of the method was evaluated in milk samples, and the results were in accordance with the reference method.