An immunoblot-based optical biosensor for screening of osteoarthritis using a smartphone-embedded illuminometer†
We report a new smartphone-based immunosensing system that integrates an immunoblotting assay and a built-in illumination sensor to assay an osteoarthritis marker. The simple optical biosensing system developed in this study effectively uses smartphone-embedded components such as a white light-emitting diode and an illumination sensor as the light source and optical receiver, respectively. In contrast to conventional optical sensors, which utilize a specific spectrum and focused wavelength, the illumination sensor sensitively responds to the variations in external light intensity over a wide range of wavelengths. This functionality of the illumination sensor in the smartphone was employed as a signal transducer in the optical system. The immunoblotting technique, which uniformly changes the intensity of light because of the precipitation reaction, was introduced into the developed optical system. The horseradish peroxidase-induced insoluble precipitate interferes with the penetration of incident light, thereby facilitating the variation of applied light intensity. Subsequently, the quantity of light passing through the biosensing channel was immediately analysed using a lux meter in the mobile application. Herein, the urinary C-terminal telopeptide fragment of type II collagen (uCTX-II) was selected as an osteoarthritis biomarker and analysed to demonstrate the feasibility of the developed illumination sensor. The results indicate an obvious change in the lux value in accordance with the uCTX-II concentration ranging from 0 to 10 ng mL−1. The results were highly reproducible and sensitive to the variations in the concentration of the analyte. This suggests the potential use of the developed illumination sensor as a promising tool for the quantitative diagnosis of target analytes and point-of-care testing.