The various smartphone-embedded high technical electronic elements were integrated with biological analytic principle for utilization of simple, low-cost, and user-centered biosensing platform. Currently, the high electronic components such as magnetic sensor, infra-red (IR) sensor, illumination sensor, and charge-coupled (CCD) were contained in the smart IT device. Among them, the illumination sensor and CCD camera were employed to develop the smartphone-based simple optical biosensing system. First, to demonstrate the illumination sensor-based optical biosensing principle, the immunosensing principle was integrated with an immunoblotting assay and a built-in illumination sensor to analyze an osteoarthritis marker. In the various smartphone elements, the illumination sensor sensitively responds to the external light intensity, allowing the application for a simple optical system as a signal transducer. In this study, horseradish peroxidase (HRP)-induced immunoblotting assay was employed to induce the precipitation. The precipitation-induced biosensing channel altered the light intensity according to the analyte which was registered by the illumination sensor. The ambient lights, sunlight and fluorescent, were used as light sources to minimize the composition of the developed optical sensor and increase the usability. Using this, the values of 0–10 ng/mL of urinary C-terminal telopeptide fragment of type II collagen (uCTX-II) were sensitively quantified with good reproducibility. Second, a smartphone-embedded CCD camera was integrated with the paper-based analytical device (PAD) for glucose monitoring. The smartphone-embedded CCD camera has the high technical element, enabling the acquirement of the high-resolution images. To effectively analyze the glucose, a colorimetric glucose assay method using glucose oxidase (GOx) and HRP were employed, implanting on the paper-based analytical device. To confirm the changes in optical signal intensity from the glucose assay, the resulting image was registered by a CCD camera from a smartphone. The experiment was performed in a specifically designed light-tight box mounted with smartphone. By using the developed biosensing system, various concentrations of glucose samples in PBS (0 ~ 20 mM) and human serum (5 ~ 17 mM) were simply and quantitatively analyzed within a few minutes. Third, a simple quantification principle was developed by employing the smartphone-embedded CCD camera with countable microbeads-based biochemical analysis principle for detection of CTX-II. A CCD camera on the smartphone was integrated with the simple prism, filter, and laser for realization of the minimized fluorescence microscope. To detect the biospecific immunoassay for the CTX-II, the quantum-dot (QD) particle having a maximum emission spectrum at 620 nm was employed as an optical signaling probe. The 405 nm laser was installed into the developed biosensing platform as a light source to excite the QD particle. The result images were observed and registered by smartphone-embedded CCD camera, and the immune-specific signal was quantitatively analyzed by counting the number of fluorescent microbeads from the registered images. Using the approach, the sandwich (sCTX-II) and competition (uCTX-II) assays could be immediately quantified on a single chip. The smartphone-based assay would be a promising tool for monitoring of osteoarthritis as a point-of-care testing (POCT) device. Based on these findings, I successfully established a versatile biosensing platform employing the simple utilization of smartphone-embedded high-technical electronics components which can be used for practical disease diagnosis as a POCT device.