The transformation of common office supplies into a low-cost optical biosensing platform.

By reassembling common office supplies, an optical biosensing system was developed. A laser pointer and the solar cell from a calculator were utilized in the developed optical biosensing system as the light source and signal transducer, respectively. For intuitive signal evaluation, a multimeter was used. The following two types of conventional enzymatic colorimetric assays were employed with the optical biosensing system: (i) the Trinder׳s reaction-based enzymatic assay; and (ii) the competitive enzyme-linked immunosorbent assay. These colorimetric assays were performed in reaction channels made from transparent polymer and glass. By matching the maximum absorption spectra of the colored end products from the assays with the emission spectra of the laser diodes, the biochemical reaction rate was manifested as a change in the intensity of the laser beam. This change was then converted by the solar cell into voltage and displayed on the connected multimeter. To verify the detection performance of the system, glucose and an osteoarthritis biomarker (urinary collagen type II C-telopeptide fragments [uCTX-II]) were quantified. With glucose, the voltages registered were linearly correlated with the glucose concentration, from 0 to 10 mM. Using a competitive immunoassay for uCTX-II, the system exhibited a calibration curve with a dynamic detection range between 1.3 and 10 ng/mL uCTX-II. Given the advantages of the proposed biosensing system, including its high sensitivity, facile fabrication, and the high obtainability and cost-effectiveness of the components used to make it, we expect that this study will provide a basis for the production of a low-cost optical biosensor.