A simple smartphone-based thermochemiluminescent immunosensor for valproic acid detection using 1,2-dioxetane analogue-doped nanoparticles as a label

Point-of-care testing devices for companion diagnostic applications is a growing area in immunobiosensor technology. With the widespread diffusion of smartphones and improved enclosed photocamera technology, fast and accurate point-of-care diagnosis could be developed for delivering optical biosensing abilities to the general population. Herein, we propose a smartphone-based immunosensor employing a paper-based format coupled with thermochemiluminescence (TCL) detection, that was optimized for valproic acid (VPA) detection in blood and saliva samples. TCL is a chemical luminescence phenomenon in which photons are emitted upon thermally-induced fragmentation of a suitable molecule, with production of a moiety in its singlet electronically excited state. The latter emits a photon while decaying to its ground state. TCL peculiar characteristics combine high detectability and reagent-less nature of the measurement. A one-step competitive immunoassay for VPA detection based on vertical flow immunoassay (VFIA) format was developed, employing silica nanoparticles doped with a TCL 1,2-dioxetane derivative as a label. The VFIA sensor is a stack of paper-based layers functionalized with reagents stored in a stable form, allowing to complete the test in 12 min simply upon sample addition. By 3D printing, simple accessories were produced to turn a smartphone into a biosensing device that provides a power source for the heat shock required to trigger the TCL reaction and a sensitive camera for measuring emitted photons. The developed biosensor allowed VPA detection in blood and saliva, with limits of detection (4 and 0.05 μg mL−1 respectively) and dynamic ranges (4–300 and 0.05–20 μg mL-1) suitable for therapeutic drug monitoring. The integrated device offers an innovative analytical platform for rapid one-step biosensors exploitable in a variety of point-of-care applications.