Portable smartphone platform integrated with paper strip-assisted fluorescence sensor for ultrasensitive and visual quantitation of ascorbic acid.

It is significant to develop low-cost, sensitive, and portable sensing platform for point-of-care testing of ascorbic acid (AA) in food quality evaluation. Herein, a smart point-of-care (SPOC) sensor, consisting of fluorescent paper chip, 3D printed-accessories and smartphone, was developed for ultrasensitive and visual quantitative detection of AA. Fluorescent paper chip was made through printing silicon doped carbon dots (SiCDs)-Fe as "ink" onto filter paper, in which SiCDs emitting strong fluorescence signal quenched by Fe, and then recovered by AA owing to releasing -NH/-OH and introducing defects on SiCDs. The smartphone with an application named "AA-Tester" was established to analyze AA and exhibited high sensitivity with low detection limits of 18.12 nmol/L. HPLC method was used to verify the SPOC sensor and obtained satisfactory accuracy with relative standard deviations of 0.79-2.31 %. The portable sensing platform integrated fluorescence sensor with smartphone-device will be favorable for ultrasensitive and on-the-spot detection of AA.