Monitoring of Metabolic Disorders Through Electro-Sensing of Riboflavin by Novel Super-Conductive Silver Ink Modified Paper.

Riboflavin (RIB), or vitamin B2, plays a key role in cellular protection against oxidative stress, and its deficiency can cause severe physiological complications, including metabolic disorders, photosensitivity, anaemia, growth delay and gastrointestinal problems. Rapid and accurate quantification of RIB in real biological samples is important. In this study, a novel paper-based electrochemical microsensor was fabricated for RIB detection in blood plasma samples. Highly conductive silver ink was synthesized and loaded into a ballpoint pen, enabling direct drawing of microscale (∼85.78 µm) electrodes onto a cellulose substrate. Owing to the optimized ink formulation, the drawn electrodes dried immediately (∼3 s) at room temperature, producing uniform, well-defined and highly conductive patterns without spreading. In the presence of induced stress conditions, the electrodes exhibited excellent thermal, mechanical and moisture stability, with resistances remaining stable at 1.5 Ω (at 150°C), 2.9 Ω (humidity exposure) and 2 Ω (mechanical bending). The three-dimensional network formed by silver ink on photographic paper substrate preserved conductivity under stress and prevented structural cracking. RIB was detected using cyclic voltammetry, square-wave voltammetry, chronoamperometry and differential pulse voltammetry. Under optimized conditions, the sensor showed a linear response over 0.4-10 µM with a lower limit of quantification of 0.4 µM. Intra-day and inter-day repeatability ranged from 1.47% to 6.35% and 3.4% to 8.04%, respectively.