A Blue-Emitting Ionic Liquid-Based Nano-Optode for Ultra-Sensitive Detection of Dextran Sulfate

Dextran sulfate sodium (DSS), a polysaccharide, can cause adverse effects such as joint pain, stiffness, and hair loss when used excessively. Rapid, accurate detection of DSS in biological samples is vital for timely clinical diagnosis and treatment decisions. However, current literature on analytical techniques for DSS detection remains limited. For this purpose, we have prepared a fluorescent, room-temperature ionic liquid, trihexyltetradecylphosphonium 2-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazolate (MTNP), and its low-dimensional materials, nMTNP, and characterized them using various spectroscopic and microscopic techniques. The neat MTNP functioned effectively as a solvent-free fluorescent ink, offering excellent performance for secure writing. The intense cyan fluorescence of nMTNP permits precise, efficient sensing of DSS in both aqueous media and on paper-strip formats, with a lowest detection limit of 7.30 ng/mL, which is lower than the lowest standard concentration used (0.12 μM). Owing to its strong fluorescence, the sensor enabled sensitive and selective DSS analysis in real water samples. We have also developed a smartphone-based detection technique for on-spot detection. The developed sensor enables fast, accurate, and highly sensitive detection of DSS, with clear potential to enhance targeted environmental applications and medical diagnosis.