Polydentate Aromatic Nanoparticles Complexed with Cu²⁺ for the Detection of Cysteamine Using a Smartphone as a Portable Diagnostic Tool

Despite the significant therapeutic use of cysteamine as drug in cystinosis, it also has some serious health issues such as idiopathic intracranial hypertension (IIH), Ehlers–Danlos syndrome, and eye related problems including blurred or loss of vision and pain due to eye movement, etc. Thus, it is important to measure accurate cysteamine levels in the body for clinical studies. However, most of the conventional methods used to detect cysteamine are time-consuming and expensive in nature. Therefore, in this regard, we have developed a chromogenic sensor which sequentially determines the Cu2+ metal ion and, consequently, exhibits potential ratiometric and selective colorimetric quantification of cysteamine in an aqueous/biological system. The morphology of the sensor was characterized by TEM, and it revealed some interesting features in that receptor 1 nanoparticles undergo self-assembly with the addition of Cu2+ metal ions which results in the filament formation (comet type) in aqueous medium and on subsequent addition of cysteamine to resultant complex 1·Cu2+; these comet type nanoparticle filaments undergo further aggregation process and develop into three-dimensional tree-like structure. Further, on the basis of obtained colorimetric results, we developed silica-based solid state sensor strips impregnated with complex 1·Cu2+, which displays colorimetric changes in accordance with present concentrations of cysteamine in blood serum and urine samples, wherein the intensity of yellow color decreased gradually after the addition of cysteamine, as revealed by HSV parameter through lab-on-mobile based diagnostics. The low detection limit (with naked eye) exhibited by developed solid state sensors leads to affordable and economic platforms for easy-to-use, reliable, and rapid colorimetric sensing of cysteamine in aqueous as well as biological test systems.