Smartphone Platform for Low-Cost Point-of-Care Quantitative Detection of Vitamin B₁₂ Utilizing a Biodegradable Bioplastic Nanocomposite-Based Fluorescence Nanosensor

A portable, low-cost, efficient, disposable, and simple nanosensor for point-of-care or on-site monitoring of vitamin B₁₂ remains a challenge for quality control in the food, beverage, and pharmaceutical industries. A solid-state fluorescence nanosensor probe based on N-, K-, and Ca-doped carbon quantum dots (CQDs) embedded in a bioplastic nanocomposite for quantitative detection of vitamin B₁₂ with good sensitivity and accuracy is demonstrated here. A wide range of morphological, physiochemical, compositional, crystallinity, and functional groups have been investigated. The pH-responsive, tunable solid-state fluorescence properties of the N-, K-, and Ca-doped CQDs at bioplastic nanocomposite probes are reported. For on-site monitoring of vitamin B₁₂, a dual response via fluorescence and colorimetric change has been demonstrated using a smartphone camera to capture images in RGB (red, green, and blue) format and simultaneously analyzed by a customized Android app, with quantitative results displayed on the smartphone. It was possible to determine a linear range of 0.1 mM to 10 nM with limits of detection and quantification of 916 (1241.19 pg/mL) and 3054 pM (4138.21 pg/mL), respectively. Without sample pretreatment or matrix-interfering effects, this approach was effectively used to evaluate vitamin B₁₂ in commercial beverages and pharmaceutical supplements. The performance parameters of the developed nanosensor were validated using a standard reference approach utilizing the Pearson's correlation study, which indicates a good positive correlation (Pearson's coefficient, r = 0.96, p < 0.001) between the two methods. Moreover, potential fluoresce quenching mechanisms have been suggested. Besides, the disposable and biodegradable nature of the nanosensor probe was studied by discarding it into the soil in the natural environment, where it degraded spontaneously by 80–85% within 2 weeks.