This study introduces a highly sensitive and selective method for detecting caffeine in energy drinks by using red florescence iron and nitrogen co doped carbon dots (Fe-NCDs) as a florescent prob. The Fe-NCDs were synthesized by using an eco-friendly hydrothermal. Providing uniform, quasi-spherical nanoparticles. The photoluminescence properties of the Fe-NCDs exhibit strong red emission making them suitable for fluorescence-based sensing. A microfluidic paper analytical device (µPAD) was developed and coupled with a smartphone-based detection system to facilitate portable, low-cost caffeine quantification. The Fe-NCDs were embedded in the µPADs, enabling fluorescence enhancement upon interaction with caffeine. This enhancement was quantitatively analyzed using the smartphone camera and ImageJ software, revealing a strong linear correlation in the range of 1 to 40 µg/mL when both Gray Value (G.V) and Red-Green-Blue (RGB) of reaction analyzed by the software. The limit of detection (LOD) was of 0.024 µg/mL and 0.032 µg/mL respectively for both applied principles. The methods indicate remarkable selectivity for caffeine, and was validated through accurate recovery studies in commercial samples. This innovative method provides a powerful, cost-effective, and environmentally sustainable solution for on-site caffeine detection in energy drinks, offering significant potential for application in food safety and quality control.