Standardized Quantification of Melatonin: Analytical Framework and Emerging Biosensor Technologies for Agricultural Biotechnology

Melatonin is evolutionarily preserved across nature, while accurate analysis faces huge challenges because concentrations vary by 8 orders of magnitude depending on the matrix. Here, chromatography-based techniques such as HPLC/UHPLC-MS are compared with immunoanalytical methods like ELISA/RIA and biosensor approaches. In this sense, LC-MS/MS has demonstrated higher sensitivity (fmol-level) with higher selectivity, only 5% CV, although at higher costs. Immunoassays showed 15-40% cross-reactivity with structural analogues, leading to overestimations of melatonin levels. Moreover, sample processing and melatonin stability have raised additional uncertainties beyond the analytical capability. This review discusses the validation principles of analytical methods and nanomaterial-based biosensors for online plant stress analysis within agriculture. The following areas of future research need to be focused on: a) uniform analytical recommendations for melatonin analysis, b) establishing internationally valid Certified Reference Materials that guarantee traceable interlaboratory harmonization, and c) translation of biosensors to precision agriculture applications.