Simple Colorimetric and Fluorometric Assay Based on 2,3-Naphthalenedialdehyde for Melatonin in Human Saliva

Abstract

In this paper, 2,3-naphthalenedialdehyde (2,3-Nda) was selected as color reagent with colorimetric and fluorometric assay for detecting melatonin in human saliva. 2,3-naphthalenedialdehyde reacted with melatonin under the catalysis of hydrochloric acid and Fe3+, which the color change was observed sensitively from colorless to yellow with the naked eye. On the other hand, the product of the reaction had a large conjugate structure with strong fluorescence for the fluorometric analysis. Under optimized experimental conditions, a concentration range of melatonin was 2.5–37.5 µM (R2 = 0.998) by colorimetry with the limit of detection for 1.288 µM (S/N = 3), and 0.01–0.1 µM (R2 = 0.997) by fluorometry with the limit of detection for 0.004 µM (S/N = 3). The two assays were successfully applied to the determination of melatonin in human saliva, which average recoveries were 97.80% and 95.96%, respectively, which has the potential in fast clinical examination of melatonin in human saliva.