Spectrofluorometric determination of nasal cGMP using a propidium iodide supramolecular probe for diagnosis and monitoring of chronic olfactory dysfunction

Abstract Cyclic guanosine monophosphate (cGMP) serves as a critical second messenger in olfactory signal transduction. This study developed and validated a novel, highly sensitive spectrofluorometric method for cGMP determination in human nasal secretions based on its site-specific supramolecular interaction with propidium iodide (PI) at pH 3.0. The formation of a 1:1 ion-pair complex, stabilized by hydrogen bonding and π–π stacking, induced a significant hyperchromic shift. The fluorophore (PI) and cGMP exhibited fluorescence quantum yields of $$\\:{{\\Phi\\:}}_{\\text{P}\\text{I}}$$ = 0.19 and $$\\:{{\\Phi\\:}}_{\\text{c}\\text{G}\\text{M}\\text{P}\\:}$$ = 0.07 respectively, while formation of the PI–cGMP complex increased the fluorescence quantum yield to $$\\:{{\\Phi\\:}}_{\\text{P}\\text{I}-\\text{c}\\text{G}\\text{M}\\text{P}}$$ = 0.62. Under optimized conditions, the method exhibited a linear relationship over a concentration range of 1–100 ng/mL, with a limit of detection of 0.21 ng/mL and a limit of quantification of 0.63 ng/mL. Clinical application in a cohort of 100 participants revealed that normosmic individuals ( n = 50) possessed mean cGMP levels of 37.88 ± 4.25 ng/mL, whereas patients with chronic olfactory dysfunction ( n = 50) exhibited significantly decreased levels of 8.25 ± 1.14 ng/mL ( p < 0.0001). The 4.6-fold reduction in cGMP concentration underscores its potential as a robust biochemical biomarker. Compared to previously reported analytical methods, the proposed method offers a wider dynamic range and greater sensitivity, making it an objective tool for the clinical diagnosis and long-term monitoring of olfactory dysfunctions.