Rapid and non-invasive diagnosis of gingivitis using an uncoated optical fiber-based Mach-Zehnder interferometer salivary pH sensor

In this study, an uncoated optical fiber–based Mach–Zehnder interferometer (SMF–NCF–SMF) salivary pH sensor is developed and experimentally evaluated as a rapid, non-invasive diagnostic tool for gingivitis screening. The sensor exploits multimode interference and refractive index sensitivity, enabling wavelength-shift demodulation of pH-induced spectral changes in saliva. Clinical validation was performed on 83 individuals, of whom 38 exhibited clinically healthy gingiva, and 37 were diagnosed with gingivitis. The proposed sensing structure demonstrated a sensitivity of 1.5 nm/pH and strong linearity exceeding 98%, with gingivitis patients exhibiting significantly more alkaline salivary conditions compared with healthy subjects (p < 0.001). To further support diagnostic reliability, salivary IL-1β levels were quantified using ELISA, revealing elevated concentrations in gingivitis cases and reinforcing the association between salivary biochemical changes and inflammatory periodontal status. The presented optical fiber sensor exhibits high stability, rapid response, and clinical feasibility, highlighting its potential as a practical chairside screening tool for early gingivitis detection.