Polymer-free Viscoelastic Microfluidics-Integrated Graphene Transistor Biosensing of Saliva Porphyromonas gingivalis for Periodontitis Diagnosis

Porphyromonas gingivalis ( P. gingivalis ) as a keystone pathogen of periodontal diseases has been increasingly associated with periodontitis and systemic comorbidities. The rapid and sensitive detection of P. gingivalis in saliva remains challenging because of the complex salivary matrix and insufficient sample preparation in conventional assays. To address these limitations, we developed an integrated saliva-compatible biosensing platform by combining polymer-free viscoelastic microfluidic pretreatment with an electrolyte-gated graphene field-effect transistor (GFET) biosensor. The microfluidic module exploits saliva’s intrinsic viscoelasticity to enable additive-free particle focusing by co-flowing viscoelastic saliva with Newtonian PBS. This self-conditioning generates synergistic inertial and elastic lift forces that laterally separate P. gingivalis from the salivary matrix, achieving 93.8% bacterial recovery and 82.1% protein removal. To enhance measurement reliability on the antibody-functionalized Au side-gate, a reference-gate-based differential calibration strategy was implemented to suppress common-mode interference and environmental drift. With this calibration, the integrated GFET biosensor achieved a limit of detection of 291 CFU/mL over a linear range of 1 × 10 3 –1 × 10 8 CFU/mL, and the clinical validation demonstrated robust discrimination between periodontitis and healthy controls with a high sensitivity of 94.1%. This integrated biosensor provides a compact, low-consumption, and automation-friendly route for saliva-compatible transistor biosensing and advances practical point-of-care periodontal diagnostics.