pH-Responsive Protein Corona for Caries Risk Assessment

Objectives: Plaque pH is a critical biophysical driver of dental caries. A pH sensor to map Stephan Curve and identify high caries-risk individuals for targeted caries prevention is clinically needed, but effective options are limited. Here, we report on a fluorescent, pH-responsive, protein corona candidate sensor that is highly-sensitive, broad-ranged and reliable in detecting real-time biofilm-pH for caries-risk assessment.
Methods: Protein corona was synthesized by coating silica nanoparticles (SiO₂-NPs) with fetal bovine serum that has been pre-loaded with Oregon Green (OG) and Methylene Blue (MB). Corona formation and stability were characterized by transmission electron microscopy and bicinchoninic acid protein assay. Ratiometric emissions of OG (522nm) and MB (699nm) were plotted as a function of pH. Sensor specificity was tested in multiple biofilm ions (NaF, CaCl₂, MgCl₂ and NaCl) and human saliva. The method was validated against a conventional pH-electrode. Stephan Curve of differential concentrations (0, 0.05, 0.2 and 0.5 OD) of planktonic Streptococcus Mutans (SM), in 1% glucose, was measured, and the area under the curve (AUC, below pH 5.5) was computed.
Results: Spherical monodispersed SiO₂-NPs with average diameter of 25nm had uniform protein corona layer of about 15nm. Protein loading was 328.7±5.1µg protein/mg NP. 85 – 91% of protein corona remained adsorbed after dispersion in pH 4.0 – 8.0 for 30mins at 37°C, indicating good corona stability. Sensor response was highly-sensitive with 13.4 fold-increase in ratio-change over a broad pH range of 3.0 – 8.0, enabling precise measurement of Stephan Curve. Sensor specificity was accurate within 0.18 pH units. Measurement was comparable with conventional pH-electrode to within 5.3% deviation. Notably, medium (0.2 OD) and high (0.5 OD) bacterial concentrations could only be distinguished by AUC (p<0.05), but not by minimum pH, demonstrating greater diagnostic utility compared to end-point measurement.
Conclusions: The pH-responsive protein corona offers new prospects for clinical caries-risk assessment by enabling high-quality biofilm-pH detection.