TiO₂-Coated Silica Photonic Crystal Capillaries for Plasmon-Free SERS Analysis

The rapid and simple development of a point-of-care testing (POCT) device with convenience, easy operation, reusability, and high selectivity and sensitivity remains a challenge. Herein, we developed a simple and economical technique to fabricate a novel POCT sensor for plasmon-free surface-enhanced Raman scattering (SERS) analysis. In practice, a capillary and silica photonic crystal were used as the support and framework, respectively, and then, this is followed by atomic layer deposition (ALD) of titanium dioxide (TiO₂) on the photonic crystal framework for the formation of a shell structure. It was found that the sensor gained the enhancement factor (EF) of 3.63 × 10⁴, and it exhibited a highly selective and sensitive detection for methylene blue (MB) with a good linearity in the range from 10^-7 to 10^-2 M (R² = 0.997) and the detection limit of 72 nM, which is attributed to the enhanced matter-light interaction by whispering gallery mode (WGM) resonance and multiple light scattering with the TiO₂-coated photonic crystal capillary (TiO₂-PCC) as well as the chemical enhancement of TiO₂. More importantly, the as-proposed sensor could be regenerated under simple irradiation of UV light because of the photocatalytic property of TiO₂. We anticipate this sensor to be widely used in the POCT field of resource-constrained areas.