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.