Smietana Mateusz, Koba Marcin, Brzozowska Ewa, Krogulski Krzysztof, Nakonieczny Jakub, Wachnicki Lukasz, Mikulic Predrag, Godlewski Marek, Bock Wojtek J
Opt Express. 2015 Apr 6;23(7):8441-53. doi: 10.1364/OE.23.008441.
In this paper, we discuss an impact of thin titanium dioxide (TiO(2)) coatings on refractive index (RI) sensitivity and biofunctionalization of long-period gratings (LPGs). The TiO(2) overlays on the LPG surfaces have been obtained using atomic layer deposition (ALD) method. This method allows for a deposition of conformal, thickness-controlled, with well-defined optical properties, and high-RI thin films which are highly desired for optical fiber sensors. It has been found that for LPGs working at a dispersion turning point of higher order cladding modes only tens of nanometers of TiO(2) overlay thickness allow to obtain cladding mode transition effect, and thus significant improvement of RI sensitivity. When the TiO(2) overlay thickness reaches 70 nm, it is possible to obtain RI sensitivity exceeding 6200 nm/RIU in RI range where label-free sensors operate. Moreover, LPGs with TiO(2)-enhanced RI sensitivity have shown improved sensitivity to bacteria endotoxin (E. coli B lipopolysaccharide) detection, when TiO(2) surface is functionalized with endotoxin binding protein (adhesin) of T4 bacteriophage.
在本文中，我们讨论了薄二氧化钛（TiO₂）涂层对长周期光栅（LPG）的折射率（RI）灵敏度和生物功能化的影响。LPG表面的TiO₂覆盖层是使用原子层沉积（ALD）方法获得的。这种方法能够沉积出保形、厚度可控、具有明确光学性质且折射率高的薄膜，这对于光纤传感器来说是非常理想的。已经发现，对于在高阶包层模的色散转折点工作的LPG，仅几十纳米的TiO₂覆盖层厚度就能实现包层模转换效应，从而显著提高RI灵敏度。当TiO₂覆盖层厚度达到70 nm时，在无标记传感器工作的RI范围内，有可能获得超过6200 nm/RIU的RI灵敏度。此外，当用T4噬菌体的内毒素结合蛋白（粘附素）对TiO₂表面进行功能化时，具有TiO₂增强RI灵敏度的LPG对细菌内毒素（大肠杆菌B脂多糖）检测的灵敏度有所提高。
