Abstract
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.
Highlights
Numerous of chemical and biological substances can be detected by measurement of refractive index (RI) of their liquid solutions, e.g [1]
In contradiction to Al2O3 films, deposited with atomic layer deposition (ALD), where n decreases with thickness [14], at initial stage of the film growth the n of TiO2 increases reaching about 2.27 RI units (RIU) at λ = 1550 nm, Fig. 1(b)
Besides application of TiO2 as antireflection coatings, the TiO2 film can be successfully applied for effective tuning of RI sensitivity of long-period gratings (LPGs)
Summary
Numerous of chemical and biological substances can be detected by measurement of refractive index (RI) of their liquid solutions, e.g [1]. Since Al2O3 belongs to a group of relatively low-refractive-index materials (n at λ = 1550 nm reaches 1.62 RIU), the thickness of the deposited overlay must be high (over 200 nm for optimal thickness at ≈1.3330 RIU) in order to effectively tune RI sensitivity of the devices [15]. For such thick overlays long ALD processes are required, which may be both time consuming and expensive. The system allows for the sensor’s regeneration [37]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
