Label-free sensitivity of long-period gratings enhanced by atomic layer deposited TiO_2 nano-overlays

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.

Opto-Electrochemical Sensing Device Based on Long-Period Grating Coated with Boron-Doped Diamond Thin Film

“…The coupling is wavelength-dependent, so one can obtain a spectrally selective loss. A number of sensors based on the LPGs have been proposed for temperature, humidity, strain, hydrostatic pressure, bending and RI sensing, including a number of biosensors [3][4][5][6].…”

Regeneration of titanium oxide nano-coated long-period grating biosensor

“…Optical properties as well thickness of TiO x was chosen for tuning LPG sensitivity up to the RI range of the aqueous solutions (n D =1.333-1.340 RIU), which is important for label-free biosensing applications [3]. In Figure 1 the dispersion curves of n and k are shown for the obtained TiO x nano-films.…”

“…LPGs were manufactured using germanium-doped Corning SMF-28 single-mode optical fiber by UV irradiation and coated with TiO x thin film fabricated with ALD method [3]. Then LPGs were subjected to a biofunctionalization process, which consist of three steps: silanization, biotin termination and avidin linking, respectively.…”

“…Simultaneously to LPG measurements, the influence of the biofunctionalization process on optical properties, i.e., n and extinction coefficient (k), as well as thickness of the TiO x and biofilm (biotin-avidin complex) were investigated on reference TiO x -coated silicon wafers using Horiba Jobin-Yvon UVISEL spectroscopic ellipsometer (ES) in wavelength range 260 to 830 nm [3,9].…”

“…The high-n coating can also enhance RI sensitivity when its properties i.e., n and thickness, are precisely defined. In order to improve the LPG sensitivity, a titanium oxide (TiO x ) nano-coating was deposited with atomic layer deposition (ALD) method on LPG surface [3]. The ALD method allows us for deposition thin films of welldefined properties [4].…”