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Label-Free Optical Biochemical Sensors via Liquid-Cladding-Induced Modulation of Waveguide Modes
Tran, Nhu Hoa Thi,Kim, Jisoo,Phan, Thang Bach,Khym, Sungwon,Ju, Heongkyu American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>We demonstrated modulation of the waveguide mode mismatch via liquid cladding of the controllable refractive index for label-free quantitative detection of concentration of chemical or biological substances. A multi mode optical fiber with its core exposed was used as the sensor head with the suitable chemical modification of its surface. Injected analyte liquid itself formed the liquid cladding for the waveguide. We found that modulation of the concentration of analyte injected enables a degree of the waveguide mode mismatch to be controlled, resulting in sensitive change in optical power transmission, which was utilized for its real-time quantitative assay. We applied the device to quantitating concentration of glycerol and bovine serum albumin (BSA) solutions. We obtained experimentally the limit of detection (LOD) of glycerol concentration, 0.001% (volume ratio), corresponding to the resolvable index resolution of similar to 1.02 x 10(-6) RIU (refractive index unit). The presented sensors also exhibited reasonably good reproducibility. In BSA detection, the sensor device response was sensitive to change in the refractive indices not only of liquid bulk but also of layers just above the sensing surface with higher sensitivity, providing the LOD experimentally as similar to 3.7 ng/mL (mass coverage of similar to 30 pg/mm(2)). A theoretical model was also presented to invoke both mode mismatch modulation and evanescent field absorption for understanding of the transmission change, offering a theoretical background for designing the sensor head structure for a given analyte. Interestingly, the device sensing length played little role in the important sensor characteristics such as sensitivity, unlike most of the waveguide-based sensors. This unraveled the possibility of realizing a highly simple structured label-free sensor for point-of-care testing in a real-time manner via an optical waveguide with liquid cladding. This required neither metal nor dielectric coating but still produced sensitivity comparable to those of other types of label-free sensors such as plasmonic fiber ones.</P>
Relaxor Behaviors in xBaTiO₃–(1-x)CoFe₂O₄ Materials
Cao Thi My Dung,Nhu Hoa Tran Thi,Kieu Hanh Thi Ta,Vinh Cao Tran,Bao Thu Le Nguyen,Van Hieu Le,Phuong Anh Do,Anh Tuan Dang,Heongkyu Ju,Bach Thang Phan 한국자기학회 2015 Journal of Magnetics Vol.20 No.4
Dielectric properties of xBaTiO₃–(1-x)CoFe₂O₄ composite materials have been investigated. Dielectric properties of BaTiO₃, CoFe₂O₄ and 0.5BaTiO₃–0.5CoFe₂O₄ samples show frequency dependence, which is classified as relaxor behavior with different relaxing degree. The relaxor behaviors were described using the modified Curier-Weiss and Vogel–Fulcher laws. Among three above samples, the BaTiO₃ sample has highest relaxing degree. Photoluminescence spectral indicated defects, which might in turn control relaxing degree.