Sialic acid (SA) exists as a sialic acid complex and participates in a variety of important physiological functions of the body, such as cell recognition. The increase in the concentration of sialic acid in human biological samples exceeds the normal concentration and is related to the development of various cancers. The SPR based label-free detection of small targeted molecules is a great challenge and require substantial signal amplification for the accurate and precise quantification. We have developed an SA sensor based on boric acid fiber-optic SPR in the form of Sialic acid. The signal enhancement technology of 4-mercaptophenylboronic acid (MPBA) modified gold nanoprobe is used for the high-sensitivity detection of sialic acid. Under optimal conditions, the SA concentration has a linear relationship between 0.0001 and 1 mM. The detection limit reached 100 nM. Fiber-based SPR sensing technology not only has high sensitivity and detection, but also avoids damage to biological samples, which has a wide range of application potential in biological non-destructive sensing.
We report a dual-band perfect absorber based on nanodisk array for sensing application in the visible region. Due to the excitation of the magnetic resonance mode, a narrow band absorption peak appears and the absorption rate is greater than 99.9%. The other is due to the excitation of local surface plasmon resonance mode, exhibiting broadband absorption characteristics, and the absorption value is greater than 80%. This structure has a wide angular range absorption characteristic. Finally, we calculated the sensing performance of the structure with refractive index ranging from 1.33 to 1.37. The refractive index sensitivity is 250 nm/RIU and 170 nm/RIU. Therefore, our research provides an important theoretical guidance for narrow-band absorption in the visible region for sensing measurements. This has important application prospects in imaging, sensing and optoelectronic devices.
In this paper, a method of detecting mercury ion (Hg2+) concentration in water samples by using Thymine-1-aceticAcid (T-COOH) functionalized Au nanoparticles enhanced fiber optic SPR sensor is proposed. Firstly, we coat the surface of the optical fiber with Au film, then assemble a layer of mercaptoethymine on the surface of the Au film, and formed the Au-S bond by chemical reaction between the sulfhydryl group and the Au, and exposed the amine group on the surface of the fiber sensing region. Then we use T-COOH to modify the thymine on the fiber optic by the chemical reaction between amine and carboxyl. Similarly, mercaptoethymine and T-COOH were used to modify thymine on the surface of Au nanoparticles, and the optimal ratio of T-COOH : Au nanoparticles = 3:50 was obtained through modification optimization. Then the sandwich structure of Au-T—Hg2+—T-Au NPs was formed when mercury ion was detected, which effectively improved the accuracy and sensitivity of mercury ion detection. Then the concentration of ions is measured. By analyzing the influence of other metal ions and mercury ions in the same concentration of water samples, it is concluded that the fiber optic SPR sensor designed in this paper has high selectivity for mercury ions, so this method has high feasibility.
A novel and simple optical fiber structure with a section of no-core fiber for measuring hydrogen concentration is presented. Palladium is sputtered to form the coating on the no-core fiber by magnetron sputtering coater. Under different hydrogen conditions, the absorption of hydrogen induced refractive index changes on the outside coating of no core fiber will lead to the variations of the optical output spectrum. Different concentrations of hydrogen are tested, from 4%-0.5%, shows the concentration is relevant with the response time and recovery time. The response time of this sensor is from 300s (4% H2) to 1800s (0.5% H2) depending on the hydrogen concentration. The recovery time of this sensor is from 1200s (4% H2) to 4800s (0.5% H2) depending on the hydrogen concentration. Furthermore, the repeatability and response time of the sensor of this study are investigated experimentally.
We proposed a compact and cost-effective red–green dual-color fiber optic surface plasmon resonance (SPR) sensor based on the smartphone. Inherent color selectivity of phone cameras was utilized for real-time monitoring of red and green color channels simultaneously, which can reduce the chance of false detection and improve the sensitivity. Because there are no external prisms, complex optical lenses, or diffraction grating, simple optical configuration is realized. It has a linear response in a refractive index range of 1.326 to 1.351 (R2 = 0.991) with a resolution of 2.3 × 10 − 4 RIU. We apply it for immunoglobulin G (IgG) concentration measurement. Experimental results demonstrate that a linear SPR response was achieved for IgG concentrations varying from 0.02 to 0.30 mg / ml with good repeatability. It may find promising applications in the fields of public health and environment monitoring owing to its simple optics design and applicability in real-time, label-free biodetection.
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