Calibration of fiber optic based surface plasmon resonance sensors in aqueous systems

Antimonene-Coated Uniform-Waist Tapered Fiber Optic Surface Plasmon Resonance Biosensor for the Detection of Cancerous Cells: Design and Optimization

For early-stage cancer detection, a novel design of graphene-antimonene-coated uniform-waist tapered fiber optic surface plasmon resonance (SPR) biosensor is demonstrated. The proposed optical biosensor outperforms over a wide range of refractive index (RI) variations including biological solutions and is designed to detect various cancerous cells in the human body whose RIs are in the range of 1.36-1.4. Here, antimonene is used to enhance the performance of the designed SPR sensor for sensing cancer analytes because of its high binding energy toward adsorption of biomolecules and large active surface area. The design and analysis of the sensor are done with the help of a transfer matrix method-based simulation platform, and the effect of the taper ratio is also studied. The performance of the proposed SPR biosensor is evaluated with performance parameters such as sensitivity, full width at half maximum, detection accuracy (DA), figure of merit (FOM), and limit of detection (LOD). The numerical results show that the designed sensor is able to provide a sensitivity of 7.3465, 10.9250, 11.8914, and 15.2414 μm/RIU, respectively, for sensing skin, cervical, blood, and adrenal gland cancer with a maximum FOM of 131.1525 RIU^-1, DA of 14.2126 μm^-1, and LOD of 7.2 × 10^-5 RIU. Based on the derived results, the authors believe that the designed SPR sensor could practically find its potential applications in the field of medical science for the early-stage diagnosis of cancer and hence, opens a new window in the field of biosensing.

Parallel-incidence-type waveguide-mode sensor with spectral-readout setup

A waveguide-mode sensor of the spectral-readout type can be used to detect changes in the complex refractive index in the vicinity of the surface of a sensing plate by observing the change in the spectrum of light reflected on the surface. The sensor's configuration can be simplified by adopting a parallel-incidence-type optical setup. To obtain a high sensitivity, the optimization of the sensing-plate structure, incidence angle, and detection wavelength band is essential for the sensor. In the present report, the results predicted by simulations are compared with experimental results in order to evaluate their validity. A discussion of the optimal design for the parallel-incidence-type sensor is also presented, according to the results obtained.

Surface plasmon resonance-based fiber-optic hydrogen gas sensor utilizing palladium supported zinc oxide multilayers and their nanocomposite

We analyze surface plasmon resonance-based fiber-optic sensor for sensing of small concentrations of hydrogen gas in the visible region of the electromagnetic spectrum. One of the two probes considered has multilayers of zinc oxide (ZnO) and palladium (Pd) while the other has layer of their composite over a silver coated unclad core of the fiber. The analysis is carried out for different volume fractions of palladium nanoparticles dispersed in zinc oxide host material in the nanocomposite layer. For the analysis, a Maxwell-Garnett model is adopted for calculating the dielectric function of a ZnO:Pd nanocomposite having nanoparticles of dimensions smaller than the wavelength of radiation used. The effects of the volume fraction of the nanoparticles in the nanocomposite and the thickness of the nanocomposite layer on the figure of merit of the sensor have been studied. The film thickness of the layer and the volume fraction of nanoparticles in the ZnO:Pd nanocomposite layer have been optimized to achieve the maximum value of the figure of merit of the sensor. It has been found that the figure of merit of the sensing probe coated with ZnO:Pd nanocomposite is more than twofold of the sensing probe coated with multilayers of Pd and ZnO over a silver coated unclad core of the fiber; hence, the sensor with a nanocomposite layer works better than that with multilayers of zinc oxide and palladium. The sensor can be used for online monitoring and remote sensing of hydrogen gas.

Surface plasmon resonance based fiber optic sensor for the IR region using a conducting metal oxide film

Theoretical modeling of a surface plasmon resonance (SPR) based fiber optic sensor with a conducting metal oxide [indium tin oxide (ITO)] as the SPR active material is proposed. The theoretical analysis reveals that the proposed sensing probe can be utilized for sensing in the IR region, where most of the gases show their absorption regime. Comparison of sensitivity predicts that an ITO-layer-coated SPR-based fiber optic sensor is about 60% more sensitive than a gold-coated fiber optic sensor. The physical reasons behind sensitivity enhancement are provided. Apart from this, various advantageous features of the ITO over the noble metals, silver and gold, are addressed.

Highly specific detection of interleukin-6 (IL-6) protein using combination tapered fiber-optic biosensor dip-probe

We are reporting highly specific and sensitive detection of human interleukin-6 (IL-6) protein using combination tapered fiber-optic biosensor (CTFOB) dip-probe. With these probes we could successfully detect IL-6, down to a concentration of 5 pM (0.12 ng/ml) in the presence of much higher concentration of a non specific protein. Sandwich immunoassay was used to generate specific fluorescence signal. A novel strategy is developed to eliminate the false signal from non specific binding. In this new strategy it is not required to pre-treat probe surface with any kind of blocking buffer. The specificity of the sensor was established by incubating negative control probes in high concentration (1 nM) of another cytokine IL-8.

Nondestructive monitoring of the photochromic state of dithienylethene monolayers by surface plasmon resonance

The use of surface plasmon resonance (SPR) as a nondestructive, nonerasing readout of the isomerization state of a photochromic dithienylethene covalently linked to a chemically modified gold surface was investigated. Four different binding layers were examined: 11-mercaptoundecanol (MUO), an amine-modified 11-mercaptoundecanol (MUO-NH2), dextran, and an amine-modified dextran. The binding of dithienylethene to the modified gold surface and photoisomerization of the photochrome in the bound state were established by FTIR. Solvent effects were measured for every layer tested using ethanol and hexanes. In general, large, easily measurable SPR signal changes could be detected under conditions where photoisomerization of the dithienylethene photochrome was not quenched by the gold plasmon, establishing SPR as a viable form of readout for potential dithienylethene-based optical data storage or processing devices. Dextran-bound photochrome in ethanol exhibited the largest SPR response upon photoisomerization, but is more prone to time-dependent fluctuations resulting from swelling of the dextran layer (caused by slow diffusion of the solvent) than the other layers. Large responses are also provided by MUO-NH2 and MUO, and the signal is much more stable than that for dextran.

Fiber-optic surface plasmon resonance for vapor phase analyses

Fiber-optic sensors based on surface plasmon resonance (SPR) for direct refractive index (RI) measurements of samples with the RI between 1.00 and 1.30 are described. Most applications of SPR sensors are designed to function near the refractive index of water (1.3330 RI). The RI changes of aqueous solution (RI, ca. 1.34) can easily be monitored by silica-fiber (RI, 1.4601 at 550 nm) based SPR sensor. With regard to gas species detection, the fiber-optic SPR sensor must be modified for sensitivity to changes in refractive index near 1.0008 (i.e., RI of air). However, the silica waveguide has a prohibitively high RI for unmodified monitoring of the RI changes of gas. The silica-fiber based SPR probe design presented here is based upon the modification of the probe geometry to the ability to tune the SPR coupling wavelength/angle pair. In this study, the tapered silica-based fiber SPR sensors are shown to directly determine the RI changes of gas species and the density change of dry air.