Surrounding Refractive Index Changes Research Articles

Specific detection of CA242 by antibody-modified chiral symmetric double “N” metasurface biosensor

In this work, a biosensor based on Fano resonance metasurface is proposed for the specific detection of CA242 which is a typical marker of pancreatic cancer. The biosensor consists of a chiral symmetric plasma double “N” structure, which utilises coherent coupling of bright and dark modes to generate Fano resonance, achieving suppression of radiation loss, concentrating and storing energy more efficiently in the structure, and contributing to increased sensitivity to changes in ambient refractive index, resulting in a sensitivity of the sensor of up to 842.8 nm /RIU. After a series of antibody functionalization modifications, the metasurface has become an immune biosensor that can specifically detect the tumor marker CA242 of pancreatic cancer. The detection of mixed and single antigen solutions with different concentrations has verified the high sensitivity, high specificity, and high linear relationship of the biosensor to CA242, and the detection limit is as low as 0.0692 ng/mL. It is superior to other common methods and breaks the traditional disadvantages of lower detection accuracy and greater damage in tumour detection methods. The detection of the wavelength shift of localized surface plasmon resonance in plasma metasurface has been successfully applied to the highly sensitive detection of tumor markers. This study demonstrates the sensitivity and maneuverability of the chiral symmetric double “N” plasmonic metasurface biosensor, suggesting the potential application of metamaterials in biosensing based on environmental refractive index changes.

Glucose sensing on reproducible and tunable plasmonic nanostructures formed on annealed coverslips coated with thin layers of gold and indium tin oxide

In the present study, coverslips were used as solid support for the synthesis of nanoparticles (NPs) through two annealing protocols at 550 °C: (i) monometallic Au NPs (Au-4 nm/3 h and Au-4 nm/8 h NPs) (named one step annealing) and (ii) ITO-Au hybrid 16 h NPs (ITO/Au and Au/ITO NPs) (named two steps annealing). The obtained active NPs were investigated for their stability performances in aqueous saline buffer (PBS buffer) and LSPR sensitivity related to the changes of refractive index (RI) in air and glucose solutions. The experiments proved the great stability of annealed Au-4 nm/8 h NPs, ITO/Au /16 h NPs, and Au/ITO/16 h NPs in the presence of PBS buffer. Moreover, LSPR sensing of low (0.2–3 mg/mL) and high glucose concentrations (25 % (w/v)) in wet and dry conditions on Au-4 nm/8 h NPs and ITO/Au NPs coated coverslips of reproducible sensitivity to the environmental RI changes over time is also reported.

Determination of Cr(III) ions based on plasmonic sensing and anodic stripping voltammetry with amplification of Ag nanoparticles

In this paper mercapto succinic acid (MSA) capped gold nanoparticles (AuNPs) upon indium tin oxide (ITO) glass strips (ITO/AuNPs/MSA) have been used as platform for detection of Cr(III) ions. Cr(III) ions can be immobilized on the surface of AuNPs through formation of complex with MSA, allowing the development of plasmonic and electrochemical methods in assays. The plasmonic sensing is based on the formation of complex between ITO/AuNPs/MSA-Cr(III) and BSA as the second complexant, resulting the red-shift of plasmonic AuNP peak due to the change of environmental refractive index. The concentration of Cr(III) ions could be detected in the linear range of 10 nM–1 mM. On the other hand, the electrochemical method is based on the formation of complex between ITO/AuNPs/MSA-Cr(III) and MSA capped silver nanoparticles (MSA/AgNPs), in which Ag can be detected by anodic stripping voltammetry. With the amplification of AgNPs, the sensitivity of the Cr(III) detection was further improved. The stripping current was found to be linearly proportional to the concentration of Cr(III) ions from 0.1 to 10 nM with detection limit of 0.05 nM. The proposed both methods have great potential in the design of chemical sensors for detection of metal ions in field analyses.

Introduction to Photonics: Principles and the Most Recent Applications of Microstructures.

Light has found applications in data transmission, such as optical fibers and waveguides and in optoelectronics. It consists of a series of electromagnetic waves, with particle behavior. Photonics involves the proper use of light as a tool for the benefit of humans. It is derived from the root word “photon”, which connotes the tiniest entity of light analogous to an electron in electricity. Photonics have a broad range of scientific and technological applications that are practically limitless and include medical diagnostics, organic synthesis, communications, as well as fusion energy. This will enhance the quality of life in many areas such as communications and information technology, advanced manufacturing, defense, health, medicine, and energy. The signal transmission methods used in wireless photonic systems are digital baseband and RoF (Radio-over-Fiber) optical communication. Microwave photonics is considered to be one of the emerging research fields. The mid infrared (mid-IR) spectroscopy offers a principal means for biological structure analysis as well as nonintrusive measurements. There is a lower loss in the propagations involving waveguides. Waveguides have simple structures and are cost-efficient in comparison with optical fibers. These are important components due to their compactness, low profile, and many advantages over conventional metallic waveguides. Among the waveguides, optofluidic waveguides have been found to provide a very powerful foundation for building optofluidic sensors. These can be used to fabricate the biosensors based on fluorescence. In an optical fiber, the evanescent field excitation is employed to sense the environmental refractive index changes. Optical fibers as waveguides can be used as sensors to measure strain, temperature, pressure, displacements, vibrations, and other quantities by modifying a fiber. For some application areas, however, fiber-optic sensors are increasingly recognized as a technology with very interesting possibilities. In this review, we present the most common and recent applications of the optical fiber-based sensors. These kinds of sensors can be fabricated by a modification of the waveguide structures to enhance the evanescent field; therefore, direct interactions of the measurand with electromagnetic waves can be performed. In this research, the most recent applications of photonics components are studied and discussed.

Dual-wavelength highly-sensitive refractive index sensor.

We report and demonstrate a highly-sensitive refractive index (RI) sensor based on a linear-cavity dual-wavelength erbium-doped fiber laser (DWEDFL). The optical spectrum of the laser varies as the external environmental RI changes from 1.3 to 1.335. The DWEDFL has a linear-cavity configuration with two fiber Bragg gratings (FBGs) with central wavelengths < 1 nm apart. Since both FBGs share the same EDF gain medium, gain competition occurs in the cavity. Optical loss of one wavelength can be introduced by immersing the sensing component, a 15 mm micro-fiber (MF), in a solution under test. Experimental results demonstrate a high sensitivity of -231.1 dB/RIU (refractive index unit) and 42.6 dB/RIU in the range from 1.300 to 1.335. The relative power change at the two FBG wavelengths reveals a higher sensitivity of -273.7 dB/RIU with better stability due to reduced light source jitter and external perturbation. Due to its high sensitivity and simple structure, the dual wavelengths gain competition RI sensor has potential applications in chemical and biochemical sensing fields.

Transmittance characteristics and tunable sensor performances of plasmonic graphene ribbons

We investigate the transmittance characteristics of graphene ribbons numerically. It is found that the transmission dips originate from the transverse and longitudinal resonances of edge graphene plasmon modes, supported by the graphene ribbon resonator. The environmental refractive index changes are detected by measuring the resulting spectral shifts of the resonant transmission dip, so the graphene ribbons can be applied to plasmonic sensor in infrared. Simulation results show that sensing performances for each resonant mode are similar, and figure of merit can be up to 6. Beside, thanks to the tunable permittivity of graphene by bias voltages, the transmittance spectra and sensor performances can be easily tuned.

Refractometric Sensing Using High-Order Diffraction Spots From Ordered Vertical Silicon Nanowire Arrays

We propose to use high-order diffraction spots from 2-D silicon nanowire (NW) arrays for refractive index sensing based on spatial changes in the diffractive spots position. The NW arrays act both as a refractive index sensor and as dispersive elements, eliminating the need for external spectrometers for the measurement of refractive index changes. The setup uses a simple laser diode source and a low-cost camera and results in higher sensitivity to environmental refractive index changes, as compared with previously demonstrated colorimetric sensors. The sensitivity is greater for higher order diffraction spots, as compared with the lower order ones due to a larger dispersion angle change at higher orders. We also demonstrate that the observed diffraction angle and efficiency of the diffractive orders depend on a number of factors, such as excitation wavelength, NW diameters, pitch, and surrounding medium index. The simple solution of using diffraction spot displacements on a 2-D detector array would provide a novel means of sensing refractive index changes in the surrounding medium of NWs without the burden of complicated spectral analysis.

Bitapered fiber sensor: Signal analysis

We apply a novel signal analysis of our transmission data to extract a phase shift related to detection of environmental refractive index changes around a bitapered fiber. A high order mode (HOM) and the fundamental mode generate an oscillatory response of the optical fiber sensor as the wavelength is scanned. In our analysis we decompose the signal data into Fourier components and use the dominant oscillation frequency for further analysis. The signal analysis enables improved high-resolution detection.

Isotropic spiral plasmonic metamaterial for sensing large refractive index change

We numerically investigate the optical properties of a spiral G-shaped metamaterial, which exhibits both a sharp resonance with a high-quality factor and a broad resonance with a long linear slope in the near-infrared region. By employing the sharp resonating mode, refractive index sensing with sensitivity up to 410 nm/RIU is demonstrated theoretically. In addition, the metamaterial shows single wavelength sensing ability, which allows fast determination of environmental refractive index changes as large as 0.5 by simply monitoring variations in the transmitted intensity of a certain wavelength, which will be beneficial to the development of refractive index sensors based on monochromatic light sources and detectors. As the resonances are independent of the polarization direction of a linearly polarized wave, the sensor manufacturing process will benefit as a result of the lack of an alignment requirement for the axis of polarizers with the metamaterials' orientation.

Hybrid plasmonic biosensor for simultaneous measurement of both thickness and refractive index

A novel hybrid plasmonic biosensor using a sub-wavelength reflection metal grating is proposed and analyzed. The simulation results show that the hybrid plasmonic-cavity (HPCM) are wavelength dependent on both the refractive index (RI) and thickness of the surrounding analyte layer, with a sensitivity of 448nm/RIU (refractive index unit) and 75nm/μm, respectively. However wavelength related to the cavity resonant mode (CRM) is only sensitive to the environmental refractive index changes. In principle it is possible to determine both RI and thickness of the coating layer simultaneously.

Substrate effect on refractive index dependence of plasmon resonance for individual silver nanoparticles observed using darkfield microspectroscopy

We use optical darkfield micro-spectroscopy to characterize the plasmon resonance of individual silver nanoparticles in the presence of a substrate. The optical system permits multiple individual nanoparticles to be identified visually for simultaneous spectroscopic study. For silver particles bound to a silanated glass substrate, we observe changes in the Plasmon resonance due to induced variations in the local refractive index. The shifts in the plasmon resonance are investigated using a simple analytical theory in which the contributions from the substrate and environment are weighted with distance from the nanoparticle. The theory is compared with experimental results to determine a weighting factor which facilitates modeling of environmental refractive index changes using standard Mie code. Use of the optical system for characterizing nanoparticles attached to substrates for biosensing applications is discussed.