Surface Phonon Resonance Assisted Refractive Index Sensing in Mid-Infrared Wavelength Range

We propose a highly sensitive refractive index sensor based on the surface phonon resonance (SPhR) in the mid-IR spectral range. Surface phonon polaritons (SPhPs) are formed on polar dielectrics such as SiC in mid-IR wavelength range and can be excited with the help of a metallic grating at specific wavelength termed as resonance wavelength. The resonance wavelength of SPhP is significantly affected by the refractive index of the analyte medium placed over the grating. This forms the basis of a refractive index sensor. We have numerically evaluated the performance of such an SPhP-based refractive index sensor by using rigorous coupled wave analysis (RCWA) in terms of sensitivity, detection accuracy, and quality factor. The quality factor and detection accuracy of the sensor formed on SiC substrate are found to be 225.1 RIU^–1 (inverse of refractive index unit) and 6.75, respectively. We have also extended the study for other polar dielectric substrates cBN and GaN and observed considerable enhancement in the performance of the sensor for GaN. The values of quality factor and detection accuracy could be increased to 361.2 RIU^–1 and 10.84, respectively, by using GaN substrate. The proposed sensor finds applications in refractive index sensing of liquids and biomolecules having refractive index in the range 1.33–1.36.

     

Hybrid Dielectric-Plasmonic Nanocomposite Arrays for Bulk and Local Refractive Index Sensing

Plasmonics - Plasmonics-based biosensors are often limited by material losses in the form of joule heating while all dielectric nanoparticles systems have relatively smaller local electric field...     

Plasmon-Induced Transparency and Refractive Index Sensing in Side-Coupled Stub-Hexagon Resonators

Plasmonics - A nanoscale structure which comprises metal-insulator-metal (MIM) waveguide, stub resonator, and hexagonal resonator is proposed to realize plasmon-induced transparency (PIT) response....     

Dynamic-Shift Single- and Double-Negative Refractive Index in a Novel Three-Dimensional Metamaterial

A novel three-dimensional terahertz metamaterial by integrating planar and standup resonators on a sapphire substrate is proposed. This structure shows the capability of dynamic-shifting single- and double-negative refractive index bands under temperature control. When the temperature rises from 160 K to 290 K, the single- and double-negative bands of the metamaterials exhibit blue-shift, which is attributed by the simultaneously tuning of the electromagnetic resonance frequencies of the resonators. If the temperature rises to 300 K, the bianisotropy of the metamaterials increases rapidly, while it performs stable between 160 K and 290 K.

     

Optimization of Multimode Fibers for Surface Plasmon Resonance Based Sensors Under Spectral and Single Wavelength Intensity Interrogation

Plasmonics - In an optical fiber based SPR sensor, a segment of metal clad silica fiber is used as the sensing element and resonant coupling occurs to the surface plasmon mode excited at the...     

Black Phosphorous-Based Nanostructures for Refractive Index Sensing with High Figure of Merit in the Mid-infrared

Plasmonics - Two-dimensional materials have emerged as new type of smart materials that may impact advanced photonic devices. Here, to increase the light absorption, a black phosphorus-based...     

Scaling of Surface Plasmon Resonances in Triangular Silver Nanoplate Sols for Enhanced Refractive Index Sensing

The plasmonic spectra of solution phase ensembles of triangular silver nanoplates have been analysed in order to examine the fundamental properties underlying their size-dependent enhanced refractive index sensitivities. Linewidth studies highlight variations in the response of these solution phase nanostructures to those previously reported for single immobilized triangular nanostructures. The observation of insignificant broadening of the resonance linewidth for larger edge length nanoplates highlights minimal contribution of radiative damping processes at these dimensions. Comparative single nanoplate studies using discrete dipole approximations were performed to analyse the dephasing processes contributing to these reduced linewidths and to determine the key parameters defining the underlying plasmonic response. These single nanoplate approximations highlight the dominance of absorption processes over radiative processes and demonstrate that this dominance can be attributed to the platelet nature/geometry of the nanoplates. These calculations indicate that the higher aspect ratio allows for the maintenance of coherent plasmon oscillations as the edge length of the triangular platelet increases within the sols. Thickness studies verify that this reduction in radiation damping is due to high aspect ratio and can act to confine electromagnetic fields at the nanoplate surface, thereby increasing near-field enhancement and hence the resultant plasmonic refractive index sensitivity.     

Short-Term Stability in Refractive Status Despite Large Fluctuations in Glucose Levels in Diabetes Mellitus Type 1 and 2

Purpose

This work investigates how short-term changes in blood glucose concentration affect the refractive components of the diabetic eye in patients with long-term Type 1 and Type 2 diabetes.

Methods

Blood glucose concentration, refractive error components (mean spherical equivalent MSE, J0, J45), central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), axial length (AL) and ocular aberrations were monitored at two-hourly intervals over a 12-hour period in: 20 T1DM patients (mean age ± SD) 38±14 years, baseline HbA1c 8.6±1.9%; 21 T2DM patients (mean age ± SD) 56±11 years, HbA1c 7.5±1.8%; and in 20 control subjects (mean age ± SD) 49±23 years, HbA1c 5.5±0.5%. The refractive and biometric results were compared with the corresponding changes in blood glucose concentration.

Results

Blood glucose concentration at different times was found to vary significantly within (p<0.0005) and between groups (p<0.0005). However, the refractive error components and ocular aberrations were not found to alter significantly over the day in either the diabetic patients or the control subjects (p>0.05). Minor changes of marginal statistical or optical significance were observed in some biometric parameters. Similarly there were some marginally significant differences between the baseline biometric parameters of well-controlled and poorly-controlled diabetic subjects.

Conclusion

This work suggests that normal, short-term fluctuations (of up to about 6 mM/l on a timescale of a few hours) in the blood glucose levels of diabetics are not usually associated with acute changes in refractive error or ocular wavefront aberrations. It is therefore possible that factors other than refractive error fluctuations are sometimes responsible for the transient visual problems often reported by diabetic patients.     

Tuning the Fano Resonance Between Localized and Propagating Surface Plasmon Resonances for Refractive Index Sensing Applications

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.     

An Anterior-Posterior Gradient of Refractive Index in the Ameba and Its Significance in Ameboid Movement

Sustained locomotion in Amoeba proteus and Amoeba dubia results in the establishment of a measureable gradient of refractive index along the anterior-posterior axis of the cell, provided thickness of the specimens is kept constant by even compression under a selected coverglass supported by quartz beams of uniform diameter. The tail region of the ameba develops a higher refractive index, indicative of from 6 to 40 per cent more organic matter (expressed as protein) there than present in the front. This gradient fades on cessation of movement. The average protein concentrations in the crystal-free tails and fronts of 15 A. proteus were 3.9 and 3.4 per cent, respectively. In individual experiments, the tail-front difference ranged from one to eight times the accuracy of the method. Since the gradient of refractive index was shown not to result from extraction of water from the tail by the contractile vacuole, it was interpreted as displacement of water toward the anterior part of the cell during movement. It is suggested that contraction of the ectoplasm drives forward a "tide" of syncretic fluid, the anterior border of which is visible as the hyaline cap, which contains less than 1 per cent protein. The movement of the granular endoplasm into the hyaline cap would then complete the cycle by imbibition of the fluid tide. The theoretical positions of Pantin and of Dellinger have been combined in the proposal that ameba cytoplasm consists of a network of a contractile phase which is able to expel (by syneresis) a highly mobile fluid phase. Some other possible interpretations are discussed.     

Electromagnetically Induced Transparency and Refractive Index Sensing for a Plasmonic Waveguide with a Stub Coupled Ring Resonator

A plasmonic refractive index sensor based on electromagnetically induced transparency (EIT) composed of a metal-insulator-metal (MIM) waveguide with stub resonators and a ring resonator is presented. The transmission properties and the refractive index sensitivity are numerically studied with the finite element method (FEM). The results revealed an EIT-like transmission spectrum with an asymmetric line profile and a refractive index sensitivity of 1057 nm/RIU are obtained. The coupled mode theory (CMT) based on transmission line theory is adopted to illustrate the EIT-like phenomenon. Multiple EIT-like peaks are observed in the transmission spectrum of the derived structures based on the MIM waveguide with stub resonator coupled ring resonator. To analyze the multiple EIT-like modes of the derived structures, the H _z field distribution is calculated. In addition, the effect of the structural parameters on the EIT-like effect is also studied. These results provide a new method for the dynamic control of light in the nanoscale.     

Size-Exclusion Chromatography with On-Line Light-Scattering, Absorbance, and Refractive Index Detectors for Studying Proteins and Their Interactions

Techniques of using size-exclusion chromatography (SEC) with on-line light-scattering, uv absorbance, and refractive index detectors to characterize the polypeptide molecular weights of simple proteins or glycoproteins or to determine the stoichiometry of protein complexes are described. Two unique advantages of this approach over conventional SEC are that the molecular weight measurement is independent of elution position and can exclude the contributions from carbohydrates. When a protein or complex contains no carbohydrates, a two-detector method, i.e., light scattering combined with refractive index, can be used to calculate the molecular weight. When a protein contains carbohydrates, a three-detector method is used to calculate the molecular weight of polypeptide alone. Finally, a self-consistent three-detector method is used to determine the stoichiometry of a protein complex containing carbohydrates. Example applications for all these methodologies are described.     

Negative Refraction and Focusing of Photonic Crystals with Graded Negative Index in Visible Regime

In this paper, we designed a hexagonal lattice photonic crystal (PC) which presents negative refraction behavior in the broadband visible region. By varying the PC parameters, a graded index PC was obtained for the purpose of focusing a plane wave with large transmission. Finite-difference and time-domain algorithm-based numerical calculation was adopted to demonstrate the negative refraction and analyze the focusing effect. Calculation results demonstrate that the designed PCs have good focusing property together with large transmission. The proposed structures provide an approach for designing the negative refraction-based imaging systems.     

Design Optimization and Fabrication of Graphene/J-Aggregate Kretschmann-Raether Devices for Refractive Index Sensing Using Plasmon-Induced Transparency Phenomena

Plasmonics - Here, a novel plasmon-induced transparency (PIT) sensing platform based on a Kretschmann–Raether configuration with graphene/J-aggregate materials is proposed. The J-aggregate...     

1-D Metal-Dielectric-Metal Grating Structure as an Ultra-Narrowband Perfect Plasmonic Absorber in the Visible and Its Application in Glucose Detection

The need for an easy to fabricate perfect and narrowband light absorber in the visible range of electromagnetic (EM) spectrum has always been in demand for many scientific and device applications. Here, we propose a metal-dielectric-metal (MDM) 1-D grating plasmonic structure as a perfect narrow band light absorber in the visible and its application in glucose detection. The proposed structure consists of a 1- D grating of gold on the top of a dielectric layer on a gold film. Optimization for dielectric grating index (n), grating thickness (t), grating width (W), and grating period (P) has been done to improve the performance of plasmonic structure by calculating its quality factor and figure-of-merit (FOM). The optimized plasmonic structure behaves as a perfect narrowband light absorber. The flexibility to work at a specific wavelength is also offered by the proposed structure through an appropriate selection of the geometrical parameters and refractive index of the dielectric grating. The equivalent RC model is used to understand different components of the proposed structure on the optical response. The absorption response of the structure is invariant to the incident angle. Moreover, the calculated absorbance of the proposed plasmonic structure is ~ 100% with a narrow full-width half maxima (FWHM) of ~ 2.8 nm. We have numerically demonstrated a potential application of the proposed MDM absorber as a plasmonic glucose sensor in the visible range with detection sensitivity in the range of 140 to 195 nm/RIU.

     

Std1 and Mth1 Proteins Interact with the Glucose Sensors To Control Glucose-Regulated Gene Expression in Saccharomyces cerevisiae

The Std1 protein modulates the expression of glucose-regulated genes, but its exact molecular role in this process is unclear. A two-hybrid screen for Std1-interacting proteins identified the hydrophilic C-terminal domains of the glucose sensors, Snf3 and Rgt2. The homologue of Std1, Mth1, behaves differently from Std1 in this assay by interacting with Snf3 but not Rgt2. Genetic interactions between STD1, MTH1, SNF3, and RGT2 suggest that the glucose signaling is mediated, at least in part, through interactions of the products of these four genes. Mutations in MTH1 can suppress the raffinose growth defect of a snf3 mutant as well as the glucose fermentation defect present in cells lacking both glucose sensors (snf3 rgt2). Genetic suppression by mutations in MTH1 is likely to be due to the increased and unregulated expression of hexose transporter genes. In media lacking glucose or with low levels of glucose, the hexose transporter genes are subject to repression by a mechanism that requires the Std1 and Mth1 proteins. An additional mechanism for glucose sensing must exist since a strain lacking all four genes (snf3 rgt2 std1 mth1) is still able to regulate SUC2 gene expression in response to changes in glucose concentration. Finally, studies with green fluorescent protein fusions indicate that Std1 is localized to the cell periphery and the cell nucleus, supporting the idea that it may transduce signals from the plasma membrane to the nucleus.     

Microfabrication of Bubbular Cavities in PDMS for Cell Sorting and Microcell Culture Applications

We describe a novel technique, low surface energy Gas Expansion Molding （GEM）, to fabricate microbubble arrays in polydimethylsiloxane （PDMS） which are incorporated into parallel plate flow chambers and tested in cell sorting and microcell cuTture applications. This architecture confers several operational advantages that distinguish this technology approach from currently used methods. Herein we describe the GEM process and the parameters that are used to control microbubble formation and a Vacuum-Assisted Coating （VAC） process developed to selectively and spatially alter the PDMS surface chemistry in the wells and on the microchannel surface. We describe results from microflow image visualization studies conducted to investigate fluid streams above and within microbubble wells and conclude with a discussion of cell culture studies in PDMS.