Index Sensitivity Research Articles

Fano Resonant Sensing in MIM Waveguide Structures Based on Multiple Circular Split-Ring Resonant Cavities

In this work, a non-through metal–insulator–metal (MIM) waveguide capable of exciting three Fano resonances was designed and numerically studied using the finite element method. Fano resonances are achieved through the interaction between the modes of multiple circular split-ring resonator cavities and the waveguide. The effect of coupling between different resonators on the Fano resonance peaks is investigated. Independent tuning of the Fano resonance wavelength and transmission rate is accomplished by modifying the structural rotation angle and geometric parameters. After optimizing these parameters, the structure achieves an optimal refractive index sensitivity of 946.88 nm/RIU and a figure of merit of 99.17. The proposed structure holds potential for guiding the design of nanosensors.

Association of gestational and childhood circulating C-peptide concentrations in the hyperglycemia and adverse pregnancy outcomes follow-up study.

This study examined the association of gravida C-peptide with progeny islet function and insulin sensitivity in the Hyperglycemia and Adverse Pregnancy Outcome Follow-up Study (HAPO FUS). Pregnancy 3rd trimester oral glucose tolerance test (OGTT), cord blood, and offspring OGTT glucose, C-peptide and insulin at age 10-14years were analyzed for 4,121 mother-child dyads. Gravida fasting and 1-hour C-peptide concentration correlations with cord blood and childhood C-peptide, insulin, insulinogenic index and insulin sensitivity, and insulin resistance [HOMA-IR]), were assessed by multiple linear regression. Maternal covariates included age, gestational age, BMI and glucose at OGTT; child covariates included age, sex, pubertal stage, BMI z score and glucose. Gravida fasting and 1-hour OGTT C-peptide was positively correlated with cord blood C-peptide, offspring OGTT C-peptide and insulin concentrations at fasting, 30min, 1-hour and 2-hour at 10-14years of age. Maternal fasting and 1-hour C-peptide concentrations were positively correlated with the insulinogenic index and HOMA-IR but inversely correlated with insulin sensitivity. Maternal C-peptide explained more variance than maternal glucose concentrations (3.0-17.9% vs 0.2-3.5%). The correlation between gravida and offspring C-peptide suggests that without crossing the placenta, insulin may influence the offspring pancreatic beta-cell development and insulin sensitivity.

Sensitivity of communities' trait-based indices to species selection.

Trait-based indicators offer insights into environmental impacts on communities but are often limited by the availability of species traits data, relying on subsets that may omit less studied taxa, leading to bias. To address this, we tested the species selection's influence on trait-based indices using filters based on occurrence, species' distributions, and abundance. Using data from two bottom-trawl surveys, we compiled 15 traits for the 246 most common demersal species in two temperate ecosystems in the North-East Atlantic and Mediterranean Sea. Our analyses revealed that trait data is strongly biased toward abundant and large species, particularly those of commercial importance or conservation concern. While species selection had minimal impact on community traits, excluding invertebrates strongly affected the results, highlighting their key role in community dynamics.

Simulation study on ultra-wideband and ultra-narrowband switchable terahertz metamaterial absorbers based on deep neural networks

Supported by deep neural networks (DNNs), a simulation study on an ultra-wideband (UWB) to ultra-narrowband (UNB) switchable terahertz metamaterial absorbers (THz MAs) was designed and optimized. By leveraging the phase transition properties of vanadium dioxide (VO2), the device achieves nearly perfect absorption, switching between UWB and UNB modes. Finite element analysis was used to simulate and analyze the constructed model. Simulation results indicate that when VO2 is in its metallic state, the device functions as a UWB absorber with an absorption bandwidth of 11.54 THz over the 3.88–15.42 THz range, achieving an absorption rate exceeding 90% and a relative bandwidth (RBW) of 119.6%. When VO2 is in its insulating state, the device switches to a UNB absorber, reaching an absorption rate close to 100% at 13.927 THz. In this state, material detection was conducted, revealing that the device has a maximum refractive index sensitivity (S) of 0.33 THz/RIU and a corresponding quality factor (Q) of up to 515.8, enabling high sensing functionality. Its absorption performance is insensitive to TE and TM polarizations. Additionally, the effects of incident and polarization angles on the operating characteristics were studied. The proposed absorber demonstrates excellent polarization insensitivity, angle stability, and UWB and UNB advantages, offering valuable insights for new multifunctional THz device research. It holds significant application potential in short-range wireless THz communication, ultra-fast optical switching, sensing, transient spectroscopy, and electromagnetic stealth.

Tunable multiband asymmetric transmission based on flexible chiral metamaterial for refractive index sensing

Tunable multiband asymmetric transmission (AT) effect is effectively demonstrated using a polydimethylsiloxane (PDMS)-based flexible chiral metamaterial (FCM) in the mid-infrared region. The unit cell of the FCM comprises J-shaped and F-shaped gold patterns to achieve three-dimensional (3D) chirality, and a multiband AT effect can be realized. Due to the excitation of enantiomerically sensitive plasmons, the FCM can realize a tunable multiband AT effect that is rarely reported, whose peak values can reach 51.89%, 37.72%, and 28.91% at resonance wavelengths of 9.03 µm, 10.25 µm, and 12.77 µm, respectively. The tunability of the FCM demonstrated that the peaks of AT shift to longer wavelengths when stretching along different directions respectively. Compared with reported refractive index sensors based on chiral metamaterial, FCM has tunable multibands and better refractive index sensitivity, which can reach 7875 nm/RIU, 3375 nm/RIU, and 1625 nm/RIU, respectively. Our proposed FCM opens an avenue to develop refractive index sensors.

Dual-function terahertz metamaterial absorber based on microfluidic structures

In recent years, terahertz metamaterial sensors have shown great potential in label-free biosensing; yet, the detection of high-absorption liquid samples that are sensitive to terahertz waves remains a significant challenge. In this study, a dual-function absorber capable of dynamically switching between broadband absorption and high-sensitivity sensing is proposed based on the microfluidic technology and phase change characteristics of vanadium dioxide (VO2). Compared with traditional terahertz microfluidic sensors, this structure differs in that it incorporates a VO2 film as a separation layer in the sensor cover plate and a VO2 square resonator on top. This configuration not only exhibits high-sensitivity sensing but can also function as an absorber for broadband absorption. When VO2 is in the metallic state, the structure acts as a broadband absorber with an absorption rate exceeding 90% across the 1.09–3.02 THz range. When VO2 is in the insulating state, the structure functions as a microfluidic sensor, achieving an absorption rate above 99.9% at 1.438 and 2.068 THz, with nearly perfect absorption and refractive index sensitivities of 532 and 785 GHz/RIU, respectively; the quality factor is 17.6 and 23.5, respectively, indicating excellent sensing performance. Moreover, due to the symmetry of the metal micro-structured layer and the VO2 square resonator, the device exhibits polarization insensitivity and stability at large incident angles. In summary, this structure significantly broadens the applications of traditional absorbers and sensors and holds promise for future applications in electromagnetic cloaking, energy harvesting, and biomedical detection.

Higher visceral and lower peripheral adiposity characterize fat distribution and insulin resistance in Asian Indian women with Polycystic Ovary Syndrome in Mauritius.

Introduction There are controversies about whether women with polycystic ovary syndrome (PCOS) show a disproportionately higher visceral adiposity, and its relevance to their higher cardiometabolic risks. We investigated in women of Asian Indian descent in Mauritius, a population inherently prone to abdominal obesity, whether those with PCOS will show a more adverse cardiometabolic risk profile that could be explained by abnormalities in fat distribution. Methods Young women newly diagnosed with PCOS (n=25) were compared with a reference control cohort (n =139) for the following measurements made after an overnight fast: body mass index (BMI), waist circumference (WC), body composition by dual-energy x-ray absorptiometry, blood pressure and blood assays for glycemic (glucose, HbA1c, insulin) and lipid (triglycerides, cholesterols) profiles. Results Compared to controls, women with PCOS showed, on average, higher BMI, WC, fat mass and lean mass (p<0.01), but linear regression analyses indicate that, for the same BMI (or same WC), the two groups showed no significant differences in fat mass and lean mass. By contrast, linear regression plots indicate that for the same total fat mass, women with PCOS showed higher trunk, android and visceral fat (p<0.01), no difference in abdominal subcutaneous fat, and lower peripheral (gynoid or limb) fat (p<0.05). Furthermore, the women with PCOS showed higher fasting plasma insulin, insulin resistance (HOMA-IR) index and lower insulin sensitivity index QUICKI (all p<0.001), which were completely or markedly abolished after adjusting for visceral fat or central-to-peripheral fat ratios. Conclusion In Mauritius, young women of Asian Indian descent with PCOS show altered fat distribution characterized by a disproportionately higher visceral (hazardous) adiposity in parallel to lower peripheral (protective) adiposity, which together explain their exacerbated state of hyperinsulinemia and insulin resistance.

Designing a terahertz optical sensor based on helically twisted photonic crystal fiber for toxic gas sensing

A novel helically twisted photonic crystal fiber (PCF) is designed and proposed for sensing toxic gases with refractive indices ranging from 1.00 to 1.08. The PCF consists of twelve hollow pipes arranged circularly around the hollow core to support THz radiation propagation. Low-loss polymer Topas is used as the background material of cladding. The fiber is twisted 360° over 50 cm to enhance anti-resonance in the THz region. The fundamental LP01 mode is analyzed using the finite-difference eigenmode (FDE) method. The sensor operates across four frequency bands (0.2 to 3.0 THz) with minimal transmission loss (~ 10⁻⁴ 1/cm). Key parameters such as refractive index sensitivity, relative sensitivity, resolution, and figure of merit (FOM) are evaluated. The average refractive index sensitivities are 1450, 2250, 3000, and 2550 for Bands 1 to 4, respectively, with 100% relative sensitivity across all bands. The sensor detects refractive index changes as small as 10⁻⁴. The FOM, defined as the inverse of the full width at half maximum, exceeds 30 1/RIU, reaching up to 250 1/RIU due to sharp resonance peaks. Compared to other THz sensors, this design offers enhanced performance in sensing gases like SOx, NOx, and CO, while maintaining a simple structure.

Fiber ring laser biosensor based on no-core fibers for label-free DNA biomolecule measurements.

An erbium-doped fiber ring laser based on a single-mode fiber-no-core fiber-single-mode fiber (SMF-NCF-SMF) structure was constructed and experimentally demonstrated for label-free DNA hybridization measurement. The SMF-NCF-SMF structure acts as a sensing element and a filter to select the laser wavelength. The proposed fiber ring laser sensor exhibits a high optical signal-to-noise ratio (SNR, >50 dB) and narrow full width at half maximum (FWHM, <0.05 nm). Its refractive index sensitivity is 116.8 nm per RIU in the range of 1.3406-1.3705, and its detection limit is 1.79 × 10-4 RIU. By continuously monitoring the laser wavelength, we successfully achieved label-free measurement of complementary DNA (cDNA) at concentrations as low as 1 μM. Subsequently, the specificity of the sensor was detected by non-complementary DNA (N-cDNA). Experimental results show that the fiber ring laser biosensor has the advantages of simple operation, label-free measurement, and high specificity. Furthermore, it shows a broad application prospect in several fields, especially in key areas such as medical diagnosis and cancer screening.

Comparative Sensitivity of MRI Indices for Myelin Assessment in Spinal Cord Regions.

Background/Objectives: Although multiple magnetic resonance imaging (MRI) indices are known to be sensitive to the noninvasive assessment of myelin integrity, their relative sensitivities have not been directly compared. This study aimed to identify the most sensitive MRI index for characterizing myelin composition in the spinal cord's gray matter (GM) and white matter (WM). Methods: MRI was performed on a deer's ex vivo cervical spinal cord. Quantitative indices known to be sensitive to myelin, including the myelin water fraction (MWF), magnetization transfer ratio (MTR), the signal ratio between T1- and T2-weighted images (T1W/T2W), fractional anisotropy (FA), mean diffusivity (MD), electrical conductivity (σ), and T1, T2, and T1ρ relaxation times were calculated. Their mean values were compared using repeated measures analysis of variance (ANOVA) and post hoc Bonferroni tests or Friedman and post hoc Wilcoxon tests to identify differences across GM and WM columns possessing distinct myelin distributions, as revealed by histological analysis. Relationships among the indices were examined using Spearman's rank-order correlation analysis. Corrected p < 0.05 was considered statistically significant. Results: All indices except σ differed significantly between GM and all WM columns. Two of the three WM columns had significantly different MWF, FA, MD, and T2, whereas one WM column had significantly different MTR, σ, T1, and T1ρ from the others. A significant moderate to very strong correlation was observed among most indices. Conclusions: The sensitivity of MRI indices in distinguishing spinal cord regions varied. A strategic combination of two or more indices may allow the accurate differentiation of spinal cord regions.

Mid-infrared surface plasmon resonance fiber optic sensors.

We propose and experimentally demonstrate what we believe to be the first mid-infrared surface plasmon resonance (SPR) fiber optic sensor using a D-shaped multimode silica optical fiber coated with a 105 nm indium tin oxide (ITO) layer. The sensor shows resonance around 2700 nm, with a refractive index sensitivity of 1065.70 nm per refractive index unit (nm/RIU) for refractive indices ranging from 1.33 to 1.42. Since the evanescent wave outside the fiber decays within approximately 1/3 of its wavelength, the use of mid-infrared wavelengths can significantly increase the probing depth of SPR sensors compared to what is obtained when using visible light. This would allow SPR sensors to probe a larger volume, potentially improving sensitivity and signal-to-noise ratio. In addition, the mid-infrared region aligns with the molecular fingerprint region, which can unlock the potential for gas detection.

Numerical simulation of electromagnetically induced transparency in composite metamaterial

Abstract In high-refractive-index dielectric nanostructure, the Mie resonance become evident, and the destructive interference of the radiation fields from electric and toroidal dipole moments results in the excitation of anapole state, which has the unique optical properties of a dark state and can support the excitation of more diverse optical phenomena, such as the electromagnetically induced transparency (EIT) effect. In this study, we performed numerical simulations of a composite metamaterial consisting of Si nanocubes and gold nanorods. The Au-Si composite structure produces an electromagnetically induced transparency spectrum based on the coupling of the optical dark channel (i. e. anapole state) and bright channel (i. e. localized surface plasmon resonance). By tailoring the surface structure of the dielectric Si cube, the surface charge and current distributions can be modified, and finally, the nonradiative anapole state may be influenced and manipulated. The results show that the modified metal/dielectric metamaterial can realize an electromagnetically induced transparency effect with a transmission of up to 95% and a refractive index sensitivity of 170 nm RIU−1.

Simultaneous tri-parameter surface plasmon resonance photonic crystal fiber sensor

Abstract This study presents a photonic crystal fiber (PCF) integrated with a surface plasmon resonance (SPR) sensor that utilizes two orthogonal polarization core modes for sensing. The PCF features a thin indium tin oxide (ITO) layer on the inner channel and lower polished surface, an upper polished surface with a thin gold film, and an inner channel filled with magnetic fluid (MF) for magnetic field detection. Additionally, a temperature and refractive index sensitive material polydimethylsiloxane (PDMS) is placed on the lower polished surface, while the upper polished surface is designed for refractive index measurement. This multifunctional PCF-SPR sensor offers a compact and efficient solution for simultaneous detection of magnetic fields, temperature, and refractive index variations. The highest magnetic field sensitivity in the range of 0~12Oe is 11.1nm/Oe, the highest temperature sensitivity in the range of 20~400℃ is -0.5nm/℃, and the highest refractive index sensitivity in the range of 1.17~1.35μm is 1000nm/RIU. The designed sensor effectively mitigates the cross-sensitivity issues during concurrent measurements of the magnetic field, temperature, and refractive index simultaneously, presenting significant potential for applications in complex environment, including mineral resource exploration, geological and environmental assessments.&amp;#xD;

Deposition of plasmonic ITO nanoparticles by near-infrared laser ablation

Compound nanoparticles (NPs) attract attention because of their unique electrical, optical, and catalytic properties. Among them, plasmonic tin-doped indium oxide (ITO) NPs are characterized by transparency in the visible wavelength range and tunable localized surface plasmon resonance (LSPR) in the near-infrared (NIR) range due to high electronic conductivity. To date, they have been usually synthesized by a chemical solution process. However, the chemically synthesized ITO NPs are capped with organic protecting agents, which often block exchange of charge carriers and access of chemical species to the NPs, limiting some applications. In the present study, we propose a method for direct deposition of ITO NPs on a glass or plastic substrate using commercially available ITO-coated glass via NIR laser ablation. The LSPR characteristics of the ITO NPs, thus, prepared were controlled by changing the ablation conditions such as laser power. In addition, the potential applications of the ITO NPs were also investigated through measurements of their refractive index sensitivity and magnetic circular dichroism.

Improved Refractive Index Sensitivity with Gold-Coated D-Shaped Coreless Fiber Sensors

Improved Refractive Index Sensitivity with Gold-Coated D-Shaped Coreless Fiber Sensors

Metasurface-Enabled Microphotonic Biosensors via BIC Modes

Photonic biosensors based on bound states in the continuum (BIC) resonant modes exhibit a transformative potential for high-sensitivity, label-free detection across various diagnostic applications. BIC-enabled metasurfaces, utilizing dielectric, plasmonic, and hybrid structures, achieve ultra-high Q-factors and amplify target molecule interactions on functionalized sensor surfaces. These unique properties result in increased refractive index sensitivity and low detection limits, essential for monitoring biomolecules in clinical diagnostics, environmental analysis, and food safety. Recent advancements in BIC-enabled metasurfaces have demonstrated ultra-low detection limits in the zeptomolar range, making these devices highly promising for real-world applications. This review paper critically discusses the design principles of BIC-based biosensors, emphasizing key factors such as material selection, structural asymmetry, and functionalization strategies that enhance both sensitivity and specificity. Additionally, recent advancements in fabrication techniques that enable precise BIC control with scalable approaches for practical biosensing applications are examined. Case studies demonstrate the effectiveness of BIC metasurfaces for real-time, low-concentration detection, highlighting their versatility and adaptability. Finally, the review discusses future challenges and opportunities, such as integration with microfluidics for point-of-care testing and multiplexed sensing, underscoring the potential of BIC-based platforms to revolutionize the field of biosensing.

Glasgow coma scale may be a predictive factor for delayed neurological sequelae after carbon monoxide poisoning: a retrospective analysis of a nationwide multicenter observational registry in Japan

Acute carbon monoxide poisoning (ACOP) is a cause of accidental or deliberate deaths worldwide. Subsequent complications, particularly delayed neurological sequelae (DNS), are preventable and treatable based on their pathophysiology. Hyperbaric oxygenation therapy (HBO) is a potential procedure for preventing and treating DNS; however, the effects of HBO on DNS are unclear and debated. In the present study, we investigated which factors are associated with the development of DNS and the effects of HBO in patients with ACOP. We performed retrospective subanalyses of the COP-J registry, focusing on adults who underwent HBO, regardless of whether they developed DNS. The multivariable analysis showed that the Glasgow coma scale (GCS) on admission was significantly associated with DNS (odds ratio 0.736; 95% confidence interval 0.608-0.892; P = 0.002). The receiver operating characteristic curve analysis of GCS for DNS revealed a cutoff value of 12.5 according to Youden's index (sensitivity 80.8%, specificity 76.9%). This retrospective analysis of a nationwide Japanese registry of ACOP showed that low GCS scores on admission could be a predictive factor for DNS, with a possible cutoff value of ≤12, in patients who undergo HBO.

Association between sensitivity to thyroid hormone indices and type 2 diabetic microvascular complications in euthyroid patients

The correlation between thyroid hormone (TH) sensitivity and microvascular complications of type 2 diabetes mellitus (T2DM) remains uncertain. This study aimed to explore the association between TH sensitivity and the risk of diabetic kidney disease (DKD), diabetic retinopathy (DR), and diabetic neuropathy (DNP) in euthyroid T2DM patients. This study included a total of 946 hospitalized T2DM patients and calculated their sensitivity to the TH index, and each patient completed screenings for DKD, DR, and DNP. Multivariate logistic regression, generalized additive modeling, and subgroup analysis were used to assess the association between TH index sensitivity and the risks of DKD, DR, and DNP. After adjusting for confounding factors, a significant linear correlation was observed between the sensitivity of the thyroid feedback quartile index 3 (TFQI3) and DKD risk. However, the sensitivities of thyroid-stimulating hormone index (TSHI), thyrotropin thyroxine resistance index (TT4RI) and partial thyroid feedback quartile index (PTFQI) exhibited nonlinear correlations with the risk of developing DKD. The effect sizes to the left of the inflection point for TSHI, TT4RI and PTFQI were (odd ratio [OR] = 0.53, 95% confidence interval [CI]: 0.288–0.977), (OR = 0.863, 95%Cl: 0.751–0.992) and (OR = 0.007, 95%Cl: 0-0.724), respectively. However, there was no significant correlation between TH index sensitivity and DR/DNP risk. This study provides valuable insights into the relationship between TH sensitivity and the risks of DKD, DR, and DNP, with substantial clinical implications for individual prediction among T2DM patients.

Portal vein pulsatility is associated with the cumulative fluid balance: A post hoc longitudinal analysis of a prospective, general intensive care unit cohort.

Previous studies have explored tools for evaluating the effects of positive fluid balance, with recent emphasis, and controversies, on venous ultrasound parameters and composite scores. The portal vein pulsatility index and the renal venous pattern have emerged as the most promising indicators of volume-induced venous congestion. But in the general intensive care unit (ICU), numerous factors influence cardiovascular homeostasis, affecting venous function. This study aimed to evaluate the factors associated with portal vein pulsatility index in general ICU patients. Secondary objectives were to examine the correlations between pulsatility index and additional markers of congestion. This exploratory study was a post hoc analysis of a prospective, multicentric, observational database. The data collection was performed in four ICUs in university-affiliated or tertiary hospitals. This study included adult patients within 24 h of general ICU admission with an expected ICU length of stay of more than 2 days. Patients underwent clinical, biological, and echocardiographic assessments at several times: ICU admission, day 1, day 2, day 5 and the last day of ICU. The study primary endpoint was the portal vein pulsatility index during the course of the patients' stay on the ICU. One hundred forty-five patients and 514 haemodynamic evaluations were analysed. The mean age of the patients was 64 ± 15 years, 41% were women, with a median [IQR] admission simplified acute physiology score II of 46 [37 to 59]. The univariable followed by multivariable mixed-effects linear regression analyses demonstrated an association between portal vein pulsatility index, heart rate [estimate -0.002 (95% CI, -0.003 to -0.001), P < 0.001] and the cumulative fluid balance [estimate 0.0007 (95% CI, 0.00007 to 0.001), P = 0.024]. Portal vein pulsatility index showed no agreement with CVP of at least 12 mmHg (kappa correlation -0.008, P = 0.811), negative passive leg raising (kappa correlation -0.036, P = 0.430), mean inferior vena caval (IVC) diameter greater than 2 cm (kappa correlation -0.090, P = 0.025), maximal IVC diameter greater than 2 cm (kappa correlation -0.010, P = 0.835), hepatic vein systolic/diastolic ratio less than 1 (kappa correlation 0.043, P = 0.276), or renal vein pulsatile pattern (kappa correlation -0.243, P < 0.001). The study findings emphasise the unique sensitivity of portal vein pulsatility index in assessing fluid balance in general ICU patients. The lack of correlation between portal vein pulsatility index and other parameters of venous congestion underscores its potential to provide distinctive insights into venous congestion.

Hyperbolic-Metamaterial-Based Optical Fiber SPR Sensor Enhanced by a Smart Hydrogel for Perspiration pH Measurements.

An optical fiber surface plasmon resonance (SPR) sensor, leveraging hyperbolic metamaterials (HMMs) and pH-sensitive hydrogels, has been devised for pH detection in perspiration. Dispersion-tunable HMMs enable the sensor to transcend the inherent structural constraints of an optical fiber and enhance its refractive index (RI) sensitivity. pH-sensitive hydrogels exhibit diverse swelling behaviors due to varying ionization degrees of carboxyl groups under different solution pH conditions, leading to a notable RI change. The sensor achieves a high RI sensitivity of 6963.64 nm RIU-1 and remarkable pH sensitivity of -64.04 and -30.63 nm pH-1 within the pH ranges of 2.7 to 4.7 and 4.7 to 7.5, respectively. Compared to the sensitivity of three other constituents in perspiration, namely, urea, sodium chloride, and glucose, the sensor demonstrates exceptional pH selectivity. Additionally, it maintains good stability during operation and after prolonged storage. It is believed that the sensor has potential in health monitoring, medical diagnosis, disease treatment, etc.