Index Unit Research Articles

Stretching the Limits of Refractometric Sensing in Water Using Whispering-Gallery-Mode Resonators

A novel application of microresonators for refractometric sensing in aqueous media is presented. To carry out this approach, microspheres of different materials and sizes were fabricated and doped with Nd3+ ions. Under 532 nm excitation, the microspheres presented typical NIR Nd3+ emission bands with superimposed sharp peaks, related to the Whispering Gallery Modes (WGMs), due to the geometry of the microspheres. When the microspheres were submerged in water with increasing concentrations of glycerol, spectral shifts for the WGMs were observed as a function of the glycerol concentration. These spectral shifts were studied and calibrated for three different microspheres and validated with the theoretical shifts, obtained by solving the Helmholtz equations for the electromagnetic field, considering the geometry of the system, and also by calculating the extinction cross-section. WGM shifts strongly depend on the diameter of the microspheres and their refractive index (RI) difference compared with the external medium, and are greater for decreasing values of the diameter and lower values of RI difference. Experimental sensitivities ranging from 2.18 to 113.36 nm/RIU (refractive index unit) were obtained for different microspheres. Furthermore, reproducibility measurements were carried out, leading to a repeatability of 2.3 pm and a limit of detection of 5 × 10−4 RIU. The proposed sensors, taking advantage of confocal microscopy for excitation and detection, offer a robust, reliable, and contactless alternative for environmental water analysis.

All-Metal Metamaterial-Based Sensor with Novel Geometry and Enhanced Sensing Capability at Terahertz Frequency.

This research proposes an all-metal metamaterial-based absorber with a novel geometry capable of refractive index sensing in the terahertz (THz) range. The structure consists of four concentric diamond-shaped gold resonators on the top of a gold metal plate; the resonators increase in height by 2 µm moving from the outer to the inner resonators, making the design distinctive. This novel configuration has played a very significant role in achieving multiple ultra-narrow resonant absorption peaks that produce very high sensitivity when employed as a refractive index sensor. Numerical simulations demonstrate that it can achieve six significant ultra-narrow absorption peaks within the frequency range of 5 to 8 THz. The sensor has a maximum absorptivity of 99.98% at 6.97 THz. The proposed absorber also produces very high-quality factors at each resonance. The average sensitivity is 7.57/Refractive Index Unit (THz/RIU), which is significantly high when compared to the current state of the art. This high sensitivity is instrumental in detecting smaller traces of samples that have very correlated refractive indices, like several harmful gases. Hence, the proposed metamaterial-based sensor can be used as a potential gas detector at terahertz frequency. Furthermore, the structure proves to be polarization-insensitive and produces a stable absorption response when the angle of incidence is increased up to 60°. At terahertz wavelength, the proposed design can be used for any value of the aforementioned angles, targeting THz spectroscopy-based biomolecular fingerprint detection and energy harvesting applications.

Resonant Young's Slit Interferometer for Sensitive Detection of Low-Molecular-Weight Biomarkers.

The detection of low-molecular-weight biomarkers is essential for diagnosing and managing various diseases, including neurodegenerative conditions such as Alzheimer's disease. A biomarker's low molecular weight is a challenge for label-free optical modalities, as the phase change they detect is directly proportional to the mass bound on the sensor's surface. To address this challenge, we used a resonant Young's slit interferometer geometry and implemented several innovations, such as phase noise matching and optimisation of the fringe spacing, to maximise the signal-to-noise ratio. As a result, we achieved a limit of detection of 2.9 × 10-6 refractive index units (RIU). We validated our sensor's low molecular weight capability by demonstrating the detection of Aβ-42, a 4.5 kDa peptide indicative of Alzheimer's disease, and reached the clinically relevant pg/mL regime. This system builds on the guided mode resonance modality we previously showed to be compatible with handheld operation using low-cost components. We expect this development will have far-reaching applications beyond Aβ-42 and become a workhorse tool for the label-free detection of low-molecular-weight biomarkers across a range of disease types.

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.

Comparative efficacy of In-office and walking bleach techniques in whitening of non-vital teeth.

This study aimed to compare the efficacy of two non vital whitening techniques, In-office and Walking Bleach, using 35% hydrogen peroxide. The primary research question was to determine which technique achieves greater tooth color improvement. Fifty non-vital anterior teeth with discoloration were randomly assigned to either the In-office (n = 25) or Walking Bleach (n = 25) groups. Tooth color was measured using a Vita EasyShade V® spectrophotometer and visual scales (Vita Classical and Bleachguide) before treatment, after each bleaching session, and at a one-month follow-up. ΔE00, Whiteness Index (WID), and Shade Guide Unit (ΔSGU) values were calculated. Statistical analysis was performed using the Kruskal-Wallis and Mann-Whitney tests. Both techniques improved tooth color, with final ΔE00 values of 10.08 for In-office and 8.12 for Walking Bleach. WID values were significantly higher in the In-office group, indicating greater whitening efficacy. Significant differences favoring the In-office method were seen after the first bleaching (p = 0.0337), and one-month follow-up (p = 0.0327). Both the In-office and Walking Bleach techniques effectively improve the color of non-vital teeth, with the In-office method showing slight advantages at certain times. Clinicians can choose either technique based on safety, patient needs, and clinical context to achieve optimal results. This study provides evidence that both bleaching techniques are viable options for non-vital teeth whitening. The findings help clinicians choose the most appropriate technique based on biological safety and patient needs and desired outcomes, with the In-office technique being preferable for faster results.

Effects of Escherichia coli Nissle 1917 on immunity, blood constituents, antioxidant capacity, egg quality and performance in laying Japanese quail.

This study was conducted to evaluate the effects of E.coli Nissle 1917 (EcN) on immune responses, blood parameters, oxidative stress, egg quality, and performance of laying Japanese quail. A total of one-hundred day-old quail chicks were assigned to 1 of 4 treatments based on probiotic concentration: 1 (0 CFU/mL; control), 2 (104 CFU/mL), 3 (106 CFU/mL), and 4 (108 CFU/mL). The average egg production throughout the 8 wks of the laying phase increased with the increase in EcN supplementation (R2= 0.96). The egg production was also significantly different in wk 4, 7, and 8 of the laying phase with the control group demonstrating the poorest performance. External egg quality parameters, including shell strength, Roche index, albumen height, yolk weight, shell weight, shell thickness, and Haugh unit, also showed higher values in groups receiving EcN. Likewise, these groups demonstrated heavier egg weight (EW) and lower MDA in the meat sample. The MDA concentration of fresh yolk samples in groups receiving EcN was higher but diminished after iron-inducing (P < 0.05). No differences were observed in ADFI, FCR, EM, yolk cholesterol and triglyceride, hematocrit, SRBC, NDV, CMI immune responses (DNCB and PHA), H:L ratio, and internal organ weights. Plasma cholesterol and uric acid were the only blood constituents showing higher values in male birds in groups of EcN (P < 0.05); no appreciable differences were observed in the rest of the blood parameters in male birds and none in females. Further, a substantially higher Avian Influenza Virus (AIV) titer resulted from treatments 3 and 4 in male birds among humoral immune responses. These results demonstrated that EcN in the birds' drinking water could profoundly influence laying performance, egg quality, immune function, and enhanced antioxidant capacity.

A Polarization-Insensitive and Highly Sensitive THz Metamaterial Multi-Band Perfect Absorber.

In this article, we present a terahertz (THz) metamaterial absorber that blends two types of coordinated materials: Dirac semimetals and vanadium dioxide. Compared to other absorbers on the market, which are currently non-adjustable or have a single adjustment method, our absorber is superior because it has two coordinated modes with maximum adjustment ranges of 80.7% and 0.288 THz. The device contains four flawless absorption peaks (M1, M2, M3, and M4) spanning the frequency range of 2.0 THz to 6.0 THz, all with absorption rates greater than 99%. After calculation, the relative impedance of the device matches with that in free space, resulting in perfect absorption. In addition, our absorber has extremely excellent polarization insensitivity but is highly sensitive to changes in the environmental refractive index, with the highest environmental refractive index sensitivity of 716 GHz/RIU (gigahertz per refractive index unit). To sum up, the terahertz metamaterial absorber we showed has four perfect absorption peaks, high sensitivity, and stable polarization. This means it could be useful in areas like changing electromagnetic waves, making new sensors, and switching.

Triple ultraviolet to visible perfect absorptions of lifted metamaterial for highly sensitive sensing and slow light

Achieving multiple perfect absorptions from ultraviolet (UV) to near-infrared (IR) region is practically important for metamaterial-based efficient harvesting of photons and biosensor. Here, we theoretically demonstrate a triple narrow and broad perfect absorptions (PAs) from visible to UV range in a lifted metamaterial made of aluminum vertical split-ring resonators (Al VSRR) on silica nanostrip /Al mirror. The three simultaneously achieved narrowband and broadband PAs with bandwidth of 283.3 nm, 8.9 nm and 18.2 nm are excited from magnetic plasmon resonance, surface plasmons polariton and plasmon standing wave mode, respectively, which is further explained by the impedance matching theory. The triple-band absorption peaks are further tailored by changing the size of the structure. The group index of the lifted Al VSRR array can reach as large as 2.5 × 103 in the UV range. Moreover, due to the designed metamaterial being lifted with the reduced substrate effect, the figure of merit (FoM*) and sensitivity (S) in the UV range are as high as 1.1 × 106 and 306 nm per refractive index unit‌ (306 nm/RIU), respectively. The proposed lifted metamaterial could have a considerable effect on the development of various UV plasmonic applications, including slow light nanodevices and optical sensor.

Physical, optical properties and antibacterial activity of silver nanoparticles: Nanoclusters to nanoparticles formation on glass substrate by in-situ annealing

Silver nanoparticles (AgNPs) formed on in-situ annealed microscopic glass substrates from silver nanoclusters (AgNCs) generated by DC magnetron sputtering with inert gas condensation (IGC) technique. The substrate’s annealing temperature was below and above the glass transition temperature of 500 ºC and 600 ºC. The influence of annealing temperature on the surface morphology was studied using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were employed to investigate the surface composition, chemical states, and electronic states of the AgNPs on the glass substrates. On the in-situ annealed glass substrate at 500 ºC, the produced AgNPs revealed accumulation and aggregation. For in-situ annealed at 600 ºC, a homogeneous distribution of AgNPs on the glass substrate was witnessed. The refractive index test revealed that AgNPs deposition at 600 ºC achieved higher sensitivity with 27 nm/RIU (Refractive index unit). The antibacterial activity of AgNPs was also investigated using Escherichia coli and Bacillus cereus. In contrast, better antibacterial activity was obtained with in-situ annealing at 500 ºC, where 4-fold reductions compared with the control sample. Pre-determined properties can be precisely executed to achieve the desired performance as the so-called application-oriented engineered surface in the UHV system is established. This research highlighted the differences between two different annealing temperatures' effect on the base substrate material, which subsequently impacts the structure of AgNPs and their applications. Furthermore, the outcome of this work could contribute to the multifunctional surface for detecting heavy metals, various organic pollutants, and disinfection of water and food-borne pathogenic diseases.

Highly sensitive photonic spin Hall effect sensor with graphene-coated surface exciton polariton structure

The photonic spin Hall effect (PSHE) in a graphene-coated surface exciton polariton (SEP) structure is investigated in this work. The transverse shift of 32.95λ0 (17.53 μm) is achieved with the optimum graphene-coated SEP structure in the gaseous environment under λ0 = 532 nm illumination, which provides a 2.46-fold improvement compared to the optimum conventional SEP structure. The transverse shift is further improved to 76.39λ0 (i.e., 40.64 μm) with the graphene-coated long-range SEP (LRSEP) in the aqueous environment. Refractive index sensors based on the enhanced PSHE are proposed for sensing applications in the gaseous and aqueous environment, respectively, which possess the bulk refractive index sensitivities of 24424.4λ0 (12993.78 µm) 1/RIU (RIU: refractive index unit) and 57336.6λ0 (30503.1 µm) 1/RIU. The combination of SEP (LRSEP) and graphene layers provides a promising approach for enhancing the transverse shift of PSHE, and may find potential applications in gas sensing, chemical sensing, and biosensing base on the enhanced PSHE.

Risk Factors for Early Subsidence of 3D-Printed Artificial Vertebral After Anterior Cervical Corpectomy and Fusion

ObjectiveThe subsidence of vertebral body replacement may occur after anterior cervical corpectomy and fusion (ACCF) , which may lead to cervical kyphosis, spinal cord compression and neurological dysfunction. The authors aim to investigate the risk factors for early subsidence of 3D printed artificial vertebral (3D-PAVB) after ACCF surgery and to provide guidance for clinical practice. MethodsA retrospective analysis was conducted on the data of consecutive patients with cervical spondylosis who underwent ACCF surgery at Bethune Hospital of Shanxi from 2017 to 2020. The statistical data included age, gender, disease type, body mass index (BMI), surgical segment, vertebral height, Cobb Angle, and Hounsfeld Units (HU) values of the vertebral body and endplate. The clinical efficacy of the surgery was evaluated using Visual Analog Scale (VAS), Japanese Orthopedic Association (JOA), and Neck Disability Index (NDI). Follow-up data, such as VAS, JOA, NDI, and Cobb Angle, were obtained using a repeated-measures ANOVA analysis. Univariate analysis was conducted to identify the factors contributing to the early subsidence of the3D-PAVB, and independent risk factors were determined using logistic regression. The HU value was analyzed using the Receiver Operating Characteristic (ROC) curve and the area under the Area Under Curve (AUC) to predict the subsidence of the 3D-PAVB. ResultsA total of 66 patients were included in the study, out of which 19 patients experienced subsidence of 3D-PAVB,resulting in an incidence rate of 28.8%. The postoperative JOA, VAS, and NDI scores showed significant improvement in both the subsidence and non-subsidence groups. Upon conducting univariate analysis, significant differences were observed between the two groups in terms of age, diabetes, smoking, and lower vertebral Computed Tomography (CT) values. The average HU value of the subsidence group (251.39±52.615, n=19) was significantly lower than that of the non-subsidence group (317.06±73.587, n=47, p＜0.01). Multivariate analysis revealed that smoking and HU of the lower vertebra were independent risk factors for 3D-PAVB subsidence, with an AUC of 0.772 and an optimal threshold of 272 for HU (sensitivity 78.9%, specificity 74.5%). ConclusionThe occurrence of early subsidence of 3D-PAVB post ACCF surgery is influenced by two independent risk factors - smoking and low HU. To predict the likelihood of this outcome, it is advisable to consider smoking history and measure CT HU value prior to surgery. A lower CT HU value is indicative of a greater risk of subsidence.

A comparative dosimetric evaluation of dynamic conformal arc therapy and volumetric modulated arc therapy for lung stereotactic body radiotherapy

PurposeThis study assesses the viability of utilizing dynamic conformal arc therapy (DCAT) as an alternative to volumetric-modulated arc therapy (VMAT) in stereotactic body radiation therapy (SBRT) for lung cancer, with a focus on four-dimensional computed tomography (4DCT) in free-breathing conditions. Materials and methodsWe selected four non-small cell lung cancer (NSCLC) patients who had previously undergone VMAT SBRT and re-planned their treatment using DCAT. We compared the DCAT and VMAT plans based on dose distribution, conformity index (CI), homogeneity index (HI), gradient index (GI), and total monitor units (MUs). Quality assurance (QA) assessments for both plans were conducted using the Octavius 4D system (PTW, Freiburg, Germany). ResultsThe results showed that CIPaddick was 0.80 ± 0.06 and 0.79 ± 0.04 (p-value >0.05), HI was 1.16 ± 0.03 (p-value <0.05) and 1.07 ± 0.02, GI was 3.91 ± 0.05 and 3.40 ± 0.05 (p-value <0.05), and MU was 1880.42 ± 135.19 and 5020.82 ± 188.03 for DCAT and VMAT, respectively (p-value <0.05). The average gamma passing rate exceeded 95 % with a 2 %/2 mm criteria. The dose distribution displayed remarkable similarity between DCAT and VMAT. ConclusionThe DCAT technique exhibits the capacity to deliver PTV dose distributions comparable to those achieved with VMAT, while significantly reducing treatment duration.

Detection of vaccinia virus proteins in wastewater environment using biofunctionalized optical fiber semi-distributed FBG-assisted interferometric probes

In this work, we present the detection of proteins expressed by poxvirus with fiber-optic probes based on a semi-distributed interferometer (SDI) assisted by a fiber Bragg grating (FBG), performing the measurement directly into a wastewater sample. Modern biosafety applications benefit from real-time, dynamic-sensing technologies that can perform diagnostic tasks into a wide set of analytes, with a particular emphasis on wastewater, which appears to collect a significant number of viral titers in urban and indoor environments. The SDI/FBG probe can perform substantial progress in this field, as it embeds a dual sensitivity mechanism to refractive index changes (sensitivity up to 266.1 dB/RIU (refractive index units)) that can be exploited in biosensing, while simultaneously having the capability to measure the temperature (sensitivity 9.888 pm/°C), thus providing an intrinsic cross-sensitivity compensation. In addition, a standard FBG analyzer can be used as an interrogator, improving affordability and real-time detection over previous works. The probes have been functionalized with antibodies specific for L1, A27 and A33 vaccinia virus proteins, performing detection of a protein concentration in a scenario compatible with online viral threat detection. Direct detection of wastewater samples shows that the L1-functionalized sensor has a higher response, 9.1–11.3 times higher than A33 and A27, respectively, with a maximum response of up to 1.99 dB and excellent specificity. Dynamic detection in wastewater shows that the sensors have a response over multiple detection cycles, with a sensitivity of 0.024–0.153 dB for each 10-fold increase of concentration.

Enhanced Sensing of Diseased Blood Samples through One-Dimensional MgO-SiO2 Photonic Crystal Sensor

In this investigation, we present a tailored one-dimensional photonic crystal sensor (1D PCS), magnesium oxide (MgO) and silicon dioxide (SiO2) layers designed for the specific detection of diseased blood samples components, including plasma, platelets, red blood cells, and uric acid concentrations. The sensor structure is architecturally optimized for 6, 8,10,12,14, and 20 periods, encapsulating a central defect cavity that facilitates the interaction with the blood samples. Upon introducing the blood samples into this cavity, the transmittance spectrum is meticulously analyzed using the transfer matrix method to observe the variations in the defect mode’s wavelength. The study is conducted over a range of incident waves from wavelength 450 to 750 μm, enhancing the understanding of the sensor’s effect on the detection mechanism. In this context, our sensor demonstrates a remarkable sensitivity of approximately 815 nm per refractive index unit (RIU-1). It achieves a detection limit of 10–5, showcasing an exceptional ability to detect low concentrations of the infected blood components.Moreover, Q Factor of 3795 and FOM of 3369.18 indicate the sensor’s high precision in differentiating between healthy and infected blood samples.These findings underscore the potential of the proposed MgO-SiO2-based 1D PhC sensor in serving as a high-fidelity tool for biosensing application.

Multi-Frequency Asymmetric Absorption-Transmission Metastructures-Photonic Crystals and Their Application as a Refractive Index Sensor.

In this paper, a kind of metastructure-photonic crystal (MPC) with multi-frequency asymmetric absorption-transmission properties is proposed. It is composed of various dielectric layers arranged in a periodically tilting pattern. When electromagnetic waves (EMWs) enter from the opposite direction, MPC shows an obvious asymmetry. EMWs are absorbed at 13.71 GHz, 14.37 GHz, and 17.10 GHz in forward incidence, with maximum absorptions of 0.919, 0.917, and 0.956, respectively. In the case of backward incidence, transmission above 0.877 is achieved. Additionally, the MPC is utilized for refractive index (RI) sensing, allowing for wide RI range detection. The refractive index unit is denoted as RIU. The RI detection range is 1.4~3.0, with the corresponding absorption peak variation range being 17.054~17.194 GHz, and a sensitivity of 86 MHz/RIU. By adjusting the number of MPC cycles and tilt angle, the sensing performance and operating frequency band can be tailored to meet various operational requirements. This MPC-based RI sensor is simple to fabricate and has the potential to be used in the development of high-performance and compact sensing devices.

[formula omitted] modified U-shaped fiber surface plasmon resonance sensor with high sensitivity

Design of optical fiber structure and sensitive material coating are two effective performance improvement approaches for fiber optic surface plasmon resonance (SPR) sensors. Here, a tungsten diselenide (WSe2) modified U-shaped fiber optic SPR sensor is proposed. It is found that the sensing performances of the proposed U-shaped probe can be controlled with the thickness of gold film, WSe2 layers, and bending radius of the U-shaped fiber. A sensitivity of 27520 nm/RIU (RIU: refractive index unit) is obtained with the optimized U-shaped probe, which is about 11.56-fold and 12.29-fold improvements over the traditional in-line transmission fiber optic SPR sensors without WSe2 coating and with monolayer WSe2, respectively. These results demonstrate a promising approach for sensitivity improvement of fiber optic SPR sensors, and the proposed WSe2 modified U-shaped fiber optic SPR sensor may have prospective potential applications in biological sensing, chemical sensing, and environmental monitoring.

COMPARATIVE EGG QUALITY EVALUATION OF ISA BROWN AND FUNAAB ALPHA LAYERS REARED ON BATTERY-CAGE IN A ZAMFARA POULTRY FARM

Quality of eggs determines the acceptability to consumers. Egg quality differs in meaning as consumers’ assessments of quality are influenced by the intended use of the eggs. Thus, a study on comparative egg quality evaluation of Institut de Sélection Animale Brown (ISA Brown) and FUNAAB alpha layers reared on battery-cage was carried out. In this study, 300 table eggs, 150 each of the Institut de Sélection Animale, Brown (IB) and the FUNAAB Alpha (FA), were sourced from Magaji Memorial Farm in Gusau, Zamfara State, and transported to the Physical Laboratory of Faculty of Agriculture, Usmanu Danfodiyo University, Sokoto for quality evaluation within 24 hours of laying. On weekly basis for a period of five weeks, a total of 70 eggs (35 eggs from each strain) of uniform size were randomly selected and analysed for quality variations. Data were analysed statistically using student T-test. The results showed that among all indices only egg weight, eggshell surface, albumen index and Haugh unit were significantly (P≤0.05) different between both strains of layer chickens. The FA eggs were significantly heavier in weight (FA:59.50 ± 4.64g; IB:57.16 ± 5.17g) and better in shell surface area (FA:71.32 ± 3.65; IB:69.19 ± 4.16) than eggs of IB layers. However, the IB layer eggs had significantly (P≤0.05) better albumen index (IB:0.12 ± 0.11; FA:0.04 ± 0.01) and Haugh unit (IB:80.77 ± 13.29; FA:72.80 ± 14.57) than eggs of FA layers. It can be concluded that although IB eggs are better in term of internal qualities, eggs of FA layers are more likely to gain acceptability of consumers who care for better external qualities, like egg weight and shell quality.

Plasmonic sensor using generative adversarial networks integration

Machine learning (ML) has emerged as a pivotal force in enhancing the capabilities of sensing technologies across a broad spectrum of applications, from environmental monitoring and biosensing to agriculture, industrial automation, and so on. This study explores integrating ML techniques with photonic crystal fiber (PCF)-based plasmonic sensing techniques to elevate sensor performance. The PCF has two open channels to augment mode coupling, effectively reducing the gap between the analyte channel and core. Moreover, a thin layer of gold within the open channels of the PCF initiates efficient plasmon generation. The results demonstrate a maximum wavelength sensitivity of 9000 nm/refractive index unit (RIU), which can detect a wide range of analyte refractive index (RI) values from 1.33 to 1.40. The sensor exhibits the maximum amplitude sensitivity of 490.41 RIU−1. It also boasts a resolution of 1.11 × 10−5 RIU and the maximum figure-of-merit (FOM) achieved is 138.04 RIU−1 at an analyte RI of 1.39. Furthermore, this research introduces a method utilizing generative adversarial networks (GAN) to expand training data for an artificial neural network (ANN) model. This approach substantially improves the prediction of confinement loss across various analytes and wavelengths in a unique geometric configuration. The sensor’s versatility makes it ideal for various applications, including chemical sensing and medical diagnostics.

High-Sensitivity Janus Sensor Enabled by Multilayered Metastructure Based on the Photonic Spin Hall Effect and Its Potential Applications in Bio-Sensing.

The refractive index (RI) of biological tissues is a fundamental material parameter that characterizes how light interacts with tissues, making accurate measurement of RI crucial for biomedical diagnostics and environmental monitoring. A Janus sensor (JBS) is designed in this paper, and the photonic spin Hall effect (PSHE) is used to detect subtle changes in RI in biological tissues. The asymmetric arrangement of the dielectric layers breaks spatial parity symmetry, resulting in significantly different PSHE displacements during the forward and backward propagation of electromagnetic waves, thereby realizing the Janus effect. The designed JBS can detect the RI range of 1.3~1.55 RIU when electromagnetic waves are incident along the +z-axis, with a sensitivity of 96.29°/refractive index unit (RIU). In the reverse direction, blood glucose concentrations are identified by the JBS, achieving a sensitivity of 18.30°/RIU. Detecting different RI range from forward and backward scales not only overcomes the limitation that single-scale sensors can only detect a single RI range, but also provides new insights and applications for optical biological detection through high-sensitivity, label-free and non-contact detection.

Analysis of the causal effect of the Covid-19 pandemic on parcel delivery: The case of Belo Horizonte, Brazil

The impact of the COVID-19 pandemic on e-commerce is evident and well-reported. However, few studies have measured the effect of restrictive measures on e-commerce. Therefore, this article aims to explore the causal effect of the COVID-19 pandemic on parcel deliveries. For this purpose, different techniques (interrupted time series analysis, counterfactual analysis, and structural equation modelling) were used to verify to what extent the number of cases and deaths from COVID-19 and the rigour of the restriction measures (measured by the stringency index) increased parcel deliveries in Belo Horizonte, Brazil. The results confirm the causal effect of the stringency index that positively influences parcel deliveries. The marginal effect of the stringency index on parcel deliveries was 5.44 deliveries per day during the pandemic compared to before the pandemic. This result means that each unit of stringency index increases the number of parcel deliveries by 5.44. The effects vary depending on the technique used; however, all showed the contribution of stringency index on parcel deliveries.