Resonance Wavelength Shift Research Articles

Towards early diagnosis and screening of Alzheimer’s disease using frequency locked whispering gallery mode microtoroids

Alzheimer’s disease (AD) is a form of dementia marked by amyloid plaques and neurofibrillary tangles in the brain. Amyloid beta (Aβ) is an AD biomarker which is linked to these plaques and tangles. Measuring Aβ levels can help with early AD diagnosis and aid in drug studies and delaying dementia. This is challenging, however, due to low AD biomarker levels in biofluids. Here we use FLOWER (frequency-locked optical whispering evanescent resonator) to quantify levels of post-mortem cerebrospinal fluid (CSF) Aβ42 in control, mild cognitive impairment (MCI), and AD participants. FLOWER measures the resonant wavelength shift of a microtoroid due to changes in the refractive index within its evanescent field. FLOWER can measure CSF Aβ42 (area under curve, AUC = 0.92) with higher performance than ELISA (AUC = 0.82) and can distinguish between control and MCI samples. This demonstrates FLOWER’s ability to screen CSF samples for diagnosis of AD.

Chitosan-stabilized gold nanoparticles decorated with a thiodiacetic acid nanoprobe for selective detection of arsenic(iii) in rice and water samples.

A sensitive and selective method for the detection of arsenic(iii) (As3+) based on chitosan-stabilized gold nanoparticles (CS/AuNPs) decorated with a 2,2'-thiodiacetic acid (TDA) nanoprobe was developed and used to detect and indicate the contamination of rice, drinking water and environmental water samples. AuNPs were reduced and stabilized with CS and subsequently functionalized with TDA. As3+ interacted with the carboxylate group of TDA to form an As-TDA complex, inducing the aggregation of CS/AuNPs@TDA. The aggregation of CS/AuNPs@TDA was accompanied with a change in color from red to bluish purple and a shift in surface plasmon resonance wavelength from 525 nm to 645 nm. The response for the detection of As3+ was linear at concentrations from 10 to 1000 μg L-1 with a limit of detection of 6.1 μg L-1. The method exhibited selectivity toward As3+ among various cations (As5+, Cu2+, Fe3+, Fe2+, Hg2+, Al3+, Cr3+, Cd2+, Co2+, Ni2+, Pb2+ and Zn2+) and anions (Br-, Cl-, F-, SO4 2-, NO3 - and PO4 2-). The CS/AuNPs@TDA nanoprobe was applied to detect As3+ in rice, drinking water and environmental water samples. The results were consistent with those obtained via inductively coupled plasma-optical emission spectrometry (ICP-OES). Satisfactory recoveries ranging from 88.22% to 105.74% (RSDs of 0.25-2.99%) were obtained from spiked samples.

Exploring Aptamer‐Based Metasurfaces for Label‐Free Plasmonic Biosensing of Breast Tumor‐Derived Exosomes

AbstractExosomes are critical tumor biomarkers, which can be detected by label‐free sensing of plasmonic metasurfaces with expensive antibody functionalization. Due to their low cost and small size, aptamers should be promising to replace antibodies in plasmonic metasensing of exosomes. However, research on aptamer‐based plasmonic metasensing of exosomes is still unexplored. Here, the optical near‐field sensing mechanism of aptamer‐based plasmonic metasurface (APM) is investigated. Based on the study of the evanescent field of APM, using thiol‐modified aptamer boosts the utilization rate of resonance wavelength shift from 27.5% to 83.3% compared to biotinylated aptamers, attributed to a significant reduction in the near‐field occupation of the biofunction layer. Moreover, APM biosensors effectively detect clinical serum exosomes for breast cancer (BC) diagnosis and classification. The receiver operating characteristic analysis shows an area under the curve of 99.3% for APM diagnosis, surpassing the 79.1% for hematological tests of the conventional BC biomarker CA153. The results also indicate that APM biosensors can be a noninvasive tool for molecular classification of BC with great distinguishment of P < 0.0001. The research demonstrates that APM biosensors are enabling a reliable and convenient platform to facilitate clinical hematological tests of exosomes for auxiliary diagnosis of cancer.

Near-infrared Sb2S3 metasurface with giant and tunable circular dichroism

Tunable circular dichroism (CD) is crucial for the development of chiral imaging, biosensing, and optical communication etc Herein, by employing the ultralow loss reversible phase-change materials Sb2S3, we achieved the giant and tunable CD signal in a chiral double-L array. Numerical results show that CD strength of the Sb2S3 metasurface can be over 0.9 in both amorphous and crystalline states. Strikingly, the resonant wavelength shift induced by the phase change of Sb2S3 reaches 93 nm, proving that the proposed metasurface possesses excellent tunability. In addition, the physical mechanism of the giant CD response is explained via multipole analysis. The proposed Sb2S3 metasurface capable of giant and tunable CD effect will facilitate the design of tunable dichroic devices.

Multiple Fano Resonance Modes based Plasmonic Refractive Index Sensor for Edible Oil Adulteration Detection

Surface plasmon polariton (SPP)-based plasmonic sensors are increasingly replacing traditional bulky sensors in refractive index sensing, biosensing, food adulteration detection, and other applications due to their unique optical features and different Metal-Insulator-Metal (MIM) topologies. The present research introduces a new design for a highly sensitive MIM waveguide-based refractive index sensor. This design incorporates an innovative combination of an inverted U-shaped rectangular split-ring resonator (RSRR), a semi-circle-split-ring resonator (SCSRR), and a stub. The sensor’s wave-guiding capabilities, such as electromagnetic wave transmission, field profile distribution, and sensitivity, are meticulously analyzed using a two-dimensional finite-element method. The key objective of this device is to identify slight differences in the refractive index by observing shifts in resonant wavelength through the light’s interaction with the plasmonic structure. Moreover, optimizing the geometric parameters significantly enhances the sensor’s performance. The optimized sensor achieves a maximum refractive index sensitivity of 2400 nm/RIU, a figure of merit (FOM) of 45.28, and a Q-factor of 39.86, as demonstrated by simulation results. Further investigations reveal the MIM structure’s capacity to detect adulteration in edible oils, underscoring the sensor’s adaptability and its potential for widespread biosensing applications.

Design and analysis of D-shaped fiber optic plasmonic sensors using triangular corrugation of silver: transmittance and field analysis

In this study, the wave optics module of COMSOL Multiphysics is used to simulate a D-shaped optical fibre plasmonic sensor with triangular corrugation structures made of silver. The transmittance and electric field-based performance defining parameters i.e., resonance wavelength (λ r), shift in resonance wavelength (∆λ r), minimum transmittance (Tmin), bandwidth (BW), penetration depth (PD), and propagation length (PL) are examined. The obtained sensitivity of the proposed sensor is 10.2 μm RIU−1. It is seen that the proposed sensor structure increases the sensitivity by 41% with respect to planar Ag and 40.2% with respect to rectangular grating of Ag. Also, the PD increases 36.6% with respect to planar Ag and 30% with respect to rectangular grating Ag.

A novel refractive index based-fiber optic sensor for milk adulteration detection

Milk adulteration poses a significant risk to public health and consumer trust, compromising its nutritional value. To address this, we've developed an optical fiber-based sensor using a Lossy Mode Resonance (LMR) approach. Antimony Oxide (Sb2O3) serves as the sensing layer, deposited onto the optical fiber's unclad core using Radio Frequency Magnetron sputtering. The sensing layer underwent comprehensive characterization, including X-Ray diffraction (XRD), UV–Vis spectroscopy, Ellipsometer, Atomic Force Microscopy (AFM), EDAX, and Field Emission Scanning Microscopy (FESEM). The sensor was tested for formaldehyde and water adulteration across normal milk type 1, full-fat milk type 2, vendor milk type 3, and, with concentrations ranging from 0 % to 10 %. Observations included resonance wavelength shifts and sensing parameters such as sensor response, sensitivity, and repeatability. For Sb2O3-coated sensor probes, responses to formaldehyde and water adulteration for type 1 milk is 2.05 % and 2.22 %, type 2 milk is 2.17 % and 2.4 %, and type 3 milk is 1.90 % and 1.95 %. Sensitivity for Sb2O3-coated probe to formaldehyde are 2.2 nm/v% (type 1 milk),1.9 nm/v% (type 2 milk) and 1.5 nm/v% (type 3 milk). For water in milk, the sensitivities are 1.7 nm/v%, 1.5 nm/v%, and 1.2 nm/v%. Furthermore, a prototype sensor probe has been developed for continuous milk adulteration monitoring, interfaced with Arduino and Thing Speak.

Observation of the liquid metal phase transition in optofluidic microcavities

Gallium (Ga) exhibits remarkable potential in flexible electronics, chemistry, and biomedicine due to its exceptional physical properties. The phase transition and supercooling characteristics of Ga have led to the emergence of numerous valuable applications. In this paper, we capitalize on this foundation by utilizing optofluidic microcavities supporting both high quality factor optical and optomechanical modes to investigate the phase transformation process and supercooling properties of Ga. Our study provides comprehensive insights into the dynamic behavior of Ga during the complete phase transition, such as measuring a hysteresis loop between the solid-to-liquid and liquid-to-solid transitions, revealing nonreciprocal resonance wavelength shift, and identifying a unique metastability state of Ga during melting. The linear thermal expansion coefficients of Ga were precisely measured to be 0.41 × 10−5 K−1 and −0.75 × 10−5 K−1 for solid and liquid Ga, respectively. Our research provides a comprehensive and versatile monitoring platform for newly fabricated liquid metal alloys, offering multidimensional insights into their phase transition behavior.

Gold nanowire-infused square-clad SPR-PCF biosensor for detection of various cancer cells

This research work introduces a Surface Plasmon Resonance (SPR) based Photonic Crystal Fiber (PCF) sensor using gold nanowires as plasmonic material designed for the detection of various cancer cells, boasting remarkable sensitivity and ease of fabrication. The sensor's structure was devised and analyzed using the Finite Element Method (FEM) of COMSOL v5.5, with a focus on exploring the impact of varying geometric parameters on its overall performance. The simulation utilized extremely fine mesh elements to ensure the utmost accuracy. Excitation between the core and plasmonic modes is achieved using Gold (Au) nanowires. The determination of the sensor's wavelength sensitivity involves assessing the resonance wavelength shift between samples of normal and cancerous cells. Simultaneously, the measurement of amplitude sensitivity is accomplished through a comparison of the amplitudes associated with their respective confinement losses. Various parameters of the PCF were varied during the experimentation, leading to the achievement of exceptionally high Amplitude Sensitivity (AS) of −273.16 RIU−1, −286.58 RIU−1, −455.59 RIU−1, −698.76 RIU−1, −1172.72 RIU−1 and −1971.30 RIU−1 for Skin Cancer, Cervical Cancer, Blood Cancer, Adrenal Gland Cancer, Breast Type-1 Cancer and Breast Type-2 Cancer respectively. Additionally, the Wavelength Sensitivity (WS) values were found to be 6500 nm/RIU, 14583.33 nm/RIU, 16428.57 nm/RIU, 25714.28 nm/RIU, 32857.14 nm/RIU, and 35714.28 nm/RIU for the same cancer types, respectively. The achieved resolutions for wavelength sensitivity are 1.54×10−5 RIU, 6.86×10−6 RIU, 6.09×10−6 RIU, 3.89×10−6 RIU, 3.04×10−6 RIU and 2.80×10−6 RIU, while the resolutions for amplitude sensitivity are 7.32×10−5 RIU, 8.37×10−5 RIU, 3.07×10−5 RIU, 2.00×10−5 RIU, 1.19×10−5 RIU and 7.10×10−6 RIU for the respective cancer types mentioned above. The design of the presented biosensor is notably uncomplicated and can be readily manufactured using contemporary fabrication techniques. In summary, the remarkable sensitivity exhibited by the proposed SPR-based PCF (SPR-PCF) biosensor, shows significant potential for enhancing the detection of cancer cells.

Electrical field-induced Fano resonance tunability in photonic crystal slabs

The creation of tunable Fano resonances in a photonic crystal structure with a side-coupled nanocavity and a waveguide with a partially transmitting element is investigated in this paper. In the proposed structure, the nanocavity’s central hole is made up of two cylinders with different radii that are nested inside each other. The outer and inner cylinders are made of quartz and liquid crystal, respectively. The performance of this device is analyzed using the three-dimensional finite-difference time-domain. The transmission spectrum, resonance wavelength, and quality factor of the proposed structure are calculated for various applied voltages. It is demonstrated that as the applied voltage increases, the quality factor changes and the Fano resonance wavelength shifts. Based on the findings, a tuning range of 5.2 nm is achievable with an excellent transmission contrast within this range. The presented structure is appropriate for applications such as tunable switches and filters.

Design and simulation of a resonant nanoring-based two-dimensional photonic crystal biosensor for cancer cell detection

This article introduces a novel two-dimensional photonic crystal biosensor designed for the detection of various cancer cell types and the verification of associated parameters. The proposed structure features a circular resonator nanoring with a sensing region at its center, facilitating the connection with cancer cells. The sensor has been tested with a diverse range of cancer cell types including skin, cervical, blood, adrenal, and two subtypes of breast cancer cells (Sort 1 and Sort 2). All outputs of the structure were studied at two different wavelengths and its parameters were analyzed separately. The best quality factor obtained for normal and abnormal cells of the target structure is 13,353 and 3053, respectively. Due to its high-quality factor and high FOM and low DL, this sensor has an acceptable sensitivity of 214.28(nm/RIU). FOM and DL in this sensor are equal to 172.35(RIU−1) and 5.80 × 10−4(RIU), respectively. The resonant wavelength shift of this structure is a relatively good value due to the coupling distance between the input wave and the resonator nanoring.

Plasmonic sensor combined with a microcuvette device for monitoring molecule binding processes at ultra-low concentrations

A novel sensing strategy is presented to monitor receptor-target pair interactions at ultra-low concentrations without functionalization processes. The biosensing is made by a sensitive chip and a surface plasmon resonance (SPR) probe connected in series, both built up on multimode plastic optical fibers (POFs). The SPR probe is a conventional D-shaped POF platform, while the capture platform consists of three microholes, containing a few hundred nanoliters each, made in the core of a modified POF. The microholes are filled with a specific receptor solution, which selectively captures the target present in the samples dropped over the filled microholes. Any variation occurring in the microholes due to the molecule binding processes changes the mode profile of the propagated light in the POF's core, modifying the plasmonic effects proportionally to the phenomena under scrutiny. As a proof of concept, the interactions of two receptor-target pairs, estradiol and cortisol to the respective receptors, namely Estrogen Receptor alpha protein (ER) and Glucocorticoid Receptor (GR), were monitored over time in the attomolar range. The receptor-target pair interactions are observed at ultra-low concentrations (order of aM) by monitoring the resonance wavelength shift over time. The proposed sensing approach stands for a novel class of laboratory instrumentation with unprecedented capabilities in terms of compactness, ultra-high sensitivity and low-cost.

Highly-Sensitive Polymer Optical Fiber SPR Sensor for Fast Immunoassay

A new type of human immunoglobulin G (IgG) sensors based on the surface plasmon resonance (SPR) in the low refractive index (RI) plastic optical fiber (POF) and an antibody immobilization method is presented. A 50-nm-thick gold film was formed on the polished D-shaped fiber surface by magnetron sputtering. The RI response of the POF sensor is 30 049.61 nm/RIU, which is 26.5 times higher than that of single mode fiber (SMF) SPR sensors. The proposed SPR biosensor can be developed by simple and rapid modification of the gold film with 11-mercapto undecanoic acid (MUA). Upon immobilization of the goat anti-human IgG antibody, the resonance wavelength shifts by 11.2 nm. The sensor can be used to specifically detect and quantify the human IgG at concentrations down to 245.4 ng/mL with the sensitivity of 1.327 7 nm per µg/mL, which offers an enhancement of 12.5-fold compared to that of the conventional SMF based SPR sensors. The proposed device may find the potential applications in the case of use at the point of care.

Silicon Microring Resonator Biosensor for Detection of Nucleocapsid Protein of SARS-CoV-2.

A high-sensitivity silicon microring (Si MRR) optical biosensor for detecting the nucleocapsid protein of SARS-CoV-2 is proposed and demonstrated. In the proposed biosensor, the surface of a Si MRR waveguide is modified with antibodies, and the target protein is detected by measuring a resonant wavelength shift of the MRR caused by the selective adsorption of the protein to the surface of the waveguide. A Si MRR is fabricated on a silicon-on-insulator substrate using a CMOS-compatible fabrication process. The quality factor of the MRR is approximately 20,000. The resonant wavelength shift of the MRR and the detection limit for the environmental refractive index change are evaluated to be 89 nm/refractive index unit (RIU) and 10-4 RIU, respectively. The sensing characteristics are examined using a polydimethylsiloxane flow channel after the surface of the Si MRR waveguide is modified with the IgG antibodies through the Si-tagged protein. First, the selective detection of the protein by the MRR sensor is experimentally demonstrated by the detection of bovine serum albumin and human serum albumin. Next, various concentrations of nucleocapsid protein solutions are measured by the MRR, in which the waveguide surface is modified with the IgG antibodies through the Si-tagged protein. Although the experimental results are very preliminary, they show that the proposed sensor has a potential nucleocapsid sensitivity in the order of 10 pg/mL, which is comparable to the sensitivity of current antigen tests. The detection time is less than 10 min, which is much shorter than those of other antigen tests.

Multilayer SPR hydrogen sensor based on a heterogeneous metal nanolayer

In this study, we created a multilayer SPR hydrogen sensor that is primarily based on an Ag-nd or Au-nd heterogeneous metal nanolayer. To characterize the response of the suggested structure, we used the Matlab program and the transfer matrix method (TMatrix) in this investigation. We developed a set of sensors (n1/Ag-nd/Pd Or n1/Aund/Pd) with varying densities of metal nanoparticles N = 400[1/µm3 ], 600[1/µm3 ], 800[1/µm3 ], and 1000 [1/µm3 ], respectively, to verify the sensor's performance. They are assessed using a number of conventional standards, including sensitivity and minimum reflectance (Rmin). The sensor with Ag-nd layer and N = 1000 [1/µm3 ] was found to attain the lowest Rmin of 0.04 and the highest sensitivity of S = 7.99[nm] with a maximum resonance wavelength shift of 2.4 [nm]. The suggested SPR hydrogen sensor may detect changes in palladium (Pd)'s optical characteristics and, consequently, leaks of hydrogen gas, according to simulation data.

Spatially selective narrow band and broadband absorption in Ag/SiO2/Ag based trilayer thin films by oblique angle deposition of SiO2 layer

We have experimentally demonstrated spatially selective absorption in Ag-SiO2-Ag based trilayer thin films by tuning the deposition angle of SiO2 layer. These structures generate cavity resonance which can be tuned across the substrate locations due to spatially selective thickness and refractive index of silicon oxide (SiO2) film sandwiched between metallic silver (Ag) mirrors. Spatially selective property of SiO2 film is obtained by oblique angle deposition technique using an electron beam evaporation system. The resonance wavelength of absorption in this trilayer structure shifts across the substrate locations along the direction of oblique deposition. The extent of shift in resonance increases with increase in angle of deposition of SiO2 layer. 4.14 nm mm−1 average shift of resonance wavelength is observed when SiO2 is deposited at 40° whereas 4.76 nm mm−1 average shift is observed when SiO2 is deposited at 60°. We observed that the width of resonance increases with angle of deposition of the cavity layer and ultimately the resonant absorption disappears and becomes broadband when SiO2 is deposited at glancing angle deposition (GLAD) configuration. Our study reveals that there is a suitable range of oblique angle of deposition from 40° to 60° for higher spatial tunability and resonant absorption whereas the absorption becomes broadband for glancing angle deposition.

Integrated LSPR Biosensing Signal Processing Strategy and Visualization Implementation.

The LSPR biosensor chip is a groundbreaking tool popular in laboratory settings for identifying disease markers. However, its use in clinical environments is not as widespread. One notable gap is the lack of a universal signal processing tool for LSPR biosensing. To escalate its precision, there is an emerging need for software that not only optimizes signal processing but also incorporates self-verification functionalities within LSPR biochemical sensors. Enter the visual LSPR sensor software-an innovative platform that processes real-time transmission or reflection spectra. This advanced software adeptly captures the nuanced structural changes at the nanostructure interface prompted by environmental fluctuations. It diligently records and computes a suite of parameters, including the resonance wavelength shift, full width at half maximum, sensitivity, and quality factor. These features empower users to tailor processing algorithms for each data capture session. Transcending traditional instruments, this method accommodates a multitude of parameters and ensures robust result validation while tactfully navigating nanostructure morphology complexities. Forsaking third-party tool dependencies, the software tackles challenges of precision and cost-effectiveness head-on, heralding a significant leap forward in nanophotonics, especially for high-throughput LSPR biosensing applications. This user-centric innovation marks substantial progress in biochemical detection. It is designed to serve both researchers and practitioners in the field of nanophotonic sensing technology, simplifying complexity while enhancing reliability and efficiency.

Characteristics of highly sensitive hydrogen gas sensor based on Pt-SiO2/Si microring resonator

A hydrogen gas sensor based on a silicon microring resonator (MRR) with a Pt–SiO2 thin film as a hydrogen-sensitive film is proposed and investigated to realize a high-sensitivity hydrogen sensor. The sensor detects hydrogen on the basis of the resonant wavelength shift caused by the reaction heat generated in the Pt–SiO2 film. In the hydrogen exposure measurement, resonant wavelength shifts of approximately 5.0 and 2.4 nm were observed at hydrogen concentrations of 4.0 and 0.4 vol%, respectively, showing the high sensitivity of the proposed sensor. In addition, an MRR sensor with an upper Al2O3 cladding layer is proposed and its higher sensitivity is theoretically demonstrated.

A Silicon-Based ROTE Sensor for High-Q and Label-Free Carcinoembryonic Antigen Detection.

This paper presents a biosensor based on the resonant optical tunneling effect (ROTE) for detecting a carcinoembryonic antigen (CEA). In this design, sensing is accomplished through the interaction of the evanescent wave with the CEA immobilized on the sensor's surface. When CEA binds to the anti-CEA, it alters the effective refractive index (RI) on the sensor's surface, leading to shifts in wavelength. This shift can be identified through the cascade coupling of the FP cavity and ROTE cavity in the same mode. Experimental results further show that the shift in resonance wavelength increases with the concentration of CEA. The biosensor responded linearly to CEA concentrations ranging from 1 to 5 ng/mL with a limit of detection (LOD) of 0.5 ng/mL and a total Q factor of 9500. This research introduces a new avenue for identifying biomolecules and cancer biomarkers, which are crucial for early cancer detection.

Optical properties of thin films monitored in real-time at high gamma radiation doses using long period fiber gratings

In this work, we report an all-optical-fiber-based method to monitor in real-time the changes in thin film optical properties when exposed to harsh environments such as high doses of gamma radiation. The method is based on a long period grating (LPG) inscribed in a radiation resistant optical fiber, which is coated with a thin film to be analyzed. Due to impact of the environment on the film properties, the transmission spectrum of the LPG changes. To validate this methodology, we deposited oxides of various metals, i.e. aluminum (Al2O3), titanium (TiO2), and tantalum (Ta2O5), as well as a polymeric film, namely polystyrene (PS), on the LPG surface and measured the resonant wavelength shift induced by high doses of gamma exposure (dose rate of 2.3 kGy/h, up to a total dose of 46 kGy). The changes could be observed in real-time up to maximum reached dose and during the recovery period. The results are significantly dependent on thin film material. Among the oxides, TiO2 thin film demonstrated the highest susceptibility to irradiation, whereas Al2O3 exhibited the least impact. Additionally, a good recovery potential for Ta2O5 thin film was observed, hinting at its promising application in dosimetry. Conversely, the PS film exhibited a permanent effect induced by irradiation. This is the first real-time experimental study of the impact of high dose gamma radiation on thin film optical properties using a universal optical-fiber-based device. The findings pave the way for assessing radiation hardness of thin film materials or utilizing such a method to optimize material treatment involving ionizing radiation.