Optical Surface Plasmon Resonance Research Articles

Structure Design and Sensitivity Optimization of Optical Fiber Biosensor Based Au Nano Column - TiO2 Heterostructure

An investigation on a single mode optical fiber sensor-based surface plasmon resonance was carried out in this work. A titanium dioxide (TiO2) coated gold Nano-column (Au) are deposited on the proposed sensor and theoretically analyzed using COMSOL Muliphysics software 5.3. Presence of TiO2 over the Au Nano-column can improve the sensitivity of the sensor and tune the resonance peak of transmission spectrum from visible region to near-infrared region. The size effect of TiO2 nanoparticles on the sensor performance is studied. The optimum parameters of such as Au size and separation width between the Au Nano-column have been selected to enhance the performance of the sensor. In comparison, the sensor with TiO2 over Au Nano-column is significantly improve the sensitivity and develop the sensor performance. The greater sensitivity of 5243.76 nm/RIU (refractive index unit) is obtained of sensor with TiO2 over Au Nano-column when the external refractive index of analyte is varying from 1.33 to 1.39, while sensitivity of the sensor coated with Au Nano-column is obtained to be 4643.17 nm/RIU for the same analyte range. Above results can be used to predict the best parameters values of the sensor that corresponding to the greatest sensitivities of detection and finally opening new study in the field of gas sensors. HIGHLIGHTS Optical fiber biosensors are a devices that use to measure the analyte by using the optical field Optical fiber biosensors have a high detection speed and low-cost, compared to congenital sensors The optical fiber sensors based SPR are widely used for biosensor applications The novelty in this research is the fabricate of optical fiber sensor coated with TiO2 over Au Nano-column based SPR foe gas detection GRAPHICAL ABSTRACT

Smartphone-based selective and sensitive detection of vitamin B1 in synthetic urine using U-bend SPR optical fiber probe

This paper introduces an innovative optical fiber surface plasmon resonance (SPR) biosensor designed for smartphone assistance, aiming at detecting vitamin B1 in synthetic urine. The key novelty lies in the amalgamation of silver nanocoated cysteine with a gold-plated optical fiber probe, fostering efficient detection through the robust electrostatic interaction between negatively charged Cys-capped AgNPs and positively charged vitamin B1 molecules. Notably, this biosensor leverages the smartphone's digital camera capabilities to discern varying color intensities. A self-developed application ensures real-time monitoring of green and red channel intensities in the SPR signal, thereby mitigating the risk of false detections. Moreover, the integration of the fabricated optical fiber probe with the smartphone is achieved through a 3D-printed casing, endowing the biosensor with the advantages of portability, handheld operation, and cost-effectiveness. The proposed U-shaped optical fiber SPR biosensor, coupled with smartphone technology, demonstrates the ability to detect vitamin B1 within the concentration range of 2–10 μM, yielding a commendable R2 value of 0.9973. Experimental findings affirm that this novel biosensor, built on the U-shaped SPR optical fiber architecture and empowered by smartphones, is an economical, uncomplicated, and portable device adept at accurately and efficiently detecting vitamin B1 across a broad concentration spectrum. Its potential applications extend to the area of low-cost biochemical component identification.

High sensitive optical fiber SPR sensor for label-free detection of Staphylococcus aureus

Optical fiber bacterial sensors have attracted attention in many fields due to their unique advantages. However, it is still difficult to promote its practicality which is mainly subject to their low sensitivity, inferior stability, and reliability. This work reported here an optical fiber surface plasmon resonance (SPR) biosensor enhanced by gold nanoparticles (AuNPs)/Au film coupling for label-free detection the Staphylococcus aureus (S. aureus), while both the gold substrates were successfully biofunctionalized with goat anti-human immunoglobulin G (IgG) as the probe to capture and detect the bacteria. In the experiment, the refractive index（RI） sensitivity of the Multimode-Singlemode-Multimode optical fiber (MSMOF) coated with Au film was improved by 19 % after the AuNPs were homogeneously decorated on the Au film surface. To detect S. aureus by the sensor, the SPR wavelength variation in the transmission spectrum was recorded, and its limit of detection (LOD) was demonstrated experimentally to be about 50 CFU/mL and was obtained theoretically to be 1.18 CFU/mL during its concentration range of 50–108 CFU/mL. Also, it shows great linearity in the range of 102-108 CFU/mL and the sensor exhibits excellent specificity and stability. This kind of SPR-enhanced optical fiber biosensor is fully promising for its applications in biomedicine, food safety, pharmaceuticals, etc.

Analysis of Tapered Fibre Optic Surface Plasmon Resonance Bio-Sensor Chip with highly Perturbed Taper Profiles.

A numerical model based on the Transfer matrix method (TMM) is proposed for the first time to study the gold coated tapered fibre optic surface plasmon resonance (SPR) with eight different types of taper profiles namely linear, exponential-linear, Gaussian, quadratic, sinusoidal, error function type and highly perturbed taper profile so-called chirp type of profile. The performance in terms of sensitivity, full width at half maximum (FWHM), detection accuracy (D.A.), amplitude dip, and half power points are estimated with respect to tapering ratio and choices of taper profile. It is found that sensitivity increased almost linearly with the taper ratio of each taper choice for the account of the reduction of detection accuracy. It has been found that sensitivity is highest for the case of chirp taper profile and lowest for the case of quadratic taper profile at low taper ratio. In this study, the aqueous solution is considered for sensor development which is adulterated by biomolecules species like DNA, blood samples, etc.

Diagnosis of thrombotic thrombocytopenic purpura: easy-to-use fiber optic surface plasmon resonance immunoassays for automated ADAMTS-13 antigen and conformation evaluation

BackgroundLaboratory diagnosis of immune-mediated thrombotic thrombocytopenic purpura (iTTP) remains challenging when ADAMTS-13 activity ranges between 10% and 20%. To prevent misdiagnosis, open ADAMTS-13 conformation gained clinical attention as a novel biomarker, especially to diagnose acute iTTP in patients with diagnostic undecisive ADAMTS-13 activity. Plasma ADAMTS-13 conformation analysis corrects for ADAMTS-13 antigen, with both parameters being characterized in enzyme-linked immunosorbent assay (ELISA)-based reference assays requiring expert technicians. ObjectivesTo design ADAMTS-13 antigen and conformation assays on automated, easy-to-use fiber optic surface plasmon resonance (FO-SPR) technology to promote assay accessibility and diagnose challenging iTTP patients. MethodsADAMTS-13 antigen and conformation assays were designed on FO-SPR technology. Plasma of 20 healthy donors and 20 acute iTTP patients were quantified, and data from FO-SPR and ELISA reference assays were compared. ResultsFollowing assay design, both antigen and conformation FO-SPR assays were optimized and characterized, presenting strong analytical sensitivity (detection limit of 0.001 μg/mL) and repeatability (interassay variation of 14.4%). Comparative analysis suggested positive correlation (Spearman r of .92) and good agreement between FO-SPR and ELISA assays. As expected, FO-SPR assays showed a closed or open ADAMTS-13 conformation in healthy donors and acute iTTP patients, respectively. ConclusionBoth ADAMTS-13 antigen and conformation assays were transferred onto automated, easy-to-use FO-SPR technology, displaying potent analytical sensitivity and reproducibility. ADAMTS-13 antigen and conformation were determined for healthy donors and acute iTTP patients showing strong correlation with ELISA reference. Introducing FO-SPR technology in clinical context could support routine diagnosis of acute iTTP patients, notably when ADAMTS-13 activity fluctuates between 10% and 20%.

High-sensitivity optical fiber SPR temperature sensing probe based on Au-PDMS@Au coating

To enhance the sensitivity of polydimethylsiloxane (PDMS)-based optical fiber surface plasmon resonance (SPR) temperature sensing probes, we propose a new prototype with a PDMS@Au sensing layer on the gold (Au) film of the multi-mode fiber (MMF)-single-mode fiber (SMF)-MMF heterojunction structure. This designed probe has improved the temperature sensitivity from −1.26 nm/°C (Au-PDMS) to −2.14 nm/°C (Au-PDMS@Au), maintaining good repeatability and stability. Moreover, the probe can be fabricated with simple procedures at a low cost. Therefore, this probe is a promising tool for temperature sensing in various applications.

Optical fiber surface plasmon resonance sensor using electroless-plated gold film for thrombin detection.

This paper describes the simple and label-free detection of thrombin using optical fiber surface plasmon resonance (SPR) sensors based on gold films prepared by the cost-effective method of electroless plating. The plating conditions for simultaneously obtaining gold film on cylindrical core and end surfaces of anoptical fiber suitable for measurement were optimized. The fabricated sensor exhibited a linear refractive index sensitivity of 2150 nm/RIU and 7.136 (a.u.)/RIU in the refractive index of 1.3329-1.3605 interrogated by resonance wavelength and amplitude methods respectively and a single wavelength monitoring method was proposed to investigate the sensing performance of this sensor. Polyadenine diblock and thiolated thrombin aptamers were immobilized on gold nanoparticles and gold films respectively to implement asandwich optical fiber assay for thrombin. The developed optical fiber SPR sensors were successfully used in the determination of thrombin down to 0.56 nM over a wide range from 2 to 100 nM and showed good selectivity for thrombin, which indicated their potential clinical applications for biomedical samples.

MMF-SMF-MMF optic surface plasmon resonance sensor based on hexagonal plate-like [formula omitted] structure

The manuscript introduces a fiber-optic MSM SPR sensor employing a hexagonal plate-like structure of Co(OH)2/TiO2/Au for surface plasmon resonance (SPR) sensing. This article aims to improve it through optimization of material composition and structure. The MSM structure SPR sensors were fabricated on the surface of single-mode fiber optic using chemical precipitation and physical vapor deposition, where Co(OH)2 and TiO2 served as sensitive materials. The experimental results demonstrate that the proposed sensor exhibited significantly higher sensitivity and broader application potential than the gold film control group and the gold film/TiO2 control group. Specifically, the gold film control group had a sensitivity of 1778.44 nm/RIU, while the sensitivity of the TiO2/Au control group was 2230.9 nm/RIU. In contrast, the Co(OH)2/TiO2/Au structure SPR sensor had a sensitivity of 3106.5 nm/RIU, which is far superior to the two control groups. Moreover, the results of repeated measurements indicated that the resonant wavelength error was only within 2 nm. These findings suggest that the Co(OH)2/TiO2/Au structure SPR sensor has promising stability and repeatability, making it suitable for applications in various fields, including chemical sensing and biological sensing.

Silver-coated hollow fiber surface plasmon resonance sensor for glucose detection with enhanced limit of detection.

A fiber-optic surface plasmon resonance (SPR) biosensor based on a silver-coated hollow fiber (HF) structure for glucose detection is presented. The sensor surface was immobilized with 4-mercaptophenylboronic acid (PMBA) acting as a glucose recognition monolayer. Then, gold nanoparticles (AuNPs) modified with 2-aminoethanethiol (2-AET) and PMBA were introduced onto the sensor surface after glucose was captured to enhance the wavelength shift of the SPR phenomenon excited by the light transmitted in the wall of the HF sensor. Instead of the conventional one-step sensitization pretreatment commonly used in the deposition process of silver films for fiber-optic SPR sensors, a sensitization-activation two-step activation method was adopted in the fabrication of the proposed sensor. Experiments for glucose detection were performed on the fabricated sensors in the concentration range of 1 nM-1 mM. Results showed that the sensor fabricated by the two-step activation method has a much larger shift of resonance wavelength than the sensor fabricated using the one-step sensitization method. The resonance wavelength shift was found to be linear to the logarithm of the concentration in the range of 1 nM-1 mM. The sensor achieved a limit of detection (LOD) of as low as 1 nM, which is at least an order of magnitude lower than that of other fiber-optic sensors for glucose detection reported previously. The presented HF glucose sensor has the potential for biosensing applications and provides a large reference value in the study of optical fiber SPR sensors for biosensing.

Advanced Integration of Glutathione-Functionalized Optical Fiber SPR Sensor for Ultra-Sensitive Detection of Lead Ions.

It is crucial to detect Pb2+ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb2+ concentration, in which the refractive index (RI) sensitivity of the multimode-singlemode-multimode (MSM) hetero-core fiber is largely enhanced by the gold nanoparticles (AuNPs)/Au film coupling SPR effect. The GSH is modified on the fiber as the sensing probe to capture and identify Pb2+ specifically. Its working principle is that the Pb2+ chemically reacts with deprotonated carboxyl groups in GSH through ligand bonding, resulting in the formation of stable and specific chelates, inducing the variation of the local RI on the sensor surface, which in turn leads to the SPR wavelength shift in the transmission spectrum. Attributing to the AuNPs, both the Au substrates can be fully functionalized with the GSH molecules as the probes, which largely increases the number of active sites for Pb2+ trapping. Combined with the SPR effect, the sensor achieves a sensitivity of 2.32 × 1011 nm/M and a limit of detection (LOD) of 0.43 pM. It also demonstrates exceptional specificity, stability, and reproducibility, making it suitable for various applications in water pollution, biomedicine, and food safety.

A Point-of-Care Testing Device Utilizing Graphene-Enhanced Fiber Optic SPR Sensor for Real-Time Detection of Infectious Pathogens.

Timely detection of highly infectious pathogens is essential for preventing and controlling public health risks. However, most traditional testing instruments require multiple tedious steps and ultimately testing in hospitals and third-party laboratories. The sample transfer process significantly prolongs the time to obtain test results. To tackle this aspect, a portable fiber optic surface plasmon resonance (FO-SPR) device was developed for the real-time detection of infectious pathogens. The portable device innovatively integrated a compact FO-SPR sensing component, a signal acquisition and processing system, and an embedded power supply unit. A gold-plated fiber is used as the FO-SPR sensing probe. Compared with traditional SPR sensing systems, the device is smaller size, lighter weight, and higher convenience. To enhance the detection capacity of pathogens, a monolayer graphene was coated on the sensing region of the FO-SPR sensing probe. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was used to evaluate the performance of the portable device. The device can accurately detect the SARS-CoV-2 spike S1 protein in phosphate-buffered saline (PBS) and artificial saliva within just 20 min, and the device successfully detected cultured SARS-CoV-2 virus. Furthermore, the FO-SPR probe has long-term stability, remaining stable for up to 8 days. It could distinguish between the SARS-CoV-2 spike protein and the MERS-CoV spike protein. Hence, this FO-SPR device provides reliable, rapid, and portable access to test results. It provides a promising point-of-care testing (POCT) tool for on-site screening of infectious pathogens.

High refractive index sensing highly sensitive and low loss SPR sensor based on hollow-core D-shaped optical fiber

A hollow-core D-shaped optical fiber-based surface plasmon resonance (SPR) sensor for low-loss and highly sensitive liquid analytes detection is theoretically investigated. The gold (Au) metal nanolayer is coated on the cladding etched D-shaped flat surface to develop the plasmonic effect. The nanolayer coating on the outer flat surface is very easy compared to the inside hollow-core, so our hollow-core sensor manufacturing is too easy compared to other hollow-core refractive indices (RIs) detection sensors. The resonance effect between analytes filled fundamental guided core mode and surface plasmon polariton mode of the D-shaped hollow-core optical fiber sensor is used to obtain the detections of analytes RIs variations. We have found good linear results ([Formula: see text]) in analytes RIs versus resonance wavelength for gold layers thicknesses for the analytes RIs range of 1.45–1.52. This hollow-core D-shaped optical fiber sensor achieves the maximum wavelength sensitivity of 23500[Formula: see text]nm RIU[Formula: see text] and a corresponding resolution of [Formula: see text] RIU. We have obtained the maximum figure of merit (FOM) of 228 1/RIU. The proposed sensor may be highly active in detecting the biological and chemical liquid analytes.

Construction of the fiber optic LSPR sensor for highly sensitive detection of miR-103 by a dual signal enhancement strategy based on the hot-spot effect and HexSG4 catalysis

MicroRNAs are important tumor biomarkers. How to effectively detect them by sensors is a challenge because of their extremely low concentrations. We proposed a dual signal enhancement strategy to develop the fiber optic (FO) localized surface plasmon resonance (LSPR) sensor for the highly sensitive detection of miR-103. It included two stages, one was to obtain the hot-spot by constructing the multimer structure, AuNP-spacer- AuNPs, and another was the combination of capturing miR-103 by the probe and catalytic amplification by Hexagonal star G-quadruplex catalyzing 4-chloro-1-naphthol to generate benzo-4-chlorohexadienone, which deposited on the AuNPs, resulting in the generation of LSPR peak redshift. The parameters of the preparation and detection application were systematically optimized. The redshift values had a good linear relationship with the logarithms of miR-103 concentrations, with high R2 0.9973, wide detection range 102 - 107 fM, and low LOD 6.4 fM. The method had high specificity, repeatability, and reproducibility, and was also successfully validated with real samples. Therefore, the dual signal strategy for constructing FO LSPR sensors can achieve the high sensitivity detection of extremely low concentration of MicroRNAs, which will have great application prospects in medicine and life science.

Simulation of a Sensitive Mid-infrared (MIR) D-Shaped Optical Fiber Water Pollutant Sensor

AbstractIn this work, an efficient optical sensor is proposed for the sensitive detection of various pollutants in water. The suggested optical sensor is based on an indium fluoride (InF3) glass fabricated as a D-shaped optical fiber. The polished surface of the D-shaped fiber is coated with a gold grating to induce the surface plasmon resonance (SPR). The SPR depends on the optical properties of the polluted water analyte in physical contact with the grating. The proposed optical SPR fiber sensor operates within the mid-infrared (MIR) range (3000–4500 nm) to detect any slight change in the water refractive index (RI) due to any pollutants. The full vectorial finite element method (FVFEM) is utilized to calculate the modal properties of the reported sensor. High sensor sensitivity of 17,834 nm/RIU (refractive index units) is achieved for the detection of dissolution of nitric acid (HNO3) in water at a concentration of 14% v/v (volume/volume). Additionally, the reported sensor detects the dissolution of hydrogen peroxide (H2O2) in water investigated at concentrations of 15% v/v and 30% v/v, with sensitivities of 12,308 nm/RIU and 17,143 nm/RIU, respectively. Further, suspending polystyrene beads of diameter 0.1 μm in the water at a concentration of 10% v/v gives a maximum sensitivity of 5333 nm/RIU. Therefore, the proposed sensor provides a promising approach for the detection of water pollutants in the MIR wavelength regime, rather than the weaker response in the near infrared.

High-sensitivity optical fiber SPR sensor with cascaded biconical fiber and hetero-core structure for simultaneous measurement of seawater salinity and temperature

A novel dual-channel optical fiber surface plasmon resonance (SPR) sensor, which achieves high-sensitivity simultaneous measurement of seawater salinity and temperature, was designed and verified. The hetero-core structure based on no-core fiber (NCF) with 40 nm thick Au film and polydimethylsiloxane (PDMS) overlaying was utilized to excite the SPR effect and serve as the temperature sensing channel. In order to effectively separate from the temperature SPR dip, a silver/gold bimetallic film was deposited on the surface of the biconical fiber with a grinding angle of 14° to construct the salinity channel cascaded with the temperature channel, where the metal thickness was determined as Ag/Au: 30 nm/10 nm. The simulation and experimental results showed that the bimetallic film used in this article can significantly improve the figure of merit (FOM) of the sensor compared with the optical fiber SPR sensor deposited with a single kind of metal film. In addition, further experimental results on salinity and temperature indicated that the proposed sensor had a salinity sensitivity of 0.73 nm/‰ and a temperature sensitivity of −2.43 nm/℃, and demonstrated the advantages of ease of manufacturing, acceptable repeatability, and good stability. Therefore, the proposed dual-channel optical fiber SPR sensor has high research value and application prospects in the field of ocean measurement.

Temperature-compensated fiber-optic SPR microfluidic sensor based on micro-nano 3D printing.

The current temperature-compensated fiber-optic surface plasmon resonance (SPR) biosensors are mainly open-ended outside the sensing structure, and there is a lack of temperature compensation schemes in fiber-optic microfluidic chips. In this paper, we proposed a temperature-compensated optical fiber SPR microfluidic sensor based on micro-nano 3D printing. Through the optical fiber micro-machining technology, the two sensing areas were designed on both sides of the same sensing fiber. The wavelength division multiplexing technology was used to collect the sensing light signals of the two sensing areas at the same time. The specific measurement of berberine and the detection of ambient temperature in the optical fiber SPR biological microfluidic channel were realized, and the temperature compensation matrix relationship was constructed, and then the temperature compensation was realized when measuring berberine biomolecules. Experiments have shown that the temperature sensitivity of the optical fiber SPR microfluidic sensor was 2.18 nm/°C, the sensitivity of the detection of berberine was 0.2646 nm/(µg/ml), the detection limit (LOD) was 0.38 µg/ml, and in a mixed solution showed an excellent specific detection impact.

Efficacy of 15 nm Gold Nanoparticles for Image-Guided Gliosarcoma Radiotherapy

Targeted brain cancer treatments are sorely needed to improve long-term prognosis, particularly for gliosarcoma and glioblastoma patients. Gold nanoparticles (GNPs) have unique properties including high atomic number, biocompatibility, and small size for cancer cell internalization. GNPs are consequently an ideal candidate for improved cancer targeting using image-guided radiotherapy. This work investigated 15 nm AuroVistTM GNPs for image-guided gliosarcoma radiotherapy and identified optimum GNP concentrations. The GNPs were found to be 15–20 nm using optical surface plasmon resonance absorption, with a (41.3 ± 0.3) nm hydrodynamic diameter. Confocal imaging showed that 50–500 µg/mL of the GNPs was well-internalized into the 9L cells within 24–48 h. γ-H2AX assays showed that 50–500 µg/mL of the GNPs radiosensitized the 9L cells irradiated with 125 and 150 kVp X-rays. However, only 500 µg/mL of the GNPs produced significant long-term dose enhancement with 150 kVp X-rays (with a sensitization enhancement ratio at 10% survival of 1.43, and 1.13 with 50 µg/mL) using clonogenic assay. CT imaging of the GNPs in the 9L tumors in Fischer rats further showed that GNP concentrations above 500 µg/mL were required to distinguish the tumor from the brain, and the GNPs were detected 48 h after injection. These promising results indicate that the GNPs can be used for selective gliosarcoma treatment with image-guided X-ray radiotherapy at concentrations above 500 µg/mL.

Experimental investigation of indium tin oxide and indium nitride based fiber optic surface plasmon resonance sensor

Experimental investigation of indium tin oxide and indium nitride based fiber optic surface plasmon resonance sensor

Online underwater abscission tracking of the ZnO film deposited on the optical fiber surface employing SPR technology

In this work, an optical fiber surface plasmon resonance (SPR) sensing technology is used to monitor the thickness of zinc oxide (ZnO) film in water online, and then study the hydrophilicity of ZnO film deposited by magnetron sputtering. Experimental results show that the ZnO films deposited on the surface of optical fiber, although different in thickness, will eventually detach from the fiber over time in the water. The surface characteristics of ZnO film before and after being soaked in water are compared to prove the existence of abscission of the film. Additionally, ultraviolet (UV) with different wavelengths and intensities affects the hydrophilicity of ZnO, which benefits from the adsorption of water molecules by more oxygen vacancies generated by photogenerated carriers. The ability of 365 nm UV in improving hydrophilicity increases with UV intensity and is much higher than that of 395 nm UV. It has been proved that hydrophilicity affects the performance of ZnO devices, so the proposed method is meaningful for the basic research on surface hydrophilicity and the application of controllable wettability of ZnO films.

Air-silica core microstructured optical fiber-based SPR sensor for temperature and refractive index measurement

We propose an air-silica core microstructured optical fiber-based surface plasmon resonance (SPR) sensor to simultaneously measure temperature and refractive index (RI). The sensing channel is formed by coating the outside of the fiber with a gold film and a polydimethylsiloxane (PDMS) layer as a temperature sensing medium, and then being immersed into the liquid analyte. The plasmon mode can penetrate through the PDMS layer and then into the analyte, therefore both the temperature and the analyte RI changings can lead to the variations of SPR spectra that will be measured. Our numerical results demonstrate that the proposed sensor can support two resonance peaks in the x-polarized core mode and one resonance peak in the y-polarized core mode, therefore providing two detection approaches, peak-based and polarization-based approaches. By measuring the two peaks in the x-polarized core mode, for the peak-based approach, the temperature coefficients are −2.077 nm/°C and −2.723 nm/°C, and the RI coefficients are 1252 nm/RIU and 1931 nm/RIU, respectively. While by measuring the second peak in x-polarized core mode and the peak in y-polarized core mode, for the polarization-based approach, the temperature coefficients are −2.723 nm/°C and −3.401 nm/°C, and the RI coefficients are 1931 nm/RIU and 2973 nm/RIU, respectively.