Resonance Optical Sensor Research Articles

Label-free Binding Analysis of 4-(2-Pyridylazo)-resorcinol-based Composite Layer with Cobalt Ion Using Surface Plasmon Resonance Optical Sensor

Label-free measurements of small-molecule binding interactions are of high interest to researchers across multiple scientific disciplines. Label-free optical sensors based on surface plasmon resonance (SPR) have been widely used for detecting various targets including toxic heavy metals in solutions. In this research, an SPR optical sensor enhanced with a 4-(2-pyridylazo)-resorcinol (PAR)-based composite layer was employed for the detection of the cobalt ion (Co2+). A binding analysis study was conducted by monitoring the interaction between Co2+ and the sensing layer thin film. In our experiment, there were no changes in SPR angle for a gold layer in contact with Co2+ of different concentrations, whereas the enhanced SPR sensor produced a maximum SPR angle shift of 0.328°. From the relationship between the angle shift and the concentration of Co2+, the sensor had a sensitivity of 0.2375° ppm−1 for concentrations of less than 1 ppm, 0.0044° ppm−1 for concentrations of 1 to 10 ppm, and 0.00069° ppm−1 for concentrations from 10 to 100 ppm. Further analysis was also carried out by calculating the full width at half maximum (FWHM), detection accuracy (DA), and signal-to-noise ratio (SNR). In the binding analysis, the experimental results were fitted with Langmuir, Freundlich, and Sips isotherm equations. It was found that the Sips isotherm equation most closely fitted the experimental data with an R2 value of 0.96716 and a binding affinity of 1.649 ppm−1.

Highly Sensitive D-Shaped Optical Fiber Surface Plasmon Resonance Refractive Index Sensor Based on Ag-α-Fe 2 O 3 Grating

This work proposed the simulation of a highly sensitive surface plasmon resonance (SPR) optical fibre sensor equipped with a hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ) layer coated with silver gratings on the surface of a D-shaped optical fibre. $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterial film was utilised as the sensing layer. Free electrons on the metal surface were stimulated via evanescent waves on the fibre surface to generate surface plasmon waves. The resonance absorption peaks were monitored to determine the changes in refractive index (RI). The SPR fibre sensor was optimised using the finite element method to analyse the structural parameters of the D-shaped optical fibre and silver gratings. This method was also applied to examine the effect of the thickness of the hematite sensing layer on sensor sensitivity (S). The hematite-coated silver gratings significantly enhanced the sensor as revealed by the simulation outcomes. In this work, the maximum response S of the sensor can reach $6.4~\mu \text{m}$ /RIU when the external RI was changed from 1.33 to 1.39 with 45 nm thick silver grating, 50 nm width air gaps and 12 nm thick hematite ( $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ ). The results suggest the high potential of $\alpha -\textit {Fe}_{\sf 2}{O}_{\sf 3}$ nanomaterials in optical fibre-sensing applications.

Effect of thermal annealing on sensing properties of optical fiber sensors coated with indium tin oxide nano-overlays

In this work we discuss an effect of thermal annealing on optical and electrical properties of indium tin oxide (ITO) thin films deposited on a short section of multimode polymer-clad silica (PCS) optical fiber core. ITO films were deposited using different configuration of high power impulse magnetron sputtering (HiPIMS) and radio frequency magnetron sputtering (RF MS) cathodes. Due to tuned ITO film thickness it was possible to observe for these structures a lossy-mode resonance (LMR) and trace changes in properties of the films. Electrical resistance of the ITO overlays was also measured. Both optical and electrical measurements were repeated after annealing at 200°C in a tube furnace and nitrogen atmosphere. The measurements have shown that thermal annealing changes optical response to external refractive index (RI) of the fiber sensor and also changes the ITO layer resistivity. As an effect of thermal annealing we observed a shift of the LMR towards longer wavelengths. In addition as a result of annealing, the resistivity of the ITO layer was reduced. Full Text: PDF ReferencesM. Sobaszek et al., "Optical monitoring of thin film electro-polymerization on surface of ITO-coated lossy-mode resonance sensor", Proc. SPIE, vol. 10323, pp. 103234W, 2017. CrossRef I. Del Villar et al., " Generation of lossy mode resonances by deposition of high-refractive-index coatings on uncladded multimode optical fibers", J. Opt., vol. 12, no. 9, pp. 95503, 2010. CrossRef M. Śmietana et al., "Simultaneous optical and electrochemical label-free biosensing with ITO-coated lossy-mode resonance sensor", Biosensors and Bioelectronics, vol. 154, pp. 112050, 2020. CrossRef P. Niedziałkowski et al., " Electrochemical performance of indium-tin-oxide-coated lossy-mode resonance optical fiber sensor", Sensors and Actuators B: Chemical, vol. 301, no. 12, pp. 1-10, 2019. CrossRef V. Stranak et al., "Effect of mid-frequency discharge assistance on dual-high power impulse magnetron sputtering", Surface & Coatings Technology, vol. 206, no. 11-12. pp. 2801-2809, 2012. CrossRef I. Del Villar et al., "Design rules for lossy mode resonance based sensors", Appl. Opt., vol. 51, no. 19, pp. 4298-4307, 2012. CrossRef W. F. Wu and B. S. Chiou, "Effect of annealing on electrical and optical properties of RF magnetron sputtered indium tin oxide films", Appl. Surf. Sci., vol. 68, no. 4, pp. 497-504, 1993. CrossRef M. Smietana et al., "Optical Monitoring of Electrochemical Processes With ITO-Based Lossy-Mode Resonance Optical Fiber Sensor Applied as an Electrode", J. Light. Technol., vol. 36, no. 4, pp. 954-960, 2018. CrossRef M. Śmietana et al., "Study on Combined Optical and Electrochemical Analysis Using Indium‐tin‐oxide‐coated Optical Fiber Sensor", Electroanalysis, vol. 31, no.2, pp. 398-404, 2019. CrossRef

Electrochemically directed biofunctionalization of a lossy-mode resonance optical fiber sensor.

In this work, we present a direct electrochemical biofunctionalization of an indium-tin-oxide-coated lossy-mode resonance optical fiber sensor. The functionalization using a biotin derivative was performed by cyclic voltammetry in a 10 mM biotin hydrazide solution. All stages of the experiment were simultaneously verified with optical and electrochemical techniques. Performed measurements indicate the presence of a poly-biotin layer on the sensor's surface. Furthermore, dual-domain detection of 0.01 and 0.1 mg/mL of avidin confirms the sensor's viability for label-free detection.

Narrow resonance and ultrahigh sensitivity plasmonic waveguide refractive index sensor

A surface plasmon resonance optical refractive index sensor (for aqueous medium) with high angular and spectral sensitivities S, very small full width at half maxima (FWHM) w (narrow resonance), and very high quality factor, χ = S/w, is proposed, which operates in both angular and spectral interrogation modes. The structure consists of a prism and a composite plasmonic waveguide consisting of a high-index dielectic layer and a thin metal (Ag) film, separated by a low-index layer. Above the metal film, the medium is analyte. It is shown that even with a prism of low index, the proposed sensor offers very small FWHM of reflection spectra, which improves the sensor performance. Numerically, an angular sensitivity of 168°RIU−1 and a quality factor χ = 1680 can be achieved for the proposed configuration. Spectral sensitivity comes out to be 6000 nm RIU−1.

Double-Slot Optical Ring Resonator Sensor

Optical micro-ring resonator (MRR) sensors are an emerging technology that attracts attention not only because it’s small footprint but also because of its high-quality features. In this work, a Silicon on Insulator (SOI)-based MRR sensor is studied for a practical label-free sensor. After the analysis of this study, it is found that a smaller (compare to previous studies) label-free optical sensor with a sensitivity of 206nm/RIU and a q-factor of 17900 can be obtained when the optimal designed parameters are used. Thus, it is believed that, this work would shed a light on optical sensor technology for more compact-efficient, low-cost and complementary metal-oxide-semiconductor (CMOS)-compatible sensors for daily life usage.

Experimental evaluation on surface plasmon resonance sensor performance based on sensitive hyperbranched polymer nanocomposite thin films

The plethora of optical techniques have been developed to detect the dengue virus, regrettably, the existing techniques are cumbersome and have limitations to provide early identification of the low-level of dengue virus. For this purpose, surface plasmon resonance (SPR) optical sensor was designed with a highly sensitive thin film based on hyperbranched polymer nanocomposites for conjugation of antibodies that specifically detect the dengue virus type II (DENV). In particular, we investigate the SPR sensing performance for gold/cadmium sulfide quantum dots-polyamidoamine/antibody (Au/CdS QDs-PAMAM/IgM) sensor film in terms of linear sensitivity, binding affinity, detection accuracy, full-width-half-maximum, selectivity, and spike and recovery test. The results show a strong affinity value, good sensitivity and selectivity, high accuracy, and excellent recovery value, obeying the ideal value based on conventional assay analysis. Additionally, this Au/CdS QDs-PAMAM/IgM based SPR sensor was successfully applied for the lowest detection of 1 pM of DENV E-proteins. To this end, a highly sensitive Au/CdS QDs-PAMAM/IgM sensor film was characterized using Raman spectroscopy, ultraviolet-visible (UV–Vis-NIR) spectroscopy, and atomic force microscopy (AFM) to confirm the binding of DENV.

Wavelength Shift Measurement With Resonance Characteristic Prediction Algorithm Using Intensities at Discrete Wavelengths

In this article, we proposed a resonance characteristic prediction algorithm (RCPA) for calculating resonance characteristics using intensities at discrete points of wavelength. Given fundamental information of the resonator, such as free spectral range (FSR) and full-width half maximum (FWHM), the RCPA can be easily applied to reduce the cost and size of the measurement system for an optical resonator sensor. For example, with intensities at two wavelength points, the whole wavelength characteristics of the resonator can be generated from the derived fitting equation. To verify the RCPA, we designed and fabricated a Fabry-Perot interferometer (FPI) using 300 μm of SU-8 2100 as a cavity medium and 100 nm of Cr thin film on a glass substrate. The fabricated FPI had an FSR of 2.35 nm and an FWHM of 1.59 nm. We observed that the wavelength characteristics of the FPI (1535-1537.5 nm) shifted by 0.33 nm/°C when the temperature changed from 25.3 °C to 27.1 °C in steps of 0.2 °C. With an optimized wavelength spacing of 0.31 nm adopted for this article, we confirmed that the resonance characteristic generated from the RCPA followed the same tendency with an average error of 6 pm and a maximum error of 14 pm, as compared with the full spectrum result from the optical spectrum analyzer. We also analyzed the errors due to the changing point number and point spacing. Based on the experimental results, we verified that the resonance characteristic can be measured successfully using at least two intensities at different wavelengths.

Graphene oxide coated side polished surface plasmon resonance optical fibre sensor with varying polishing losses

Four batches of side-polished SMF optical fibres with different polishing losses, − 0.5 dBm, − 5 dBm, − 10 dBm and − 15 dBm were coated with a graphene oxide layer of ~ 0.5 μm via drop casting. TE polarized light was propagated through the light during experiments and four different transformer oils with different water contents were dropped onto the sensor. The drop in the power of transmitted light was recorded. The responses of the sensors showed good linearity for all, but the least polished fibre showed the weakest response in terms of power drop towards change in concentration. The − 5 dBm fibre showed the best response per unit concentration change. Additional tests showed the increased response for a GO coated side polished sensor compared to an uncoated side polished sensor. Simulation using COMSOL was performed to show the effects on the electric field of a sensor with and without GO coating. Another set of simulations were performed to show the effects of reducing cladding thickness on the coupling of the electric field. Simulations show that the optimal cladding thickness is not the most polished fibre, coinciding with our results that − 15 dBm loss fibre did not show the most response per unit change in the analyte.

Design and analysis of surface plasmon resonance optical sensor for determining cobalt ion based on chitosan-graphene oxide decorated quantum dots-modified gold active layer.

In this study, the incorporation of surface plasmon resonance (SPR) spectroscopy with novel chitosan-graphene oxide/cadmium sulphide quantum dots (CdS QDs) active layer for cobalt ion (Co2+) detection has been developed. The interaction of different Co2+ concentrations with the novel modified active layer was monitored using the SPR technique. From the SPR results, detection range, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analysed. The results showed the detection range of this optical sensor was 0.01 to 10 ppm, and it was saturated for higher concentration of Co2+. The sensitivity obtained was 0.1188 ppm-1 for low concentration of Co2+ ranged from 0.01 to 1 ppm. The FWHM and DA were consistent for all concentration of Co2+, while the SNR of the SPR signal increased with the Co2+ concentration. The SPR angle shifts were also fitted using Langmuir, Freundlich and Sips (Langmuir-Freundlich) isotherm models, where Sips model fitted the best with the binding affinity of 0.939 ppm-1. The results proved that the novel chitosan-graphene oxide/CdS QDs modified gold thin film can detect Co2+ via SPR spectroscopy.

Molecularly Imprinted Sol-Gel for TNT Detection with Optical Micro-Ring Resonator Sensor Chips.

A sensor for trinitrotoluene (TNT) detection was developed by using a combination of optical micro-ring technology and a receptor coating based on molecularly imprinted sol-gel layers. Two techniques for deposition of receptor layers were compared: Airbrush technology and electrospray ionization. A concentration of less than 5 ppb for TNT in the gas-phase, using electrospray deposition of the receptor layer, was detected. The cross-sensitivities to organic substances and further nitro-based explosives were compared. As a result, the sensitivity to TNT is about one order of magnitude higher in comparison to the explosives 2,4-dinitrotoluene (DNT) or 1,3-dinitrobenzene (DNB) and about four orders of magnitude higher than the organic substances phenol, ethanol, and acetone. The signal response of the sensor is fast, and the compact sensor design enables the deposition of different receptor layers on multiple optical micro-rings on one chip, which allows a more precise analysis and reduction of side effects and false alarms.

Polydopamine-Assisted Fabrication of Stable Silver Nanoparticles on Optical Fiber for Enhanced Plasmonic Sensing

We present a facile and effective method for fabrication of the localized surface plasmon resonance (LSPR) optical fiber sensor assisted by two polydopamine (PDA) layers with enhanced plasmonic sensing performance. The first PDA layer was self-polymerized onto the bare optical fiber to provide the catechol groups for the reduction from Ag+ to Ago through chelating and redox activity. As the reduction of Ag+ proceeds, Ag nanoparticles (NPs) were grown in-situ on the PDA layer with uniform distribution. The second PDA layer was applied to prevent Ag NPs from oxidating and achieve an improvement of LSPR signal. The PDA/Ag/PDA-based optical fiber sensor has an enhanced LSPR sensitivity of 961 nm/RIU and excellent oxidation resistance. The stable PDA/Ag/PDA-based LSPR sensor with high optical performance is very promising for future application in optical sensing field.

Electrochemical performance of indium-tin-oxide-coated lossy-mode resonance optical fiber sensor

Analysis of liquids performed in multiple domain, e.g., optical and electrochemical (EC), has recently focus significant attention. Our previous works have shown that a simple device based on indium-tin-oxide (ITO) coated optical fiber core may be used for optical monitoring of EC processes. At satisfying optical properties and thickness of ITO a lossy-mode resonance (LMR) effect can be obtained and used for monitoring of optical properties of an analyte in proximity of the ITO surface. However, EC response of the ITO-LMR device to a redox probe has not been achieved for ITO-LMR sensor whereas it is generally observed for commercially available ITO electrodes. The changes in the response to a redox probe are typically used as a sensing parameter when EC label-free sensing is considered, so it is crucial for further development of combined LMR-EC sensing concept. In this work, we focus on enhancing the EC activity of the device by tuning ITO magnetron sputtering deposition parameters. Influence of the deposition pressure on the ITO properties has been the main consideration. Both optical and EC readouts in 0.1 M KCl containing such redox probes as 1 mM of K3[Fe(CN)6] or 1 mM 1,1′-Ferrocenedimethanol were discussed at different scan rate. The performed studies confirm that for optimized ITO properties the ITO-LMR sensor used as the EC electrode may also show excellent EC performance. The observed EC processes are quasi-reversible and diffusion-controlled. Moreover, for the devices, which offer improved EC response, an optical monitoring of the EC process is also possible. According to our best knowledge, fully functional combined optical and EC sensor, where optical effect is resonance-based and other than well-known surface plasmon resonance, is presented for the first time.

An Immunosensor Based on Au-Ag Bimetallic NPs Patterned on a Thermal Resistant Flexible Polymer Substrate for In-Vitro Protein Detection.

Nanosensors based on flexible polymers have emerged as powerful tools for next generation smart devices in the recent years. Here, we report a facile protocol to fabricate an immunosensor supported by a thermally resistant flexible polymer substrate (polyarylene ether nitrile, PEN). The immunosensor is a localized surface plasmon resonance (LSPR) optical sensor for in-vitro protein detection based on anti-body coated gold-silver bimetallic nanoparticles (Au-Ag NPs) immobilized on a PEN substrate. Plasmonic spectroscopy and morphological characterization show that the Au-Ag NPs essentially exhibit a more uniform size distribution and higher quality factors than those from single-component Au NPs. Furthermore, it should be noted that the robust PEN substrate in this nanosensor acts a flexible substrate to support Au-Ag NPs and immobilize the nanoparticles via quick thermal annealing at 290 °C. Thanks to these merits, a prostate-specific antigen (PSA) concentration as low as 1 ng/mL can be specifically discriminated via the prepared PEN/Au-Au NPs, which confirms that the protocol reported in this work can be readily adapted for the construction of various flexible immunosensors for different applications.

Electrochemical Plasmonic Fiber-optic Sensors for Ultra-Sensitive Heavy Metal Detection

Real-time and high-sensitivity monitoring of heavy metal ions in solution is of great significance in environmental monitoring. The traditional electrochemical methods suffer from electrochemical noise and environmental interferences for heavy metal trace detection. To address these issues, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor. The sensor comprises a tilted fiber Bragg grating imprinted in a commercial single-mode fiber and coated with a nanoscale gold film for high-efficiency SPR excitation. The gold-coated optical fiber serves as a working electrode, performing the dual functions of anodic stripping voltammetry and SPR optical sensing. We demonstrate detection of Pb2+ as an example of a typical heavy metal ion. We show a stable and reproducible correlation between the real-time ion deposition–stripping cycles and the optical transmission of the optical fiber, with a limit of detection of 10−10 M and a dynamic range of nearly five orders of magnitude. Moreover, by taking derivative of the SPR amplitude change, we can clearly identify the peak stripping potential of the detected ions, and therefore, realize specific ion identification. The method proposed is inherently immune to temperature cross-talk because the core mode is temperature dependent but insensitive to the surrounding media. The proposed EC-SPR fiber-optic sensor has the advantages of compact size, flexible shape, and remote operation capability, thereby, opening the way for other opportunities for electrochemical monitoring in various hard-to-reach locations and remote environments.

Highly Sensitive Surface Plasmon Resonance Optical Sensor for Detection of Copper, Zinc, and Nickel Ions

Highly Sensitive Surface Plasmon Resonance Optical Sensor for Detection of Copper, Zinc, and Nickel Ions

High Sensitivity Au-based Kretschmann Surface Plasmon Resonance Sensor for Urea Detection

Kretschmann-based Surface Plasmon Resonance (SPR) optical sensor was applied to detect the presence of kidney wastes such as urea in solutions. To enhance the sensitivity of the SPR sensor, nanolaminated gold film (thickness of 50 nm) was used. In this work, the SPR response to urea in various concentrations were measured and investigated using optical wavelengths of 670 nm and 785 nm. The signals were compared between pure urea solution versus mixed solution in the presence of the 0.227 μmol urease enzyme. The proposed mixed solution is to eliminate doping and gel entrapment process for enzyme immobilization in conventional method. Angular interrogation technique was used to measure the sensor performance in urea detection using pure and mixed solutions with urea concentration of 0 - 800 mM. Upon exposure to mixed solution using 785 nm optical wavelength, the nanolaminated gold film exhibited higher SPR sensitivity as much as 7.8 M-1 than a pure urea solution (1.4 M-1). The coupling activity between urea and urease molecules in the mixed solution near the nanolaminated gold film surface lead to sensitivity enhancement. Angle shifting of mixed solution on 50 nm-thick nanolaminated gold film using 670 nm optical wavelength was greater by ~50% compared to 785 nm. Sensorgram data shows a steady and linear increment in SPR incident angle shifting when urea concentration increased. To the best of our knowledge, this is the first time that Kretschmann-based SPR has been used for urea sensing at 670 nm and 785 nm optical wavelengths.

Enhancing electrochemical properties of an ITO-coated lossy-mode resonance optical fiber sensor by electrodeposition of PEDOT:PSS

A sensor working in multiple domains may offer enhanced information about the properties of an investigated analyte, including those containing biological species. It has already been shown that a dual-domain sensing capability, i.e., in optical and electrochemical domains, can be offered by lossy-mode resonance (LMR) sensors based on indium-tin-oxide (ITO) thin film. The spectral response of the LMR sensors depends on the refractive index (RI) at the ITO surface. In this work, we discuss a capability for enhancing the electrochemical properties of these sensors by electrodeposition of poly(3,4-ethylenedioxythiophene)–poly(4-styrenesulfonate) (PEDOT:PSS) on the ITO surface. This conjugated polymer shows high electrical conductivity, high optical transmittance, as well as good chemical stability, and thus can be used as a transparent electrode. We have found that the PEDOT:PSS deposition improves the reversibility of the electrochemical reduction/oxidation reactions by 2.5 times with no negative impact on LMR-based measurements of the RI of the analyte.

Development of a Graphene-Based Surface Plasmon Resonance Optical Sensor Chip for Potential Biomedical Application.

The emergence of unintentional poisoning and uncontrolled vector diseases have contributed to sensor technologies development, leading to the more effective detection of diseases. In this study, we present the combination of graphene-based material with surface plasmon resonance technique. Two different graphene-based material sensor chips were prepared for rapid and quantitative detection of dengue virus (DENV) and cobalt ion (Co2+) as an example of typical metal ions. As the fundamental concept of surface plasmon resonance (SPR) sensor that relies on the refractive index of the sensor chip surface, this research focused on the SPR signal when the DENV and Co2+ interact with the graphene-based material sensor chip. The results demonstrated that the proposed sensor-based graphene layer was able to detect DENV and Co2+ as low as 0.1 pM and 0.1 ppm respectively. Further details in the detection and quantification of analyte were also discussed in terms of sensitivity, affinity, and selectivity of the sensor.

Lossy mode resonance optical sensors based on indium-gallium-zinc oxide thin film

This work discusses an application of electrically conductive and optically transparent indium-gallium-zinc oxide (IGZO) thin films for fabrication of lossy mode resonance (LMR) based optical fiber refractometers. The films have been deposited on both 200 μm in diameter multimode fused silica fiber and D-shaped fiber structure. A sensitivity of 12,929 nm/RIU was obtained in the refractive index range between 1.39 and 1.42. In case of D-shaped fiber structure the effect of polishing depth on the LMR phenomenon has also been studied.