Spectral Surface Plasmon Resonance Research Articles

GAS SENSOR BASED ON THE SPECTRAL SPR EFFECT WITH COLORIMETRIC REGISTRATION OF RESPONSES

A new variant of the optoelectronic sensor for the detection of gas molecules based on the effect of spectral surface plasmon resonance (SPR) in the chromatic mode with colorimetric registration of the color components of the reflected light is proposed. As an optical sensitive element, a thin silver film was used on the base face of the prism in the Kretschmann geometry, which made it possible to realize a full-fledged SPR effect in the entire visible spectral range from 450 to 700 nm. To measure the optical response, the method of video registration of R, G, B components of reflected light by color webcam was used. The optical scheme of the set-up allowed to simultaneously obtain the full spectrum of plasmon-reflected light without the use of rotating mechanical parts. The sensory effect was a change in the refractive index of the surrounding medium under the action of gases, which directly affected the parameters of the spectral SPR. A laboratory prototype of an optoelectronic sensor device was created, and the effectiveness of the proposed method was evaluated by detection of a number of organic analytes vapors .

Intercalation of anticancer drug mitoxantrone into DNA: Studied by spectral and surface plasmon resonance methods

Studying DNA interaction with different drugs is interesting and important in discovering the interaction mechanism and developing novel drugs. Mitoxantrone (MTX) is a potent antitumor drug used to treat certain types of cancer. In this work, we evaluated the binding strength of MTX to 16 base pair double strands (ds) DNA. For the first time, this work investigates the intercalation of anticancer drugs into DNA by spectral fluorescence spectroscopy and SPR (surface plasmon resonance) based methods. Furthermore, the thermodynamic and kinetic parameters, including KD, KA, entropy change (ΔS), enthalpy change (ΔH), and ΔG, were calculated using different concentrations of ds DNA at three different temperatures. The results indicated that MTX binding to DNA was an exothermic and spontaneous process. The negative value of both ΔH and ΔS calculated by SPR and fluorescence data analysis showed that hydrogen bonding was the major binding force for the complexation of MTX to DNA. In addition, fluorescence data analysis revealed that MTX could quench the DNA fluorescence via the static quenching mechanism. This study shows that the investigation of intercalation anticancer drugs into DNA can be studied by spectral methods and can be investigated using SPR based method, and obtained data from the SPR method is as reliable as the fluorescence method. The present work shows hydrogen bonding is the major binding force in intercalating MTX to DNA.

Detection of necrotrophic DNA marker of anthracnose causing Colletotrichum gloeosporioides fungi in harvested produce using surface plasmon resonance

Agriculture and food crops monitoring is extremely important for securing the food supply chain to human society. Here, we developed a highly specific detection method for monitoring pathogenic fungus Colletotrichum gloeosporioides using necrotrophic DNA biomarker as the recognition element and surface plasmon resonance (SPR) as transducing mechanism in the prism coupling configuration. The sensor shows its response for a wide range of concentrations from pM to μM of target DNA sequence using a complementary DNA probe immobilized on the sensor surface, which could detect concentrations as low as 7 pM. The detection limit is found to be comparable with conventional molecular-based detection platforms, achieved due to optimized spectral SPR bimetallic substrate with subpixel resolution obtained by post processing. The response time of the sensor for detection is less than 30 min at room temperature. The quick detection scheme of the sensor may facilitate the screening of a large number of samples acquired for the sorting of harvested produce. This sensor is fast, reliable, cost-effective, and can be miniaturized for portability for the screening of real samples (mRNA) in the field and packaging house.

Abstract P-11: Microscale Thermophoresis of Mycobacterial Cytochrome P450 with Azole Drugs

Background: Cytochrome P450 family members are found in most organisms where they are involved in the metabolism and synthesis of steroids, bile acids, unsaturated fatty acids, phenolic metabolites as well as exogenic chemicals. Drugs targeting cytochrome P450 have been shown to inhibit the growth of Mycobacterium tuberculosis, the causative agent of one of the deadliest diseases – tuberculosis. Recently, we showed that CYP124, CYP125, and CYP142 can bind and metabolize a panel of human immunoactive oxysterols in vitro (Varaksa et al., 2021) and one of them (CYP124) can metabolize antituberculosis drugs (Bukhdruker et al., 2020). Thus, inhibition of cytochrome P450 is a promising strategy for the development of new anti-tubercular drugs. The existing methods used to assess protein-ligand interactions for cytochromes P450 (spectral titration and Surface Plasmon Resonance) have a number of limitations. In this regard, we used an alternative approach for this purposes – microscale thermophoresis (MST) which was not previously used for proteins of the cytochrome P450 superfamily Methods: Here we show that MST can be used to determine the micromolar-range dissociation constants (Kd) of membrane-associated mycobacterial cytochrome CYP124 with small-molecule azole drugs. CYP124 was fluorescently labeled with Cy3-NHS and MST curves were collected at Monolith NT.115 instrument (blue/green channel, NanoTemper Technologies) in presence of various concentrations of azole compounds: econazole, ketoconazole, itraconazole, and miconazole. The experimental results were approximated by the second-order bimolecular binding equation as well as by the Hill-Langmuir equation. Results: Therefore, MST is a valuable method for the assessment of cytochrome P450 binding to their ligands for cases when traditional approaches are not applicable. The binding regime of CYP124 with azole derivatives was characterized by the structure of the CYP124 complex with carbethoxyhexyl imidazole solved with ~1Å resolution.

Surface Plasmon Resonance-Based Fiber-Optic Metallic Multilayer Biosensors.

Accurate and quick sensing of various biomolecules relevant to different health conditions is indispensable in modern diagnosis and treatment procedures. Different multilayer metallic surface plasmon resonance (SPR) biosensor configurations comprising Au, Ag, Al, and Cu are analyzed in this work by employing an N-layer matrix formalism as applied to the fixed-angle spectral SPR sensing methodology. Stringent standards for sensitivity, detection accuracy, and figure of merit (FOM) of the sensor configurations are set to analyze the relative merits of one configuration over another. It is observed that three- and four-layer configurations using Al and Cu provide the best FOM among all sensors that passed the set standard criteria. The highest FOM (1433.82/RIU) is observed for the four-layer Al/Cu/Al/Cu sensor for an analyte refractive index of 1.408. The sensors are best suited for detecting analytes with a refractive index range of 1.350–1.414.

Ultrahigh Sensitivity Surface Plasmon Resonance–Based Fiber-Optic Sensors Using Metal-Graphene Layers with Ti3C2Tx MXene Overlayers

Precise detection of volatile organic compounds (VOCs) using high-sensitivity fiber-optic probes is highly desirable for rapid screening in the fields of medicine and food processing. A novel spectral surface plasmon resonance (SPR)–based fiber-optic sensor incorporating metal/graphene/Ti3C2Tx MXene layers for the detection of VOCs such as acetone and ethanol is proposed in this study. For the detection of acetone, optimum sensitivities of 5150, 4500, and 4200 nm/refractive index unit (RIU) are obtained using simulations, for sensors with Au, Ag, and Al, respectively, as metal layer. The highest sensitivity achieved at reasonably good detection accuracy is 19,750 nm/RIU, using a Au/graphene/Ti3C2Tx sensor, for VOCs with refractive index 1.434.

Self-referenced plasmonic sensor with TiO2 grating on thin Au layer: simulated performance analysis in optical communication band

Dielectric grating–based surface plasmon resonance (SPR) sensors with self-referenced capability are relatively less explored. A self-referenced SPR sensor incorporating titanium oxide (TiO2) grating on thin gold (Au) film atop dielectric substrates is proposed in the optical communication band. The rigorous coupled wave analysis (RCWA) method is used for sensor simulation and evaluation of performance parameters. The finite-element method-based field strength analysis is performed to study the behavior of two plasmon modes (analyte mode and substrate mode) at respective resonance conditions. Further, the influence of various grating variables on sensor performance is analyzed. As a major result, in the optical communication band, an average spectral sensitivity and SPR curve width of 693.88 nm/RIU and 26.03 nm, respectively, are achieved for the optimized values of grating variables. Proposed TiO2 grating on Au film atop SiO2 substrate can provide greater sensitivity than the existing grating-based plasmonic sensors for a broad range of analyte refractive indices.

Application of ellipsometry, spr-technic and raman-spectroscopy into diagnosis of colorectal cancer

Experiments with application of the “Ellips-SPEK” spectral ellipsometric SPR (Surface Plasmon Resonance) analyzer, validating the results on the basis of ProteOn XPR36, revealed the differences in the values of velocity constants of specific interactions of monoclonal highly specific antibodies with tumor M2-pyruvate kinase on the surface of blood serum biochips in patients with various stages colorectal carcinoma (CRC) and location of metastases (AUC 0.89). Scanning ellipsometry enabled to reveal a significant increase of biomolecule surface effective thickness resulting from the specific “antigen-antibody” interaction in the group of patients with extrahepatic and hepatic metastases, as compared to the control group with healthy patients (p<0.0001–0.05). Raman spectroscopy of blood serum demonstrated the differences in peak intensity within the range of 1005–1520 cm-1 in the same groups of patients (p<0.0001–0.05) with a 90% predictive accuracy of the method applied at early stages of the disease. The results obtained can be used for development of methods for early diagnosis of CRC, localization of different metastases, relapses and control of the quality of administered therapy.

Gold-Silver Alloy Film Based Spectral Surface Plasmon Resonance Imaging Sensor with High Sensitivity

Gold-Silver Alloy Film Based Spectral Surface Plasmon Resonance Imaging Sensor with High Sensitivity

Spectral Imaging Analysis for Ultrasensitive Biomolecular Detection Using Gold-Capped Nanowire Arrays.

A spectral integration combined with a threshold method for the analysis of spectral scanning surface plasmon resonance (SPR) images can significantly increase signal recognition at low concentration of antibody solution. The 12-well SPR sensing plates consisted of gold-capped nanowire arrays with 500-nm period, 80-nm linewidth and 50-nm gold thickness which were used for generating multiple SPR images. A threshold method is introduced to eliminate background noises in spectral scanning images. Combining spectral integration and the threshold method, the detection limit of antibody concentration was 1.23 ng/mL. Using multiple-well SPR sensing plates and the proposed analytical method, multiple kinetic responses with spectral and spatial information on different sensing areas can be sensitively measured.

Spectropolarimetric Surface Plasmon Resonance Sensor and the Selection of the Best Polarimetric Function

Intensity based spectral surface plasmon resonance (SPR) sensors are becoming more and more used due to the availability of miniature and low-cost spectrometers, however, they still lack the low limit of detection, because the SPR dip spectral width is around 50 nm even though the spectral sensitivity is considered relatively high. Profiting from the sharp jump in phase under SPR, several works suggested the extraction of the phase of the reflected wave. In this work, we propose a simple spectral polarimetric setup, which involves the addition of an analyzer at three different orientations and performing measurements of the intensity spectrum. Measurements at different concentrations of ethylene glycol in water were carried out using this technique and showed a comparable performance to some of the best spectral interrogation techniques. Theoretical simulations showed that the derivative of the phase difference between the TM and TE waves gives the highest resolution, although practically the more directly measured cosine function of the phase difference is the best one to use. Another important result is that the tolerance on the metal layer thickness is improved significantly when the spectropolarimetric method is used.

Wavelength-Scanning SPR Imaging Sensors Based on an Acousto-Optic Tunable Filter and a White Light Laser.

A fast surface plasmon resonance (SPR) imaging biosensor system based on wavelength interrogation using an acousto-optic tunable filter (AOTF) and a white light laser is presented. The system combines the merits of a wide-dynamic detection range and high sensitivity offered by the spectral approach with multiplexed high-throughput data collection and a two-dimensional (2D) biosensor array. The key feature is the use of AOTF to realize wavelength scan from a white laser source and thus to achieve fast tracking of the SPR dip movement caused by target molecules binding to the sensor surface. Experimental results show that the system is capable of completing a SPR dip measurement within 0.35 s. To the best of our knowledge, this is the fastest time ever reported in the literature for imaging spectral interrogation. Based on a spectral window with a width of approximately 100 nm, a dynamic detection range and resolution of 4.63 × 10−2 refractive index unit (RIU) and 1.27 × 10−6 RIU achieved in a 2D-array sensor is reported here. The spectral SPR imaging sensor scheme has the capability of performing fast high-throughput detection of biomolecular interactions from 2D sensor arrays. The design has no mechanical moving parts, thus making the scheme completely solid-state.

Fast spectral surface plasmon resonance imaging sensor for real-time high-throughput detection of biomolecular interactions.

A fast surface plasmon resonance (SPR) imaging biosensor system based on wavelength interrogation using a liquid crystal tunable filter (LCTF) is presented. The system combines the merits of wide-dynamic detection range offered by the spectral approach and multiplexed high-throughput data collection with a two-dimensional (2-D) biosensor array. The key feature of the reported scheme is a feedback loop that drives the LCTF to achieve fast tracking of the SPR dip movement caused by the binding of target molecules to the sensor surface. Experimental results show that the system is capable of completing an SPR dip measurement within 4 s. Based on using a spectral window of about 100 nm, the experimental dynamic detection range and refractive index resolution are 4.63×10?2??RIU and 5.87×10?6??RIU, respectively. As also demonstrated herein using 2-D microsensor arrays, among the spectral SPR sensors, the reported system is most suitable for multiplexed label-free biosensing applications.

High-throughput imaging surface plasmon resonance biosensing based on an adaptive spectral-dip tracking scheme.

Imaging-based spectral surface plasmon resonance (λSPR) biosensing is predominantly limited by data throughput because of the multiplied data capacity emerging from 2-dimensional sensor array sites and the many data points required to produce an accurate measurement of the absorption dip. Here we present an adaptive feedback approach to address the data throughput issue in λSPR biosensing. A feedback loop constantly tracks the dip location while target-molecule binding occurs at the sensor surface. An adaptive window is then imposed to reduce the number of data points that each pixel has to capture without compromising measurement accuracy. Rapid wavelength scanning is performed with a liquid crystal tunable filter (LCTF). With the use of a feedback loop, our demonstration system can produce a dip measurement within 700ms, thus confirming that the reported λSPR approach is most suitable for real-time micro-array label-free biosensing applications.

Instantaneous detection of melamine by interference biosynthesis of silver nanoparticles

Instantaneous detection of melamine, a potential milk adulterant has been demonstrated at room temperature by means of interference biosynthesis of silver nanoparticles. The sensing mechanism is based on the colorimetric change observed during the synthesis of silver nanoparticles due to the presence of melamine added during the biosynthesis. Presence and absence of melamine led to either inhibition of nanoparticle formation or enable partial synthesis of nanoparticles which is detected spectrally. A limit of detection (LOD) of 0.1ppm in water and 0.5ppm in raw milk was detected by the proposed technique at room temperature. UV–vis spectroscopy and High Resolution Transmission Electron Microscopy (HR-TEM) have been used to detect the spectral Surface Plasmon Resonance (SPR) and morphological changes of synthesized silver nanoparticle with and without the presence of the analyte melamine. Further, interference synthesis based sensing of melamine was done with caffeic acid as a reducing agent which confirms the role of caffeic acid a major constituent of Parthenium leaf extract for interference biosynthesis based sensing. Melamine is detected from raw milk by interference biosynthesis based sensing after a facile milk pre-processing step. Thus the method can be converted into a workable handheld prototype for detection of melamine for in-situ field applications.

MicroRNA biosensing through spectral interferometry‐based surface plasmon resonance using telecommunication wavelength

The polarisation maintaining (PM) fibre constructed the spectral interferometry-based surface plasmon resonance to detect the very small molecule micro ribonucleic acid (miRNA) with a big biological impact on cancer diagnosis. Other than the linear polariser and birefringence crystal in the input of the traditional spectral interferometry, the polarisation controller was simply placed on the injected light to control the transverse electric and transverse magnetic polarised magnitudes through the stable polarisation state of PM fibres for distinct dynamic-range fringes on the optical spectrum analyser (OSA). Owing to the high precision and stability control of operating wavelengths in optical fibre communications, the low-coherence telecommunication source was utilised to detect 21-mer deoxyribonucleic acid which changed U to T according the miRNA-21 sequence. The sensitivity with probing was showing 0.065 nm/(μg/ml), which implied the resolution as 0.3 μg/ml under the 0.02 nm wavelength accuracy on OSA.

Clenbuterol Assay by Spectral Imaging Surface Plasmon Resonance Biosensor System.

To prevent illegal use of clenbuterol and for quality control in the food industry, more efficient and reliable methods for clenbuterol detection are needed. In this study, clenbuterol was detected using a spectral imaging surface plasmon resonance sensor system via two inhibition methods: (1) the target site compensation method, in which anti-clenbuterol antibody was immobilized on the sensor chip as a bioprobe and (2) the solution competition method in which a clenbuterol-BSA conjugate was immobilized on the sensor chip as the bioprobe. The detectable clenbuterol concentration ranged between 6.25 and 100μg/mL for both methods. The clenbuterol limit of detection for the target site compensation method and solution competition method are estimated to be 6.7 and 4.5μg/mL, respectively. The proposed methods were successfully applied to the detection of clenbuterol molecules and were found to have high specificity and high-throughput and were label free and operationally convenient.

Spectral interferometry-based surface plasmon resonance sensor

A two-step spectral interferometric technique is used to measure a surface plasmon resonance (SPR) phase difference from the spectral interferograms recorded in the Kretschmann configuration. The technique employs a polarimetry setup with a white-light source and birefringent crystal and allows one to obtain a channeled spectrum. Two such spectra, one including reflection of p- and s-polarized waves from the SPR structure for air when the SPR phenomenon does not occur in the source spectral range, and the other one for an analyte when the SPR phenomenon occurs, are used to retrieve the wavelength-dependent SPR phase difference. The new method is applied for aqueous solutions of ethanol with different parameters, the concentration of ethanol in water in a range from 0 to 60 weight percent and the refractive index in a range from 1.333 to 1.362. The sensing scheme uses a wavelength interrogation method and the position of a sharp maximum in the spectral derivative of the SPR phase change is measured as a function of the analyte parameter in a range from 644 to 690nm. In the same setup, the spectral dependence of the ratio between the reflectances of both polarization states is measured as a function of the analyte parameter. It is revealed that the detection accuracy of the interferometric measurements is more than three times higher than that of the polarimetric measurements.

In situ study of self-assembled nanocomposite films by spectral SPR sensor.

Spectral surface plasmon resonance (SPR) sensor with a time-resolved charge-coupled device (CCD) detector is a powerful analytical tool for label-free detection of biomolecular interaction at the liquid/solid interface and for in situ study of molecular adsorption behavior. In this work, the layer-by-layer self-assembly processes for three nanocomposite films were monitored in real time using a broadband spectral SPR sensor with a large dynamic range. Kinetics studies suggest that cytochrome c (Cyt c) and deoxy ribonucleic acid (DNA) adsorptions obey the Langmuir-isotherm theory, while gold nanoparticle (GNP) adsorption follows the Diffusion-controlled model. Using poly(sodium 4-styrenesulfonate) (PSS) and poly(dimethyldiallylammonium chloride) (PDDA) as the positively charged agents, three kinds of multilayer films such as the PSS/Cyt c, GNP/Cyt c and PDDA/DNA binary nanocomposites were fabricated on the SPR chips by the electrostatic attraction based on self-assemble. The SPR response in terms of ΔλR was measured to linear increase with increasing the number of layers for a six-bilayer PSS/Cyt c nanocomposite film, indicating that every PSS/Cyt c layer has equal mass coverage. In contrast, the nonlinear dependences of ΔλR on the number of bilayers were observed for the GNP/Cyt c and PDDA/DNA nanocomposite multilayer films.

Silver nanoparticle arrays enhanced spectral surface plasmon resonance optical sensor

An on-chip spectral surface plasmon resonance (SPR) optical sensor with a silver nanoparticle (Ag NP) array has been designed. Dextran (Dex)-capped Ag NP (Dex-Ag NP) arrays were initially self-assembled on the gold (Au) sensing film. The large perturbations and increased penetration depth of the evanescent field, which is caused by the use of the Dex-Ag NP array self-assembled on the Au sensing film, can effectively enhance the SPR spectral shift response. Compared with the bare Au sensing film configuration, the Au sensing film with a Dex-Ag NP array configuration improves sensitivity from 5492 to 6613 nm/RIU.