Surface Plasmon Resonance Angular Shift Research Articles

Investigation of Acetone Vapour Sensing Properties of a Ternary Composite of Doped Polyaniline, Reduced Graphene Oxide and Chitosan Using Surface Plasmon Resonance Biosensor.

This work reports the use of a ternary composite that integrates p-Toluene sulfonic acid doped polyaniline (PANI), chitosan, and reduced graphene oxide (RGO) as the active sensing layer of a surface plasmon resonance (SPR) sensor. The SPR sensor is intended for application in the non-invasive monitoring and screening of diabetes through the detection of low concentrations of acetone vapour of less than or equal to 5 ppm, which falls within the range of breath acetone concentration in diabetic patients. The ternary composite film was spin-coated on a 50-nm-thick gold layer at 6000 rpm for 30 s. The structure, morphology and chemical composition of the ternary composite samples were characterized by FTIR, UV-VIS, FESEM, EDX, AFM, XPS, and TGA and the response to acetone vapour at different concentrations in the range of 0.5 ppm to 5 ppm was measured at room temperature using SPR technique. The ternary composite-based SPR sensor showed good sensitivity and linearity towards acetone vapour in the range considered. It was determined that the sensor could detect acetone vapour down to 0.88 ppb with a sensitivity of 0.69 degree/ppm with a linearity correlation coefficient of 0.997 in the average SPR angular shift as a function of the acetone vapour concentration in air. The selectivity, repeatability, reversibility, and stability of the sensor were also studied. The acetone response was 87%, 94%, and 99% higher compared to common interfering volatile organic compounds such as propanol, methanol, and ethanol, respectively. The attained lowest detection limit (LOD) of 0.88 ppb confirms the potential for the utilisation of the sensor in the non-invasive monitoring and screening of diabetes.

Study of Computational Theory of Surface Plasmon Resonance (SPR) for Porcine Gelatin Detected Sensor Based Nanomaterial Fe3O4–CNT in Otto’s Configuration

Accurate biomolecular detection can be performed through the Surface Plasmon Resonance (SPR) phenomenon. This study was conducted to determine the effect of the addition of Fe3O4 and Carbon Nanotube (CNT) nanomaterials in the Otto configurations and their use as porcine detection sensors. The research was conducted theoretically by finding the equation of reflectance and computationally using Matlab software version 7.12.0 to know SPR angle and reflectance value. This research uses ATR method with Otto configuration. The modeling was finished using HeNe laser light on 632.8 nm wavelength, semi-circle prism type BK7, metal layer of gold nanoparticles. The results of the research can be used in the detection of porcine gelatin by Otto configurations. The best air gap thickness is 30 nm. The best thickness of the gold layer and Fe3O4 layer are 50 nm and 0.05 nm. The applied of MWCNT nanoparticles is not effective in the detection of biomolecules based SPR. While the thickness of SWCNT used is 1 nm. The SWCNT material also proved to be better used in SPR systems. The addition of porcine gelatin layer in the system shows a graphic change in the form of increasing reflectance value and SPR angular shift.

Laser-induced thermal effect in surface plasmon resonance

In this work, thermal effect inherent in long-term irradiation of a focused laser beam may become a major source of error in surface plasmon resonance (SPR) measurements, especially when infinitesimal signals (e.g., reorganization of monolayers or conformational changes of immobilized proteins) are measured. The laser-induced thermal effect was examined by continuously monitoring changes brought about by injecting 2% ethanol solution into a flow cell housing bare and chemically modified gold films that had been irradiated by a laser beam for various times, and a maximum relative error of 21% was obtained. Factors affecting the SPR response, namely solution flow rate, compactness of the adsorbate layer, and power of the laser beam, were examined. The SPR dip shift (SPR angular shift) was shown to be dependent not only on the magnitude of the laser power but also on the thermal dissipation at the metal–solution interface. With a better understanding of the parameters affecting the thermal energy dissipation and the temperature dependence of the SPR signals, measures can be taken to improve the accuracy of SPR data. We show as an example that, if the laser-induced thermal effect is not considered or reduced, accuracy in determinating redox-triggered reorganization of a pre-immobilized 11-ferrocenylundecanethiol self-assembled monolayer (SAM) may be decreased by more than 40%, leading to an erroneous conclusion.

Ultrasensitive detection of mercury (II) ions using electrochemical surface plasmon resonance with magnetohydrodynamic convection

A high-precision technique that can detect mercury (II) ions down to 1 fM concentration in aqueous solutions is introduced. The technique combines the conventional electrochemical method, surface plasmon resonance (SPR), and magnetohydrodynamic (MHD) convection. Mercury ions are electroplated onto a gold SPR sensing surface, and then detected quantitatively by applying a potential scan with cyclic voltammetry. Both the SPR angular shift and the electrochemical current signal are recorded for identification and quantification of the mercury ions. The detection sensitivity is further enhanced by applying an MHD convection in the presence of a magnetic field, which does not require any moving parts intruding into the aqueous solution. The technique thus has a great advantage for small detection volume. In the presence of supporting electrolytes, 1 mM nitric acid and 10 mM potassium nitrate, Hg 2+ ionic solutions with concentrations ranging from 1 fM to 1 μM are tested under different magnetic flux densities of B = 0 , 0.27, 0.53, and 0.71 T. The experimental results demonstrate that the stripping signals of the 1 fM to 1 μM Hg 2+ ions are enhanced by 10–60% with the flux density B = 0.71 T .

Detection of Heavy Metal Ions in Water by High-Resolution Surface Plasmon Resonance Spectroscopy Combined with Anodic Stripping Voltammetry

High-resolution differential surface plasmon resonance (SPR) with anodic stripping voltammetry (ASV) capability has been demonstrated for detecting heavy metal ions in water. Metal ions are electroplated onto the gold SPR sensing surface and are quantitatively detected by stripping voltammetry. Both the SPR angular shift and electrochemical current signal are recorded to identify the type and amount of the metal ions in water. The performance of the combined approach is further enhanced by a differential detection approach. The gold sensor surface is divided into a reference and a sensing area, and the difference in the SPR angles from the two areas is detected with a quadrant cell photodetector as a differential signal. Our system demonstrated quantitative detection of copper, lead, and mercury ions in water from part-per-million to sub-part-per-billion levels with good linearity.

Characterization of Micropatterned Lipid Membranes on a Gold Surface by Surface Plasmon Resonance Imaging and Electrochemical Signaling of a Pore-Forming Protein

We report the fabrication and characterization of a micropatterned membrane electrode for electrochemical signaling of a bacterial pore-forming toxin, Streptolysin O (SLO) from S. pyogenes. Microcontact printing of an alkylthiol monolayer was used to fabricate an array template, onto which cholesterol-containing DMPC vesicles were fused to form lipid layer structures. The construction of the supported membranes, including pattern transfer and vesicle fusion, was characterized by in-situ surface plasmon resonance (SPR) imaging and electrochemistry. Quantitative analysis of the resulting membrane by using SPR angular shift measurements indicates that the membranes in the hydrophilic pockets have an average thickness of 8.2 +/- 0.4 nm. Together with fluorescence microscopy studies, the results suggest that this could be a mixed lipid assembly that may consist of a bilayer, vesicle fragments, and lipid junctions. The voltammetric response of the redox probe ferrocene carboxylic acid (FCA) was measured to quantify the toxin action on the supported membrane. The electrochemical measurements indicate that fusion of vesicles on the template blocked the access of FCA, whereas the injection of SLO toxin restored the redox response. The anodic peak current of FCA was found to increase with toxin concentration until a plateau was reached at 40 HU/mL. The method is highly sensitive such that 0.1 HU/mL of SLO (1.25 pM) can yield a well-defined response. In addition, it eliminates the need for a highly insulating layer in membrane sensing, which opens up new avenues in developing novel sensing interfaces for membrane-targeting proteins and peptides.

Construction of DNA-Au Nanoparticles Multilayer and Its Application to Detection of DNA Hybridization

We have developed a sensitive detection system for DNA hybridization containing DNA-Au nanoparticles (DNA-GPs) multilayer which leads to the enhancement of the detection sensitivity of surface plasmon resonance (SPR) signals. The SPR angular shift, which is the difference in the SPR angles before and after hybridization, becomes amplified with increasing number of layers of the DNA-GPs. A similar increase in SPR angular shift was obtained for the target DNA with low concentration. The reason for the enhancement is attributed to the interaction between Au nanoparticles and the Au film, as well as the increase in immobilized probe DNA content on the substrate.

High-performance differential surface plasmon resonance sensor using quadrant cell photodetector

We describe a simple, stable, and high-resolution surface plasmon resonance (SPR) sensor using a quadrant cell photodetector. The sensor focuses a diode laser through a prism onto a gold film that is divided into two areas, one for reference and the other for sensing analyte. The angular shifts of the SPR generated in the two areas are detected with a quadrant cell photodetector. Because signals from the two areas are produced and detected with the same laser, optics, and photodetector, the difference in the SPR angular shifts eliminates errors due to thermal drift, mechanical noise, and laser fluctuations. It also removes the SPR angular shift due to the change in the refractive index of the bulk solution as an analyte solution is introduced into the sample cell each time, and thus gives an accurate detection of the specific adsorption of analyte.

Surface plasmon resonance enhanced optical absorption spectroscopy for studying molecular adsorbates

We present an automated setup to measure the surface plasmon resonance (SPR)-enhanced optical absorption spectra of molecular adsorbates. The setup detects the reflectivity at the SPR resonance angle as a function of the incident light wavelength. Because the resonance angle is wavelength dependent, a feedback mechanism adjusts the photodetector position to follow the resonance angle when the wavelength varies. Both theoretical calculations and experimental measurements show a signal enhancement of up to ∼40 times over the conventional absorption spectroscopy. The SPR-based absorption spectroscopy is surface specific because the optical field is localized near the surface at resonance. In addition, the SPR angular shift is simultaneously measured, which provides adsorbate coverage and adsorption kinetic information. We anticipate that with our automated system, the method could be used in the study of adsorbed molecules and in chemical and biosensor applications.

High-sensitivity stark spectroscopy obtained by surface plasmon resonance measurement.

The effect (Stark effect) of an applied electric field on the electronic states of molecular adsorbates was studied by measuring surface plasmon resonance (SPR) as a function of the wavelength of the incident light that excites the SPR. Using the Kramers-Kronig relation, Stark spectra comparable to those obtained with conventional methods were extracted from the electric field-induced SPR angular shift for several organic adsorbates. Because this method relies on detecting the SPR angular shift that can be measured precisely, high-sensitivity Stark spectroscopy can be achieved. In addition, the adsorbate coverage information can be determined from the SPR angular shift upon molecular adsorption.