Advantage Of Surface Plasmon Resonance Research Articles

Can classical surface plasmon resonance advance via the coupling to other analytical approaches?

For nearly 40 years, surface plasmon resonance (SPR) analysis has been used to better understand the binding interaction strength between surface immobilized bioreceptors and the analytes of interest. The advantage of surface plasmon resonance, over other affinity sensing approaches such as Western blots and ELISAs approaches, resides in its possibility to reveal binding kinetics in a label-free manner. The concept of surface plasmon resonance has in addition been widely employed for the development of biosensors capitalizing on its direct assay format, short response times, simple sample treatments along with multiplexed sensing possibilities. To this must be added the possibility to reach high sensitivity due to the capability of surface plasmon resonance to detect very small changes in refractive index at the sensing interfaces in particular for analytes of larger size such as cells (e.g., bacteria), proteins, peptides and oligonucleotides. Challenges inherent to all affinity approaches call for further research and include non-specific surface binding events, mass transportation restrictions, steric hindrance, and the risk of data misinterpretation in case of lack of selective analyte binding. This opinion article is devoted to outlining the different approaches proposed to address these challenges by e.g., coupling with fluorescence read out, electrochemical sensing, mass spectroscopy analysis and more recently to integrate lateral flow concepts into surface plasmon resonance. Other plasmonic methods such as localized surface plasmon resonance (LSPR), surface enhanced Raman spectroscopy (SERS) will not be considered in detail, as such techniques have nowadays their own standing.

SPR Analysis of SUMO-Murine Rap1-Interacting Factor 1 C-Terminal Domain Interaction with G4.

One of the advantages of surface plasmon resonance is its sensitivity and real-time analyses performed by this method. These characteristics allow us to further investigate the interactions of challenging proteins like Rap1-interacting factor 1 (Rif1). Rif1 is a crucial protein responsible for regulating different cellular processes including DNA replication, repair, and transcription. Mammalian Rif1 is yet to be fully characterized, partly because it is predicted to be intrinsically disordered for a large portion of its polypeptide. This protein has recently been the target of research as a potential biomarker in many cancers. Therefore, finding its most potent interacting partner is of utmost importance. Previous studies showed Rif1’s affinity towards structured DNAs and amongst them, T6G24 was superior. Recent studies have shown mouse Rif1 (muRif1) C-terminal domain’s (CTD) role in binding to G-quadruplexes (G4). There were many concerns in investigating the Rif1 and G4 interaction, which can be minimized using SPR. Therefore, for the first time, we have assessed its binding with G4 at nano-molar concentrations with SPR which seems to be crucial for its binding analyses. Our results indicate that muRif1-CTD has a high affinity for this G4 sequence as it shows a very low KD (6 ± 1 nM).

Analysis of Dual-Channel Simultaneous Detection of Photonic Crystal Fiber Sensors

Photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) has broad application prospects in the detection of biological proteins, DNA/RNA, and toxic chemicals. However, there are many problems in application process, such as inhomogeneous metal nanofilm, low filling speed of analyte, and low detection efficiency, which limit the development of this technology. In this paper, a dual-channel PCF sensor based on simultaneous detection which has the advantages of SPR and PCF was proposed to improve the detection efficiency of samples. By optimizing the dielectric layer, the identification ability of channels is effectively improved, and wavelength sensitivities of two channels could reached 11,600 nm/RIU and 10,600 nm/RIU, respectively. Based on this, the horizontal polishing structure was proposed, then the PCF could be immersed in the liquid analyte directly, which can reduce the difficulty of coating and avoid the filling of microfluid. The proposed structure has important scientific significance and application value to promote the practical development of SPR technology with high sensitivity in biochemical sensing and reduce the process complexity in the detection of multi-sample.

The Use of Tunable Optical Absorption Plasmonic Au and Ag Decorated TiO2 Structures as Efficient Visible Light Photocatalysts

Exploring solar-excited heterogeneous photocatalysts by taking advantage of surface plasmon resonance (SPR) has drawn growing research attention. As it could help to pave the way for global sustainable development. The decoration of TiO2 particles with noble metals possessing SPR effects is regarded as one of the most effective solutions. The perfect match of the SPR absorption band with the spectrum of incident light is an essential factor for plasmonic enhancement. However, modifying with sole noble metal is often limited as it tunes wavelength of only several nanometers. To overcome this drawback, an alternative approach can be offered by decoration with more than one noble metal. For instance, Au-Ag co-decoration displays greatly adjustable, composition-dependent SPR agent over a broad range of the visible light spectrum (ca. from 415 to 525 nm). Hence Au-Ag complex is a remarkable candidate for tuning the photo adsorption of TiO2 from UV to visible light. This study presents a novel and tailored method for the fabrication of Au-Ag co-modified TiO2 particles, and how Au-Ag dependent SPR was applied as the visible light-responsive TiO2 based photocatalysts in a simple but reliable way. The fabricated Au-Ag co-decorated TiO2 (AuxAg(1−x)/TiO2) was characterized and proved to own excellent stability and large specific surface area. The optimization of these particles against the wavelength of maximal solar light intensity was confirmed by photo degradation of methylene blue under visible light radiation. This work may provide further insight into the design of TiO2-based composites with improved photocatalytic properties for environmental remediation and renewable energy utilization.

Synergistic integration of metallic Bi and defects on BiOI: Enhanced photocatalytic NO removal and conversion pathway

Surface plasmon resonance (SPR) of metals may provide a way to improve light absorption and utilization of semiconductors, achieving better solar light conversion and photocatalysis efficiency. This study uses the advantages of SPR in metallic Bi and artificial defects to cooperatively enhance the photocatalytic performance of BiOI. The catalysts were prepared by partial reduction of BiOI to form Bi@defective BiOI, which showed highly enhanced visible photocatalytic activity for NOx removal. The effects of reductant quantity on the photocatalytic performance of Bi@defective BiOI were investigated. The as-prepared photocatalyst (Bi/BiOI-2) using 2 mmol of reductant NaBH4 showed the most efficient visible light photocatalytic activity. This enhanced activity can be ascribed to the synergistic effects of metallic Bi and oxygen vacancies. The electrons from the valence band tend to accumulate at vacancy states; therefore, the increased charge density would cause the adsorbed oxygen to transform more easily into superoxide radicals and, further, into hydroxyl radicals. These radicals are the main active species that oxidize NO into final products. The SPR effect of elemental Bi enables the improvement of visible light absorption efficiency and the promotion of charge carrier separation, which are crucial factors in boosting photocatalysis. NO adsorption and reaction processes on Bi/BiOI-2 were dynamically monitored by in situ infrared spectroscopy (FT-IR). The Bi/BiOI photocatalysis mechanism co-mediated by elemental Bi and oxygen vacancies was proposed based on the analysis of intermediate products and DFT calculations. This present work could provide new insights into the design of high-performance photocatalysts and understanding of the photocatalysis reaction mechanism for air-purification applications.

Novel Wet Micro-Contact Deprinting Method for Patterning Gold Nanoparticles on PEG-Hydrogels and Thereby Controlling Cell Adhesion.

In the present work we introduce a novel method to create linear and rectangular micro-patterns of gold nanoparticles (Au NPs) on poly(ethylene glycol) (PEG) hydrogels. The strategy consists of removing Au NPs from defined regions of the silicon wafer by virtue of the swelling effect of the hydrogel. Using this method, which we denote as “Wet Micro-Contact Deprinting”, well-defined micro-patterns of Au NPs on silicon can be created. This resulting pattern is then transferred from the hard substrate to the soft surface of PEG-hydrogels. These unique micro- and nano-patterned hydrogels were cultured with mouse fibroblasts L929 cells. The cells selectively adhered on the Au NPs coated area and avoided the pure PEG material. These patterned, nanocomposite biointerfaces are not only useful for biological and biomedical applications, such as tissue engineering and diagnostics, but also, for biosensor applications taking advantage of surface plasmon resonance (SPR) or surface enhanced Raman scattering (SERS) effects, due to the optical properties of the Au NPs.

Synthesis of hydrophobic nanoparticles for real-time lysozyme detection using surface plasmon resonance sensor.

Diagnostic biomarkers such as proteins and enzymes are generally hard to detect because of the low abundance in biological fluids. To solve this problem, the advantages of surface plasmon resonance (SPR) and nanomaterial technologies have been combined. The SPR sensors are easy to prepare, no requirement of labelling and can be detected in real time. In addition, they have high specificity and sensitivity with low cost. The nanomaterials have also crucial functions such as efficiency improvement, selectivity, and sensitivity of the detection systems. In this report, an SPR-based sensor is developed to detect lysozyme with hydrophobic poly (N-methacryloyl-(L)-phenylalanine) (PMAPA) nanoparticles. The SPR sensor was first characterized by attenuated total reflection-Fourier transform infrared, atomic force microscope, and water contact angle measurements and performed with aqueous lysozyme solutions. Various concentrations of lysozyme solution were used to calculate kinetic and affinity coefficients. The equilibrium and adsorption isotherm models of interactions between lysozyme solutions and SPR sensor were determined and the maximum reflection, association, and dissociation constants were calculated by Langmuir model as 4.87, 0.019nM-1 , and 54nM, respectively. The selectivity studies of SPR sensor were investigated with competitive agents, hemoglobin, and myoglobin. Also, the SPR sensor was used four times in adsorption/desorption/recovery cycles and results showed that, the combination of optical SPR sensor with hydrophobic ionizable PMAPA nanoparticles in one mode enabled the detection of lysozyme molecule with high accuracy, good sensivity, real-time, label-free, and a low-detection limit of 0.66nM from lysozyme solutions. Lysozyme detection in a real sample was performed by using chicken egg white to evaluate interfering molecules present in the medium.

Opening windows on new biology and disease mechanisms: development of real-time in vivo sensors

From X-ray radiology to blood panels, medicine is informed by the status of in vivo systems and their deviations from normal ranges. It is now widely acknowledged that the fundamental aetiology of many disease states can be understood at the molecular level. Over the past half a century there has been a push towards the development of novel technologies to probe the in vivo molecular status of biological systems for diagnosis, prognosis and response to therapies [1]. This Theme Issue will highlight some of the most recent exciting work in the fields of molecular-, nano-, and micro-scale devices for real-time in vivo sensing. Although this field is already large and growing, this Introduction will attempt to provide context and background for understanding this set of papers, and how they attempt to address the unique challenges that arise in the development of these novel and powerful devices. At the most fundamental level, a sensor is simply a device capable of quantifying or detecting a specific, biologically relevant analyte. Practically, this consists of a detector (such as an electrode, antibody, aptamer, peptide or enzyme) paired with a detection method (which may be optical, electrochemical or magnetic, among others). In this Theme Issue, we will focus on biosensors capable of interrogating the status of biological systems in vivo and at high temporal resolution. These in vivo sensors promise to have great utility in the future, as they will allow continuous, rapid monitoring of biological systems in the context of disease, response to therapy, cell–drug interactions or understanding normal biology. The first real-time in vivo sensors were electrochemical glucose detectors that took advantage of the catalytic activity of glucose oxidase to reliably and simply detect glucose levels over time [2]. These electrochemical detection modalities have since been improved upon and incorporated into devices capable of detecting numerous analytes, including xanthine and lactate [3]. Optical sensors have recently become increasingly popular owing to their high potential for multiplexing and ease of adaptation from existing in vitro assays. For high spatial resolution, these detectors require complex imaging modalities, such as two-photon confocal imaging, for reliable temporal and spatial resolution. Feasible use of such sensors in human patients will probably sacrifice spatial resolution for broad in vivo accuracy, as in embedded optical glucose sensors [4]. Positron emission tomography sensors are well established, with a growing list of increasingly validated substrates for in vivo sensing including glucose metabolism, oxygenation, neurotransmitters and proteases. Detection methods commonly used with in vitro sensors, such asthose that take advantage of surface plasmon resonance or the piezoelectric effect have not yet found wide utility with in vivo sensors. Adaptation of these techniques for in vivo sensing will surely expand the breadth of in vivo sensors in the future. Yasun et al. [5] specifically review recent advances in the field of gold nanorods with exciting potential for in vivo applications, including the development of photoacoustic imaging techniques for cancer. Although the range of in vitro biosensors is enormous, encompassing a huge variety of detection modalities with exquisite sensitivity, the range of in vivo

Bio-interface Detection by Surface Plasmon-field Enhanced Fluorescence Spectroscopy (SPFS)

Surface plasmon resonance (SPR) has recently been one of the powerful tools to study surface or interface in the field of biology, since it was applied to biochip array. The advantage of SPR is that the binding or adsorption of a small amount of sample to the interface can be sensitively detected without labeling a fluorescent probe. Surface plasmon-field enhanced fluorescence spectroscopy (SPFS) is based on SPR principle in which SPR field is used as an excited field for fluorescent probe. Therefore, it is available to the interface detection due to the advantages of higher sensitivity and lower background (noise). The author introduces here results of the research projects studied by SPR-SPFS, i.e., affinity of double strands in DNA-DNA hybridization and formation process of substrate supported phospholipid membranes.

Surface plasmon resonance biosensor analysis of RNA-small molecule interactions

Surface plasmon resonance (SPR) biosensors are firmly established for monitoring macromolecular interactions and are becoming a popular technique for characterizing small molecule complexes. SPR biosensors are amenable to the study of kinetics and equilibrium properties of many systems as well as screening of combinatorial libraries, and the potential applications of biosensors are rapidly expanding. Only more recently, however, has the technology advanced to the point that small molecule systems can be studied without the need for a high molecular weight tag. SPR biosensors offer an excellent method for investigating small molecule-macromolecule systems because many small molecules are either not fluorescent or do not yield notable gel band shifts on binding to macromolecules. In addition, such small quantities are required so that precious or sparse samples can be investigated with minimal material requirements. This is in direct contrast to UV or CD spectroscopies, where a 10- to 100-fold increase in sample quantity may be necessary to obtain a satisfactory signal-to-noise ratio. An advantage of SPR is that the method simultaneously can provide kinetic and equilibrium characterization of the interactions of active compounds with macromolecules. When one of the interacting species can be captured on a biosensor surface, the advantages of SPR over conventional interaction analyses can be numerous. SPR monitors molecular interactions in real time and is a significant improvement over optical methods for systems involving strong binding and/or low absorbance or fluorescence.

Near-Infrared Surface Plasmon Resonance Measurements of Ultrathin Films. 1. Angle Shift and SPR Imaging Experiments

The application of surface plasmon resonance (SPR) measurements to the study of ultrathin organic and inorganic films adsorbed onto gold surfaces utilizing near-infrared (NIR) excitation from 800 to 1152 nm is described. SPR scanning angle measurements of film thickness are demonstrated at 814 and 1152 nm using low-power diode and HeNe laser sources, respectively. Several advantages of SPR in the NIR are noted. The in situ reflectivity versus angle of incidence curves sharpen greatly (as compared to 632.8 nm) at longer wavelengths so that there is no loss in sensitivity in the measurement of film thickness despite a doubling of the excitation wavelength. The sharper resonance and longer wavelengths also allow for the measurement of thicker films. Examples of SPR thickness measurements for self-assembled alkanethiol monolayers and composite biopolymer/SiO2 nanoparticle electrostatic multilayer films are given. SPR imaging experiments are also performed at various NIR wavelengths using an incoherent white light source and narrow band-pass filters. The incoherent white light source eliminates laser fringes that have been observed in previous SPR imaging experiments, and the use of narrow band-pass filters allows for the easy selection and variation of excitation wavelength. The narrowness of the reflectivity versus angle curves leads to greater contrast in NIR SPR images compared to the same features examined with excitation from visible light. The combination of these changes results in nearly 1 order of magnitude enhancement in the SPR differential reflectivity image, indicating that SPR imaging is best conducted with incoherent NIR excitation. One disadvantage of using NIR wavelengths for SPR imaging is that the surface plasmon propagation length increases in the NIR so that the lateral image resolution is reduced; however, image features larger than 50 μm can easily be resolved. A NIR SPR image of a DNA array onto which single-stranded DNA binding protein has bound is shown as an example of how NIR SPR imaging experiments have sufficient sensitivity to monitor DNA−protein interactions.