Surface plasmon resonance detection using antibody-linked magnetic nanoparticles for analyte capture, purification, concentration, and signal amplification.

In this study, we applied two stringency control strategies for surface plasmon resonance (SPR) detection of DNA hybridization and discrimination of completely and partially complementary 24-mer sequences. These sequences are specific to the human normal bcr and the hybrid bcr-abl genes, protein products of which are responsible for some leukemia. SPR sensors based on resonance phenomena in nanoscale gold films are well suited for label-free, real-time investigations of the macromolecule interactions. Thermodynamic parameters obtained using the web server DINAMelt allowed supposing the possibility for realization (a) stringency control based on the ionic strength of the hybridization buffer and (b) stringency control based on the temperature elevation. The first one resulted in that the discrimination index of completely complementary and partially complementary oligonucleotides depending on the target concentration varied from 1.3 to 1.8 in 2 × SSC and from 2.0 to 2.9 in 0.5 × SSC. For implementation of the second stringency control strategy, SPR spectrometer measuring flow cell with built-in high-precision temperature control and regulation as well as corresponding software was created. It is shown that the duplexes formed by the immobilized probes mod-Ph and completely complementary oligonucleotides P1 remained without significant changes until ~50 °C, while the duplexes formed with partially complementary oligonucleotide Bcrex14 almost entirely disrupted at 40 °C. Thus, the absolutely effective thermodiscrimination of this pair of oligonucleotides was achieved in this temperature range (40–50 °C).

Novel surface plasmon resonance sensor for the detection of heme at biological levels via highly selective recognition by apo-hemoglobin

Measuring the glucose concentration of interstitial fluid in human body is an effectively way to control and treat diabetes. A surface plasmon resonance (SPR) system based on a miniature integrated SPR sensor is presented in this paper to measure the glucose concentration in interstitial fluid. D-galactose/D-glucose Binding Protein (GGBP) which can specifically absorb glucose is immobilized onto the SPR sensor surface by amine coupling method for higher sensitivity. The experiment result is affected by various factors, such as baseline, flow velocity, mass transfer effect, temperature, bubbles. In this paper these factors are studied systemically by experiments and some solutions are proposed accordingly: (1) Dynamic baseline can provide the best baseline location during the measurement. (2) Flow velocity of 10uL/min-30uL/min is supposed to be chosen. (3) The density of protein immobilized on the sensor surface should maintain lower to avoid the mass transfer effect. (4) Higher response is got when the temperature is between 26 °C and 30 °C and it is important to keep temperature constant during the experiment. (5) Samples should be degassed and filtered before the experiment and make sure there is no air in the pipeline. Through optimizing the experiment conditions, the sensitivity and stability of measurement are improved.

Dispersion curve-based sensitivity engineering for enhanced surface plasmon resonance detection

The rapid detection of pathogenic bacteria is important for the global public health field. Existing detection technologies are generally limited by log efficiency, high costs, and susceptibility to contamination. Advanced detection methods, such as surface plasmon resonance (SPR), have been proposed to break these limitations, with the advantages of fast detection speed and high sensitivity. SPR operates on the principle of attenuated total internal reflection at a metal–dielectric interface. This technique exploits the resonant absorption of incident photons by surface plasmons, facilitating the detection of tiny variations in the local refractive index by tracking the resonance condition change. This review provides a comprehensive overview of the development in the detection of foodborne pathogens using SPR technology, including a detailed discussion of the working principles of SPR, related instrumentation, and various detection methods. Specifically, this review focuses on a discussion of different SPR detection methods in terms of assembly processes, detection specificity, sensitivity, and detection limits in SPR biosensors, aiming to provide the readers with a fundamental knowledge of SPR.

Prion protein (PrPSc) has drawn widespread attention due to its pathological potential to prion diseases. In this work, we constructed a novel surface plasmon resonance (SPR) detection assay involving magnetic microspheres (MMs) and its controlled release property, for selective capture, embedding, concentration, and SPR detection of PrPSc with high sensitivity and specificity. Aptamer-modified magnetic particles (AMNPs) were used to specifically capture PrPSc. Amphiphilic copolymer was used to embed the labeled PrPSc and form magnetic microspheres to isolate PrPSc from the external environment. Static magnetic and alternating magnetic fields were used to concentrate and control release the embedded PrPSc, respectively. Finally, the released AMNPs-labeled PrPSc was detected by SPR which was equipped with a bare gold sensing film. A good linear relationship was obtained between SPR responses and the logarithm of PrPSc concentrations over a range of 0.01–1000 ng/mL. The detection sensitivity for PrPSc was improved by 10 fold compared with SPR direct detection format. The specificity of the present biosensor was also determined by PrPC and other reagents as controls. This proposed approach could also be used to isolate and detect other highly pathogenic biomolecules with similar structural characteristics by altering the corresponding aptamer in the AMNPs conjugates.

A heterodyne optical measurement system for studying the phase shift of surface plasmon resonance (SPR) is presented. The system utilizes a frequency-stabilized Zeeman laser as a detection light source and is suitable for real-time phase measurement in SPR-sensing applications. The phase shift in an angular dispersion SPR excitation setup was measured ranging from +180 degrees to -120 degrees around the SPR excitation region. The experimental results fit well with the theoretical analysis. Compared with the reflection coefficient variation that is widely investigated in SPR studies, phase shift is estimated to provide a higher sensitivity to sensor systems and more information about the resonance phenomenon.

Dopamine (DA) is an important catecholamine neurotransmitter involved in neural and hormonal functions. Neural diseases, as Parkinson's, are connected to a significant lowering of DA concentration to picomolar levels in cerebrospinal fluid. So, in this contribution, a hybrid active layer based on a perylene bisimide (PBI) derivative and multishaped Au nanostructures is proposed for the development of surface plasmon resonance (SPR) dopamine detection system. PBI molecules, transferred as thin film by the dip coating approach, are demonstrated to be able to detect dopamine down to 10–12 m by SPR method. The presence of Au nanostructures promotes an important surface enhanced Raman scattering effect of Raman PBI signals highlighting a strong energetic communication between the two species. In this way, when PBI/Au nanostructures (AuNS) films are deposited by the layer‐by‐layer method and used for DA SPR detection, the sensitivity toward dopamine 10−12 m is doubled. The PBI/AuNS hybrid layer is able to detect picomolar concentration of dopamine, due to the coupling of localized (AuNS) and propagating surface plasmons on SPR slide. In particular, an interfacial coupling among localized surface plasmon resonance on AuNS and the propagating plasmon on Au thin film (of SPR slide) can be promoted.

The construction and performance of a novel electrochemical (EC) surface plasmon resonance (SPR) instrument based on a mini three electrode flow cell that was designed and manufactured by MEMS technology is described. The working electrode is 50nm gold and counter and reference electrodes, made of Au and Ag/AgCl separately, are 0.6 mm in diameter. The flow channel is made of polydimethylsiloxane (PDMS) with 1mm in width, 200μm in depth, 5μL in volume. The process for activating and modifying the working electrode is given by the real-time SPR detection. The Cyclic voltammetry (CV) and SPR detection are conducted simultaneously in potassium ferricyanide solution system. It is proved that the signal of redox reaction and the change of refractive index have a well correlation by the potential sweep experiment. Four kinds of concentration of potassium ferricyanide are analyzed and the peak oxidizing current, obtained from the curve, is proportional to the respective concentration of the sample. The EC-SPR experiment is also carried out in CuSO4 system and the results is similar to potassium ferricyanide.

The aim was to develop a simple route to coupling microchip CE (MCE) to surface plasmon resonance (SPR). MCE is a microfluidic technology that utilizes microfabrication techniques to connect interacting fluid reservoirs. Its advantages include rapid analysis (typically seconds), easy integration of multiple analytical steps and parallel operation. SPR detects changes in refractive index within a short distance from the surface of a thin metal film as variations in light intensity reflected from the back of the film and, thus, does not require labeling. There is a great demand for developing hyphenated techniques like MCE-SPR that are fast, sensitive and inexpensive to analyze biological materials. The separation channel and flow cell exist as overlapping regions constructed during the microchip production and buffer solution was delivered mechanically. Such a design has successfully isolated the electrical field inherent in the MCE from the SPR detector. Consequently, the potential interference to the SPR signal (or modulation of the density of surface plasmons at the gold chip) is circumvented. The limits of detection for bovine serum albumin and sodium fluorescein were determined to be 7.5 µM and 3.1 mM, respectively. The technique described, herein, has been successfully applied in the separation of two species. The method offers the advantages of a near zero connection dead volume, electrical shielding from the separation voltage and minimization of the mass transfer effect.

We present an improved optical sensor based on surface plasmon resonance and phase detection. The sensor incorporates a surface plasmon resonance (SPR) device and a total internal reflection (TIR) device. In addition, a quarter-wave-plate (QWP) is placed in front of and behind the sensor. This gives rise to the optimization of the response curve and then the sensitivity. Theoretical simulations have been developed and verified by experimental results. With this new design, we obtain a sensitivity-tunable optical sensor whose resolving ability of refractive index is 1 x 10-6 RI.

A method for refractive index of air measurement is presented based on surface plasmon resonance (SPR) and phase detection using a dual-frequency laser interferometer. Theoretical analyses indicate that the phase-difference variation of the measurement signal versus the reference signal is linear with refractive index of air (RIA) fluctuation, and the calculation formula of RIA is derived. The structure design of the self-adaptive SPR sensor greatly reduces the measurement error resulting from the incident angle shift and improves the sensitivity. The experiments show that measurement uncertainty of 10(-6) order has been achieved when phase detection precision is 0.1°. The phenomenon of sudden phase variation during air pumping and air filling, which is caused by temperature fluctuation, is discussed.

Chemokine Detection Using Receptors Immobilized on an SPR Sensor Surface.

A graphene-based long-period fiber grating (LPFG) surface plasmon resonance (SPR) sensor is proposed. A monolayer of graphene is coated onto the Ag film surface of the LPFG SPR sensor, which increases the intensity of the evanescent field on the surface of the fiber and thereby enhances the interaction between the SPR wave and molecules. Such features significantly improve the sensitivity of the sensor. The experimental results demonstrate that the sensitivity of the graphene-based LPFG SPR sensor can reach 0.344 nm%−1 for methane, which is improved 2.96 and 1.31 times with respect to the traditional LPFG sensor and Ag-coated LPFG SPR sensor, respectively. Meanwhile, the graphene-based LPFG SPR sensor exhibits excellent response characteristics and repeatability. Such a SPR sensing scheme offers a promising platform to achieve high sensitivity for gas-sensing applications.

Nine laboratories participated in an AOAC collaborative study to determine bovine immunoglobulin G (IgG) levels in selected dairy powders and dietary supplements by surface plasmon resonance (SPR) methodology. Each sample matrix was dissolved in buffer and suitably diluted to fit within the standard curve. The sample extract was injected over a surface functionalized with affinity-purified, polyclonal goat anti-bovine IgG (H+L) antibody; IgG was then detected. SPR detection was used for the direct immunoassay and quantification was made against a calibration curve prepared from bovine serum IgG. Between each standard and sample, the surface was regenerated using 10 mM glycine at pH 1.5. The samples analyzed included the likely matrixes for which the assay would find commercial use, namely, high- and low-protein-content colostrum powders, tablets containing colostrum powder, infant formula containing colostrum powder, and some IgG-containing dairy powders, i.e., milk protein isolate, whey protein concentrate, and skim milk powder. Each laboratory provided data for the study and assayed blind duplicates of seven materials. Due to gross outliers in the majority of results from one laboratory, the data from eight laboratories were used for the statistical analysis. The repeatability RSD (RSDr) values ranged from 3.2 to 7.3%, and the reproducibility RSDR values from 13.0 to 22.6%.