Long-range Surface Plasmon Resonance Research Articles

Cellular micromotion monitored by long-range surface plasmon resonance with optical fluctuation analysis.

Long-range surface plasmon resonance (LRSPR) is a powerful biosensing technology due to a substantially larger probing depth into the medium and sensitivity, compared with conventional SPR. We demonstrate here that LRSPR can provide sensitive noninvasive measurement of the dynamic fluctuation of adherent cells, often referred to as the cellular micromotion. Proof of concept was achieved using confluent layers of 3T3 fibroblast cells and MDA-MB-231 cancer cells. The slope of the power spectral density (PSD) of the optical fluctuations was calculated to determine the micromotion index, and significant differences were measured between live and fixed cell layers. Furthermore, the performances of LRSPR and conventional surface plasmon resonance (cSPR) were compared with respect to micromotion monitoring. Our study showed that the micromotion index of cells measured by LRSPR sensors was higher than when measured with cSPR, suggesting a higher sensitivity of LRSPR to the micromotion of cells. To investigate further this finding, simulations were conducted to establish the relative sensitivities of LRSPR and cSPR to membrane fluctuations. Increased signal intensity was predicted for LRSPR in comparison to cSPR, suggesting that membrane fluctuations play a significant role in the optical micromotion measured in LRSPR. Analogous to cellular micromotion measured using impedance techniques, LRSPR micromotion has the potential to provide important biological information on the metabolic activity and viability of adherent cells.

Systematic study of the surface plasmon resonance signals generated by cells for sensors with different characteristic lengths.

The objectives of this study were to establish an in-depth understanding of the signals induced by mammalian cells in surface plasmon resonance (SPR) sensing. To this end, two plasmonic structures with different propagation and penetration distances were used: conventional surface plasmon resonance and long-range surface plasmon resonance. Long-range SPR showed a lesser sensitivity to the absolute number of round cells but a greater resolution due to its very narrow spectral dip. The effect of cell spreading was also investigated and the resonance angle of long-range SPR was mostly insensitive unlike in the conventional SPR counterpart. Experimental data was compared with suitable models used in the SPR literature. Although these simple averaging models could be used to describe some of the experimental data, important deviations were observed which could be related to the fact that they do not take into consideration critical parameters such as plasmon scattering losses, which is particularly crucial in the case of long-range SPR structures. The comparison between conventional and long-range SPR for cellular schemes revealed important fundamental differences in their responses to the presence of cells, opening new horizons for SPR-based cell assays. From this study, long-range SPR is expected to be more sensitive towards both the detection of intracellular events resulting from biological stimulation and the detection of microorganisms captured from complex biological samples.

A Revised LRSPR Sensor with Sharp Reflection Spectrum

In this work, we have proposed a novel long-range surface plasmon resonance (LRSPR) sensor with sharp reflection spectrum, which consists of a glass prism, a (A/B)4-type waveguide-coupled layer and a metal layer. To reveal its sharp reflection spectrum perfectly, we have simulated the effects of all factors of this LRSPR sensor on the reflection spectrum, and finally presented the optimal parameters of the LRSPR sensor with sharp reflection spectrum.

Long-range surface plasmon resonance immunosensor based on water-stable electrospun poly(acrylic acid) fibers

Water-stable poly(acrylic acid) (PAA) fibers were fabricated on flat gold thin films via an electrospinning technique. The obtained fibers were then used to construct long-range surface plasmon resonance (LR-SPR) biosensors. Because LR-SPR spectroscopy has a greater evanescent field intensity and penetration depth than conventional surface plasmon resonance (SPR) spectroscopy, the increased surface area of the PAA fibers within the surface plasmon evanescent field was efficiently utilized for biosensor applications. The water-stable electrospun PAA fibers were obtained by adding β-cyclodextrin as a crosslinker, followed by thermal treatment at 150°C for 40min. In addition, the layer-by-layer deposition of poly(diallyldimethylammonium chloride) and PAA ultrathin films on the electrospun PAA fibers functionalized their surfaces and further increased their water-stability by increasing the number of active carboxylic acid groups. Fiber surfaces were then successfully activated for the construction of immunosensors for the detection of human immunoglobulin G. Therefore, the present study demonstrates the potential of electrospun fibers for LR-SPR biosensor applications.

Multichannel, Line-Monitoring Sensing Approach Based on Long-Range Surface Plasmons

The refractive index resolution of a surface plasmon resonance (SPR) sensor has been significantly improved these years; however, higher sensing performance is always desired. In this work, we propose a line-monitoring, long-range SPR sensor whose resolution is much better than conventional SPR sensors. Also, in contrast to mono-channel detection, multichannel detection, using line-monitoring technique, can detect multiple channels concurrently. In this way, this system achieves a refractive index resolution of 4.0 × 10− 7 refractive index units and can monitor multiple molecular interactions simultaneously. Finally, a model experiment detecting the Escherichia coli bacteria has demonstrated the potential for biomedical applications of this system.

对称型长程表面等离子体共振分析系统

Applications of the Long Range Surface Plasmon Resonance(LRSPR)technology from the SPRs are hard to be popularized because of its special film matching conditions,namely,the refractive index of the buffer layer must be similar to that of the tested sample.To improve the applicability of the traditional LRSPR technology,a symmetric LRSPR technology was proposed.A symmetric film structure(buffer dielectric layer+ metal film + buffer dielectric layer)was designed to break the limitations of the matching conditions and to further improve the penetration depth of electromagnetic field and the resonance peak depth.The symmetric film structure was analyzed theoretically,and an angular spectrum SPR detection system was built by using a Light Emitting Diode(LED)as the light source.The measuring system was used to measure the refractivity resolution of different glucose solutions,and the algorithm proposed was optimized.The results show that the refractivity resolution of the system can reach 6.1×10-7 RIU,the sensitivity is 1.22×105 pixel/RIU and a better linearity is obtained in a refractivity measuring range.

All-optical sensor based on surface plasmon polaritons in multi-layers metal-dielectric structure

We study all-optical sensing characteristics based on long-range surface plasmon resonance in a four-layered metal-dielectric structure immersed in the liquid to be measured. The resonance peaks in the reflection angle spectra depend on different refractive indices from 1.30 to 1.38, which are calculated and compared in three typical wavelengths of 532, 632.8 and 780 nm, respectively. Compared with 532 nm, the incident light of 780 nm results in an unstable sensing stability, but the resolution enhances two times. The sensitivity of this refractive index sensor at an incident angle of 45° is about 236.7 nm/RIU which uses 532-nm laser as the light source.

Long range surface plasmon resonance for increased sensitivity in living cell biosensing through greater probing depth

Long range surface plasmon resonance (LRSPR) was used to improve over standard SPR for the detection and monitoring of toxicity with living cells. With a greater evanescent field penetration depth into the sensing medium and increased sensitivity to optical scattering, LRSPR shows a higher sensitivity for measurements involving molecular content redistribution associated with cellular morphology changes. LRSPR and SPR sensitivity to real and imaginary refractive index component variations was evaluated separately using calibrated oil solutions and dilutions of polystyrene beads, respectively. An increase in reflectance at the minimum along with a broadening of the curve was observed for LRSPR as a result of evanescent field scattering. Angular scans for SPR were marginally affected, due to an evanescent field too shallow for the beads to produce significant scattering. Methylene blue dilutions in water were used to evaluate sensitivity to complex refractive index variations. Finally, LRSPR and SPR were used to measure the response of a HEK-293 cell monolayer under stimulation at different concentrations by a toxin, lipopolysaccharides. The experimental results presented confirm that living cells must be modeled as a dielectric medium with a complex refractive index in LRSPR measurements and that LRSPR exhibits a 50% greater sensitivity compared to standard SPR for toxicity measurements based on living cells.

Passivation of KMPR microfluidic channels with bovine serum albumin (BSA) for improved hemocompatibility characterized with metal-clad waveguides

Abstract KMPR is an epoxy-based photoresist, similar to SU-8, featuring shorter processing times and superior resistance to fissuring. As such, KMPR is a material well-suited to microfluidic device fabrication in miniaturized biomedical instrumentation. However, like SU-8, KMPR requires surface treatment for hemocompatibility. In this work, we demonstrate that KMPR can be efficiently passivated with bovine serum albumin (BSA), improving hemocompatibility of the material surfaces. Experimental validation was conducted using fibrinogen adsorption as a hemocompatibility model. Protein adsorption to KMPR surfaces was measured using metal-clad waveguides (MCWG) with a KMPR film acting as the waveguide core layer. Passivation efficiency was compared both on natively hydrophobic KMPR and on hydrophilic KMPR treated with HNO3 catalyzed with ceric ammonium nitrate (CAN). Results show that the surface treatment significantly increases hemocompatibility for both hydrophilic and hydrophobic surfaces, with slightly better results in the case of hydrophobic surfaces. Post-treatment ultrasound wash had no observable effect, demonstrating that BSA adsorption to KMPR is robust. MCWG-based protein adhesion measurements were compared to that from conventional surface plasmon resonance (SPR) and long-range surface plasmon resonance (LR-SPR), confirming the validity of the measurements.

Interactions of alginate-producing and -deficient Pseudomonas aeruginosa with zwitterionic polymers

In this work, we report a study of the interactions between bacteria and zwitterionic polymers using a long-range surface plasmon resonance (LR-SPR) sensor. The LR-SPR with an extended probing field allows one to perform in-situ monitoring of bacterial adhesion and to investigate bacteria–surface interactions under various conditions. Alginate-producing and -deficient Pseudomonas aeruginosa were used in order to study the role of capsular exopolysaccharide in bacterial adhesion onto a surface. Polycarboxybetaine polymers with one and two carbons in spaces between two oppositely charged moieties on polymer side chains (pCBAA-1 and pCBAA-2) were prepared in order to unveil the effects of material properties on surface resistance to bacterial adhesion. In addition, environmental factors (e.g., divalent cations) were investigated. This work demonstrates the role of polysaccharides beyond proteins in bacteria adhesion and the effective resistance of pCBAA-1 against bacterial adhesion.

Large positive and negative lateral optical beam shift due to long-range surface plasmon resonance

In this paper, we examine theoretically the beam shift at visible wavelengths on a long-range surface plasmon (LRSP) configuration by using the stationary-phase approach. We report that the lateral beam shift at the resonance of LRSP can be two orders of magnitude greater than a wavelength. It is also found that the sign of the lateral beam shift depends on the magnitude of the intrinsic damping relative to that of the radiative damping. Negative lateral beam shift occurs when the former is larger than the latter.

Long-range surface plasmon resonance sensor with liquid micro-channels to maintain the symmetry condition of the refractive index

We propose a method to maintain the symmetry of the refractive index with respect to an Au film, in which the refractive indices are the same near both surfaces of the Au film, for LRSPR (long-range surface plasmon resonance) sensors. Maintenance of the symmetry is necessary for exciting the LRSPR mode. However, because the buffer layer under the Au film is usually made of a solid dielectric material with a constant refractive index, the quality of the measurement is reduced when the refractive index of the analyte used is dramatically different from that of the buffer layer. To solve this problem, the proposed sensor is equipped with liquid channels under the Au film. The Au film used in this study was supported by a thin (100 nm) polymer film forming parallel, one-dimensional liquid channels with a 29 µm pitch. Because the analyte solution flows in the channels, both surfaces of the Au film face the same analyte. Thus, this configuration automatically satisfies the symmetry condition for analytes with a wide range of refractive indices. We examined the validity of the sensor and compared it to that of a conventional sensor by measuring the LRSPR for five analyte solutions with different refractive indices. LRSPR dips were clearly observed for all of the analytes tested. The dip of the conventional LRSPR sensor became shallow when the refractive index increased, with the final dip depth being 65% of the initial dip depth for a refractive index of 1.358. In contrast, the dip depth of the proposed LRSPR sensor remained constant over the entire measured refractive index range of 1.331 to 1.358. These results indicate that the proposed sensor maintains the symmetry condition and confirm that the proposed method is effective for highly sensitive LRSPR measurements for a wide variety of analyte species.

Registration of long-range surface plasmon resonance by angle-scanning feedback and its implementation for optical hydrogen sensing

An optical technique devised for the detection of the ultrasharp angular resonance of long-range surface plasmons (LRSPs) is described. The LRSPs propagate along an 8 nm-thick palladium (Pd) film deposited on a one-dimensional photonic crystal structure and bordering a gas environment at another Pd film interface. At such a small metal film thickness, the scattering attenuation losses prevail over dissipation losses inside the film and we use this scattering as an input signal to pick up the angle of the surface plasmon resonance by a closed feedback loop via an angle-scanning piezomirror. As an implementation of this technique, we detected a 0.5% hydrogen concentration in nitrogen at room temperature with a signal/noise ratio of approximately 100 and response and recovery times of about 5 and 15 s, respectively.

Quantitative Serum Proteomics from Surface Plasmon Resonance Imaging

The detection and quantification of specific proteins in complex mixtures is a major challenge for proteomics. For example, the development of disease-related biomarker panels will require fast and efficient methods for obtaining multiparameter protein profiles. We established a high throughput, label-free method for analyzing serum using surface plasmon resonance imaging of antibody microarrays. Microarrays were fabricated using standard pin spotting on bare gold substrates, and samples were applied for binding analysis using a camera-based surface plasmon resonance system. We validated the system by measuring the concentrations of four serum proteins using part of a 792-feature microarray. Transferrin concentrations were measured to be 2.1 mg/ml in human serum and 1.2 mg/ml in murine serum, which closely matched ELISA determinations of 2.6 and 1.2 mg/ml, respectively. In agreement with expected values, human and mouse albumin levels were measured to be 24.3 and 23.6 mg/ml, respectively. The lower limits of detection for the four measurements ranged from 14 to 58 ng/ml or 175 to 755 pm. Where purified target proteins are not available for calibration, the microarrays can be used for relative protein quantification. We used the antibody microarray to compare the serum protein profiles from three liver cancer patients and three non-liver cancer patients. Hierarchical clustering of the serum protein levels clearly distinguished two distinct profiles. Thirty-nine significant protein changes were detected (p < 0.05), 10 of which have been observed previously in serum. alpha-Fetoprotein, a known liver cancer marker, was observed to increase. These results demonstrate the feasibility of this high throughput approach for both absolute and relative protein expression profiling.

Fibre optic sensor based on long-range surface plasmon resonance: a theoretical analysis

Fibre optic sensor based on long-range surface plasmon resonance: a theoretical analysis

Temperature dependence of the sensitivity of a long-range surface plasmon optical sensor

The temperature dependence of the sensitivity of an optical sensor based on long-range surface plasmon resonance (LRSPR) is studied via theoretical modeling. Both the ‘angular interrogation’ and the ‘wavelength interrogation’ modes of operation are studied. In addition, the variation of the full width at half maximum of the LRSPR ‘reflectance dip’ is also studied as a function of temperature, which ultimately determines the temperature dependence of the sensitivity of the sensor when the reflectance is monitored at a fixed incident angle (‘reflectance interrogation’). It is found that while most of the time only the ‘reflectance interrogation’ mode leads to improved sensitivity for the LRSPR sensor compared to a conventional SPR sensor, the temperature stability of the operation of the LRSPR sensor is generally higher than (or at least comparable to) that of the SPR sensor.

Fibre optic sensor based on long-range surface plasmon resonance: a theoretical analysis

A theoretical analysis is carried out to estimate the performance of a fibre optic sensor based on long-range surface plasmon resonance (LRSPR). The performance is evaluated in terms of the sensitivity of the sensor. The results are compared with those for a conventional surface plasmon resonance (SPR) based fibre optic sensor. It is shown that a sensor based on LRSPR has a better sensitivity as compared to a conventional SPR sensor. Its drawback is the higher value of full width at half-minimum (FWHM) of the SPR spectrum.

A sensitivity comparison of optical biosensors based on four different surface plasmon resonance modes

Current surface plasmon resonance (SPR) modes based on the attenuated total reflection (ATR) method can broadly be categorized as: conventional SPR, long-range SPR (LRSPR), coupled plasmon-waveguide resonance (CPWR), and waveguide-coupled SPR (WCSPR). Although the features of optical biosensors are dependent upon their particular SPR mode, a common requirement for all biosensors utilized for biomolecular interaction analysis (BIA) is a high degree of sensitivity. The current paper presents a theoretical analysis and comparison of the sensitivity and resolution of these four types of SPR biosensors when employed in three of the most prevalent detection methods, namely angular interrogation, wavelength interrogation, and intensity measurement. This study develops a detailed understanding of the influences of various biosensor design parameters in order to enhance the sensitivity and detection limit capabilities of such devices.

Long-range surface plasmons for high-resolution surface plasmon resonance sensors

We present the application of long-range surface plasmons to a wavelength-modulated surface plasmon resonance sensor. Theoretical design parameters and experimental data are presented for two sensor designs, using either magnesium fluoride or Teflon AF-1600 as a dielectric buffer layer. The demonstrated sensitivity of the long-range surface plasmon resonance sensor in refractometric experiments is up to seven times higher than that of an equivalent conventional surface plasmon resonance (SPR) sensor, while the measured resolution is comparable. According to theoretical design calculations presented, further optimization of materials and layer thickness could reduce the resonance width while achieving even higher sensitivities, thereby creating a sensor with significantly better resolution than conventional SPR sensors.