Jiří Homola

Surface plasmon resonance sensors based on diffraction gratings and prism couplers: sensitivity comparison

Abstract Theoretical analysis and comparison of the sensitivity of surface plasmon resonance (SPR) sensors using diffraction at gratings and attenuated total reflection (ATR) in prism couplers for two detection methods-resonant angle interrogation and resonant wavelength interrogation is presented. Analytical expressions for sensitivity of these SPR sensors are derived and the influence of the major design parameters of the sensing structures on the sensor sensitivity is discussed. The analysis shows that grating-based SPR sensors using wavelength interrogation are much less sensitive then their prism coupler-based counterparts. In the angular interrogation mode, the sensitivity of SPR sensors using diffraction gratings depends on the diffraction order and does not differ much from that of SPR sensors based on prism couplers.

Surface plasmon resonance (SPR) sensors: approaching their limits?

We report on a unified theoretical model of the resolution of SPR sensors which makes it possible to predict the ultimate performance of all major configurations of SPR sensors. The theory indicates that the performance of SPR sensors is independent of the method of excitation of surface plasmons (prism or grating coupling) or the method of modulation (amplitude, angular or wavelength) and depends dominantly on the noise properties of the light source and detector. Results of the theoretical analysis are compared with the performance reported for several SPR sensors to illustrate that the best state-of-art SPR sensors are approaching their theoretical limits. Possibilities for further advances in the performance of SPR sensor technology are discussed.

Ultralow fouling and functionalizable surface chemistry based on a zwitterionic polymer enabling sensitive and specific protein detection in undiluted blood plasma.

A crucial step in the development of implanted medical devices, in vivo diagnostics, and microarrays is the effective prevention of nonspecific protein adsorption from real-world complex media such as blood plasma or serum. In this work, a zwitterionic poly(carboxybetaine acrylamide) (polyCBAA) biomimetic material was employed to create a unique biorecognition coating with an ultralow fouling background, enabling the sensitive and specific detection of proteins in blood plasma. Conditions for surface activation, protein immobilization, and surface deactivation of the carboxylate groups in the polyCBAA coating were determined. An antibody-functionalized polyCBAA surface platform was used to detect a target protein in blood plasma using a sensitive surface plasmon resonance (SPR) sensor. A selective protein was directly detected from 100% human blood plasma with extraordinary specificity and sensitivity. The total nonspecific protein adsorption on the functionalized polyCBAA surface was very low (<3 ng/cm (2) for undiluted blood plasma). Because of the significant reduction of nonspecific protein adsorption, it was possible to monitor the kinetics of antigen-antibody interactions in undiluted blood plasma. The functionalization effectiveness and detection characteristics using a cancer protein marker candidate of polyCBAA were compared with those of the conventional nonfouling oligo(ethylene glycol)-based surface chemistry.

On the sensitivity of surface plasmon resonance sensors with spectral interrogation

Abstract Theoretical analysis of the sensitivity of surface plasmon resonance (SPR) sensors with spectral interrogation is presented. Two basic configurations of SPR sensors with spectral interrogation are investigated—for the measurement of variations in the refractive index of bulk media, and for the monitoring of variations in the thickness of thin films. In both cases, analytical expressions allowing the sensitivity of SPR sensors to be calculated are derived and validated. On the basis of the theoretical analysis, the optimization of a spectral SPR sensor in terms of the operation wavelength and the choice of metal layer is carried out. It is demonstrated that spectral SPR sensors may attain higher sensitivity if operating at longer wavelengths and if using metal layers with a higher modulus of the real part of the dielectric constant.

Spectral surface plasmon resonance biosensor for detection of staphylococcal enterotoxin B in milk

This work evaluates a newly developed wavelength modulation-based SPR biosensor for the detection of staphylococcal enterotoxin B (SEB) in milk. Two modes of operation of the SPR biosensor are described: direct detection of SEB and sandwich assay. In the sandwich assay detection mode, secondary antibodies are bound to the already captured toxin to amplify sensor response. Samples including SEB in buffer and SEB in milk were analyzed in this work. The SPR biosensor has been shown to be capable of directly detecting concentrations of SEB in buffer as low as 5 ng/ml. In sandwich detection mode, the lowest detection limit was determined to be 0.5 ng/ml for both buffer and milk samples. The reported wavelength modulation-based SPR sensor provides a generic platform which can be tailored for detection of various foodborne pathogens and agents for food analysis and testing.

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

Abstract 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.

Novel spectral fiber optic sensor based on surface plasmon resonance

Abstract A novel fiber optic surface plasmon resonance (SPR) sensing device based on spectral interrogation of SPR in a miniature fiber optic sensing element using depolarized light is reported. Optimization analysis of the sensor based on the equivalent planar waveguide approach and the mode expansion and propagation method is presented. A laboratory prototype of the sensor has been proved to be able to measure refractive index variations as small as 5×10−7. Suitability of the sensor for biosensing has been demonstrated by detecting IgG via respective monoclonal antibodies immobilized on the SPR sensor surface.

Surface plasmon resonance sensor based on a single-mode polarization-maintaining optical fiber

Abstract A novel wavelength modulation-based fiber-optic surface plasmon resonance (SPR) sensor is reported which utilizes both polarization separation and broad band radiation depolarization in polarization-maintaining fibers to enhance sensor stability. Theoretical analysis of the sensing structure with ideally separated polarizations based on the mode of expansion and propagation method is presented. The effect of polarization cross-coupling was also analyzed in the approximation of an equivalent bulk optic structure. A laboratory prototype of the fiber-optic SPR sensor was characterized in terms of sensitivity and resolution. Experimental results indicate that this fiber-optic SPR sensor is able to resolve refractive index changes as low as 4×10−6 under moderate fiber deformations.

Optical fiber sensor based on surface plasmon excitation

A very sensitive sensor structure for measurement of small changes of the refractive index employing the interaction between the surface plasmon and the guided mode of a single-mode optical fiber is reported. The theoretical treatment of the proposed sensor structure based on planar waveguide approximation is presented. The analysis of the influence of the main parameters of the sensor structure on the sensor performance is carried out with the aim of finding an optimum strategy for designing optical sensors with high sensitivity. The possibility of connecting the sensor to a broadband light source is also discussed.

A miniature fiber optic surface plasmon resonance sensor for fast detection of Staphylococcal enterotoxin B.

A fiber optic surface plasmon resonance (SPR) biosensor for detection of Staphylococcal enterotoxin B (SEB) is reported. The sensor is based on spectral interrogation of surface plasmons in a miniature sensing element based on a side-polished single-mode optical fiber with a thin metal overlayer. For specific detection of SEB, the SPR sensor is functionalized with a covalently crosslinked double-layer of antibodies against SEB. The SPR biosensor is demonstrated to be able to detect ng/ml concentrations of SEB in less than 10 min.