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This paper reviews fundamentals of optical affinity biosensors based on plasmonic nanostructures and discusses recent advances in the development of this technology, including plasmonic nanostructures and surface plasmon phenomena, advances in sensor instrumentation, and functional coatings. Examples of applications for both the detection of chemical and biological substances as well as the investigation of biomolecular interactions are also given.

We have examined the noise sources for a surface plasmon resonance (SPR) sensor system to facilitate optimization of SPR sensor instrumentation and data-processing methods for high-resolution SPR sensing. We found detector shot noise to be the dominant source of noise in the SPR sensor, and investigated the propagation of noise through a commonly used SPR sensor data-processing algorithm. Deriving an expression relating the detector noise level to the noise of the output data, we used measurements of the magnitude and distribution of both charge-coupled device and photodiode array detector noise to predict the noise levels observed in the sensor output. We used this method to optimize the parameters of the algorithm and introduced a modified algorithm with enhanced resistance to correlated light level noise. In addition, we evaluated the noise performance of alternative SPR sensor designs, including a sensor with no polarization optics and another with optics producing an inverted SPR absorption feature. Experimental SPR sensor data demonstrated good agreement with predicted noise levels.

We report a system, which combines electrochemical and surface plasmon resonance (SPR) techniques on the same sensing chip. Each channel of a four-channel laboratory SPR sensor is supplemented with two planar gold electrodes (the reference and the counter electrodes), whereas the gold layer of SPR chip is used as the working electrode. A custom electronics enables to set an arbitrary potential between the reference and working electrodes and to measure the current flow between the counter and the working electrodes. Information from standard electrochemical techniques, i.e. cyclovoltammetry and chronoamperometry can be acquired with the system while simultaneously monitoring the shift in the surface plasmon resonance. The electrochemical SPR biosensor was used to study desorption of thiolated DNA probes with a negative potential. By comparing the acquired electrochemical and SPR signals, we show that DNA probes as well as a monolayer of alkanethiols can be desorbed by applying negative potentials to the SPR chip surface. Moreover, it is shown that the DNA probes can be reabsorbed on the SPR sensor surface and the complementary DNA can be detected without loss in detection sensitivity.

A finite element method based on the full-vectorial H-field formulation has been employed to achieve the maximum field penetration in the sensing medium of the slot-waveguide-based ring resonator biosensor. The use of nanometer scale guiding structure where optical mode is confined in a low-index region permits a very compact sensor with high optical intensity in the region, which makes it possible to detect minimum refractive index change, and offers higher sensitivities. We analyze the change in effective refractive index of mode, sensitivity, and power confinement of the proposed slot-waveguide-based ring resonator biosensor for the detection of DNA hybridization. The biosensor exhibited theoretical sensitivity of 856 nm per refractive index unit (RIU) and a detection limit of 1.43×10(-6) RIU.

Here we present a theoretical study of the sensing capability of a biosensor based on localized surface plasmons (LSP). The sensing structure consists of an array of gold cylinders which support coupling of LSP with Rayleigh anomalies, resulting in a narrow line spectrum. We utilize numerical simulations pertaining to both the photonic and masstransfer aspects of this sensor, where the sensor performance as a function of various fabrication parameters is investigated and compared with a conventional surface plasmon resonance sensor. The simulations predict an improvement in the limit of detection (LOD) of such a device.

Optical affinity biosensors are devices that incorporate a biomolecular recognition element (e.g. antibody) which specifically recognizes a particular analyte and an optical transduction system which allows quantification of the interaction between the analyte and the biomolecular recognition element. In the last decade we have witnessed development of numerous optical transduction methods, including both label-based methods such as fluorescence spectroscopy and label-free methods such as optical interferometry, spectroscopy of guided modes of optical waveguides, and surface plasmon resonance. Label-free optical biosensors present unique technology that enables direct observation of molecular interaction in real-time and offer benefits of rapid, sensitive and label-free detection of chemical and biological species with potential applications in numerous important areas including proteomics, medical diagnostics, environmental monitoring, food analysis, agriculture, and security.

This contribution reviews the present state of the art in the development of surface plasmon resonance (SPR) (bio)sensor technology, discusses emerging trends, and presents recent results of research into SPR biosensors at the Institute of Photonics and Electronics, Prague. The developments discussed in detail include a high-performance SPR sensor for parallelized observation of biomolecular interactions, a miniature fiber optic SPR sensor for localized measurements, and sensing based on localized surface plasmons on gold nanoparticles.

We report a SPR biosensor based on long-range (LR) and short-range (SR) surface plasmon (SP) modes excited simultaneously on a diffraction grating. Employing the LRSP and SRSP in the grating-coupled SPR sensor offers several interesting features such as extended probe depth of the LRSP and ability to distinguish sensor response caused by bulk and surface refractive index changes. Prototype device based on wavelength interrogation of SPs was developed and be tested in model refractometric experiment. This paper presents results of theoretical analysis and experimental characterization of the sensor. Sensitivity of the laboratory prototype of the sensor agrees well with the theory. The sensor is shown to be able to detect changes in the refractive index as small as 3.5 x 10-6 RIU (refractive index unit).

We report a surface plasmon resonance (SPR) sensor based on two-plasmon-spectroscopy on a special bi-diffractive grating and investigate its ability to distinguish contributions to sensor response due to surface refractive index changes (i.e. binding) and due to refractive index changes in the whole sample. Theoretical analysis yielding an estimate of an error of such decomposition is presented and used to compare performance of this sensor to that of an alternative approach based on simultaneous excitation of short-range and long-range surface plasmons on a thin metallic layer.

The simultaneous detection of multiple analytes is an important consideration for the advancement of biosensor technology. Currently, few sensor systems possess the capability to accurately and precisely detect multiple antigens. This work presents a simple approach for the functionalization of sensor surfaces suitable for multichannel detection. This approach utilizes self-assembled monolayer (SAM) chemistry to create a nonfouling, functional sensor platform based on biotinylated single-stranded DNA immobilized via a streptavidin bridge to a mixed SAM of biotinylated alkanethiol and oligo(ethylene glycol). Nonspecific binding is minimized with the nonfouling background of the sensor surface. A usable protein chip is generated by applying protein-DNA conjugates which are directed to specific sites on the sensor chip surface by utilizing the specificity of DNA hybridization. The described platform is demonstrated in a custom-built surface plasmon resonance biosensor. The detection capabilities of a sensor using this protein array have been characterized using human chorionic gonadotropin (hCG). The platform shows a higher sensitivity in detection of hCG than that observed using biotinylated antibodies. Results also show excellent specificity in protein immobilization to the proper locations in the array. The vast number of possible DNA sequences combine with the selectivity of base-pairing makes this platform an excellent candidate for a sensor capable of multichannel protein detection.

We present an optical sensor based on excitation of surface plasma waves in optical fiber structure consisting of a side-polished single-mode polarization-maintaining fiber and a metal overlayer. We describe two modes of operation of the sensor in which variations in the refractive index of the sample are determined by measuring changes in the transmitted optical power at a fixed wavelength (amplitude mode) and by measuring changes in the wavelength at which the resonant attenuation of the fiber mode occurs (spectral mode). We demonstrate that this design allows suppressing sensitivity of the sensor to deformation of the fiber yielding an improved stability and resolution.

We present a novel surface plasmon resonance (SPR) sensor based on serial organization of sensing channels and sequential spectral encoding of responses from sensing channels into an optical spectrum. This approach allows probing interfacial processes by surface plasmons of different field profiles which makes it possible to distinguish surface and bulk contributions to SPR sensor response. We illustrate this unique feature of the presented approach in a model biosensing experiment in which the detection of human chorigonadotropin (hCG) is compensated for background refractive index interference.

A novel approach to multichannel SPR sensing based on encoding information from separate sensing channels into a single optical spectrum is presented. A dual channel SPR sensor using this approach is demonstrated. Attention is given to exploitation of the dual-channel SPR sensor for compensation for background interference and non-specific adsorption of the biomolecules to the surface of the SPR biosensor. Experimental results indicate that background refractive index changes were compensated with accuracy better than 8 X 10-5 RIU (refractive index unit); the effect of a temperature change of 3.6 K was reduced by a factor of 13 by the dual-channel sensor. SPR biosensor-based detection of monoclonal anti-dinitrophenyl antibody (a-DNP) with compensation for non-specific adsorption is demonstrated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical waveguide surface plasmon resonance (SPR) sensors are presented which exploit the phenomenon of the resonant excitation of surface plasmon waves by guided modes of optical fibers and integrated optical waveguides. Theoretical analysis of the SPR waveguide sensing structures is based on the mode expansion and propagation method. The integrated optical waveguide SPR sensor is composed of an optical waveguide fabricated by the K + --Na + ion exchange in a glass substrate and gold as a surface plasmon resonance overlayer. The optical fiber SPR sensor is realized on a side-polished single-mode optical fiber which is locally coated with a thin gold film. Experimental study of the realized samples of the sensors has shown that variations in the refractive index of the sensed medium below 5X10 -5 can be resolved with the sensors.

The exploitation of surface plasmon resonance (SPR) sensing principle for the study of formation of multilayers of human immunoglobulin (hlgG) and monoclonal antibody against human choriogonadotropin (a-hCG) as well as for monitoring immunoreaction between the immobilized a-hCG and human choriogonadotropin (hCG) is reported. It is demonstrated that even a very small attachment of proteins (due to the adsorption or the specific interaction) may be detected by the presented SPR sensor. An immobilization technique is described which allows to form stable multilayers of antibodies on the gold surface.

A novel dual-channel surface plasmon resonance sensor is described which uses a high refractive index overlayer to spectrally separate sensing channels, allowing for their simultaneous interrogation using a single spectrograph. A theoretical analysis of the sensor is presented as well as experimental results demonstrating its capability as a biosensor.

We present a novel surface plasmon resonance (SPR) biosensor for detection of human interferon gamma (hIFNγ), an important diagnostic marker for several infectious diseases. The biosensor employs engineered proteins derived from albumin binding domain (ABD) and selected with ribosome display to provide high affinity towards hIFNγ. We demonstrate that the biosensor provides rapid, sensitive, and cost-effective platform for the detection of hIFNγ and allows its detection at nanomolar levels both in buffer and diluted human plasma.

We present a dual-channel surface plasmon resonance (SPR) biosensor and demonstrate its applicability to detection of foodborne pathogens such as Staphylococcal enterotoxin B (SEB). Experimental results indicate that the SPR biosensor can detect SEB at very low concentrations: 5 ng/ml in pure samples directly, 0.5 ng/ml in both pure samples and in milk using a sandwich assay.

We report a new optical sensor based on excitation of a surface plasmon in an optical fiber Bragg grating (FBG) structure. The sensing device consists of a side-polished single-mode optical fiber with a Bragg grating written into a fiber core and a thin gold overlayer supporting SP. If a coupling between a guided mode of the optical fiber and a SP mode is established, any change in the refractive index of analyte affects propagation constant of the fiber mode producing a change in the amount of light reflected by the FBG. A laboratory prototype of the sensor has been developed and its potential for refractometry has been examined. It has been demonstrated that the sensor's sensitivity to refractive index is as high as 750 dB/RIU.

Laser beam profiling technology in the UV spectrum of light is evolving with the increase of excimer lasers and lamps applications, that span from lithography for VLSI circuits to eye surgery. The development of a beam-profiler, able to capture the excimer laser single pulse and process the acquired pixel current signals in the time period between each pulse, is mandatory for such applications. 1D and 2D array detectors have been realized on polycrystalline CVD diamond specimens. The fast diamond photoresponse, in the ns time regime, suggests the suitability of such devices for fine tuning feedback of high-power pulsed-laser cavities, whereas solar-blindness guarantees high performance in UV beam diagnostics, also under high intensity background illumination. Offering unique properties in terms of thermal conductivity and visible-light transparency, diamond represents one of the most suitable candidate for the detection of high-power UV laser emission. The relatively high resistivity of diamond in the dark has allowed the fabrication of photoconductive vertical pixel-detectors. A semitransparent light-receiving back-side contact has been used for detector biasing. Each pixel signal has been conditioned by a multi-channel read-out electronics made up of a high-sensitive integrator and a Σ-Δ A/D converter. The 500 μs conversion time has allowed a data acquisition rate up to 2 kSPS (Sample Per Second).

Diatoms are monocellular micro-algae provided with external valves, the frustules, made of amorphous hydrated silica. Frustules present patterns of regular arrays of holes, the areolae, characterized by sub-micrometric dimensions. Frustules from centric diatoms are characterized by a radial disposition of areolae and exhibit several optical properties, such as photoluminescence, lens-like behavior and, in general, photonic-crystal-like behavior as long as confinement of electromagnetic field is concerned. In particular, intrinsic photoluminescence from frustules is strongly influenced by the surrounding atmosphere: on exposure to gases, the induced luminescence changes both in the optical intensity and peaks positions. To give specificity against a target analyte, a key feature for an optical sensor, a biomolecular probe, which naturally recognizes its ligand, can be covalently linked to the diatom surface. We explored the photoluminescence emission properties of frustules of Coscinodiscus wailesii centric species, characterized by a diameter of about 100-200 μm, on exposure to different vapours and in presence of specific bioprobes interacting with target analytes. Very high sensitivities have been observed due to the characteristic morphology of diatoms shells. Particular attention has been devoted to the emission properties of single frustules. Diatoms are monocellular micro-algae provided with external valves, the frustules, made of amorphous hydrated silica. Frustules present patterns of regular arrays of holes, the areolae, characterized by sub-micrometric dimensions. Frustules from centric diatoms are characterized by a radial disposition of areolae and exhibit several optical properties, such as photoluminescence, lens-like behavior and, in general, photonic-crystal-like behavior as long as confinement of electromagnetic field is concerned. In particular, intrinsic photoluminescence from frustules is strongly influenced by the surrounding atmosphere: on exposure to gases, the induced luminescence changes both in the optical intensity and peaks positions. To give specificity against a target analyte, a key feature for an optical sensor, a biomolecular probe, which naturally recognizes its ligand, can be covalently linked to the diatom surface.We explored the photoluminescence emission properties of frustules of Coscinodiscus wailesii centric species, characterized by a diameter of about 100-200 mu m, on exposure to different vapours and in presence of specific bioprobes interacting with target analytes. Very high sensitivities have been observed due to the characteristic morphology of diatoms shells. Particular attention has been devoted to the emission properties of single frustules.