Jakub Dostalek

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.

Plasmon-Enhanced Fluorescence Biosensors: a Review

Surfaces of metallic films and metallic nanoparticles can strongly confine electromagnetic field through its coupling to propagating or localized surface plasmons. This interaction is associated with large enhancement of the field intensity and local optical density of states which provides means to increase excitation rate, raise quantum yield, and control far field angular distribution of fluorescence light emitted by organic dyes and quantum dots. Such emitters are commonly used as labels in assays for detection of chemical and biological species. Their interaction with surface plasmons allows amplifying fluorescence signal (brightness) that accompanies molecular binding events by several orders of magnitude. In conjunction with interfacial architectures for the specific capture of target analyte on a metallic surface, plasmon-enhanced fluorescence (PEF) that is also referred to as metal-enhanced fluorescence (MEF) represents an attractive method for shortening detection times and increasing sensitivity of various fluorescence-based analytical technologies. This review provides an introduction to fundamentals of PEF, illustrates current developments in design of metallic nanostructures for efficient fluorescence signal amplification that utilizes propagating and localized surface plasmons, and summarizes current implementations to biosensors for detection of trace amounts of biomarkers, toxins, and pathogens that are relevant to medical diagnostics and food control.

A novel multichannel surface plasmon resonance biosensor

Abstract We report a novel multichannel surface plasmon resonance (SPR) sensor based on the combination of parallel sensing channel architecture and the method of spectral discrimination of sensing channels. This sensor configuration provides multichannel performance and, through probing surface processes (e.g. binding of immobilized antibody and antigen in solution) with surface plasmons with different field distributions, it allows distinguishing sensor response to surface and bulk effects, enabling more accurate quantification of biomolecular interaction events. The potential of this mixed-architecture sensor is illustrated in a model biosensing experiment in which the detection of monoclonal anti-dinitrophenyl antibody (a-DNP) is compensated for non-specific adsorption and background refractive index interferences.

Long-Range Surface Plasmon-Enhanced Fluorescence Spectroscopy Biosensor for Ultrasensitive Detection of E. coli O157:H7

A new biosensor platform for the detection of bacterial pathogens based on long-range surface plasmon-enhanced fluorescence spectroscopy (LRSP-FS) is presented. The resonant excitation of LRSP modes provides an enhanced intensity of the electromagnetic field, which is directly translated to an increased strength of fluorescence signal measured upon the capture of target analyte at the sensor surface. LRSPs originate from a coupling of surface plasmons across a thin metallic film embedded in dielectrics with similar refractive indices. With respect to regular surface plasmon-enhanced fluorescence spectroscopy, the excitation of LRSPs offers the advantage of a larger enhancement of the evanescent field intensity and a micrometer probing depth that is comparable to the size of target bacterial pathogens. The potential of the developed sensor platform is demonstrated in an experiment in which the detection of E. coli O157:H7 was carried out using sandwich immunoassays. The limit of detection below 10 cfu mL(-1) and detection time of 40 min were achieved.

Prostate Specific Antigen Biosensor Based on Long Range Surface Plasmon-Enhanced Fluorescence Spectroscopy and Dextran Hydrogel Binding Matrix

A new biosensor based on surface plasmon-enhanced fluorescence spectroscopy (SPFS), which employs long-range surface plasmons (LRSP) and a photo-cross-linkable carboxymethyl dextran (PCDM) hydrogel binding matrix, is reported. LRSPs are surface plasmon modes that propagate along a thin metallic film with orders of magnitude lower damping compared to regular surface plasmons. Therefore, their excitation provides strong enhancement of the intensity of the electromagnetic field and a greatly increased fluorescence signal measured upon binding of fluorophore-labeled molecules on the sensor surface. In addition, these modes exhibit highly extended evanescent fields penetrating up to micrometers in distance from the metallic sensor surface. Therefore, a PCDM hydrogel with approximately micrometer thickness was anchored on the sensor surface to serve as the binding matrix. We show that this approach provides large binding capacity and allows for the ultrasensitive detection. In a model experiment, the developed biosensor platform was applied for the detection of free prostate specific antigen (f-PSA) in buffer and human serum by using a sandwich immunoassay. The limit of detection at the low femtomolar range was achieved, which is approximately 4 orders of magnitude lower than that for direct detection of f-PSA based on the monitoring of binding-induced refractive index changes.

Bacterial Pathogen Surface Plasmon Resonance Biosensor Advanced by Long Range Surface Plasmons and Magnetic Nanoparticle Assays

A new approach to surface plasmon resonance (SPR) biosensors for rapid and highly sensitive detection of bacterial pathogens is reported. It is based on the spectroscopy of grating-coupled long-range surface plasmons (LRSPs) combined with magnetic nanoparticle (MNP) assay. The interrogation of LRSPs allows increasing the biosensor figure of merit (FOM), and the employment of MNPs further enhances the sensor response by a fast delivery of the analyte to the sensor surface and through the amplified refractive index changes associated with the capture of target analyte. This amplification strategy is particularly attractive for detection of large analytes that diffuse slowly from the analyzed sample to the sensor surface. The potential of the presented approach is demonstrated in a model experiment in which Escherichia coli O157:H7 was detected at concentrations as low as 50 cfu mL(-1), 4 orders of magnitude better than the limit of detection achieved by regular grating-coupled SPR with direct detection format.

Thin Hydrogel Films for Optical Biosensor Applications

Hydrogel materials consisting of water-swollen polymer networks exhibit a large number of specific properties highly attractive for a variety of optical biosensor applications. This properties profile embraces the aqueous swelling medium as the basis of biocompatibility, non-fouling behavior, and being not cell toxic, while providing high optical quality and transparency. The present review focuses on some of the most interesting aspects of surface-attached hydrogel films as active binding matrices in optical biosensors based on surface plasmon resonance and optical waveguide mode spectroscopy. In particular, the chemical nature, specific properties, and applications of such hydrogel surface architectures for highly sensitive affinity biosensors based on evanescent wave optics are discussed. The specific class of responsive hydrogel systems, which can change their physical state in response to externally applied stimuli, have found large interest as sophisticated materials that provide a complex behavior to hydrogel-based sensing devices.

Biosensors based on surface plasmon-enhanced fluorescence spectroscopy (Review)

The implementation of surface plasmon-enhanced fluorescence spectroscopy (SPFS) to surface plasmon resonance (SPR) biosensors enables increasing their sensitivity by several orders of magnitude. In SPR-based biosensors, surface plasmons probe the binding of target molecules contained in a liquid sample by their affinity partners attached to a metallic sensor surface. SPR biosensors relying on the detection of refractive index changes allow for direct observation of the binding of large and medium size molecules that produces sufficiently large refractive index changes. In SPR biosensors exploiting SPFS, the capture of fluorophore-labeled molecules to the sensor surface is observed by the detection of fluorescence light emitted from the surface. This technique takes advantage of the enhanced intensity of electromagnetic field accompanied with the resonant excitation of surface plasmons. The interaction with surface plasmons can greatly increase the measured fluorescence signal through enhancing the excitation rate of fluorophores and by more efficient collecting of fluorescence light. SPFS-based biosensors were shown to enable the analysis of samples with extremely low analyte concentrations and the detection of small molecules. In this review, we describe the fundamental principles, implementations, and current state of the art applications of SPFS biosensors. This review focuses on SPFS-based biosensors employing the excitation of surface plasmons on continuous metal-dielectric interfaces.

Long range surface plasmon-enhanced fluorescence spectroscopy for the detection of aflatoxin M1 in milk

A novel biosensor for the highly sensitive detection of aflatoxin M(1) (AFM(1)) in milk was developed. This biosensor is based on surface plasmon-enhanced fluorescence spectroscopy (SPFS) which was advanced through the excitation of long range surface plasmons (LRSPs). In SPFS, the binding of fluorophore-labeled molecules to the sensor surface is probed with surface plasmons (SPs) and the emitted fluorescence light is detected. This approach takes advantages of the enhanced intensity of electromagnetic field occurring upon the resonant excitation of SPs which directly increases the fluorescence signal. For the detection of AFM(1), LRSP-enhanced fluorescence spectroscopy was combined with an inhibition immunoassay in which a derivative of AFM(1) was immobilized on the sensor surface and antibodies against AFM(1) were used as recognition elements. The developed biosensor allowed for the detection of AFM(1) in milk within 53min at concentrations as low as 0.6pgmL(-1). The achieved limit of detection was about two orders of magnitude lower than the maximum AFM(1) residue level in milk stipulated by the European Commission legislation.

Biosensor based on hydrogel optical waveguide spectroscopy

A novel label-free biosensor based on the measurement of binding-induced refractive index changes by hydrogel optical waveguide spectroscopy (HOWS) is reported. This biosensor is implemented by using a surface plasmon resonance (SPR) optical setup in which a carboxylated poly(N-isoproprylacrylamide) (PNIPAAm) hydrogel film is attached on a metallic surface and modified by protein catcher molecules through amine coupling chemistry. The swollen hydrogel with micrometer thickness serves both as a binding matrix and optical waveguide. We show that compared to regular SPR biosensor with thiol self-assembled monolayer (SAM), HOWS provides an order of magnitude improved resolution in the refractive index measurements and enlarged binding capacity owing to its low damping and large swelling ratio, respectively. A model immunoassay experiment revealed that HOWS allowed detection of IgG molecules (molecular weight 150 kDa) with a 10 pM limit of detection that was 5-fold lower than that achieved for SPR with thiol SAM. For the high capacity hydrogel matrix, the affinity binding was mass transport limited. Therefore, we envisage that HOWS will provide further improved detection limit for low molecular weight analytes or for assays employing lower affinity catcher molecules.