Jiri Homola

Data analysis for optical sensors based on spectroscopy of surface plasmons

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.

Surface plasmon resonance biosensors

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.

Hybrid surface platform for the simultaneous detection of proteins and DNAs using a surface plasmon resonance imaging sensor.

In this work, we present a novel surface and assay for the simultaneous detection of DNA and protein analytes on a surface plasmon resonance (SPR) imaging sensor. A mixed DNA/oligo (ethylene glycol) (OEG) self-assembled monolayer (SAM) is created using a microarrayer. Thiol-modified single-stranded DNA sequences are spotted onto a gold-coated glass substrate. Backfilling with an OEG-modified alkanethiol creates a protein-resistant surface background. Antibodies conjugated to complementary single-stranded DNA sequences are immobilized on the surface through DNA hybridization. By converting only part of the DNA array into a protein array, simultaneous detections of DNA and protein analytes are possible. A model system of two cDNA sequences and two human pregnancy hormones are used to demonstrate the assay. No cross-reactivity was observed between DNA or protein analytes and nontargeted immobilized cDNA sequence or antibodies. A response from a detection of a single analyte in a mixture of protein and DNA analytes corresponds well with that of a single-analyte solution.

Diffraction grating-coupled surface plasmon resonance sensor based on spectroscopy of long-range and short-range surface plasmons

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).

Novel approach to surface plasmon resonance multichannel sensing

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.

Advances in development of miniature fiber optic surface plasmon resonance sensors

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.

Novel approach to multichannel SPR sensing

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.

SPR sensor based on a bi-diffractive grating

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.

Reference-compensated surface plasmon resonance biosensor for detection of foodborne pathogens

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.

Neuroinflammation and Complexes of 17β -Hydroxysteroid Dehydrogenase type 10 - Amyloid β in Alzheimer's Disease

Multifunctional mitochondrial enzyme 17β-hydroxysteroid dehydrogenase type 10 plays a role in the development of Alzheimers disease. However, changes in its expression in the brain or cerebrospinal fluid are not fully specific for this type of dementia. Our previous study revealed that complexes of the enzyme and amyloid β in cerebrospinal fluid could serve as a more specific biomarker of Alzheimers disease than either the enzyme or amyloid β individually when compared to autoimmune multiple sclerosis. In this study, enzyme-linked immunosorbent assay and the surface plasmon resonance biosensor method were used to analyse cerebrospinal fluid of patients with various neuroinflammatory diseases. Significant differences in the levels of the total enzyme, complexes, amyloid β 1-42 and total τ/phospho-τ were found in Alzheimers disease patients while differences in complexes, total amyloid β and amyloid β 1- 42 were observed in patients with neuroinflammatory diseases (except for multiple sclerosis) when compared to non-neuroinflammatory controls. The interactions of the enzyme with amyloid β appeared to depend strongly on neuroinflammation-sensitive amyloid β. Our data demonstrated that oligomerisation/aggregation of intracellular amyloid β peptides was important in Alzheimers disease while extracellular amyloid β could play a role in neuroinflammatory diseases. Phospho-τ is currently the best biomarker of Alzheimers disease.