Bo Liedberg

Surface plasmon resonance for gas detection and biosensing

Abstract Surface plasmon resonance is a new optical technique in the field of chemical sensing. Under proper conditions the reflectivity of a thin metal film is extremely sensitive to optical variations in the medium on one side of it. This is due to the fact that surface plasmons are sensitive probes of the boundary conditions. The effect can be utilized in many ways. A description of how it can be used for gas detection is given, together with results from exploratory experiments with relevance to biosensing.

Gas detection by means of surface plasmon resonance

Abstract A theoretical and experimental investigation of the possibilities of using surface plasmon resonance for gas detection is presented. The system used in the experiments was an organic layer that reversibly absorbs the anaesthetic gas halothane. The method was shown to be sensitive to variations in the optical properties of the film upon gas exposure down to the ppm range. Possible developments of the method are also discussed.

Structure of 3-aminopropyl triethoxy silane on silicon oxide

Abstract 3-Aminopropyl triethoxy silane (APTES) was deposited onto silicon oxide surfaces under various conditions of solvent, heat, and time, and then exposed to different curing environments, including air, heat, and ethanol. The macro- and micromolecular structure of APTES was probed on different levels using different techniques. The thickness of APTES layers was measured by ellipsometry, macromolecular structures were identified using microscopic methods (scanning electron microscopy and atomic force microscopy), and chemical form was investigated using angle-resolved X-ray photoelectron spectroscopy and also reflection infrared spectroscopy of APTES on gold and aluminum oxide surfaces. Coverage equivalent to one monolayer was achieved using very mild reaction and curing conditions (reaction in dry toluene for 15 min at room temperature, curing in air, or 15 min in 200°C oven), whereas thick layers were made by increasing reaction and curing times. APTES initially adsorbed to the surface, and curing was necessary to complete covalent binding between APTES and the surface. Deposition of APTES from water gave thin layers, probably electrostatically bound to silicon.

Principles of biosensing with an extended coupling matrix and surface plasmon resonance

Abstract Surface plasmon resonance is one of the surface-oriented biosensing techniques that can be used to monitor biomolecular interactions. It is utilized in instrumentation for real-time biospecific interaction analysis capable of determining not only the concentrations of biomolecules but also kinetic constants, binding specificity, etc. In this contribution biosensing with surface plasmon resonance is reviewed. Special attention is given to an extended interaction matrix on the sensing surface, which enables the covalent binding of, e.g., antigens or antibodies. The surface plasmon resonance angle shifts are calculated as a function of the amount of organic material in the matrix. The influence of physical parameters, such as matrix thickness and wavelength of the light, on the expected performance is considered. Finally, a few illustrative experimental results obtained with a recently introduced commercial instrument are given.

Bioanalysis with surface plasmon resonance

Abstract Research and development work has made surface plasmon resonance (SPR) into an accurate, sensitive and fast method with several bioanalytical applications. The first commercial instrument has also recently been introduced on the market. The present contribution reviews the use of SPR for biospecific interaction analysis and describes a recently developed SPR instrument. Special attention is paid to the use of a dextran layer on the surface of the thin metal film (gold) used for SPR. It is shown that with such a matrix on the surface, the evanescent electric field outside the metal surface is used more efficiently, which improves the analytical performance of the method. Furthermore, the matrix provides a convenient way of covalently binding biomolecules to the sensing surface, thus providing its necessary biospecificity. The chemistry of the coupling matrix is described as well as the optical and liquid-handling systems used. Finally, a few applications of the SPR instrument are demonstrated.

A high-density poly(ethylene glycol) polymer brush for immobilization on glass-type surfaces

Label-free heterogeneous phase detection critically depends on the properties of the interfacial layer. We have obtained high-density monomolecular poly(ethylene glycol) (PEG) layers by solvent-free coupling of homo-bifunctional PEGs (2,000 g/mol) at 75 degrees C to silica surfaces silanized with glycidyloxipropyltrimethoxysilane (GOPTS). Characterization by ellipsometry and contact angles revealed that PEG layers up to 3.4 ng/mm2 with low roughness and flexibility were obtained. Specific and non-specific binding at these PEG surfaces was monitored by reflectometric interference spectroscopy (RIfS). No significant non-specific adsorption upon incubation of 1 mg/ml ovalbumin was detectable (< 10 pg/mm2), and 150 pg/mm2 upon incubation of 10% calf serum, less than 10% of the amount adsorbed to the solely silanized surfaces. The terminal functional groups of the PEG layers were utilized to couple ligands and a protein. Specific protein interaction with these immobilized compounds was detected with saturation loadings in the range of protein monolayers (2-4 ng/mm2). The excellent functional properties, the high stability of the layers, the generic and practical coupling procedure and the versatility for immobilizing compounds of very different functionality make these PEG layers very attractive for application in label-free detection with silica or metal-oxide based transducers.

Protein adsorption studies on model organic surfaces : an ellipsometric and infrared spectroscopic approach

The development of accurate analytical tools to control the interfacial properties of solid substrates is of importance for the design of new biomaterials, as well as for the understanding of biomolecular interactions on surfaces. Considerable research efforts are presently devoted to this area on different levels of molecular complexity, i.e. both in the presence and in the absence of the biomolecules. In this contribution we review briefly applications of infrared reflection-absorption spectroscopy (IRAS) and ellipsometry as tools for analysis of the chemical properties of model surfaces, and their biological response in vitro when in contact with blood plasma or serum, respectively. The strength of the combination of the techniques is demonstrated by determination of protein adsorption patterns on a series of chemically well-defined so-called self-assembled alkanethiolate monolayers (SAMs) of 16-thiohexadecanol (HS-(CH2)16-OH) and n-hexadecanethiol (HS-(CH2)15-CH3) on gold. The protein adsorption patterns after incubations in plasma were determined by the specific binding of antibodies to the surfaces.

Label-free, electrochemical detection of methicillin-resistant staphylococcus aureus DNA with reduced graphene oxide-modified electrodes

Reduced graphene oxide (rGO)-modified glassy carbon electrode is used to detect the methicillin-resistant Staphylococcus aureus (MRSA) DNA by using electrochemical impedance spectroscopy. Our experiments confirm that ssDNA, before and after hybridization with target DNA, are successfully anchored on the rGO surface. After the probe DNA, pre-adsorbed on rGO electrode, hybridizes with target DNA, the measured impedance increases dramatically. It provides a new method to detect DNA with high sensitivity (10(-13)M, i.e., 100 fM) and selectivity.

Imaging surface plasmon resonance sensor based on multiple wavelengths: Sensitivity considerations

A new, multiple wavelength surface plasmon resonance apparatus for imaging applications is presented. It can be used for biosensing, e.g., for monitoring of chemical and biological reactions in real time with label-free molecules. A setup with a fixed incident angle in the Kretschmann configuration with gold as the supporting metal is described, both theoretically and experimentally. Simulations of the sensor response based on independently recorded optical (ellipsometric) data of gold show that the sensitivity for three-dimensional recognition layers (bulk) increases with increasing wavelength. For two-dimensional recognition layers (adlayer) maximum sensitivity is obtained within a limited wavelength range. In this situation, the rejection of bulk disturbances, e.g., emanating from temperature variations, decreases, with increasing wavelength. For imaging surface plasmon resonance the spatial resolution decreases with increasing wavelength. Hence, there is always a compromise between spatial resolution, bulk disturbance rejection, and sensitivity. Most importantly, by simultaneously using multiple wavelengths, it is possible to maintain a high sensitivity and accuracy over a large dynamic range. Furthermore, our simulations show that the sensitivity is independent of the refractive index of the prism

The interaction between ammonia and poly(pyrrole)

Abstract Reversible and irreversible interactions between ammonia and poly-(pyrrole) have been studied using electrical conductivity measurements, optical spectroscopy, Fourier transform infrared spectroscopy (FT i.r.), X-ray photoelectron spectroscopy (XPS) and elemental analysis. The results show that in addition to the previously reported reversible change of the electronic properties of poly(pyrrole) upon treatment with ammonia, there is also a large irreversible change if the material is exposed to high concentrations of ammonia or ammonia plus water vapour for a long period of time. The measurements also indicate that amide-type carbonyl groups, amine groups and ammonium ions could be present in the irreversibly changed polymer. The results are used as a basis for a discussion on the interaction between conducting polymers and ammonia in general and between poly-(pyrrole) and ammonia in particular.