Inger Vikholm-Lundin

Electrolyte‐Gated Organic Field‐Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer

Anchored, biotinylated phospholipids forming the capturing layers in an electrolyte-gated organic field-effect transistor (EGOFET) allow label-free electronic specific detection at a concentration level of 10 nM in a high ionic strength solution. The sensing mechanism is based on a clear capacitive effect across the PL layers involving the charges of the target molecules.

Detection beyond Debye's length with an electrolyte-gated organic field-effect transistor.

Electrolyte-gated organic field-effect transistors are successfully used as biosensors to detect binding events occurring at distances from the transistor electronic channel that are much larger than the Debye length in highly concentrated solutions. The sensing mechanism is mainly capacitive and is due to the formation of Donnans equilibria within the protein layer, leading to an extra capacitance (CDON) in series to the gating system.

CMOS-Integrated Film Bulk Acoustic Resonators for Label-Free Biosensing

The throughput is an important parameter for label-free biosensors. Acoustic resonators like the quartz crystal microbalance have a low throughput because the number of sensors which can be used at the same time is limited. Here we present an array of 64 CMOS-integrated film bulk acoustic resonators. We compare the performance with surface plasmon resonance and the quartz crystal microbalance and demonstrate the performance of the sensor for multiplexed detection of DNA.

3D-Printable Bioactivated Nanocellulose–Alginate Hydrogels

We describe herein a nanocellulose-alginate hydrogel suitable for 3D printing. The composition of the hydrogel was optimized based on material characterization methods and 3D printing experiments, and its behavior during the printing process was studied using computational fluid dynamics simulations. The hydrogel was biofunctionalized by the covalent coupling of an enhanced avidin protein to the cellulose nanofibrils. Ionic cross-linking of the hydrogel using calcium ions improved the performance of the material. The resulting hydrogel is suitable for 3D printing, its mechanical properties indicate good tissue compatibility, and the hydrogel absorbs water in moist conditions, suggesting potential in applications such as wound dressings. The biofunctionalization potential was shown by attaching a biotinylated fluorescent protein and a biotinylated fluorescent small molecule via avidin and monitoring the material using confocal microscopy. The 3D-printable bioactivated nanocellulose-alginate hydrogel offers a platform for the development of biomedical devices, wearable sensors, and drug-releasing materials.

Structural and functional characteristics of chimeric avidins physically adsorbed onto functionalized polythiophene thin films.

Stabilized bioreceptor layers are of great importance in the design of novel biosensors. In earlier work, chimeric avidins enabled immobilization of biotinylated antibodies onto gold surfaces with greater stability compared to more conventional avidins (wild-type avidin and streptavidin). In the present study, the applicability of chimeric avidins as a general binding scaffold for biotinylated antibodies on spin-coated functionalized polythiophene thin films has been studied by surface plasmon resonance and atomic force microscopy. Novel chimeric avidins showed remarkably increased binding characteristics compared with other avidins, such as wild-type avidin, streptavidin, and bacterial avidin when merely physically adsorbed onto the polythiophene surface. They gave the highest binding capacities, the highest affinity constant, and the highest stability for biotinylated probe immobilization. Introduction of carboxylic acid groups to polythiophene layer further enhanced the binding level of the avidins. Polythiophene layers functionalized with chimeric avidins thus offered a promising generic platform for biosensor applications.

Improved functionality of antibody-colloidal gold conjugates with the aid of lipoamide-grafted N-[tris(hydroxymethyl)methyl]acrylamide polymers

Colloidal gold has been used as a label in sandwich assays for human IgG, in which intercalating N-[tris(hydroxymethyl)methyl]acrylamide (pTHMMAA) polymers have been employed to stabilise the particles coated with antibody fragments. A direct absorbance reading of the particles could be obtained from sandwich assays on polystyrene, and a strongly amplified response was observed in similar assays based on Surface Plasmon Resonance (SPR): for h-IgG, detection limits below 100 pg/mL could be achieved. Three different polymer lengths and two different particles sizes were compared in sandwich assays performed on polystyrene and gold. The resulting binding curves fitted well to the Langmuir-Freundlich isotherm and the binding constants were in good agreement with the values found in earlier studies. The amplification afforded by the nanoparticles was strongly dependent on the antigen concentration, on the type of polymer and on the particle size. Compared to the direct response of the antigen, amplification factors larger than 100 could be achieved. The study proves that the polymers give stabilised particles, which can be used in highly sensitive sandwich assays.

Surface Plasmon Resonance on Nanoscale Organic Films

Over the past 20 years, surface plasmon resonance (SPR) has evolved into a very versatile detection method, particularly in bioscience applications. Not only the scientific literature has greatly expanded, but also the various commercial vendors of instrumentation, detection chips, and reagents have emerged. In the scientific sphere, the accent lies more and more on fabrication of nanostructures with interesting optical behavior (plasmonics), while in the R&D area, there are many new miniaturization efforts and combination with other detection methods, such as electrochemistry and quartz crystal microbalance (QCM). The present chapter will focus on the latest developments in making functional biochemical coatings for SPR detection as well as will review the basic theory behind the detection techniques.

An antibody surface for selective neuronal cell attachment

An optimal surface for culturing human embryonic stem cell (hESC)-derived neuronal cells is of high interest. In this study, a specific antibody to a neural cell adhesion molecule (NCAM) was immobilised on a solid surface of polystyrene and used as a selective matrix for culturing of hESC-derived neuronal cells. Thereafter, hESC-derived neurospheres were seeded on the matrix. The neurospheres did not attach to the NCAM antibody containing matrix whereas individual neuronal cells did. The neuronal cell attachment was depended on the NCAM antibody concentration. The neuronal cells were viable on the NCAM antibody containing matrix during an 8 day follow-up and exhibited typical bipolar morphology of immature neurons. Specific binding of the NCAM antigen to an immunoglobulin-polymer coated surface was verified by surface plasmon resonance (SPR) measurements. This study is to our knowledge the first demonstrating the use of an antibody layer as a selective surface for hESC-derived neuronal cells.

New probe immobilizations by lipoate-diethalonamines or ethylene-glycol molecules for capacitance DNA chip

Label-free DNA detection is of crucial role to when developing point-of-care biochips to be used in personalized therapy. Capacitance detection is a promising technology for label-free DNA detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To solve these problems, alkanethiol molecules such as mercapto-hexanol are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, florescence microscopy, and capacitance measurements are used to demonstrate the new lipoates molecules. Moreover precursor layers obtained by using Ethylene-glycol alkanethiols offer further improvements in terms of diminished detection errors. Film structure is investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and Ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.

Capacitance DNA bio-chips improved by new probe immobilization strategies

Label-free DNA detection plays a crucial role in developing point-of-care biochips. Capacitance detection is a promising technology for label-free detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To address these problems, mercapto-hexanol or similar alkanethiols are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, florescence microscopy, and capacitance measurements are used to investigate new lipoate and ethylene-glycol molecules. The new surfaces offer further improvements in terms of diminished detection errors. Film structures are investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.