Bioassays are a vital routine in hospitals for detecting biological molecules, toxins, viruses, bacteria, and whole cells. Advanced laboratory techniques and rigorously controlled environments guarantee accurate results. Proper sample preparation is essential for the effectiveness of these assays, as biological samples often require dilution or the addition of specific buffer solutions to prevent cross-reactions and non-specific protein binding in concentrated samples. Dr. Nenad Gajovic-Eichelmann and Dr. Marina Neumann from Fraunhofer IZI-BB are exploring the sustainable TruContact® coating, which could further improve assay performance. The introduction of this innovative coating technology has the potential to eliminate dilution steps, conserve reagents and samples, and enhance the sensitivity of the assays.

Assays in concentrated samples without non-specific binding of proteins 

Biological samples from whole blood or serum are very concentrated media that contain a large number of bioactive molecules in addition to the analyte. The non-specific binding of proteins is a well-known problem in immunoassays, which is usually minimized by diluting the samples. However, this dilution also leads to a reduction in the concentration of the analyte being sought.

Dr. Gajovic-Eichelmann states that TruContact® can enhance detection in multiple ways: »With our hydrophilic TruContact® coating technology, we attain a low affinity for the binding of non-specific proteins. Compared to assays on polystyrene surfaces, it is therefore possible to dilute the samples less: A 1:2 dilution is usually sufficient.« In certain instances, it was even feasible to measure undiluted samples. As a result, it enables the use of a smaller sample volume while still detecting the same quantity of analyte. 

Over 50 Percent Savings on Antibodies and Samples

In standard 96-well microtiter plates made of polystyrene, typically used for bioassays, a sample volume of 50 to 100 microliters is standard. While modern pipetting robots, commonly found in hospitals and many laboratories, can easily handle volumes of 20 or even 15 microliters, using smaller amounts can lead to incomplete wetting of the well bottoms, resulting in inaccurate test results. However, wells coated with TruContact® only require 15 microliters for uniform wetting. This combination of the wetting TruContact® surface and pipetting robots could save more than 50 percent in reagents and biological samples. Additionally, hydrophilic-coated surfaces provide pipetting robots with the advantage of safely and quickly transferring even the smallest doses of a few microliters into the wells, without the need to wipe the pipette tip on the vessel wall, even when the wells are dry. The sample is effectively attracted by the highly hydrophilic surface, distributing aqueous fluid evenly throughout the well.

Innovative TruContact^® Technology Promotes Sensitivity

TruContact^® creates a hydrophilic surface that is also chemically reactive and ideally suited for rapid coating with functional molecules such as antibodies. In contrast to the hydrophobic, high-binding polystyrene surfaces commonly used today, the interaction with functional molecules such as antibodies in TruContact^® is not based on adsorption. Instead, the functional molecules are irreversibly immobilized via a covalent bond. Proteins, enzymes, peptides or small molecules can be fixed to the solid phase via their nucleophilic hydroxide, thiol or amino groups. Dr. Marina Neumann highlights that »binding occurs quite rapidly within 15 to 60 minutes and is very gentle; only a small percentage of the antibodies are denatured on the surface.” Compared to immunoassays employing the adsorption technique in conventional microtitre plates, up to 90 percent of antibodies can be saved during the immobilization phase. The high proportion of active, covalently immobilized antibodies leads to a lower detection limit compared to adsorptively coupled antibodies. Dr. Neumann has already successfully demonstrated this effect for several sandwich ELISA (e.g. myoglobin, CRP) and competitive ELISA (THC, estradiol, human IgG). 

Combining Durability with Cost-Effectiveness

Reactive coatings tend to become inactive after a short time due to moisture, oxygen and light exposure. In contrast, the TruContact^® coating remains reactive even after two years of storage at 45°C, retaining nearly its full immobilization capacity. This coating, based on non-toxic, plant-derived raw materials, is also extremely cost-effective and can be applied using simple liquid handling equipment.