Overview of the technology

The Residue Plex technology

The RnAssays® product-line is based on a multi-analyte Plex assay that quantifies multiple microbial and non-microbial contaminations simultaneously in a single sample. Minimal animal-derived sample volumes are required, representing a significant advantage in effectiveness and productivity over traditional ELISA assays.

The Residue Plex is a Flow Cytomatric Immune Affinity assay (FCIA). It uses monoclonal and polyclonal antibodies and natural receptors fixed on distinct sized microspheres (Fig. 3) for binding antibiotics.

Discrimination of the individual microspheresis arranged by different internal fluorescent intensities, which lead to the analysis of multipleanalytic results per sample. 

                         Fig. 3 - RnAssays FCIA Suspension Array Technology

With flow cytometry not only fluorescent intensities of microspheres, but also small size variations can be distinguished. In the Plex assay technology, this combination of bead sizes and fluorescent intensities offers the possibility to detect tens of bead variants.

Thisallows the simultaneous detection of many antibiotic families each containing multiple individual antibiotics.


Residue Plex: Receptors not Antibodies

Antibiotics exert their effects through inhibition of the activity of cell components essential for the homeostasis of the affected bacteria. The receptive component can be any bacterial functional macromolecule. In a test system, receptors are by far favoured over antibodies as receptors are more selective, specific and have higher affinities for the targeted analytes.

They outperform the best antibody, as they react by definition with pharmacological active substances of interest including their active metabolites. Typical drawbacks of antibodies as non-specific binding and limited cross-reactivity with certain constituents of an antibiotic family are not the case with receptors.

RnAssays’ tetracycline and β-lactam tests are based on the licensed use of patented receptors. The products detect all relevant tetracycline variants including their 4-epimer derivatives, and β-lactam substances, including the first, second and third generation components.


Universal and simple sample preparation

Residue Plex assays have a single sample clean-up process for all antibiotic tests. And it is much simpler than solid-phase extraction (SPE), as shown below in Fig. 4. 

                            Fig. 4 - Simple Residue Plex sample extraction procedure


Ability to detect all antibiotic families

As described earlier, Residue Plex already detects three of the main families of antibiotics, including (fluoro)quinolones, which cannot be detected by traditional plate tests. But more than that, because Residue Plex relies on natural receptors rather than on antibodies for analyte capture, the assay technology will detect any target antibiotic.

And remember, the bead/size combination allows for detection of tens of analytes simultaneously! So in practice, unlike other affinity tests, there is virtually no limit to the number of antibiotics that can be detected from one sample in one run and in one test.


Unique Tetracycline meat drip test

Residue Tetra-Plex has been validated for the detection of Tetracyclines directly from meat drip samples using a 'dilute and shoot' method. This means that the Tetracycline test can be carried out with minimal sample preparation while retaining the required sensitivity to respect testing against MRL concentrations.


Flexible assay format

RnAssays flexible approach to assay design and production, together with the underlying robustness and simplicity of the bead-based flow cytometry, means that multiplex assays can be tailored to the needs of a specific laboratory.

Whether you need to test for zoonoses, animal diseases, residues or combinations of all three groups, RnAssays will be pleased to give careful consideration to your requirements.

Choice of instrument platform

RnAssays' Plex assays have been validated on several flow cytometer platforms, including Accuri, Millipore and Beckman Coulter. If your laboratory is already using a flow cytometer, RnAssays will be able to advise how to run the Plex assays on it.

If not, then RnAssays offers various placement options: rental, reagent rental and sale, including full service and maintenance contracts and a 48h swap service in the unlikely event of break-down.

Fig. 5 - One of the several flow cytometers upon which Residue Plex has been validated

For laboratories requiring high throughput and full automation, RnAssays also offers a custom built robot washer capable of handling multiple units of 96 well plates, again with a range of placement options.

RnAssays’ academic & commercial pedigree

RnAssays is the inventor of RnAssays® product line comprising assays developed at the Utrecht University, and owns patents for the innovative covalent coupling of antigenic and receptor structures to solid surfaces, such as those of well-defined microspheres, sensor-surfaces or sensor-tips.

RnAssays is specialized in the development and application of time- and cost-saving diagnostic assays for safety and quality control in the primary and secondary food production sectors with the focus on food of animal origin.

They received the World Poultry Award 2006 for its innovative Plex™ technology and was awarded the international Eureka status in October 2007.