Surgical and diagnostic instruments are heavily contaminated after use, so careful reprocessing is necessary to ensure patient safety.

According to the KRINKO/BfArM-recommendation, instruments must be carefully cleaned, disinfected and, if necessary, sterilised. Specialised units (AEMP) in hospitals, medical and dental practices and medical care centres are responsible for reprocessing.

The Medical Devices Operator Ordinance (MPBetreibV) requires that reprocessing is carried out using validated procedures and checked regularly.

Regular checks of the instruments ensure that no contamination remains that could impair the disinfection and, if necessary, sterilisation processes.

The residual protein content serves as a guiding parameter when checking the cleaning process. The KRINKO/BfArM-recommendation stipulates that a residual protein content of 100 µg per instrument or 3 µg/cm2 of instrument surface must not be exceeded (warning level).

The most difficult component of blood contaminations to remove is fibrin, which is not soluble in water and cannot be recovered by standard elution methods.

A method based on a fibrin-binding hybrid molecule was developed for easy control of the cleaning effect and enables the measurement of fibrin residues directly on the instrument surface (at site quantification).

The hybrid molecule developed consists of a carrier oligonucleotide, a fibrin-binding CREKA pentapeptide and signalling oligonucleotides, which are released at elevated temperatures and can be eluted and quantified.

The specific binding of the hybrid molecule to fibrin (at site) was detected by fluorescence microscopy.

The released signalling oligonucleotides can be quantified using a fluorescence indicator that has been developed and is based on a so-called flip-up mechanism.

Here, the thermally released signal oligonucleotides bind to special flip-up oligonucleotides, whereby the flip-up oligonucleotides are detached from graphene oxide, resulting in the generation of a fluorescence signal.

The at-site quantification method was successfully applied to Crile artery clamps heavily contaminated with blood after automated cleaning and intermediate rinsing. The results demonstrate the suitability of the method, meaning that insoluble fibrin residues can now be easily and reliably quantified for the first time without special and often destructive examination methods.

The research report is available on request from FRT.