A New Analytical Method for Determination of Cathepsin L Based on the Surface Plasmon Resonance Imaging Biosensor

The purpose of this study was to develop a new method for a determination of the cathepsin L—biosensor based on the Surface Plasmon Resonance Imaging technique. The cathepsin L is an endopeptidase, which degrades proteins and plays an important role in various processes occurring in the human body. The detection technique, Surface Plasmon Resonance Imaging, is an optical, label-free technique, which can be used for quantitative determination of the different proteins. In order to bind the enzyme, the cathepsin L inhibitor—RKLLW-NH(2) was used. The validation process showed that parameters: precision, accuracy, and selectivity of the method were acceptable. The analytically useful range of the standard curve was 0.50 ng/mL—15.00 ng/mL. The detection and quantification limit of method was 1.67 pg/mL and 5.07 pg/mL, respectively. The usefulness of the developed method was confirmed by the determination of the cathepsin L concentration in the blood plasma of some healthy persons and in the blood plasma of patients. The obtained results were compared with the results obtained by the ELISA. It was found that the correlation between these two methods was very strong, what suggest that the developed method can be used as the competitive method to the ELISA.