Interleukin-6 (IL-6) is a biomarker of inflammation, the advanced stage of COVID-19, and several cancers, including ovarian cancer. Two biosensors for the determination of IL-6 in blood plasma by array SPRi have been developed. One of these biosensors consists of the mouse monoclonal anti-IL-6 antibody as the receptor immobilized via the cysteamine linker. The second contains galiellalactone as the receptor, being an inhibitor specific for IL-6, immobilized via octadecanethiol (ODM) as the linker. Both biosensors are specific for IL-6. The biosensor with the antibody as the receptor gives a linear analytical response between 3 (LOQ) and 20 pg mL-1 and has a precision between 8% and 9.8% and recovery between 97% and 107%, depending on the IL-6 concentration. The biosensor with galiellalactone as the receptor gives a linear analytical response between 1.1 (LOQ) and 20 pg mL-1, and has a precision between 3.5% and 9.3% and recovery between 101% and 105%, depending on IL-6 concentration. Both biosensors were validated. Changes in IL-6 concentration in blood plasma before and after resection of ovarian tumor and endometrial cyst, as determined by the two developed biosensors, are given as an example of a real clinical application.

Cathepsin G (CatG) is an endopeptidase that is associated with the early immune response. The synthetic compound cathepsin G inhibitor I (CGI-I) was tested for its ability to inhibit the activity of CatG via a new surface plasmon resonance imaging assay. CGI-I was immobilized on the gold surface of an SPR sensor that was first modified with 1-octadecanethiol. A concentration of CGI-I equal to 4.0 μg·mL-1 and a pH of 8.0 were found to give the best results. The dynamic response of the sensor ranges from 0.25 to 1.5 ng·mL-1, and the detection limit is 0.12 ng·mL-1. The sensor was applied to detect CatG in human saliva and white blood cells.FigureThe synthetic compound cathepsin G inhibitor I (CGI-I) was tested for its ability to inhibit the activity of cathepsin G via a newly developed surface plasmon resonance imaging assay. The sensor was applied to detect cathepsin G in human saliva and white blood cells.

The 20S proteasome, released into the circulation, is a novel cancer biomarker. It exists in two forms: the constitutive proteasome (20Sc) and the immunoproteasome (20Si), which both have separate diagnostic significance. The aim of this work was to develop new methods for 20Si and 20Sc determination. Five alternative specific biosensors usable with the surface plasmon resonance imaging (SPRI) technique for 20Si determination have been developed. Specific 20Si entrapment on the biosensor surface from an analyzed solution was achieved by means of an immobilized specific 20Si receptor. Four of the biosensors contain newly synthesized specific 20Si receptors, while the fifth contains the inhibitor ONX 0914. A method for 20Sc determination using an SPRI biosensor containing PSI inhibitor has been developed. By the introduction of an inhibitor blocking 20Si, 20Sc is selectively determined. All of the methods developed for 20Si and 20Sc determination exhibit good selectivity and satisfactory precision, recoveries and dynamic response ranges. 20Si and 20Sc were determined in blood plasma samples from healthy donors and patients with acute leukemia. In the case of these patients 20Si was the major component, and its level was more than one order of magnitude higher than in the healthy donors.

The 20S proteasome is a multicatalytic enzyme complex responsible for intracellular protein degradation in mammalian cells. Its antigen level or enzymatic activity in blood plasma are potentially useful markers for various malignant and nonmalignant diseases. We have developed a method for highly selective determination of the 20S proteasome using a Surface Plasmon Resonance Imaging (SPRI) technique. It is based on the highly selective interaction between the proteasome's catalytic β5 subunit and immobilized inhibitors (the synthetic peptide PSI and epoxomicin). Inhibitor concentration and pH were optimized. Analytical responses, linear ranges, accuracy, precision and interferences were investigated. Biosensors based on either PSI and epoxomicin were found to be suitable for quantitative determination of the proteasome, with a precision of ±10% for each, and recoveries of 102% and 113%, respectively, and with little interference by albumin, trypsin, chymotrypsin, cathepsin B and papain. The proteasome also was determined in plasma of healthy subjects and of patients suffering from acute leukemia. Both biosensors gave comparable results (2860 ng·mL-1 on average for control, and 42300 ng·mL-1 on average for leukemia patients).FigureThe synthetic peptide aldehyde Z-Ile-Glu(OBut)-Ala-Leu-H (PSI) and a microbial α',β' epoxyketone peptide epoxomicin was used to develop SPRI biosensor for the highly selective determination of the 20S proteasome concentration, and to evaluate the sensor applicability for the determination of 20S proteasome in human blood plasma.