Laparoscopy as a diagnostic tool for patients with suspected endometriosis is associated with several potentially life-threatening complications. Therefore, it is imperative to identify reliable, non-invasive biomarkers of the disease. The aim of this study was to analyse the concentrations of fibronectin and type IV collagen in peritoneal fluid and plasma to assess their role as potential biomarkers in the diagnosis of endometriosis. Fibronectin and collagen IV protein levels were assessed by surface plasmon resonance imaging (SPRi) biosensors with the usage of monoclonal antibodies. All patients enrolled in the study were referred for laparoscopy for the diagnosis of infertility or chronic pelvic pain (n = 84). The study group included patients with endometriosis confirmed during surgery (n = 49). The concentration of fibronectin in the plasma (329.3 ± 98.5 mg/L) and peritoneal fluid (26.8 ± 11.1 μg/L) in women with endometriosis was significantly higher than in the control group (251.2 ± 84.0 mg/L, 7.0 ± 5.9 μg/L). Fibronectin levels were independent of endometriosis stage (p = 0.874, p = 0.469). No significant differences were observed in collagen IV levels (p = 0.385, p = 0.465). The presence of elevated levels of fibronectin may indicate abnormalities in cell–ECM signalling during the course of endometriosis, and may be a potential biomarker for early detection.

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.

The array SPR imaging (SPRi) technique is well suited to the determination of biomarkers in body fluids, called liquid biopsy. No signal enhancement or analyte preconcentration is required. With the aim of achieving signal enhancement and lowering the cost of a single determination, the replacement of gold-covered chips by silver–gold chips was investigated. The aim of this work was to investigate the analytical characteristics of a biosensor formed on a Ag/Au chip and to compare them with those of a biosensor formed on a gold chip. A biosensor for the determination of cathepsin S (Cath S) was chosen as an example. The biosensor consisted of the linker cysteamine and an immobilized rat monoclonal antibody specific for cathepsin S. Both biosensors exhibited a Langmuirian response to Cath S concentration, with linear response ranging from LOQ to 1.5 ng mL⁻¹. The LOQ is 0.1 ng mL⁻¹ for the biosensor formed on the Ag/Au chip, and 0.22 ng mL⁻¹ for that formed on the gold chip. Recoveries and precision for medium and high Cath S concentrations were acceptable for both biosensors, i.e., precision better than 10% and recoveries within the range 102–105%. However, the results for the lowest Cath S concentration were better for the biosensor formed on the Ag/Au chip (9.4 and 106% for precision and recovery, respectively). Generally, no significant differences in analytical characteristics were observed between the Ag/Au and Au chips. The two biosensors were also compared in the determination of Cath S in real samples. Nine plasma samples from healthy donors and nine from patients with ovarian cancer were analyzed for Cath S concentration with the biosensors formed on Ag/Au and Au chips. The results obtained with the two biosensors were very similar and show no significant differences on the Bland–Altman plot. The Cath S concentration in the blood plasma of ovarian cancer patients was elevated by one order of magnitude as compared with the control (12.6 ± 3.6 vs. 1.6 ± 1.2 ng mL⁻¹).

Cortisol is a hormone which plays an essential role in the immune, endocrine, cardiovascular, renal and skeletal systems. Its level increases in response to stress, illness, injury or exhaustion, and it is therefore a significant diagnostic biomarker of stress. An immunosensor for the determination of cortisol by SPRi array was developed. The receptive part of the immunosensor is mouse monoclonal antibody against cortisol, immobilized via cysteamine linker. The optimum pH of the immunosensor is 7.4, and the optimum concentration of the antibody is 50 ng mL⁻¹. The immunosensor is specific for cortisol, and its linear response ranges from 0.20 ng mL⁻¹ (LOQ) to 8 ng mL⁻¹. The precision of the determination was between 3.1% and 3.3%, and the recovery between 99% and 102%. The immunosensor was validated by simultaneous determination of cortisol in serum and saliva samples by a standard method, with good agreement between the results.

A new method was developed for the simultaneous determination of vascular endothelial growth factor (VEGF-A) and fibroblast growth factor-2 (FGF-2) in blood serum, using biosensors with array Surface Plasmon Resonance imaging (SPRi) detection. It can be applied as a single method for simultaneous VEGF-A and FGF-2 determination or as two separate methods for testing only one selected protein in each case. Validation was carried out for each method. Limit of detection (LOD) and limit of quantification (LOQ) values were determined and were found not to differ significantly from the parameters obtained in comparisons with commercial enzyme-linked immunosorbent assay (ELISA) tests. Tests were carried out to check the robustness of the method. The results indicate a lack of robustness of the analytical method to elevated temperature and pH values other than those recommended by the manufacturers of the reagents (recommended pH = 7.40). The values of recoveries were determined and confirmed the reliability of the results obtained with the use of the newly developed method. The selectivity studies showed no negative influence of other proteins present in the matrix of the tested samples on the results of the VEGF-A and FGF-2 concentration measurements. The developed method is also characterized by high reproducibility of the results obtained and agreement with the VEGF-A and FGF-2 concentration values obtained with commercial ELISA tests. The proposed method offers fast, reproducible, and accurate simultaneous quantification of VEGF-A and FGF-2 in human body fluids. Only 4 µL of test sample are required for simultaneous analysis. The total time for simultaneous analysis of both biomarkers does not exceed 20 min. The developed analytical method is superior to ELISA in terms of analysis time and sample volume for analysis, and it offers lower LOD and LOQ values and allows for the simultaneous analysis of two biomarkers. There is also no need to collect a large number of samples. Standard ELISAs usually have 96 reaction wells. The proposed biosensor can be used to analyse only one sample, without the need to waste reagents on unused reaction sites. In addition, it is possible to regenerate the biosensor and reuse it.

Brain gliomas constitute the vast majority of malignant tumors of the nervous system. There is still a lack of fast, reliable and non-invasive methods of diagnostics. Our work focuses on the quantification of cathepsin B, D and S in glioma. The research was conducted with the use of SPRi biosensors sensitive to individual cathepsins. Changes in the quantity of selected cathepsins (cathepsins B, D and S), depending on the advancement of glioma and the presence or absence of important features or comorbidities in the selected patient, were examined. The results were statistically analyzed and interpreted based on the available clinical description. Statistical significance was observed in the difference in the concentration of the studied cathepsins, mainly between the groups Control and G3/G4 and G1/G2 and G3/G4. The strength of the correlation between the concentrations of individual cathepsins and the age of the patient and the size of the tumor, as well as the correlation between individual proteins, was investigated. The influence of IDH 1/2 status on the concentration of determined cathepsins was investigated and ROC analysis was performed. As a result of our research, we have developed a method for the diagnosis of brain glioma that allows us to distinguish grades G1/G2 from G3/G4 and the control group from G3/G4. We found an average positive correlation between the concentrations of the proteins tested and the age of the patient and a high positive correlation between the cathepsins tested. Comparative analysis of the effect of the presence of IDH 1/2 mutations on the number of proteins tested allowed us to demonstrate that the cathepsins assayed can be independent markers.