Phospho-Tau 181 quantification method for Alzheimer's disease based on an array 2D biosensor combined with surface plasmon resonance imaging

Alzheimer's disease is among the neurodegenerative diseases for which there is a lack of rapid, effective, and non-invasive diagnostic methods. The development of a phospho-Tau 181 assay biosensor is therefore a response to the need for methods to diagnose AD. The present work was aimed at developing a fast, selective, and repeatable method for the quantitative determination of phospho-Tau 181, which could be used even during routine blood tests. Our method is a form of what is called liquid biopsy. The developed method underwent validation, as a result of which its analytical parameters were determined. An LOQ of 3.35 pg mL-1 was obtained, confirming the possibility of trace analysis of phospho-Tau 181 in human plasma. Relative percentage error values below 15 % and CVs in the range 1.47-7.09 % attest to the high accuracy and precision of the presented method. Also, the sample matrix was not found to significantly affect the results obtained for phospho-Tau 181 concentrations. The new SPRi biosensor provides reproducible measurements of the analyte under study (CV = 3.18-4.26 %). Although the method requires absolute adherence to the recommendations of the analytical procedure protocol, it achieves high selectivity and provides 90 % certainty of the correctness of the diagnosis based on measurements of phospho-Tau 181 concentration.

Changes in the Concentrations of Proangiogenic Cytokines in Human Brain Glioma and Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) and glioma are some of the most common malignancies, with ALL most often affecting children and glioma affecting adult men. Proangiogenic cytokines and growth factors play an important role in the development of both of these tumors. Glioma is characterized by an extremely extensive network of blood vessels, which continues to expand mainly in the process of neoangiogenesis, the direct inducers of which are cytokines from the family of vascular endothelial growth factors, i.e., vascular endothelial growth factor (VEGF-A) and its receptor vascular endothelial growth factor receptor 2 (VEGF-R2), as well as a cytokine from the fibroblast growth factor family, fibroblast growth factor 2 (FGF-2 or bFGF). Growth factors are known primarily for their involvement in the progression and development of solid tumors, but there is evidence that local bone marrow angiogenesis and increased blood vessel density are also present in hematological malignancies, including leukemias. The aim of this study was to examine changes in the concentrations of VEGF-A, VEGF-R2, and FGF-2 (with a molecular weight of 17 kDa) in a group of patients divided into specific grades of malignancy (glioma) and a control group; changes of VEGF-A and FGF-2 concentrations in childhood acute lymphoblastic leukemia and a control group; and to determine correlations between the individual proteins as well as the influence of the patient's age, diet, and other conditions that may place the patient in the risk group. During the statistical analysis, significant differences in concentrations were found between the patient and control groups in samples from people with diagnosed glioma and from children with acute lymphoblastic leukemia, but in general, there are no significant differences in the concentrations of VEGF-A, VEGF-R2, and FGF-2 between different grades of glioma malignancy. Among individuals treated for glioma, there was no significant impact from the patient's gender and age, consumption of food from plastic packaging, frequency of eating vegetables and fruit, smoking of tobacco products, the intensity of physical exercise, or the general condition of the body (Karnofsky score) on the concentrations of the determined cytokines and receptor. The listed factors do not bring about an actual increase in the risk of developing brain glioma.

Comparison of Fluidic and Non-Fluidic Surface Plasmon Resonance Biosensor Variants for Angular and Intensity Modulation Measurements

Fluidic and non-fluidic surface plasmon resonance measurements were realized for the same type of sensory layer and using the same mouse IgG antibody and anti-mouse IgG antibody biomolecular system. A comparison of the thicknesses of the anti-mouse IgG antibody layers bound to the ligand at increasing analyte concentrations ranging from 0.0 μg mL-1 to 5.0 μg mL-1 in the non-fluidic and the fluidic variant showed that the thickness of the bound anti-mouse antibody layers in the fluidic variant was approximately 1.5-3 times larger than in the non-fluidic variant. The greater thicknesses of the deposited layers were also reflected in the larger increment of the resonant angle in the fluidic variant compared to the non-fluidic variant in the considered range of analyte concentrations. The choice between fluidic and non-fluidic surface plasmon resonance biosensors may be justified by the availability of analyte volume and the intended modulation technique. When working with limited analyte, non-fluidic biosensors with intensity modulation are more advantageous. For larger analyte quantities, fluidic biosensors with angular modulation are recommended, primarily due to their slightly higher sensitivity in this measurement mode.

Development of an SPRi Test for the Quantitative Detection of Cadherin 12 in Human Plasma and Peritoneal Fluid

A new method for the determination of cadherin 12 (CDH12)-an adhesive protein that has a significant impact on the development, growth, and movement of cancer cells-was developed and validated. The method is based on a biosensor using surface plasmon resonance imaging (SPRi) detection. A quartz crystal microbalance was used to analyze the characteristics of the formation of successive layers of the biosensor, from the linker monolayer to the final capture of CDH12 from solution. The association equilibrium constant (KA = 1.66 × 1011 dm3 mol-1) and the dissociation equilibrium constant (KD = 7.52 × 10-12 mol dm-3) of the anti-CDH12 antibody-CDH12 protein complex were determined. The determined analytical parameters, namely the values determining the accuracy, precision, and repeatability of the method, do not exceed the permissible 20% deviations specified by the aforementioned institutions. The proposed method is also selective with respect to possible potential interferents, occurring in up to 100-fold excess concentration relative to the CDH12 concentration. The determined Limit of Quantification (LOQ = 4.92 pg mL-1) indicates the possibility of performing quantitative analysis in human plasma or peritoneal fluid without the need to concentrate the samples; however, particular attention should be paid to their storage conditions, as the analyte does not exhibit high stability. The Passing-Bablok regression model revealed good agreement between the reference method and the SPRi biosensor, with ρSpearman values of 0.961 and 0.925.

An Array SPRi Biosensor for the Determination on PARP-1 in Blood Plasma

A biosensor was developed for the quantification of poly(ADP-ribose) polymerase-1 (PARP-1) in body fluids. An antibody specific for PARP-1 was placed on a chip with cysteamine (linker) and a gold layer. This biosensor has a linear response range (10-1000 pg∙mL^-1) under appropriate pH conditions and with an antibody ligand concentration of 5 ng∙mL^-1. Plasma samples were diluted with PBS buffer in appropriate quantities so that they fell within the linear range of the calibration curve. The biosensor exhibited suitable precision and accuracy, and good recovery (at levels from 95% to 105%). The method was validated by means of PARP-1 determinations in plasma samples from patients with endometriosis and a control group, using surface plasmon resonance imaging (SPRi) biosensors and an enzyme-linked immunosorbent assay (ELISA) test. The Spearman correlation coefficient was close to 1. PARP-1 may be a marker providing information about pathological changes in the body during endometriosis.

Two Biosensors for the Determination of VEGF-R2 in Plasma by Array SPRi

Vascular endothelial growth factor receptor 2 (VEGF-R2) is a marker of angiogenesis and metastasis of cancer. Two biosensors for the determination of VEGF-R2 in plasma have been developed. One of them is based on a pure gold chip, and the other on a silver/gold bimetallic chip; both have the receptor, monoclonal rabbit antibody specific for human VEGF-R2, attached to the chip via a cysteamine linker. The biosensor with the gold chip exhibits linearity of the analytical signal between 0.03 and 2 ng/mL, a precision of 1.4% and recovery between 99% and 102%. The biosensor with the bimetallic chip exhibits linearity between 0.03 and 1 ng/mL, a precision of 2.2% and recovery between 99% and 103%. Both biosensors tolerate a 1:100 excess of VEGF, VEGF-R1 and VEGF-R3. Both biosensors were validated by parallel determination of VEGF-R2 in 27 different plasma samples using the ELISA immunosensor assay, with very good agreement of the results. Thermodynamic parameters of the interaction of VEGF-R2 with the antibody were determined by QCM (Quartz Crystal Microbalance) and SPRi (Surface Plasmon Resonance imaging) measurements.

An Immunosensor for the Determination of Cortisol in Serum and Saliva by Array SPRi

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.

MMP-1, UCH-L1, and 20S Proteasome as Potential Biomarkers Supporting the Diagnosis of Brain Glioma

The diagnosis of brain gliomas is mainly based on imaging methods. The gold standard in this area is MRI. Recommendations for the prevention, diagnosis, and treatment of gliomas are periodically modified and updated. One of the diagnostic techniques used when a brain glioma is suspected is liquid biopsy. However, this technique requires further development to confirm its effectiveness. This paper presents a proposal of three potential biomarkers of brain gliomas—extracellular matrix metalloproteinase-1 (MMP-1), ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), and the 20S proteasome—which were quantified in blood plasma using SPRi biosensors. A statistical analysis of the results indicated no significant changes in the concentrations between the control group (K) and grades G1 and G2, and similarly between grades G3 and G4. However, the differences in the concentrations between the groups K/G1/G2 and G3/G4 were statistically significant. A positive average correlation was found between the concentrations of the proteins and the patient’s age. The individual tested proteins were also highly correlated with each other. Our work proposes a new diagnostic technique that may aid in the diagnosis of brain gliomas.

Laminin-5, Fibronectin, and Type IV Collagen as Potential Biomarkers of Brain Glioma Malignancy

The presented work is based on the quantification of LN-5, FN, and COL IV in blood plasma as potential biomarkers in patients diagnosed with glioma in grades G1 to G4. The obtained concentration results were compared with the protein content in the control group, which consisted of smokers of different ages. The obtained results were statistically analysed and interpreted based on the available clinical description. Quantitative determinations of LN-5, FN, and COL IV were performed with the use of SPRi biosensors specific to the tested proteins. Comparing groups K and G4, as well as G2 and G4, statistically significant relationships between changes in the concentration of individual proteins, were observed. The analysis showed significant correlations between FN and LN-5, between FN and COL IV, and between LN-5 and COL IV. There was a moderate positive correlation between individual proteins and the age of the patient. The ROC analysis distinguished patients with advanced disease from the control group. The results of the research show that LN-5, FN, and COL IV are effective biomarkers of brain glioma that may be helpful in non-invasive diagnosis and determining the grade of the disease.

Two Biosensors for the Determination of Interleukin-6 in Blood Plasma by Array SPRi

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.

An Immunosensor for the Determination of Cathepsin S in Blood Plasma by Array SPRi-A Comparison of Analytical Properties of Silver-Gold and Pure Gold Chips

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).