Molecular Form Differences Between Prostate-Specific Antigen (PSA) Standards Create Quantitative Discordances in PSA ELISA Measurements

Phage Display's Prospects for Early Diagnosis of Prostate Cancer

Prostate cancer (PC) is the second most diagnosed cancer among men. It was observed that early diagnosis of disease is highly beneficial for the survival of cancer patients. Therefore, the extension and increasing quality of life of PC patients can be achieved by broadening the cancer screening programs that are aimed at the identification of cancer manifestation in patients at earlier stages, before they demonstrate well-understood signs of the disease. Therefore, there is an urgent need for standard, sensitive, robust, and commonly available screening and diagnosis tools for the identification of early signs of cancer pathologies. In this respect, the "Holy Grail" of cancer researchers and bioengineers for decades has been molecular sensing probes that would allow for the diagnosis, prognosis, and monitoring of cancer diseases via their interaction with cell-secreted and cell-associated PC biomarkers, e.g., PSA and PSMA, respectively. At present, most PSA tests are performed at centralized laboratories using high-throughput total PSA immune analyzers, which are suitable for dedicated laboratories and are not readily available for broad health screenings. Therefore, the current trend in the detection of PC is the development of portable biosensors for mobile laboratories and individual use. Phage display, since its conception by George Smith in 1985, has emerged as a premier tool in molecular biology with widespread application. This review describes the role of the molecular evolution and phage display paradigm in revolutionizing the methods for the early diagnosis and monitoring of PC.

Multispectral plasmonic biosensors based on a Penta-supercell metamaterial for detection of prostate-specific antigen: Ultrasensitive in LC resonance mode

Here, the detection of prostate-specific antigen (PSA) was done using a refractive index sensor based on a plasmonic Penta-supercells metamaterial array. The proposed Penta-supercells metamaterial array consists of four split ring-shaped supercells and a multiplication-shaped supercell in the middle. The results were validated using the three-dimensional Finite-difference time-domain (FDTD) numerical method. The detection of low-concentration biomolecules is a typical drawback of conventional plasmonic biosensors. Our designed Penta-supercells shape biosensor benefits from an ultra-sensitivity. In our designed biosensor, simultaneous excitations of three main plasmon (inductance-capacitance (LC), quadrupole, and dipole) modes can occur, and the LC mode shows a superior sensitivity. The structure was designed optimally, and three different types of metals (Au, Ag, and Al) were examined. LC mode appeiers in Ag and Au and this mode is not seen in Al. Also, the results of this study show the superiority of Ag to Au and Al. Based on the results of this study, the proposed structure achieves a record high sensitivity of 2256 nm/RIU in LC mode and high sensitivity of 1022 nm/RIU in quadrupole mode, and 494 nm/RIU in dipole mode. As another result, the proposed structure is insensitive to orthogonal polarization. The full utilization of these three resonance plasmon modes shows bright prospects for multi-spectral application. In the case of biosensor application, the designed Penta-supercells-based biosensor and its ultra-high sensitivity of 2256 nm/RIU (4.5 times larger than the sensitivity of conventional plasmonic structures) can help the medical to detect low concentrations.

Measurement of total and free prostate specific antigen (PSA) in human serum samples using an ultra-microanalytical system

Prostate specific antigen (PSA) is a serine protease used for the screening of prostate cancer. The total portion of PSA (tPSA) can be found in its free form (fPSA), or bound to other proteins forming a stable complex. A heterogeneous sandwich-type UltraMicro Enzyme-Linked ImmunoSorbent Assay (UMELISA) has been developed for the measurement of tPSA and fPSA in human serum samples. Strips coated with a high affinity monoclonal antibody (MAb) directed against PSA are used as solid phase, to ensure the specificity of the assay. Biotinylated MAbs specific for tPSA and fPSA ensured sensitivity, given the high affinity binding to streptavidin. The assay was completed in 1.5 h, with a measuring range 0.019-20 µg/L (tPSA), and 0.009-20 µg/L (fPSA). The intra- and inter-assay CV were lower than 9%. Recovery percentages were 96-105%. High correlations were found between the values of the UMELISA PSA standards and the International Reference Standards 96/670 (R² = 0.9996) and 96/688 (R² = 0.9989). The assay did not recognize any of the interfering molecules tested. Regression analysis of serum samples showed a good correlation with Roche Elecsys total PSA (n = 631, R² = 0.986, ρc = 0.992), BioMérieux VIDAS TPSA (n = 631, R² = 0.989, ρc = 0.993) and Roche Elecsys free PSA (n = 164, R² = 0.973, ρc = 0.979), all with a relative difference below 15%, and a p < 0.001. A retrospective study of the use of UMELISA PSA in Cuba was carried out. The analytical performance characteristics of UMELISA PSA support its use for the quantification of tPSA and fPSA in human serum samples in a single kit, making it an affordable diagnostic assay available to Cuban Public Health System and developing countries. Between the years 2014-2020, more than 3 million Cuban patients have benefited from the test for free.

Lateral Flow Immunoassay with Quantum-Dot-Embedded Silica Nanoparticles for Prostate-Specific Antigen Detection

Prostate cancer can be detected early by testing the presence of prostate-specific antigen (PSA) in the blood. Lateral flow immunoassay (LFIA) has been used because it is cost effective and easy to use and also has a rapid sample-to-answer process. Quantum dots (QDs) with very bright fluorescence have been previously used to improve the detection sensitivity of LFIAs. In the current study, a highly sensitive LFIA kit was devised using QD-embedded silica nanoparticles. In the present study, only a smartphone and a computer software program, ImageJ, were used, because the developed system had high sensitivity by using very bright nanoprobes. The limit of PSA detection of the developed LFIA system was 0.138 ng/mL. The area under the curve of this system was calculated as 0.852. The system did not show any false-negative result when 47 human serum samples were analyzed; it only detected PSA and did not detect alpha-fetoprotein and newborn calf serum in the samples. Additionally, fluorescence was maintained on the strip for 10 d after the test. With its high sensitivity and convenience, the devised LFIA kit can be used for the diagnosis of prostate cancer.

Electrochemical sandwich-type immunosensor for the detection of PSA based on a trimetallic AgAuPt nanocomposite synthesized using the galvanic replacement reaction

A sandwich-type electrochemical immunoassay was introduced for the determination of the prostate-specific antigen (PSA) biomarker. A direct and simple galvanic replacement reaction was performed between the Ag framework and metallic salts of tetrachloroauric(iii) acid trihydrate and chloroplatinic acid to produce a trimetallic composite of AgAuPt. The trimetallic composite of AgAuPt was applied to the preparation of the capture layer of the immunoassay for stabilizing the primary Ab at the surface of the prepared composite. The immunoassay detection layer was also prepared using a labeled antibody containing a bimetallic composite of AgPt as a label. The various procedures in the immunoassay fabrication were monitored step by step using cyclic voltammetry and electrochemical impedance spectroscopy. Also, the electrochemical determination of PSA was performed using differential pulse voltammetry in the presence of the ferrocene redox probe and H₂O₂. Furthermore, the effective parameters in the fabrication of the immunoassay included the drop volume of the AgAuPt trimetallic composite and the incubation time for the immobilization of biomolecules (i.e., Ab₁, BSA, PSA, and labeled Ab₂), and the concentration of H₂O₂ were optimized during the determination of PSA. Then, the determination of PSA was performed under optimized conditions. It could be seen that there was a linear relation between the PSA concentration and DPV responses in the concentration range of 50 pg mL^-1 to 500 ng mL^-1 and the limit of detection (LOD) for the proposed immunoassay was calculated as 17.0 pg mL^-1. In the following investigation, the cross-reactivity of the proposed immunoassay was studied in the presence of BSA, CEA, IgG, and human hepatitis surface antigen, in which the results showed a negligible change in the performance of the immunoassay.

Interference-Free Duplex Detection of Total and Active Enzyme Concentrations at a Single Working Electrode

The duplex detection of both total and active enzyme concentrations without interferences at a single working electrode is challenging, especially when two different assays are combined. It is also challenging to obtain two different redox-cycling reactions without interference. Here, we present a simple but sensitive combined assay that is based on two redox-cycling reactions using two incubation periods and applied potentials at a single electrode. The assay combines an immunoassay for the determination of the total enzyme (total prostate-specific antigen, tPSA) concentration with a protease assay for the determination of the active enzyme (free PSA, fPSA) concentration. The immunoassay label and fPSA that are affinity-bound to the electrode are used for high sensitivity and specificity in the protease assay as well as the immunoassay. In the immunoassay, electrochemical-enzymatic (EN) redox cycling involving ferrocenemethanol is obtained at 0.1 V versus Ag/AgCl without incubation before the proteolytically released 4-amino-1-naphthol is generated. In the protease assay, EN redox cycling involving 4-amino-1-naphthol is obtained at 0.0 V after 30 min of incubation without ferrocenemethanol electro-oxidation. The detection procedure is almost the same as common electrochemical sandwich-type immunoassays, although the two different assays are combined. The duplex detection in buffer and serum is highly interference-free, specific, and sensitive. The detection limits for tPSA and fPSA are approximately 10 and 1 pg/mL, respectively.

Focusing aptamer selection on the glycan structure of prostate-specific antigen: Toward more specific detection of prostate cancer

The development of chemical sensors capable of detecting the specific glycosylation patterns of proteins offers a powerful mean for the early detection of cancer. Unfortunately, this strategy is scarcely explored because receptors recognizing the glycans linked to proteins are challenging to discover. In this work, we describe a simple method for directing the selection of aptamers toward the glycan structure of the glycoproteins, with prostate-specific antigen (PSA) as a model target. Using this strategy, we identified one aptamer (PSA-1) that binds the glycan moiety of PSA with reasonable affinity (a dissociation constant of 177 ± 65 nM). Interestingly, an electrochemical sensor with a sandwich format employing the identified aptamer as a signaling receptor, provides a tool of discriminating human PSA from the unglycosylated protein, with a limit of detection of 0.66 ng/mL. The sensor responds to different levels of PSA in serum, correlating well with chemiluminescence ELISA used in hospitals even with higher potential to discriminate clinically meaningful prostate cancer. Although validation on a larger cohort is needed, this is the first demonstration of an aptamer-based sensor to detect PSA by focusing in its glycan moiety.

Selected landscape phage probe as selective recognition interface for sensitive total prostate-specific antigen immunosensor

The level of total prostate-specific antigen (t-PSA) is generally known as the key index of prostate cancer. Here, phage probes against t-PSA were selected from f8/8 landscape phage library. After three rounds of biopanning, four t-PSA-binding phage clones were isolated and identified by the DNA sequencing. Based on the phage capture assay, the phage clone displaying the fusion peptide ATRSANGM showed highest affinity and specificity against t-PSA. Subsequently, the t-PSA-specific phage was used as t-PSA capture probe in a sandwich enzyme-linked immunosorbent assay (ELISA) and differential pulse voltammetry (DPV) assay systems. Both assay methods showed high specificity and acceptable reliability for real serum samples analysis. By comparison, DPV method showed wider linear range (0.01-100 ng mL^-1) and lower limit of detection (3 pg mL^-1) than those (3.3-330 ng mL^-1 and 1.6 ng mL^-1) of ELISA. Moreover, DPV system showed smaller distinction to the authoritative method in real samples assay. Excitingly, the phage probe based DPV immunosensor showed high sensitivity for the detection of t-PSA and LOD achieved the pg mL^-1 level, which was far lower than those values (usually above 0.1 ng mL^-1) for reported immunosensors based on antibodies. Due to the biocompatibility, multivalency, stability, and high structural homogeneity, the t-PSA-specific landscape phage demonstrates as a novel specific interface in biosensors.

Innovative Diagnostic Methods for Early Prostate Cancer Detection through Urine Analysis: A Review

Prostate cancer is the second most common cause of cancer death among men. It is an asymptomatic and slow growing tumour, which starts occurring in young men, but can be detected only around the age of 40&ndash;50. Although its long latency period and potential curability make prostate cancer a perfect candidate for screening programs, the current procedure lacks in specificity. Researchers are rising to the challenge of developing innovative tools able of detecting the disease during its early stage that is the most curable. In recent years, the interest in characterisation of biological fluids aimed at the identification of tumour-specific compounds has increased significantly, since cell neoplastic transformation causes metabolic alterations leading to volatile organic compounds release. In the scientific literature, different approaches have been proposed. Many studies focus on the identification of a cancer-characteristic &ldquo;odour fingerprint&rdquo; emanated from biological samples through the application of sensorial or senso-instrumental analyses, others suggest a chemical characterisation of biological fluids with the aim of identifying prostate cancer (PCa)-specific biomarkers. This paper focuses on the review of literary studies in the field of prostate cancer diagnosis, in order to provide an overview of innovative methods based on the analysis of urine, thereby comparing them with the traditional diagnostic procedures.