Prostate Specific Antigen Detection Using Microgapped Electrode Array Immunosensor with Enzymatic Silver Deposition

Electrochemical prostate-specific antigen biosensors based on electroconductive nanomaterials and polymers

Prostate cancer (PCa), the second most malignant neoplasm in men, is also the fifth leading cause of cancer-related deaths in men globally. Unfortunately, this malignancy remains largely asymptomatic until late-stage emergence when treatment is limited due to the lack of effective metastatic PCa therapeutics. Due to these limitations, early PCa detection through prostate-specific antigen (PSA) screening has become increasingly important, resulting in a more than 50% decrease in mortality. Conventional assays for PSA detection, such as enzyme-linked immunosorbent assay (ELISA), are labor intensive, relatively expensive, operator-dependent and do not provide adequate sensitivity. Electrochemical biosensors overcome these limitations because they are rapid, cost-effective, simple to use and ultrasensitive. This article reviews electrochemical PSA biosensors using electroconductive nanomaterials such as carbon-, metal-, metal oxide- and peptide-based nanostructures, as well as polymers to significantly improve conductivity and enhance sensitivity. Challenges associated with the development of these devices are discussed thus providing additional insight into their analytic strength as well as their potential use in early PCa detection.

Electrochemically Controlled ATRP for Cleavage-Based Electrochemical Detection of the Prostate-Specific Antigen at Femtomolar Level Concentrations

As a single-chain glycoprotein with endopeptidase activity, the prostate-specific antigen (PSA) is valuable as an informative serum marker in diagnosing, staging, and prognosis of prostate cancer. In this report, an electrochemical biosensor based on the target-induced cleavage of a specific peptide substrate (PSA peptide) is designed for the highly selective detection of PSA at the femtomolar level, using electrochemically controlled atom transfer radical polymerization (eATRP) as a method for signal amplification. The PSA peptides, without free carboxyl sites, are attached to the gold surface via the N-terminal cysteine residue. The target-induced cleavage of PSA peptides results in the generation of carboxyl sites, to which the alkyl halide initiator α-bromophenylacetic acid (BPAA) is linked via the Zr(IV) linkers. Subsequently, the potentiostatic eATRP of ferrocenylmethyl methacrylate (FcMMA, as the monomer) leads to the surface-initiated grafting of high-density ferrocenyl polymers. As a result, a large amount of Fc redox tags can be recruited for signal amplification, through which the limit of detection (LOD) for PSA can be down to 3.2 fM. As the recognition element, the PSA peptide is easy to synthesize, chemically and thermally stable, and low-cost. Without the necessity of enzyme or nanoparticle labels, the eATRP-based amplification method is easy to operate and low-cost. Results also show that the cleavage-based electrochemical PSA biosensor is highly selective and applicable to PSA detection in complex biological samples. In view of these merits, the integration of the eATRP-based amplification method into cleavage-based recognition is believed to hold great promise for the electrochemical detection of PSA in clinical applications.

Ultrasensitive cholesterol biosensor based on enzymatic silver deposition on gold nanoparticles modified screen-printed carbon electrode

Cholesterol is one of the essential structural constituents of cell membranes. Determination of cholesterol is of great importance in clinical analysis because the level of cholesterol in serum is an indicator in the diagnosis and prevention of heart diseases. In this work, a simple and ultrasensitive cholesterol biosensor based on enzymatic silver deposition was designed by immobilizing cholesterol oxidase (CHOD) and cholesterol esterase (CHER) onto the surface of gold nanoparticles (Au NPs) modified screen-printed carbon electrode (SPE). By the catalytic action of CHER and CHOD, the cholesterol was hydrolyzed to generate hydrogen peroxide (H₂O₂) which can reduced the silver (Ag) ions in the solution for the deposition of metallic Ag on the surface of Au NPs modified SPE. The ultrasensitive detection of cholesterol was achieved by anodic stripping voltammetry (ASV) measurement of the enzymatically deposited Ag. The influence of relevant experimental variables was optimized. The anodic stripping peak current of Ag depended linearly on the concentration of cholesterol in the range of 5-5000μg/mL with the regression correlation coefficient of 0.9983. A detection limit of 3.0μg/mL was attained by 3 sigma-rule. In addition, the ultrasensitive cholesterol biosensor exhibited higher specificity, acceptable reproducibility and excellent recoveries for cholesterol detection.

Highly sensitive covalently functionalized light-addressable potentiometric sensor for determination of biomarker

A biomarker is related to the biological status of a living organism and shows great promise for the early prediction of a related disease. Herein we presented a novel structured light-addressable potentiometric sensor (LAPS) for the determination of a model biomarker, human immunoglobulin G (hIgG). In this system, the goat anti-human immunoglobulin G antibody was used as recognition element and covalently immobilized on the surface of light-addressable potentiometric sensor chip to capture human immunoglobulin G. Due to the light addressable capability of light-addressable potentiometric sensor, human immunoglobulin G dissolved in the supporting electrolyte solution can be detected by monitoring the potential shifts of the sensor. In order to produce a stable photocurrent, the laser diode controlled by field-programmable gate array was used as the light emitter to drive the light-addressable potentiometric sensor. A linear correlation between the potential shift response and the concentration of human immunoglobulin G was achieved and the corresponding regression equation was ΔV (V)=0.00714ChIgG (μg/mL)-0.0147 with a correlation coefficient of 0.9968 over a range 0-150 μg/mL. Moreover, the light-addressable potentiometric sensor system also showed acceptable stability and reproducibility. All the results demonstrated that the system was more applicable to detection of disease biomarkers with simple operation, multiple-sample format and might hold great promise in various environmental, food, and clinical applications.

Diagnosis of prostate cancer via nanotechnological approach

Prostate cancer is one of the leading causes of cancer-related deaths among the Caucasian adult males in Europe and the USA. Currently available diagnostic strategies for patients with prostate cancer are invasive and unpleasant and have poor accuracy. Many patients have been overly or underly treated resulting in a controversy regarding the reliability of current conventional diagnostic approaches. This review discusses the state-of-the-art research in the development of novel noninvasive prostate cancer diagnostics using nanotechnology coupled with suggested diagnostic strategies for their clinical implication.

Recent progress in prostate-specific antigen and HIV proteases detection

Proteases mediate a wide variety of biological events and have a critical role in the development of many diseases. Protease detection methods can be hindered by the limitation of assay safety, sensitivity, specificity, time constraints and ease of on-site analysis. Notably, the implementation of various detection methods on biosensing platforms translates them into practical biosensing applications. Currently, the detection of prostate cancer and AIDS at the earliest occasion is one of the major research obstacles. Therefore, recent advances focus on the development of portable detection systems toward point-of-care testing. These detection systems should be highly sensitive and specific for the detection of their prognostic biomarkers, such as the prostate-specific antigen and HIV load assay for prostate cancer and AIDS, respectively. These methods will also facilitate decision-making on a treatment regimen.

Self-catalytic growth of unmodified gold nanoparticles as conductive bridges mediated gap-electrical signal transduction for DNA hybridization detection

A simple and sensitive gap-electrical biosensor based on self-catalytic growth of unmodified gold nanoparticles (AuNPs) as conductive bridges has been developed for amplifying DNA hybridization events. In this strategy, the signal amplification degree of such conductive bridges is closely related to the variation of the glucose oxidase (GOx)-like catalytic activity of AuNPs upon interaction with single- and double-stranded DNA (ssDNA and dsDNA), respectively. In the presence of target DNA, the obtained dsDNA product cannot adsorb onto the surface of AuNPs due to electrostatic interaction, which makes the unmodified AuNPs exhibit excellent GOx-like catalytic activity. Such catalytic activity can enlarge the diameters of AuNPs in the glucose and HAuCl4 solution and result in a connection between most of the AuNPs and a conductive gold film formation with a dramatically increased conductance. For the control sample, the catalytic activity sites of AuNPs are fully blocked by ssDNA due to the noncovalent interaction between nucleotide bases and AuNPs. Thus, the growth of the assembled AuNPs will not happen and the conductance between microelectrodes will be not changed. Under the optimal experimental conditions, the developed strategy exhibited a sensitive response to target DNA with a high signal-to-noise ratio. Moreover, this strategy was also demonstrated to provide excellent differentiation ability for single-nucleotide polymorphism. Such performances indicated the great potential of this label-free electrical strategy for clinical diagnostics and genetic analysis under real biological sample separation.

In situ enzymatic silver enhancement based on functionalized graphene oxide and layer-by-layer assembled gold nanoparticles for ultrasensitive detection of thrombin

A highly specific in situ amplification strategy was designed for ultrasensitive detection of thrombin by combining the layer-by-layer (LBL) assembled amplification with alkaline phosphatase (ALP) and gold nanoparticles (Au) mediated silver deposition. High-density carboxyl functionalized graphene oxide (FGO) was introduced as a nanocarrier for LBL assembling of alkaline phosphatase decorated gold nanoparticles (ALP-Au), which was further adopted to label thrombin aptamer II. After sandwich-type reaction, numerous ALP were captured onto the aptasensor surface and catalyzed the hydrolysis of ascorbic acid 2-phosphate (AAP), which in situ generated ascorbic acid (AA), reducing Ag(+) to Ag nanoparticles (AgNPs) for electrochemical readout. Inspiringly, the in situ amplification strategy with ethanolamine as an effective blocking agent showed remarkable amplification efficiency, very little nonspecific adsorption, and low background signal, which was favorable to enhance the sensitivity of aptasensor. Our novel dramatic signal amplification strategy, with a detection limit of 2.7 fM, showed about 2-3 orders of magnitude improvement in the sensitivity for thrombin detection compared to other universal enzyme-based electrochemical assay.

Portable and quantitative detection of protein biomarkers and small molecular toxins using antibodies and ubiquitous personal glucose meters

Developing portable and low-cost methods for quantitative detection of large protein biomarkers and small molecular toxins can play a significant role in controlling and preventing diseases or toxins outbreaks. Despite years of research, most current methods still require laboratory-based or customized devices that are not widely available to the general public for quantitative analysis. We have previously demonstrated the use of personal glucose meters (PGMs) and functional DNAs for the detection of many nonglucose targets. However, the range of targets detectable by functional DNAs is limited at the current stage. To expand the range of targets that can be detected by PGMs, we report here the use of antibodies in combination with sandwich and competitive assays for quantitative detection of protein biomarkers (PSA, with a detection limit of 0.4 ng/mL) and small molecular toxins (Ochratoxin A, with a detection limit of 6.8 ng/mL), respectively. In both assay methods, with invertase conjugates as the link, quantitative detection is achieved via the dependence between the concentrations of the targets in the sample and the glucose measured by PGMs. Given the wide availability of antibodies for numerous targets, the methods demonstrated here can expand the range of target detection by PGMs significantly.