Detection of C Reactive Protein (CRP) in Serum by an Electrochemical Aptamer-Based Sandwich Assay

Development of an electrochemical RNA-aptasensor to detect human osteopontin

Electrochemical aptasensors may be used to detect protein biomarkers related to tumor activity. Osteopontin (OPN), a protein present in several body fluids, has been suggested as a potential biomarker since its overexpression seems to be associated with breast cancer progression and metastasis. In this work, a simple and label-free voltammetric aptasensor for the detection of OPN, using an RNA aptamer previously reported to have affinity for human OPN as the molecular recognition element, and the ferro/ferricyanide solution as a redox probe, was developed. The RNA aptamer was synthetized and immobilized in a working microelectrode gold surface (diameter of 0.8mm) of a screen-printed strip with a silver pseudo-reference electrode and a gold counter electrode. The electrochemical behavior of the electrode surface after each preparation step of the aptasensor was studied using cyclic voltammetry and square wave voltammetry. The resulting voltammetric aptasensor was used to detect OPN in standard solutions. Cyclic voltammetry results showed that the aptasensor has reasonable detection and quantification limits (3.7 ± 0.6 nM and 11 ± 2 nM, respectively). Indeed, the detection limit falls within the osteopontin levels reported in the literature for patients with metastatic breast cancer. Moreover, the aptasensor is able to selectively detect the target protein in the presence of other interfering proteins, except for thrombin. Considering the overall results, a possible application of the aptasensor for cancer prognosis may be foreseen in a near future.

Development of a bead-based aptamer/antibody detection system for C-reactive protein

A multiplexing bead-based platform provides an approach for the development of assays targeting specific analytes for biomonitoring and biosensing applications. Multi-Analyte Profiling (xMAP) assays typically employ a sandwich-type format using antibodies for the capture and detection of analytes of interest, and the system permits the simultaneous quantitation of multiple targets. In this study, an aptamer/antibody assay for the detection of C-reactive protein (CRP) was developed. CRP is an acute phase marker of inflammation whose elevated basal levels are correlated with an increased risk for a number of pathologies. For this assay, an RNA aptamer that binds CRP was conjugated to beads to act as the capture agent. Biotinylated anti-CRP antibody coupled to fluorescently labeled streptavidin was used for quantification of CRP. The detection limit of the CRP assay was 0.4 mg/L in diluted serum. The assay was then used to detect spiked CRP samples in the range of 0.4 to 10mg/L in diluted serum with acceptable recoveries (extrapolated values of 70-130%), including that of a certified reference material (129% recovery). The successful incorporation of the CRP aptamer into this platform demonstrates that the exploration of other aptamer-target systems could increase the number of analytes measurable using xMAP-type assays.

Sensitive detection of C-reactive protein using optical fiber Bragg gratings

An accurate and highly sensitive sensor platform has been demonstrated for the detection of C-reactive protein (CRP) using optical fiber Bragg gratings (FBGs). The CRP detection has been carried out by monitoring the shift in Bragg wavelength (ΔλB) of an etched FBG (eFBG) coated with an anti-CRP antibody (aCRP)-graphene oxide (GO) complex. The complex is characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. A limit of detection of 0.01mg/L has been achieved with a linear range of detection from 0.01mg/L to 100mg/L which includes clinical range of CRP. The eFBG sensor coated with only aCRP (without GO) show much less sensitivity than that of aCRP-GO complex coated eFBG. The eFBG sensors show high specificity to CRP even in the presence of other interfering factors such as urea, creatinine and glucose. The affinity constant of ∼1.1×10(10)M(-1) has been extracted from the data of normalized shift (ΔλB/λB) as a function of CRP concentration.

Cardiovascular disease detection using bio-sensing techniques

Universally, cardiovascular disease (CVD) is recognised as the prime cause of death with estimates exceeding 20 million by 2015 due to heart disease and stroke. Facts regarding the disease, its classification and diagnosis are still lacking. Hence, understanding the issues involved in its initiation, its symptoms and early detection will reduce the high risk of sudden death associated with it. Biosensors developed to be used as rapid screening tools to detect disease biomarkers at the earliest stage and able to classify the condition are revolutionising CVD diagnosis and prognosis. Advances in interdisciplinary research areas have made biosensors faster, highly accurate, portable and environmentally friendly diagnostic devices. The recent advances in microfluidics and the advent of nanotechnology have resulted in the development of improved diagnostics through reduction of analysis time and integration of several clinical assays into a single, portable device as lab-on-a-chip (LOC). The development of such affinity based systems is a major drive of the rapidly growing nanotechnology industry which involves a multidisciplinary research effort encompassing nanofluidics, microelectronics and analytical chemistry. This review summarised the classification of CVD, the biomarkers used for its diagnosis, biosensors and their application including the latest developments in the field of heart-disease detection.

Aptamer-based thrombin assay on microfluidic platform

A facile and sensitive aptamer-based protocol has been developed for protein assay on microfluidic platform with fluorescence detection using an off-chip microarray scanner. Aptamer-functionalized magnetic beads were used to capture thrombin that binds to a second aptamer fluorescently labeled by Cy3. Experimental conditions, such as incubation time and temperature, washing time, interfering proteins, and aptamer, etc., were optimized for the microchip method. This work demonstrated there was a good relationship between fluorescence intensity and thrombin concentration in the range of 65-1000 ng/mL with the RSD less than 8%. Notably, an analysis only needs 1 μL volume of sample injection and this system can capture extremely tiny amount thrombin (0.4 fmol). This method has been successfully applied to assay of thrombin in human serum with the recovery of 79.74-95.94%.

Electrochemical bioassay for the detection of TNF-α using magnetic beads and disposable screen-printed array of electrodes

BACKGROUND

In this study we have developed an electrochemical bioassay for the analysis of TNF-α, coupling magnetic beads with disposable electrochemical platforms. TNF-α is a pro inflammatory cytokine that participates in the regulation of immune defense against various pathogens and the recovery from injury. It plays a central role in the development of many inflammatory diseases. The bioassay was based on a sandwich format using alkaline phosphatase as an enzymatic label and an eight-sensor screen-printed array as an electrochemical transducer.

RESULTS

The modified magnetic beads were captured by a magnet on the surface of each graphite working electrode of the array and the electrochemical detection was thus achieved through the addition of the alkaline phosphatase substrate (1-naphthylphosphate); 1-naphthol produced during the enzymatic reaction was detected using differential pulse voltammetry. The parameters influencing the different steps of the assay were optimized in order to reach the best sensitivity and specificity.

CONCLUSION

The proposed strategy offers great promise for analysis of clinical diagnostics, considering also that arrays allow the simultaneous analysis of different samples.

An optimised electrochemical biosensor for the label-free detection of C-reactive protein in blood

C-reactive protein (CRP) is an acute phase protein whose levels are increased in many disorders. There exists, in particular, a great deal of interest in the correlation between blood serum levels and the severity of risk for cardiovascular disease. A sensitive, label-free, non-amplified and reusable electrochemical impedimetric biosensor for the detection of CRP in blood serum was developed herein based on controlled and coverage optimised antibody immobilization on standard polycrystalline gold electrodes. Charge transfer resistance changes were highly target specific, linear with log CRP concentration across a 0.5-50nM range and associated with a limit of detection of 176pM. Significantly, the detection limits are better than those of current CRP clinical methods and the assays are potentially cheap, relatively automated, reusable, multiplexed and highly portable. The generated interfaces were capable not only of comfortably quantifying CRP across a clinically relevant range of concentrations but also of doing this in whole blood serum with interfaces that were, subsequently, reusable. The importance of optimising receptor layer resistance in maximising assay sensitivity is also detailed.

Electrochemical nanomaterial-based nucleic acid aptasensors

Recent progress in the development of electrochemical nanomaterial-aptamer-based biosensors is summarized. Aptamers are nucleic acid ligands that can be generated against amino acids, drugs, proteins, and other molecules. They are isolated from a large random library of synthetic nucleic acids by an iterative process of binding, separation, and amplification, called systematic evolution of ligands by exponential enrichment (SELEX). In this review, different methods of integrating aptamers with different nanomaterials and nanoparticles for electrochemical biosensing application are described.

Magnetic particles in ultrasensitive biomarker protein measurements for cancer detection and monitoring

IMPORTANCE OF THE FIELD: Devices for the reliable detection of panels of biomarker proteins facilitated by magnetic bead-based technologies have the potential to greatly improve future cancer diagnostics. The reason for this review is to highlight promising research on emerging procedures for protein capture, transport and detection featuring magnetic particles. AREAS COVERED IN THIS REVIEW: The review covers applications of magnetic particles in protein immunoassays in emerging research and commercial methods, and stresses multiplexed protein assays for reliable future cancer diagnostics. Research literature over the past dozen years has been surveyed and specific examples are presented in detail. EXPERT OPINION: Magnetic particles are important components of emerging protein detection systems. They need to be integrated into simple inexpensive systems for accurate, sensitive detection of fully validated panels of biomarker proteins to be widely useful in clinical cancer diagnostics.

A Renewable C Reactive Protein Amperometric Immunosensor Based on Magnetic Multiwalled Carbon Nanotubes Probles Modified Electrode

A disposable, magnetism-controlled, and amperometric immunosensor was fabricated for the determination of C reactive protein (CRP). Firstly, Fe3O4 (core)/Au (shell) nanoparticle (GMP)–coated multiwalled carbon nanotubes (MWCNT–GMP) were prepared. Then, monoclonal antibody (anti-CRP) was immobilized on MWCNT–GMP to prepare MWCNT–GMP/anti-CRP composite magnetic probes. At last, the probes was adsorbed on the surface of N,N''-bis-(2-hydroxy-methylene)-o-phenylenediamine cobalt (CoRb) modified, screen-printed carbon electrodes through external magnetic field.The amount of CRP in the serum sample was determined by one-step immunoassay. When different concentrations of CRP were added into25μL of phosphate-buffered solution (pH7.0) containing10-4M H2O2, the percentage of DPV cathodic peak current decrease (CR%) exhibited a linear relationship with the concentration of CRP in the range of 0.3–100 μg L-1.The detection limit was 0.16 μg L-1(3б).The immunosensor was used to determine CRP in serum samples of patients with heart diseases, and the results were consistent with those of the traditional ELISA method. The proposed amperometric immunosensor was sensitive, rapid, magnetic field–controlled, and disposable; therefore, it could be used to determine even traces of CRP in the blood serums of patients with heart diseases.

Electrochemical Aptamer-Based Biosensors: Recent Advances and Perspectives

This paper reviews the advancements of a wide range of electrochemical aptamer-based biosensors, electrochemical aptasensors, for target analytes monitoring. Methods for immobilizing aptamers onto an electrode surface are discussed. Aptasensors are presented according to their detection strategies. Many of these are simply electrochemical, aptamer-based equivalents of traditional immunochemical approaches, sandwich and competition assays employing electroactive signaling moieties. Others, exploiting the unusual physical properties of aptamers, are signal-on (positive readout signal) and signal-off (negative readout signal) aptasensors based on target binding-induced conformational change of aptamers. Aptamer label-free devices are also discussed.

An electrochemical competitive biosensor for ochratoxin A based on a DNA biotinylated aptamer

Ochratoxin A (OTA) is one of the most important mycotoxin contaminants of foods, particularly cereals and cereal products, with strict low regulatory levels (of ppb) in many countries worldwide. An electrochemical competitive aptamer-based biosensor for OTA is described. Paramagnetic microparticle beads (MBs) were functionalized with an aptamer specific to OTA, and were allowed to compete with a solution of the mycotoxin conjugated to the enzyme horseradish peroxidase (OTA-HRP) and free OTA. After separation and washing steps helped with magnetic separations, the modified MBs were localized on disposable screen-printed carbon electrodes (SPCEs) under a magnetic field, and the product of the enzymatic reaction with the substrate was detected with differential-pulse voltammetry. In addition to magnetic separation assays, other competitive schemes (direct/indirect aptasensors performed on the SPCEs surface or using gold nanoparticles functionalized with the aptamer) were preliminary tested, optimized and compared. The magnetic aptasensor showed a linear response to OTA in the range 0.78-8.74 ng mL(-1) and a limit of detection of 0.07±0.01 ng mL(-1), and was accurately applied to extracts of certified and spiked wheat samples with an RSD lower than about 8%.