A rapid method for detection of PrP by surface plasmon resonance (SPR)

A microfluidic biosensor for the diagnosis of chronic wasting disease

Cervids are affected by a neurologic disease that is always fatal to individuals and has population effects. This disease is called chronic wasting disease (CWD) and is caused by a misfolded prion protein. The disease is transmitted via contact with contaminated body fluids and tissue or exposure to the environment, such as drinking water or food. Current CWD diagnosis depends on ELISA screening of cervid lymph nodes and subsequent immunohistochemistry (IHC) confirmation of ELISA-positive results. The disease has proven to be difficult to control in part because of sensitivity and specificity issues with the current test regimen. We have investigated an accurate, rapid, and low-cost microfluidic microelectromechanical system (MEMS) biosensing device for the detection of CWD pathologic prions in retropharyngeal lymph nodes (RLNs), which is the current standard type of CWD diagnostic sample. The device consists of three novel regions for concentrating, trapping, and detecting the prion. The detection region includes an array of electrodes coated with a monoclonal antibody against pathologic prions. The experimental conditions were optimized using an engineered prion control antigen. Testing could be completed in less than 1 hour with high sensitivity and selectivity. The biosensor detected the engineered prion antigen at a 1:24 dilution, while ELISA detected the same antigen at a 1:8 dilution. The relative limit of detection (rLOD) of the biosensor was a 1:1000 dilution of a known strong positive RLN sample, whereas ELISA showed a rLOD of 1:100 dilution. Thus, the biosensor was 10 times more sensitive than ELISA, which is the currently approved CWD diagnostic test. The biosensor's specificity and selectivity were confirmed using known negative RPLN samples, a negative control antibody (monoclonal antibody against bovine coronavirus BCV), and two negative control antigens (bluetongue virus and Epizootic hemorrhagic disease virus). The biosensor's ability to detect pathogenic prions was verified by testing proteinase-digested positive RLN samples.

A new photoelectrochemical immunosensor for ultrasensitive assay of prion protein based on hemin-induced photocurrent direction switching

As a significant biomarker of prion diseases, ultrasensitive assay of infectious isoform of prion (PrP^Sc) is highly desirable for early diagnostics of prion diseases. Herein, taking normal cellular form of prion (PrP^C) as a model owing to a high risk of pathogenicity of PrP^Sc, a new photoelectrochemical immunosensor has been developed based on hemin-induced switching of photocurrent direction. In the presence of PrP^C, nitrogen-doped porous carbon-hemin polyhedra labeled with secondary antibody were introduced onto the CdS-chitosan (CS) nanoparticles-modified indium-tin oxide (ITO) electrode via the antigen-antibody specific recognition. Because of the matched energy level between CdS and hemin, the high-efficiency switch of photocurrent direction of the ITO/CdS-CS photoelectrode from anodic to cathodic photocurrent was observed even at very low concentration (0.4 aM) of PrP^C. Through changing the specific antibody, this method can be easily expanded to PrP^Sc assay. Such low detectable limit is very useful in the early diagnosis and screening of prion diseases. The developed method has also promising applications in bioanalysis, disease diagnostics, and clinical biomedicine.

Qualitative and Quantitative Detection of PrPSc Based on the Controlled Release Property of Magnetic Microspheres Using Surface Plasmon Resonance (SPR)

Prion protein (PrP^Sc) has drawn widespread attention due to its pathological potential to prion diseases. In this work, we constructed a novel surface plasmon resonance (SPR) detection assay involving magnetic microspheres (MMs) and its controlled release property, for selective capture, embedding, concentration, and SPR detection of PrP^Sc with high sensitivity and specificity. Aptamer-modified magnetic particles (AMNPs) were used to specifically capture PrP^Sc. Amphiphilic copolymer was used to embed the labeled PrP^Sc and form magnetic microspheres to isolate PrP^Sc from the external environment. Static magnetic and alternating magnetic fields were used to concentrate and control release the embedded PrP^Sc, respectively. Finally, the released AMNPs-labeled PrP^Sc was detected by SPR which was equipped with a bare gold sensing film. A good linear relationship was obtained between SPR responses and the logarithm of PrP^Sc concentrations over a range of 0.01-1000 ng/mL. The detection sensitivity for PrP^Sc was improved by 10 fold compared with SPR direct detection format. The specificity of the present biosensor was also determined by PrP^C and other reagents as controls. This proposed approach could also be used to isolate and detect other highly pathogenic biomolecules with similar structural characteristics by altering the corresponding aptamer in the AMNPs conjugates.

A new electrochemical immunoassay for prion protein based on hybridization chain reaction with hemin/G-quadruplex DNAzyme

In this work, a new electrochemical immunosensor was developed for prion protein assay based on hybridization chain reaction (HCR) with hemin/G-quadruplex DNAzyme for signal amplification. In this amplification system, the hemin/G-quadruplex DNAzyme simultaneously mimicked the biocatalytic functions for H₂O₂ reduction and L-cysteine oxidation. In the presence of L-cysteine, the hemin/G-quadruplex catalyzed the oxidation of L-cysteine to L-cystine. At the same time, H₂O₂ was produced under the oxygen condition. Then, the hemin/G-quadruplex could quickly catalyze the reduction of H₂O₂, mimicking the catalytic performance of horseradish peroxidase (HRP). Under the optimal conditions, the immunosensor showed a wide linear response range from 0.5 pg/mL to 100 ng/mL with the low detection limit of 0.38 pg/mL (3σ). By changing the specific antibody, this strategy could be easily extended to detect the infectious isoform of prion (PrP^Sc) and other proteins. Based on its good analytical performance, the developed method shows great potential applications in diagnosis of prion diseases at presymptomatic stage and bioanalysis.

A new electrochemical immunosensor for sensitive detection of prion based on Prussian blue analogue

Based on Co-Co Prussian blue analogue (Co-Co PBA), a novel immunosensor has been developed for sensitive detection of prion protein (PrP^C). Gold nanoparticles (AuNPs)-modified Co-Co PBA nanocubes (PBA-AuNPs) worked as a support of the antibody (Ab2) of PrP^C to obtain Ab2-PBA-AuNPs composite and also as the signal source for PrP^C assay. When PrP^C existed, Ab2-PBA-AuNPs could be introduced to the surface of another antibody of PrP^C (Ab1) modified AuNPs/GC electrode (the gold nanoparticles-modified glassy carbon electrode) through specific antigen-antibody interaction between PrP^C and its antibodies to form the Ab1-PrP^C-Ab2 sandwich structure. With the help of KOH aqueous solution, PBA generated a large DPV response. The response peak currents were linear with the logarithmic values of the concentration of PrP^C in the range from 0.075pgmL^-1 to 100pgmL^-1 with the detection limit of 0.014pgmL^-1. Also, the immunosensor showed good selectivity and reproducibility. Based on the simple sensing structure and good analytical performance, the developed immunosensor may have promising applications in practical assay of infectious isoform of prion (PrP^Sc) and other proteins by simply changing the related antibody.

Quick and sensitive SPR detection of prion disease-associated isoform (PrPSc) based on its self-assembling behavior on bare gold film and specific interactions with aptamer-graphene oxide (AGO)

Herein, we constructed a novel sandwich surface plasmon resonance (SPR) detection assay for sensitive prion disease-associated isoform (PrP^Sc) detection, utilizing bare gold film and apatamer-graphene oxide (AGO). Due to the self-assembling behavior of PrP^Sc on gold surface, the non-modified gold surface can be directly used as sensing surface for the quick detection, for the purpose to avoid the interference from the traditional, complex and changeable probe-modified sensing surface. And due to the highly specific affinity of AGO towards PrP^Sc, the sandwich type SPR sensor exhibits excellent analytical performance towards the discrimination and quantitation of PrP^Sc. A good linear relationship was obtained between SPR responses and the logarithm of PrP^Sc concentrations over a range of 0.001-1ng/mL. The detection sensitivity for PrP^Sc was improved by ∼156 orders of AGO compared with SPR direct detection format. Besides, morphological changes of the sensing film surfaces were investigated by high resolution AFM imaging, confirming the capture of PrP^Sc molecules and their further specific recognition by AGO. The specificity of the present biosensor was also investigated by PrP^C and other regents as controls. By compared with other reported methods, the AGO enhanced sandwich SPR assay was confirmed to be efficient, sensitive, and with wide working range.

Surface plasmon resonance based biosensor: A new platform for rapid diagnosis of livestock diseases

Surface plasmon resonance (SPR) based biosensors are the most advanced and developed optical label-free biosensor technique used for powerful detection with vast applications in environmental protection, biotechnology, medical diagnostics, drug screening, food safety, and security as well in livestock sector. The livestock sector which contributes the largest economy of India, harbors many bacterial, viral, and fungal diseases impacting a great loss to the production and productive potential which is a major concern in both small and large ruminants. Hence, an accurate, sensitive, and rapid diagnosis is required for prevention of these above-mentioned diseases. SPR based biosensor assay may fulfill the above characteristics which lead to a greater platform for rapid diagnosis of different livestock diseases. Hence, this review may give a detail idea about the principle, recent development of SPR based biosensor techniques and its application in livestock sector.

A label-free and cascaded dual-signaling amplified electrochemical aptasensing platform for sensitive prion assay

Prion proteins, as an important biomarker of prion disease, are responsible for the transmissible spongiform encephalopathies (a group of fatal neurodegenerative diseases). Hence, the sensitive detection of prion protein is very essential for biological studies and medical diagnostics. In this paper, a novel label-free and cascaded dual-signaling amplified electrochemical strategy was developed for sensitive and selective analysis of cellular prion protein (PrP(C)). The recognition elements included double-stranded DNA consisted of PrP(C)-binding aptamer (DNA1) and its partially complementary DNA (DNA2), and ordered mesoporous carbon probe (OMCP) fabricated by sealing the electroactive ferrocenecarboxylic acid (Fc) into its inner pores and then using single-stranded DNA (DNA3) as the gatekeeper. In the presence of PrP(C), DNA1 could bind the target protein and free DNA2. More importantly, DNA2 could hybridize with DNA3 to form a rigid duplex DNA and thus triggered the exonuclease III (Exo III) cleavage process to realize the DNA2 recycling, accompanied by opening more biogates and releasing more Fc. The released Fc could be further used as a competitive guest of β-cyclodextrin (β-CD) to displace the Rhodamine B (RhB) on the electrode. As a result, an amplified oxidation peak current of Fc (RhB) increased (decreased) with the increase of PrP(C) concentration. When "ΔI=ΔIFc+|ΔIRhB|" (ΔIFc and ΔIRhB were the change values of the oxidation peak currents of Fc and RhB, respectively.) was used as the response signal for quantitative determination of PrP(C), the detection limit was 7.6fM (3σ), which was much lower than that of the most reported methods for PrP(C) assay. This strategy provided a simple and sensitive approach for the detection of PrP(C) and has a great potential for bioanalysis, disease diagnostics, and clinical biomedicine applications.

Smart protein biogate as a mediator to regulate competitive host-guest interaction for sensitive ratiometric electrochemical assay of prion

A novel competitive host-guest strategy regulated by protein biogate was developed for sensitive and selective analysis of prion protein. The methylene blue (MB)-tagged prion aptamer (MB-Apt) was introduced to the multiwalled carbon nanotubes-β-cyclodextrins (MWCNTs-β-CD) composites-modified glassy carbon (GC) electrode through the host-guest interaction between β-CD and MB. In the absence of prion, MB-Apt could be displaced by ferrocenecarboxylic acid (FCA) due to its stronger binding affinity to β-CD, resulting in a large oxidation peak of FCA. However, in the presence of prion, the specific prion-aptamer interaction drove the formation of protein biogate to seal the cavity of β-CD, which hindered the guest displacement of MB by FCA and resulted in the oxidation peak current of MB (I_MB) increased and that of FCA (I_FCA) decreased. The developed aptasensor showed good response towards the target (prion protein) with a low detection limit of 160 fM. By changing the specific aptamers, this strategy could be easily extended to detect other proteins, showing promising potential for extensive applications in bioanalysis.

Development of a biological protocol for endotoxin detection using quartz crystal microbalance (QCM)

In this paper, a biological protocol for endotoxin detection has been developed and optimized by quartz crystal microbalance (QCM). The parameters involved in the formation of the self-assembled monolayer (SAM) have been analyzed, and a study of the pH of the ligand buffer has been performed in order to find the best condition for the ligand immobilization and, in consequence, for the endotoxin detection. The detection limit obtained with the characterized biological protocol corresponds to 1.90 μg/ml. The effectiveness of the optimized biological protocol has been analyzed by cyclic voltammetry analysis.

Electrochemical aptasensor of human cellular prion based on multiwalled carbon nanotubes modified with dendrimers: a platform for connecting redox markers and aptamers

The present work aims to develop an electrochemical biosensor based on aptamer able to detect human cellular prions PrP(C) as a model biomarker of prion disease with high sensitivity. We designed the biosensor using multiwalled carbon nanotubes (MWCNTs) modified with polyamidoamine dendrimers of fourth generation (PAMAM G4) which in turn were coupled to DNA aptamers used as bioreceptors. Electrochemical signal was detected by a ferrocenyl redox marker incorporated between the dendrimers and aptamers interlayer. MWCNTs, thanks to their nanostructure organization and electrical properties, allow the distribution of aptamers and redox markers over the electrode surface. We demonstrated that the interaction between aptamers and prion proteins leads to variation in the electrochemical signal of the ferrocenyl group. High sensitivity with a detection limit of 0.5 pM and a wide linear range of detection from 1 pM to 10 μM has been demonstrated. Detection of PrP(C) in spiked blood plasma has been achieved in the same range of concentrations as for detection of PrP(C) in buffer. The sensor demonstrated a recovery of minimum 85% corresponding to 1 nM PrP(C) and a maximum of 127% corresponding to 1 pM PrP(C).

Binding kinetics of human cellular prion detection by DNA aptamers immobilized on a conducting polypyrrole

We developed a biosensor based on the surface plasmon resonance (SPR) method for the study of the binding kinetics and detection of human cellular prions (PrP(C)) using DNA aptamers as bioreceptors. The biosensor was formed by immobilization of various biotinylated DNA aptamers on a surface of conducting polypyrrole modified by streptavidin. We demonstrated that PrP(C) interaction with DNA aptamers could be followed by measuring the variation of the resonance angle. This was studied using DNA aptamers of various configurations, including conventional single-stranded aptamers that contained a rigid double-stranded supporting part and aptamer dimers containing two binding sites. The kinetic constants determined by the SPR method suggest strong interaction of PrP(C) with various DNA aptamers depending on their configuration. SPR aptasensors have a high selectivity to PrP(C) and were regenerable by a brief wash in 0.1 M NaOH. The best limit of detection (4 nM) has been achieved with this biosensor based on DNA aptamers with one binding site but containing a double-stranded supporting part.