Application of RNA Aptamers as Recognition Layers for the Electrochemical Analysis of C-Reactive Protein

Recent trends in aptamer-based nanobiosensors for detection of vascular endothelial growth factors (VEGFs) biomarker: A review

Vascular endothelial growth factor (VEGF) is a remarkable cytokine that plays an important role in regulating vascular formation during the angiogenesis process. Therefore, real-time detection and quantification of VEGF is essential for clinical diagnosis and treatment due to its overexpression in various tumors. Among various sensing strategies, the aptamer-based sensors in combination with biological molecules improve the detection ability VEGFs. Aptamers are suitable biological recognition agents for the preparation of sensitive and reproducible aptasensors (Apt-sensors) due to their low immunogenicity, simple and straightforward chemical modification, and high resistance to denaturation. Here, a summary of the strategies for immobilization of aptamers (e.g., direct or self-assembled monolayer (SAM) attachment, etc.) on different types of electrodes was provided. Moreover, we discussed nanoparticle deposition techniques and surface modification methods used for signal amplification in the detection of VEGF. Furthermore, we are investigating various types of optical and electrochemical Apt-sensors used to improve sensor characterization in the detection of VEGF biomarkers.

Highly Sensitive RNA-Based Electrochemical Aptasensor for the Determination of C-Reactive Protein Using Carbon Nanofiber-Chitosan Modified Screen-Printed Electrode

C-reactive protein (CRP) is one of the biomarkers related to coronavirus disease 2019 (COVID-19). Therefore, it is crucial to develop a highly sensitive, selective, and cost-effective biosensor for the determination of CRP. In this study, we designed an electrochemical aptasensor. For this purpose, the surface of a carbon screen-printed electrode was first modified with a carbon nanofiber-chitosan (CNFs-CHIT) nanocomposite. After that, the amino-terminal RNA aptamer probes were linked to the amino groups of CHIT via glutaraldehyde as the cross-linker. Finally, methylene blue (MB) as a redox probe was self-assembled on the surface of the aptasensor. The obtained results indicated that the CNFs-CHIT nanocomposite increased the surface coverage of the aptamer up to 5.9 times. The square-wave voltammetry was used for the measurement of CRP concentration in the linear range of 1.0–150.0 pM. The obtained results indicated that the signal had a logarithmic relationship with the concentration of CRP. The limit of detection (LOD) was obtained to be 0.37 pM. The dissociation constant (K_d) that demonstrates the affinity of the aptamer probe to its target was found to be 0.93 pM. The analytical performances of the proposed RNA aptasensor were better than the previously reported aptasensors for CRP. The proposed aptasensor was also applied for the determination of CRP in the human plasma samples. The obtained results indicated that there were no statistically significant differences between the responses of the proposed RNA aptasensor and an enzyme-linked immunosorbent assay kit (ELISA). The analytical performances of the proposed RNA aptasensor described in this paper are better than previously reported aptasensors for CRP determination.

Immobilization Techniques for Aptamers on Gold Electrodes for the Electrochemical Detection of Proteins: A Review

The development of reliable biosensing platforms plays a key role in the detection of proteins in clinically and environmentally derived samples for diagnostics, as well as for process monitoring in biotechnological productions. For this purpose, the biosensor has to be stable and reproducible, and highly sensitive to detect potentially extremely low concentrations and prevent the nonspecific binding of interfering compounds. In this review, we present an overview of recently published (2017–2019) immobilization techniques for aptamers on gold electrodes for the electrochemical detection of proteins. These include the direct immobilization of thiolated aptamers and the utilization of short linkers, streptavidin/biotin interaction, as well as DNA nanostructures and reduced graphene oxide as immobilization platforms. Applied strategies for signal amplification and the prevention of biofouling are additionally discussed, as they play a crucial role in the design of biosensors. While a wide variety of amplification strategies are already available, future investigations should aim to establish suitable antifouling strategies that are compatible with electrochemical measurements. The focus of our review lies on the detailed discussion of the underlying principles and the presentation of utilized chemical protocols in order to provide the reader with promising ideas and profound knowledge of the subject, as well as an update on recent discoveries and achievements.

A simple aptamer-based colorimetric assay for rapid detection of C-reactive protein using gold nanoparticles

C-reactive protein (CRP) is a clinical biomarker for inflammatory diseases. In this work, we present a simple and fast colorimetric method for CRP detection that employs citrate-capped gold nanoparticles (AuNPs) and a CRP-binding aptamer as sensing elements. The aptamer consisted in a guanine rich single-stranded DNA (ssDNA) that adsorbs onto the surface of the AuNPs. In the presence of the CRP, the ssDNA releases from the AuNPs surface to interact preferentially with the protein to form guanine-quadruplexes. The exposure of the unprotected AuNPs to buffer salts leads to aggregation and subsequent color change from red-wine to blue-purple that was readily seen by the naked eye. The AuNPs aggregation was monitored using UV-Vis spectroscopy and the CRP concentration in the samples could be correlated with the aggregation ratio (A_670nm/A_520nm). A linear sensing range of 0.889-20.7 μg/mL was found. The detection limit (LOD) was 1.2 μg/mL which is comparable to the typical clinical cutoff concentration in high-sensitivity CRP assays (1 μg/mL) and lower than the detection limit of nephelometric methods used in clinical practice. This method can provide a fast (5 min analysis time), simple, and sensitive way for CRP detection, with negligible interference of bovine serum albumin (BSA) up to concentrations of 100 nM.

Development of DNA aptamer-based sensor for electrochemical detection of C-reactive protein

C-reactive protein (CRP) is a crucial biomarker of cardiovascular diseases and for its detection both optical and electrochemical techniques were applied. This study concerns the application of DNA aptamer as recognition layer for CRP detection. For that purpose aptamer immobilization method on gold surface was selected and the content of receptor layer was optimized to ensure an efficient binding to target protein. The quality of the monolayer was verified by the application of chronocoulometry and atomic force microscopy. Using thiolated aptamers provided the formation of layers of highest density and stability. The square-wave voltammetry experiments performed in the presence of methylene blue redox indicator revealed a linear response of aptasensor towards CRP in the range from 1 to 100 pM. Moreover, a DNA aptamer - based sensor showed good selectivity towards C-reactive protein in comparison to interfering proteins including BSA and IgE. Finally, the analysis of CRP in serum sample was conducted using the developed aptasensor.