A novel electrochemical biosensing method with double-layered polymer brush modified electrode

We developed a novel electrochemical biosensor electrode that has a potential to reduce background noise for which we constructed an original conductive substrate modified with a double-layered polymer brush structure that is water impermeable and can control biomolecules adsorption/desorption. In this study, a hydrophobic poly(tert-butyl methacrylate) brush layer was prepared on a gold electrode, and then, the tert-butyl group near the outermost surface was dissociated by the acid treatment to obtain a hydrophilic carboxy group, thereby fabricating a conductive substrate with the double-layered polymer brush structure. Formation of the double-layered polymer brush structure was indicated by surface wettability and optical analyses. The potential difference and hydrogen ion concentration, which is a typical parameter of the surrounding environment, were linearly correlated with the gold electrode having a double-layered polymer brush structure with carboxyl groups. However, there was no correlation on gold electrodes with self-assembled monolayers presenting carboxy groups. It is considered that the pH responsiveness of the carboxy groups on the outermost surface could be exhibited remarkably because the charge state in the vicinity of the surface became constant due to the hydrophobic polymer brush layer having a certain thickness. The target DNA could be captured more efficiently at the probe DNA-immobilized electrode with the double-layered polymer brush structure than when using COOH-SAM. This is the first report of the application of the double-layered polymer brush structure for the electrochemical biosensing, and it will be an excellent surface modification method to reduce background noise.

Functional nucleic acid biosensors utilizing rolling circle amplification

Functional nucleic acids regulate rolling circle amplification to produce multiple detection outputs suitable for the development of point-of-care diagnostic devices.

Recent advances in biological detection with rolling circle amplification: design strategy, biosensing mechanism, and practical applications

Rolling circle amplification (RCA) is a simple and isothermal DNA amplification technique that is used to generate thousands of repeating DNA sequences using circular templates under the catalysis of DNA polymerase.

A DNA Electrochemical Sensor via Terminal Protection of Small-Molecule-Linked DNA for Highly Sensitive Protein Detection

The qualitative and quantitative determination of marker protein is of great significance in the life sciences and in medicine. Here, we developed an electrochemical DNA biosensor for protein detection based on DNA self-assembly and the terminal protecting effects of small-molecule-linked DNA. This strategy is demonstrated using the small molecule biotin and its receptor protein streptavidin (SA). We immobilized DNA with a designed structure and sequence on the surface of the gold electrode, and we named it M1-Biotin DNA. M1-Biotin DNA selectively combines with SA to generate M1-Biotin-SA DNA and protects M1-Biotin DNA from digestion by EXO III; therefore, M1-Biotin DNA remains intact on the electrode surface. M1-Biotin-SA DNA was modified with methylene blue (MB); the MB reporter molecule is located near the surface of the gold electrode, which generates a substantial electrochemical signal during the detection of SA. Through this strategy, we can exploit the presence or absence of an electrochemical signal to provide qualitative target protein determination as well as the strength of the electrochemical signal to quantitatively analyze the target protein concentration. This strategy has been proven to be used for the quantitative analysis of the interaction between biotin and streptavidin (SA). Under optimal conditions, the detection limit of the proposed biosensor is as low as 18.8 pM, and the linear range is from 0.5 nM to 5 μM, showing high sensitivity. The detection ability of this DNA biosensor in complex serum samples has also been studied. At the same time, we detected the folate receptor (FR) to confirm that this strategy can be used to detect other proteins. Therefore, this electrochemical DNA biosensor provides a sensitive, low-cost, and fast target protein detection platform, which may provide a reliable and powerful tool for early disease diagnosis.

Protein detection based on rolling circle amplification sensors

Rolling circle amplification (RCA) is an isothermal process under the action of DNA polymerases. Large-scale DNA templates have been generated using RCA for target detection. Some signal amplification strategies including optical sensors and electrochemical sensors based on RCA have been applied to achieve sensitive detection. Sensors based on RCA have attracted increasing interest. Advances in RCA-based sensors for protein detection are reviewed in this paper. The advantages and detection mechanisms of sensors based on RCA are revealed and discussed. Finally, possible challenges and future perspectives are also outlined.

A novel steric effect-regulated isothermal exponential amplification technology for the one-step homogeneous sensing of proteins

A novel approach utilizing the steric effect and isothermal exponential amplification for one-step homogeneous sensing of proteins.

Revealing and Resolving the Restrained Enzymatic Cleavage of DNA Self-Assembled Monolayers on Gold: Electrochemical Quantitation and ESI-MS Confirmation

Herein, we report a combined electrochemical and ESI-MS study of the enzymatic hydrolysis efficiency of DNA self-assembled monolayers (SAMs) on gold, platform systems for understanding nucleic acid surface chemistry, and for constructing DNA-based biosensors. Our electrochemical approach is based on the comparison of the amounts of surface-tethered DNA nucleotides before and after exonuclease I (Exo I) incubation using electrostatically bound [Ru(NH₃)₆]³⁺ as redox indicators. It is surprising to reveal that the hydrolysis efficiency of ssDNA SAMs does not depend on the packing density and base sequence, and that the cleavage ends with surface-bound shorter strands (9-13 mers). The ex-situ ESI-MS observations confirmed that the hydrolysis products for ssDNA SAMs (from 24 to 56 mers) are dominated with 10-15 mer fragments, in contrast to the complete digestion in solution. Such surface-restrained hydrolysis behavior is due to the steric hindrance of the underneath electrode to the Exo I/DNA binding, which is essential for the occurrence of Exo I-catalyzed processive cleavage. More importantly, we have shown that the hydrolysis efficiency of ssDNA SAMs can be remarkably improved by adopting long alkyl linkers (locating DNA strands further away from the substrates).

The analysis of proteins and small molecules based on sterically tunable nucleic acid hyperbranched rolling circle amplification

In this work, we succeeded in establishing a new method for proteins and small molecules analysis based on the small molecule-linked DNA and nucleic acid hyperbranched rolling circle amplification (HRCA). Small molecule linked DNA by chemical modification was used as a flexible tool to study protein-small molecule interactions. The HRCA reaction which would produce signal amplification was regulated by the steric effect depending on whether the target proteins were present. In the implement of the proposed strategy, streptavidin (SA)-biotin and anti-digoxin antibody (anti-Dig)-digoxin were chosen as two model partners. Experimental results showed that the quantitative detection of SA and anti-Dig was realized both with nanomolar detection limits. The small molecules biotin and digoxin were also detected at nanomolar levels in a wide range of 1nM~100µM and 1nM~10µM, respectively. Meanwhile, the results indicated that the method had a favorable specificity in analyzing proteins or small molecules. Thus, it may be expected to quantitatively analyze some protein markers and small molecular drugs in complex biological samples.

A WS2 nanosheet-based nanosensor for the ultrasensitive detection of small molecule–protein interaction via terminal protection of small molecule-linked DNA and Nt.BstNBI-assisted recycling amplification

A novel, ultrasensitive and specific fluorescent nanosensor for the detection of small molecule–protein interaction based on the terminal protection of small molecule-linked DNA and Nt.BstNBI-assisted recycling amplification was reported.

High performance system for protein assays: synergistic effect of terminal protection strategy and graphene oxide platform

A straightforward biosensor for protein assay has been developed based on terminal protection of small molecule-linked DNA by target protein and the difference in affinity of graphene oxide for ssDNA containing different numbers of bases in length.

Real-time detection of H5N1influenza virus through hyperbranched rolling circle amplification

In the HRCA process, by replacing heat shock by pH shock, H₅N₁was detected at 9 fM more easily and safely.

Terminal protection of small molecule-linked DNA for small molecule-protein interaction assays

Methods for the detection of specific interactions between diverse proteins and various small-molecule ligands are of significant importance in understanding the mechanisms of many critical physiological processes of organisms. The techniques also represent a major avenue to drug screening, molecular diagnostics, and public safety monitoring. Terminal protection assay of small molecule-linked DNA is a demonstrated novel methodology which has exhibited great potential for the development of simple, sensitive, specific and high-throughput methods for the detection of small molecule–protein interactions. Herein, we review the basic principle of terminal protection assay, the development of associated methods, and the signal amplification strategies adopted for performance improving in small molecule–protein interaction assay.