Zr4+-mediated hybrid chain reaction and its application for highly sensitive electrochemical detection of protein kinase A

A ratiometric electrochemical biosensor based on ARGET ATRP for detection of HER2 gene

Human epidermal growth factor receptor 2 (HER2), a common proto-oncogene, is overexpressed in a subset of breast cancer patients. It is essential to track HER2 expression for early breast cancer diagnosis. Herein, a ratiometric electrochemical biosensor for detection of HER2 based on activators generated by electron transfer for atom transfer radical polymerisation (AGET ATRP) and hairpin DNA was developed. Specifically, hairpin DNA was first self-assembled on the gold electrode by Au-S bond. Upon capturing HER2, the stem-loop structure of hairpin DNA was unfolded, the signal value of methylene blue (MB) decreased as it moved away from the electrode surface. cDNA was linked with HER2 by complementary base pairing to introduce amino group. Then, the initiator 2-bromo-2-methylpropionic acid (BMP) were connected to the amino group on the cDNA to activate ARGET ATRP. The detection performance of biosensors for HER2 was explored by the ratio signal between two signal molecules. Under optimal conditions, this ratiometric electrochemical biosensor shows good selectivity and stability with a wide detection range of 1-1 × 106 pM and a detection limit of 78.47 fM. Furthermore, the biosensor exhibits satisfactory anti-interference ability due to the hairpin DNA and dual signal system, and has promising application prospects in the detection of other DNA disease markers.

Zr4+-mediated DNAzyme-driven DNA walker amplification strategy for electrochemical assay of protein kinase a activity and inhibition

Protein kinase A (PKA) can regulate many cellular biological processes by phosphorylation substrate peptide or protein. Sensitive detection of PKA activity is critical for the PKA-related drug discovery and disease diagnosis. A new electrochemical biosensing method was developed for detection of PKA activity based on Zr⁴⁺-mediated DNAzyme-driven DNA walker signal amplification strategy. In this strategy, the special designed substrate peptide and a thiolated methylene blue-labeled hairpin DNA (MB-hpDNA) containing a single ribonucleic acid group (rA) could be anchored on the surface of gold electrode by Au-S bond. In the presence of adenosine triphosphate (ATP) and PKA, substrate peptide was phosphorylated and linked with walker DNA (WD) via the robust phosphate-Zr⁴⁺-phosphate chemistry. The linked WD hybridized with the loop region of MB-hpDNA to form a Mn²⁺-dependent deoxynuclease (DNAzyme), which cleaved the MB-hpDNA into MB-labeled fragment releasing away from electrode surface, resulting in a dramatic decrease of electrochemical signal and providing an electrochemical sensing platform for PKA activity detection. The response signal of the developed biosensor is proportional to the logarithm of PKA concentration in the range of 0.05 U mL^-1 to 100 U mL^-1, with a detection limit of 0.017 U mL^-1 at a signal to noise ratio of 3. Furthermore, the proposed method can also be applied for the evaluation of PKA inhibition and PKA activity assay in cell samples. Therefore, the proposed biosensor shows great promise as a universal tool for diagnostics and drug discovery of PKA-related diseases.

Traditional and new applications of the HCR in biosensing and biomedicine

The hybridization chain reaction is a very popular isothermal nucleic acid amplification technology. A single-stranded DNA initiator triggers an alternate hybridization event between two hairpins forming a double helix polymer. Due to isothermal, enzyme-free and high amplification efficiency characteristics, the HCR is often used as a signal amplification technology for various biosensing and biomedicine fields. However, as an enzyme-free self-assembly reaction, it has some inevitable shortcomings of relatively slow kinetics, low cell internalization efficiency, weak biostability of DNA probes and uncontrollable reaction in these applications. More and more researchers use this reaction system to synthesize new materials. New materials can avoid these problems skillfully by virtue of their inherent biological characteristics, molecular recognition ability, sequence programmability and biocompatibility. Here, we summarized the traditional application of the HCR in biosensing and biomedicine in recent years, and also introduced its new application in the synthesis of new materials for biosensing and biomedicine. Finally, we summarized the development and challenges of the HCR in biosensing and biomedicine in recent years. We hope to give readers some enlightenment and help.

Highly Accurate and Fast Electrochemical Detection of Scrub Typhus DNA via a Nanoflower NiFe-Based Biosensor

Owing to the lack of specific diagnostic methods, Scrub typhus can sometimes be difficult to diagnose in the Asia-Pacific region. Therefore, an efficient and rapid detection method urgently needs to be developed. Based on competitive single-stranded DNA over modified glassy carbon electrode (GCE), an electrochemical biosensor was established to detect the disease. The nano-flower NiFe layered double hydroxide (NiFe-LDH) modified GCE has a large specific surface area, which supported a large amount of gold nanoparticles, so that a wide linear detection range from 25 fM to 0.5 μM was obtained. The beacon DNA (B-DNA) with the same sequence as the Scrub typhus DNA (T-DNA), but labeled with methylene blue, was used to construct a competitive relationship. When T-DNA and B-DNA were present on the sensor simultaneously, they would hybridize with probe DNA in a strong competition, and the corresponding electrochemical response signal would be generated via testing. It contributed to reducing tedious experimental procedures and excessive response time, and achieved fast electrochemical detection of DNA. The strategy provides a worthy avenue and possesses promising applications in disease diagnosis.