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Herein, a gold nanoparticles/graphene aerogels (AuNPs/GAs) modified electrochemical biosensor with catalytic hairpin assembly (CHA) and Y-shaped DNA nanostructure dual-signal amplification approaches for ultrasensitive microRNA-21 (miR-21) detection was successfully constructed, which displayed an ultra-wide detection linear range from 5 fM to 50 nM, as well as a relatively low detection limit (LOD) of 14.70 aM (S/N = 3). Furthermore, the sensing strategy had excellent specificity among highly homologous miRNA family members and exhibited satisfactory analytical performance for miRNA detection. [ABSTRACT FROM AUTHOR]

Herein, an ultrasensitive electrochemical biosensor for microRNA-155 (miR-155) detection based on the powerful catalytic and continuous walking signal amplification capability of 3D DNAzyme walker and the gold nanoparticles/graphene aerogels carbon fiber paper-based (AuNPs/GAs/CFP) flexible sensing electrode with excellent electrochemical performance was successfully constructed. In a proof-of-concept experiment, in the presence of miR-155, the DNAzyme strands anchored on the streptavidin-modified magnetic beads (MBs) silenced by locked strands can be activated, thus generating the walking arm of the 3D DNAzyme walker. Meanwhile, the substrate strands modified with Fe-MOF-NH 2 nanoparticles were evenly distributed on the surface of MBs and served as tracks of the 3D DNAzyme walker. Once the DNAzyme strand was activated, the catalytic site in the substrate strand can be cleaved in the presence of Mn2+, and a large number of stumps modified with Fe-MOF-NH 2 nanoparticles (output@Fe-MOF-NH 2) will be generated during the continuous and efficient walking cleavage of the DNAzyme walker, driving the recognition-catalysis-release cycle process for signal amplification. Immediately afterwards, the signal was read out through the base complementary pairing of capture probe (PS) immobilized on the surface of the paper-based flexible sensing electrode AuNPs/GAs/CFP and signal probes output@Fe-MOF-NH 2 , thus achieving the quantitative detection of miR-155. Under optimal experimental conditions, the designed 3D DNAzyme walker-based biosensor exhibited a relatively lower limit of detection (LOD) of 56.23 aM, with a linear range of 100 aM to 100 nM. Overall, the proposed 3D DNAzyme walker biosensor exhibited good interference and reproducibility, demonstrating a promising future in the field of clinical disease diagnosis. [Display omitted] • An electrochemical biosensor based on AuNPs/GAs/CFP electrode for miR-155 detection was successfully constructed. • Target-responsive 3D DNAzyme walker provided an important guarantee for ultrasensitive detection of miR-155. • The designed 3D DNAzyme walker-based biosensor exhibited a relatively lower limit of detection (LOD) of 56.23 aM. [ABSTRACT FROM AUTHOR]

• The MoS 2 -AuNPs probe showed uniquely inherited structure and excellent electrochemical characteristic. • The carbon paper functionalized with MoS 2 -AuNPs demonstrated the outstanding detection performance of p53 gene. • The biosensor exhibits a relatively lower detection limit of 68 fM for p53 gene detection. • The planned biosensor could discriminate well between the mutated and wild type p53 gene extracted from tumor cells. p53 gene is one of the most important anticancer genes and has been recognized as a typical biomarker for the early diagnosis, classification, and prognosis evaluation of cancers. In this work, a novel biosensing strategy integrating MoS 2 -AuNPs modified carbon paper (CP) conductive substrate and enzyme signal amplification technique was developed for p53 gene detection. We constructed an immobilized DNA S1 probe and a biotinylated DNA S3 probe, which could induce the formation of an S1-p53-S3 DNA sandwich complex in the presence of target sequence p53. After conjugating avidin-HRP via biotin-avidin reaction, 3,3',5,5'-tetramethylbenzidine would be catalyzed for signal amplification in the presence of H 2 O 2 so that the induced electrochemical response would change with proportional to the abundance of p53 gene. The proposed biosensor exhibited two linearities in the range of 1.0 × 10−15 ∼ 1.0 × 10-12 M and 1.0 × 10-12 ∼ 1.0 × 10-6 M, and the limit of detection (LOD) was 68 fM. No significant interferences were observed during detecting real serum samples. Moreover, it is worth pointing out that the biosensor together with its disposable, low-cost, and stable features can discriminate well between the mutated and wild type p53 gene extracted from tumor cells (wtTP53 in MCF-7 and mutated in SK-BR-3), demonstrating a promising applicability for clinical test. [ABSTRACT FROM AUTHOR]

A sandwich electrochemical biosensing strategy for ultrasensitive detection of miRNA-21 was developed by using graphene oxide incorporated 3D-flower-like MoS2 (3D MoS2-rGO) nanocomposites as the substrate and horseradish peroxidase (HRP)-functionalized DNA strand 1 (S1)-gold nanoparticles (S1-AuNPs-HRP) as signal amplification probes. Herein, 3D MoS2-rGO nanocomposites not only had a large specific surface area and excellent conductivity, but also provided more attachment sites for electrodepositing AuNPs. In the presence of target miRNA, a sandwich structure was formed, and the determination of the miRNA-21 was carried out by measuring the DPV response of H2O2 mediated by hydroquinone (HQ) at a potential of + 0.052 V (vs AgCl reference electrode). Under the optimal experimental conditions, the as-prepared biosensor enabled the ultrasensitive detection of miRNA-21 from 5 fM to 0.5 μM with the low detection limit of 0.54 fM (S/N = 3), comparable or lower than previous reported methods for miRNA-21 detection, which benefited from the synergistic amplification of 3D MoS2-rGO and AuNPs-HRP. The prepared biosensor showed satisfactory selectivity, reproducibility, and stability towards miRNA-21 detection. The biosensor was feasible for accurate and quantitative detection of miRNA-21 in normal human serum samples with RSD below 5.86%, which showed a great potential in clinical analysis and disease diagnosis. [ABSTRACT FROM AUTHOR]