Enzyme-free Electrochemical Biosensor Research Articles

Enzyme-free electrochemical biosensor based on bio-barcode amplification for ultra-sensitive detection of microRNA.

The rapid and accurate detection of miRNAs is of great significance for early diagnosis and treatment of cancer. Hence, a novel enzyme-free and label-free electrochemical biosensor based on bio-barcode amplification for detecting miRNAs was presented. Sandwich structures constructed of magnetic nanoparticles modified with DNA probes, gold nanoparticles with numerous barcoded DNA strands that hybridized with target miRNAs were fabricated as the amplifier. The released barcoded DNA strands then acted as the secondary targets and triggered the electrochemical sensor with a significant electrochemical response. A highly sensitive (detection limit of 0.24 fM) and selective electrochemical miRNA detection was realized, which has great potential for application in miRNA-related clinical diagnosis and biochemical research.

Enzymeless electrochemical biosensor platform utilizing Cu2O-Au nanohybrids for point-of-care creatinine testing in complex biological fluids

Herein, we developed a novel, enzyme-free electrochemical biosensor that can directly quantify creatinine within complex biological fluids in a highly specific and sensitive manner. Our approach utilizes the synergistic effects of zwitterion-functionalized Cu2O-Au core satellite nanohybrids with sophisticated 3D granular structures, which were synthesized via a rapid room-temperature combinatory protocol. Through nanoscale zwitterion surface engineering, outstanding antifouling capabilities were obtained and interferents were effectively eliminated by generating a pseudo proton exchange membrane (PEM). This pseudo-PEM can potentially serve as an alternative to traditional methods of removing interference; thus, analytes can be directly detected in untreated biofluids. The optimized biosensor platform demonstrated a linear response to creatinine with exceptional reproducibility and an excellent limit of detection (LOD) in the following sensing ranges: (i) 10.0–200 µM (R2 =0.99, RSD=1.22 %, n = 10, LOD=0.72 µM) and (ii) 1.00–35.0 mM (R2 =0.99, RSD=1.32 %, n = 10, LOD=2.41 mM). These ranges are clinically relevant and cover the entire physiological range of creatinine in human serum and urine, respectively. Furthermore, we successfully detected creatinine directly in untreated human urine samples and observed a high correlation with clinically determined values (r = 0.98). Overall, our proposed biosensor platform offers significant improvements over existing methods and provides a reliable and efficient approach for practical point-of-care (POC) creatinine quantification.

High-efficient Pt@COF nanospheres-based electrochemical-chemical-chemical redox cycling for ultrasensitive microRNAs biosensing

MicroRNAs (miRNAs) have been perceived as important regulators in multifarious biological processes as well as potential biomarkers in clinical diagnosis. Exploring high-efficient sensing platforms for tracing miRNAs in complex biological samples is of great vital. Herein, an ultrasensitive and enzyme-free electrochemical biosensor was constructed based on integration of efficiently catalytic electrochemical−chemical−chemical (ECC) redox cycling with target-induced magnetic DNAzyme walker. Employing porous and easily functionalized covalent organic framework (COF) as carriers, Pt@COF nanospheres (Pt@COF NSs) were facilely prepared by in-situ reduction of platinum precursors in the nanopores-structure of COF. This not only addressed the inevitable migration of pure Pt nanoparticles, but endowed Pt@COF NSs with desirable stability and excellent catalytic activity to boost ECC redox cycling for effective signal enhancement. On this basis, a target-induced magnetic DNAzyme walker was obediently induced to recognize, separate and convert low-abundant miRNA-21 targets into plentiful output DNA chains for accumulated signal amplification. Finally, the as-prepared robust biosensor manifested highly sensitive and selective determination of miRNA-21 with a wide detection range from 100 aM to 10 pM and a low detection limit of 47.5 aM. Meanwhile, the credible detectability and anti-interference were also demonstrated in serum and cell samples, indicating its promising application toward diseases warning.

Specific capture and determination of glycoprotein using a hybrid epitopes and monomers-mediated molecular-imprinted polymer enzyme-free electrochemical biosensor

A novel molecular-imprinted polymer (MIP)-based enzyme-free biosensor was created for the selective detection of glycoprotein transferrin (Trf). For this purpose, MIP-based biosensor for Trf was prepared by electrochemical co-polymerization of novel hybrid monomers 3-aminophenylboronic acid (M-APBA) and pyrrole on aglassy carbon electrode (GCE) modified with carboxylated multi-walled carbon nanotubes (cMWCNTs). Hybrid epitopes of Trf (C-terminal fragment and glycan) have been selected as templates. The produced sensor exhibited great selective recognition ability toward Trf under optimal preparation conditions, offering good analytical range (0.125-1.25μM) with a detection limit of 0.024μM. Theproposed hybrid epitope in combination with hybrid monomer-mediated imprinting strategy was successfully applied to detect Trf in spiked human serum samples, with recoveries and relative standard deviations ranging from 94.7 to 106.0% and 2.64 to 5.32%, respectively. This study provided a reliable protocol for preparing hybrid epitopes and monomers-mediated MIP for the synergistic and effective determination of glycoprotein in complicated biological samples.

An enzyme-free electrochemical biosensor based on NiCoP@PtCu nanozyme and multi-MNAzyme junctions for ultrasensitive Uracil-DNA glycosylase detection

Abnormal expressions of uracil-DNA glycosylase (UDG) have been associated with various diseases. We proposed a novel electrochemical biosensing platform-based strategy for UDG detection. This method combined NiCoP@PtCu nanozyme with multi-MNAzyme junctions. The U base was deleted in the presence of UDG, resulting in self-assembly of multi-MNAzyme junctions with the ability to continually cleave DNA hairpins and release various products. The products could bind the protective probes, exposing capture probes on the electrode’s surface. Moreover, the exposed probes hybridized with the sDNAs-labeled NiCoP@PtCu nanozyme, yielding a significant electrochemical signal. The established biosensor was enzyme-free and with an ultrahigh sensitivity. Benefiting from the twofold amplification of multi-MNAzyme junctions and nanozyme, the sensing technique exhibited a large dynamic range, from 0.001 to 1.0 U mL −1 and a low detection of 6.6 × 10−4 U mL −1. In addition, the method was effectively used for UDG detection in lysed cells. Therefore, the biosensor we established has broad prospects in clinical diagnosis and biomedical research.

Application of green synthesized WO3-poly glutamic acid nanobiocomposite for early stage biosensing of breast cancer using electrochemical approach

Biopolymer films have drawn growing demand for their application in the point of care domain owing to their biocompatibility, eco-friendly, and eligibility for in vivo analyses. However, their poor conductivity restricts their sensitivity in diagnostics. For high-quality electrochemical biosensor monitoring, two vital factors to be greatly paid attention are the effective merge of amplification modifiers with transducing surface and the superior linking across the recognition interface. Here, we introduce an enzyme-free electrochemical biosensor based on electrosynthesized biocompatible WO3/poly glutamic acid nano-biocomposites to address the hardships specific to the analysis of circulating proteins clinical samples. In addition to its green synthesis route, the poor tendency of both components of the prepared nano-biocomposite to amine groups makes it excellent working in untreated biological samples with high contents of proteins. Several electrochemical and morphological investigations (SEM, EDX, and dot mapping) were fulfilled to gain a reliable and trustful standpoint of the framework. By using this nanobiosensor, the concentration of HER-2 was detectable as low as 1 fg mL−1 with a wide linear response between 1 ng mL−1 and 1 fg mL−1. Meanwhile, the protocol depicted ideal specificity, stability, and reproducibility for the detection of HER-2 protein in untreated serum samples of breast cancer patients.

A novel electrochemical aptamer biosensor based on tetrahedral DNA nanostructures and catalytic hairpin assembly for CEA detection

At present, carcinoembryonic antigen (CEA) is a commonly used biomarker to diagnose cancers. Accurate and specific detection of CEA in clinical samples is of great significance for the diagnosis, treatment and prognosis of related cancers. In this research, we developed an enzyme-free electrochemical aptamer biosensor for highly sensitive detection of CEA based on tetrahedral DNA nanostructures (TDNs) and target-assisted catalytic hairpin assembly (CHA). A long single strand (Trigger), five oligonucleotide chains (S1-S5) and CEA aptamer were designed to form TDN-aptamer and TDN-H1 respectively. In the presence of CEA, the aptamer designed at the top of TDN-aptamer specifically bound to CEA, while trigger was released to open H1 immobilized on the top of TDN-H1. This reaction initiated the CHA cycle with the participation of H2 modified by Methylene blue (MB). Subsequently, a large number of MB modified H1-H2 double strands were connected to the electrode surface through TDN structures, which generated significant current signals. This proposed biosensor could detect CEA down to 0.04567 pg mL−1 with a wide linear range from 1 pg mL−1 to 30000 pg mL−1. Furthermore, the electrochemical aptamer biosensor could detect CEA in serum samples accurately, it provided an effective alternative platform for clinical detections of CEA.

Electrochemical aptasensor based on proximity binding-induced DNA networked for enzyme-free and ultrasensitive detection of thrombin

The abnormal change of thrombin concentration is closely related with various diseases. By using proximity binding-induced DNA network assembled by nonlinear hybridization chain reaction (HCR), we here developed an enzyme-free and ultrasensitive electrochemical strategy for analyzing thrombin in human serums. The binding of the two different aptamers to a thrombin enhanced the local concentration of the aptamers and facilitates the formation of an intact strand. Subsequently, the formed strand caused nonlinear HCR, forming DNA network. The DNA network bound to the capture probes (CP)-modified electrode, producing electrochemical signal of MB. Benefiting from the proximity binding-induced DNA network, the proposed biosensor exhibited a wide linear range from 1.0 pM to 1.0 nM with a low detection limit of 0.56 pM and high specificity. More importantly, the developed enzyme-free electrochemical biosensor has been used to detect thrombin in serum samples with good performance. This makes such a strategy possess potential promise in the application of clinical diagnosis.

A Novel Electrochemical Aptamer Biosensor Based on Tetrahedral DNA Nanostructures and Catalytic Hairpin Assembly for CEA Detection

At present, carcinoembryonic antigen (CEA) is a commonly used biomarker to diagnose cancers. Accurate and specific detection of CEA in clinical samples is of great significance for the diagnosis, treatment and prognosis of related cancers. In this research, we developed an enzyme-free electrochemical apatmer biosensor for highly sensitive detection of CEA based on tetrahedral DNA nanostructures (TDNs) and target-assisted catalytic hairpin assembly (CHA). A long single strand (Trigger), five oligonucleotide chains (S1-S5) and CEA aptamer were designed to form TDN-aptamer and TDN-H1 respectively. In the presence of CEA, the aptamer designed at the top of TDN-aptamer specifically bound to CEA, while trigger was released to open H1 immobilized on the top of TDN-H1. This reaction initiated the CHA cycle with the participation of H2 modified by Methylene blue (MB). Subsequently, a large number of MB modified H1-H2 double strands were connected to the electrode surface through TDN structures, which generated significant current signals. This proposed biosensor could detect CEA down to 0.04567 pg mL-1 with a wide linear range from 1 pg mL-1 to 30000 pg mL-1. Furthermore, the electrochemical apatmer biosensor could detect CEA in serum samples accurately, it provided an effective alternative platform for clinical detections of CEA.

Co-catalytic Fc/HGQs/Fe3O4 nanocomposite mediated enzyme-free electrochemical biosensor for ultrasensitive detection of MicroRNA.

Herein, a novel co-catalytic ferrocene/hemin/G-quadruplexes/Fe3O4 nanoparticles (Fc/HGQs/Fe3O4) nanocomposite was synthesized to significantly magnify the electrochemical signal of ferrocene (Fc) using the synergistic catalysis of hemin/G-quadruplexes (HGQs) and Fe3O4 nanoparticles as hydrogen peroxide enzyme mimics for the construction of ultrasensitive electrochemical biosensors. The fabricated electrochemical biosensor can achieve ultrasensitive detection of miRNA-155 ranging from 0.1 fM to 1 nM, as well as a limit of detection of 74.8 aM. This strategy provides a new route to exploring efficient signal labels for signal amplification and provides an impetus to find novel methods for the construction of biosensors for biological detection and the early clinic diagnosis of diseases.

Synthesis, characterization and electrochemical analysis of TiO2 nanostructures for sensing l-Cysteine and hydrogen peroxide

Abstract l -Cyteine is a form of amino acid found in human body. Retaining the exact quantity of l -Cyteine is important for better functioning of the body. A novel hybrid TiO2 nanostructure (H-TNTs) was prepared on both sides of Ti sheet using the first-step anodization in used (residual) ethylene glycol (EG) based electrolyte. The H-TNTs was explored as an enzyme-free electrochemical biosensor for the detection of l -Cysteine (L-Cyst) and hydrogen peroxide (H2O2). Structural analysis revealed that annealed H-TNTs was anatase with uniform tube morphology and narrow pore size distribution of the top thin nanoporous layer. Electrochemical measurements demonstrated excellent electrocatalytic activities of H-TNTs with sensitivity and rapid response of L-Cyst (0.9914 μA mM−1 cm−2,

An enzyme-free electrochemical biosensor based on target-catalytic hairpin assembly and Pd@UiO-66 for the ultrasensitive detection of microRNA-21

MicroRNA-21 (miR-21) has been widely investigated as important biomarkers for cancer diagnosis and treatment. Herein, a highly sensitive nonenzymatic electrochemical biosensor based on Pd@metal-organic frameworks (Pd@UiO-66) and target-catalytic hairpin assembly (CHA) with target recycling approach has been proposed for the detection of miR-21. The proposed biosensor integrates the efficient CHA strategy and excellent electrocatalytic performance of Pd@UiO-66 nanocomposites. The concentration of miRNA-21 is related to the amount of the adsorbed electrocatalyst, leading to the different electrochemical signals for readout towards paracetamol (AP). This biosensor shows a low limit of detection of 0.713 fM with the dynamic range of 20 fM −600 pM under the optimal experimental conditions, providing a powerful platform for detecting miR-21. Furthermore, the designed biochemical self-assembly strategy of this electrochemical biosensor is promising candidate for potential applications in the analysis of other important genetic biomarkers for early diagnosis of cancers.

Enzyme-Free Electrochemical Biosensor Based on Localized DNA Cascade Displacement Reaction and Versatile DNA Nanosheets for Ultrasensitive Detection of Exosomal MicroRNA.

MicroRNA existing in exosomes (exo-miRNA) is a crucial and reliable biomarker for cancer screening and diagnosis. However, accurate detection of ultralow exo-miRNA amounts in real samples remains a challenge. Herein, a robust and ultrasensitive electrochemical biosensor was developed based on localized DNA cascade displacement reaction (L-DCDR) and versatile DNA nanosheets (DNSs) for enzyme-free analysis of exo-miRNA. The target activated L-DCDR repeatedly by consecutive toehold-mediated strand displacement, which released plentiful P strands to hybridize with capture probes immobilized on the electrode surface and DNS tags, generating an amplified electrochemical signal for the detection of exo-miRNA. The DNS could label-free load various electroactive molecules. The electrochemical biosensor revealed high sensitivity ranging from 0.1 fM to 1 nM with a limit of detection of 65 aM and good specificity. The constructed biosensor was demonstrated to be able to detect exo-miRNA derived from gastric cancer cell line (SGC-7901) and gastric cancer patients. In addition, the developed biosensor possessed several considerable advantages including simple substrate assembly, improved reaction rate, and high signal-to-noise ratio. Therefore, this strategy has great potential in bioanalysis and clinical diagnostics.

Enzyme-free electrochemical biosensor based on amplification of proximity-dependent surface hybridization chain reaction for ultrasensitive mRNA detection

The ability to recognize mRNA with high efficiency in cells would greatly facilitate the elucidation of mRNA-mediated cellular cascades and their disease associations. However, most traditional electrochemical strategies targeting nucleotides are always confronted with cumbersome interface operation and washing procedures, as well as the high cost of labeling and the strict reaction conditions of tool enzymes, limiting their potential applications. To address these issues, herein we reported, for the first time, a simple label-free, isothermal, non-enzymatic, and ultrasensitive homogeneous electrochemical biosensor based on autonomous proximity-dependent surface hybridization chain reaction (HCR), for sensitive signal amplification and highly specific detection of target survivin mRNA with a detection limit of 3 fM. The target triggers hybridization chain reaction and mRNA-fueled surface hybridization of ferrocene-tagged metastable DNA hairpin probes on proximity-dependent surface hybridization, resulting in the formation of multiple long-range duplex DNA chains which are immobilized onto the gold electrodes with a substantially stable ferrocene-mediated redox current. Thus, a significant electrochemical signal increase is observed dependent on the concentration of the target RNA, with a very low detection limit. Mo-reover, this molecular biosensor also exhibits excellent specificity to distinguish even single base mismatched, with strong reliability. The developed biosensor provides a novel promising tool for ultra-sensitive and selective detection, and it has great potential to be applied in mRNA-related biochemical research and clinical cancer diagnostics in more detail.

Enzyme-free electrochemical biosensor based on double signal amplification strategy for the ultra-sensitive detection of exosomal microRNAs in biological samples

Growing evidence suggests that exosomes-encapsulated miRNAs detection is of paramount significance in early diagnostics of cancer due to protection from degradation by ribonuclease. However, exosomal microRNAs with low abundance and subtle variation have restricted their clinical application. Herein, an electrochemical biosensor for highly sensitive detection of exosomal microRNAs has been fabricated based on the double signal amplification strategy. Our proposed amplifier consists of two steps: target miRNA cyclic signal amplification induced by strand displacement reaction (SDR) and subsequent deposition of silver nanoparticles induced by streptavidin-biotin interaction. Consequently, this method shows ultrahigh sensitivity to detect miRNA. Taking miRNA-21 in exosomes as a model analyte, a detection limit of 0.4 fM (S/N = 3) can be obtained. Meanwhile, the method is relatively simple and low-cost without the requirement of enzyme, which has been applied in biological samples successfully. Therefore, our miRNA assay method has shown great promise as molecular tool in the detection of exosomal miRNA and could be widely used in clinic in the future.

A novel high performance non-enzymatic electrochemical glucose biosensor based on activated carbon-supported Pt-Ni nanocomposite

In this study, a novel enzyme-free electrochemical biosensor has been developed for glucose determination. For this purpose, the electrochemical biosensor is prepared by the modification of a glassy carbon electrode surface with activated carbon-supported PtNi nanocomposites (PtNi@AC). The surface morphology and structure of the nanocomposite are analyzed by TEM, XRD, XPS, and Raman spectroscopy. The electrocatalytic properties of the nanocomposite are evaluated by cyclic voltammetry and chronoamperometry. The results indicate that PtNi@AC nanocomposites efficiently catalyst the oxidation of glucose without any enzymes. A wide linear range (0.025 to 12 mM) and also a low detection limit (LOD) of 0.052 μM are obtained. Also, the prepared biosensor showed excellent sensitivity, stability, repeatability and good selectivity that does not cause any interaction with the tested major interferences. Moreover, the prepared glucose biosensor has been successfully utilized for the determination of glucose in real serum samples.

An enzyme-free electrochemical biosensor based on well monodisperse Au nanorods for ultra-sensitive detection of telomerase activity

Efficient platforms for detecting telomerase activity are essential for early tumor monitoring and diagnosis. Herein, an enzyme-free electroanalytical strategy was developed for reliable and highly sensitive telomerase activity assay based on the increased electrochemical signals of methylene blue (MB) catalyzed by well monodisperse Au nanorods (AuNRs). In the presence of dNTPs and telomerase extracts, the assistant DNA 1 in the double stranded DNA can be extended to telomere repeat units (TTAGGG)n, which could form a hairpin structure by telomerase-triggered extension. The assistant DNA 2 was ingeniously dissociated from the double stranded DNA to combine with capture DNA. As a result, a large amount of AuNRs could be anchored on the surface of these sequences and used for electrocatalytic oxidation of MB. The developed biosensor showed a low limit of detection of 8.20 HeLa cells mL−1 and a wide dynamic range from 30 to 1.04 × 107 HeLa cells mL−1 for the determination of telomerase activity, which can provide a new way for telomerase activity assays in early diagnosis for cancers.

An enzyme-free electrochemical biosensor for simultaneous detection of two hemophilia A biomarkers: Combining target recycling with quantum dots-encapsulated metal-organic frameworks for signal amplification

A sensitive and selective electrochemical method for simultaneous detection of two hemophilia A-related microRNAs (miR-1246 and miR-4521) was developed. This detection tactic was based on gold nanoparticles (AuNPs), heavy metals quantum dots-encapsulated metal-organic frameworks (QDs@ZIF-8), and catalytic hairpin assembly (CHA) for signal application. Primarily, hairpins H1 and H2 were hybridized with targets miR-1246 (T1) and miR-4521 (T2) for forming H1-T1 and H2-T2 duplex stranded DNAs (dsDNAs) that were able to open the hairpins H3 and H4 for the formation of H1–H3 and H2–H4 dsDNAs. Meanwhile, lots of H1–H3 and H2–H4 dsDNAs were created by releasing the target to take part in the next cycle for signal amplification. And then single stranded fragments of H1–H3 and H2–H4 dsDNAs were utilized for hybridizing the PbS@ZIF-8-S1 and CdS@ZIF-8-S2 in order to amplify the electrochemical signal. The diagnosis of corresponding target miRs using differential pulse voltammetry has been possible by releasing Pb (II) and Cd (II) ions from PbS@ZIF-8 and CdS@ZIF-8 tags by HCI leaching. In this context, encapsulation of heavy metals quantum dots (QDs) was done in zeolitic imidazolate framework-8 (ZIF-8) to form QDs@ZIF-8 muti-core-shell particles by in situ growth of ZIF-8 in the presence of QDs. Since the quantity of QDs tagged to each target miRs grows massively, being resulted from a huge number of QDs that encapsulated in each QDs@ZIF-8 label, the sensitivity of the biosensor using QDs@ZIF-8 particles as signal tags is about 15 times that of a biosensor using QDs as signal tags. Several conditions of determination like incubation time for labeling and capture probe, HCl leaching time, and reaction time of CHA were optimized. Under the optimized conditions, this assay allowed the detection of target miRs in the range of 1 fM to 1 μM with detection limits of 0.19 fM and 0.28 fM for miR-1246 and miR-4521 (S/N = 3). The biosensor can discriminate complementary, 1-base mismatched and non-complementary sequences quite well, according to the catalytic hairpin assembly. Furthermore, the biosensor was utilized efficiently for quick and direct analysis of microRNAs in human serum. Thus, this tactic presents an innovative platform for microRNAs expression profiling in biomedical research and clinical diagnosis.

A novel enzyme-free electrochemical biosensor for rapid detection of Pseudomonas aeruginosa based on high catalytic Cu-ZrMOF and conductive Super P

Pseudomonas aeruginosa (P. aeruginosa) is one of the most intractable multidrug-resistant bacteria of nosocomial infections. The conventional detection methods for P. aeruginosa are time-consuming or low detection sensitivity. Here, a novel enzyme-free electrochemical biosensor was constructed to detect P. aeruginosa rapidly and sensitively. Firstly, the ZrMOF with large surface area was synthesized, which offers excellent adsorption. Further, it was connected with a specific amount of Cu2+ to synthesize Cu-ZrMOF with high catalytic activity. Then the Cu-ZrMOF@Aptamer@DNA nanocomposite was composed and served as the signal probe to catalyse the decomposition of H2O2. Moreover, high conductive Super P was introduced to increase the electron transfer for satisfactory detection sensitivity. The proposed biosensor was constructed and used to quantify P. aeruginosa with a wide linearity range of 10–106 CFU mL−1 and a low limit of detection of 2 CFU mL−1 (S/N = 3). Compared with conventional methods, the new method of present biosensor is more sensitive, and less time-consuming (only within 120 min). The analytical performance evaluation indicated that the biosensor exhibits good reproducibility and specificity. Finally, the biosensor was successfully applied to quantify P. aeruginosa in spiked urine samples. These results show that the proposed electrochemical biosensor might be a potential laboratory tool for detecting P. aeruginosa in the clinic.

An enzyme-free electrochemical biosensor combining target recycling with Fe3O4/CeO2@Au nanocatalysts for microRNA-21 detection

In this study, an electrochemical biosensor was proposed for microRNA-21 detection based on Fe3O4/CeO2 @Au magnetite nanoparticles (Fe3O4/CeO2 @Au MNPs) as nanocatalyst and catalytic hairpin assembly (CHA) for signal application. Firstly, target microRNA-21 hybridized with hairpin H2 to form H2-T duplex stranded DNA (dsDNA), which could further open the hairpin H1 for the formation of H1-H2 dsDNA. Simultaneously, the Fe3O4/CeO2 @Au-S1 not only hybridized with single stranded fragment of H1-H2 dsDNA with producing long dsDNA to absorb a large amount of electroactive substances of methylene blue (MB), but also acted as nanocatalyst to directly catalyze the reduction of MB for amplifying the electrochemical signal. Herein, compared with pure Fe3O4 nanoparticles, Fe3O4/CeO2 @Au MNPs exhibited excellent catalytic performance since the cerium oxide (CeO2) nanoparticles and Au nanoparticles can greatly improve the catalytic activity of Fe3O4 nanoparticles and effectively prevent the agglomeration of Fe3O4 nanoparticles. Owing to the signal amplification strategy, the proposed biosensor provided a wide linear range of 1 fM to 1 nM with a low detection limit of 0.33 fM (defined as S/N = 3) for microRNA-21 detection, and exhibited excellent specificity and sensitivity. This strategy provided a novel avenue for the detection of other biomarkers in electrochemical biosensors.