Fabricating Pt/Sn–In2O3 Nanoflower with Advanced Oxygen Reduction Reaction Performance for High-Sensitivity MicroRNA Electrochemical Detection

S-induced Phase Change Forming In2 O3 /In2 S3 Heterostructure for Photoelectrochemical Glucose Sensor

In the past several decades, Photoelectrochemical (PEC) sensing still remains a great challenge to design highly-efficient semiconductor photocatalysts via a facile method. It is of much importance to design and synthesize various novel nanostructured sensing materials for further improving the response performance. Herein, we present an In2 O3 /In2 S3 heterostructure obtained by combining microwave assisted hydrothermal method with S-induced phase change, whose energy band and electronic structure could be adjusted by changing the S content. Combining theoretical calculation and spectroscopic techniques, the introduction of sulfur was proved to produce multifunctional interfaces, inducing the change of phase, oxygen vacancies and band gap, which accelerates the separation of photoexcited carriers and reduces their recombination, improving the electronic injection efficiency around the interface of In2 O3 /In2 S3 . As anticipated, an enhanced glucose response performance with a photocurrent of 0.6 mA cm-2 , a linear range of 0.1-1 mM and a detection limit as low as 14.5 μM has been achieved based on the In2 O3 /In2 S3 heterostructure, which is significant superior over its pure In2 O3 and S-doped In2 O3 counterparts. This efficient interfacial strategy may open a new route to manipulate the electrical structure, and energy band structure regulation of sensing material to improve the performance of photoelectrodes for PEC.

Utilizing the Oxygen Reduction Reaction in Particle Impact Electrochemistry: A Step toward Mediator-Free Digital Electrochemical Sensors

The current blockade particle impact method opens a route toward highly parallelized single-entity electrochemical assays. An important limitation is, however, that a redox mediator must be present in the sample, which can detrimentally interfere with molecular recognition processes. Dissolved O2 that is naturally present in aqueous solutions under ambient conditions can in principle serve as a suitable mediator via the oxygen reduction reaction (ORR). Here, we demonstrate the validity of this concept by performing current blockade experiments to capture and detect individual microparticles at Pt microelectrodes using solely the ORR. The readout modality is independent of the absolute O2 concentration, allowing operation under varying conditions. We further determine how the trajectories of individual microparticles are influenced by the combination of electrophoresis and electroosmotic flows and how these can be utilized to provide continuous detection of cationic particles in water for environmental monitoring.

Unique Electron-Transfer-Mediated Electrochemiluminescence of AuPt Bimetallic Nanoclusters and the Application in Cancer Immunoassay

Noble Metal nanoclusters (NCs) are promising electrochemiluminescence (ECL) emitters due to their amazing optical properties and excellent biocompatibility. They have been widely used in the detection of ions, pollutant molecules, biomolecules, etc. Herein, we found that glutathione-capped AuPt bimetallic NCs (GSH-AuPt NCs) emitted strong anodic ECL signals with triethylamine as co-reactants which had no fluorescence (FL) response. Due to the synergistic effect of bimetallic structures, the ECL signals of AuPt NCs were 6.8 and 94 times higher than those of monometallic Au and Pt NCs, respectively. The electric and optical properties of GSH-AuPt NCs differed from those of Au and Pt NCs completely. An electron-transfer mediated ECL mechanism was proposed. The excited electrons may be neutralized by Pt(II) in GSH-Pt and GSH-AuPt NCs, resulting in the vanished FL. Furthermore, abundant TEA radicals formed on the anode contributed electrons to the highest unoccupied molecular orbital of GSH-Au_2.5Pt NCs and Pt(II), booming intense ECL signals. Because of the ligand effect and ensemble effect, bimetallic AuPt NCs exhibited much stronger ECL than GSH-Au NCs. A sandwich-type immunoassay for alpha fetoprotein (AFP) cancer biomarkers was fabricated with GSH-AuPt NCs as signal tags, which displayed a wide linear range from 0.01 to 1000 ng·mL^-1 and a limit of detection (LOD) down to 1.0 pg·mL^-1 at 3S/N. Compared to previous ECL AFP immunoassays, this method not only had a wider linear range but also a lower LOD. The recoveries of AFP in human serum were around 108%, providing a wonderful strategy for fast, sensitive, and accurate cancer diagnosis.

In situ detection of miRNA-21 in MCF-7 cell-derived extracellular vesicles using the red blood cell membrane vesicle strategy

In this work, we constructed a novel membrane fusion strategy for extracellular vesicles (EVs) and red blood cell membrane vesicles (RVs). A nanoscale space is formed, which can improve the efficiency of the probe reaction with miRNA-21, which allows the in situ fluorescence detection of miRNA-21 in EVs.

Rapid electrochemical detection of MiRNA-21 facilitated by the excellent catalytic ability of Pt@CeO2 nanospheres

Pt@CeO2 nanospheres (NSs) were first synthesized by simply mixing Ce(NO3)3 and K2PtCl4 under the protection of pure argon at 70 °C for 1 h, which exhibited excellent catalytic ability toward hydrogen peroxide (H2O2). An electrochemical biosensor was successfully developed using Pt@CeO2 NSs as a capture probe for the ultra-sensitive and fast detection of miRNA-21, a new type of biomarker for disease diagnostics, especially for cancer. During the step-by-step construction process of the RNA sensor, Pt@CeO2 NSs were functionalized with streptavidin (SA) to obtain SA-Pt@CeO2 NSs through amide bonds. Gold nanoparticles (Au NPs) were electrodeposited on the surface of the glassy carbon electrode to improve the transmission capacity of electrons and provided Au atoms for fixing the thiolated capture probe (SH-CP) with a hairpin structure on the electrode via forming Au-S bonds. The target miRNA-21 specifically hybridized with SH-CP and opened the hairpin structure to form a rigid duplex so as to activate the biotin at the end of the capture probe. SA-Pt@CeO2 NSs were thus specially attached to the electrode surface through the biotin-streptavidin affinity interaction, finally leading to the significant signal amplification. The ultra-sensitive and rapid detection of miRNA-21 was finally realized as expected benefiting from the excellent catalytic ability of Pt@CeO2 NSs toward H2O2 in a wide linear concentration range from 10 fM to 1 nM with the detection limit as low as 1.41 fM. The results achieved with this new RNA sensor were quite satisfactory during the blood sample analysis.

Sandwich-type microRNA biosensor based on graphene oxide incorporated 3D-flower-like MoS2 and AuNPs coupling with HRP enzyme signal amplification

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.

Iodide-modified Ag nanoparticles coupled with DSN-Assisted cycling amplification for label-free and ultrasensitive SERS detection of MicroRNA-21

With the emergence of microRNA (miRNA) as a key player in early clinical disease diagnosis, development of rapidly sensitive and quantitative miRNA detection methods are imperative. Herein, a label-free SERS assay coupled with duplex-specific nuclease (DSN) signal amplification strategy was proposed for facilely ultrasensitive and quantitative analysis of miRNA-21. Firstly, magnetic beads assembled with excessive capture DNA were utilized to hybridize the target miRNA-21. These DNA-RNA heteroduplexes were cleaved by DSN to generate small nucleotide fragments into the supernatant and the miRNA-21 released and rehybridized another DNA, going to the next DSN cycle. Consequently, numerous of small nucleotide fragments of capture DNA were released from magnetic beads and the miRNA-21 signal was transferred and amplified by the SERS signals of total phosphate backbones which are abundant in nucleotide. Furthermore, iodide-modified Ag nanoparticles (AgINPs) was employed to generate a strong and reproducible SERS signal. The proposed method displayed excellent performance for miRNA-21 detection with the linear range from 0.33 fM to 3.3 pM, and a lower detection limit of 42 aM. Moreover, this strategy exhibited effectively base discrimination capability and was successfully applied for monitoring the expression levels of miRNA-21 in different cancer cell lines and human serum.

Methylene blue embedded duplex DNA as an efficient signal stimulator of petal-like BiVO4 for ultrasensitive photoelectrochemical bioassay

Conventionally, the photoelectrochemistry relies on freely diffusive signal molecules in solution to stimulate the photocurrent output, leading to limited sensing strategies. Herein, we showcase the methylene blue (MB) embedded duplex DNA for efficient signal stimuli and its application for ultrasensitive photoelectrochemical (PEC) bioassay. Specifically, the MB embedded duplex DNA scavenged the photogenerated holes of petal-like BiVO₄ efficiently, and thus greatly augmented the anodic photocurrent output. Taking the miRNA-21 as a model target, whose biorecognition reaction was aided by the rolling circle amplification (RCA) reaction to finally produce an amplified amount of double-stranded DNA (dsDNA) with embedded MB on the photoelectrode's surface, a "label-free" and "signal-on" PEC biosensing platform was implemented with ultra-sensitivity and high selectivity. The proposed strategy could detect miRNA-21 in the concentration range of 5.0 fM to 10 nM, with the detection limit as low as 0.3 fM. This work opens up the utilization of redox substance intercalated duplex DNA for an efficient signal stimulator, which hints the prospect of other more intercalators embedded DNA for versatile biosensing purposes. Importantly, considering the large quantities of bioreactions that involve duplex DNA as reactants/products, the developed signal transduction strategy may further find wide applications in bioanalysis for targeting more analytes.

Photoelectrochemical Biosensor for MicroRNA-21 Based on High Photocurrent of TiO2/Two-Dimensional Coordination Polymer CuClx(MBA)y Photoelectrode

Conventional photosensitive materials such as TiO₂ suffer from restricted absorption in the ultraviolet region, fast recombination of photogenerated electron-hole pairs, and a lack of functional groups for biocoupling, which hinder their application in photoelectrochemical (PEC) biosensing. Herein, a new coordination polymer (CP) based on Cu(I), chloridion, and 4-mercaptobenzoic acid (MBA) has been designed and synthesized (called CuCl_x(MBA)_y). The prepared p-type CuCl_x(MBA)_y exhibits visible-light absorption due to its narrow optical band gap (2.59 eV), and its proper band edge position enables it to form a p-n junction with TiO₂. Through layer-by-layer assembling, the photocurrent intensity of the CuCl_x(MBA)_y/TiO₂/FTO composite photoelectrode was 3.7-fold higher than that of a TiO₂/FTO electrode and 35-fold higher than a CuCl_x(MBA)_y/FTO electrode. The potential enhancement mechanism was discussed, which lies in the contributions of CuCl_x(MBA)_y in enhancing absorption in the visible-light region and boosting the separation of electron-hole pairs of TiO₂ by the p-n junction. Furthermore, CuCl_x(MBA)_y nanosheets can realize bioconjugation directly, thanks to its abundant carboxyl groups. The CuCl_x(MBA)_y/TiO₂/FTO composite photoelectrodes were applied to develop a sensitive PEC biosensor for microRNA-21 (model target). By subtly exploiting the energy transfer between CuCl_x(MBA)_y and Au nanoparticles (AuNPs), AuNPs served as effective quenchers. In the presence of the target, AuNP-labeled sDNA1 connected to the electrode surface, and thus, a decreased photocurrent was obtained. The proposed biosensor has a low detection limit of 0.29 fM (S/N = 3), good selectivity, and reproducibility. The proposed system was applied to monitor microRNA in cancer cells with satisfying results.

A dual-model "on-super off" photoelectrochemical/ratiometric electrochemical biosensor for ultrasensitive and accurate detection of microRNA-224

A dual-model "on-super off" photoelectrochemical (PEC)/ratiometric electrochemical (EC) biosensor based on signal enhancing and quenching combining three-dimensional (3D) DNA walker strategy was designed for the ultrasensitive and accurate detection of microRNA-224 (miRNA-224). The "signal on" PEC state was achieved by methylene blue labeled hairpin DNA (MB-DNA) for sensitizing CdS QDs. Then numerous transformational ferrocene labeled DNAs (Fc-DNAs) converted by target-induced 3D DNA walker amplification with the help of Ag nanocubes (NCs) label DNA (Ag-DNA) were introduced to open hairpin MB-DNA. Such configuration change would relocate the sensitizer MB and the quencher Fc, whereas energy transfer placed between Ag NCs and CdS QDs, thereby significantly quenching the PEC signal to obtain "super off" state. Meanwhile, these changes resulted in a decreased oxidation peak current of MB (I_MB) and an increased that of Fc (I_Fc). MiRNA-224 was also detected on basis of the dual-signaling EC ratiometric method for complementary PEC detection. Benefiting from different mechanisms and relatively independent signal transduction, this approach not only avoided interference from difficult assembly but also outstandingly increased sensitivity by distance-controllable signal enhancing and quenching strategies. As a result, the detection ranges of 0.1-1000 fM with a low detection limit of 0.019 fM for PEC, and 0.52 to 500 fM with a low detection limit of 0.061 fM for EC, were obtained for miRNA-224, which opens a new avenue for designing numerous elegant biosensors with potential utility in bioanalysis and early disease diagnosis.

Handheld pH meter-assisted immunoassay for C-reactive protein using glucose oxidase-conjugated dendrimer loaded with platinum nanozymes

A simple and feasible pH meter-based immunoassay is reported for detection of C-reactive protein (CRP) using glucose oxidase (GOD)-conjugated dendrimer loaded with platinum nanozyme. Initially, platinum nanozymes were loaded into the dendrimers through an in situ synthetic method. Then, GOD and monoclonal anti-CRP antibody with a high molar ratio were covalently conjugated onto carboxylated dendrimers via typical carbodiimide coupling. The immunoreaction was carried out with a competitive mode in a CRP-coated microplate. Along with formation of immunocomplex, the added glucose was oxidized into gluconic acid and hydrogen peroxide by GOD, and the latter was further decomposed by platinum nanozyme, thus accelerating chemical reaction in the positive direction. The produced gluconic acid changed the pH of detection solution, which was determined using a handheld pH meter. Under optimum conditions, the pH meter-based immunoassay gave a good signal toward target CRP from 0.01 to 100 ng mL-1. The limit of detection was 5.9 pg mL-1. An intermediate precision ≤ 11.2% was acquired with batch-to-batch identification. No nonspecific adsorption was observed during a series of procedures to detect target CRP, and the cross-reaction against other biomarkers was very low. Importantly, our system gave well-matched results for analysis of human serum samples relative to a referenced ELISA kit.Graphical abstract.

Electrochemical Biosensors for Detection of MicroRNA as a Cancer Biomarker: Pros and Cons

Cancer is the second most fatal disease in the world and an early diagnosis is important for a successful treatment. Thus, it is necessary to develop fast, sensitive, simple, and inexpensive analytical tools for cancer biomarker detection. MicroRNA (miRNA) is an RNA cancer biomarker where the expression level in body fluid is strongly correlated to cancer. Various biosensors involving the detection of miRNA for cancer diagnosis were developed. The present review offers a comprehensive overview of the recent developments in electrochemical biosensor for miRNA cancer marker detection from 2015 to 2020. The review focuses on the approaches to direct miRNA detection based on the electrochemical signal. It includes a RedOx-labeled probe with different designs, RedOx DNA-intercalating agents, various kinds of RedOx catalysts used to produce a signal response, and finally a free RedOx indicator. Furthermore, the advantages and drawbacks of these approaches are highlighted.

Three-Dimensional DNA Nanomachine Combined with Toehold-Mediated Strand Displacement Reaction for Sensitive Electrochemical Detection of MiRNA

MicroRNA (miRNA) serves as an ideal biomarker for diagnosis, prognosis, and therapy of various human cancers. The rationally designed three-dimensional (3D) DNA nanomachine was constructed on the matrixes of magnetic beads, and the high density of gold nanoparticles (AuNPs) on each magnetic bead and further enlargement of the AuNPs lead to the anchoring of numerous DNA walkers and signal probes on the AuNPs. With the combination of toehold-mediated strand displacement reaction (SDR), amplified electrochemical detection of miRNA is performed. The existence of miRNA triggers the toehold-mediated SDR and the released DNA walker probe is hybridized with the ferrocene (Fc)-tagged signal probe. The cleavage of the duplex by the nicking endonuclease detaches the signal probe from the magnetic nanocomposites. The oxidation current of Fc moieties was found to be inversely proportional to the concentrations of miRNA-182 between 1.0 fM and 2 pM. The assay is highly selective for discrimination of miRNAs with similar sequences. The feasibility of the method for sensitive detection of the expression levels of miRNA-182 from serum samples of glioma patients at different stages was demonstrated. The sensing protocol holds great promise for early diagnosis and prognosis of the cancer cases with abnormal miRNA expression.

Ultrasensitive analysis of microRNAs with gold nanoparticle-decorated molybdenum disulfide nanohybrid-based multilayer nanoprobes

The nanoprobe-based signal amplification strategy is a powerful way to ultrasensitively detect biomolecules. Herein, a gold nanoparticle-decorated molybdenum disulfide (MoS₂-AuNP)-based multilayer nanoprobe (MLNP) was designed for ultrasensitive analysis of microRNA-21 (miRNA-21). The MLNP-amplified electrochemical biosensor exhibited an ultrawide dynamic range (10 aM-1 μM) and an ultralow detection limit (38 aM) for target miRNA-21 analysis. Furthermore, this biosensor can determine miRNA-21 expression in cell lysates of 100 human cervical cancer (HeLa) cells. Our results demonstrate that MoS₂-AuNP nanocomposites have great potential in constructing biosensors for target molecule analysis.

Label-free and enzyme-free detection of microRNA based on a hybridization chain reaction with hemin/G-quadruplex enzymatic catalysis-induced MoS2 quantum dots via the inner filter effect

A new simple, sensitive and specific strategy for microRNA analysis has been described based on a hybridization chain reaction with hemin/G-quadruplex enzymatic catalysis-induced MoS2 quantum dots via the inner filter effect. The target microRNA triggers the hybridization chain reaction between two DNA probes to generate long dsDNA with many hemin/G-quadruplex DNAzymes in the presence of hemin. With the assistance of H2O2, the produced hemin/G-quadruplex DNAzyme could oxidize o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) directly, resulting in the fluorescence quenching of MoS2 quantum dots via the inner filter effect. As an example, the fluorescence response of MoS2 quantum dots is linearly related with the logarithm of the microRNA let-7a concentration with a detection limit of 42 fM. The proposed label-free assay has promising potential to be applied in practical diagnosis.

Programmable mismatch-fueled high-efficiency DNA signal converter

Herein, by directly introducing mismatched reactant DNA, high-reactivity and high-threshold enzyme-free target recycling amplification (EFTRA) is explored. The developed high-efficiency EFTRA (HEEFTRA) was applied as a programmable DNA signal converter, possessing higher conversion efficiency than the traditional one with perfect complement owing to the more negative reaction standard free energy (ΔG). Once traces of input target miRNA interact with the mismatched reactant DNA, amounts of ferrocene (Fc)-labeled output DNA could be converted via the EFTRA. Impressively, the Fc-labeled output DNA could be easily captured by the DNA tetrahedron nanoprobes (DTNPs) on the electrode surface to form triplex-forming oligonucleotide (TFO) at pH = 7.0 for sensitive electrochemical signal generation and the DTNPs could be regenerated at pH = 10.0, from which the conversion efficiency (N) will be accurately obtained, benefiting the selection of suitable mismatched bases to obtain high-efficiency EFTRA (HEEFTRA). As a proof of concept, the HEEFTRA as an evolved DNA signal converter is successfully applied for the ultrasensitive detection of miRNA-21, which gives impetus to the design of other signal converters with excellent efficiency for ultimate applications in sensing analysis, clinical diagnosis, and other areas.

N-Doped Graphene Oxide Decorated with PtCo Nanoparticles for Immobilization of Double-Stranded Deoxyribonucleic Acid and Investigation of Clenbuterol-Induced DNA Damage

We demonstrate here a facile hydrothermal-assisted formation of PtCo alloy nanoparticles (NPs) and their simultaneous anchoring on the graphitic surface of N-doped graphene oxide (NGO). Doping induced nanopores in the carbon surface to facilitate the uniform and homogeneous anchoring of alloy nanoparticles. It was revealed that the formation of PtCo NPs on an NGO interface plodded excellent tendency toward double-stranded deoxyribonucleic acid (dsDNA). The dsDNA immobilization was enabled by the presence of several oxidation states of Pt and Co. The same property was further used to monitor the direct detection of dsDNA damage induced by clenbuterol via screen-printed carbon electrodes. Cyclic voltammetric and electrochemical impedance spectroscopic characterization traced well the dsDNA attachment on the modified electrode surface. Differential pulsed voltammetry was further used as a tool to monitor the characteristic guanine peak before and after incubating with clenbuterol used as a damage probe for the dsDNA. The findings can further be appurtenant in exploring dsDNA immobilization protocols and developing analytical methods for determination of various dsDNA damaging agents.

Amplified oxygen reduction signal at a Pt-Sn-modified TiO2 nanocomposite on an electrochemical aptasensor

In this work, a metallic composite with strong electrocatalytic property was designed by uniformly decorating Pt and Sn nanoparticles on the surface of TiO₂ nanorods (Pt-Sn@TiO₂). A detection scheme was then developed based on a dual signal amplification strategy involving the Pt-Sn@TiO₂ composite and exonuclease assisted target recycling. The Pt-Sn@TiO₂ composite exhibited an enhanced oxygen reduction current owing to the synergistic effect between Pt and Sn, as well as high exposure of Pt (111) crystal face. Initially, a Pt-Sn@TiO₂ modified glassy carbon electrode produced an amplified electrochemical signal for the reduction of dissolved oxygen in the analyte solution. Next, a DNA with a complementary sequence to a streptomycin aptamer (cDNA) was immobilised on the Pt-Sn@TiO₂ modified electrode, followed by the streptomycin aptamer that hybridised with cDNA. The corresponding oxygen reduction current was diminished by 51% attributable to the hindrance from the biomolecules. After a mixture of streptomycin and RecJ_f exonuclease was introduced, both the streptomycin-aptamer complex and the cDNA were cleaved from the electrode, making the Pt-Sn and Pt (111) surface available for oxygen reduction. RecJ_f would also release streptomycin from the streptomycin-aptamer complex, allowing it to complex again with aptamers on the electrode. This has then promoted a cyclic amplification of the oxygen reduction current by 85%, which is quantitatively related to streptomycin. Under optimal conditions, the aptasensor exhibited a linear range of 0.05-1500 nM and a limit of detection of 0.02±0.0045 nM streptomycin. The sensor was then used in the real-life sample detection of streptomycin to demonstrate its potential applications to bioanalysis.

Rolling circle amplification-mediated in situ synthesis of palladium nanoparticles for the ultrasensitive electrochemical detection of microRNA

Herein, an ultrasensitive and label-free electrochemical biosensor was developed for microRNA (miRNA) based on rolling circle amplification (RCA)-mediated palladium nanoparticles (PdNPs). The sensor was fabricated by immobilizing dual-functionalized hairpin probes onto an electrode. The specific recognition of target miRNA-21 by the hairpin probes could trigger the RCA reaction, which produced numerous guanine (G)-rich long single-stranded DNAs (ssDNAs). Based on the interaction of the Pd^II species with the nitrogen atoms of the G bases, these G-rich long ssDNAs served as specific templates in the in situ synthesis of massive PdNPs as electrochemical indicators. The formation of PdNPs was demonstrated to be exactly along the RCA products by high-resolution transmission electron microscopy. Using this cascade signal amplification strategy, the developed biosensor achieved a linear range of 50 aM-100 fM with an ultralow detection limit of 8.6 aM miRNA-21. Furthermore, the developed biosensor exhibited good selectivity, reproducibility, stability and satisfactory feasibility for miRNA-21 detection in human serum samples; this ensured significant potential of this biosensor in disease diagnosis and prognosis applications.

Cancer Cell Membrane Camouflaged Nanoprobe for Catalytic Ratiometric Photoacoustic Imaging of MicroRNA in Living Mice

Herein, a cancer cell (MCF-7 cell) membrane-encapsulated dendritic mesoporous silica nanoparticle simultaneously functionalized with DNA-photoacoustic (DNA-PA) probes and glutathione (GSH)-responsive DNA fuel strands for PA imaging of tumor-related miRNA in living mice with signal amplification ability is developed. It is demonstrated that one target miRNA can trigger disassembly of multiple PA fluorophore probes from the quencher with the aid of GSH-responsive DNA fuel strands via the entropy-driven process, resulting remarkable amplified change of PA signal ratio. Using oncogenic miRNA-21 as a model, a linear relationship between miRNA-21 concentrations and PA ratio in a dynamic range from 10 × 10^-12 m to 100 × 10^-9 m and a limit of detection down to 11.69 × 10^-12 m are established. The accurate PA signal observation related to miRNA-21s in the tumor area in living mice is demonstrated, and the PA signal ratio increases significantly via the injection of miRNA-21. It is anticipated that the catalytic ratiometric PA imaging system can be applied to an array of molecular detection in living system by rational detection probe design.

Sensitively distinguishing intracellular precursor and mature microRNA abundance

Mature microRNAs (miRNAs) produced from precursor microRNAs (pre-miRNAs) by the RNase Dicer have showed significant potential for cancer diagnosis and prognosis due to their key regulatory roles in various pathological processes. However, discriminatory detection of low-abundance miRNAs and pre-miRNAs remains a key challenge since the mature sequence is also present in the pre-miRNA forms. Herein, we report a novel cascade reaction to sensitively distinguish miRNAs versus pre-miRNAs in living cells based on two pairs of programmable hairpin oligonucleotide probes with a simple sequence design. The programmable hairpin probes can metastably coexist until the introduction of miRNAs or pre-miRNAs, which can trigger a specific hybridization chain reaction (HCR), respectively, leading to the self-assembly of nicked DNA duplex structures and a remarkable specific fluorescence intensity increase. The system can readily and sensitively assess the miRNA or pre-miRNA abundance in a homogeneous solution. The intracellular miRNA and pre-miRNA expression level assessment in different living cells is realized. Thus, we provide a novel investigation tool for discriminatorily and accurately assessing miRNA and pre-miRNA abundance, which could be useful for the biomedical application of miRNAs.

Recent advances in nanomaterial-based electrochemical and optical sensing platforms for microRNA assays

This review describes recent efforts in the application of nanomaterials as sensing elements in electrochemical and optical miRNAs assays.

High-performance non-enzymatic biofuel cells based on an organic copper complex cathode and a nanoporous gold nanoparticle anode

We developed non-enzymatic biofuel cells based on organic copper complex and nanoporous gold nanoparticle electrocatalysts in a neutral medium.

A facile DNA strand displacement reaction sensing strategy of electrochemical biosensor based on N-carboxymethyl chitosan/molybdenum carbide nanocomposite for microRNA-21 detection

Herein, we report a facile enzyme-free microRNA (miRNA) target-triggered strand displacement reaction (SDR) amplification strategy with ferrocene (Fc) as a signal molecule to fabricate a two-dimensional electroactive molybdenum carbide (Mo₂C)-based biosensor. In the presence of miRNA-21, SDR was initiated and many hairpin DNA1 (HDNA1) and hairpin DNA2 (HDNA2) duplexes, which could be captured by probe DNA leading the Fc-modified HDNA2 close to the electrode surface, were produced continuously. MiRNA-21 could be detected by monitoring the redox signal of Fc. The prepared N-carboxymethyl chitosan/Mo₂C nanocomposite featured excellent conductivity, great dispersion, and multiple functional groups (amine groups). When the nanocomposite was introduced to a miRNA biosensor electrode interface to ensure its strong connection to the DNA probe, the developed miRNA-21 biosensor demonstrated a reliable linear range of 1.0 fM to 1.0 nM with a detection limit of 0.34 fM and showed good selectivity, reproducibility, and stability. The biosensor was employed to detect miRNA-21 in human serum samples, and it showed great potential in the early clinical diagnosis of various genetic diseases.

Ultrasensitive Simultaneous Detection of Multiplex Disease-Related Nucleic Acids Using Double-Enhanced Surface-Enhanced Raman Scattering Nanosensors

Developing ultrasensitive probes holds great significance for simultaneous detection of multiplexed cancer-associated nucleic acids. Bimetallic nanoparticles containing silver may be exploited as nanoprobes for disease detection, which can produce stable and strong surface-enhanced Raman scattering (SERS) signals. However, it remains extremely challenging that such SERS nanoprobes are directly synthesized. Herein gold-silver nanosnowmen, grown via a DNA-mediated approach and attached to thiol-containing Raman dyes, are successfully synthesized. Stable SERS-enhanced gold substrates are also prepared and used as the enriching containers, where the capture DNAs are tethered to sense the target genes jointly enhanced by the SERS nanoprobes in a sandwich hybridization assay. This means detection of the target gene can obtain a limit of detection close to 0.839 fM. Such double-enhanced SERS nanosensors are further employed to simultaneously detect the three types of prostate carcinoma-related genes with high sensitivity and specificity, which meanwhile exhibit robust capacity of resisting disturbance in practical samples. Simultaneous and multiplexed detection of cancer-related genes may provide further biomedical applications with new opportunity.

Colorimetric PCR-Based microRNA Detection Method Based on Small Organic Dye and Single Enzyme

microRNAs (miRNAs) have been a class of promising disease diagnostic biomarkers and therapeutic targets for their important biological functions. However, because of the high homology, interference from precursors (pri-miRNA, pre-miRNA), as well as limitations in the current assay technologies, it poses high demand and challenge for a specific, efficient, and economic miRNA assay method. Here, we propose a new miRNA detection method based on a label-free probe and a small organic dye with sequence dependence, realizing the sequence-specific and colorimetric detection of target miRNA. What is pleasantly surprising, only one enzyme is enough to propel the whole miRNA assay process, greatly simplifying the reaction component and detection process. Together with PCR amplification for the high enough sensitivity and three checks for specificity control, a detection limit of 5 fM was obtained and even one mutation could be discriminated visually. Overall, the new method makes much progress in convenience and economy of PCR-based miRNA assay method so that miRNA assay is going to be more friendly and affordable.

Ratiometric electrochemical assay for sensitive detecting microRNA based on dual-amplification mechanism of duplex-specific nuclease and hybridization chain reaction

We propose a ratiometric electrochemical assay for detecting microRNA (miRNA) on the basis of dual-amplification mechanism by using distinguishable electrochemical signals from thionine (Thi) and ferrocene (Fc). The thiol-modified and ferrocene-labeled hairpin capture probes (CP) are first immobilized on an Au electrode via Au-S reaction. The target miRNA hybridizes with CP and unfolding the hairpin structure of CP to form miRNA-DNA duplexes. Then, kamchatka crab duplex specific nuclease (DSN) specifically cleaves the DNA in miRNA-DNA duplexes, leading to the release of miRNA and another cleaves cycle, meanwhile, numerous Fc leaves away from the electrode surface and leads to the signal-off of Fc. The residual fragment on electrode surface acts as a HCR primer to form dsDNA polymers through in situ HCR with the presence of the primer and two probes (HDNA and HDNA'), resulting in the capture of numerous DNA/Au NPs/Thi and the signal-on of Thi. The dual-amplification mechanism significantly amplifies the decrease of Fc signal and the increase of Thi signal for ratiometric readout (I_Thi/I_Fc), thus providing a sensitive method for the selective detection of miR-141 with a detection limit down to 11aM. The dual-signal ratiometric outputs have an intrinsic self-calibration to the effects from system, which is promising to be applied in biosensing and clinical diagnosis.

Electro-Grafted Electrode with Graphene-Oxide-Like DNA Affinity for Ratiometric Homogeneous Electrochemical Biosensing of MicroRNA

This work demonstrated for the first time a simple and rapid approach to endow the electrode with the excellent discrimination ability over single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) through the robust electrochemical grafting of in situ generated 1-naphthalenesulfonate (NS^-) diazonium salt onto the surface of indium tin oxide (ITO) electrode. On the basis of understanding the influence of sequence and length on the binding affinity of ssDNA and dsDNA toward NS^- grafted ITO (NS^--ITO) electrode, these interesting findings were successfully employed to rationally develop a ratiometric homogeneous electrochemical biosensing platform for microRNA based on the affinity-mediated signal transduction. The achievement of ultrasensitive detection of microRNA lies in a compatibly designed T7 exonuclease-assisted isothermal amplification strategy, in which the presence of target microRNA initiated the continual and opposite affinity inversion of two rationally engineered electrochemical signal reporters, methylene blue (MB) labeled hairpin reporter and ferrocene (Fc) labeled dsDNA reporter, toward NS^--ITO electrode, thereby providing the ratiometric transduction and amplification of the homogeneous electrochemical output signal. By measuring the distinct variation in the peak current intensity ratios of Fc and MB tags, this ratiometric homogeneous electrochemical microRNA biosensing platform showed a detection limit of 25 aM, which is much lower than that of the reported homogeneous electrochemical biosensors. Therefore, we envision that the proposed approach will find useful applications in disease molecular diagnoses and biomedicine.