Photoelectrochemical Detection of Exosomal miRNAs by Combining Target-Programmed Controllable Signal Quenching Engineering

Metal-organic framework (MOF)-based biosensors for miRNA detection

MicroRNAs (miRNAs) play several crucial roles in the physiological and pathological processes of the human body. They are considered as important biomarkers for the diagnosis of various disorders. Thus, rapid, sensitive, selective, and affordable detection of miRNAs is of great importance. However, the small size, low abundance, and highly similar sequences of miRNAs impose major challenges to their accurate detection in biological samples. In recent years, metal-organic frameworks (MOFs) have been applied as promising sensing materials for the fabrication of different biosensors due to their distinctive characteristics, such as high porosity and surface area, tunable pores, outstanding adsorption affinities, and ease of functionalization. In this review, the applications of MOFs and MOF-derived materials in the fabrication of fluorescence, electrochemical, chemiluminescence, electrochemiluminescent, and photoelectrochemical biosensors for the detection of miRNAs and their detection principle and analytical performance are discussed. This paper attempts to provide readers with a comprehensive knowledge of the fabrication and sensing mechanisms of miRNA detection platforms.

Anthracene-based dual channel donor-acceptor triazine-containing covalent organic frameworks for superior photoelectrochemical sensing

Covalent organic frameworks (COFs) exhibit excellent photoelectrically active structures and serve as channels for photon capture and charge carrier transport. However, their relatively high charge-carrier recombination rates and lack of specific recognition sites limit their application in photoelectrochemical sensing. This paper reports a functionalized donor-acceptor (D-A) COF comprising electron-rich polycyclic aromatic moieties and electron-deficient triazines (Tz) incorporating boronic acid through ligand exchange. The number of aromatic rings in the polycyclic aromatic moiety is crucial for establishing an efficient D-A system within COF. In the absence of an external electron donor, the anthracene-based COF exhibited a five-fold enhancement in photocurrent compared to the naphthalene-based COF. The resulting anthracene-based D-A COF exhibited enhanced orbital overlap and electron push-pull interactions, facilitating more effective charge separation. Furthermore, introducing boronic acid enabled the selective enrichment of low-concentration external electron donors, such as dopamine, in the inner Helmholtz plane. This ingenious approach establishes a unique dual-channel D-A system that allows direct measurement of dopamine in serum. Under optimized conditions, the test platform achieves good correspondence for dopamine at 1 to 100 nM and 0.5 to 100 μM with a detecting limit of 0.36 nM (3σ/S, n = 11). This strategy introduces a novel dimension to photoelectrochemical sensing, focusing on the effect of spatial separation between the external electron donor and the photoelectrode interface that intricately shapes the behavior and enhances the performance of the photoelectric system.

Exponential Amplification-Induced Activation of CRISPR/Cas9 for Sensitive Detection of Exosomal miRNA

As an important component of highly heterogeneous exosomes, exosomal microRNAs (miRNAs) have great potential as noninvasive biomarkers for cancer diagnosis. Therefore, a sensitive and simple sensor is the key for its clinical application. Herein, we designed an exponential amplification reaction (EXPAR) to induce the reactivation of the CRISPR-associated protein 9/small guide RNA (Cas9/sgRNA) complex, thus achieving sensitive and visual exosomal miRNAs-21 (miR-21) fluorescence sensing. In this design, we inactivated the sgRNA by hybridizing sgRNA and blocker DNA. Then, we used a trigger DNA to hybridize with miR-21 and produced a lot of activated DNA by EXPAR. Those activated DNA further hybridized with blocker DNA and released the free sgRNA to form the activated Cas9/sgRNA complex. Based on the quick cleavage of activated Cas9/sgRNA complex, the reporter DNA labeled by SYBR Green I was released from the surface of the magnetic nanoparticles (MNPs) into the supernatant, and thus was used to sensitively quantify the miRNAs concentration with a limit of detection of 3 × 103 particles/mL. In addition, this fluorescence sensor has also been successfully employed to distinguish healthy people and cancer patients by naked-eye observation of the fluorescence, thus demonstrating its great potential for accurate and point-of-care cancer diagnosis.

Superoxide dismutase-like cerium dioxide hollow sphere-based highly specific photoelectrochemical biosensing for ascorbic acid

Conventional N-type semiconductor-based photoelectrochemical (PEC) sensors are difficult to achieve high selectivity for ascorbic acid (AA) detection in real samples because co-existing reducing agents act as hole sacrificial agents like AA to promote the increase of photocurrent. Cerium dioxide (CeO2) is a superoxide dismutase-like nanozyme with the reversible Ce3+/Ce4+ redox pair as well as one of alternative N-type semiconductors. To address the problem of PEC detection selectivity of AA, bifunctional CeO2 is a good choice. Herein, a novel and rational PEC biosensor for AA is constructed based on CeO2 hollow spheres as both AA superoxide dismutase-like nanozyme and the photoelectric beacon, which enable the PEC approach with high selectivity. In this protocol, AA can selectively induce a decrease in the CeO2-based photoanode current, which is significantly different from the conventional N-type semiconductor-based PEC sensor, this unique working mechanism is also proposed. The results show that the CeO2-based photocurrent response decreases linearly with AA concentrations in the ranges of 1 μM-600 μM and 600 μM-3000 μM, with a limit of detection of 0.33 μM. Moreover, the fabricated PEC biosensor has advantages of cost-effectiveness, replicability, and stability. Additionally, the sensor is competent for AA determination in practical settings and has achieved satisfactory results.

Integrating Reliable Pt-S Bond-Mediated 3D DNA Nanomachine with Magnetic Separation in a Homogeneous Electrochemical Strategy for Exosomal MicroRNA Detection with Low Background and High Sensitivity

Precise and sensitive analysis of exosomal microRNA (miRNA) is of great importance for noninvasive early disease diagnosis, but it remains a great challenge to detect exosomal miRNA in human blood samples because of their small size, high sequence homology, and low abundance. Herein, we integrated reliable Pt-S bond-mediated three-dimensional (3D) DNA nanomachine and magnetic separation in a homogeneous electrochemical strategy for the detection of exosomal miRNA with low background and high sensitivity. The 3D DNA nanomachine was easily prepared via a facile and rapid freezing method, and it was capable of resisting the influence of biothiols, thus endowing it with high stability. Notably, the as-developed magnetic 3D DNA nanomachine not only enabled the detection system to have a low background but also coupled with liposome nanocarriers to synergistically amplify the current signal. Consequently, by ingeniously combining the low background and multiple signal-amplification strategies in homogeneous electrochemical biosensing, highly sensitive detection of exosomal miRNA was successfully achieved. More significantly, with good anti-interference ability, the as-proposed method could effectively discriminate plasma samples from cancer patients and healthy subjects, thus showing a high potential for application in the nondestructive early clinical diagnosis of disease.

Dual AuNPs detecting probe enhanced the NanoSPR effect for the high-throughput detection of the cancer microRNA21 biomarker

The microRNA21 (miR-21), a specific tumor biomarker, is crucial for the diagnosis of several cancer types, and investigation of its overexpression pattern is important for cancer diagnosis. Herein, we report a low-cost, rapid, ultrasensitive, and convenient biosensing strategy for the detection of miR-21 using a nanoplasmonic array chip coupled with gold nanoparticles (AuNPs). This sensing platform combines the surface plasmon resonance effect of nanoplasmonics (NanoSPR) and the localized surface plasmon resonance (LSPR) effect, which allows the real-time monitoring of the subtle optical density (OD) changes caused by the variations in the dielectric constant in the process of the hybridization of the target miRNA. Using this method, the miRNA achieves a broad detection range from 100 aM to 1 μM, and with a limit of detection (LoD) of 1.85 aM. Furthermore, this assay also has a single-base resolution to discriminate the highly homologous miRNAs. More importantly, this platform has high throughput characteristics (96 samples can be detected simultaneously). This strategy exhibits more than 86.5 times enhancement in terms of sensitivity compared to that of traditional biosensors.

AuNPs/graphdiyne self-powered sensing platform for sensitive detection of microRNA with DNAzyme walker for signal amplification

A novel self-powered biosensor is engineered by the integration of DNAzyme walker and AuNPs/graphdiyne biosensing interface, realizing sensitive detection of target microRNA. The cleverly constructed DNAzyme walker with outstanding signal transduction ability to obtain an amplified signal response. In addition, the AuNPs/graphdiyne significantly improves electron transport speed of biosensing interface for improving the sensitivity of biosensor. A dynamic linear range of 0.05 fM-10 pM with a low detection limit of 0.015 fM (S/N = 3) is obtained by utilizing the self-powered biosensor. Meanwhile, the developed self-powered biosensor is capable of assaying miRNA-21 in human serum samples with satisfactory recoveries. This strategy provides a valid method for the sensitive microRNA detection, and shows great potential in point-care detection of tumor biomarker.

Practical tips and new trends in electrochemical biosensing of cancer-related extracellular vesicles

To tackle cancer and provide prompt diagnoses and prognoses, the constantly evolving biosensing field is continuously on the lookout for novel markers that can be non-invasively analysed. Extracellular vesicles (EVs) may represent a promising biomarker that also works as a source of biomarkers. The augmented cellular activity of cancerous cells leads to the production of higher numbers of EVs, which can give direct information on the disease due to the presence of general and cancer-specific surface-tethered molecules. Moreover, the intravesicular space is enriched with other molecules that can considerably help in the early detection of neoplasia. Even though EV-targeted research has indubitably received broad attention lately, there still is a wide lack of practical and effective quantitative procedures due to difficulties in pre-analytical and analytical phases. This review aims at providing an exhaustive outline of the recent progress in EV detection using electrochemical and photoelectrochemical biosensors, with a focus on handling approaches and trends in the selection of bioreceptors and molecular targets related to EVs that might guide researchers that are approaching such an unstandardised field.

Electrochemical nano-sensing interface for exosomes analysis and cancer diagnosis

Exosomes are a class of the nanosized extracellular vesicles, which have emerged as representative liquid biopsy biomarkers. To date, the electrochemical nanosensors are of great significance in the exosome detection with the advantages of easy operation, high accuracy and reliable repeatability. Especially, the growing field of nano interface has provided the electrochemical sensing platforms for the accurate exosomes analysis. The incorporation of multiple nanomaterials can take advantages and synergistic properties of functional units. So, based on the integration of with nanomaterial-based signal transduction and specific biorecognition, the nano-sensing interface provides excellent electrochemical features owing to rapid mass transport and excellent conductivity. The nano-sensing interface with a wide variety of morphologies and structure also provides the large active surface area for the immobilization of bio-capturing agents. Furthermore, through the design of nanostructured electrode array, the efficiency of transducer can be greatly improved. It should be noticed that the elaboration of a proper sensor requires the profound knowledge of the nano-sensing interface. Therefore, this article presents a review of the recent advance in exosomes detection based on the electrochemical nano-sensing interface, including electrochemical analysis principles, exosome sensing mechanisms, nano-interface construction strategies, as well as the typical diagnosis application. In particular, the article is focused on the exploration of the various electrochemical sensing performance of nano-interface in the exosome detection. We have also prospected the future trend and challenge of the electrochemical nano-sensing interface for exosomes analysis in clinical cancer diagnosis.

AuNPs/CdS QDs/CeO2 ternary nanocomposite coupled with scrollable three-dimensional DNA walker mediated cycling amplification for sensitive photoelectrochemical miRNA assay

Herein, a novel ternary nanocomposite (AuNPs/CdS QDs/CeO₂) with excellent photoelectrochemical (PEC) performance was synthesized as signal probe to construct a near-zero background biosensor for sensitive miRNA-182-5p detection, by integrating with a scrollable three-dimensional (3D) DNA walker mediated cleavage cycling amplification. Impressively, the formation and rolling of scrollable 3D DNA walker triggered by target could realize dynamic, rapid and specific digestion of hairpin DNA on electrode with the aid of Exonuclease III (Exo III), which thus exposed abundant binding sites for assembling stable DNA labeled AuNPs/CdS QDs/CeO₂ nanoprobes. Thanks to the formation of type-II heterojunction (between CeO₂ and CdS QDs) and Schottky junction (generated by CeO₂ and AuNPs), an ideal photoelectric conversion efficiency accompanied with stunningly improved photocurrent was thus acquired for significantly improving the detection sensitivity. It turned out that the detection limit (LOD) of biosensor was ultralow (31 aM). Significantly, the proposed PEC biosensor would exhibit great potential for the composite as a splendid indicator and provide an avenue for constructing the sensing platform with excellent sensitivity and ultralow background.

Piezotronic Effect-Assisted Photoelectrochemical Exosomal MicroRNA Monitoring Based on an Electron Donor Self-Supplying Strategy

Exosomal microRNAs (miRNAs) as newly emerging reliable and noninvasive biomarkers have demonstrated a significant function in early cancer diagnosis. Photoelectrochemical (PEC) biosensing has attracted unprecedented attention in exosomal miRNA monitoring due to its inherent advantages of both electrochemical and optical techniques; however, the severe charge carrier recombination greatly restricts the PEC assay performance. Herein, a high-sensitive PEC strategy assisted by the piezoelectric effect is designed based on Bi₂WO₆/Cu₂S heterojunctions and implemented for the monitoring of exosomal miRNAs. The introduction of the piezoelectric effect enables promoted electron-hole transfer and separation, thereby improving the analytical sensitivity. In addition, a target reprogramming metal-organic framework-capped CaO₂ (MOF@CaO₂) hybrids is prepared, in which MOF@CaO₂ being responsive to exosomal miRNAs induces exposure of the capped CaO₂ to H₂O and then triggers self-supplying of H₂O₂, which effectively suppresses the electron-hole recombination, giving rise to an amplified photocurrent and a decrease in the cost of the reaction. Benefiting from the coupled sensitization strategy, the as-fabricated PEC strategy exhibits high sensitivity, specificity, low cost, and ease of use for real-time analysis of exosomal miRNAs within the effectiveness linear range of 0.1 fM-1 μM. The present work demonstrates promising external field coupling-enhanced PEC bioassay and offers innovative thoughts for applying this strategy in other fields.

Au nanoclusters-decorated WO3 nanorods for ultrasensitive photoelectrochemical sensing of Hg2+

Ultrasensitive photoelectrochemical sensing of Hg2+ is achieved using Au nanocluster-decorated WO3 nanorods as photoactive materials.