Detection of microRNA-21 based on smartly designed ratiometric electrochemical sensor and dual-signal amplification

MicroRNA (miRNA) serves as an effective and viable biomarker for early diagnosis and monitoring of cancer disorders. It is highly expressed in tumor cells, including lung cancer, liver cancer and lymphoma. Herein, we propose a ratiometric electrochemical sensor for ultrasensitive detection of miRNA-21 using dual signal amplification, hybridization chain reaction and Exo III assisted-amplification. Methylene blue (MB) and Hemin are chosen as two electrochemical species. Then the ratiometric electrochemical sensor were developed, which showed favorable performance of miRNA-21 detection, and exhibited a detection concentration range from 1 fM to 10 nM. Notably, the limit of detection for this biosensor was 0.15 fM. Overall, this strategy for miRNA detection holds significant promise for early cancer screening.

Near-infrared fluorescent probe visual detection of Hg2+ and its application in biological system and ecological system

Mercury ion (Hg2+), a heavy metal cation with greater toxicity, is widely present in the ecological environment and has become a serious threat to human health and environmental safety. Currently, developing a solution to simultaneously visualize and monitor Hg2+ in environmental samples, including water, soil, and plants, remains a great challenge. In this work, we created and synthesized a near-infrared fluorescent probe, BBN-Hg, and utilized Hg2+ to trigger the partial cleavage of the carbon sulfate ester in BBN-Hg as a sensing mechanism, and the fluorescence intensity of BBN-Hg was significantly enhanced at 650 nm, thus realizing the visualization of Hg2+ with good selectivity (detection limit, 53 nM). In live cells and zebrafish, the probe BBN-Hg enhances the red fluorescence signal in the presence of Hg2+, and successfully performs 3D imaging on zebrafish, making it a powerful tool for detecting Hg2+ in living systems. More importantly, with BBN-Hg, we are able to detect Hg2+ in actual water samples, soil and plant seedling roots. Furthermore, the probe was prepared as a test strip for on-site determination of Hg2+ with the assistance of a smartphone. Therefore, this study offers an easy-to-use and useful method for tracking Hg2+ levels in living organisms and their surroundings.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

A dicyanoisophorone-based ICT fluorescent probe for the detection of Hg2+ in water/food sample analysis and live cell imaging

Mercury ions are notoriously difficult to biodegradable, and its abnormal bioaccumulation in the human body through the food chain can cause various diseases. Therefore, the quantitative and real-time detection of Hg²⁺ is very extremely important. Herein, we have brilliant designed and synthesized (E)-O-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenyl) O-phenyl carbonothioate (ICM-Hg) as a selective fluorescent probe for Hg²⁺ detection in real samples and intracellular staining. ICM-Hg displayed high specificity toward Hg²⁺ by activating the intramolecular charge transfer (ICT) process, resulting in distinguished color change from colorless to bright yellow along with noticeable switch on yellow fluorescence emission. The fluorescent intensity of ICM-Hg at 585 nm shows a well linear relationship in the range of Hg²⁺ concentration (0-45 μM), and the detection of limit for Hg²⁺ is calculated to be 231 nM. Promisingly, ICM-Hg can efficiently detect Hg²⁺ in real samples including tap water, tea, shrimp, and crab with quantitative recovery as well as the intracellular fluorescence imaging.

Electrochemical detection of methyl-paraoxon based on bifunctional cerium oxide nanozyme with catalytic activity and signal amplification effect

A new electrochemical sensor for organophosphate pesticide (methyl-paraoxon) detection based on bifunctional cerium oxide (CeO₂) nanozyme is here reported for the first time. Methyl-paraoxon was degraded into p-nitrophenol by using CeO₂ with phosphatase mimicking activity. The CeO₂ nanozyme-modified electrode was then synthesized to detect p-nitrophenol. Cyclic voltammetry was applied to investigate the electrochemical behavior of the modified electrode, which indicates that the signal enhancement effect may attribute to the coating of CeO₂ nanozyme. The current research also studied and discussed the main parameters affecting the analytical signal, including accumulation potential, accumulation time, and pH. Under the optimum conditions, the present method provided a wider linear range from 0.1 to 100 μmol/L for methyl-paraoxon with a detection limit of 0.06 μmol/L. To validate the proof of concept, the electrochemical sensor was then successfully applied for the determination of methyl-paraoxon in three herb samples, i.e., Coix lacryma-jobi, Adenophora stricta and Semen nelumbinis. Our findings may provide new insights into the application of bifunctional nanozyme in electrochemical detection of organophosphorus pesticide.

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A new electrochemical method for methyl-paraoxon detection by using bifunctional nanozyme was presented.

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The cerium oxide nanozyme modified glassy carbon electrode was prepared to improve the sensitivity.

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The developed method has been successfully applied in three herbal plant samples.

Ultrasensitive colorimetric strategy for Hg2+ detection based on T-Hg2+-T configuration and target recycling amplification

A novelty aptasensor for ultrasensitive detection of Hg²⁺ is developed, exploiting the combination of plasmonic properties of gold nanoparticles (AuNPs) and exonuclease III (Exo III)-assisted target recycling for signal amplification. In the presence of Hg²⁺, a DNA duplex can be formed due to the strong coordination of Hg²⁺ and T bases of single-stranded DNA (ssDNA) probe. Exo III digests the DNA duplex from the 3' to 5' direction, resulting in the releasing of Hg²⁺. Then, the released Hg²⁺ binds with another ssDNA probe through T-Hg²⁺-T coordination. After Exo III-assisted Hg²⁺ cycles, numerous ssDNA probes are exhausted, which promotes poly(diallyldimethylammonium chloride) (PDDA)-induced AuNP aggregation, leading to an obvious color change and aggregation-induced plasmon red shift of AuNPs (from 520 to 610 nm). Therefore, this biosensor is ultrasensitive, which is applicable to the detection of trace level of Hg²⁺ with a linear range from 5 pM to 0.6 nM and an ultralow detection limit of 0.2 pM. Furthermore, it enables visual detection of Hg²⁺ as low as 50 pM by the naked eye. More importantly, the assay can be applied to the reliable determination of spiked Hg²⁺ in sea water samples with good recovery.

Impedimetric and Plasmonic Sensing of Collagen I Using a Half-Antibody-Supported, Au-Modified, Self-Assembled Monolayer System

This research presents an electrochemical immunosensor for collagen I detection using a self-assembled monolayer (SAM) of gold nanoparticles (AuNPs) and covalently immobilized half-reduced monoclonal antibody as a receptor; this allowed for the validation of the collagen I concentration through two different independent methods: electrochemically by Electrochemical Impedance Spectroscopy (EIS), and optically by Surface Plasmon Resonance (SPR). The high unique advantage of the proposed sensor is based on the performance of the stable covalent immobilization of the AuNPs and enzymatically reduced half-IgG collagen I antibodies, which ensured their appropriate orientation onto the sensor's surface, good stability, and sensitivity properties. The detection of collagen type I was performed in a concentration range from 1 to 5 pg/mL. Moreover, SPR was utilized to confirm the immobilization of the monoclonal half-antibodies and sensing of collagen I versus time. Furthermore, EIS experiments revealed a limit of detection (LOD) of 0.38 pg/mL. The selectivity of the performed immunosensor was confirmed by negligible responses for BSA. The performed approach of the immunosensor is a novel, innovative attempt that enables the detection of collagen I with very high sensitivity in the range of pg/mL, which is significantly lower than the commonly used enzyme-linked immunosorbent assay (ELISA).

Ultrasensitive electrochemical detection of microRNA based on in-situ catalytic hairpin assembly actuated DNA tetrahedral interfacial probes

Selective and sensitive detection of microRNA is crucial for early diagnosis and pathogenesis of disease. Here, we established a novel electrochemical biosensor for simple and accurate analysis of the tumor biomarker microRNA-141, which was based on in-situ catalytic hairpin assembly (CHA) actuated DNA tetrahedral (DTN) interfacial probes. Two hairpin structures used for CHA reaction were placed on the DTN, in which the hairpin H1 on the one vertex of DTN and hairpin H2 embedded in adjacent edge, respective. The target microRNA-141 could open the hairpin H1 and activated the in-situ CHA reaction between H1 and H2 to alter the conformational of DTN, increasing the chances of the direct interaction between methylene blue (MB) and the electrode surface, leading to an increase in the electrochemical signal. Meanwhile, the released miRNA-141 could unfold another H1, enabling the enzyme-free recycling of the target to obtain amplified electrochemical signals. Moreover, the in-situ catalytic hairpin assembly reaction on DTN could shorten the reaction time and enhance the sensitivity. The established biosensor exhibited a wide linear dynamic range of miRNA-141 from 1 fM to 100 pM with a detection limit of 0.32 fM. Besides, the approach can discriminate the target miRNA from mismatched ones with excellent selectivity and can be successfully applied in diluted serum samples, holding great potential for sensitive detection of various biomarkers clinically.

Light-responsive Au nanoclusters with oxidase-like activity for fluorescent detection of total antioxidant capacity

A fluorescent assay for total antioxidant capacity (TAC) detection based on the light-responsive oxidase-like activity of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) has been developed. Thiamine (TH) as the peroxidase substrate usually works at alkaline conditions and thus limits its practical applications. Here, by utilization the light-responsive oxidase-like activity of BSA-AuNCs, TH is oxidized to fluorescent thiochrome under neutral condition in two minutes due to the single oxygen generated by BSA-AuNCs upon light irradiation. After the introduction of antioxidants into the BSA-AuNCs-TH system, the formation of thiochrome is inhibited resulting in the fluorescence decrease. On the basis of the above facts, BSA-AuNCs-TH-based assay has been fabricated and applied successfully to detect antioxidants and the TAC of vitamin C tablets as well as some commercial fruit juice with satisfied results. This work may provide novel insights into developing light-responsive nanozymes-based fluorescent assays.

Reversible regulation of enzyme-like activity of molybdenum disulfide quantum dots for colorimetric pharmaceutical analysis

Regulating the catalytic activity of nanozymes is significant for their applications in various fields. Here, we demonstrate a new strategy to achieve reversible regulation of the nanozyme's activity for sensing purpose. This strategy involves the use of zero-dimensional MoS₂ quantum dots (MQDs) as the building blocks of nanozymes which display very weak peroxidase (POD)-like activity. Interestingly, such POD-like activity of the MQDs largely enhances in the presence of Fe³⁺ while diminishes with the addition of captopril thereafter. Further investigations identify the mechanism of Fe³⁺-mediated aggregation-induced enhancement of the POD-like activity and the inhibitory effect of captopril on the enhancement, which is highly dependent on their concentrations. Based on this finding, a colorimetric method for the detection of captopril is developed. This sensing approach exhibits the merits of simplicity, rapidness, reliability, and low cost, which has been successfully applied in quality control of captopril in pharmaceutical products. Moreover, the present sensing platform allows smartphone read-out, which has promising applications in point-of-care testing devices for clinical diagnosis and drug analysis.

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A new post-synthesis strategy is developed to achieve reversible regulation of nanozyme's activity.

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Fe³⁺-mediated aggregation can enhance the peroxidase-like activity of MoS₂ quantum dots more than 10 times.

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Quality control of captopril in pharmaceutical products is realized by manipulating nanozyme's catalytical activity.

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This sensing approach allows smartphone read-out, which has promising applications in point-of-care testing.

An enzyme cascade sensor with resistance to the inherent intermediate product by logic-controlled peroxidase mimic catalysis

Enzyme cascade sensors usually could not discriminate between the target and intermediate product. Herein, based on "AND" logic-controlled activation of the glucose oxidase-copper peroxide sensing system, enzyme cascade detection for glucose with resistance to inherently existing intermediate product H₂O₂ was reported for the first time, which may provide a novel way for facilitating enzyme cascade sensing.

Applications of DNA-nanozyme-based sensors

Since the discovery of the enzyme-like activities of nanomaterials, the study of nanozymes has become one of the most popular research frontiers of diverse areas including biosensors. DNA also plays a very important role in the construction of biosensors. Thus, the idea of combined applications of nanozymes with DNA (DNA-nanozyme) is very attractive for the development of nanozyme-based biosensors, which has attracted considerable interest of researchers. To date, many sensors based on DNA-functionalized or templated nanozymes have been reported for the detection of various targets and highly accelerated the development of nanozyme-based sensors. In this review, we summarize the main applications and advances of DNA-nanozyme-based sensors. Additionally, perspectives and challenges are also discussed at the end of the review.

Nanozymes as Enzyme Inhibitors

Nanozyme is a type of nanomaterial with intrinsic enzyme-like activity. Following the discovery of nanozymes in 2007, nanozyme technology has become an emerging field bridging nanotechnology and biology, attracting research from multi-disciplinary areas focused on the design and synthesis of catalytically active nanozymes. However, various types of enzymes can be mimicked by nanomaterials, and our current understanding of nanozymes as enzyme inhibitors is limited. Here, we provide a brief overview of the utility of nanozymes as inhibitors of enzymes, such as R-chymotrypsin (ChT), β-galactosidase (β-Gal), β-lactamase, and mitochondrial F0F1-ATPase, and the mechanisms underlying inhibitory activity. The advantages, challenges and future research directions of nanozymes as enzyme inhibitors for biomedical research are further discussed.