Living-Cell MicroRNA Imaging with Self-Assembling Fragments of Fluorescent Protein-Mimic RNA Aptamer

Fluorogenic Aptamer-Based Hybridization Chain Reaction for Signal-Amplified Imaging of Apurinic/Apyrimidinic Endonuclease 1 in Living Cells

A fluorogenic aptamer (FA)-based hybridization chain reaction (HCR) could provide a sensitive and label-free signal amplification method for imaging molecules in living cells. However, existing FA-HCR methods usually face some problems, such as a complicated design and significant background leakage, which greatly limit their application. Herein, we developed an FA-centered HCR (FAC-HCR) method based on a remote toehold-mediated strand displacement reaction. Compared to traditional HCRs mediated by four hairpin probes (HPs) and two HPs, the FAC-HCR displayed significantly decreased background leakage and improved sensitivity. Furthermore, the FAC-HCR was used to test a non-nucleic acid target, apurinic/apyrimidinic endonuclease 1 (APE1), an important BER-involved endonuclease. The fluorescence analysis results confirmed that FAC-HCR can reach a detection limit of 0.1174 U/mL. By using the two HPs for FAC-HCR with polyetherimide-based nanoparticles, the activity of APE1 in living cells can be imaged. In summary, this study could provide a new idea to design an FA-based HCR and improve the performance of HCRs in live cell imaging.

In Vivo Imaging MicroRNA with Bright Fluorescent RNA Aptamer Through Target-Mediated Entropy-Driven Toehold Exchange

MicroRNAs (miRNAs) play vital roles in biological activities, but their in vivo imaging is still challenging due to the low abundance and the lack of efficient fluorescent tools. RNA aptamers with high affinity and low background emerge for bioimaging yet suffering from low brightness. We introduce a rational design based on target-mediated entropy-driven toehold exchange (EDTE) to induce the release of RNA aptamer and subsequently light up corresponding fluorophore, which achieves selective imaging of miRNAs with good stability in both living cells and tumor-bearing mouse. Through tailoring recognition unit of the EDTE probes, highly sensitive imaging of different miRNAs including miRNA-125b and miRNA-21 is achieved, confirming its universal bioimaging applications. In comparison with the reported "one-to-one" model, the EDTE strategy shows a remarkable 4.6-time improvement in signal/noise ratio for intracellular imaging of the same miRNA. Particularly, it realizes sensitive imaging of miRNA in vivo, providing a promising tool in investigating functions and interactions of disease-associated miRNAs.

Fluorogenic RNA Aptamer-Based Amplification and Transcription Strategy for Label-free Sensing of Methyltransferase Activity in Complex Matrixes

DNA methyltransferase is significant in cellular activities and gene expression, and its aberrant expression is closely linked to various cancers during initiation and progression. Currently, there is a great demand for reliable and label-free techniques for DNA methyltransferase evaluation in tumor diagnosis and cancer therapy. Herein, a low-background fluorescent RNA aptamer-based sensing approach for label-free quantification of cytosine-guanine (CpG) dinucleotides methyltransferase (M.SssI) is reported. The fluorogenic light-up RNA aptamers-based strategy exhibits high selectivity via restriction endonuclease, padlock-based recognition, and RNA transcription. By combining rolling circle amplification (RCA), and RNA transcription with fluorescence response of RNA aptamers of Spinach-dye compound, the proposed platform exhibited efficiently ultrahigh sensitivity toward M.SssI. Eventually, the detection can be achieved in a linear range of 0.02-100 U mL-1 with a detection limit of 1.6 × 10-3 U mL-1. Owing to these superior features, the method is further applied in serum samples spiked M.SssI, which delivers a recovery ranging from 92.0 to 107.0% and a relative standard deviation <7.0%, providing a promising and practical tool for determining M.SssI in complex biological matrices.

Simultaneous detection of dual microRNAs related to EV71 using ICP-MS based on metal nanoparticle labeling with hybridization chain reaction

BACKGROUND

Hand, foot, and mouth (HMFD) disease caused by enterovirus 71 (EV 71), is closely associated with severe clinical manifestations and can be deadly. Early detection of EV 71 can be achieved by detecting the increment in miR296 and miR16 in the serum. Using HCR to amplify signals and convert biological signals into metal nanoparticle signals detectable by ICP-MS is a detection method that can collect more accurate and reliable information, compared with traditional methods, in the detection of biological samples.

RESULTS

We described a strategy for the simultaneous detection of miR296 and miR16 by ICP-MS based on metal nanoparticles (NPs) labeling with HCR. Briefly, single-stranded DNA (ssDNA) and magnetic beads (MBs), as well as NPs and signal probes for miRNA (Sp-miR) were firstly conjugated via the streptavidin-biotin recognition system, constituting ssDNA-MBs and NPs-Sp-miR complex, respectively. The latter complex then hybridized with the former through HCR, generating the nanosensors for targets. Then, the targets were added and hybridized with ssDNA, and the HCR complex with NPs was released into the solution. Finally, the corresponding signals of the NPs were measured by ICP-MS. Results demonstrated that the developed method had good sensitivity and satisfactory selectivity and precision. Furthermore, when applied to biological samples with a complex matrix, the developed method also showed good recovery (88 % - 92 %) and reproducibility (RSD<10 %).

SIGNIFICANCE

This method contributes to the early diagnosis of HFMD and opens up ideas for the further development of high-throughput biomarker detection. The strategy has practical potential for miR296 and miR16 detection in biological samples and provides a promising tool for multiple miRNA detection.

Ultrasensitive Ochratoxin A Detection in Cereal Products Using a Fluorescent Aptasensor Based on RecJf Exonuclease-Assisted Target Recycling

Ochratoxin A (OTA) is a mycotoxin widely found in foodstuffs such as cereal grains. It greatly threatens human health owing to its strong toxicity and high stability. Aptasensors have emerged as promising tools for the analysis of small molecule contaminants. Nucleic-acid-based signal amplification enables detectable signals to be obtained from aptasensors. However, this strategy often requires the use of complex primers or multiple enzymes, entailing problems such as complex system instability. Herein, we propose a fluorescent aptasensor for the ultrasensitive detection of OTA in cereal products, with signal amplification through RecJf exonuclease-assisted target recycling. The aptamer/fluorescein-labeled complementary DNA (cDNA-FAM) duplex was effectively used as the target-recognition unit as well as the potential substrate for RecJf exonuclease cleavage. When the target invaded the aptamer-cDNA-FAM duplex to release cDNA-FAM, RecJf exonuclease could cleave the aptamer bonded with the target and release the target. Thus, the target-triggered cleavage cycling would continuously generate cDNA-FAM as a signaling group, specifically amplifying the response signal. The proposed exonuclease-assisted fluorescent aptasensor exhibited a good linear relationship with OTA concentration in the range from 1 pg/mL to 10 ng/mL with an ultralow limit of detection (6.2 ng/kg of cereal). The analytical method showed that recoveries of the cereal samples ranged from 83.7 to 109.3% with a repeatability relative standard deviation below 8%. Importantly, the proposed strategy is expected to become a common detection model because it can be adapted for other targets by replacing the aptamer. Thus, this model can guide the development of facile approaches for point-of-care testing applications.

Engineered aptamers for molecular imaging

Molecular imaging, including quantification and molecular interaction studies, plays a crucial role in visualizing and analysing molecular events occurring within cells or organisms, thus facilitating the understanding of biological processes. Moreover, molecular imaging offers promising applications for early disease diagnosis and therapeutic evaluation. Aptamers are oligonucleotides that can recognize targets with a high affinity and specificity by folding themselves into various three-dimensional structures, thus serving as ideal molecular recognition elements in molecular imaging. This review summarizes the commonly employed aptamers in molecular imaging and outlines the prevalent design approaches for their applications. Furthermore, it highlights the successful application of aptamers to a wide range of targets and imaging modalities. Finally, the review concludes with a forward-looking perspective on future advancements in aptamer-based molecular imaging.

NIR Photocontrolled Fluorescent Nanosensor under a Six-Branched DNA Nanowheel-Induced Nucleic Acid Confinement Effect for High-Performance Bioimaging

Although DNA nanotechnology is a promising option for fluorescent biosensors to perform bioimaging, the uncontrollable target identification during biological delivery and the spatially free molecular collision of nucleic acids may cause unsatisfactory imaging precision and sensitivity, respectively. Aiming at solving these challenges, we herein integrate some productive notions. On the one hand, the target recognition component is inserted with a photocleavage bond and a core-shell structured upconversion nanoparticle with a low thermal effect is further employed to act as the ultraviolet light generation source, under which a precise near-infrared photocontrolled sensing is achieved through a simple external 808 nm light irradiation. On the other hand, the collision of all of the hairpin nucleic acid reactants is confined by a DNA linker to form a six-branched DNA nanowheel, after which their local reaction concentrations are vastly enhanced (∼27.48 times) to induce a special nucleic acid confinement effect to guarantee highly sensitive detection. By selecting a lung cancer-associated short noncoding microRNA sequence (miRNA-155) as a model low-abundance analyte, it is demonstrated that the newly established fluorescent nanosensor not only presents good in vitro assay performance but also exhibits a high-performance bioimaging competence in live biosystems including cells and mouse body, propelling the progress of DNA nanotechnology in the biosensing field.

Applications of Smartphone-Based Aptasensor for Diverse Targets Detection

Aptamers are a particular class of functional recognition ligands with high specificity and affinity to their targets. As the candidate recognition layer of biosensors, aptamers can be used to sense biomolecules. Aptasensors, aptamer-based biosensors, have been demonstrated to be specific, sensitive, and cost-effective. Furthermore, smartphone-based devices have shown their advantages in binding to aptasensors for point-of-care testing (POCT), which offers an immediate or spontaneous responding time for biological testing. This review describes smartphone-based aptasensors to detect various targets such as metal ions, nucleic acids, proteins, and cells. Additionally, the focus is also on aptasensors-related technologies and configurations.

Monitoring Clinical-Pathological Grading of Hepatocellular Carcinoma Using MicroRNA-Guided Semiconducting Polymer Dots

MicroRNAs (miRNAs) are a class of small, noncoding RNAs involved in nearly all genetic central dogma processes and human biological behavior, which also play a significant role in the pathological activity of tumors, such as gene transcription, protein translation, and exosome secretion. Therefore, through the navigation of certain specific miRNAs, we can trace the specific physiological processes or image some specific tissues. Designing and accurately positioning microRNA (miRNA)-sensitive fluorescent nanoprobes with benign specificity and recognition in cells or tissues are a challenging research field. To solve the difficulties, we introduce four semiconducting polymer dots (Pdots) as nanoprobes linked by specific miRNA antisense sequences for monitoring the pathological grading by the variation in miRNA expression. Based on the base pairing principle, these miRNA-sensitive Pdots could bind to specific miRNAs within the cancerous cells. As impacted by the background of different pathology gradings, the proportions of the four hepatocellular carcinoma (HCC)-specific miRNAs within the cancerous cell are different, and the pathological grading of the patient tissues can be determined by comparing the palette combinations. The short single-stranded RNA-functionalized Pdots, which have excellent microRNA sensitivity, are observed in an experimental cell model and a series of tissue specimens from HCC patients for the first time. Using the Förster (or fluorescence) resonance energy transfer (FRET) model of Pdots and Cy3dt tag to simulate in vivo miRNA detection, the superior sensitivity and specificity of these nanoprobes are verified. The interference of subjective factors in traditional single/bis-dye emission intensity detection is abandoned, and multiple label staining is used to enhance sensitivity further and reduce the false-positive rate. The feasibility exhibited by this novel staining method is verified in normal hepatocellular HCC cell lines and 16 frozen ultrathin tissue sections, which are employed to quantify pathological grading-related color presentation systems for clinical doctors and pathologists' use. The intelligently designed miRNA-guided Pdots will emerge as an ideal platform with promising biological imaging.

Label- and enzyme-free plasmon-enhanced single molecule fluorescence detection of HIV DNA fragments based on a catalytic hairpin assembly

We developed a label- and enzyme-free single molecule fluorescence counting strategy for HIV DNA fragments detection. The nucleic acid biosensor consists of a 5' terminal connected with a triangular gold nanoplate, 3' terminal rich in guanine hairpin probe (HP1) and a hairpin probe HP2 complementary to the partial sequence of HP1. Without the existence of the target DNA, the DNA fragment rich in the guanine region is locked in a hairpin structure and cannot form a G-quadruplex, hence NMM exhibits a low fluorescence signal. When the target DNA exists, the hairpin assembly will trigger a strand displacement amplification reaction that produces a great number of G-quadruplexes, and the fluorescence brightness of NMM will be enhanced. The plasmon resonance effect of the triangular gold nanoplates will further amplify the fluorescence signal. This method can analyze the target DNA with high sensitivity and selectivity, and the detection limit is 0.83 fM. The analysis of the HIV DNA fragments in diluted human serum samples was successfully achieved, and the recovery rate was 92%-104%. Because of its easy operation and low cost, it has broad development potential in biochemical analysis and clinical applications.