SDR-ELISA: Ultrasensitive and high-throughput nucleic acid detection based on antibody-like DNA nanostructure

A double methylene blue labeled single-stranded DNA and hairpin DNA coupling biosensor for the detection of Fusarium oxysporum f. sp. cubense race 4

The DCL gene in Fusarium oxysporum f. sp. cubense Race 4 (Foc4) is a pivotal pathogenic factor causing banana fusarium wilt. Precise DCL detection is crucial for Foc4 containment. Here, we present a novel ssDNA-hDNA coupling electrochemical biosensor for highly specific DCL detection. The sensing interface was formed via electrodeposition of a composite containing reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) onto a carbon screen-printed electrode (SPE), followed by thiol-modified ssDNA functionalization. Additionally, the incorporation of hDNA, with methylene blue (MB) at both ends, binds to ssDNA through base complementarity, forming an ssDNA-hDNA coupling probe with bismethylene blue. This sensing strategy relies on DCL recognition by the hDNA probe, leading to DNA hairpin unfolding and detachment of hDNA bearing two MBs from ssDNA, generating a robust "on-off" signal. Empirical results demonstrate the sensor's amplified electrical signals, reduced background currents, and an extended detection range (6.02 × 106-3.01 × 1010 copies/μL) with a limit of detection (3.01 × 106 copies/μL) for DCL identification. We applied this sensor to analyze soil, banana leaves, and fruit samples, confirming its high specificity and stability. Moreover, post-sample detection, the sensor exhibits reusability, offering a cost-effective and rapid approach for banana wilt detection.

Dual-functional DNAzyme powered CRISPR-Cas12a sensor for ultrasensitive and high-throughput detection of Pb2+ in freshwater

Freshwater lead pollution has posed severe threat to the environment and human health, underscoring the urgent necessity for accurate and user-friendly detection methods. Herein, we introduce a novel Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR-Cas) sensor for highly sensitive Pb2+ detection. To accomplish this, we designed a dual-functional deoxyribozyme (df-DNAzyme) probe that functions as an activator for the CRISPR-Cas12a system while also recognizing Pb2+. The df-DNAzyme probe was subsequently combined with gold nanoparticles (AuNPs) to fabricate a DNAzyme/AuNP nanoprobe, facilitating the activation of CRISPR-Cas12a in a one-to-multiple manner. Upon exposure to Pb2+, the df-DNAzyme is cleaved, causing disintegration of the DNAzyme/AuNP nanoprobe from magnetic beads. The degraded DNAzyme/AuNP containing multiple double-stranded DNA activators efficiently triggers CRISPR-Cas12a activity, initiating cleavage of fluorescence-quenched reporter DNA and generating amplified signals accordingly. The amplified fluorescence signal is accurately quantified using a quantitative polymerase chain reaction (qPCR) instrument capable of measuring 96 or 384 samples simultaneously at the microliter scale. This technique demonstrates ultra-sensitive detection capability for Pb2+ at concentrations as low as 1 pg/L within a range from 1 pg/L to 10 μg/L, surpassing limits set by World Health Organization (WHO) and United States Environmental Protection Agency (US EPA) guidelines. This study offers an ultrasensitive and high-throughput method for the detection of Pb2+ in freshwater, thereby advancing a novel approach towards the development of precise and convenient techniques for detecting harmful contaminants.

Catalytic hairpin DNA assembly-based chemiluminescent assay for the detection of short SARS-CoV-2 target cDNA

Colorimetric sensors are recognized as a promising means for target molecule detection as they provide rapid, cost-effective, and facile sensing visible to the naked eye. Challenges remain though in terms of their detection sensitivity and specificity for short-length target genes. Herein, we demonstrate the successful combination of the catalytic hairpin DNA assembly (CHA) approach with enzyme-linked immunosorbent assay (ELISA)-mimicking techniques for a simple, sensitive, and sequence-specific colorimetric assay to detect short SARS-CoV-2 target cDNA. In the developed CHA-based chemiluminescent assay, a low concentration of target cDNA is continuously recycled to amplify dimeric DNA probes from two biotinylated hairpin DNA until the hairpin DNA is completely consumed. The dimeric DNA probes are effectively immobilized in a neutravidin-coated microplate well and then capture neutravidin-conjugated horseradish peroxidase via biotin-neutravidin interactions, resulting in a sensitive and selective colorless-to-blue color change. The developed sensing system exhibits a high sensitivity with a detection limit of ~1 nM for target cDNA as well as the ability to precisely distinguish a single-base mismatched mutant gene within 2 h. As the proposed system does not require complex protocols or expensive equipment to amplify target cDNA, it has the potential to be utilized as a powerful tool to improve the detection sensitivity of target genes for clinical diagnostics with colorimetric detection.

Nucleic Acid Tests for Clinical Translation

Nucleic acids, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are natural biopolymers composed of nucleotides that store, transmit, and express genetic information. Overexpressed or underexpressed as well as mutated nucleic acids have been implicated in many diseases. Therefore, nucleic acid tests (NATs) are extremely important. Inspired by intracellular DNA replication and RNA transcription, in vitro NATs have been extensively developed to improve the detection specificity, sensitivity, and simplicity. The principles of NATs can be in general classified into three categories: nucleic acid hybridization, thermal-cycle or isothermal amplification, and signal amplification. Driven by pressing needs in clinical diagnosis and prevention of infectious diseases, NATs have evolved to be a rapidly advancing field. During the past ten years, an explosive increase of research interest in both basic research and clinical translation has been witnessed. In this review, we aim to provide comprehensive coverage of the progress to analyze nucleic acids, use nucleic acids as recognition probes, construct detection devices based on nucleic acids, and utilize nucleic acids in clinical diagnosis and other important fields. We also discuss the new frontiers in the field and the challenges to be addressed.

Label-Free and Sensitive Electrochemical Biosensor for Amplification Detection of Target Nucleic Acids Based on Transduction Hairpins and Three-Leg DNAzyme Walkers

Nucleic acids are regarded as reliable biomarkers for the early diagnosis of various diseases. By ingeniously combining a transduction hairpin (THP) with the toehold-mediated strand displacement reaction (TSDR) to form three-leg DNAzyme walkers, for the first time, we constructed a label-free and sensitive electrochemical sensing system for the amplification detection of target nucleic acids. With microRNA-155 (miR-155) as a model target, the feasibility of the biosensing strategy and the conformational states of DNA in the recognition process were studied in detail on the basis of electrochemical and dual polarization interferometry techniques. With the assistance of THP, miR-155 indirectly triggered the TSDR between three hairpins (H1, H2, and H3), then massive Mg2+-dependent three-leg DNAzyme walkers were formed in aqueous solutions. After the binding/cleaving/moving process of three-leg DNAzyme walkers on the electrode surface modified with substrate hairpins (SHPs), a number of single-stranded DNAs (ssDNAs) were generated. Hence, the interaction of methylene blue (MB) with the duplex section of SHPs was impeded, which brought about a decreased electrochemical signal. Benefiting from the cyclic amplification of the TSDR and the higher cleavage activity of three-leg DNAzyme walkers, the proposed sensing strategy showed remarkable improvement in sensitivity with a low detection limit of 0.27 fM for miR-155. Owing to the precise design of the THP, this method exhibited excellent specificity to distinguish miR-155 from the single-base and triplex-base mismatched sequences. This sensing strategy importing the flexible THP can be utilized to detect various nucleic acid biomarkers by only redesigning the THP without changing the main circuit or reporter constructs, showing the great versatility and potential for the early diagnostics and biological analysis.

Engineering high-performance hairpin stacking circuits for logic gate operation and highly sensitive biosensing assay of microRNA

Recently, hairpin stacking circuits (HSC) based on toehold-mediated strand displacement have been engineered to detect nucleic acids and proteins. However, the three metastable hairpins in a HSC system can potentially react non-specifically in the absence of a catalyst, limiting its practical application. Here, we developed a unique hairpin design guideline to eliminate circuit leakage of HSC, and the high-performance HSC was successfully implemented on logic gate building and biosensing. We began by analyzing the sources of circuit leakage and optimizing the toehold lengths of hairpins in the HSC system based on the surface plasmon resonance (SPR) technique. Next, a novel strategy of substituting two nucleotides in a specific domain, termed 'loop-domain substitution', was introduced to eliminate leakages. We also systematically altered the positions and numbers of the introduced substitutions to probe their potential contribution to circuit leakage suppression. Through these efforts, the circuit leakage of HSC was significantly reduced. Finally, by designing different DNA input strands, the logic gates could be activated to achieve the output signal. Using miRNA as a model analyte, this strategy could detect miRNA down to pM levels with minimized circuit leakage. We believe these work indicate significant progress in the DNA circuitry.

Rational construction of a DNA nanomachine for HIV nucleic acid ultrasensitive sensing

HIV nucleic acids, one kind of significant biomarker, play an important role in fundamental studies and clinical diagnosis. Importantly, the early accurate diagnosis for HIV nucleic acids at ultralow concentrations can potentially extend the life of patients. In the current work, we developed a DNA nanomachine on gold nanoparticles (AuNPs) coupling rolling circle amplification and DNA walker cascade amplification for ultrasensitive detection of HIV nucleic acids. This DNA nanomachine sensing strategy exhibits a significantly low detection limit down to 1.46 fM. Furthermore, this DNA nanomachine biosensor is capable of detecting target DNA in real samples because of its high selectivity and sensitivity. Moreover, the DNA nanomachine biosensor is capable of discriminating single-base mismatch lower than 3.5 pM. The results showed that this DNA nanomachine biosensor has the potential for biomedical studies and clinical applications.

Decomposable quantum-dots/DNA nanosphere for rapid and ultrasensitive detection of extracellular respiring bacteria

Extracellular respiring bacteria (ERB) are a group of bacteria capable of transferring electrons to extracellular acceptors and have important application in environmental remediation. In this study, a decomposable quantum-dots (QDs)/DNA nanosphere probe was developed for rapid and ultrasensitive detection of ERB. The QDs/DNA nanosphere was self-assembled from QDs-streptavidin conjugate (QDs-SA) and Y-shaped DNA nanostructure that is constructed based on toehold-mediated strand displacement. It can release numerous fluorescent QDs-SA in immunomagnetic separation (IMS)-based immunoassay via simple biotin displacement, which remarkably amplifies the signal of antigen-antibody recognizing event. This QDs/DNA-nanosphere-based IMS-fluorescent immunoassay is ultrasensitive for model ERB Shewanella oneidensis, showing a wide detection range between 1.0 cfu/mL and 1.0 × 10⁸ cfu/mL with a low detection limit of 1.37 cfu/mL. Moreover, the proposed IMS-fluorescent immunoassay exhibits high specificity, acceptable reproducibility and stability. Furthermore, the proposed method shows acceptable recovery (92.4-101.4%) for detection of S. oneidensis spiked in river water samples. The proposed IMS-fluorescent immunoassay advances an intelligent strategy for rapid and ultrasensitive quantitation of low-abundance analyte and thus holds promising potential in food, medical and environmental applications.