Fluorescence polarization-based detection of cancer-related mutations using target-initiated rolling circle amplification

Colorimetric detection of single-nucleotide mutations based on rolling circle amplification and G-quadruplex-based DNAzyme

In this work, we proposed a sensitive and selective colorimetric assay for single nucleotide mutation (SNM) detection combining rolling circle amplification (RCA) and G-quadruplex/hemin DNAzyme complex formation. In the detection principle, the first step involves ssDNA hybridization with a padlock probe (PLP) DNA, which can discriminate a single base mismatch. The successful ligation is followed by an RCA event to generate an abundance of G-quadruplexes (GQ-RCA) which are then transformed into a DNAzyme (G-quadruplex/hemin complex) by the addition of hemin. The color change from colorless 3,3',5,5'-tetramethylbenzidine (TMB) into colored oxTMB when hydrogen peroxide (H2O2) is added indicated the presence of a mutation. The assay had a limit of detection (LOD) of 2.14 pM. Mutations in samples from breast cancer patients were successfully detected with an accuracy of 100% when compared to Sanger sequencing results. The method is easily applicable even in resource poor setting regions given that it doesn't require any sophisticated or expensive instruments, and the signal readout is detectable simply by the naked eye. Our assay might be a useful tool for genetic analysis and clinical molecular diagnosis for breast cancer risk assessment and early detection.

One-pot, one-step, label-free miRNA detection method based on the structural transition of dumbbell probe

In this study, we present a one-pot, one-step, label-free miRNA detection method through a structural transition of a specially designed dumbbell-shape probe, initiating a rolling circle transition (RCT). In principle, target miRNA binds to right loop of the dumbbell probe (DP), which allows structural change of the DP to circular form, exposing a sequence complementary to the T7 promoter (T7p) previously hidden within the stem. This exposure allows T7 RNA polymerase to initiate RCT, producing a repetitive Mango aptamer sequence. TO1-biotin, fluorescent dye, binds to the aptamer, inducing a detectable enhancement of fluorescence intensity. Without miR-141, the DP stays closed, RCT is prevented, and the fluorescence intensity remains low. By employing this novel strategy, target miRNA was successfully identified with a detection of 73 pM and a dynamic linear range of 0-10 nM. Additionally, the method developed enables one-pot, one-step, and label-free detection of miRNA, demonstrating potential for point-of-care testing (POCT) applications. Furthermore, the practical application of the designed technique was demonstrated by reliably detecting the target miRNA in the human serum sample. We also believe that the conceived approach could be widely used to detect not only miRNAs but also diverse biomolecules by simply replacing the detection probe.

T790M mutation upconversion fluorescence biosensor via mild ATRP strategy and site-specific DNA cleavage of restriction endonuclease

A unique combination of a specific nucleic acid restriction endonuclease (REase) and atom transfer radical polymerization (ATRP) signal amplification strategy was employed for the detection of T790M mutations prevalent in the adjuvant diagnosis of lung cancer. REase selectively recognizes and cleaves T790M mutation sites on double-stranded DNA formed by hybridization of a capture sequence and a target sequence. At the same time, the ATRP strategy resulted in the massive aggregation of upconverted nanoparticles (UCNPs), which significantly improved the sensitivity of the biosensor. In addition, the UCNPs have excellent optical properties and can eliminate the interference of autofluorescence in the samples, thus further improving the detection sensitivity. The proposed upconversion fluorescent biosensor is characterized by high specificity, high sensitivity, mild reaction conditions, fast response time, and a detection limit as low as 0.14 fM. The performance of the proposed biosensor is comparable to that of clinical PCR methods when applied to clinical samples. This work presents a new perspective for assisted diagnosis in the pre-intervention stage of tumor diagnostics in the early stage of precision oncology treatments.

Recent Progress in Single-Nucleotide Polymorphism Biosensors

Single-nucleotide polymorphisms (SNPs), the most common form of genetic variation in the human genome, are the main cause of individual differences. Furthermore, such attractive genetic markers are emerging as important hallmarks in clinical diagnosis and treatment. A variety of destructive abnormalities, such as malignancy, cardiovascular disease, inherited metabolic disease, and autoimmune disease, are associated with single-nucleotide variants. Therefore, identification of SNPs is necessary for better understanding of the gene function and health of an individual. SNP detection with simple preparation and operational procedures, high affinity and specificity, and cost-effectiveness have been the key challenge for years. Although biosensing methods offer high specificity and sensitivity, as well, they suffer drawbacks, such as complicated designs, complicated optimization procedures, and the use of complicated chemistry designs and expensive reagents, as well as toxic chemical compounds, for signal detection and amplifications. This review aims to provide an overview on improvements for SNP biosensing based on fluorescent and electrochemical methods. Very recently, novel designs in each category have been presented in detail. Furthermore, detection limitations, advantages and disadvantages, and challenges have also been presented for each type.

Self-Assembly of Multivalent Aptamer-Tethered DNA Monolayers Dedicated to a Fluorescence Polarization-Responsive Circular Isothermal Strand Displacement Amplification for Salmonella Assay

Pathogenic bacteria are pathogens widely spread that are capable of causing mild to life-threatening diseases in human beings or other organisms. Rationally organizing the simple helical motif of double-stranded DNA (dsDNA) tiles into designed ensemble structures with architecturally defined collective properties could lead to promising biosensing applications for pathogen detection. In this work, we facilely engineered multivalent hairpin aptamer probe-tethered DNA monolayers (MHAP-DNA monolayers) and applied them to build a fluorescence polarization-responsive circular isothermal strand displacement amplification (FP-CSDA) for Salmonella assay. In this system, the MHAP-DNA monolayers were constructed based on a dsDNA tile-directed self-assembly. A FAM-labeled reporting probe (RP^FAM) with an inherent low FP signal serves as the signaling unit. The presence of target Salmonella leads to the trapping of F RP^FAM into the super DNA monolayers via a target-triggered CSDA to peel off the tethered hairpin-structured aptamer probes (HAPs) responsible for the binding of RP^FAM. As a result, the FP signal of the FAM fluorophore can be remarkably amplified due to the recycling of target Salmonella and the capacity of structural DNA materials to strongly restrict the free rotation of the FAM fluorophore but without a fluorescence quenching effect. Experimental results demonstrate that the FP assay is able to detect Salmonella with a low limit of detection (LOD) of 7.2 × 10⁰ CFU/mL and high specificity. As a proof-of-concept study, we envision our study using DNA nanoarchitecture as the foundation to modulate CSDA-based FP assays, promising to open up a new avenue for disease diagnosis, food safety detection, and biochemical studies.

Split T7 promoter-based isothermal transcription amplification for one-step fluorescence detection of SARS-CoV-2 and emerging variants

The negative global impact of the coronavirus disease pandemic has highlighted the crucial need for a rapid and convenient method of viral RNA detection. In this study, we report a novel method, termed as the split T7 promoter-based isothermal transcription amplification with light-up RNA aptamer (STAR), for one-pot detection of viral RNA. STAR uses a split T7 promoter that is applied to a three-way junction to mediate the selective transcription by the T7 RNA polymerase in the presence of target RNA. In addition, a light-up RNA aptamer is used for signal amplification. STAR can detect viral RNA in less than 30 min with high specificity and sensitivity. By testing of 60 nasopharyngeal SARS-CoV-2 samples, the STAR assay demonstrates an excellent sensitivity and specificity of 96.7% and 100%, respectively. Moreover, we provide experimental evidence of the broad applicability of this assay through the multiplex detection of SARS-CoV-2 variants (D614G mutation) and direct detection of bacterial 16S rRNA.

A Lateral Flow Assay for Nucleic Acid Detection Based on Rolling Circle Amplification Using Capture Ligand-Modified Oligonucleotides

We introduce a lateral flow assay (LFA) integrated with a modified isothermal nucleic acid amplification procedure for rapid and simple genetic testing. Padlock probes specific for the target DNA were designed for ligation, followed by rolling circle amplification (RCA) using capture ligand-modified oligonucleotides as primers. After hybridization with detection linker probes, the amplified target DNA is flowed through an LFA membrane strip for binding of gold nanoparticles as the substrate for colorimetric detection. We established and validated the "RCA-LFA" method for detection of mecA, the antibiotic resistance gene for methicillin-resistant Staphylococcus aureus (MRSA). The assay was optimized using various concentrations of primers and probes for RCA and LFA, respectively. The sensitivity was determined by performing RCA-LFA using various amounts of mecA target DNA, showing a detection limit of ~ 1.3 fmol. The specificity of the assay was examined using target DNAs for other resistance genes as the controls, which demonstrated positive detection signals only for mecA DNA, when added either individually or in combinations with the control targets. Furthermore, applying the RCA-LFA method using specifically designed probes for RNA-dependent RNA polymerase (RdRp) and receptor binding domain (RBD) gene for SARS-CoV-2, which demonstrated feasibility of the method for viral gene targets. The current method suggests a useful platform which can be universally applied for various nucleic acid targets, allowing rapid and sensitive diagnosis at point-of-care.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13206-022-00080-1.