Color-changing fluorescent DNA probe containing solvatochromic Dansyl-nucleoside surrogate for sensing local variation of DNA duplex.

A novel Dansyl-nucleoside surrogate (Dns) based on (±)-trans-4-(hydroxymethyl) piperidin-3-ol was designed and synthesized. The Dns exhibited excellent solvatochromic properties. About 90 nm of red-shift accompanied color change from green to orange could be achieved with an increase of solvent polarity. The Dns was incorporated into oligodeoxynucleotide by phosphoroamidite chemistry. Two kinds of Dns-incorporated fluorescent DNA probes were designed and synthesized for sensing variation of DNA duplexes based on color-changing manner. As a result, the color-changing DNA probe not only can detect complementary oligonucleotide, but also can distinguish mismatch flanked in Dansyl/nucleobase pair by naked eye. Moreover, the change of fluorescence color of sample solutions could be captured by smartphone, and the photographs could be digitalized by image-processing software. Thus, the Dns-incorporated fluorescent DNA probe is expected to open the way to point-of-care assays in the future.

Imaging Membrane Order and Dynamic Interactions in Living Cells with a DNA Zipper Probe.

The cell membrane is a dynamic and heterogeneous structure composed of distinct sub-compartments. Within these compartments, preferential interactions occur among various lipids and proteins. Currently, it is still challenging to image these short-lived membrane complexes, especially in living cells. In this work, we present a DNA-based probe, termed "DNA Zipper", which allows the membrane order and pattern of transient interactions to be imaged in living cells using standard fluorescence microscopes. By fine-tuning the length and binding affinity of DNA duplex, these probes can precisely extend the duration of membrane lipid interactions via dynamic DNA hybridization. The correlation between membrane order and the activation of T-cell receptor signaling has also been studied. These programmable DNA probes function after a brief cell incubation, which can be easily adapted to study lipid interactions and membrane order during different membrane signaling events.

Nicked Invader probes: multistranded and sequence-unrestricted recognition of double-stranded DNA.

Major efforts have been devoted to the development of constructs that enable sequence-specific recognition of double-stranded (ds) DNA, fueled by the promise for enabling tools for applications in molecular biology, diagnostics, and medicine. Towards this end, we have previously introduced Invader probes, i.e., short DNA duplexes with +1 interstrand zipper arrangements of intercalator-functionalized nucleotides. The individual strands of these labile probes display high affinity towards complementary DNA (cDNA), which drives sequence-unrestricted dsDNA-recognition. However, recognition of long targets is challenging due to the high stability of the corresponding probes. To address this, we recently introduced toehold Invader probes, i.e., Invader probes with 5'-single-stranded overhangs. The toehold architecture allows for shorter double-stranded segments to be used, which facilitates probe dissociation and dsDNA-recognition. As an extension thereof, we here report the biophysical and dsDNA-targeting properties of nicked Invader probes. In this probe architecture, the single-stranded overhangs of toehold Invader probes are hybridized to short intercalator-modified auxiliary strands, leading to formation of additional labile segments. The extra binding potential from the auxiliary strands imparts nicked Invader probes with greater dsDNA-affinity than the corresponding toehold or blunt-ended probes. Recognition of chromosomal DNA targets, refractory to recognition by conventional Invader probes, is demonstrated for nicked Invader probes in the context of non-denaturing FISH experiments, which highlights their utility as dsDNA-targeting tools.

A Dual-Color Tyr-FISH Method for Visualizing Genes/Markers on Plant Chromosomes to Create Integrated Genetic and Cytogenetic Maps.

In situ imaging of molecular markers on a physical chromosome is an indispensable tool for refining genetic maps and validation genome assembly at the chromosomal level. Despite the tremendous progress in genome sequencing, the plant genome assembly at the chromosome level remains a challenge. Recently developed optical and Hi-C mapping are aimed at assistance in genome assembly. For high confidence in the genome assembly at chromosome level, more independent approaches are required. The present study is aimed at refining an ultrasensitive Tyr-FISH technique and developing a reliable and simple method of in situ mapping of a short unique DNA sequences on plant chromosomes. We have carefully analyzed the critical steps of the Tyr-FISH to find out the reasons behind the flaws of this technique. The accurate visualization of markers/genes appeared to be significantly dependent on the means of chromosome slide preparation, probe design and labeling, and high stringency washing. Appropriate adjustment of these steps allowed us to detect a short DNA sequence of 1.6 Kb with a frequency of 51.6%. Based on our results, we developed a more reliable and simple protocol for dual-color Tyr-FISH visualization of unique short DNA sequences on plant chromosomes. This new protocol can allow for more accurate determination of the physical distance between markers and can be applied for faster integration of genetic and cytogenetic maps.

A 'one-tube' synthesis of a selective fluorescence 'turn off/on' DNA probe based on a C-phycocyanin-graphene oxide (CPC-GO) bio composite.

A naturally fluorescent protein, C-phycocyanin (CPC), was used as a fluorophore to study the effect of graphene oxide (GO) as a quencher. The protein was purified using established procedures and titrated with increasing GO concentrations. UV-visible titration showed a minor effect on the phycocyanobilin absorbance but significant interactions with the amino acid backbone. Fluorescence titration showed notable CPC quenching upon increasing GO concentration to 30 µg ml-1; the corresponding fluorescence dropped by ~97%. A non-linear Stern Volmer curve showed that the fluorophores did not interact directly with the quencher. Powder X-ray diffraction studies showed that the bio-composite lost the crystalline arrangement of GO and became amorphous, akin to CPC. SEM analysis showed GO sheets enfolding a protein nucleus with an increase in oxygen after the interaction compared to CPC. A 20 min incubation of the bio-composite with various biomolecules including amino acids, sugars, polydispersed exopolysaccharides (EPS), other proteins and DNA showed that only DNA could recover the CPC fluorescence. The 'turn on' effect of DNA was distinguishable even when all the other molecules were in the same sample matrix. These results showed that CPC GO could be a fluorescence 'turn off/on' DNA probe.

High-coverage SARS-CoV-2 genome sequences acquired by target capture sequencing.

In this study, we designed a set of SARS-CoV-2 enrichment probes to increase the capacity for sequence-based virus detection and obtain the comprehensive genome sequence at the same time. This universal SARS-CoV-2 enrichment probe set contains 502 120 nt single-stranded DNA biotin-labeled probes designed based on all available SARS-CoV-2 viral sequences and it can be used to enrich for SARS-CoV-2 sequences without prior knowledge of type or subtype. Following the CDC health and safety guidelines, marked enrichment was demonstrated in a virus strain sample from cell culture, three nasopharyngeal swab samples (cycle threshold [Ct ] values: 32.36, 36.72, and 38.44) from patients diagnosed with COVID-19 (positive control) and four throat swab samples from patients without COVID-19 (negative controls), respectively. Moreover, based on these high-quality sequences, we discuss the heterozygosity and viral expression during coronavirus replication and its phylogenetic relationship with other selected high-quality samples from the Genome Variation Map. Therefore, this universal SARS-CoV-2 enrichment probe system can capture and enrich SARS-CoV-2 viral sequences selectively and effectively in different samples, especially clinical swab samples with a relatively low concentration of viral particles.

Delayed Laboratory Response to COVID-19 Caused by Molecular Diagnostic Contamination.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) created an exceptional situation in which numerous laboratories in Europe simultaneously implemented SARS-CoV-2 diagnostics. These laboratories reported in February 2020 that commercial primer and probe batches for SARS-CoV-2 detection were contaminated with synthetic control material, causing delays of regional testing roll-out in various countries.

Excimer-FRET Cascade in Dual DNA Probes: Open Access to Large Stokes Shift, Enhanced Acceptor Light up, and Robust RNA Sensing.

The efficacy of fluorescent hybridization assays is often limited by the low signal-to-background ratio of the probes that can be partially overcome by sophisticated signal amplification methods. Deep understanding of the mechanisms of fluorescence quenching and energy transfer in complex DNA probes and the choice of optimal donor/acceptor pairs along with rational design can significantly enhance the performance of DNA probes. Here, we proposed and studied novel Förster resonance energy transfer (FRET) dual DNA probes with the excimer-forming pyrene pair as a donor and sulfo-Cy3 dye as an acceptor, which demonstrated remarkable 75-fold enhancement of sulfo-Cy3 fluorescence upon target capturing. Stokes shift up to 220 nm minimizes fluorescence crosstalk. Time-correlated single-photon counting revealed two excited states of pyrene excimer wherein only one is directly involved in the resonance energy transfer to sulfo-Cy3. Optimized DNA probes demonstrated high sensitivity with excellent signal-to-background ratio, which were applied for visualization of 18S rRNA by fluorescent in situ hybridization in HEK-293T cells.

Intramolecular trigger remodeling-induced HCR for amplified detection of protein-specific glycosylation.

Dynamic changes of protein-glycosylation on cell surface act as an important indicator that reflects cellular physiological states and disease developments. The enhanced visualization of protein-specific glycosylation is of great value to interpret its functions and mechanisms. Hence, we present an intramolecular trigger remodeling-induced hybridization chain reaction (HCR) for imaging protein-specific glycosylation. This strategy relies on designing two DNA probes, protein and glycan probes, labeled respectively on protein by aptamer recognition and glycan through metabolic oligosaccharide engineering (MOE). Upon the same glycoprotein was labeled, the complementary domain of two probes induces hybridization and thus to remodel an intact trigger, followed by initiating HCR assembly. Applying this strategy, we successfully achieved imaging of specific protein-glycosylation on CEM cell surface and monitored dynamic changes of the glycosylation after treating with drugs. It provides a powerful tool with high flexibility, specificity and sensitivity in the research field of protein-specific glycosylation on living cells.

Multi-signal amplification electrochemical DNA biosensor based on exonuclease III and tetraferrocene.

Homogeneous electrochemical DNA biosensors' unique qualities have been of great interest to researchers, mainly due to their high recognition efficiency in solutions. However, the processes of introducing additional markers and extra operations to obtain a signal are tedious and time consuming, which limits their overall potential applications. Herein, a novel tetraferrocene was synthesized and used as a homogeneous electrochemical DNA biosensor probe label. It contains four ferrocene units, which provide greater signaling potential compared to monoferrocene. Furthermore, the target DNA triggers the digestion of the double hairpin DNA probe with the aid of exonuclease III, promoting short single stranded DNA probe formation. With the combination of the incorporated tetraferrocene labeled short DNA probe strands and graphene's ability to adsorb single stranded DNA, the hybridization process can produce an electrode signal provided by tetraferrocene. A low detection limit of 8.2 fM toward target DNA with excellent selectivity was achieved. The proposed sensing system avoids tedious and time-consuming steps of DNA modification, making the experimental processes simpler and convenient. The advantages of high sensitivity, selectivity and simple operation make this strategy applicable to DNA detection.

A gold nanoparticle-based colorimetric mercury(II) biosensor using a DNA probe with phosphorothioate RNA modification and exonuclease III-assisted signal amplification.

Herein, we report a rapid and sensitive colorimetric detection of Hg2+ by designing a specific DNA probe with phosphorothioate RNA modification (PS-probe) for Hg2+ recognition and utilizing DNA-modified gold nanoparticles (DNA-AuNPs) as the transducer. The distance between two DNA-AuNPs is controlled by a linker DNA, providing the linker DNA-regulated aggregation or dispersion status of AuNPs in solution. Exonuclease III (Exo III) can trigger the recycled digestion of linker DNA strands, inhibiting the reformation of aggregated nanoparticles and hence leading to a color shift from purple to red. However, the Hg2+-induced cleavage of the PS-probe can efficiently prevent the digestion of linker DNA strands by Exo III and hence reassemble the modified AuNPs to form aggregates in purple color. Thus, a positive correlation between the linker DNA strands left and the addition of Hg2+ provides a quantitative basis for Hg2+ sensing. A linear range of A520/A700 versus Hg2+ concentration is achieved in the range 2-100 nM associated with a detection limit as low as 1.30 ± 0.04 nM. Moreover, the biosensor exhibits excellent selectivity for Hg2+. The strong selectivity behavior was confirmed by recoveries ranging from 96 to 114% in real water samples. Graphical abstractSchematic representation of sensing mechanism of Hg2+ using a DNA probe with phosphorothioate RNA modification (PS-probe) and Exo III-assisted signal amplification.

Designing expanded bipyridinium as redox and optical probes for DNA.

We report on the light-switch behaviour of two head-to-tail expanded bipyridinium species as a function of their interaction with calf thymus DNA and polynucleotides. In particular, both DNA and polynucleotides containing exclusively adenine or guanine moieties quench the luminescence of the fused expanded bipyridinium species. This behaviour has been rationalized demonstrating that a reductive photoinduced electron transfer process takes place involving both adenine or guanine moieties. The charge separated state so produced recombines in the tens of picoseconds. These results could help in designing new organic substrates for application in DNA probing technology and lab on chip-based sensing systems.

Tuning of Oxidation Potential of Ferrocene for Ratiometric Redox Labeling and Coding of Nucleotides and DNA.

Three sets of 7-deazaadenine and cytosine nucleosides and nucleoside triphosphates bearing either unsubstituted ferrocene, octamethylferrocene and ferrocenecarboxamide linked through an alkyne tether to position 7 or 5, respectively, were designed and synthesized. The modified dNFcX TPs were good substrates for KOD XL DNA polymerase in primer extension and were used for enzymatic synthesis of redox-labelled DNA probes. Square-wave voltammetry showed that the octamethylferrocene oxidation potential was shifted to lower values, whilst the ferrocenecarboxamide was shifted to higher potentials, as compared to ferrocene. Tailed PEX products containing different ratios of Fc-labelled A (dAFc ) and FcPa-labelled C (dCFcPa ) were synthesized and hybridized with capture oligonucleotides immobilized on gold electrodes to study the electrochemistry of the redox-labelled DNA. Clearly distinguishable, fully orthogonal and ratiometric peaks were observed for the dAFc and dCFcPa bases in DNA, demonstrating their potential for use in redox coding of nucleobases and for the direct electrochemical measurement of the relative ratio of nucleobases in an unknown sequence of DNA.

Catalytic hairpin assembly induced dual signal enhancement for rapid detection of miRNA using fluorescence light-up silver nanocluster.

A novel method of catalytic hairpin assembly (CHA) induced dual signal enhancement is developed for rapid detection of miRNA based on fluorescence light-up silver nanocluster (Ag NC). By the hybridization of a hairpin DNA and a single-stranded DNA, a unique probe is firstly designed. In the terminals of this probe, DNA-Ag NCs can be formed and display very weak fluorescence. In the presence of the target miRNA, the reaction of CHA can be triggered, forming two kinds of double-stranded complexes, in which the terminal DNA-Ag NCs are in close proximity to G-rich overhangs and the fluorescent signal can be dramatically enhanced. Compared with many other enzyme-based amplification strategies, this one exhibits distinct advantages of simplicity in experimental operation and a rapid detection process (within 1 h). Moreover, this assay exhibits an excellent selectivity and is successfully applied in the detection of miRNAs in complex biological media, which confirms the reliability and practicality of this protocol.

Enzymatic Synthesis of Base-Functionalized Nucleic Acids for Sensing, Cross-linking, and Modulation of Protein-DNA Binding and Transcription.

Protein-DNA interactions are important in replication, transcription, repair, as well as epigenetic modifications of DNA, which involve methylation and demethylation of DNA resulting in regulation of gene expression. Understanding of these processes and chemical tools for studying and perhaps even modulating them could be of great relevance and importance not only in chemical biology but also in real diagnostics and treatment of diseases. In the past decade, we have been working on development of synthesis of base-modified 2'-deoxyribo- or ribonucleoside triphosphates (dNTPs or NTPs) and their use in enzymatic synthesis of modified nucleic acids using DNA or RNA polymerases. These synthetic and enzymatic methods are briefly summarized with focus on recent development and outlining of scope, limitations, and further challenges. The main focus of this Account is on applications of base-modified nucleic acids in sensing of protein-DNA interactions, in covalent cross-linking to DNA-binding proteins ,and in modulation of protein-DNA binding and transcription. Several environment-sensitive fluorescent nucleotides were incorporated to DNA probes which responded to protein binding by light-up, changing of color, or lifetime of fluorescence. Using a cyclodextrin-peptide transporter, fluorescent nucleotides can be transported through the cell membrane and incorporated to genomic DNA. Several dNTPs bearing reactive groups (i.e., vinylsulfonamide or chloroacetamide) were used for polymerase synthesis of DNA reactive probes which cross-link to Cys, His, or Lys in peptides or proteins. An attractive challenge is to use DNA modifications and bioorthogonal reactions in the major groove of DNA for modulation and switching of protein-DNA interactions. We have systematically explored the influence of major-groove modifications on recognition and cleavage of DNA by restriction endonucleases and constructed simple chemical switches of DNA cleavage. Systematic study of the influence of major-groove modifications on transcription with bacterial RNA polymerases revealed not only that some modified bases are tolerated, but also that the presence of 5-hydroxymethyluracil or -cytosine can even enhance the transcription (350 or 250% compared to native DNA). Based on these results, we have constructed the first chemical switch of transcription based on photocaging of hydroxymethylpyrimidines in DNA by 2-nitrobenzyl protection (transcription off), photochemical deprotection of the DNA (transcription on), and enzymatic phosphorylation (only for 5-hydroxymethyluracil, transcription off). Although it has been so far demonstrated only in vitro, it is the proof-of-principle first step toward chemical epigenetics.

Proximity-Induced Bioorthogonal Chemistry Using Inverse Electron Demand Diels-Alder Reaction.

Bioorthogonal chemistry techniques enable the selective and targeted manipulation of living systems. In order to yield universally applicable techniques, it is of great importance for bioorthogonal reactions to take place rapidly, selectively, and with the formation of only benign side products. One of the reactions that match these criteria well is the inverse electron demand Diels-Alder reaction (DAinv) between tetrazines and strained dienophiles. However, even this prime technique comes with the disadvantage of its reactants having limited stability under physiological conditions. In our protocol, an unreactive and therefore stable DAinv diene/dienophile pair reacts rapidly using DNA hybridization as secondary rate-accelerating process. Due to the fluorogenicity of the presented tetrazine rhodamine conjugate, this method enables the selective screening and evaluation of reactant pairs for proximity-mediated bioorthogonal chemistry.

T7 exo-mediated FRET-breaking combined with DSN-RNAse-TdT for the detection of microRNA with ultrahigh signal-amplification.

A DSN-RNAse-TdT-T7 exo probing system allows the detection of miRNA 21 with very high sensitivity (LOD = 2.57 fM) and selectivity-the result of (i) avoiding the false-positive signal from miRNA reacting with TdT polymerase and (ii) signal amplification occurring through a FRET-breaking mechanism involving T7 exo.

Target-triggered dynamic hairpin assembly for signal amplification of microRNA and oncogenes and its application in live-cell imaging.

Based on target-triggered dynamic hairpin assembly (DHA) in both unidirectional and bilateral growth manners DNA nanobrushes are constructed, which realize sensitive and selective detection of short miRNA (miR-21) and long DNA (BRCA1), respectively. Moreover, the unidirectional DHA strategy is readily applied to in situ imaging of miR-21 in different live cells.

Bio-barcode technology for detection of Staphylococcus aureus protein A based on gold and iron nanoparticles.

S. aureus is one of important causes of disease, food poisoning in humans and animals. The generally methods for detection of S. aureus is time consuming. Therefore, a new method is necessary for rapid, sensitive and specific diagnosis of S. aureus. In the present study, two probes and a Bio-barcode DNA were designed for detection of S. aureus (Protein A). Firstly, magnetic nanoparticle (MNPs) and gold nanoparticle (AuNPs) were synthesized at 80 °C and 100 °C, respectively. The AuNPs and the MNPs were functionalized with probe1, Bio-barcode DNA and probe2, respectively. Target DNA was added into the nanomaterial's system containing bio-barcode DNA-AuNPs-probe1 and probe2-MNPs to formed bio-barcode DNA-AuNPs-probe1-target DNA-probe2-MNPs complex. The bio-barcode DNA-AuNPs-probe1-target DNA-probe2-MNPs complex was separated with magnetic field. Finally, the bio-barcode DNA was released from surface of complex using DTT (0.8 M) and there was isolated of nanoparticles by magnetic field and centrifuge. The fluorescence intensity of bio-barcode DNA was measured in different concentrations of S. aureus (101 to 108 CFU mL-1) by fluorescence spectrophotometry. The results showed that standard curve was linearly from 102 to 107 CFU mL-1. Limit of detection of bio-barcode assay for both PBS and real samples was 86 CFU mL-1.

Synthesis of Fluorescence Turn-On DNA Hybridization Probe Using the DEA tC 2'-Deoxycytidine Analog.

DEA tC is a tricyclic 2'-deoxycytidine analog that can be incorporated into oligonucleotides by solid-phase synthesis and that exhibits a large fluorescence enhancement when correctly base-paired with a guanine base in a DNA-DNA duplex. The synthesis of DEA tC begins with 5-amino-2-methylbenzothiazole and provides the DEA tC nucleobase analog over five synthetic steps. This nucleobase analog is then silylated using N,O-bis(trimethylsilyl)acetamide and conjugated to Hoffer's chlorosugar to provide the protected DEA tC nucleoside in good yield. Following protective-group removal and chromatographic isolation of the ß-anomer, dimethoxytritylation and phosphoramidite synthesis offer the monomer for solid-phase DNA synthesis. Solid-phase DNA synthesis conditions using extended coupling of the DEA tC amidite and a short deprotection time are employed to maximize efficiency. By following the protocols described in this unit, the DEA tC fluorescent probe can be synthesized and can be incorporated into any desired synthetic DNA oligonucleotide. © 2018 by John Wiley & Sons, Inc.