Fluorescent Oligonucleotides with Bis(prop-2-yn-1-yloxy)butane-1,3-diol Scaffold Rapidly Detect Disease-Associated Nucleic Acids

Multilabel hybridization probes for sequence-specific detection of sepsis-related drug resistance genes in plasmids

Emerging antimicrobial drug resistance is increasing the complexity involved in treating critical conditions such as bacterial induced sepsis. Methods for diagnosing specific drug resistance tend to be rapid or sensitive, but not both. Detection methods like sequence-specific single-molecule analysis could address this concern if they could be adapted to work on smaller targets similar to those produced in traditional clinical situations. In this work we demonstrate that a 120 bp double stranded polynucleotide with an overhanging single stranded 25 bp probe sequence can be created by immobilizing DNA with a biotin/streptavidin magnetic bead system, labeling with SYBR Gold, and rinsing the excess away while the probe retains multiple fluorophores. These probes with multiple fluorophores can then be used to label a bacterial plasmid target in a sequence-specific manner. These probes enabled the detection of 1 pM plasmid samples containing a portion of an antibiotic resistance gene sequence. This system shows the possibility of improving capture and fluorescence labeling of small nucleic acid fragments, generating lower limits of detection for clinically relevant samples while maintaining rapid processing times.

Complete Mesoscopic Parameterization of Single LNA Modifications in DNA Applied to Oncogene Probe Design

The use of mesoscopic models to describe the thermodynamic properties of locked nucleic acid (LNA)-modified nucleotides can provide useful insights into their properties, such as hydrogen-bonding and stacking interactions. In addition, the mesoscopic parameters can be used to optimize LNA insertion in probes, to achieve accurate melting temperature predictions, and to obtain duplex opening profiles at the base-pair level. Here, we applied this type of model to parameterize a large set of melting temperatures for LNA-modified sequences, from published sources, covering all possible nearest-neighbor configurations. We have found a very large increase in Morse potentials, which indicates very strong hydrogen bonding as the main cause of improved LNA thermodynamic stability. LNA-modified adenine-thymine (AT) was found to have similar hydrogen bonding to unmodified cytosine-guanine (CG) base pairs, while for LNA CG, we found exceptionally large hydrogen bonding. In contrast, stacking interactions, which were thought to be behind the stability of LNA, were similar to unmodified DNA in most cases. We applied the new LNA parameters to the design of BRAF, KRAS, and EGFR oncogene variants by testing all possible LNA modifications. Selected sequences were then synthesized and had their hybridization temperatures measured, achieving a prediction accuracy within 1 °C. We performed a detailed base-pair opening analysis to discuss specific aspects of these probe hybridizations that may be relevant for probe design.

Complementary Oligonucleotide Conjugated Multicolor Carbon Dots for Intracellular Recognition of Biological Events

By using complementary DNA sequences as surface ligands, we selectively allow two individual diffusing "dual-color" carbon dots to interact in situ and in vitro. Spontaneous nanoscale oxidation of surface-abundant nitroso-/nitro-functionalities leads to two distinctly colored carbon dots (CD) which are isolated by polarity driven chromatographic separation. Green- and red-emitting carbon dots (gCD and rCD) were decorated by complementary single-stranded DNAs which produce a marked increase in the fluorescence emission of the respective carbon dots. Mutual colloidal interactions are achieved through hybridization of complementary DNA base pairs attached to the respective particles, resulting in quenching of their photoluminescence. The observed post-hybridization quenching is presumably due to a combined effect from an aggregation of CDs post duplex DNA formation and close proximity of multicolored CDs, having overlapped spectral regions leading to a nonradiative energy transfer process possibly released as heat. This strategy may contribute to the rational design of mutually interacting carbon dots for a better control over the resulting assembly structure for studying different biological phenomenon including molecular cytogenetics. One of the newly synthesized CDs was successfully used to image intracellular location of GAPDH mRNA using an event of change in fluorescence intensity (FI) of CDs. This selectivity was introduced by conjugating an oligonucleotide harboring complementary sequence to GAPDH mRNA. FI of this conjugated carbon dot, rCD-GAPDH, was also found to decrease in the presence of Ca2+, varied in relation to H+ concentrations, and could serve as a tool to quantify the intracellular concentrations of Ca2+ and pH value (H+) which can give important information about cell survival. Therefore, CD-oligonucleotide conjugates could serve as efficient probes for cellular events and interventions.