Carbon nano-strings as reporters in lateral flow devices for DNA sensing by hybridization

Presently, there is a growing interest in the development of lateral flow devices for nucleic acid analysis that enable visual detection of the target sequence (analyte) while eliminating several steps required for pipetting, incubation, and washing out the excess of reactants. In this paper, we present, for the first time, lateral flow tests exploiting oligonucleotide-functionalized and antibody-functionalized carbon nanoparticles (carbon nano-strings, CBNS) as reporters that enable confirmation of the target DNA sequence by hybridization. The CBNS reporters were applied to (a) the detection of PCR products and (b) visual genotyping of single nucleotide polymorphisms in human genomic DNA. Biotinylated PCR product was hybridized with a dA-tailed probe. In one assay configuration, the hybrid is captured at the test zone of the strip by immobilized streptavidin and detected by (dT) ₃₀ -CBNS. In a second configuration, the hybrids are captured from immobilized (dA) strands and detected by antibiotin-CBNS. As low as 2.5 fmol of amplified DNA can be detected. For visual genotyping, allele-specific primers with a 5′ oligo(dA) segment are extended by DNA polymerase with a concomitant incorporation of biotin moieties. Extension products are detected either by (dT) ₃₀ -CBNS or by antibiotin-CBNS. Only three cycles of extension reaction are sufficient for detection. No purification of the PCR products or the extension product is required.     

Lateral flow devices for nucleic acid analysis exploiting quantum dots as reporters

There is a growing interest in the development of biosensors in the form of simple lateral flow devices that enable visual detection of nucleic acid sequences while eliminating several steps required for pipetting, incubation and washing out the excess of reactants. In this work, we present the first dipstick-type nucleic acid biosensors based on quantum dots (QDs) as reporters. The biosensors enable sequence confirmation of the target DNA by hybridization and simple visual detection of the emitted fluorescence under a UV lamp. The ‘diagnostic’ membrane of the biosensor contains a test zone (TZ) and a control zone (CZ). The CZ always fluoresces in order to confirm the proper function of the biosensor. Fluorescence is emitted from the TZ, only when the specific nucleic acid sequence is present. We have developed two general types of QD-based nucleic acid biosensors, namely, Type I and Type II, in which the TZ consists of either immobilized streptavidin (Type I) or immobilized oligodeoxynucleotides (Type II). The control zone consists of immobilized biotinylated albumin. No purification steps are required prior to the application of the DNA sample on the strip. The QD-based nucleic acid biosensors performed accurately and reproducibly when applied to (a) the visual detection of PCR amplification products and (b) visual genotyping of single nucleotide polymorphisms (SNPs) in human genomic DNA from clinical samples. As low as 1.5 fmol of double-stranded DNA were clearly detected by naked eye and the dynamic range extended to 200 fmol. The %CV were estimated to be 4.3–8.2.     

Diboryl and Diboranyl Porphyrin Complexes: Synthesis,Structural Motifs,and Redox Chemistry: Diborenyl Porphyrin or Diboranyl Isophlorin?

The syntheses of diboryl porphyrin complexes [(BX2)2(ttp)] (ttp: dianion of tetra-p-tolylporphyrin) and the B-B single-bond diboranyl complexes [(BX)2(ttp)] (X=F, Cl, Br, I) are given. The former are prepared from the reactions of BX3 (X=F, Cl) with [Li2(ttp)] and the latter from B(2)Cl(4) (X=Cl), the reaction of SbF3 with [(BCl)2(ttp)] (for X=F), and, in the cases of X=Br or I, in a remarkable reductive coupling reaction resulting directly from the reaction of BBr3 or BI3 with [Li2(ttp)]. Density functional theory (DFT) calculations on the thermochemical parameters for the reductive coupling reactions (and those calculated for related dipyrromethene complexes) indicate that a combination of the reducing ability of bromide and iodide ions combined with the constrained environment of the porphyrin ligand contribute to the driving force. The reductive coupling is also observed in the reaction of [(BCl2)2(ttp)] with nBuLi to give [(BnBu)2(ttp)], which was characterised crystallographically. The reaction of [(BCl)2(ttp)] with catechol gives a boron catecholato porphyrin complex, [B2(O(2)C(6)H(4))(ttp)]. Chloride abstraction from [(BCl)2(ttp)] gives the planar dication [B2(ttp)]2+, whereas chemical reduction of [(BCl)2(ttp)] by using magnesium anthracenide gives a neutral complex, [B(2)(ttp)], in which the TTP ligand has been reduced by two electrons to give an unusual example of an isophlorin complex. The cationic and neutral complexes [B2(ttp)]2+ and [B2(ttp)] were characterised through a combination of spectroscopic data that is supported by DFT calculations on the porphine analogues.     

The alkaloids of Delphiniumbicolor nutt.

The structures of alkaloid-$\text{A}$ and -$\text{B}$ were established via X-ray crystallography of the former as its HI salt, and its chemical conversion to the latter.