Rapid, non-separation electrochemiluminescent DNA hybridization assays for PCR products, using 3'-labelled oligonucleotide probes

Synthesis of a platinum(II) complex with 2-(4-methoxy-phenyl) imidazo [4,5-f]-[1,10] phenanthrolin and study of its antitumor activity

A new platinum(II) complex of [Pt(II)(L) (pn)]Cl·2H2O (1) (pn = 1,3-propanediamine) with 2-(4-methoxy-phenyl)imidazo [4,5-f]-[1,10]phenanthrolin (H-L) was synthesized and characterized. In complex 1, the platinum adopts a four-coordinated square planar geometry. Complex 1 exhibited selective cytotoxicity against NCI-H460, BEL-7402, SK-OV-3, SK-OV-3/DDP and HeLa cell lines with IC50 values in the micromolar range (9.7-35.8 μM), but low cytotoxicity toward normal human liver HL-7702 cells. Complex 1 caused HeLa cell cycle arrest at S phase and it induced HeLa apoptosis by the activation of caspase-3/9. Various experiments showed that complex 1 preferred to bind with G-quadruplex in c-myc. Taken together, we found that complex 1 exerted its antitumor activity mainly via inhibiting telomerase by interaction with c-myc quadruplex and activation of caspase-3/9.

Electro-chemiluminescent biosensing

The present review draws a general picture of the bioanalytical applications of electro-chemiluminescent reactions (ECL). Only the two main ECL reactions-i.e. the luminol-based and Ru(bpy)(3)(2+)-based reactions-are considered for application in the fields of enzyme biosensors, immunochemical biosensors, DNA biosensors, and biochips. The mechanism, principle, and experimental conditions of these two reactions are described. Then, for each category of analytical tools, experimental set-ups and performances are presented and discussed.

An improved electrochemiluminescence polymerase chain reaction method for highly sensitive detection of plant viruses

Recently, we have reported an electrochemiluminescence polymerase chain reaction (ECL-PCR) method for detection of genetically modified organisms. The ECL-PCR method was further improved in the current study by introducing a multi-purpose nucleic acid sequence that was specific to the tris(bipyridine) ruthenium (TBR) labeled probe, into the 5' terminal of the primers. The method was applied to detect plant viruses. Conserved sequence of the plant viruses was amplified by PCR. The product was hybridized with a biotin labeled probe and a TBR labeled probe. The hybridization product was separated by streptavidin-coated magnetic beads, and detected by measuring the ECL signals of the TBR labeled. Under the optimized conditions, the experiment results show that the detection limit is 50 fmol of PCR products, and the signal-to-noise ratio is in excess of 14.6. The method was used to detect banana streak virus, banana bunchy top virus, and papaya leaf curl virus. The experiment results show that this method could reliably identity viruses infected plant samples. The improved ECL-PCR approach has higher sensitivity and lower cost than previous approach. It can effectively detect the plant viruses with simplicity, stability, and high sensitivity.

Detection methods of microsphere based single-step bioaffinity and in vitro diagnostics assays

Microspheres provide a solid phase substrate for bioaffinity binding similar to the walls of traditional test tubes and the wells of microtiter plates. The coated microsphere concentrates analyte molecules in the reaction volume on its surface. When the bioaffinity binding reaction has reached an equilibrium, the local concentration of the analyte in close proximity of the microsphere is orders of magnitude higher than the concentration of the analyte in the total reaction volume. The preparation and quality control of microspheres coated with bioactive material is less costly and labour intensive when compared to test tube or microwell plate coating procedures. In addition, the cost for logistics and transportation of microsphere reagents is lower than that of coated tubes or plates. Moreover, microspheres can be easily used in miniaturised assay formats and several different detection schemes can be employed in the measurement of microsphere-based assays. Several different types of microspheres are commercially available. The microspheres can be manufactured in different sizes from many materials, such as polystyrene, acrylate, and glass. The surface of the microspheres can be activated to enable covalent binding of biomolecules. Further, the microspheres may contain internal fluorochrome or magnetic material, for identification or separation purposes. In this paper we review different assay formats for single-step measurement of bioaffinity assays employing microspheres. The term single-step is used to describe assays where all reagents and the sample are mixed, incubated and measured without separate washing steps.

Development and evaluation of the nuclisens basic kit NASBA for the detection of RNA from Candida species frequently resistant to antifungal drugs

We describe a Nucleic Acid Sequence Based Amplification (NASBA) protocol to detect 6 different Candida species (Candida krusei, Candida glabrata, Candida inconspicua, Candida dubliniensis, Candida norvegensis, Candida lusitaniae) and compare it to a PCR assay. NASBA showed a sensitivity of 1 Colony Forming Unit and detected RNA from all 6 Candida species within 1 working day. All 5 patients with documented candidiasis showed identical results by both methods. This assay offers a sensitive, specific and fast possibility to detect yeast RNA.

Nucleic acid sequence-based amplification of Aspergillus RNA in blood samples

Nucleic acid sequence-based amplification (NASBA), an isothermal amplification technique, was established and evaluated for the detection of Aspergillus RNA and compared with a previously published, well-defined real-time PCR assay amplifying a region of the Aspergillus 18S rRNA gene. NASBA showed a lower detection limit of 1 CFU and detected RNA from five different clinically relevant Aspergillus species, including Aspergillus fumigatus. All 77 blood samples tested by PCR and NASBA showed identical results in both assays. Results with the NASBA technique were obtained within 6 h. Thus, the NASBA technique provided a valuable tool for sensitive, specific, fast, and reliable detection of Aspergillus RNA with potential for routine diagnosis, including the possibility to test the viability of cells.

An RNA transcription-based amplification technique (NASBA) for the detection of viable Salmonella enterica

Possession of mRNA is indicative of cell viability. RTPCR is not appropriate for mRNA detection as it cannot unambiguously detect mRNA in a DNA background. The alternative amplification technique, NASBA, avoids the disadvantages of RTPCR. We have devised a method for detection of viable Salmonella enterica. This involves NASBA amplification of mRNA transcribed from the dnaK gene. Amplification of mRNA extracted from viable and heat-killed cells from the same population produced consistent and highly significant (P > 0.01) differences between the respective signals. The signal obtained from viable cells was completely eradicated by RNase treatment, while PCR amplification of treated and untreated samples was unaffected, indicating that NASBA was unaffected by background DNA.

Characterization of the quantitative HCV NASBA assay

A quantitative nucleic acid sequence-based amplification assay (NASBA-QT) for detection of hepatitis C virus RNA (HCV-RNA) was evaluated and compared with the HCV branched-DNA (bDNA) assay (Chiron Corporation) and the HCV MONITOR assay (Roche Diagnostic Systems). For this evaluation five panels were designed: (1) serial dilutions of genotype 1b in-vitro HCV-RNA; (2) standards of in-vitro HCV-RNA genotypes 1a, 1b, 2, 3, 4, and 5; (3) a proficiency panel consisting of 12 HCV-RNA positive plasma samples of different genotypes and HCV-RNA concentrations and a genotype 1a and 1b 3-fold dilution series; (4) a panel of 67 HCV-RNA positive plasma samples obtained from patients with HCV infection and (5) an HCV-RNA positive control sample, diluted 50-fold in 25 different HCV-RNA negative plasma samples. The quantitative detection limit was found to be 10(3) copies per 100 microl and the qualitative detection limit 10(2.3) per 100 microl. The amplification efficiency was independent of the plasma matrix, but dependent on the HCV genotype. The HCV NASBA-QT assay was more than 10 times as sensitive as the bDNA assay while the quantitative results of both assays were highly concordant. The HCV NASBA-QT assay was comparable in sensitivity with the HCV MONITOR assay, but the HCV MONITOR assay yielded consistently lower values. It is concluded that the HCV NASBA-QT assay is a reliable assay for quantitative HCV-RNA detection in various settings.

A flash-type bioluminescent immunoassay that is more sensitive than radioimaging: quantitative detection of cytokine cDNA in activated and resting human cells

Because of its high sensitivity, bioluminescence (BL) is an excellent alternative to radioactive quantitation of cytokine RT-PCR-derived products. BL also allows detection of amplicons at cycle numbers not normally detectable using radioactivity. No direct comparisons between these two methods have been made. In this study, the sensitivities of BL using recombinant aequorin, a flash-type luminescent tag capable of detecting signal to attomolar (10(-18) M) levels and radio imaging (RI) were directly compared. In addition, the application of BL for detecting cytokine message from biologic samples was examined. BL was 30- to 60-fold more sensitive than RI in detecting human IL-2 and CD3delta amplicons. This difference was particularly found during low cycle PCR, but was less at higher cycle numbers. The ability of BL to detect differences in cytokine message in stimulated and unstimulated human peripheral blood mononuclear cells was also evaluated. Using linear regression analysis, we observed up to 5,000-fold increases in RT-PCR amplified-mRNA in stimulated cells for IL-1alpha, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-10 and GM-CSF compared to unstimulated cells. Changes in CD3delta, TNF alpha or IL-12 were not observed or quantitated. We present a novel aequorin-based application of bioluminescent technology to directly quantitate RT-PCR amplicons and to investigate the induction of human cytokine expression. Significant advantages of this sensitive bioluminescent method compared with radioactive methods are its abilities to quantitate amplicons in a PCR cycle range where linear detection is most robust and to analyze products in an automated, open-architecture microtiter plate format.

Quantitation of RT-PCR amplified cytokine mRNA by aequorin-based bioluminescence immunoassay

We described here a bioluminescence-based immunoassay for the quantitation of RT-PCR amplified cytokine mRNA. This technique uses a standard RT-PCR procedure, with the following modifications. The forward primer in the PCR reaction is labeled with a 5' biotin molecule. Following PCR, a digoxigenin-conjugated oligonucleotide probe is hybridized to the target biotin-labeled DNA template. The hybridized duplex is captured onto a streptavidin-coated microtiter plate. The bound product is quantitated by adding digoxigenin-specific antibodies conjugated with the photoprotein aequorin. The amount of specific DNA captured onto the plate is quantitated by triggering the bioluminescence reaction through the addition of calcium ions. This technique detected as low as 40 amol of amplified cytokine products, or 500 copies of templates when 27 PCR cycles were used. The high sensitivity of this technique enables the quantitation of target DNA during the exponential phase of the PCR reaction. The aequorin-bioluminescence assay is an alterative non-radioactive method for the quantitation of PCR products.

Quantitative analysis in molecular diagnostics

Quantitative analysis of DNA products derived from polymerase chain reaction (PCR)-based assays depends on the careful optimization of each of the reaction parameters to achieve highly efficient amplification of target sequences. In practice, however, measurement of the accumulated PCR product is reliable only when analyses are performed at points in the exponential phase of the PCR amplification curve and before the onset of the plateau phase. The recent development of more sensitive DNA product detection systems has permitted the analysis of PCR assays after fewer amplification cycles, where the accumulation of product approaches linearity, while at the same time maintaining superior assay specificity. These methods include the use of high performance liquid chromatography, automated fluorescence detection, electrochemiluminescence, and the ligase chain reaction. Clinical applications of these methods are numerous and include diagnostic testing as well as therapeutic monitoring for neoplastic, infectious, and inherited genetic disease.