This preliminary study was performed to prove the feasibility of a direct capacitive DNA biosensor for detection of nucleic acids. Two different methods for immobilization of the oligonucleotide probes were used. The ®rst type of sensor was composed of a gold rod with a self-assembled monolayer of a 26-base long oligonucleotide probe, modi®ed with an SH-group at the 5 H -end. Coverage studies showed that only around 20% of the surface was covered, probably due to the bulky nature of the probes. Hybridization studies performed in a¯ow-through cell showed selectivity towards a DNA sample containing single stranded fragments of cytomegalo virus (CMV) possessing a complementary sequence. As few as 25 molecules could be detected at sample concentrations of 0.2 attomolar with an injection volume of 250 mL. Controls with fragments of double-stranded CMV and single-stranded hepatitis B virus and tyrosinase mRNA gave all lower responses. The other type of sensor was modi®ed by covalent immobilization of a phosphorylated 8-base long oligonucleotide probe to a self-assembled monolayer of cysteamine. This biosensor also showed selectivity against single stranded fragments of CMV and also in this case as few as 25 molecules could be detected.

No abstract

A cloned partial cDNA copy of the coxsackievirus B3 genome was used for detecting enteroviruses in infected cells by employing a nucleic acid hybridization procedure. Cells infected with coxsackieviruses A and B, echovirus, and poliovirus gave positive hybridization signals, whereas cells infected with nonrelated viruses did not.

No abstract

The biological phenotype of HIV-2 isolates can be divided into two groups, rapid/high and slow/low, based on the ability to infect CD4+ tumor cell lines. Similar differences in the biological phenotype of HIV-1 isolates are largely determined by the charge of two specific amino acids in the V3 loop of the envelope protein gp120. In this study we have sequenced the V3 loop and flanking regions of 14 HIV-2 isolates from Guinea-Bissau and the Ivory Coast and correlated the results to the biological phenotype of the isolates. The sequences were obtained by PCR amplification of DNA from peripheral blood mononuclear cells infected with the different isolates, followed by direct sequencing of the amplified products. Eleven other HIV-2 isolates with known V3 sequence and biological phenotype were also included. Thirteen of the 14 new isolates were classified as subtype A of HIV-2 and one as subtype B. The V3 loop of rapid/high HIV-2 isolates differed significantly from slow/low isolates in that it was more heterogeneous in sequence and had higher net charge. Mutations at two specific amino acid positions (313 and 314), often to positively charged amino acids, were also significantly associated with the rapid/high phenotype. There were no sequence differences between rapid/high and slow/low isolates in the regions that flank the V3 loop. Our findings indicate that there may be a high degree of similarity in the molecular features that underlie the biological phenotypes of HIV-1 and HIV-2 isolates.