Sample preparation: a challenge in the development of point-of-care nucleic acid-based assays for resource-limited settings

Currently available nucleic acid testing (NAT)-based assays are complex and time-consuming, and they require expensive instrumentation and dedicated laboratory spaces for sample preparation as well as for amplification and detection of the nucleic acid target. Reagents required for these tests are also expensive and must be transported and stored refrigerated or frozen. These characteristics have limited the use of such assays for point-of-care (POC) testing, especially in resource-poor settings. Efforts to develop simple and rapid NAT-based assays have focused predominantly on the amplification and detection steps, with sample preparation and nucleic acid extraction remaining the bottleneck in the development of NAT systems suitable for POC applications or resource-limited settings. A review of NAT platforms and technologies currently under development and validation for rapid field testing revealed that, in addition to requiring expensive and complex instrumentation, many of these systems also require off-line sample preparation and reagent handling. In their current format, they are therefore not appropriate for POC testing in resource-limited settings. We evaluated several commercially available technologies and procedures for the isolation of nucleic acid with the extraction of HIV-1 RNA from human plasma as a model system. Our results indicate that solid-phase extraction with silica or glass in the presence of a chaotropic salt provides the highest extraction efficiency. However, none of the existing methods and technologies is readily adaptable to a POC system. The integration of sample preparation procedures well suited to NAT-based assays in resource-limited settings therefore remains a challenge.