Microfluidic centrifugation assisted precipitation based DNA quantification.

Nucleic acid amplification methods are increasingly being used to detect trace quantities of DNA in samples for various diagnostic applications. However, quantifying the amount of DNA from such methods often requires time consuming purification, washing or labeling steps. Here, we report a novel microfluidic centrifugation assisted precipitation (µCAP) method for single-step DNA quantification. The method is based on formation of a visible precipitate, which can be quantified, when an intercalating dye (GelRed) is added to the DNA sample and centrifuged for a few seconds. We describe the mechanism leading to the precipitation phenomenon. We utilize centrifugal microfluidics to precisely control the formation of the visible and quantifiable mass. Using a standard CMOS sensor for imaging, we report a detection limit of 45 ng µl-1. Furthermore, using an integrated lab-on-DVD platform we recently developed, the detection limit is lowered to 10 ng µl-1, which is comparable to those of current commercially available instruments for DNA quantification. As a proof of principle, we demonstrate the quantification of LAMP products for a HIV-1B type genome containing plasmid on the lab-on-DVD platform. The simple DNA quantification system could facilitate advanced point of care molecular diagnostics.

A high rate of HIV-1 acquisition post immigration among migrants in Sweden determined by a CD4 T-cell decline trajectory model.

OBJECTIVES: There is a lack of knowledge about the extent to which migrants become HIV-1 infected after arrival in European countries. The objective of this study was to assess the extent to which migrants to Sweden become HIV-1 infected post immigration using a CD4 T-cell decline trajectory model. METHODS: All migrants (n = 2268) who were ≥ 15 years old, were diagnosed with HIV-1 infection in the period 1983-2013, had a known year of arrival in Sweden, did not have primary HIV infection and were not infected via mother-to-child transmission were included in the study. The CD4 T-cell decline trajectory model was applied and estimates of HIV acquisition were compared to the clinical reports. Phylogenetic analysis was performed in a subset of patients to explore whether this would favour the model or the doctor's estimate. RESULTS: The model estimated 19% of individuals to have been infected after arrival in Sweden, whereas the physician's estimate was 12%. In 79% of cases the estimates agreed. Discordance was predominantly seen when the doctor estimated HIV acquisition to have occurred before arrival in Sweden, while the model estimated it to have occurred after arrival in Sweden, and this type of discordance was seen in 10% of all patients. The probability of a discordance was greater for older patients, those with a high first CD4 T-cell count and those infected via heterosexual transmission. The phylogenetic analysis showed a higher concordance with the CD4 model than with the clinical reports (36 vs. 13%, respectively). CONCLUSIONS: The model indicated that a substantially higher proportion of migrants are infected after arrival in Sweden than estimated using clinical routine reports. It is therefore important to further emphasize primary preventive measures among migrants who have established themselves in their new country.