A finger prick nucleic acid testing (NAT) USB-interfaced device can increase accessibility to HIV self-testing, according to findings of a study published in Biosensors and Bioelectronics.
A team of investigators created a device containing a microfluidic reagent cartridge and a compact NAT-on-USB analyzer that is able to extract results from a 100-μL sample of blood obtained from a finger prick. The user places a drop of blood into the collection tube containing a lysis buffer and loads the lysate onto the microfluidic cartridge. The cartridge and analyzer then process the sample through reverse-transcription loop-mediated isothermal amplification (RT-LAMP). The device can be connected to a personal computer through a USB port, and the test result can be viewed on a custom-built graphical user interface in approximately 60 minutes.
In the study, the researchers validated automatic sample preparation, tested the HIV-1 RT-LAMP assay, and assessed diagnostic accuracy of the device.
Automation of sample preparation was facilitated by a novel programmable electromagnetic pulse method that controls beads on the cartridge. This method streamlined nucleic acid binding, purification, and elution. Using this technique, the sample could be prepared in approximately 15 minutes.
To test the interaction between the blood and the reagent on the HIV-1 RT-LAMP assay, the researchers created mock whole blood HIV-positive samples by spiking healthy whole blood with HIV-1 RNA. The samples contained between 10 and 106 copies/mL, and testing of each sample was performed 6 times. Results were visualized via fluorescent images under UV light and through gel electrophoresis, and the researchers reported agreement of the images.
The researchers estimated the limit of detection of whole blood HIV-1 RT-LAMP assay by observing the hit rates at different RNA concentrations. The hit rate, defined as the number of amplified samples over all samples, was 214 copies/mL at a 95% confidence level, which is higher than that obtained with HIV-1 quantitative panels.
For intradevice verification, the researchers tested mock samples at different HIV-1 RNA concentrations. The samples were amplified successfully, and a linear fit showed an R2 of 0.85, indicating that the device can be used as a semiquantitative test for whole blood and is capable of differentiating low, medium, and high viral loads. For interdevice verification, samples across 4 devices were tested; Pearson correlation coefficients ranged from 0.79 to 0.92, reflecting good quantitative agreement among the devices.
To determine the diagnostic capabilities of this device, the researchers performed testing on an equal number of HIV-positive and HIV-negative samples (N=104); 50 of 52 HIV-positive blood samples and 46 of 52 HIV-negative blood samples were accurately detected. The sensitivity of the test was 96.2% (95% CI, 90.9-100), and the specificity of the test was 88.5% (95% CI, 79.8-97.1). The device demonstrated 93% accuracy in differentiating the clinically relevant viral load threshold of 1000 copies/mL, which is a threshold often used to monitor HIV in settings with limited resources.
Limitations of the study include the lack of validation with clinical HIV-positive samples, assessment of device accuracy for HIV-1 subtype B only, and the absence of an internal control.
“Through these innovations, we anticipate that HIV self-testing could be performed as simply as a home blood glucose test. The rapid, low-cost, easy-to-use HIV NAT-on-USB would be particularly useful for the high-risk populations seeking private, highly sensitive self-testing at home,” study authors concluded.
Liu T, Choi G, Tang Z, Kshirsagar A, Politza AJ, Guan W. Fingerpick blood-based nucleic acid testing on a USB interfaced device towards HIV self-testing. Biosens Bioelectron. Published online April 8, 2022. doi:10.1016/j.bios.2022.114255