Sensitivity, specificity for both infections are comparable to ELISA
A palm-sized dongle connected to a smartphone will soon be able to diagnose HIV and syphilis with good accuracy. The device, which was recently field-tested on 96 patients in Rwanda, had high sensitivity and specificity for both HIV and syphilis. The results are published today (February 5) in the journal Science Translational Medicine.
Sensitivity and specificity for both the infections are comparable to the lab-based ELISA. In the case of HIV, the sensitivity was 100 per cent and specificity was 87 per cent. For syphilis, the sensitivity was 92-100 per cent and specificity was 79-92 per cent. “Two types of syphilis antibodies are looked for to confirm infection and prevent over-treatment,” Dr. Tiffany W. Guo of the Department of Biomedical Engineering, Columbia University said in an email to this Correspondent. He is one of the authors of the paper.
“By increasing detection of syphilis infections, we might be able to reduce deaths by 10-fold. And for large-scale screening where the dongle's high sensitivity with few false negatives is critical, we might be able to scale up HIV testing at the community level with immediate antiretroviral therapy that could nearly stop HIV transmissions and approach elimination of this devastating disease,” Dr. Tassaneewan Laksanasopin of the Department of Biomedical Engineering, Columbia University and the corresponding author noted in a release.
The device has several highlights. For instance, both HIV and syphilis can be diagnosed in about 15 minutes and at a fraction of the cost of a lab-based ELISA test. The dongle cost under $34 compared with an astronomical $18,450 for ELISA equipment. Also, the material and reagent required for testing HIV and syphilis cost no more than $1.44; in the case of conventional lab-based equipment the cost for testing these infections is $8.50.
What makes the device particularly interesting is the very low power consumed to run it. This would be of immense value when the device is used in the field where power may not be available 24x7.
This became possible as the device does not use a power-consuming electrical pump to generate vacuum but a rubber bulb (as in the case of the manual blood pressure measuring instrument — sphygmomanometer) which when pressed creates a negative pressure. The negative pressure, in turn, moves a sequence of reagents that are already stored in a cassette. Other electrical components used consume very little power.
The total power consumed by the device for a test is 1.6 mW. By comparison, a smartphone uses 751 mW on a 3G network; even in a standby mode, a smartphone consumes as much as 17.5 mW.
The researchers came out with a second innovation to power the device using a smartphone. The audio jack of iPhone sends a 19-kHz audio signal that is converted into a stable DC 3 volt. This innovation made the use of a battery redundant. Since audio jacks are standardized among smartphones, the dongle can be attached to any compatible smart device.
“We designed our device to minimize power consumption (e.g. get rid of the electrical pump) and the only component that requires power (which is very little) is the optics. So the power converted from the audio signal is sufficient to run the device,”said Dr. Guo.
It is very easy to operate the dongle. Health workers needed all of 30 minutes of training before they started using the device.
Fingerprick whole-blood specimen was sufficient to diagnose both the infections. During the trial, the freshly collected whole-blood was diluted before testing the sample. “This field testing was a first time performance on freshly collected whole blood, which our cassettes [where the reagents are preloaded] were not best optimised for. Subsequent to the trial, we changed the amount of antigens coated on plastic cassettes which can detect undiluted whole blood,” Dr. Guo said.
There are five detection zones on the microfluidic cassette. Each zone is coated with antigens/antibodies specific to diseases plus internal negative and positive controls. Blood sample is flowed through the microfluidic channel, passing through each detection zone in sequence.
The dongle detects the presence of antibodies against HIV and syphilis from blood samples by capturing these antibodies using specific antigens in the microfluidic channel.
“The dongle is used as an analyser to quantify the amount of antibodies from blood samples and display results as positive or negative,” said Dr. Guo.
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