Ultra-rapid, sensitive and specific digital diagnosis of HIV with a dual-channel SAW biosensor in a pilot clinical study

Abstract

Despite widened access to HIV testing, around half of those infected worldwide are unaware of their HIV-positive status and linkage to care remains a major challenge. Current rapid HIV tests are typically analogue risking incorrect interpretation, no facile electronic data capture, poor linkage to care and data loss for public health. Smartphone-connected diagnostic devices have potential to dramatically improve access to testing and patient retention with electronic data capture and wireless connectivity. We report a pilot clinical study of surface acoustic wave biosensors based on low-cost components found in smartphones to diagnose HIV in 133 patient samples. We engineered a small, portable, laboratory prototype and dual-channel biochips, with in-situ reference control coating and miniaturised configuration, requiring only 6 µL plasma. The dual-channel biochips were functionalized by ink-jet printing with capture coatings to detect either anti-p24 or anti-gp41 antibodies, and a reference control. Biochips were tested with 31 plasma samples from patients with HIV, and 102 healthy volunteers. SH-SAW biosensors showed excellent sensitivity, specificity, low sample volumes and rapid time to result, and were benchmarked to commercial rapid HIV tests. Testing for individual biomarkers found sensitivities of 100% (anti-gp41) and 64.5% (anti-p24) (combined sensitivity of 100%) and 100% specificity, within 5 min. All positive results were recorded within 60 s of sample addition with an electronic readout. Next steps will focus on a smartphone-connected device prototype and user-friendly app interface for larger scale evaluation and field studies, towards our ultimate goal of a new generation of affordable, connected point-of-care HIV tests.

Keywords: Biosensors; HIV infections; Infectious-disease diagnostics.

Fig. 1

SH-SAW biosensor and biochips. a Key characteristics of dual-channel biochips. b Dimensions of disposable laboratory-use biochips. Channels are surrounded by black resin, with electrodes under glass protection. c Laboratory-based biochip holders and prototype reader (biochips in b are beneath metal covers). This was the reader used in this study. White scale bar shows 2 cm

Fig. 2

Raw signal readout from anti-gp41 and anti-p24 biochip individual runs. Shown are reference (dashed lines) and analyte (continuous) channels for a anti-gp41 and b anti-p24 biochips; (i) a single HIV-positive sample, two biochips; (ii) a single healthy donor sample on two biochips; for calibration samples at (iii) 25 μg/ml; and (iv) 0 μg/ml. The differential signal is indicated in a (i) (analyte minus reference channels)

Fig. 3

Combined biochip data. a Differential signals for 31 HIV-positive (duplicate averages) and 102 healthy volunteer samples on anti-gp41 and anti-p24 biochips. Means are shown with standard deviations for each group. Green lines, positive threshold cut-offs. b (i) Time-resolved sensitivity for HIV-positive samples. By 53 s (grey marker) all positives gave a reactive result. (ii) Time-resolved specificity data. After 5 min, all negative samples gave negative results. Inset: Enlarged Y-axis view