(65e) Towards Point-of-Care HIV-1 Detection Through Electrical Sensing-On-a-Chip

HIV diagnostics in resource-limited settings play a critical role to provide appropriate and timely care to patients. More than 95% of deaths due to infectious diseases (malaria, HIV, and tuberculosis (TB) have been reported to occur in developing countries [1-4]. 67% of the HIV-1 infected population (33.3 million people worldwide) are livening in Sub-Saharan Africa [5]. The World Health Organization (WHO) is rapidly expanding the number of AIDS patients receiving antiretroviral therapy (ART) in resource-constrained settings to control this disease. Current technical approaches for HIV diagnosis in developed world market utilizing IgG, IgG/p24, DNA, RNA, reverse-transcriptase activity biomarkers are time consuming and require sophisticated laboratory infrastructures and consequently are not compatible with resource-limited settings. These efforts, however, are significantly restricted by the prohibitive cost to implement.

ART monitoring tools, i.e., CD4 cell counts by flow cytometry, and HIV viral load monitoring by reverse transcription-polymerase chain reaction (RT-PCR) are costly and require experts to implement the tests, which consequently restrict our ability to control this pandemic. Several methods have been investigated and developed to design portable CD4 cell counter tools, including electrical sensing, microfluidic lensless imaging, fluorescence staining, microscopy counting, and flow cytometry. Although CD4 cell count can be used to initiate and monitor treatment, this method cannot detect early virological failure and HIV viral load tests must be implemented. Current technologies available for viral load tests require expensive instruments and reagents, experts to conduct the tests, and advanced laboratories, which are not available at the point-of-care (POC). Thus there is an immediate and unmet need to create and develop an easy to use, portable, and inexpensive point-of-care (POC) diagnostic tool for HIV1 detection testing at resource-limited settings to monitor AIDS patients and facilitate the access to ART treatment.

In biosensor technology, microfluidics have shown promising and important advantages such as sample pretreatment including preconcentration, separation and detection, portability, handling of small sample volumes, and high-throughput analysis [6]. Due to the above advantages, one of the most promising opportunities of microfluidic platforms is reported to be in POC diagnostics and treatment monitoring applications. Biosensing technologies including optical, fluorescent, electrical and electrochemical sensing methods are compatible with microfluidic platforms. Due to easy microfabrication of interdigitated electrodes using photolithography, easy integration of microelectrodes into multi-array or microprocessor-controlled diagnostic tools, electrochemical sensing is a promising and powerful technology. This method eliminates the labeling step for sensing which consequently reduces the nonspecific detection. Furthermore, utilizing interdigitated microelectrodes, the impedance change at the surface of the microelectrodes and signal/noise ratio can be maximized and the interfering of nontarget analytes in the solution can be minimized.

Microfluidics-based electrical sensing has provided a means of probing cellular concentration, size, membrane capacitance, cytoplasmic conductivity and permittivity. Electrical measurements on mammalian cells through Coulter counting and DEP (Dielectrophoresis) have provided means of probing cellular concentration, size, membrane capacitance, cytoplasmic conductivity and permittivity. The electrical data recorded by these means can possibly be used to distinguish cells without using fluorescent or magnetic markers. Living cells are insulators at low frequencies. This monitoring has been used to study the behavior of macrophages, endothelial cells and fibroblasts. Sohn et al. [7] demonstrated the linearity between cellular capacitance in eukaryotic cells and the intracellular DNA content. There have been successful efforts to utilize electrical sensing using carbon nanotubes to detect single viruses [8]. However, current designs only detect a virus that passes by and are not specific to a virus and not adaptable for the POC in resource-limited settings. Also, use of magnetic particles have been attempted to attach to viral particles, however, separating nanoparticles with and without captured viruses is challenging for the counting step especially for POC applications [9].

In this study, we have successfully isolated, enriched, and detected HIV-1 particles utilizing a microfluidic device. Spiked samples with HIV1 were mixed with magnetic beads conjugated with gp120 antibodies to selectively capture target viruses. Our results show that this label-free method is capable of capturing and detecting HIV1 in a rapid, simple, and inexpensive fashion. This method can be potentially used in the detection of HIV at seroconversion (4-5 weeks) and asymptomatic (up to 12 years) period of the disease.

References:

1.            Yager, P., G.J. Domingo, and J. Gerdes, Point-of-care diagnostics for global health. Annu Rev Biomed Eng, 2008. 10: p. 107-44.

2.            Urdea, M., et al., Requirements for high impact diagnostics in the developing world. Nature, 2006. 444 Suppl 1: p. 73-9.

3.            Hay Burgess, D.C., J. Wasserman, and C.A. Dahl, Global health diagnostics. Nature, 2006. 444 Suppl 1: p. 1-2.

4.            Girosi, F., et al., Developing and interpreting models to improve diagnostics in developing countries. Nature, 2006. 444 Suppl 1: p. 3-8.

5.            UNAIDS, Report on the Global AIDS Epidemic. 2010: p. http://www.unaids.org/globalreport/global_report.htm.

6.            Wang, J., A. Ibanez, and M.P. Chatrathi, On-chip integration of enzyme and immunoassays: simultaneous measurements of insulin and glucose. J AM Chem Soc, 2003. 125(28): p. 8444-5.

7.            Sohn, L.L., et al., Capacitance cytometry: measuring biological cells one by one. Proc Natl Acad Sci U S A, 2000. 97(20): p. 10687-90.

8.            Patolsky, F., et al., Electrical detection of single viruses. Proc Natl Acad Sci U S A, 2004. 101(39): p. 14017-22.

9.            Chen, G.D., et al., Concentration and purification of human immunodeficiency virus type 1 virions by microfluidic separation of superparamagnetic nanoparticles. Anal Chem, 2010. 82(2): p. 723-8.