Anal. Chem. 2010, 82, 1455–1461
Single Cell Impedance Cytometry for Identification and Counting of CD4 T-Cells in Human Blood Using Impedance Labels David Holmes†,‡,§ and Hywel Morgan*,† School of Electronics and Computing Science, University of Southampton, Highfield, Southampton, SO17 1BJ, U.K., and Inflammation and Repair, School of Medicine, University of Southampton, Tremona Road, Southampton, SO16 6YD, U.K. Single cell microfluidic impedance cytometry has been used to identify cells at high speed, on the basis of their dielectric properties. However, there is no electrical analogue to a fluorescent label, meaning that it is not possible to identify subpopulations of cells. We demonstrate discrimination and enumeration of antigenically defined cell subpopulations using an alternating current (AC) impedance labeling method. Small antibody conjugated beads are mixed with cells and bind to the target population, changing the electrical properties of the target subset of cells. The principle of the technique is demonstrated by identifying and enumerating the CD4 T-lymphocyte subpopulation in human whole blood. The technique represents a simple method for detecting a subpopulation of cells within a heterogeneous mix. The impedance-based antibody identification method could form the basis of simple low-cost point of care diagnostic technologies. The first cases of acquired immunodeficiency syndrome (AIDS) were reported in 1981.1 Since then, it is estimated that over 65 million people have been infected by human immunodeficiency virus (HIV) resulting in more than 25 million deaths worldwide. The World Health Organisation (WHO) estimated that in 2006 approximately 4.3 million people became newly infected with HIV, with more than 95% of these new infections in low and middle income countries. International political pressure and the accelerated implementation of antiretroviral therapy (ART) have led to a dramatic reduction in the cost of HIV treatment, making it accessible to the developing world. However, the effective implementation of ART has been hindered by the lack of robust and affordable clinical monitoring. Currently, absolute CD4+ T-lymphocyte count is the most widely used method for monitoring disease progression, staging, and response to drug therapy in HIV infected individuals in resource poor settings. According to WHO guidelines, a CD4 count of fewer than 200 cells/µL of whole blood establishes a * To whom correspondence should be addressed. † School of Electronics and Computing Science, University of Southampton. ‡ Inflammation and Repair, School of Medicine, University of Southampton. § Present address: London Centre for Nanotechnology, University College London, Gordon Street, London, WC1H 0AH, U.K. (1) Gottlieb, M. S.; Schroff, R.; Schanker, H. M.; Weisman, J. D.; Fan, P. T.; Wolf, R. A.; Saxon, A. N. Engl. J. Med. 1981, 305, 1425–1431. 10.1021/ac902568p 2010 American Chemical Society Published on Web 01/27/2010
diagnosis of AIDS.2 Initiation of antiretroviral treatment before the CD4 count falls below 200 cells/µL is recommended, and increased frequency of clinical monitoring is advised in patients with CD4 counts between 200 and 350 cells/µL. The absolute CD4+ T-cell number in children can vary considerably, making this an unreliable staging marker. The WHO and the Centers for Disease Control (CDC) recommend that the percentage of CD4+ T-cells should be used for children under 5 years of age; with suggested cutoff values of 25% for infants up to 11 months,
