Advances in Continuous Microfluidics-Based Technologies for the Study of HIV Infection

Abstract

HIV-1 is the causative agent of acquired immunodeficiency syndrome (AIDS). It affects millions of people worldwide and the pandemic persists despite the implementation of highly active antiretroviral therapy. A wide spectrum of techniques has been implemented in order to diagnose and monitor AIDS progression over the years. Besides the conventional approaches, microfluidics has provided useful methods for monitoring HIV-1 infection. In this review, we introduce continuous microfluidics as well as the fabrication and handling of microfluidic chips. We provide a review of the different applications of continuous microfluidics in AIDS diagnosis and progression and in the basic study of the HIV-1 life cycle.

Keywords: HIV; diagnosis; infection; life cycle; microfluidics; replication; retrovirus.

Figure 1

Microfabrication of the chips by photolithography. The main steps of photolithography are: (A) Negative SU8 photoresist exposure to UV radiation in order to obtain the pattern drawn on the photomask; (B) Photoresistive development to obtain the master mold; (C) Pouring the PDMS on the master mold; (D) Curing and peeling off the PDMS stamp; finally, making holes in the PDMS for external tubing and binding to a glass slide for microscopy (right picture).

Figure 2

Summary of the different microfluidic devices developed in HIV infection.

Figure 3

Simplified schematic representation of HIV-1 particle.

Figure 4

Principle of HOLMES [34]. (A) Schematic of HOLMES with hierarchical multistages. At each stage, parallel microchannels and buffer channels are bridged by a thin nanochannel network patterned on the bottom of the microchannels. (B) Schematic of nanofluidic biomolecule concentration in massively parallel channels. Under the electrical configuration shown, biomolecules are electro-osmotically injected into the parallel channels and electronically concentrated in the ion deletion zones induced near the micronanochannel junctions. V—voltage; G—grounded; EN and ET—normal and tangential electric fields, respectively; EO—electroosmosis; EP—electrophoresis. (C) Schematic of relayed reconcentration of biomolecules from massively parallel microchannels into a single microchannel to dramatically boost the concentration performance.

Figure 5

Overall design of the QD barcode assay. Electrokinetics is used to transport QD-barcoded microbeads (Ø = 3.8 µm) into a microchannel. The flow is going from left to right: (i) magnetic barcodes are attracted by a first magnet to interact with the target ssDNA present in the upper stream, (ii) then they move toward the second magnet to interact with the reporter probe present in the lower stream, and (iii) they are pulled by the last magnet into a washing buffer and aligned for optical excitation and detection. They are individually detected by fluorescence as they pass through a focused laser spot. The figure shows the detection of one genetic target, but for multiplexed detection, the same process is done for the different ssDNA targets simultaneously [50].

Figure 6

Double Stage Cascade Device used for CD4 counting. The PDMS device harbors two distinct functions: monocyte depletion (upstream) and CD4+ T cell capture (downstream). The upstream region contains four parallel chambers (50 µm height) coated with an anti-CD14 antibody in order to specifically retain the monocytes (red spots). The monocyte depletion increases the sensitivity and specificity of CD4+ T cell (green spots) retention in the main channel (downstream), which was functionalized with an anti-CD4 antibody. After sample injection, rinsing steps are crucial to avoid shearing off captured cells [57].

Figure 7

Schematic representation of the IFAST device. It is formed by seven successive flow chambers containing three oil barriers. The magnet at the bottom of the device is moved from the input to the output wells at a rate of 1–2 mm per second. The paramagnetic particles (PMP) move with the magnet, carrying along attached cells and excluding unbound cells at the immiscible phase barrier. Isolated cells are dyed on-chip with a small molecule dye (Calcein AM) metabolized to a fluorophore to be read by a fluorometer [64].