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Sensitive Nanoparticle Assay For the Detection of HIV
Framework programme:
Project number:
EC contribution:
€ 2,026,260
36 Months
Starting date:
1st January 2007

Keywords: HIV load test, p24 antigen assay, colloidal magnetic nanoparticles, agglutination test, and micro fluidic chip


A new platform and assay for the detection of the HIV p24 antigen in serum or blood is to be developed. The advantages of a p24 test are that it can detect HIV at an early stage of the infection, before antibodies develop, and that it is quantitative. The DETECTHIV project aims at developing an extremely simple viral load test with only one reactant (grafted colloids). In a first phase, a magnetic nanoparticles assay will be developed for use in a microtiter plate with the goal to detect concentrations as low as 1 ng/ml. In a second phase, the use of nanoparticles on a microfluidic chip will allow the detection of p24, to levels as low as 0.1 picog/ml, one to two orders of magnitude more sensitive than classical Enzyme Linked Immuno-Sorbent Assay (ELISA) p24 tests. Validation of the platform will be done with bothrecombinant p24 samples and patient samples.

The test consists principally of optically detecting the formation of a colloidal gel of magnetic nanoparticles (‘agglutination test’). The gel forms in a magnetic field under the presence of antigens that are capable of linking irreversibly two colloidal particles. Therefore, the latter are grafted with antibodies that are specific to the p24 antigen. The detection is achieved and through simple optical absorbance measurements, owing to the strong optical scattering modification when passing from nanometric colloids to the gelled state.

In the microfluidic chip test, a sample solution of serum or blood is transported through a suspension of magnetic nanoparticles that are magnetically retained within a microfluidic channel. When brought into a magnetic field, the particles will be able to approach each other, form chains and will be irreversibly linked if the p24 antigen is present. Subsequently, on-chip light scattering techniques will be used to quantify the concentration of permanent chains or clustered beads, which is proportional to the p24 antigen concentration.


Given that immunoassays are the most widely used assays in clinical diagnostics, the impact of lowering their cost while enhancing their efficiency would provide a much-needed contribution towards lowering healthcare costs. The chosen assay, i.e. the p24 antigen-based viral test, would be of great benefit in the global battle against HIV infection and AIDS, especially in the developing world that constitutes over 70% of the affected world population. An arsenal of laboratory methods is available to screen blood, diagnose infection and monitor disease progression in individuals infected by HIV. ELISA is the most commonly used test to screen for HIV infection.

One advantage of the use of magnetic colloids arises from the fact that the particle surface has a very strong colloidal stability in any type of buffer, serum or plasma and has functional groups or receptors so that the particles can be further grafted with the biomolecules of interest. After trapping molecules (present in small amounts in solution) on the nanoparticles, the latter can be handled with applied magnetic fields. There is a net advantage due to faster reaction rates, trapping of the analyte and separation without losses.

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