LFAs are rapid and inexpensive diagnostics that can be used to test for a target analyte in a sample. The most common example of an LFA is a pregnancy test. A colored line at the test location indicates a positive test, and a second line at the control location indicates that the test was valid. The red color of the test and control lines in most common LFAs is due to the use of 40 nm diameter gold nanoparticles as the conjugated particle.
While 40 nm diameter gold nanoparticles have been used in LFAs for the past several decades, increases in assay sensitivity and dynamic range are possible by engineering the optical response of the reporter particle. We have utilized gold nanoshells – colloidal particles comprising a silica core with a uniform thin gold shell – as a replacement for 40 nm diameter gold particles. These gold nanoshells have a per-particle extinction that is 30× that of the gold nanoparticles, while the silica shell interior causes the particles to have a much lower mass compared to solid gold particle of the same size. These particles provide an increase in assay sensitivity while retaining many of the attractive physical properties of the smaller solid gold nanospheres in LFAs.
Drugs & Diagnostics for Tropical Diseases (DDTD), a non-profit organization with a mission to discover new treatments and diagnostics for neglected tropical diseases, developed a LFA for the detection of Loa loa, one of the parasites that cause river blindness. Gold nanoshells were used as the detection particle to increase the assay sensitivity.
After assay development by DDTD, the protocols and Product Specifications were transferred to nanoComposix (Design Input). Manufacturing batch records (MBRs) were drafted, as well as a process flow diagram and interim check points to ensure that quality control was introduced throughout the development process. Small batches were produced to define all assay specifications, test methods, and manufacturing tolerances.
The MBRs were finalized and the process was repeated to ensure efficient scale-up of procedures. Production of 3 engineering lots of 1000 test strips each were prepared under the direction of the MBRs. Verification testing of the engineering lots is required to obtain a comprehensive evaluation of the assay performance characteristics (Design Output).
Once the output satisfied all required design inputs, the assay was transferred to full scale manufacturing. Production of 3 validation lots of assays for a total of 50,000 test strips were manufactured under the direction of the MBRs and associated production documents. Quality control processes were implemented to ensure consistent results for each lot and between lots. Strips were transferred to packager for assembly into cassettes and final packaging in kits. The assays are currently under evaluation in Africa and other parts of the world.