Recently, aptamers and oligonucleotides have begun to be integrated into lateral flow assays. However, unlike antibodies, aptamers are not inherently adhesive to nitrocellulose membranes. Researchers will often use a protein to sequester the aptamer to the nitrocellulose (e.g., biotinylated aptamer bound to streptavidin). However, more components present in the test line gives a higher possibility of background binding and reintroduces the issue of protein stability.
At Cytodiagnostics, we have developed a proprietary method to directly sequester aptamers to nitrocellulose membranes. We have also optimized OligoREADY™ AptamerREADY™ gold conjugation kits for high efficiency one-step conjugation of thiolated oligonucleotides directly to the surface of gold nanoparticles. Both parts of the sandwich traditionally formed by antibodies in a lateral flow assay may therefore be substituted with aptamers. This is especially useful when an aptamer is already known for the target and low costs per test strip with high stability in a wide variety of storage conditions is desired.
Figure 1 – Using aptamers instead of antibodies as the recognition element for antigen binding.
Amplified Nucleic Acids for Lateral Flow Assays
In addition to aptamer-target binding, base pair complementarity may be exploited to detect DNA sequences, such as PCR-amplified DNA.
Polymerase chain reaction (PCR) is a powerful technique, however, to visualize the amplified products, it requires a real time PCR machine or the end product is analyzed by gel electrophoresis. The cost of real time PCR machine and the required involvement of trained personnel to operation impede its widespread on-site application as point-of-care (POC) test.
Cytodiagnostics Inc has introduced a simple highly sensitive lateral flow device (LFD) to visualize nucleic acid sequences such as single stranded DNA or an amplified PCR product in less than 10 minutes. We have developed a proprietary method to reduce non-specific binding at the test and control lines and increased loading of nucleic acids for binding.
Figure 2 – Capture of PCR Products for the presence of Nucleic acid Products (top panel); Capture of single-stranded oligonucleotides (bottom panel).
Figure 3 – LFA using nucleic acids
Overall, lateral flow assays have had a profound impact on the field of diagnostics, enabling rapid and accessible diagnosis and management across many industries. With advancing technologies such as integration of aptamers and nucleic acids, lateral flow assays will greater wide-spread utility and adoption.