Objective

There is an increasing need to reliably detect and monitor levels of small molecules in all areas of the life sciences. This need ranges from monitoring food or environmental contaminants, to pathogen or individual patient drug level monitoring. In every case, more favourable outcomes are achieved when tests are performed ‘on-site’ or at ‘point-of-care’ as immediate action can be taken. Unfortunately, monitoring small molecules often relies on expensive laboratory based methods such as chromatography and mass spectrometry. Simple field based diagnostic devices, such as lateral flow devices, are widely employed as a first pass assay to determine if more thorough analysis is required. These tests often utilise antibodies as the recognition element and frequently require a ‘sandwich-pair’ of antibodies, which is problematic for targets where antibodies are not available. The problem is greater with small molecule antigens as generation of a reliable antibody can be difficult, isolation of sandwich pairs seldom possible. As with many antibody-based applications, nucleic acid aptamers offer an alternative as they are isolated in vitro and under conditions closely resembling the end application. Many traditional aptamer selection approaches utilise immobilised target ligands. Modifying small molecules in this way often perturbs the structure and leads to ineffective aptamer selection. Here we demonstrate selection of aptamers using small molecules free in solution. We will show that this method has been successfully employed to generate aptamers specific to a small molecule, anti-cancer drug target and its major metabolite. The aptamers are able to recognise these targets specifically in samples of buffered plasma. We will also show the aptamers are readily immobilised and able to report the presence of these targets in a simple ‘dip and read’ assay format. We are currently validating the automation of this selection process.