A holographic sensor based on a biomimetic affinity ligand for the detection of cocaine

The increasing consumption of illicit drugs has become a worldwide social and medical problem. Eradicating the supply and use of these drugs requires the development of devices that provide a fast, selective and simple response in seized powder samples. This paper describes a novel strategy for the design and development of a holographic sensor modified with a rationally designed receptor for the detection of cocaine. The receptor was designed by reviewing protein-cocaine interactions, particularly those of human carboxylesterase-1 and catalytic monoclonal antibody GNL7A1, and constructing a four-component Ugi library of putative cocaine-binding ligands. A hybrid hydrogel of poly (2-hydroxyethyl methacrylate-co-ethylene dimethacrylate-co-methacrolein) was used as the carbonyl source for the Ugi reaction. A Bragg diffraction grating comprising gold nanoparticles was fabricated in the polymer gel and the replay wavelength of the combinatorial library of Ugi-modified holographic sensors measured via a spectrophotometer in response to cocaine as a function of pH and ionic strength. A smartphone-based instrument and cloud-based algorithm was developed, optimised with training and test samples of cocaine and used to assess the presence of cocaine in seized field samples. These findings confirm the potential application of this analytical method in field testing for illicit drugs.