Aptamer-Graphene Combos Pull Analytic Double Duty

Small-molecule-binding nucleic acids conjugated to graphene oxide improve extraction and ionization of analytes from biological samples, an international research team has discovered (J. Am. Chem. Soc., DOI: 10.1021/ja109042w). Weihong Tan of the University of Florida and coworkers at Stanford University and China’s Hunan University attach aptamers—single-stranded oligonucleotides that bind target molecules with high affinity—to the surface of graphene oxide via a flexible poly(ethylene glycol) linker. The linker stabilizes the construct in biological fluids and allows the aptamers to fold into their three-dimensional conformations. The researchers used graphene oxide modified with a cocaine-binding aptamer to extract cocaine from spiked plasma samples and then analyzed the drug by mass spectrometry directly from the graphene oxide surface. With unmodified graphene oxide, Tan and colleagues observed a signal-to-noise (S/N) ratio of about 15 in the mass analysis. The aptamer-modified graphene oxide efficiently captured the cocaine and boosted the S/N ratio to an average of 52. The researchers achieved similar improvements with graphene oxide attached to an adenosine-binding aptamer.