A label-free aptamer-fluorophore assembly for rapid and specific detection of cocaine in biofluids

Anal Chem. 2014 Nov 18;86(22):11100-6. doi: 10.1021/ac503360n. Epub 2014 Nov 4.


We report a rapid and specific aptamer-based method for one-step cocaine detection with minimal reagent requirements. The feasibility of aptamer-based detection has been demonstrated with sensors that operate via target-induced conformational change mechanisms, but these have generally exhibited limited target sensitivity. We have discovered that the cocaine-binding aptamer MNS-4.1 can also bind the fluorescent molecule 2-amino-5,6,7-trimethyl-1,8-naphthyridine (ATMND) and thereby quench its fluorescence. We subsequently introduced sequence changes into MNS-4.1 to engineer a new cocaine-binding aptamer (38-GC) that exhibits higher affinity to both ligands, with reduced background signal and increased signal gain. Using this aptamer, we have developed a new sensor platform that relies on the cocaine-mediated displacement of ATMND from 38-GC as a result of competitive binding. We demonstrate that our sensor can detect cocaine within seconds at concentrations as low as 200 nM, which is 50-fold lower than existing assays based on target-induced conformational change. More importantly, our assay achieves successful cocaine detection in body fluids, with a limit of detection of 10.4, 18.4, and 36 μM in undiluted saliva, urine, and serum samples, respectively.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aptamers, Nucleotide / chemistry*
  • Body Fluids / chemistry*
  • Cocaine / analysis*
  • Fluorescence
  • Fluorescent Dyes / chemistry*
  • Humans
  • Naphthyridines / chemistry*
  • Time Factors


  • 2-amino-5,6,7-trimethyl-1,8-naphthyridine
  • Aptamers, Nucleotide
  • Fluorescent Dyes
  • Naphthyridines
  • Cocaine