Single-Digit Pathogen and Attomolar Detection with the Naked Eye Using Liposome-Amplified Plasmonic Immunoassay

Nano Lett. 2015 Sep 9;15(9):6239-46. doi: 10.1021/acs.nanolett.5b02837. Epub 2015 Aug 28.


We introduce an enzyme-free plasmonic immunoassay with a binary (all-or-none) response. The presence of a single pathogen in the sample results in a chemical cascade reaction leading to a large red to dark-blue colorimetric shift visible to the naked eye. The immediate and amplified response is initiated by a triggered breakdown of cysteine-loaded nanoliposomes and subsequent aggregation of plasmonic gold nanoparticles. Our approach enabled visual detection of a single-digit live pathogen of Salmonella, Listeria, and E. coli O157 in water and food samples. Furthermore, the assay allowed a naked-eye detection of target antibody concentrations as low as 6.7 attomolar (600 molecules in 150 μL); six orders of magnitude lower than conventional enzyme-linked immunosorbent assay (ELISA).

Keywords: Plasmonic colorimetry; foodborne pathogens; gold nanoparticles; immunoassay; liposomes; signal amplification.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Colorimetry / methods
  • Enzyme-Linked Immunosorbent Assay
  • Escherichia coli Infections / microbiology
  • Escherichia coli O157 / isolation & purification*
  • Food Microbiology
  • Gold / chemistry*
  • Humans
  • Immunoassay / methods*
  • Liposomes / chemistry*
  • Liposomes / ultrastructure
  • Listeria / isolation & purification*
  • Metal Nanoparticles / chemistry*
  • Metal Nanoparticles / ultrastructure
  • Rabbits
  • Salmonella / isolation & purification*
  • Salmonella Infections / microbiology
  • Water Microbiology


  • Liposomes
  • Gold