• carbon nanotubes;
  • light scattering;
  • DNA;
  • enzymes;
  • biosensing


A label-free, enzyme-responsive nanosystem that uses a DNA/single-walled carbon nanotube (SWNT) assembly as the substrate is demonstrated for the sensitive, universal detection of restriction and nonrestriction endonucleases as well as methyltransferases in a homogeneous solution on the basis of light scattering (LS) of carbon nanotubes. This protocol is based on the different binding affinities of SWNTs to single- and double-stranded DNA. This difference can lead to different LS signals that can be used for the detection of nuclease cleavage activity. The assay only requires a label-free oligonucleotide probe, significantly reducing the typical cost. The LS technique and the use of a nuclease-specific oligonucleotide probe impart extraordinarily high sensitivity and selectivity. This light scattering assay is universal and label-free with a detection limit of 5 × 10−6 U μL−1 for S1 nuclease, 1 × 10−4 U μL−1 for EcoRI endonuclease, and 1 × 10−2 U μL−1 for EcoRI methylase. In principle, this assay can be used to detect any kind of nuclease by simply changing the DNA sequences of the specific probe.