Sensor

The present invention relates to a genetic probe for the detection of a single nucleotide polymorphism (SNP) or a single nucleotide modification of a target nucleic acid, the genetic probe comprising: —a nanoparticle; —an oligonucleotide probe anchored to the surface of the nanoparticle, comprising an oligonucleotide backbone with a tag incorporated therein via a linker group; and —a reference probe anchored to the surface of the nanoparticle, wherein the reference probe comprises a marker; wherein either (a) the tag is an organic fluorescent tag and the marker is a transition metal-based fluorescent marker; or (b) the tag is a redox-active tag and the marker is a transition metal-based redox-active marker. The invention also relates to a composition or kit containing a probe of the invention, or to the use of a probe of the invention. The invention also relates to a method of determining the percentage of single nucleotide polymorphisms (SNPs) or single nucleotide modifications of a target nucleic acid in a pool of the target nucleic acid, or to a method of determining the status of a condition associated with a known SNP in a subject