Abstract: The invention provides a method for detecting the presence of a target nucleic acid analyte, for example a pathogen or virus nucleic acid, in a sample using oligonucleotide probe-functionalised nanoparticles, where hybridisation of at least three different oligonucleotide probes to at least three different target sequences in the target analyte causes agglomeration of the nanoparticles and a visible colour change. The invention also provides a population of such oligonucleotide probe-functionalised nanoparticles and a related kit for detection of a target nucleic acid analyte.