Paper sensors based on fluorescence changes of carbon nanodots for optical detection of nanomaterials

A paper sensor was designed in order to detect the presence of nanomaterials, such as ZnO and silica nanoparticles, as well as graphene nanoplatelets (GnP), based on fluorescence changes of carbon nanodots. Paper strips were functionalized with carbon nanodots using polyvinyl alcohol (PVA) as binder. The carbon nanodots were highly fluorescent and, hence, rendered the (cellulosic) paper stripes emissive. In the presence of silica and ZnO nanoparticles, the fluorescence emission of the carbon nanodots was quenched and the emission decay was shortened, whereas in the presence of GnP only emission quenching occurred. These different photoluminescence (PL) quenching mechanisms, which are evident from lifetime measurements, convey selectivity to the sensor. The change in fluorescence of the carbon dot-functionalized paper is also evident to the naked eye under illumination with a UV lamp, which enables easy detection of the nanomaterials. The sensor was able to detect the nanomaterials upon direct contact, either by dipping it in their aqueous dispersions, or by sweeping it over their powders. The use of the proposed optical sensor permits the detection of nanomaterials in a straightforward manner, opening new ways for the development of optical sensors for practical applications.