A sensing mechanism for the detection of carbon nanotubes using selective photoluminescent probes based on ionic complexes with organic dyes

Abstract

The multifunctional properties of carbon nanotubes (CNTs) make them a powerful platform for unprecedented innovations in a variety of practical applications. As a result of the surging growth of nanotechnology, nanotubes present a potential problem as an environmental pollutant, and as such, an efficient method for their rapid detection must be established. Here, we propose a novel type of ionic sensor complex for detecting CNTs – an organic dye that responds sensitively and selectively to CNTs with a photoluminescent signal. The complexes are formed through Coulomb attractions between dye molecules with uncompensated charges and CNTs covered with an ionic surfactant in water. We demonstrate that the photoluminescent excitation of the dye can be transferred to the nanotubes, resulting in selective and strong amplification (up to a factor of 6) of the light emission from the excitonic levels of CNTs in the near-infrared spectral range, as experimentally observed via excitation-emission photoluminescence (PL) mapping. The chirality of the nanotubes and the type of ionic surfactant used to disperse the nanotubes both strongly affect the amplification; thus, the complexation provides sensing selectivity towards specific CNTs. Additionally, neither similar uncharged dyes nor CNTs covered with neutral surfactant form such complexes. As model organic molecules, we use a family of polymethine dyes with an easily tailorable molecular structure and, consequently, tunable absorbance and PL characteristics. This provides us with a versatile tool for the controllable photonic and electronic engineering of an efficient probe for CNT detection. Using photoluminescent probes, researchers have devised a sensitive and selective way of detecting carbon nanotubes. Carbon nanotubes are being produced in ever increasing amounts — currently in excess of thousands of metric tons per year — but there is some evidence that they may be toxic, making it important to develop a sensitive means for detecting them in the environment. Now, Alex Rozhin team at Aston University in the UK and collaborators have developed an efficient method for detecting carbon nanotubes that involves amplifying their photoluminescent signal through the formation of organic complexes with tailorable polymethine dyes. They discovered that the photoluminescent excitation of this dye is transferred to nanotubes, strongly amplifying light emission by up to six times. Furthermore, this amplification is sensitive to both nanotube chirality and the surfactant that the nanotubes are dispersed in.