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We report here on the interaction of the fluorescent dye rhodamine B (RB) with single-walled carbon nanotubes (SWCNTs). We observe that SWCNTs statically quench the fluorescence of RB by forming a stable ground state complex. Careful spectroscopic analysis indicates that the complex formation is efficient mainly with certain chiral forms. We propose three different applications utilizing this quenching mechanism and the associated complexation. Firstly, the quenching efficiency can be utilized as a measure for the characterization and quantification of nanotube dispersions. Secondly, we demonstrate that the specific complexation of RB can be deployed to enrich certain chiral forms in suspension. Finally, we show that RB can be effectively used to visualize nanotubes deposited on substrates.

Highly selective: Enhancement of the photoluminescence (PL) emission efficiency of selected chiral forms of semiconducting single-walled carbon nanotubes (SWCNTs) is presented (see figure). Excitation of Nile blue A in the presence of SWCNTs results in the quenching of its fluorescence. The energy is resonantly transferred to the (7,5) SWCNT whereas the (8,7) tube is not in resonance; hence, its PL remains unaffected.We report on a simple method for enhancing the efficiency of photoluminescence (PL) emission from selected chiral forms of semiconducting single-wall carbon nanotubes (SWCNTs). The method is based on the use of a fluorescent dye (Nile blue A) that shows the capability of resonant energy transfer on to nanotubes. The excitation of Nile blue A in the presence of SWCNTs results in the quenching of its fluorescence and the energy is resonantly transferred to certain chiral forms. The PL emission from these chiral forms shows a marked increase in efficiency signifying the occurrence of Förster type resonant energy transfer (FRET). Due to its simplicity, this procedure has widespread implications for the detection of carbon nanotubes as well as for their use as fluorophores in FRET-based in vivo and in vitro biological applications.

We present a novel nonenzymatic carbon nanotube sensor integrated in a microfluidic channel for the detection of sugars. The sensor is assembled as a liquid-gated field-effect transistor, with the transistor channel composed of 1 to 10 nanotubes, which are controllably functionalized with boronic acid receptors. The devices show sensitivity to glucose in a concentration range of 5 to 30 mM. Furthermore, by controlling the type of nanotube-receptor coupling (as covalent or noncovalent) and by deploying a sensitive impedance-based detection technique, we corroborate in detail the transduction mechanism of our affinity-based sensor. In the case of covalent coupling, charge carrier scattering along the nanotubes is the dominant mechanism. While in the noncovalent case, surface charge effects dominate. The identification of the mechanism along with the tunability of the chemical coupling and the cost-effective integration in microchannels constitute a solid basis for the entry of nanotube-based sensors in lab-on-a-chip applications.