Self-assembled quasi one-dimensional nanostructures of pi-conjugated molecules(1-15) may find a use in devices owing to their intriguing optoelectronic properties, which include sharp exciton transitions(1-5), strong circular dichroism(5-7) high exciton mobilities(8,9) and photoconductivity(10). However, many applications require immobilization of these nanostructures on a solid substrate, which is a challenge to achieve without destroying their delicate supramolecular structure. Here, we use a drop-flow technique to immobilize double-walled tubular J-aggregates of amphiphilic cyanine dyes without affecting their morphological or optical properties. High-resolution images of the topography and exciton fluorescence of individual J-aggregates are obtained simultaneously with polarization-resolved near-field scanning optical microscopy. These images show remarkably uniform supramolecular structure, both along individual nanotubes and between nanotubes in an ensemble, demonstrating their potential for light harvesting and energy transport.