(Invited) Carbon Nanotube Photoluminescence Solvatochromism in Biomedicine: Spectroscopy, Imaging, and Modulation
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Modulation of the carbon nanotube photoluminescence band position has implications for applications such as sensing and imaging. Carbon nanotube photoluminescence solvatochromism, the hypsochromic or bathochromic shifting of nanotube emission, can be induced via changes in the local dielectric environment. We developed methods to modulate nanotube solvatochromic behavior to improve sensor responses, and we developed tools to observe solvatochromism within live cells and, recently, live animals. We found that nanotube solvatochromism extends to variations of local electrostatic charge, induced by adsorption/desorption of polyelectrolytes on the nanotube surface, such as proteins and nucleic acids. We also found that dielectric and charge-mediated solvatochromism can be compounded to exacerbate the response. Upon triggered desorption of a polyelectrolyte, such as upon desorption of RNA upon hybridization, for instance, amphiphilic molecules can adsorb to the recently-uncovered nanotube surface. The adsorption displaces water to result in hypsochromic shifting, which can be additive, as polyelectrolyte desorption will also cause a hypsochromic shift. We found that the amphiphile may be a surfactant but, recently, we found that proteins can result in a similar response, facilitating the detection of viruses. We developed tools to image changes in nanotube emission in live cells (near-infrared hyperspectral microscopy) and, recently, live animals (preclinical, near-infrared hyperspectral imaging). Carbon nanotube solvatochromism-based sensors, in combination with spectral imaging tools, allow measurements of biomarkers, drugs, and metabolites in live cells and organisms, facilitating improvements in disease detection, drug development, and biomedical research.
