Single-walled carbon nanotubes (SWCNTs) demonstrate distinctive fluorescence properties that have motivated their use as optical sensors. Their fluorescence properties, such as quantum yield and optical responsivity and specificity towards analytes, are controlled by the non-covalent wrapping that is used to solubilize the SWCNTs in aqueous media.  Single-stranded DNA is among the most common SWCNT wrappings, whereby sensor properties such as specificity can be modulated by altering the DNA sequence. However, the relationship between the DNA sequence and its effects on the sensors are unknown, hindering the ability to engineer these sensors in a predictive manner. The state-of-the-art for developing these sensors is therefore limited to empirical approaches that yield sensors with sub-optimal performances.

Inspired by strategies in protein engineering, we have developed a bioengineering approach based on directed evolution that allows us to modulate the DNA-SWCNT optoelectronic behavior in a more controlled and directed manner. We apply this approach to develop optical nanosensors for the detection of the mycotoxins aflatoxin and fumonisin, toxic metabolites found in various foodstocks. Through directed evolution, we demonstrate a guided approach to orthogonally tuning the sensor properties, including specificity, sensitivity, brightness, and even chirality-dependent responsivity towards each of these analytes. We further explore the underlying mechanisms of the evolved sensors and demonstrate the use of these sensors in a multi-modal platform that allows us to detect multiple toxins at different wavelengths of light. Bioengineering therefore provides us an unconventional means for overcoming conventional challenges in nanotube optoelectronics.