The Effect of Humidity on the Photosensitivity of Photodetectors Based on Green Fluorescent Proteins and Carbon Nanotubes

Introduction: Bionanohybrids of carbon nanotubes (CNTs) and green fluorescent proteins (GFPs) are promising materials for optical biosensors due to their combination of unique optical and electrical properties inherent to photoactive biological objects and carbon nanomaterials. The tertiary structure of the biopolymer effectively protects the chromophore, while the cylindrical shape of carbon nanotubes minimizes the contact area with proteins, preventing damage to their native structure. This interaction ensures the stability of GFP-CNT conjugates and prevents fluorescence quenching. In this study, we investigated the effect of humidity levels on the photosensitivity of a photodetector based on a field-effect transistor with a carbon nanotube channel modified by green fluorescent protein.

Methods: We used quasi-metallic single-walled carbon nanotubes grown by chemical vapor deposition in a bottom-gate transistor configuration. The device was fabricated on a highly doped (p++) 100 mm silicon substrate with a 300 nm thermally grown SiO₂ dielectric layer and source and drain electrodes consisting of 100 nm Au and 15 nm Ti. Genetically engineered green fluorescent proteins were attached to the carbon nanotubes using a photochemical reaction based on click chemistry.

Results: Reducing the humidity by purging the samples with dry air or an inert gas leads to a decrease in photosensitivity, which can be restored by the reverse process. The likely cause is a conformational change in the GFP, its partial denaturation, and the removal of adsorbates at the GFP/CNT interface. By controlling the humidity, it is possible to regulate the operation of the photodetector, partially or completely "switching it off."

Conclusions: This paper demonstrates that humidity has a significant impact on the photosensitivity of a device based on GFPs and carbon nanotubes, allowing for the regulation of its operation and the adjustment of photodetector characteristics.