Quantum Defects in Fluorescent Carbon Nanotubes for Sensing and Mechanistic Studies

Abstract

Single-wall carbon nanotubes (SWCNT) fluoresce in the nearinfrared (NIR) region and have been assembled with biopolymers such as DNA to form highly sensitive molecular (bio)sensors. They change their fluorescence when they interact with analytes. Despite the progress in engineering these sensors, the underlying mechanisms are still not understood. Here, we identify processes and rate constants that explain the photophysical signal transduction by exploiting sp 3 quantum defects in the sp 2 carbon lattice of SWCNTs. As a model system, we use ssDNA-coated (6,5)-SWCNTs, which increase their NIR emission (E 11 , 990 nm) up to +250% in response to the important neurotransmitter dopamine. In contrast, SWCNTs coated with DNA but with a low number of NO 2 -aryl sp 3 quantum defects decrease both their E 11 (−35%) and defect-related E 11 * emission (−50%) at 1130 nm. Consequently, the interaction with the analyte does not change the radiative exciton decay pathway alone. Furthermore, the fluorescence response of pristine SWCNTs increases with SWCNT length, suggesting that exciton diffusion is affected. The quantum yield of pristine (6,5)-SWCNTs increases in response to the analyte from 0.6 to 1.3% and points to a change in non-radiative rate constants. These experimental results for dopamine and other analytes are explained by a Monte Carlo simulation of exciton diffusion, which supports a change in two non-radiative decay pathways together with an increase in exciton diffusion (three-rate constant model). The combination of such SWCNTs with defects and without defects enables the assembly of ratiometric biosensors with opposing responses at different wavelengths. In summary, we demonstrate how perturbation of a nanomaterial with quantum defects reveals the photophysical mechanism and reverses optical responses of biosensors.

Biosensing with Fluorescent Carbon Nanotubes

“…It has shown its versatility in the detection of divalent ions, [25, 109] genotoxins, [110] NO, [20] H 2 O 2 , [20, 32, 110–112] riboflavin, [49, 113, 114] doxorubicin, [115] β‐carotene, [116] endolysosomal lipids, [117] arsenite, [33] and neurotransmitters, especially dopamine [15, 49, 63, 80, 87, 118–121] . This section highlights the major advances from the last few years for different categories of biomolecules.…”

“…Defects also change the exciton decay pathways and, therefore, affect the photophysics and sensing mechanism of SWCNT‐based sensors. This approach was recently used to perturb the sensing and elucidate the rate constants that are involved [87] (Figure 6 d).…”

Biosensing with Fluorescent Carbon Nanotubes

“…In contrast, the correlation between the length of the SWCNTs and their fluorescent response seems to indicate that quenching at the ends plays a role. However, the fluorescence response was independent of the variation of defect density [87] . Together with the finding that a small number of quantum defects reverse the fluorescent response of DNA‐functionalized SWCNTs to dopamine (Figure 6 d), it follows that multiple rate constants are affected by the analyte [87] .…”

“…[87] Computationally, the experiments were best explained by athree rate constant model (3RC) that includes ad ecrease in the nonradiative decay from the E 11 state (k nr ), an increase in the exciton diffusion constant (D e ), and an increase in the nonradiative decay constant from the E 11 * (k nr * )c aused by dopamine. [87] Together,t hese insights highlight the complex interplay between photophysics and molecular recognition as well as new avenues to tailor sensing using defects. [63] with permission.C opyright2 016 American Chemical Society.…”

Detektion und Visualisierung der Pflanzen‐Pathogen‐Response durch Nah‐Infrarot‐fluoreszente Polyphenolsensoren

“…Am häufigsten werden Biopolymere wie einzelsträngige (ss)DNAander SWCNT-Oberfläche adsorbiert, was die kolloidale Stabilitäti nw ässriger Lçsung und die molekulare Erkennung des Analyten vermittelt. [35][36][37][38] Andere Design-und Sensorkonzepte basieren auf nicht-kovalenter Funktionalisierung mit Aptameren, [17,39] Phospholipiden, [40] Peptiden, [41,42] Proteinen [43] oder Peptid-DNA-Hybriden. [44,45] Kürzlich wurde auch die kovalente Modifikation fluoreszie-render SWCNTs mit (Bio-)Molekülen berichtet.…”