Near‐Infrared Fluorescent Sensors based on Single‐Walled Carbon Nanotubes for Life Sciences Applications

Abstract

Many properties of single-walled carbon nanotubes (SWCNTs) make them ideal candidates for sensors, particularly for biological systems. Both their fluorescence in the near-infrared range of 820-1600 nm, where absorption by biological tissues is often minimal, and their inherent photostability are desirable attributes for the design of in vitro and in vivo sensors. The mechanisms by which a target molecule can selectively alter the fluorescent emission include primarily changes in emission wavelength (i.e., solvatochromism) and intensity, including effects such as charge-transfer transition bleaching and exciton quenching. The central challenge lies in engineering the nanotube interface to be selective for the analyte of interest. In this work, we review the recent development in this area over the past few years, and describe the design rules that we have developed for detecting various analytes, ranging from stable small molecules and reactive oxygen species (ROS) or reactive nitrogen species (RNS) to macromolecules. Applications to in vivo sensor measurements using these sensors are also described. In addition, the emerging field of SWCNT-based single-molecule detection using band gap fluorescence and the recent efforts to accurately quantify and utilize this unique class of stochastic sensors are also described in this article.

A Ratiometric Sensor Using Single Chirality Near‐Infrared Fluorescent Carbon Nanotubes: Application to In Vivo Monitoring

“…There is relatively little change in ( ) 6,5 norm I t in the leaf tissues after exposure to H 2 O 2, which is consistent with the in vitro characterization of our H 2 O 2 ratiometric sensor. Likewise, when our leaf sections were in the presence of NO, we observed a gradual increase of R 7,6 ( t ) for 7,6 ss(GT) 15 SWCNT (Figure 7 b), as expected from our in vitro experiments. Our internal reference for the NO ratio sensor, 6,5 norm …”

“…In the presence of H 2 O 2 , we observe a gradual increase of R 7,6 ( t ) for 7,6 ss(GT) 15 SWCNT (Figure 6 b), as expected from our in vitro experiments. There is relatively little change in ( ) 6,5 norm I t in the leaf tissues after exposure to H 2 O 2, which is consistent with the in vitro characterization of our H 2 O 2 ratiometric sensor.…”

“…The R ( t ) values increase monotonically from t = 0 to t = 600 s. The linear behavior of the H 2 O 2 ratiometric sensor beyond t = 20 s can be attributed to the fact that the binding sites of SWCNT are still unsaturated at the relatively low peroxide concentrations utilized, which implies that the H 2 O 2 binding probabilities are unchanging. The intensity ratios of ( ) 6,5 norm I t at 1004 nm to that of ( ) 7,6 norm I t at 1135 nm as a function of time for a response to NO are similarly shown in Figure 4 b. The R ( t ) values increased with time from t = 0 to t = 600 s. The transient response in Figure 4 is diffusion limited, as the measurements were conducted in unstirred wells of a 96 well-plate.…”

“…and, Figure 4 a shows the dependence of the intensity ratios of absorbance for ( ) 6,5 norm I t at 984 nm to that of ( ) 7,6 norm I t at 1131 nm as a function of time for a response to H 2 O 2 . The R ( t ) values increase monotonically from t = 0 to t = 600 s. The linear behavior of the H 2 O 2 ratiometric sensor beyond t = 20 s can be attributed to the fact that the binding sites of SWCNT are still unsaturated at the relatively low peroxide concentrations utilized, which implies that the H 2 O 2 binding probabilities are unchanging.…”

“…[ 3,4 ] In particular, optical nanosensors have enabled the detection of analytes with high spatio-temporal [ 5,6 ] Semiconducting SWCNT are excellent signal transducers for nanosensors due to their fl uorescence stability, lifetime, and emission in the near-infrared (NIR). [ 7 ] Consequently, there has been much interest in developing nanosensors by noncovalent complexation of various wrappings with SWCNT, such that the SWCNT corona can recognize an analyte. [ 8 ] However, one challenge in using chemically responsive fl uorescent probes is obtaining an absolute signal such that probe intensity can be used to calculate local presence of an analyte.…”