Applied NanoFluorescence

Scientific Background

Near-infrared band-gap fluorescence from individual semiconducting single-walled carbon nanotubes (SWCNT) was discovered in Dr. Weisman's laboratory at Rice University in 2001. Subsequent research deciphered the complex pattern of absorption and emission peaks seen in mixed samples. As a result, each distinct spectroscopic feature has now been assigned to a specific nanotube structure. These structural species differ in diameter and chiral angle, and are uniquely labeled by pairs of integers denoted (n,m).

NS2 schematic 062711

The near-infrared emission spectra of nanotube samples serve as compositional "fingerprints." One can therefore use spectrofluorimetry to deduce detailed information about the compositions of bulk samples, which invariably contain mixtures of (n,m) species. However, general-purpose spectrofluorometers are not well suited to this task. Although such instruments are versatile, they are also large, slow, and produce raw data that require substantial interpretation to yield the desired analytical result. To provide a more efficient and automated alternative, ANF has developed a specialized fluorimetric instrument designed specifically for SWNT analysis. Our unique fluorimetric analyzer combines a compact, efficient optical system and sophisticated software that acquires and interprets the data. It allows users to easily and rapidly find the identities and amounts of specific (n,m) semiconducting nanotubes in their bulk samples.

 

NS1, NS2, & NS3 NanoSpectralyzer Technical Specifications


Fluorescence excitation laser λ 532, 638, 671 and 785 nm
Fluorescence geometry High numerical aperture epifluorescence
Fluorescence spectral range 900-1600 nm
Near-IR detector type 512 element TE-cooled InGaAs array
Raman* excitation laser λ 532 or 671 nm (choose when ordering)
Raman spectral range 150 to 2900 cm-1 shift
Raman spectral resolution 4 cm-1
Raman detector type 3648 pixel TE-cooled Si CCD
Absorption light source Stabilized tungsten-halogen lamp
Absorption spectral range 400-1600 nm
Absorption spectral resolution 4 nm (NIR), 1 nm (vis)
Absorption ceiling 3 AU (NIR and vis)
Visible detector type 2048 pixel Si CCD
Absorbance noise (rms), near-IR <2 x 10-4 at 0 AU for 10 s integration
Absorbance noise (rms), visible <5 x 10-4 at 0 AU for 10 s integration
Minimum sample volume 120 μL (or 50 μL with alternative cell)
Data acquisition time (typical) 2 minutes for full set of spectra
Power consumption 75 W (excluding computer)
Main optical module dimensions     12.3" W x 18.3" D x 7.7" H (310 x 465 x 195 mm)
System weight 48 lbs/22 kg (excluding computer)

*Raman available with NS2 & NS3 only


 

SWCNT Spectroscopy

Most SWCNTs can emit spectrally narrow near-IR fluorescence at wavelengths that are characteristic of their precise diameter and chiral angle. Near-IR fluorimetry therefore offers a powerful approach for identifying the structural species present in SWCNT samples. Such characterization is increasingly important for nanotube production, study, separation, and applications. Fluorescence methods are highly effective for detecting SWCNTs in challenging samples such as complex environmental or biological specimens because of the methods’ high sensitivity and selectivity and the near absence of interfering background emission at near-IR wavelengths.

Nanotube Metrology

Current SWCNT production techniques yield polydisperse samples containing many different types SWCNTs, defined by differing chiralities and lengths. Thus it is important to develop methods to produce well-characterized fractions of carbon nanotubes with controlled parameters (length, diameter, chiral angle, charge, concentration and purity), so that vendors and buyers can trade SWCNT with confidence. These methods can be collectively categorized as Nanotube Metrology. Characterization of nanotubes is critical in order to advance applications and to enable well-controlled environmental, health and safety (EHS) assessments.

National Institute of Standards and Technology (NIST) leads an ongoing collaboration among various industrial, academic and government researchers to develop such methods, and to define reference standards. These efforts were recently highlighted at a NIST-sponsored workshop. NIST also has published a Recommended Practice Guide which launched the extensive ISO activities in SWCNTs. Prof. Weisman, through his activities at Rice University and ANF, continues to make valuable contributions to this effort.