Characterization Techniques for Nanomaterials: A Spectroscopic Overview

What is spectroscopy:

Spectroscopy is a technique in which we use different electromagnetic radiations in order to characterize the nanomaterials. The internal structure, surface topology the associated functional groups can be determined through this technique. We get a spectrum that has peaks and that peaks indicate the specific nanomaterial at specific wavelength of light.

There are following spectroscopic techniques used for the characterization of the nanomaterials;

UV- Vis spectroscopy:

It is technique that has been widely used for both characterization and quantification of the nanomaterials.

This technique is used to characterize almost all types of nanomaterials like organic, inorganic and biological. We take nanomaterial suspension in cuvett that containing one opaque and other transparent side , radiations range from UV to Visible fall to the nanomaterials and amount of radiation is absorbed can be recorded in the computer system, and shows results in the form of graph, absorbed light is directly proportional to the concentration of nanomaterials. The highest peak shows the maximum absorbance called lambda max.

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Fourier transformed infrared spectroscopy:

In this spectroscopy, we use infrared radiations to hit the nanoparticles. Nanoparticles are in suspension form, and in this way graph is generated that shows the absorbance and wavelength absorbed by the nanoparticle. The data that is in the form of peaks is converted into the different functional groups that are attached to the interfacial layer of the nanoparticles.

Attenuated total reflectance- FTIR:

It is used to characterize the molecular conjugation on NPs for medicine development. In this type of use infrared radiation to analyse the nanoparticle.

[2].

Raman scattering spectroscopy:

It is used to determine the vibrations of the nanoparticles present in the matrix, so used to determine the size of that nanoparticle. In this technique we simply use monochromatic light that hit to the nanoparticles called Raman scattering i.e scattering of photons or light. [3]

X ray absorption spectroscopy:

It is used to analyse the structure of the nanoparticles like to reveal the distortions in the lattice of the nanoparticles. We use electromagnetic radiations that fall in the range of X rays to determine internal structures of nanoparticles. [4]

Pulse field gradient Nuclear magnetic resonance spectroscopy:

The nanoparticles are in aqueous solution, the spectrometer contains its own prob that is able to produce the magnetic fields when sample or nanoparticles whose size is to be determined is placed in the spectrometer, for example the size determination of PS latex nanoparticles in aqueous solution. [5].

Fluorescence correlation spectroscopy:

It is used to determine the cluster formation of nanoparticles in an optical trapping system. The nanoparticle suspension with fluorescent dye is prepared and 1064nm laser light beam is used for optical trapping and photon excitation. The fluorescence emitted from the nanoparticles is focused on a focal point and is detected by a photodiode. [6].

Dynamic light scattering spectroscopy:

In order to determine the size and stability of nanoparticles dynamic light scattering is being used. The nanoparticles suspension is hit by the laser beam, scattered light goes to detector and then signals go the computer system. The refractive index of nanoparticles and fluid is same. [7].

Auger electron spectroscopy:

This type is used to analyse the morphology or surface topology of the nanomaterials. The Auger scanning probe along with analyser is used. Small electron beam is used to excite the electrons of the inner atoms , so that exited atoms release electrons called Auger electrons. The kinetic energy of these electrons is measured that gives the information about surface of nanomaterial. [8]

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8. Rades, S.; Wirth, T.; Unger, W. Investigation of Silica Nanoparticles by Auger Electron Spectroscopy (AES): Characterization of Nanoparticles by Auger Electron Spectroscopy. Surf. Interface Anal. 2014, 46 (10–11), 952–956. https://doi.org/10.1002/sia.5378.