Nanoanalysis is an area of analytical chemistry associated with the development of principles and methods of applying nanotechnology and nanomaterials. Nanoanalysis is used for two distinct types of studies, namely, (a) morphological characters and (b) elemental composition of nano-based samples.
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Nondestructive testing (NDT) is involved with analyzing or testing samples without destroying their application or system. In other words, after the investigation of a given sample, it should be able to be used totally or partially. This ensures no wastage of samples while testing.
Nondestructive Testing Techniques in Nanoanalysis
Some of the common nondestructive testing tools used for nanoanalysis are scanning electron microscopy (SEM) coupled with energy dispersive x-ray microanalysis (EDX), Raman spectroscopy, Fourier-transform infrared (FTIR), X-ray fluorescence spectrometry (XRF), piezoquartz crystal microbalances (QCMs), Eddy current, and acoustic emission method.
Inductively coupled plasma-mass spectrometry (ICP-MS) is known as a minimally destructive process. These tools help elucidate the shape, size, and chemical composition of a given nanostructure. Some of the main NDT techniques associated with nanoanalysis are discussed below:
SEM with EDX
SEM with EDX is mostly used for the analysis of the surface of the sample. High-resolution images of the surface topography are produced using a highly focussed beam of electrons that are scanned through the surface with the energy of about 0.5–30 kV, resulting in the generation of many low-energy secondary electrons.
The intensity of the secondary electrons is associated with providing surface topography of the nano-objects.
The combination of SEM with EDX is a powerful analytical tool for morphological as well as chemical characterization of bulk or individual nanoparticles in various materials.
Although SEM-EDX is regarded as an NDT technique for surface analysis, a minute quantity of the sample is removed for analysis.
One of the limitations of this technique is that it can analyze only solid samples. Additionally, SEM-EDX can only characterize the inorganic content of the hybrid nano samples.
Piezoquartz Crystal Microbalances (QCMs)
This technique is popularly used to estimate the synthesis reproducibility of electroplated deposits.
QMS can precisely measure (with nanogram precision) the weight of the particles deposited based on their frequency shift. This nanoanalytical method is used to determine the adsorption phenomenon of nanoparticles, proteins, or polymer films, in various kinds of solid surfaces in both static and dynamic mode.
QCM can also analyze adsorption kinetics in situ.
One of the limitations of this method is that it does not provide any analytical information, i.e., chemical profile or composition of the nanohybrid.
A high-resolution ICP-MS is an NDT technique that can validate inorganic components of nanohybrid.
Besides the conventional ICP-MS technique, single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) has become a powerful NDT technique that is used for screening, detection, and characterization of hybrid nanoparticles in the solutions.
This nanoanalytical tool offers information about the elemental composition, size, size distribution, and particle number concentration with minimal sample perturbation.
The laser ablation coupled ICP-MS (LA-ICP-MS) is a nondestructive analytical technique that can perform ultra-highly sensitive chemical analysis down to parts per billion (ppb) level. In this process laser beam is targeted on a sample surface to remove particular material from the irradiated zone.
Subsequently, the ablated particles are transferred to the secondary excitation source of the ICP-MS instrument, and ultimately, it detects the elemental and isotopic nature of the sample.
LA-ICP-MS technique has been used for the characterization of various nano-objects.
Raman and FTIR Spectroscopy
Both the analytical tools offer in situ analysis of organic components of the nanohybrids without any additional sample preparation step. Scientists use FTIR spectroscopy to study the surface chemistry of hybrid nanostructures.
It also offers molecular fingerprints of the sample's organic layer (e.g., polymer membrane and enzyme layer).
Similarly, Raman spectroscopy is used to identify and quantify chemical species. They are also used for chain orientation analysis of hybrid nanomaterials, determination of crystal size, stress, and defects, in a nondestructive manner.
One of the limitations of this technique is that it fails to detect minor changes in the architecture of the nanostructure and chemical composition at a ppb level of nanohybrids.
X-ray Fluorescence (XRF)
Although this NDT technique has many variations, all of them share a common principle, i.e., low-energy photons are used to excite atoms in a sample via ionization.
Other charged particles, such as protons and helium, (CPAA), neutrons (NAA), and photons (PAA), are also used in this analytical tool.
Once the atoms are excited, they release a characteristic set of photons to come back to the ground state and these photons are detected.
The low energy stimulation of CPAA and NAA allows a low penetration into the sample, because of which this technique has been regarded as an important NDT tool for nanoanalysis.
PAA has a better penetration depth, and is, therefore, used for bulk analysis of large and small samples. XRF has been recently used to investigate nano-bio interface, which is extremely useful to improve nanoparticle-based drug delivery.
Acoustic Emission (AE)
Acoustic Emission involves the generation of mechanical vibrations by the defects encountered in the material, e.g., fiber breakage and matrix micro-cracking.
AE is predominantly used to detect imperfections in composite materials or structures. High-frequency AE is used for monitoring nanomechanical tests that include detection of nanoscratch, nanoindentation, micro-pillar compression, and nano-impact. This information is extremely important for improving material behavior at the nanoscale level.
Eddy Current Testing
This NDT technique utilizes an electric coil through which a magnetic field is created, and in the case of a conductive sample, a circular electric current is generated.
Nanoparticles have many unique properties that include magnetic and electric properties. This circular current is used to identify surface damage, cracks, and difference in the sample composition.
One of the main advantages of this technique is its superior sensitivity, compared to the acoustic method, to detect small surface cracks or other defects located below the surface layer.
Continue reading: Non-destructive Testing for Nanopackaging
References and Future Reading
Sanchez-Cano, C. et al. (2021) X-ray-Based Techniques to Study the Nano–Bio Interface. ACS Nano. 15( 3). pp. 3754–3807. Available at: https://doi.org/10.1021/acsnano.0c09563
Gupta, R. et al. (2021) A Review of Sensing Technologies for Nondestructive Evaluation of Structural Composite Materials. Journal of Composites Science. 5, 319. Available at: https://doi.org/10.3390/jcs5120319
Semenova, D. and Silina, Y.E. (2019) The Role of Nanoanalytics in the Development of Organic-Inorganic Nanohybrids—Seeing Nanomaterials as They Are. Nanomaterials. 9(12). pp. 1673. https://doi.org/10.3390/nano9121673
Tyler, C and Well, P.D. (2017) What does nondestructive analysis mean? Cogent Chemistry. 3(1). Available at: https://doi.org/10.1080/23312009.2017.1405767
Rinkevich,B.A. et al. (2010) Prospects of the Application of Nondestructive Testing to the Diagnostics of Nano- and Microstructural Materials. Russian Journal of NonDestructive testing. 46(1). pp. 10-15. Available at:https://dx.doi.org/10.1134/S1061830910010031
Rahman, Z. et al. (2010) Nondestructive methods of characterization of risperidone solid lipid nanoparticles. European Journal of Pharmaceutics Biopharmaceutics. 76(1). pp. 127-37. https://linkinghub.elsevier.com/retrieve/pii/S0939641110001396