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W. Qiu and X.-Y. Liu
6.4 Characterization Technologies
As discussed in Sect. 6.3, an accurate and quantitative method for the characterization of the secondary and tertiary structure content within SF materials is of utmost
importance. In addition, to provide comprehensive insight into the morphology and
architecture of the nanofibrils as well as the nanofibril network, advanced imaging
techniques are also in demand. So far, substantial effort has been devoted to the
development of corresponding techniques, and several structural characterization
and imaging methods have been developed. For instance, structural characterization methods include FTIR spectroscopy [47, 48], Raman spectroscopy [49, 50],
circular dichroism (CD) [51], and XRD spectroscopy [33] In addition, AFM force
spectra have also emerged as powerful tools [18, 52] for studying the nanostructures within SF materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and AFM are the most popular imaging techniques. In
this section, we provide a brief introduction to the principles and operation of the
aforementioned methods; specifically, several typical examples are also presented.
6.4.1 Structural Characterization Techniques
6.4.1.1 Overview of Structural Characterization Techniques
As introduced in Sect. 6.3, the total β-conformation can be classified into intramolecular β-sheets (β-crystallites) and intermolecular β-sheets, respectively. Given the
essential role of both β-crystallites and β-sheets, precise measurements of their
contents are of the utmost importance. In general, FTIR, Raman, and CD spectroscopy are used to quantify the total secondary structure content, while XRD is the
most commonly applied technique for analyzing the level 3 structure of SF materials [8, 53]. Moreover, polarized Raman spectroscopy is also capable of providing
information on the molecular orientation of SF materials. Wide-angle X-ray scattering (WAXS), on the other hand, was applied to calculate the β-crystallite size,
crystal density, and crystal orientation. SAXS is powerful for measuring the distance
between adjacent β-crystallites in both the horizontal and vertical directions.
6.4.1.2 Fourier Transform Infrared Spectrometer (FTIR)
Owing to its simplicity and practical usage, FTIR is the earliest and one of the most
widely applied methods for studying the secondary structures of proteins. FTIR spectroscopy can be used to obtain information from the infrared spectrum of molecular
vibrations and rotational information. Its principle is that when the bonds between
the atoms in protein polypeptides (e.g., C=O bonds and C–N bonds) stretch and
W. Qiu and X.-Y. Liu
6.4 Characterization Technologies
As discussed in Sect. 6.3, an accurate and quantitative method for the characterization of the secondary and tertiary structure content within SF materials is of utmost
importance. In addition, to provide comprehensive insight into the morphology and
architecture of the nanofibrils as well as the nanofibril network, advanced imaging
techniques are also in demand. So far, substantial effort has been devoted to the
development of corresponding techniques, and several structural characterization
and imaging methods have been developed. For instance, structural characterization methods include FTIR spectroscopy [47, 48], Raman spectroscopy [49, 50],
circular dichroism (CD) [51], and XRD spectroscopy [33] In addition, AFM force
spectra have also emerged as powerful tools [18, 52] for studying the nanostructures within SF materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and AFM are the most popular imaging techniques. In
this section, we provide a brief introduction to the principles and operation of the
aforementioned methods; specifically, several typical examples are also presented.
6.4.1 Structural Characterization Techniques
6.4.1.1 Overview of Structural Characterization Techniques
As introduced in Sect. 6.3, the total β-conformation can be classified into intramolecular β-sheets (β-crystallites) and intermolecular β-sheets, respectively. Given the
essential role of both β-crystallites and β-sheets, precise measurements of their
contents are of the utmost importance. In general, FTIR, Raman, and CD spectroscopy are used to quantify the total secondary structure content, while XRD is the
most commonly applied technique for analyzing the level 3 structure of SF materials [8, 53]. Moreover, polarized Raman spectroscopy is also capable of providing
information on the molecular orientation of SF materials. Wide-angle X-ray scattering (WAXS), on the other hand, was applied to calculate the β-crystallite size,
crystal density, and crystal orientation. SAXS is powerful for measuring the distance
between adjacent β-crystallites in both the horizontal and vertical directions.
6.4.1.2 Fourier Transform Infrared Spectrometer (FTIR)
Owing to its simplicity and practical usage, FTIR is the earliest and one of the most
widely applied methods for studying the secondary structures of proteins. FTIR spectroscopy can be used to obtain information from the infrared spectrum of molecular
vibrations and rotational information. Its principle is that when the bonds between
the atoms in protein polypeptides (e.g., C=O bonds and C–N bonds) stretch and