Applications of FTIR spectroscopy in the biological field

Recent progress of chemometrics and FTIR spectroscopy enabled researchers to explore the feasibility of the technique to acquire insight information about proteins. Protein molecules are complex by nature, hence current techniques are used to study these molecules from every corner. It is essential to have a highly resolved 3D protein structure to recognize these molecules’ mechanisms of action. Additionally, several drugs are protein active site-based designs, hence, fully resolved structures became immensely important for rational drug design approaches. FTIR spectroscopy has also been applied to investigate several therapeutic proteins [114].

Currently, X-ray diffraction is the technique of choice to study crystallizable proteins. Obtaining a highly resolved 3D structure of proteins by this powerful method has inherently few drawbacks. Preparing a well-diffracting crystal of proteins can be time-consuming and challenging [115]. Furthermore, the technique will be inadequate for solutions of proteins. Their preparation will surely be concomitant with severe denaturing. Furthermore, the protein will tend to aggregate at higher concentrations. This will ultimately be reflected in the resolution of structures obtained [116]. Several cases and techniques demonstrated that the surfaces encountered throughout the protein isolation process have a great effect on protein performance, an effect that is still requires more investigated research studies [117].

One more limitation of the current analytical protein imaging techniques considering X-ray is that the images obtained are in a static mode. It is well-established that proteins are dynamic catalysts that change their conformations constantly. These techniques will be blind-sided to such dynamics, while protein conformations are essential for its function.

FTIR spectroscopic techniques have gained attention due to its non-invasive and fast nature to explore proteins and several other biological materials [118] including DNA [119], carbohydrates, and lipids [120]. It is also applied to explore biological tissues [121,122,123], cells [124], or whole organisms [125,126]. Additionally, the technique accompanied by chemometric data analysis was employed to monitor drug target binding processes [127].

Due to the inherent limitations of current analytical techniques to obtain highly resolved quaternary structures of proteins as mentioned above, the FTIR spectroscopy provided an appealing alternative. A successful story that might demonstrate the attractiveness of FTIR spectroscopy when it provides an economic, affordable alternative has been published recently [128]. In this work, Devlin et al. have provided manufacturers and regulators with a high-quality analysis approach of crude heparin. In early 2008, the world witnessed a heparin crisis. Baxter produces half of the world supply of heparin. A contaminated lot initiated a cascade of unexplained side effects associated with heparin therapy that resulted in about 350 adverse events and more than 150 deaths in the US alone. Several other countries suffered similar occurrences that generated international attention. The FDA in collaboration with pharmaceutical industry laboratories and an international consortium immediately launched a mission to identify the responsible contaminants. The analytical tests used to identify the toxin and detect any differences between the suspected and reference heparin samples included optical rotation, capillary electrophoresis, and 1D ¹H-NMR [129]. Only then, over sulfated chondroitin sulfate was recognized as the contaminant responsible for the crisis [130].

In a recently published article [71], the authors, Khan and Rehman, argued that viral and bacterial proteins or even antibody proteins created as a response of the immune system can be efficiently detected by various vibrational spectroscopic techniques. The global fight against the SARS-CoV-2 (COVID-19) pandemic has been greatly hindered by the lack of reliable, rapid, and economic detection and monitoring testing protocols. The current standard testing of the virus is based on polymerase chain reaction principles. The test relies on the viral DNA amplification followed by detection. However, although the test is highly sensitive, it is time-consuming, and requires tedious sample preparation and lengthy procedures. The bacterial and viral infection detection based on various spectroscopic techniques and in particular IR has never been so crucial. The development of rapid and cost-effective, real-time monitoring capabilities, rigorous, and sensitive diagnostic techniques will tremendously strengthen the global fight against highly contagious merciless COVID-19. The authors emphasized that an IR or Raman spectroscopy-based methodology will not only have the potential of rapid diagnostic capabilities but also viral monitoring and drug designing. The monitoring process will reveal viral infection pathways. Consequently, a collective understanding of viral invasion can be determined and understood.

2 Drug efficiency monitoring

FTIR spectroscopy approach of enabling biomedical scientists to track biological processes and drug efficiency within samples has never been so accessible. Additionally, the technique can detect such processes on a molecular level [131].

It might be insightful to demonstrate this perspective by the work of Sundaramoorthi et al. [132]. The authors provided an interesting methodology to monitor the efficacy of metformin hydrochloride while treating type-2 diabetic patients. They were able to use a single human hair fiber to compare results obtained for pre- and post-treatment with healthy population. Results showed that significant and statistically validated differences of associated diagnostic biomarkers were obtained based on FTIR measurements.