Fourier transform infrared spectroscopy to assess molecular-level changes in microorganisms exposed to nanoparticles

Fourier transform infrared (FTIR) is a spectroscopy method that can identify variations in the total composition of microorganisms through the determination of changes in functional groups in biomolecules. FTIR measures the vibration and rotation of molecules influenced by infrared radiation at a specific wavelength. This technique allows the identification of structural changes in the molecular binding between microorganisms and metal atoms, which can provide information about the nature of their interactions. In this review article, we will describe the state of the art in current uses of FTIR for the elucidation of bacteria–nanoparticle interactions. We will describe advantages for the application of FTIR in the field of nanotoxicology, including higher signal-to-noise ratio, high energy throughput, as well as high accuracy and stability which are applicable to solid phase samples but not recommended for assays in the liquid phase. Limitations such as multiple background scans and post-processing analysis are not deniable. Comparison of FTIR with other commonly used tools such as Raman spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy is also discussed. Finally, we present an application of FTIR for the assessment of bacterial changes in response to the exposure to silver nanoparticles (AgNPs). The results showed that the AgNPs-induced structural changes in the peptide and amino acids region may lead to alterations of conformation and/or composition of Amid B and Amid III. These results showed that bacteria developed resistance toward AgNPs and resulted in changes in the genotype and expression in the phenotype. Here, ATR–FTIR provided the evidence of the AgNPs cytotoxicity-induced intracellular level alterations in bacteria.