Abstract
The development of techniques that could be useful in fields other than biological warfare agents countermeasures such as medical diagnostics, industrial microbiology, and environmental applications have become a very important subject of research. Raman spectroscopy can be used in near field or at long distances from the sample to obtain fingerprinting information of chemical composition of microorganisms. In this research, biochemical components of the cell wall and endospores of Bacillus thuringiensis (Bt) were identified by surface‐enhanced Raman scattering (SERS) spectroscopy using silver (Ag) nanoparticles (NPs) reduced by hydroxylamine and borohydride capped with sodium citrate. Activation of “hot spots”, aggregation and surface charge modification of the NPs, was studied and optimized to obtain signal enhancements from Bt by SERS. Slight aggregation of the NPs as well as surface charge modification to a more acidic ambient was induced using small‐size borohydride‐reduced NPs in the form of metallic suspensions aimed at increasing the Ag NP‐Bt interactions. Hydroxylamine‐reduced NPs required slight aggregation and no pH modifications in order to obtain high spectral quality results in bringing out SERS signatures of Bt.
Highlights
Bioterrorism’s high potential for destruction has become a subject of great concern
The results presented demonstrate that surface-enhanced Raman scattering (SERS) spectra obtained with Ag-NPs reduced by hydroxylamine and borohydride capped by citrate and were successfully used to spectroscopically characterize Bacillus thuringiensis (Bt)
Of large biological samples compared to the small size of the nanoparticles, because the electrostatic interactions that dominates the interaction of the NPs and bacterial content can occur around all the biological sample and not on one side as is the case of the Raman vibrational enhancement produced by solid metallic surfaces
Summary
Bioterrorism’s high potential for destruction has become a subject of great concern. Fast, efficient, and inexpensive detection techniques for microorganisms have become a very important subject in areas of national defense and homeland security. The bacterial endospores contain several well-known layers, from internal to external location Among these are the cortex, the core wall, the spore coat, and the exosporium. Biological samples as virus [8], pollen [9], essential components of bacterial cell wall, and bacterial endospores have been studied by SERS effect using Ag or Au metallic colloids to optimize procedures for detection, identification, and classification. Ag-borohydride NPs were modified by changing the pH of the colloid to obtain a more intimate interaction with the bacterial cell wall in which at low and high pH values (3.25 and 9.74) did not result in improved detection of Escherichia coli [13, 14]. Improved SERS signals at pH of 5 and higher were obtained for Bacillus Gram-positive species with citrate reduced nanoparticles [15] and for biological molecules with amine groups using hydroxylamine hydrochloride-reduced NPs [16]. Since no specific studies addressing these important issues of Bt using these sensing platforms were found, it was decided to study them
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