Sustained-release of nutrients by yeast extract-loaded halloysite nanotubes supports bacterial growth

Halloysite nanotubes (Hal) have been researched as carriers of various active compounds and polymer additives. Hal reinforced the polymers, while a designated trigger mechanism initiates the release of active compounds. Encapsulation of microbiological agents has been attempted to develop biological self-healing concrete, soil treatment, and environmental remediation, among others. Considering the lack of attention devoted to studying the encapsulation of the nutrients required for biological action and their release, this report presents the preparation and characterization of Hal loaded with the common microbiological nutrient yeast extract (YE) as a multifunctional nanocomposite carrier of microbiological nutrients. YE was loaded on the outer surface and inside the lumen of the Hal by using vacuum entrapment to prepare the YE-loaded Hal (HY) nanocomposites. Thermogravimetric analysis and UV–visible absorbance were used to quantify the loading and the release of YE from HY nanocomposites, showing increasing YE loading after the vacuum treatment and with higher Hal: YE ratios. Vacuumed 1:3 HY samples presented the best sustained-release profile. Field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM-EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction analysis (XRD) showed blocked lumens, and successful lumen loading of YE particles after the vacuum treatment and Hal-YE attachment by weak electrostatic bonding. Inter-particle YE-YE interactions were also evident. The YE loading procedure did not impact the interlayer space of Hal and lowered the crystallinity of the nanotubes. The HY nanocomposite effectively supported spore germination and bacterial growth, resulting in higher bacterial concentrations than conventional media after the expected bacterial death phase. The composition of the HY nanocomposite is easily adjustable, and the unloaded YE can be reused.