TiO2 nanoparticles as a soft X-ray molecular probe

Abstract

This communication reports the development of a TiO 2 -streptavidin nanoconjugate as a new biological label for X-ray bio-imaging applications; this new probe, used in conjunction with the nanogold probe, will make it possible to obtain quantitative, high-resolution information about the location of proteins using X-ray microscopy.Soft X-ray tomography generates 3D images of whole, hydrated cells at a resolution better than 50 nm. 1,2 High-contrast images of cellular structures are obtained because organic material absorbs roughly an order of magnitude more than water at this energy (517 eV). Minimal cell processing is required, as cells need only be frozen, and data collection is rapid (3-5 min per tomographic data set). X-Ray tomography is, therefore, an appealing imaging technique for those experiments that require better resolution than is possible with light microscopy. With light microscopy, fluorescent tags are routinely used to label molecules. For X-ray microscopy, we need probes that use the inherent X-ray properties and can specifically label proteins within the cellular environment. Since X-ray transmission is sensitive to absorbance and density differences in the specimen, as is transmission electron microscopy (TEM), probes used in TEM should also work for X-ray microscopy. Current approaches for localization used with TEM include labeling with Au nanoparticles or photooxidation of diaminobenzidene (DAB). Similar approaches have proven viable for soft X-ray microscopy, as demonstrated by the use of gold nanoparticles conjugated to antibodies to localize proteins in whole cells. 3Co-localization studies with light microscopy are routinely done using probes that fluoresce at two different wavelengths. For similar studies with X-ray microscopy, we need two tags that can be unambiguously identified, which means the probes need to have different absorption properties, such as an X-ray edge absorption. The dense DAB reaction product and the Au nanoparticles are directly visible in the soft X-ray microscope. However, the contrast mechanism of both probes is based on absorption density of the matter. No X-ray † Electronic supplementary information (ESI) edge absorption is available for either of them within the range of the operation energy. Therefore, indistinguishable X-ray absorption properties of these probes negate the possibility to utilize them in double labeling experiments with soft X-ray microscopy. With the rapidly expanding field of nanoscience in biology, especially the successful application of semiconductor nanocrystals in biological imaging, 4-7 additional nanoparticular materials that exhibit strong absorption in the soft X-ray spectrum are being developed. One promising candidate is TiO 2 . TiO 2 nanoparticles have been widely used in other industries due to their photocatalytic activity and UV light absorption properties. 8 They are also highly biocompatible. A recent study demonstrated the use of a TiO 2 -oligonucleotide nanocomposite as a unique light inducible nucleic acid e...

Imaging endosomes and autophagosomes in whole mammalian cells using correlative cryo-fluorescence and cryo-soft X-ray microscopy (cryo-CLXM)

“…As expected, heavy metals in the form of gold nanoparticles were easily detected by their density, as previously reported for silver nanoparticles [30,48] and titanium dioxide nanoparticles [49]. Pre-loading of cells with an anti-TfnR-gold enabled unambiguous identification of early and recycling endosomes.…”

PEGylation of Nanosubstrates (Titania) with Multifunctional Reagents: At the Crossroads between Nanoparticles and Nanocomposites

“…11 An additional advantage of TiO 2 is its radio-opacity, and titania nanoparticles can potentially be used as labels for X-ray bioimaging applications. 7 In an earlier work, we successfully developed a nonaqueous synthesis of ligand-free ("naked") anatase nanoparticles. 17 The nonaqueous process allows for good control of crystal growth also in the absence of surfactants, yielding highly crystalline particles covered by hydrophobic titanium alkoxide surface groups.…”

Functional nanoparticles in cells

“…Having gained these expertises, nowadays the research interest is shifted in making nanoparticles in demand for specific applications. [9][10][11][12][13][14] The aim of this work was to synthesize nanomaterials that can interact with HUVECs. HUVECs were chosen because they participate in key biological functions in the body assembling the walls of blood veins and being part of the blood brain barrier (BBB) that separates the brain extracellular fluid from the circulating blood.…”