Biocompatible Nanomembranes Based on PEGylation of Cross-Linked Self-Assembled Monolayers

Abstract

We present the fabrication of freestanding, biocompatible, and ultrathin membranes on the basis of selfassembled monolayers (SAMs) of 4′-nitro-1,1′-biphenol-4thiol (NBPT) on an Au(111) support. In the first step, NBPT SAMs were extensively cross-linked by exposure to low-energy electrons, resulting in a mechanically and thermally stable monolayer. Simultaneously, the terminal nitro groups of the NBPT molecules were converted to reactive amine moieties to which, in the second step, epoxy-functionalized poly(ethylene glycols) (PEG) were coupled. As far as the thickness of the coupled PEG overlayer exceeded ∼3 nm, as monitored by ellipsometry and X-ray photoelectron spectroscopy, the resulting assembly became protein-resistant, without losing this property after separation from the substrate as a freestanding membrane (third step). The use of such membranes as supports in transmission electron microscopy studies may improve essentially the resolution and structural reliability of such experiments in their specific application to sensitive biological targets. Whereas the ultimate thinness (<5 nm) and low atomic number character of the SAM-based membranes guarantee high imaging quality, their protein-repelling properties ensure the lack of protein denaturing.

Ultraflexible, Freestanding Nanomembranes Based on Poly(ethylene glycol)

“…The intensity profile across the image as well as the respective Fourier transform (inset in Figure c) correspond to the expected, hexagonal Au(111) structure of the AuNP with an interatomic distance of 282 pm close to the literature value of 288 pm . As another example, the iron core of the iron storage protein, ferritin could be imaged in a good quality (Figure d), similar to the images presented in the literature for distinctly thinner membranes . This quality can be further improved by the use of the thinner PEG membranes.…”

“…Freestanding, ultrathin membranes are an important class of low‐dimensional objects combining nanoscopic and macroscopic dimensions in a single entity . This makes them an excellent candidate for a variety of applications ranging from highly sensitive optical and mechanical sensor elements to supporting films for high‐resolution transmission electron microscopy (HRTEM) experiments . In the latter case it is of advantage to have membranes as thin as possible to achieve optimal imaging contrast.…”

“…The thinness alone is however not sufficient in certain cases. Particularly for biologically sensitive molecules such as proteins, it is desirable to have a hydrophilic and antifouling support to avoid denaturing . This requires the use of biorepulsive materials like poly(ethylene glycol) (PEG) for the membrane fabrication .…”

“…However, to the best of our knowledge, no ultrathin membranes consisting purely of PEG has been prepared so far. Only PEG‐terminated nanosheets based on crosslinked aromatic self‐assembled monolayers were reported, which however consisted only partly of PEG and required ultrahigh vacuum techniques for their fabrication …”

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

“…87 Simultaneously, the terminal nitro groups of the NBPT molecules were converted to reactive amine moieties to which epoxy functionalized PEG chains were subsequently coupled. As a result, these films exhibited protein repelling properties, which in turn ensure the lack of protein denaturation when they are used as a support in transmission electron microscopy studies.…”