Self-assembled monolayers properly hyperlink the historical past and the way forward for nanoscience and nanotechnology.
The Kavli Prize in nanoscience, awarded this yr to Jacob Sagiv, Ralph Nuzzo, David Allara and George Whitesides for his or her work on self-assembled monolayer (SAM)1, represents a second to have fun the pioneers of our discipline. It’s enjoyable to look again on the motivations and imaginative and prescient of the scientists which have made nanoscience the thriving discipline that it’s now and the way their ground-breaking discoveries took place. So, with the caveat that for 4 folks being prized, there’s a military of different researchers which have contributed, this editorial is a mini journal membership, wherein we now have re-read the primary papers on SAMs by Sagiv, Nuzzo, Allara and Whitesides.
To the modern reader, essentially the most placing characteristic of these early papers on SAMs is maybe the ingenuity by which scientists within the early 80s had been in a position to make inferences to the nanoscale world. Far sooner or later lies the invention of the atomic drive microscopy for the correct dedication of the thickness of a monolayer. In his paper displaying that n-octadecyltrichlorosilane (OTS) can chemisorb onto SiO2 surfaces upon hydrolysis of the Si–Cl bonds to Si–OH, Sagiv cross-checked the estimated thickness of the monolayer obtained by conductivity measurements utilizing a fluorescent donor–acceptor system co-chemisorbed with OTS2. The donor is straight adsorbed on the floor whereas the acceptor is at a distance of the identical size of the OTS molecule. By measuring the fluorescence quenching of the donor, aptly benchmarked to a recognized Cd-based fluorophore, he might estimate the gap of the acceptor and subsequently the thickness of the monolayer. It’s like measuring time with no stopwatch!
It was already fairly clear from the start that SAMs might be used to switch the properties of surfaces extra successfully and controllably than by utilizing polymer coating. The truth that molecules are oriented in an ordered and largely predictable method was a strong software to design oleophilic or hydrophilic surfaces; the standard of which was quantified by contact angle measurements3,4. Orientation of the SAM might be ascertained by dichroic absorption, observing that linearly polarized gentle incoming from a sure angle could be absorbed extra strongly, as a result of it aligns with the electrical dipole of the adsorbed molecule.
Vibrational spectroscopy allowed Nuzzo and Allara to grasp that the alkyl chain of their natural disulfide compounds is totally prolonged in a zig-zag conformation out of the Au floor and that the carbonyl group of the polar ester endgroup lies as an alternative extra flat with respect to the Au floor4.
Whitesides’s early papers on SAMs at all times emphasize the simplicity of the expertise for floor patterning. Their preliminary do-it-yourself setup displays this philosophy, as they make intelligent use of a Staedtler pen full of hexadecanethiol ink fastened on a micrometre xy stage to attract SAM traces5,6,7. The very fact they demonstrated that it was doable to realize options of ~100 nm, smaller than what was then doable by photolithography, allowed different labs and particularly chemistry labs unfamiliar to working in clear room situations, to experiment with SAMs “for functions akin to speedy prototyping of microelectrode arrays and different comparatively easy buildings”5. Whitesides went on to manufacture natural digital units with them8.
Whereas the preliminary motivation behind the event of SAMs was to enhance the Blodgett–Langmuir movie fabrication with a method that might be extra versatile and fewer error inclined, with time, a bio-inspired imaginative and prescient of those monolayers additionally turned clear.
It’s in all probability the foundational Evaluate article ‘Self-Assembled Monolayers of Thiolates on Metals as a Type of Nanotechnology’ of 2005 authored amongst others by each Nuzzo and Whitesides9 that, ranging from the lesson learnt from SAMs, set forth a imaginative and prescient that also has profound implications in nanoscience until today: citing, “SAMs exhibit that molecular-scale design, synthesis, and group can generate macroscopic supplies properties and features.” This basic idea that self-assembly processes bridge management over size scales, from nano to macro, has its basis and inspiration in organic buildings and it’s central in lots of modern traces of analysis in nanoscience.
Throughout an interview on the event of the Kavli prize week, held initially of September in Oslo, Norway, Sagiv, Nuzzo and Whitesides talked about their work on SAMs. The interview is accessible on YouTube (https://www.youtube.com/watch?v=8jtTRraZg6M). Many nanoscientists would straight relate to the joy that also exudes from their phrases and, strikingly, to the interdisciplinary character of the analysis that has sprouted off the event of SAMs. Particularly, it’s an actual pleasure to be taught that whereas Sagiv was attracted by the prospect of manipulating molecules one after the other — a paradigm shift from resolution chemistry taught at school — Nuzzo associated himself to bio-inspired methods and methods wherein SAMs can be utilized to work together with organic surfaces for biomedical functions; Whitesides expressed optimism in regards to the chance that SAMs can provide in useful resource poor settings as low-cost expertise for power and sensing functions.
It goes to say that SAMs are a type of foundational and ubiquitous nanoscience ideas that might resurface at any time in any subfield in numerous guises. That’s the reason it is vital for these enchanted by all issues small to familiarize themselves with the properties of those molecules that manage themselves in monolayers.
