How to Characterize Gold Nanoparticles’ Surface?

Guest post by Elena Colangelo

Our Topical Review on the characterization of gold nanoparticles (GNPs) has just been published in the Bionconjugate Chemistry Special Issue “Interfacing Inorganic Nanoparticles with Biology”.

The literature is abounding in works on GNPs for applications in biology, catalysis and sensing, among others. GNPs’ appeal resides in their optical properties, together with the well-developed methods of synthesis available and the possibility of functionalizing their surface with small molecules of interest, which can readily self-assemble on the GNPs’ surface forming a monolayer.

However, allegedly the structure and organization of self-assembled monolayers (SAMs) at the GNPs’ surface are in fact aspects too often neglected [though surely not on this blog; RL]. Such elucidation is challenging experimentally, but it is crucial not only to ensure reproducibility, but also to design nanosystems with defined (bio)physicochemical and structural properties, which could then be envisioned to assemble in more complex systems from a “bottom-up” approach.

Our Topical Review gives an overview of the current knowledge and methods available to characterize the GNPs’ surface with different molecular details.


Cartoon illustrating the different levels of GNPs’ surface characterization discussed in the Topical Review.

First, the experimental methods commonly used to provide the basic characterization of functionalized GNPs, such as identification and quantification of the ligands within the monolayer, are detailed with the aid of some examples.

Second, the experimental methods providing information on the monolayer thickness and compactness are reviewed.

Third, considering that the SAM’s thickness and compactness do not only depend on the amount of ligands within the monolayer, but also on their conformation, the experimental methods that can provide such insights are recapitulated. However, we also stressed on the limitations intrinsic to these methods and on the challenges associated to the determination of the structure of SAMs on GNPs.

Fourth, we summarized some of the approaches used to give insights into the organization of different ligands within a SAM. Indeed, mixed SAMs on GNPs are useful since they can impart to the nanoparticles different functionalities and offer a way to tune their stability.

Fifth, highlighting again the limited insights into the SAM’s structure and organization that can be gathered with experimental techniques, we detailed some examples where a combination of experimental and computational approaches was able to provide a compelling description of the system and to assess molecular details that could not have been revealed experimentally.

Overall, this Topical Review gives emphasis on the importance of GNPs’ surface characterization and on fact that even though a number of experimental techniques are available, they are intrinsically limited and they cannot provide a fully detailed picture. Hence, it is advantageous to combine experimental and theoretical approaches to design nanoparticles with desired (bio)physicochemical properties [such as, e.g., our paper under review, currently available as a preprint; RL].


Elena at the MRS

I am catching up after an holiday break. I have not spoken yet with Elena who was at the MRS spring conference in San Francisco, but, thanks to blogging, I can tell she seemed to have had a good experience.

Fellow blogger Mary Nora Dickson enjoyed Elena’s first oral presentation at an international conference:

peptide SAMs on gold NPs

Elena Colangelo spoke today in GG about her work on whether the curvature of gold NPs will affect the conformation of adsorbed proteins. This is an important topic, with wide ranging applications from drug delivery to energy. She found that more highly curved NPs inhibit hydrogen bonding, decreasing the amount of beta sheet secondary structures. This work will help to inform future investigations seeking to modify nanoparticles with functional ligands. Thanks!

Thank you Mary for the report and congratulations to Elena 😉

Elena attended some great talks:

Carlo Montemagno’s talk

What an inspiring talk!

On the last slide of his talk, Michelangelo’s quote: The greatest danger for most of us is not that our aim is too high and we miss it, but that it is too low and we reach it

He gave an overview of the cutting-edge projects (in the general areas of environment, health and energy) going on in his lab, IngenuityLab.

The project that fascinated me the most is the 4D Printer, where the fourth dimension is intended to be the functionality of the complex system built up by single molecules. The general concept is the precise assemble of the functional building blocks found in nature to give new functionalities to the system, where these functionalities are meant to address issues regarding energy, environment and human health.

It may sound too futuristic, but would you ever have imagined having your smartphone, as it looks like today, 10 years ago?

Neelkanth Bardhan’s talk

I had the pleasure to listen to Neelkanth Bardhan’s talk, Gold MRS graduate student awardee, at Symposium GG.

First, I want to say that I found his presentation very clear and easy to follow, nice layout of the slides.

He first went through the motivation of his work: there is the clinical need of safer (compared to X-rays) and less expensive (compared to MRI) detection technologies. He then presented his work aiming to answer this need: developing a biologically-templated nanomolecular probe for high-resolution in vivo sensing and detection. His modular probe is constituted of M13 virus coating single-walled carbon nanotubes (SWNTs). To this construct desired fluorescent dyes and specific targeting ligands can be attached. His results in vivo have shown how this probe is able to target tumours and can be used during real-time surgical intervention.

More details on his work and successful applications of this probe can be found here.

Elena to present at the MRS spring meeting in San Francisco

Just in case the last post made you think it is only the boss who travels… Elena Colangelo, who is spending two years of her PhD project in Singapore, will be giving a selected talk at the MRS Spring meeting in San Francisco, symposium GG: Foundations of Bio/Nano Interfaces─Synthesis, Modeling, Design Principles and Applications.

She will be speaking on Friday 10th of April. The title of her talk is: Characterizing the Organization and Investigating the Conformation of Peptide Self-Assembled Monolayers on Gold Nanoparticles: An Experimental and Computational Approach. The abstract can be found on the program page.

Not only, as the Rapha-z-lab rule demands will she write here about her meeting experience (she has done this beautifully before), the talks will apparently be recorded so you will be able to watch it through MRS OnDemand shortly after the conference!

April in Singapore – First Month, First Impressions

I am PhD student in Raphaël’s group, now in Singapore, where I will spend two years of my PhD working at the Institute of Materials Research and Engineering (IMRE).

In a couple of days it will be a month since I moved here. On my farewell night out in Liverpool, Raphaël asked me if I was going to write a post for his blog once in Singapore, I thought, why not! The idea of a blog post from Singapore then became a monthly blog from Singapore and I am now writing about my April in Singapore.

The first thing I want to talk about is quite obvious: the food. The food is great and inexpensive. According to The Economist, Singapore is the most expensive city in the world, but I am sure they haven’t considered the food prices when they came to this conclusion (they might have considered the cheese prices though 😉 ). Here there are food courts, which are food centers with stalls selling food ranging from pig’s organ soups to the five different types of Chinese noodles, from Indian fish head curry served with paratha to Singaporean chicken rice and Japanese tempura. The food courts can be fancy ones when inside air-conditioned shopping malls or open-air with more traditional dishes. And when I said that the food is inexpensive I meant that with £2 you can eat a proper dish! I am then not surprised that people here do not use to cook!
The Institute where I am working is inside the National University of Singapore campus and so far I have been in three different canteens that are basically food courts inside different departments (almost as it is in Liverpool 😉 ).
Also, the first time I went to the supermarket I was surprised to see all the products that Singapore imports from Europe; I found many Italian and French brands that I have never found in Liverpool. Huge modern shopping malls are everywhere with quite impressive lists of restaurant/fast food chains inside. I have also found the French bakery Paul and it brought back nice memories of when I used to live in Paris.
On one hand I find Singapore deeply Westernized, the number of shopping malls is something unbelievable (and somehow scary) and in each of them  there are the same fast food chains and more or less the same shops, but on the other hand I think that the culture of  food here is great and different from any other place! The food traditions of the different ethnic groups who migrated and live here (Singapore is 74% Chinese, 13% Malay, 9% Indian, and 3% Eurasian) have resisted the westernization of the country and made the Singaporean food very unique; I would even say that Singaporean cuisine is the coexistence of other Asian countries cuisines over 710 km²!

The Parkroyal Hotel Garden in Singapore. I found it very suggestive with gardens and plants merged in the glass and steel.