3D Superlocalization Microscopy Monitoring of the Formation and Activity of Individual Nanoparticle Superlattices

Axe Nanochimie

Travail de recherche commencé le 1er nov. 2017

Laboratoires co-porteurs
Keywords

Superlocalization microscopy, Self-assembly, Superlattice, Plasmonic nanoparticles. 

Projet de recherche

The assembly of nanoparticles (NPs) into periodically ordered superlattices (SLs) yields a new class of materials with properties determined both by individual nano-building blocks and collective interactions.1, 2 A major objective of this project is to develop new synthetic strategies of plasmonic NPs (silver and gold) and to follow , in situ, the process of their self-assembly into 3D SLs. The physico-chemical properties of these individual SLs are going to be monitored. This will be achieved through the in situ monitoring by superlocalization optical microscopy coupled to electrochemical activation of the SLs.3

In MONARIS laboratory, we are more concerned about the organometallic synthesis of gold and silver NPs in organic media and the control of their crystallinity to obtain ordered supercrystals and to achieve the highest plasmonic properties.4 Since the in situ optical monitoring performed at the ITODYS laboratory (back side absorbing layer microscopy, BALM) 5 requires a medium whose refractive index is not to close to that of glass (n = 1.52) water (n=1.33) is preferred to organic solvents (n = 1.46). It is then important to transfer and to stabilize these NPs in aqueous media also to control their size to be larger than 10nm which is the resolution limit of BALM and also to insure good electrical contact between the NPs and the Au layer that allows their observation by BALM. 

In this work, 10nm AuNPs were fabricated through a 2 steps approach involving a first synthesis of 5nm Au seeds followed by a seed mediated growth step to reach the 10nm size. A crystallinity segregation process was also used to separate the single crystal from polycrystal Au seeds in order to obtain single crystal and polycrystal 10nm AuNPs respectively and to compare their plasmonic properties. As expected, AuNPs showed enhanced absorption at the plasmon band region (520 nm) in case of single-domain crystalline NPs as compared to polycrystalline NPs. Despite AuNPs are very interesting to be observed by optics to track the formation of SLs , they showed some limitations for the electrochemical activation experiments. This is mainly because of the similarity in the redox potential between the AuNPs and the Au plated working electrode. For that reason, AgNPs represent a good candidate. A new synthetic approach was set to synthesize 14nm AgNPs through the reduction of AgNO3 with oleylamine (OLA) as the reducing agent. OLA plays also the role of solvent as well as ligand. AgNPs were then transferred into water through the exchange of the intial ligand with trimethyl(11-mercaptoundecyl)ammonium chloride (TMA). Very recently, we were able to monitor the electrochemical dissolution and reformation of SLs using the BALM microscope and to record the corresponding cyclic voltammograms and correlate both electrical and optical responses.

Such monitoring approach appears to be very promising technique in understanding many processes in which both optical and electrochemical properties are combined. An interesting perspective is Ag/Pt bimetallic NPs due to potential unique electronic, optical, catalytic or photocatalytic properties. The next step of this work is thus to synthesize Ag/Pt bimetallic NPs, either through chemical reduction or galvanic replacement reaction starting from AgNPs and to test them as possible optically or electrochemically activated catalysts using BALM microscope.

References
  1. Talapin, D. V.; Murray, C. B. Science 2005, 310, 86.
  2. ourty, A. J. Phys. Chem. C 2010, 114, 3719.
  3. Aubertin, P.; Ben Aissa, M. A.; Raouafi, N.; Joiret, S.; Courty, A.; Maisonhaute, E. Nano Res. 2015, 8, 1615.
  4. Chapus, L.; Aubertin P.; Joiret S.; Lucas I. T.; Maisonhaute E.; Courty A. Chem. Phys. Chem. 2017, 18, 3066.
  5. Ortega-Arroyo, J.; Kurkura, P. Phys. Chem. Chem. Phys. 2012, 14, 15626.