Lithographically-produced plasmonic structures, while offering exceptional control of light through light-matter interactions, have seen limited implementation into sensing technologies. This has been due to several factors, such as large ohmic losses and high cost of fabrication. The use of self-assembled superclusters of chemically-synthesized metallic nanoparticles has been proposed as means of overcoming some of these limitations, by exploiting their collective modes. In this work, the existence of such modes is successfully verified by 3D Raman tomography. Proof-ofprinciple experiments are also conducted to demonstrate the potential of superclusters in sensing schemes.
Assembly of nanoscale building blocks into hierarchical superstructure by self-assembly is one of the most pursued topics in nanoparticles chemistry. The possibilities obtainable when individual components arrange themselves into an ordered structure are limitless and of great interest. Spherical colloidal clusters have been proposed to possess remarkable collective supermodes with large local field enhancements, and a spectral response extending from the near-infrared to deep into the mid-infrared region. As such, these superstructures hold great promise as a sensing platform that is capable of addressing the whole spectral domain of vibrational molecular fingerprints, while simultaneously exploiting the advantages of their plasmonic constituents , .
By exploiting these properties of the self-assembled metamaterials supercluster, we report the experimental measurement of near and mid- IR plasmonic collective modes by monitoring the Raman scattering of 4-Mercaptobenzoic acid with a confocal microscope. The strongly enhanced Raman signal allows measurement of the plasmonic mode with a lateral resolution lower than 300 nm and a vertical one of 300 nm. As the supercluster structure possesses tunable optical modes, different plasmonic responses are mapped according to the cluster size and the excitation wavelength.
Moreover, as SERS allows sensitive detection of molecules, the remarkable and tunable modes excitable inside the spherical colloidal clusters can provide an efficient platform for ultra-sensitive molecular spectroscopy. To this end proof-of-principle implementation of the superclusters as an efficient platform for pH sensing of the surrounding medium is reported .
 V. A. Turek, L. N. Elliott, A. I. I. Tyler, A. Demetriadou, J. Paget, M. P. Cecchini, A. R. Kucernak, A. A. Kornyshev, and J. B. Edel, “Self-assembly and applications of ultraconcentrated nanoparticle solutions,” ACS Nano, vol. 7, no. 10, pp. 8753–8759, 2013.
 A. Lauri, L. Velleman, X. Xiao, E. Cortes, J. B. Edel, V. Giannini, A. Rakovich, and S. A. Maier, “3D Confocal Raman Tomography to Probe Field Enhancements inside Supercluster Metamaterials,” ACS Photonics, vol. 8, no. 4, p. pp 2070-2077, 2017.
Atomic layer deposition (ALD) of SiO<sub>2</sub> onto nanoporous alumina (PA) membranes was investigated with the aim of
adjusting the pore size and transport properties. PA membranes from commercial sources with a range of pore diameters
(20 nm, 100 nm and 200 nm) were used and modified by atomic layer deposition using tris(tert-butoxy)silanol and water
as the precursor couple. By adjusting the number of deposition cycles, the thickness of the conformal silica coating was
controlled, reducing the effective pore diameter, and subsequently changing the transport properties of the PA
membrane. Silica coated PA membranes with desired pore diameters from <5 nm to 100 nm were fabricated. In addition
to the pore size, the transport properties and selectivity of fabricated silica coated PA membranes were controlled by
chemical functionalisation using a silane with hydrophobic properties. Structural and chemical properties of modified
membranes were studied by dynamic secondary ion mass spectrometry (DSIMS) and scanning electron microscopy
(SEM). Spectrophotometric methods were used to evaluate the transport properties and selectivity of silica coated
membranes by permeation studies of hydrophobic and hydrophilic organic molecules. The resultant silica/PA
membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture,
bioreactors, biosensing and drug delivery.