Metal colloids have revolutionized the field of plasmonics due to their morphology-dependent exciting optical properties but also, because they constitute building blocks of more rich and complex plasmonic architectures. These colloids can be assembled into ordered arrays whose engineered optical response can be tailored to specific applications. These supercrystals serve as the ideal platform in which study coupling of different plasmonic resonances sustained by the structure. Precise ordering of these colloids is a challenging task typically achieved using complex lithographic techniques. However, great efforts are being placed to develop colloidal assembly routes that yield high resolution while being inexpensive and producing large area films.
In this work, we employ an inexpensive and scalable template-assisted assembly technique capable of arranging 52 nm gold nanospheres into regular, periodic arrays of well-defined plasmonic clusters over areas as large as 8 mm2 with features as small as 300 nm. The resulting supercrystal films exhibit tunable optical properties from the visible to the NIR range. We used patterned elastomeric molds with lattice parameters ranging from 400 nm until 1700 nm. The resulting supercrystal films exhibited both strong near-field coupling and an optical response that can be tuned from the visible through the near-infrared (NIR) range. The hierarchical order present in the supercrystals enables the coupling of the different plasmonic resonances sustained by the architecture and enables us to produce films tailored to specific wavelengths.
Furthermore, we investigated the application of these superlattices as surface enhanced Raman spectroscopy substrates. We studied the correlation between the plasmon resonances sustained by the different geometrical assemblies and their performance as SERS substrates under 785 nm excitation of the Raman probe 4-acetamidothiophenol (4-AMTP). This laser line fits the first biological optical transparency window, thus providing enhanced light penetration in tissues, and is particularly interesting for biomolecular detection in complex media.
Cristiano Matricardi,1 Christoph Hanske,2 Juan Luis Garcia-Pomar,1 Judith Langer,2 Agustín Mihi1 and Luis M Liz-Marzan2,3
1Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
2CIC biomaGUNE and Ciber-BBN, Paseo de Miramón 182, 20014 Donostia –San Sebastián, Spain
3Ikerbasque, Basque Foundation for Science, 48013 Bilbao, Spain
Gold Nanoparticle Plasmonic Superlattices as Surface-Enhanced Raman Spectroscopy Substrates
ACS nano 12 (8), 8531-8539 (2018)
Scanning electron micrograph of a square superlattice made of 52 nm gold colloids. The inset corresponds to a photograph of the sample where the colours diffracted by the large supercrystal area of 1 x 1 cm2 can be appreciated.