This book presents a method for replicating natural butterfly wing scales using a variety of metals for state-of-the-art applications requiring high surface-enhancement properties. During the past decade, three dimensional (3D) sub-micrometer structures have attracted considerable attention for optical applications. These 3D subwavelength metallic structures are, however, difficult to prepare. By contrast, the 3D superstructures of butterfly wing scales, with more than 175 000 morphologies, are efficiently engineered by nature. Natural butterfly wing scales feature 3D sub-micrometer structures that are superior to many human designs in terms of structural complexity, reproducibility, and cost. Such natural wealth offers a versatile chemical route via the replication of these structures into functional metals.
A single versatile chemical route can be used to produce butterfly scales in seven different metals. These synthesized structures have the potential for catalytic (Au, Pt, Pd), thermal (Ag, Au, Cu), electrical (Au, Cu, Ag), magnetic (Co, Ni), and optical (Au, Ag, Cu) applications. Plasmon-active Au, Cu, Ag butterfly scales have exhibited excellent properties in surface-enhanced Raman scattering (SERS). The Au scales as SERS substrates have ten times the analyte detection sensitivity and are one-tenth the cost of their human-designed commercial counterparts (KlariteTM). Preliminary mechanisms of these surface-enhancement phenomena are also reviewed.
Table of Contents
Preface.- Background.- Sub-micrometer functional structures, a promising and challenging topic.- Superstructures in nature.- Replication of natural structures in functional materials.- Metallic replicas of natural species.- Summary.- Towards metallic butterfly wing scales.- Unsuccessful methods.- High-temperature route.- Low-temperature route.- Versatile replication of butterfly structures in metals.- Design of fabrication route.- Morphologies of as-synthesized replicas.- Mechanisms of the synthesis process.- Summary.- Au butterfly wing scales as high-quality SERS substrates.- SERS properties of Au butterfly scales.- Mechanisms of the enormous enhancement of Raman signals on Au scales.- Simulation of the hotspots in Au scales.- Experimental proof of the mechanism.- Summary.- Au butterfly wing scales as high-quality MEF substrates.- Bio-diagnostics on Au scales.- Bio-imaging on Au scales.- Cell-culture on Au scales.- Bio-Imaging of HeLa cells on Au scales.- Summary.- Conclusions.- Postscript.- Acknowledgements.- References.