Yongwen Tan

Versatile Fabrication of Intact Three‐Dimensional Metallic Butterfly Wing Scales with Hierarchical Sub‐micrometer Structures

properties, which can be modulated by their intrinsicmicrostructures. Such structures, however, are quite difficultto prepare by traditional methods. One promising route tocreate these metallic structures is direct replication fromhierarchical structures of various natural species. Metals havebeen physically deposited onto biological structures tofabricate metallic structures through physical vapor deposi-tion (PVD).

Morphological Effects on Surface-Enhanced Raman Scattering from Silver Butterfly Wing Scales Synthesized via Photoreduction

Through a simple room-temperature photoreduction process, this letter conformally replicates 3D submicrometer structures of wing scales from two butterfly species into Ag to generate practical surface-enhanced Raman scattering (SERS) substrates. The Ag replicas of butterfly scales with higher structural periodicity are able to detect rhodamine 6G at a low concentration down to 10(-9) M, which is three orders of magnitude lower than the detectable concentration limit of using quasi-periodic Ag butterfly structures. This result presents a way to select suitable scale morphologies from 174,500 species of Lepidopterans to replicate, as consumable SERS substrates with low cost and high reproducibility.

Reduction of CuO Butterfly Wing Scales Generates Cu SERS Substrates for DNA Base Detection

We prepare three-dimensional Cu plasmonic structures via a reduction of CuO photonic crystals replicated from butterfly wing scales. These Cu superstructures with high purity provide surface-enhanced Raman scattering (SERS) substrates for the label-free detection of DNA bases down to a micromolar level, which is achieved for the first time on Cu and even comparable to the detection-sensitivity for DNA bases on some Ag substrates. The generation of such superstructures has provided a substantial step for the biotemplated SERS substrates with high sensitivity, high reproducibility, and ultra-low cost to detect biomolecules, and presented affordable high-quality routine SERS consumables for corresponding biolaboratories.

Metal‐Organic Frameworks Reactivate Deceased Diatoms to be Efficient CO2 Absorbents

Diatomite combined with certain metal-organic frameworks (MOFs) is shown to be an effective CO2 absorbent, although diatomite alone is regarded as inert with respect to CO2 absorption. This finding opens the prospect of reactivating millions of tons of diatomite for CO2 absorption. It also shows for the first time that diatom frustules can act as CO2 buffers, an important link in a successive biological CO2 concentration mechanism chain that impacts on global warming.

Toward Metallic Butterfly Wing Scales

Till now, natural biostructures have already been converted to a broad range of oxides. To prepare these replicas, metal ions were first coordinated on the surface of biological templates via an impregnation process. The hybrids were subsequently sintered in air under high temperatures to form desired oxides, with the original biological skeletons simultaneously removed.

Surface-Enhanced Raman Scattering (SERS) Performance of Metal Scale Replicas

Surface-enhanced Raman scattering (SERS) is one of the most important frontiers of nanostructured metals. Like IR spectroscopy, Raman spectroscopy is a basic and powerful tool to study molecular configurations. This technique can obtain similar but complementary information to IR spectroscopy, especially with the rapid development of laser technology. However, Raman spectrum is not easy to acquire as the Raman scattered beam is usually weak.

Metal Scale Replicas Prepared via Electroless Deposition

Direct deposition methods include physical vapor deposition (PVD), chemical vapor deposition (CVD), and electroplating or electroless plating, etc. PVD describes a variety of vacuum deposition methods used to deposit thin films onto a workpiece surface by the condensation of a vaporized material. These methods (e.g., magnetron sputtering and plasma bombardment) involve purely physical processes. In comparison, CVD is based on chemical reactions happening at the surface to be coated. However, the line-of-sight nature of both PVD and CVD prevents a complete replication of original 3D biomorphologies. This shading effect can be avoided by metal plating conducted in liquid environments. Electroplating uses electrical current to reduce dissolved metal cations and can form a coherent metal coating on a conductive substrate. However, since biotemplates are usually nonconductive, it is unsuitable to the replication of biostructures.

Surface-Enhanced Raman Scattering (SERS) Mechanisms of Metal Scale Replicas

As shown in Chap. 4, surface-enhanced Raman scattering (SERS) substrates with scale structure have unique advantages in terms of sensitivity, repeatability, and mass-producibility. However, the mechanism by which such performance is achieved should be clarified. This may help select appropriate biostructures from countless biological candidates for SERS application. In this chapter, we first discuss the SERS performance of differently textured metal scales, whose microstructures were regulated by changing the metal deposition time (DT). We then compare the contributions from different structural features and target the key contributor to SERS performance. Such a structure is then analyzed using a finite element method (FEM). The resulting mechanism will be checked by studying the SERS performance of Cu scales with different structures. All these results will illustrate a mechanism by which metal butterfly scale replicas can effectively enhance the Raman signals of analytes.