The gecko is a “nano-ace” in the natural world. A research conducted by scientists has revealed that it is a talented wall walker by virtue of the large contact area produced by high-density nanoscale tentacles on its toe-pads. Each and every tentacle has hundreds of thinner branches at its end. These soft nanostructures can adjust their angle in any direction to fully contact with the wall, which greatly increases the contact area between soles and the wall, thus generating strong adhesion.
Enlightened by this interesting discovery, the research team led by Prof. Han Heyou produced a gecko toe-like Surface Enhanced Raman Spectroscopy (SERS) substrate. Compared with traditional ones, this adult-nail-size substrate owns hundreds of millions of soft nano “tentacles” similar to those of geckos. When used in the multicomponent detection of pesticide residues on the surface of fruits and vegetables, these “tentacles” could greatly increase the contact area between the substrate and the sample, and create strong molecular attraction, contributing to a non-destructive, direct and rapid detection.
The team replicated the morphology of superhydrophobic-treated anodic aluminum oxide (AAO) with polydimethylsiloxane (PDMS) and then acquired the 3D nano “tentacles” in arrays, decorated with AgNPs through seed deposition. These dense “tentacles” could reach the tiny areas of samples as freely as geckos. By means of simple sampling methods such as “brush” and “paste-lift”, trace samples on the complicated surface were directly collected in a localized and non-destructive way, eliminating the cumbersome process of sample pretreatment and greatly shortening analysis time .
Moreover, substantial Raman signal "hot spots" can be produced among the AgNPs, which magnifies the Raman scattering effect (SERS intensity) on the sample surface by 12 million times, greatly improving the detection sensitivity. In experiments, magic materials have been used to effectively test, with the detection limit of 1.6 ng/cm², pesticide residues including methyl parathion, arasan and malachite green on the surfaces of apples, grapes and cucumbers. Even a billionth gram pesticide residue on the surface of an adult nail-size fruit or vegetable could be rapidly detected.
Recent days witnessed the research result published in Analytical Chemistry, an internationally prestigious journal in analytical chemistry. The title of the paper is Gecko-Inspired Nanotentacle Surface-Enhanced Raman Spectroscopy Substrate for Sampling and Reliable Detection of Pesticide Residues in Fruits and Vegetables, with Wang Pan and Wu Long as first authors and Prof. Han as the corresponding author. It’s part of the fruits that combine bionics and nanotechnology and shake off the fetters of traditional substrates preparation, after the “cicada wings-inspired SERS for detection of H5N1 and other animal viruses”. Hierarchical nanogaps within bioscaffold arrays as a high-performance SERS substrate for animal virus biosensing, was published in ACS applied materials & interfaces in 2014 as the cover paper.
The researches were funded by the National Natural Science Foundation of China, the National Key R&D Plan and the State Key Laboratory of Agricultural Microbiology.
Paper Link:http://pubs.acs.org/doi/abs/10.1021/acs.analchem.6b04324
http://news.hzau.edu.cn/2017/0323/48635.shtml
（By Pan Nan）
