Polycarbonate microchannel network with carpet of Gold NanoWires as SERS-active device

Abstract

A polycarbonate (PC) microchannel network supporting gold nanowires was developed to be a SERSactive microchip. Observations of large increases in a Raman cross-section, allowed us to collect vibrational signatures which are not easily detectable by Raman techniques due to the high fluorescence level of bare PC. Compared to other SERS experiments, this study relies on the use of dielectric polymer/metal surfaces which are well defined at microscale and nanoscale levels. This device seems a promising tool for sensing the adsorption of biomolecules.In the last few years, polymer microchips have become highly desirable for on-site detection in areas such as life science, environment, food, and medicine. Until now, optical techniques were privileged due to their sensitivity and their non-destructive character. In this context, Surface-Enhanced Raman Scattering (SERS) is one of the most sensitive techniques for single molecule detection with regard to its molecular selectivity and specificity. 1 With the same objective, Surface-Enhanced Hyper-Raman Scattering (SEHRS) was recently performed for applications of vibrational spectroscopy in biology. 2 There is an abundant literature regarding SERS active substrates of silver or gold thin films (see for example ref. 3, 4). Among the various methods used for structuring surfaces, nanolithography 5 and colloid adsorption 6-8 appear as the main two ones. Molecules adsorbed onto these nanostructured surfaces have shown an increase in enhancement factors of the order of 1 Â 10 6 to 1 Â 10 12 in terms of SERS efficiency. Following the latest published work on SERS nanoparticle tags, several groups have reached 1 Â 10 15 in terms of efficiency using, as an example, a polymer encapsulation layer. 9 In another field, metallization of polymer materials remains crucial in materials science engineering, especially for data storage of information. 10 For example, an excimer laser in a photoablation procedure can be used to enhance adhesive properties of polymer-supported thin metallic films, 11 and permits to obtain micrometre resolved cavities on thin metallic/ polymer films. Owing to the fact that recent breakthroughs 6,12,13 were obtained in the synthesis and architecturing of nanomaterials, it would be interesting to integrate these materials into polymer microchannels.A preliminary surface-enhanced Raman scattering investigation for a polymer microchip containing gold nanowires arrays is presented here. As illustrated in Fig. 1A, in order to integrate the nanowires into a microchannel, we synthesized gold nanowires using the electrocrystallization method into a track etched polycarbonate (30 mm thick) with an appropriate pore size and film thickness. Once this template filled, two layers of polyethyleneterephthalate (35 mm thick) were thermally laminated on both sides of PC (see PET1 and PET2 in Fig. 1A). The PET/PC gold nanowire/PET system was exposed to an ArF excimer laser beam in order to create a deep cavity reaching the polycarbonate surface. The polycarbonate was partially...

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