13 Combining non-magnetic and optically active materials with magnetic iron oxide helps overcome the limitations of MDSA and enables the formation of arrays of non-magnetic colloidal assemblies in the form of grating order that is suitable for optical applications and performance in terms of diffraction and wave dispersion. Also, the loss of materials from spin coating is a common demerit regarding this fabrication technique. 3,4 Although MDSA can non-intrusively organize magnetic nanoparticles (NPs) to form arrays of chains 5,6 suitable for applications in several fields such as photonics, 7–9 storage devices, 10 microfluidics, 11a,b and optical filters, 12 it is difficult to organize poorly magnetic-responsive (diamagnetic) materials such as gold NPs. The cost, complexity and scalability may improve by using a simple, rapid, and less complicated magnetically directed self-assembly (MDSA) technique. However, fabricating metal nanostructures with precise geometrical features requires time-consuming, complex, and expensive methods such as gold sputtering, electron beam lithography, and nanoimprint lithography. Metal nanostructures, such as gold gratings, have been found to be particularly useful in SEIRA, as the plasmon polariton resonance of gold gratings in the mid-IR region can be matched with molecular vibrational signals to enhance sensitivity. Surface-enhanced infrared absorption spectroscopy (SEIRA) is commonly used to improve sensitivity. 1,2 However, the sensitivity of IR spectroscopy is limited when detecting trace amounts of analytes, owing to the small cross-section of its molecular vibrational signals. For instance, its integration with microfluidics has enabled the detection of vascular endothelial growth factor (VEGF) for early disease diagnosis. 1 Introduction Infrared (IR) spectroscopy is a rapid, accurate, and robust method for the detection of molecules in a range of applications. This scalable and simple method can potentially generate low-cost patterns for antenna sensitisation. The fabricated chain-like ordered arrays have been shown to increase the local field to enhance the infrared absorption corresponding to the symmetric vibration of the –CH 2 (2918 cm −1) group present in PVA by ∼667% at a 45° grazing angle, as the chain thickness (CT) increased by 178%. Unlike the gold strips, the chain-like features in the iron oxide nanoparticle arrays were discontinuous. Techniques such as UV-visible absorption, scanning electron microscopy, and grazing-angle infrared spectroscopy were used to evaluate various parameters associated with the nanostructures. In this article, we present a simple one-step process for fabricating optically sensitive ordered arrays of a gold nanoparticle ferrofluid emulsion in polyvinyl alcohol (PVA) using a magnetic field-directed and spin-coating self-assembly (MDSCSA) process. The significant infrared absorption may serve as tuneable antenna sensitization to improve the sensor performance. Infrared absorption is enhanced by regular metallic patterns such as arrays of strips fabricated using a top-down approach such as nanolithography, although this technology is expensive and difficult. Colloidal gold island films exhibit similar enhancement however, the uneven geometrical characteristics of these films restrict the tunability of the vibrational enhancement. Molecular vibration signals were amplified by the gold strip gratings as a result of grating resonances and nearby electric field hotspots.
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