Ordered arrays of carbon nanotubes (CNT)\ud have been coated by Ni nanoparticles and Ni thin films\ud by using the chronoamperometry technique for nickel\ud reduction. Two different kinds of nanotube arrays have\ud been used: aligned bundles of CNT grown on Si\ud substrates by chemical vapour deposition (CVD) and\ud networks of CNT bundles positioned via a dielectrophoretic\ud post-synthesis process between the\ud electrodes of a multifinger device. The morphology\ud and structure of the Ni-coated CNT bundles have been\ud characterized by field emission scanning electron\ud microscopy (FE-SEM) and X-ray diffraction (XRD).\ud By changing the parameters of the electrochemical\ud process, it is possible to modulate the morphological\ud characteristics of the Ni deposits, which can be\ud obtained in form of nanoparticles uniformly distributed\ud along the whole length of the CNT bundles or of\ud Ni thin films. A qualitative study of the nucleation and\ud growth mechanism of Ni onto CNT has been performed\ud using the theoretical model for diffusioncontrolled\ud electrocrystallization, and a correlation\ud between growth mechanism and samples morphology\ud is presented and discussed. The possibility to maintain\ud the architecture of the pristine nanotube deposits\ud after the Ni coating process opens new perspectives\ud for integration of CNT/Ni systems in magnetic and\ud spintronics devices

Raman spectroscopy is a powerful optical technique based on the inelastic scattering of incident light to assess the chemical composition of a sample, including biological ones. Medical diagnostic applications of Raman spectroscopy are constantly increasing to provide biochemical and structural information on several specimens, being not affected by water interference, and potentially avoiding the constraint of additional labelling procedures. New strategies have been recently developed to overcome some Raman limitations related, for instance, to the need to deal with an adequate quantity of the sample to perform a reliable analysis. In this regard, the use of metallic nanoparticles, the optimization of fiber optic probes, and other approaches can actually enhance the signal intensity compared to spontaneous Raman scattering. Moreover, to further increase the potential of this investigation technique, aptamers can be considered as a valuable means, being synthetic, short, single, or double-stranded oligonucleotides (RNAs or DNAs) that fold up into unique 3D structures to specifically bind to selected molecules, even at very low concentrations, and thus allowing an early diagnosis of a possible disease. Due to the paramount relevance of the topic, this review focuses on the main Raman spectroscopy techniques combined with aptamer arrays in the label-free mode, providing an overview on different applications to support healthcare management.

Aptamers, synthetic single-stranded DNA or RNA molecules, can be regarded as a valuable improvement to develop novel ad hoc sensors to diagnose several clinical pathologies. Their intrinsic potential is related to the high specificity and sensitivity to the selected target biomarkers, being capable of detecting very low concentrations and thus allowing an early diagnosis of a possible disease. This kind of probe can be usefully integrated into a number of different devices in order to provide a reliable acquisition of the analyte and properly elaborate the related signal. The study presents the fabrication and characterization of a label-free aptamer sensor designed using a gold-coated silicon nanostructured substrate to map the target molecule by means of surface-enhanced Raman spectroscopy (SERS). As a proof, thrombin was used as a model at four different concentrations (i.e., 0.0873, 0.873, 8.73, and 87.3 nM). SERS mapping analysis was carried out considering each representative band of the aptamer-thrombin complex (centered at 822, 1140, and 1558 cm−1) and then combining them in order to acquire a comprehensive and unambiguous measure of the target. In both cases, a valuable correlation was evaluated, even if the first approach can suffer from some limitations in the third band related to lower definition of the characteristic peak compared to those in the other two bands.

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