Nanowire-Based Sensor Platform for Breath Analysis

Nanomaterials, such as nanowires (NWs), are enabling new directions in nanotechnology with significant applications in the biomedical sector. With the use of Surface-Enhanced Raman Spectroscopy (SERS) as an analytical technique for rapid biomarker identification, nanomaterials can play a pivotal role in shaping the next generation of non-invasive, rapid, and pain-free diagnostic devices. Potential applications include breath analysis for cancer screening.<br/>SERS is an ultrasensitive vibrational spectroscopic technique used as a tool to detect volatile organic compounds (VOCs) near the surface of plasmonic metal nanoparticles with sharp features (‘hot spots’). Conventional bottom-up approaches for sensing applications are based on the self-assembly of nanoparticles, which offers a simplistic, quick, and low-cost SERS substrate preparation. However, this approach demonstrates low reproducibility, hampering the sensor’s performance. Top-down approaches use micro- and nanofabrication techniques with better uniformity and reproducibility, but with higher manufacturing costs.<br/>We present a hybrid approach using NWs as the backbone of the SERS sensor – decorated with nanoparticles (NPs) – acting as 3D ‘hot-spot’ network for maximizing the available SERS-active surface of the device while achieving signal reliability and reproducibility.<br/>We employed this new architecture for SERS-based gas sensing. The NWs are derived from fast and cost-effective solution processing, and form higher-order structures via dielectrophoresis (DEP)-based self-assembly. DEP offers unique features, including NW alignment on predefined locations, preferential orientation, and most importantly, controllable deposition and NW densities for precise ‘hot-spot’ distribution. The self-assembly technique will be discussed and compared to conventional SERS-sensor approaches. Our solution-based technique for the rapid gold (Au) nanoparticle decoration of the 1D titanium oxide (TiO₂) NWs will be described. This novel architecture further increases the overall ‘hot-spot’ availability, and combines strong SERS signal amplification with increased sample capture, allowing the detection of analytes at low concentrations.<br/>The performance of the developed sensor was assessed by investigating the SERS signal of 4-aminothiophenol (4-ATP) in gas phase, at concentrations as low as 10 parts-per-billion (ppbv), and in liquid phase down to 24 picomolar (pM). Additionally, the SERS signals successfully separated - using the principal components analysis (PCA) – samples of exhaled breath from healthy volunteers. These findings demonstrate the applicability and potential of 1D nanomaterials in conjunction with state-of-the-art solution-processed techniques for the development of breath analysis platforms for cancer screening.<br/>The developed non-invasive NW-based breath sensor platform can provide mobile, low-cost, miniaturized, and rapid breath analysis, making it suitable for clinical deployment. The sensor is suitable for real-time point-of-care (PoC) diagnosis and can significantly improve the understanding of the complex relationship between the exhaled VOC profile and disease, and lead the way to a new clinical breath-based diagnostic tests.