Browsing by Subject "Explosive detection"

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    Design and Fabrication of Smart SERS Substrates for Forensic Science Applications
    (2023-08) Simas, Maria Vitoria; Sardar, Rajesh; Goodpaster, John; Manicke, Nicholas; Christoph, Naumann
    In the field of forensics and toxicology, it is crucial for analytical techniques to be practical, highly sensitive, and extremely accurate (specific and selective), especially when incorporating acquired data as evidence in a court case. To limit the breadth of this dissertation, the main forensic focuses are to assay (detection and quantification) drugs in patient biofluid specimens and to detect trace explosives. While currently there are a number of analytical tools such as LC/MS, GC/MS, ELISA immunoassays, and electrochemical and aptamer techniques utilized for these two applications, each one introduces its own unique drawback that hinders their accuracy, and therefore applicability, to be used in a legal environment. To overcome these disadvantages, surface enhanced Raman spectroscopy (SERS) has become increasingly popular in the forensic and toxicology field as it provides high sensitivity and specificity data while remaining flexible and efficient in critical situations such as an emergency department and/or an explosion site. In this dissertation, two different, novel SERS substrates are developed, each one designed to tackle a specific forensic application. While the fabrication method and materials of the substrates are significantly different from one another, both display ideal SERS properties due to their unique localized surface plasmon resonance (LSPR) properties at the nanoscale. LSPR is a phenomenon in which the free carriers (electrons or holes) on the surface of nanoparticles collectively oscillate upon light irradiation. In this current dissertation, we selectively focus on two different nanoparticle compositions where LSPR properties originate from the collective oscillation of free electrons. These oscillations of free carriers allow for an electromagnetic (EM) field enhancement of the incident laser which leads to an increase in the SERS enhancement. Particularly, the area in which the SERS signal is the most enhanced is the nanometer-sized gap between nanoparticles called “hot spots.” While primarily noble metal (e.g., Au and Ag) nanoparticles are heavily used for SERS substrate fabrication, this dissertation expands beyond that and focuses on both gold nanorods and oxygen deficient tungsten oxide (metal oxide semiconductor)-based SERS substrates. This dissertation is organized in three chapters, (1) Introduction, (2) Fabrication of a polymer microneedle-based, multimodal SERS and mass spectrometry substrate for the ultrasensitive detection of illicit drugs in human blood plasma, and (3) LSPR active WO3-x-based SERS substrate for the detection of explosives. In chapter 2, a multimodal substrate was strategically designed to serve as a SERS and electrospray ionization- mass spectrometry substrate by using a novel microneedle platform. The microneedles underwent a surface modification and gold nanorods were subsequently adsorbed onto the surface. Illicit drug analytes could then be drop-casted on the tip of the microneedles and left to dry for further SERS and mass spectrometry analysis. This novel platform detected two types of synthetic opioids, alprazolam and fentanyl, down to at least a picomolar limit of detection and successfully distinguished between the two when analyzing 10 patient blood plasma samples. Furthermore, the multimodal approach was confirmed through the detection of both drugs in patient plasma samples down to the ppb limit using mass spectrometry. Chapter 3 introduces an entirely new SERS substrate, which is fabricated using oxygen deficient tungsten oxide (WO3-x) nanoparticles for the detection of the target explosives, e.g., tetryl, TNT, and DNT. The oxygen deficiency in WO3-x nanoparticle lattice introduces free electrons in the conduction band that introduce LSPR properties into the nanoparticles giving rise to the EM field mechanism for SERS enhancement upon incident laser irradiation. Much like with noble metals, the oscillation of these free carriers at nanoparticle hot spots aid in the development of a functional and cheaper SERS substrate. The SERS enhancement factor (EF) of three different morphologies of WO3-x nanoparticles, i.e., nanorods, nanowires, and nanoplatelets are characterized and deemed comparable to noble metal nanoparticles. A Janowsky complex was formed using the explosive, tetryl, as the target analyte. Using our oxygen deficient WO3-x substrate, tetryl was successfully detected down to the nanomolar level. To our knowledge, this is the first time tetryl has been detected utilizing a non-noble metal-based SERS substrate. Taken together, this dissertation presents the unique aspect of nanotechnology for the development of (1) a multimodal MN-based ultrasensitive and (2) an inexpensive noble-metal comparable WO3-x-based SERS substrates, both of which that can be applied to forensic science research, specifically in forensic toxicology and explosive detection to better, and even save, the lives of individuals and improve their quality of life.
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    Nanoplasmonic efficacy of gold triangular nanoprisms in measurement science: applications ranging from biomedical to forensic sciences
    (2019-12) Liyanage, Thakshila; Sardar, Rajesh; Goodpaster, John; Naumann, Christoph; Agarwal, Mangilal
    Noble metal nanostructures display collective oscillation of the surface conduction electrons upon light irradiation as a form of localized surface plasmon resonance (LSPR) properties. Size, shape, and refractive index of the surrounding environment are the key features that control the LSPR properties. Surface passivating ligands on to the nanostructure can modify the charge density of nanostructures. Further, allow resonant wavelengths to match that of the incident light. This unique phenomenon called the “plasmoelectric effect.” According to the Drude model, red and blue shifts of LSPR peak of nanostructures are observed in the event of reducing and increasing charge density, respectively. However, herein, we report unusual LSPR properties of gold triangular nanoprisms (Au TNPs) upon functionalization with para-substituted thiophenols (X-Ph-SH, X = -NH2, -OCH3, -CH3, -H, -Cl, -CF3, and -NO2). Accordingly, we hypothesized that an appropriate energy level alignment between the Au Fermi energy and the HOMO or LUMO of ligands allows the delocalization of surface plasmon excitation at the hybrid inorganic-organic interface. Thus, provides a thermodynamically driven plasmoelectric effect. We further validated our hypothesis by calculating the HOMO and LUMO levels and work function changes of Au TNPs upon functionalization with para-substituted thiol. This reported unique finding then utilized to design ultrasensitive plasmonic substrate for biosensing of cancer microRNA in bladder cancer and cardiovascular diseases. In the discovery of early bladder cancer diagnosis platform, for the first time, we have been utilized to analyze the tumor suppressor microRNA for a more accurate diagnosis of BC. Additionally, we have been advancing our sensing platform to mitigate the false positive and negative responses of the sensing platform using surface-enhanced fluorescence technique. This noninvasive, highly sensitive, highly specific, also does not have false positives techniques that provide the strong key to detect cancer at a very early stage, hence increase the cancer survival rate. Moreover, the electromagnetic field enhancement of Surface-Enhanced Raman Scattering (SERS) and other related surface-enhanced spectroscopic processes resulted from the LSPR property. This dissertation describes the design and development of entirely new SERS nanosensors using a flexible SERS substrate based on the unique LSPR property of Au TNPs. The developed sensor shows an excellent SERS activity (enhancement factor = ~6.0 x 106) and limit of detection (as low as 56 parts-per-quadrillions) with high selectivity by chemometric analyses among three commonly used explosives (TNT, RDX, and PETN). Further, we achieved the programmable self-assembly of Au TNPs using molecular tailoring to form a 3D supper lattice array based on the substrate effect. Here we achieved the highest reported sensitivity for potent drug analysis, including opioids and synthetic cannabinoids from human plasma obtained from the emergency room. This exquisite sensitivity is mainly due to the two reasons, including molecular resonance of the adsorbate molecules and the plasmonic coupling among the nanoparticles. Altogether we are highly optimistic that our research will not only increase the patient survival rate through early detection of cancer but also help to battle the “war against drugs” that together are expected to enhance the quality of human life.