Development of Nanofiber and Surface Plasmon Resonance Sensors for VOCs, Biochemical, and Bacterial Analysis

It is important to monitor potential exposure to various chemicals and toxicants that may adversely affect both human and environmental health. Biosensors have been developed to identify and quantify these analytes of interest in early warning systems and diagnosis devices. This dissertation implements nanomaterials, such as nanofibers and nanoparticles, into the biological recognition element of a biosensor for selectively and sensitively to detect trace analytes in either gas, liquid, or solid phases.This dissertation is an agglomeration of several different projects that investigates the novel applications of nanomaterials into biosensor designs with two major application focuses: nanofibers and surface plasmon resonance (SPR) The first half of this dissertation focuses on the application of nanofiber surfaces for sensor developments. The nanofibers were fabricated through electrospinning and incorporated into various sensor designs. The first project develops polyaniline nanofibers into a chemiresistor sensor for sensitive detection of VOCs (small chain alcohols) by employing variants of reduced graphene oxides. The second project applies the nanofiber property of high surface area to volume ratio to maximize surface adsorption of EDTA-functionalized silver nanoparticles (AgNPs) as the biorecognition element of this sensor. The EDTA-AgNPs formulates a nickel ion bridge for selective capture and release of NTA and His tagged proteins that can be detected through fluorescent spectroscopy. The second half of this dissertation transitions into the application of surface plasmon resonance for the development of biosensor signal transducers. The third project focused on combining the potential of 3D printing with gold nanoparticles (AuNPs) to create a novel integrated localized SPR (LSPR) sensor surface capable of sensitive protein detection. The synthesis of gold nanoparticles in-situ on a 3D printed prism surface enables the fabrication of a biosensor device for the disposable field of site usage with qualities comparable performances with sensors using commercial optical prisms. The last project focuses on developing an SPR experimental model of a double lipid bilayer membrane. This model mimics the unique structure of the double lipid bilayer membrane system found in the chloroplast, mitochondria, and gram-negative bacteria. This novel experimental model combined with SPR analysis creates a biosensor platform that enables the interrogation of chemical and protein interactions at interfaces such as the gram-negative bacteria cell wall and membrane system

Gas Sensors Based on Conducting Polymers

Since the discovery of conducting polymers (CPs), their unique properties and tailor-made structures on-demand have shown in the last decade a renaissance and have been widely used in fields of chemistry and materials science. The chemical and thermal stability of CPs under ambient conditions greatly enhances their utilizations as active sensitive layers deposited either by in situ chemical or by electrochemical methodologies over electrodes and electrode arrays for fabricating gas sensor devices, to respond and/or detect particular toxic gases, volatile organic compounds (VOCs), and ions trapping at ambient temperature for environmental remediation and industrial quality control of production. Due to the extent of the literature on CPs, this chapter, after a concise introduction about the development of methods and techniques in fabricating CP nanomaterials, is focused exclusively on the recent advancements in gas sensor devices employing CPs and their nanocomposites. The key issues on nanostructured CPs in the development of state-of-the-art miniaturized sensor devices are carefully discussed. A perspective on next-generation sensor technology from a material point of view is demonstrated, as well. This chapter is expected to be comprehensive and useful to the chemical community interested in CPs-based gas sensor applications

A review of nanocomposite-modified electrochemical sensors for water quality monitoring

Electrochemical sensors play a significant role in detecting chemical ions, molecules, and pathogens in water and other applications. These sensors are sensitive, portable, fast, inexpensive, and suitable for online and in-situ measurements compared to other methods. They can provide the detection for any compound that can undergo certain transformations within a potential window. It enables applications in multiple ion detection, mainly since these sensors are primarily non-specific. In this paper, we provide a survey of electrochemical sensors for the detection of water contaminants, i.e., pesticides, nitrate, nitrite, phosphorus, water hardeners, disinfectant, and other emergent contaminants (phenol, estrogen, gallic acid etc.). We focus on the influence of surface modification of the working electrodes by carbon nanomaterials, metallic nanostructures, imprinted polymers and evaluate the corresponding sensing performance. Especially for pesticides, which are challenging and need special care, we highlight biosensors, such as enzymatic sensors, immunobiosensor, aptasensors, and biomimetic sensors. We discuss the sensors’ overall performance, especially concerning real-sample performance and the capability for actual field application

Development of Solution Blow Spun Nanofibers as Electrical and Whole Cell Biosensing Interfaces

Infectious pathogens place a huge burden on the US economy with more than $120 billion spent annually for direct and indirect costs for the treatment of infectious diseases. Rapid detection schemes continue to evolve in order to meet the demand of early diagnosis. In chronic wound infections, bacterial load is capable of impeding the healing process. Additionally, bacterial virulence production works coherently with bacterial load to produce toxins and molecules that prolongs the healing cycle. This work examines the use of nonwoven polymeric conductive and non-conductive nanofiber mats as synthetic biosensor scaffolds, drug delivery and biosensor interface constructs. A custom-made nanofiber platform was built to produce solution blow spun nanofibers of various polymer loading. Antimicrobial nanofiber mats were made with the use of an in-situ silver chemical reduction method. Ceria nanoparticles were incorporated to provide an additional antioxidative property. Conductivity properties were examined by using silver and multi-walled carbon nanotubes (MWCNT) as a filler material. SBS parameters were adjusted to analyze electrical conductivity properties. Nanofiber mats were used to detect bacteria concentrations in vitro. Protein adhesion to conductive nanofibers was studied using fluorescent antibodies and BCA assay. Anti-rabbit and streptavidin Alexa Flour 594 was used to examine the adsorption properties of SBS nanofiber mats. Enhancements were made to further improve interface design for specificity. SBS nanofiber electrodes were fabricated to serve as scaffold and detection site for spike protein detection. Bacteria virulence production was examined by the detection of pyocyanin and quorum sensing molecules. The opportunistic pathogen, Pseudomonas aeruginosa is a nosocomial iii pathogen found in immunocompromised patients with such as those with chronic wounds and cystic fibrosis. Pyocyanin is one of four quorum sensing molecules that the pathogen produces which can be detected electrochemically due to its inherent redox-active activity. SBS has been used to develop a sensing scheme to detect pyocyanin. This work also examines the use of a synthetic biosensor with a LasR based system capable of detecting homoserine lactone produced by P. aeruginosa and other common gram-negative pathogens. Genetic modifications were made to biosensor in order to replace a green, fluorescent reporter with a chromoprotein based reporter system for visual readout. Additionally, work related to community service and outreach regarding the encouragement of middle school students to pursue Science, Technology, Engineering and Math (STEM) was conducted. Results from outreach program showed an increase in the STEM interest among a group of middle school students. There was a general trend with STEM career knowledge, STEM self-efficacy and the level of interest in STEM careers and activities. Military research was also done with the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) to develop several assays for the detection of several highly infectious viruses and bacteria. Due to confidentiality, the work cannot be published in this manuscript

Fabrication of nitrate ion sensor based on conductive polyaniline doped with nitrate using thick film technology

Nitrate is one of the nutrients that can give an effect on the environment if it is applied in excess. It is also easily soluble in water and it has the potential to be a pollutant in groundwater by the over-process of fertilizer. Therefore, it needs a detected component to give the right measure for nitrate in the soil, called a nitrate ion sensor. It consists of three electrodes configuration, namely, working, counter, and reference electrodes with conductive polyaniline doped with Nitrate (NO₃‾) which is fabricated by thick film technology. In previous research, acidic media was used as a solvent for polyaniline, while this research used water (H2O) solvent. The result of characterization showed that particles were distributed evenly on the sample with the form of particles being small balls with a dimension of 0.18 µm and the percentage of atomic elements being: 91.96 % carbon, 3.14 % nitrogen, and 4.9 % oxygen. The performance of sensors was investigated using potentiostat with four concentrations of nitrate standard solution. The result showed good response with a voltage range in each concentration of nitrate standard solution being 0.5002 Volt (10 mg/l), 1.3552 Volt (20 mg/l), 1.1208 Volt (50 mg/l), and 0.8963 Volt (100 mg/l). It was found that nitrate sensors with nitrate-doped conductive polymer, polyaniline, as the sensitive membrane responded well to detecting nitrate elements in precision farming and the sensitivity showed that for every 1 mg/l concentration in nitrate standard solution, the voltage increases by 0.0007

Advances in Nanofibers

Book Advances in Nanofibers is a research publication that covers original research on developments within the Nanofibers field of study. The book is a collection of reviewed scholarly contributions written by different authors. Each scholarly contribution represents a chapter and each chapter is complete in itself but related to the major topics and objectives. The target audience comprises scholars and specialists in the field

Carbon-Based Nanomaterials for (Bio)Sensors Development

Carbon-based nanomaterials have been increasingly used in sensors and biosensors design due to their advantageous intrinsic properties, which include, but are not limited to, high electrical and thermal conductivity, chemical stability, optical properties, large specific surface, biocompatibility, and easy functionalization. The most commonly applied carbonaceous nanomaterials are carbon nanotubes (single- or multi-walled nanotubes) and graphene, but promising data have been also reported for (bio)sensors based on carbon quantum dots and nanocomposites, among others. The incorporation of carbon-based nanomaterials, independent of the detection scheme and developed platform type (optical, chemical, and biological, etc.), has a major beneficial effect on the (bio)sensor sensitivity, specificity, and overall performance. As a consequence, carbon-based nanomaterials have been promoting a revolution in the field of (bio)sensors with the development of increasingly sensitive devices. This Special Issue presents original research data and review articles that focus on (experimental or theoretical) advances, challenges, and outlooks concerning the preparation, characterization, and application of carbon-based nanomaterials for (bio)sensor development

Laser-Induced Functional Carbon Nanofibers for Electrochemical Sensing

The development of electrochemical sensors utilizing non-enzymatic detection strategies is a topic of high interest for many researchers in order to replace classic expensive and less stable enzymatic approaches. In this thesis, recent developments in non-enzymatic sensing were reviewed. The general principles of (nano)catalysis and preparation of nanomaterials were discussed focusing on carbon materials and metal-based catalysts. Carbon nanomaterials stand out for their great electron transfer properties and, especially for nanofibers, high surface-to-volume ratio with multiple analyte interaction sites. Doping carbon nanofibers with heteroatoms or metal nanoparticles further introduces nanocatalytic functionalities. Hereby, the type of atom and metal, respectively, determines the selectivity as well as sensitivity of the generated composite. The fabrication of laser-induced carbon materials was quite recently found to be a simple and effective way to receive such hybrids. In this regard, several substrates are suitable for being carbonized e.g. polymer films containing metal salts. Already constructed non-enzymatic platforms, based on laser-induced graphene, for sensing in aqueous solution but also with gaseous analytes were presented. The current achievements in wearables were emphasized which guide the prospective trends. Concluding, the key aspects were summarized and thoughts on improvements and suggestion for future evolvements were shared. In this thesis the strategy of one-step laser-carbonization of electrospun nanofibers to obtain carbon nanofibers was developed as a superior process over traditional chemical vapor deposition and thermal carbonization of electrospun nanofibers which are laborious, time-consuming and inflexible. Polyimide, more precisely Matrimid® 5218, served as carbon precursor and polymer solutions of it were electrospun into nanofiber mats. Afterwards, carbon nanofibers were prepared in a facile manner via direct lasing on as-spun mats at ambient conditions with a CO2-laser. This method allows the generation of electrodes with any design and shape controlled by PC software. Compared to both mentioned conventional procedures, large-scale production of carbon nanofibers at affordable costs is possible in a short time. The morphology of laser-induced carbon nanofibers (LCNFs) can not only be controlled by lasing parameters such as laser power and speed. During electrospinning, metal nanoparticles can be incorporated into nanofibers by simply doping the spinning solutions with metal salt e.g. iron(III) acetylacetonate before. This metal, as studied for iron, additionally contributes to the homogeneous carbonization during lasing process by a kind of heat transfer ability. Therefore, the respective metal content relative to the polymer also enables tuning of the obtained LCNF morphology. Continuously scribing of several electrodes in a row vs. discontinuously i.e. one electrode prior to the next also has a huge impact on the heat input because of different durations of scribing one line. It was demonstrated that the electrochemical properties of LCNF electrodes can be optimized due to the direct link to the morphology or rather electrochemical surface area. The latter was found to be much greater than the geometric area. The 3D porous network structure of LCNFs with an average pore size in low micrometer range facilitates interaction with molecules in aqueous solution and hence allows high electron transfer rates, which was displayed by very low peak-to-peak separations, as studied with [Fe(CN)6]4-/3- redox marker. The type of metal salt incorporated in LCNFs defines its catalytic properties. Nickel salt can be evenly embedded into carbon matrix with low nanometer nanoparticle size. The electrospun nanofiber diameter does not change with varying nickel content. However, it was shown that the expansion of nanofibers during carbonization is influenced assumedly by the mentioned heat transfer ability. A significant smaller increase of LCNF diameter compared to electrospun nanofibers was achieved with increasing the nickel content, which resulted in better fiberosity. In contrast to electrodeposited nickel particles, it was evinced that nickel in LCNFs is stably adhered to the carbon and does not leach out during several hours of shaking incubation in phosphate buffer at body temperature. Prevented desorption of potential toxic metals brings the application of LCNFs in vivo one step closer. With its catalytic behavior towards glucose, Ni-LCNF was utilized for amperometric glucose sensing. The electroanalytical performance with a high sensitivity and a low limit of detection turned out to be excellent and the linear range covers the real glucose levels in blood. Further, ascorbic acid and uric acid did not produce interference at their relevant levels. Those great electrochemical characteristics are attributed to derive from nickel nanocatalyst on the one hand and 3D fiberosity on the other hand. Electron microscopic images gave a hint that LNCFs could be hollow which additionally could increase the interaction of catalyst nanoparticles with analytes in solution but also gaseous molecule samples. With focus on catalysis, LCNFs with several different metals can be created to enable a variety of application possibilities. Palladium containing LCNFs were furthermore prepared in order to electrochemically detect hydrogen peroxide. In this experiments, the amperometric sensitivity towards H2O2 was enhanced by improving the electrochemical properties of Pd-LCNF either electrochemically by cyclic voltammetry cycling, application of a constant negative potential or chemically by reduction during incubating Pd-LCNF electrodes in NaBH4 solutions for some hours. By fabrication of bimetallic Pd/Fe-LCNF hybrids, the detection potential of H2O2 could be significantly reduced which gives a first hint on successful achievement of a synergistic effect. As these investigations were only preliminary ones, further optimizations to reach low micromolar limit of detection prior to final sensor development have to be carried out