The detection of biomolecules and volatile organic compounds (VOCs) greatly impacts areas such as biomedicine, biomedical diagnostics, industrial process control, air quality, and breath analysis. Concurrently, whispering gallery mode (WGM) resonators present themselves as highly sensitive and specific sensors pertaining to these applications. Polymer-based WGMs offer additional advantages such as biocompatibility, reduced material costs, and straightforward functionalization methods for tailoring towards distinct analytes. One approach to fabricating polymer WGM sensors in a single step is near-field electrospinning (NFES), a variation of far-field electrospinning (FFES) that enables precise deposition control of micron-sized fibers while maintaining the desired high-volume and rapid production. The filamentous M13 bacteriophage has also drawn attention in the field of biosensing as a promising selective bioreceptor due to the high copy numbers of its lengthwise modifiable protein coat allowing for a dense arrangement of high-affinity peptides available for analyte binding. Additionally, M13 has demonstrated a general affinity for certain charged molecules based on electrostatic interactions with its available protein coat.In this work, a modified streptavidin-binding M13 phage was mixed with poly (vinyl alcohol) and electrospun to fabricate hybrid polymer/phage microscale fibers that support WGMs in their circular cross-sections. The resulting devices were evaluated as both biosensors and VOC sensors through preliminary experiments using streptavidin and methanol as model analytes. The impact of incorporating M13 into the polymer fibers on the sensor quality factor was characterized, and an increased response to streptavidin addition with increasing surface concentration was confirmed. Furthermore, the polymer/phage device exhibited a heightened response to methanol exposure compared to the pure polymer device, indicating promising increased affinity for small polar molecules like VOCs.

Recently, the M13 bacteriophage has been developed as a versatile material template, where it has been shown to bind and grow a wide range of materials both organic and inorganic. Also, despite the discovery over 30 years ago of its ability to transform into a range of structures, far removed from its native filament, its other forms have been barely researched for their capabilities in nanostructure assembly. The M13, in all of its forms, is an asymmetric, bifunctional template, meaning it can grow two materials together, in a non-centrosymmetric fashion. Not only is this fairly unique among virus templates, but is also extremely useful in the creation of catalytic materials. A material’s catalytic properties can be augmented or enhanced when combined with other materials.

Semiconductor photocatalysts tend to be enhanced when combined with other semiconductors or metals, which help with light absorption and the charge separation necessary for catalytic reactions. The orientation and assembly of the combined materials can have significant impacts on their functionalities, where growing the materials over the surface of one another can limit their catalytic activity. For these types of particles, reactive surface area is a major contributing factor in performance. Therefore, with Janus-like, asymmetric particles, which expose equal amounts of each material, photocatalytic properties can be expected to be greatly enhanced.

In this study, we investigated the M13’s spheroid form in its controlled synthesis of ZnS and then Au, and the photocatalytic activity of these materials. We showed that the spheroid transformation process required modification with the ZnS and Au binding peptides both displayed on the virus. We then demonstrated that the growth of each material was limited to their respective protein group, and could be controlled for its size. When both Au and ZnS were present on the template, the combined particle could be used in the photocatalytic degradation of multiple dyes, and the activity of which was greater than either of materials alone. Further, the addition of Au to ZnS allowed photocatalytic activity under visible light excitation, which is normally impossible for the wide bandgap semiconductor. In the development towards a more efficient photocatalyst nanostructure, hierarchical structures were then assembled, in an effort to create so-called

core satellite structures of varying complexity. These structures made use of a Au nanoparticle as the core, with M13 filaments or spheroid decorating its surface, which could be used to synthesize ZnS. This research laid the groundwork for a much more efficient photocatalytic nanostructure.

Nature has the ability to mineralize and build intricate nanostructures of inorganic materials with a very high precision. Various bio-molecules can mineralize and control the morphology and composition of inorganic materials at ambient conditions. Inspired by nature, this work focuses on utilizing the M13 virus, a filamentous phage, 880 nm in length and 6 nm in diameter, for mineralizing copper sulfide and copper oxide semiconductor nanomaterials. The various coat proteins of the virus can easily be modified to express different peptides with specific affinity to various inorganic materials. A phage-display technique was utilized to identify a copper sulfide binding peptide expressed on the entire pVIII coat protein of the virus. This modified phage was used for synthesizing copper sulfide nanoparticles along the length of the template. To increase the yield and coverage of the mineralized material on the phage-templates, non-specific electrostatic interactions between a negatively charged phage (E3) and positively charged copper ions were utilized to synthesize copper sulfide at ambient conditions. The mineralized material coated the phage template and was identified to be cubic Cu_1.8S, a non-stoichiometric phase of the copper sulfide material system. The material showed strong optical absorption below 800 nm due to band-to-band transitions and localized surface plasmon resonance (LSPR) peaks in the infrared region. The LSPR peaks increased in absorption and the electrical resistance of the materials decreased with time indicating an increase in the number of free carriers in the material due to exposure at ambient conditions. The free carrier increase was attributed to a compositional change on the surface of the material. The synthesized Cu_1.8S was utilized to fabricate NH₃ gas sensors. These gas sensors showed a high response to NH₃ gas which may be attributed to the large surface-to-volume ratio of the viral-templated nanomaterials. Finally, utilizing the non-specific electrostatic interactions between the E3 phage and positively charged cations, copper oxide nanoparticles were also synthesized along the viral-template. These semiconductor materials were identified to be a mixture of CuO and Cu₂O with a direct optical band gap of 2.87 eV. These viral-templated semiconductor nanomaterials have potential applications for incorporation into future devices.

In recent years, the bacteriophage has been used as a versatile template to create inorganic nanomaterials and as a potential bactericidal agent to fight multidrug resistant bacteria. The M13 bacteriophage is a viable platform for bactericidal materials with an innate ability to target bacteria. The phage itself is a micron long, filamentous biological molecule. Extensive research has shown that this phage can be genetically modified to bind and biomineralize various inorganic nanostructures. Furthermore, unlike other viruses, the M13 bacteriophage has been shown to drastically change shape and aspect ratio upon contact with chloroform, morphing from its filamentous form to either rods 100s of nanometers long or sub 100 nm spheroids. These different geometries could provide an excellent platform to deliver bactericidal materials due to their compactness.

In this study, we investigated the M13 bacteriophage as a template for bactericidal ZnO and gold nanoparticles and as a E. coli targeting platform. A filamentous genetically modified M13 bacteriophage, with the DRQVDATA peptide insert, was shown to have synthesize amorphous ZnO nanoparticles. Due to the low particle count and the phage agglomerates, the ZnO was found to be unsuitable for bactericidal purposes. No further investigation into the phage geometry was performed. A different avenue was explored with gold templated phage. To create a suitable gold platform, a gold-binding phage morphology was tailored to maximize contact of gold nanoparticles to the E. coli membrane. The binding and biomineralization properties of the transformed was examined and it was found that the templates retained its binding and mineralization properties. Furthermore, the gold mineralized on the spheroids differed from the gold grown on the filaments, where spike-like structures extended outward while isotropic particles grew on the latter.

These gold/phage platforms were then studied for their targeting and photothermal bactericidal properties. It was found that the Au/template was able to target the E. coli and via the photothermal effect, kill off more than 63% of the bacteria under 532 nm irradiation. These Au/templates were shown to be effective photothermal bactericide and could be further expanded to target other bacteria and to be used in near infrared wavelengths.

With increasing development in nanotechnology, approaches for synthesis of nanomaterials with control over dimensions, grain size and crystallinity for various device applications is highly demanded. Biological building blocks such as amino acids direct assembly of intricate structures from nano- to macro-scale within the living system. Such ability of biological molecules have gained scientific interest to meet nanofabrication challenges and demands. A 1 μm long, filamentous M13 bacteriophage, in particular, is a promising biological molecule for synthesis of one-dimensional inorganic nanostructures. The genetic information can be easily manipulated to display specific peptide sequences on the M13 bacteriophage outer protein coats and has been involved in combinatorial phage display technology to identify inorganic specific peptide sequences. Furthermore, various inorganic nanomaterials have been synthesized by the M13 bacteriophage and its protein components. With our daily exposure to hazardous gases such as H2S, H2, CO, and NH3, gas sensors with high sensitivity, low detection limit, low power consumption and miniature size for mobile and continuous monitoring are in demand. Nanoscale chemiresistive gas sensors have a relatively simple configuration and can be used for sensitive monitoring of gas levels with low power consumption. The large surface area to volume ratio provides increased adsorption sites for sensor-analyte interactions and the short diffusion length allows a rapid resistance change with exposure to low gas concentrations.

In this work, a novel platform for metal-based H2S and H2 chemiresistive gas sensors has been designed based on a gold-binding bacteriophage template. Continuous nanocrystalline gold chains assembled on the M13 bacteriophage backbone displayed high sensitivity and low lowest detection limit for H2S sensing. The carboxyl and amine functional groups on the template with an affinity for sulfur added to device sensitivity. The same platform was also adapted for hybrid gold-palladium nanopeapod sensors for H2 sensing. The sensor showed high response to low H2 concentrations at ambient conditions. Moreover, bio-directed ZnO synthesis from M13 bacteriophage protein coats and peptide components were explored. Materials characterization revealed peptide concentration dependent morphology, crystallinity, and optical property tuning. This work demonstrates the promise of bio-directed nanofabrication for sensitive chemiresistive gas sensors.

The detection of biomolecules, known as biosensing, has profoundly impacted biomedical diagnostics, disease monitoring/prevention, and food/water quality control. Despite the great strides in biosensing technology, there is still a drive to develop new biosensors that can improve current performance or solve emerging biosensing concerns. An emerging approach towards biosensing is using Whispering Gallery Mode (WGM) resonators. These devices are compact, highly sensitive, and require no additional fluorescent or radioactive tag, enabling real-time label-free biosensing. Polymer-based WGM cavities offer reduced material costs, simple processing strategies, and the potential for straightforward incorporation of bioreceptors in a single process step.Concurrently, filamentous bacteriophages such as the M13 bacteriophage have attracted attention as alternative bioreceptors. The length of the virus is comprised of 2700 copies of the same protein, which can each act as a bioreceptor. Crucially, this protein coat can be modified to display a wide range of specific binding motifs, creating a dense ordered arrangement of high-affinity peptides with the proper orientation for analyte binding. In this work I focus on the fabrication of WGM polymer/M13 bacteriophage sensors/biosensing using the near-field electrospinning process (NFES). NFES is a variant of electrospinning combining the high-volume, rapid manufacturing of electrospinning with precise patterning to fabricate microfibers. An advantage of NFES is the polymer-based approach can produce fibers that incorporate dyes and biomolecules such as M13 viruses. These electrospun fibers were first utilized as refractive index sensor in water-ethanol mixtures. The successful demonstration of WGM sensing spurred the fabrication of polymer/M13 biosensor where the M13 acted as a biorecognition element. The polymer/M13 fibers demonstrated specificity and sensitivity to the target analyte due to M13 on the fiber surface. Surface concentrations of M13 virus were increased during the NFES process by carefully tuning the M13 surface charge and electric field interactions. This work demonstrates the promise of NFES and electrospinning in fabricating WGM biosensors and highlights the use of M13 as a bioreceptor.

Because of their ability to serve in chemical and biological applications, there is a growing need for sensitive, compact, readily fabricated, and inexpensive chemical sensors. In recent years, devices that utilize whispering gallery modes (WGMs) have proven versatile in many such applications, however, these reports have typically used fabrication techniques that are either complex, do not produce sensitive devices, or are costly. One possible solution is to use polymer materials in conjunction with near-field electrospinning (NFES). This direct-write fabrication approach enables fast, yet precise positioning of micron-sized fibers for low-cost, scalable sensor manufacturing. Moreover, NFES can be used to incorporate additional functionality such as emitters for optically active sensing or receptors for enhanced selectivity. Here, fluorescent dye-doped polymer fiber refractive index sensors that support WGMs within the fiber cross-section were demonstrated. Poly(vinyl) alcohol resonators were first simulated with finite-difference time-domain simulations to show that the devices needed to be several microns in size and a few hundred nanometers from the substrate to support resonance. Polymer solutions of 25 wt% PVA and doped at with varied amounts of Rhodamine 6G were mixed and shown to have consistent physicochemical properties. Resonators were fabricated using NFES by drawing fibers from the polymer solution onto substrates patterned with deep trenches. The electrospun fibers ranged from 2 to 33 µm in diameter, displayed smooth surfaces, and had circular cross sections. Using microphotoluminscence, resonant groups of peaks with Q factors as high as 14,191 were observed in the emission range of the dye, from 590-700 nm. Using size-dependent mode spacing predicted by finite-difference time domain simulations, as well as a mode-fitting technique, the resonances were identified as WGMs. The response of the resonance peaks to exposure to isopropanol and methanol vapors was evaluated using a range of fiber diameters. The fibers were also crosslinked to make them water insoluble and their in-air and in-water resonance capabilities were analyzed. The crosslinked fibers displayed Q factors as high as 19,700 when measured in air and values as high as 7,500 when measured in water. Furthermore, aqueous sensing of ethanol was performed. The WGM resonators fabricated here have demonstrated the potential of near-field electrospun polymer-based fibers for sensing applications.