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Microorganisms (e.g. bacteria, fungi, and viruses) add indispensable functionality to a range of electrospun polymer materials and devices. The optimal distribution of bioactive agents on either the interior or exterior of the fiber is application specific. Current microbe surface immobilization strategies and core-confinement techniques continue to pose a number of challenges. Here, we explore a simple strategy, utilizing electrostatic forces, to control the migration and surface concentration of the M13 bacteriophage within near-field electrospun polyvinyl alcohol (PVA) microfibers. Both the surface charge of the electrospun virus and the applied electric field polarity altered microbe placement. When doped with Rhodamine 6G (R6G), the circular microfiber cross-sections formed active whispering gallery mode (WGM) resonators. These relatively high quality (Q) optical cavities enabled us to sensitively probe the virus content of their outer layer, while functioning as label-free optical biosensors with phage-based streptavidin biorecognition elements. Coulomb forces displayed significant control over M13 surface coverage during near-field electrospinning, increasing biosensor response by nearly a factor of four to 1310 nM streptavidin. These findings are an important demonstration of electrostatic forces as a simple, yet adaptable method to enhance biohybrid fiber functionality and performance by tailoring microbe distribution. 

Virus-based nanocarriers have shown great potential for noninvasive delivery of drugs, diagnostics, and imaging agents to hard-to-reach anatomical locations. Yet, they largely depend on diffusion for transport, often lacking the force to actively penetrate biological barriers, and navigation to guide therapeutic agents. In these studies, the M13 bacteriophage, a linearly shaped virus, was converted from passive nanocarrier to actively propelled, fuel-driven nanomotor. Using the distinctive low symmetry of its capsid, a single Pt nanoparticle was added to one end of the M13 virus to form a tadpole-like structure. The Pt/M13 head/tail nanomotors exhibited notably enhanced diffusion in the presence of hydrogen peroxide fuel, and significantly improved uptake by SVOK3 ovarian cancer cells in vitro. Given the successes of the M13 bacteriophage as a nanocarrier, the demonstration of this simple, but comparatively mobile M13-based nanomotor platform represents an important step in advancing the potential therapeutic efficacy of viral nanocarriers. 

Whispering gallery mode (WGM) resonators have attracted attention as optical biosensors due to their capacity for rapid label-free detection. Separately, the M13 bacteriophage has been investigated as an alternative biorecognition element. In this work, a novel polymer WGM biosensor functionalized with filamentous virus biocapture agents was fabricated using near-field electrospinning (NFES) in a single step. Polyvinyl alcohol (PVA) was mixed with streptavidin-binding M13 bacteriophage and rhodamine 6G in aqueous solution for blend electrospinning of active cavity microfiber-based resonators. Confocal fluorescence microscopy revealed alignment of M13 bioreceptors along the fiber axis, while x-ray photoelectron spectroscopy (XPS) and streptavidin-conjugated nanoparticle binding studies indicated that bioactive M13 bacteriophage were on the fiber surface. Dye-doped, crosslinked PVA/M13 fibers supported moderate quality (Q) factor first order WGM resonances within their cross-sections that exhibited a spectral shift in response to streptavidin binding. Composite PVA/M13 microfibers demonstrated specific label-free biosensing of streptavidin with a theoretical limit of detection of 3 nM and a maximum surface coverage of 21 ± 5%. These results demonstrate the potential of NFES to fabricate WGM resonators from PVA/M13 microfibers and use them as a platform for rapid, sensitive label-free sensing. 

Non-centrosymmetric nanostructures are composed of two different materials displayed on spatially distinct surface regions. These nontrivial building blocks facilitate self assembly of hierarchical nanostructures with increased complexity and support cooperative material behaviors. The arrangement of M13 bacteriophage structural proteins within its capsid creates a promising monodisperse and readily modifiable template for these low symmetry nanomaterials. Here, a 9-mer ZnS-binding peptide was inserted into the p3 minor coat protein (capsid tip) of an M13 bacteriophage with Au-binding motif fused to its p8 major coat protein (capsid body). Multiple vortex/rest cycles with chloroform were used to convert this bifunctional, Au/ZnS (p8/p3)-binding phage from filament to spheroid. The shape transformation was studied with transmission electron microscopy, circular dichroism spectroscopy, and fluorescence spectroscopy. The effects of the p3 peptide fusion and conversion temperature were evaluated. Compared to the Au-binding phage without a p3 peptide fusion, the insertion of the ZnS-binding motif increased spheroid size, molar ellipticity loss, and intrinsic fluorescence quenching. Reduced temperature (0°C) within early transformation cycles diminished spheroid polydispersity and increased agglomeration resistance. In addition, Au/ZnS-binding spheroids retained peptide motif affinity and relative placement of the p3 and p8. Site-specific synthesis of ZnS and Au on the p3 and p8, respectively, produced non-centrosymmetric hybrid metal/semiconductor nanostructures. This work highlights the effect of a p3 mutation on filament to spheroid transformation as well as the importance of temperature in producing a robust scaffold for inorganic material synthesis. Lastly, the manufactured bifunctional M13 spheroids were used for bio-directed synthesis of noncentrosymmetric nanoparticle assemblies demonstrating the potential for heterojunction formation. 

Whispering gallery mode (WGM) resonators demonstrate great potential for photonic and sensing applications. Yet, these devices are often disadvantaged by costly materials or complex fabrication approaches, in addition to lack of manufacturing scalability. Near-field electrospinning (NFES), a recently emerged facile fiber fabrication method, offers a solution. Here, WGM resonances are reported in Rhodamine 6G-doped poly(vinyl) alcohol (PVA) microfibers via NFES. Diameters are tuned over a range of more than 10 μm by varying substrate stage speed. Fibers display uniform distribution of dye, smooth surfaces, and circular cross-sections, all critical for supporting WGMs. High quality (Q) resonances are confirmed within fiber cross-sections through polarization experiments, free-spectral range analysis, and Mie-theory-derived mode assignment. In addition to WGMs, groups of associated spiral or conical modes are observed due to taper-induced weak optical confinement along the fiber axis. Crosslinked, dye-doped PVA fibers are utilized to sense the ethanol concentration in ethanol–water mixtures and actuation mechanisms are evaluated by comparison to theoretical spectra. The demonstration of high-Q resonances within NFES polymer microfibers is a critical step toward simple, cost effective, high-volume fabrication of WGM resonators for optoelectronics and biomedical devices. 

Organized chains of copper oxide nanoparticles were synthesized, without palladium (Pd) activation, using the M13 filamentous virus as a biological template. The interaction of Cu precursor ions with the negatively charged viral coat proteins were studied with Fourier transform infrared spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. Discrete nanoparticles with an average diameter of 4.5 nm and narrow size distribution were closely spaced along the length of the high aspect ratio templates. The synthesized material was identified as a mixture of cubic Cu2O and monoclinic CuO. UV/Vis absorption measurements were completed and a direct optical band gap of 2.87 eV was determined using Tauc's method. This value was slightly larger than bulk, signaling quantum confinement effects within the templated materials. 

Copper sulfide-based ammonia (NH3) gas sensors were assembled using a genetically modified viral template. Glutamic acid residues on the filament-shaped bioscaffold surface facilitated the synthesis of nanocrystalline Cu1.8S. Each device comprised a network of biological materials decorated with a nonstoichiometric semiconductor. These chemiresistive devices had high sensitivity to NH3 concentrations from 10 to 80 ppm under room-temperature operation. Response times greater than 15 min were observed. These results demonstrate the potential of biotemplated materials for sensitive gas detection at room temperature. 

The optical and electrical stabilities of viral-templated non-stoichiometric copper sulfide, digenite (Cu1.8S) films were investigated. The films were composed of large agglomerates of randomly aligned Cu1.8S-coated M13 filamentous phage. Free carrier optical absorption associated with localized surface plasmon resonance (LSPR) was observed in the near infrared spectral region, and the films were electrically active, displaying a linear current-voltage relationship. Under ambient conditions, the magnitude of the LSPR absorption increased, following a power law relationship with time, and the electrical resistance of viral-templated films decreased significantly. In contrast, the resistance of films stored under low oxygen, low humidity conditions experienced a smaller reduction in electrical resistance. Changes in optical and electrical film properties under ambient conditions were associated with an increase in free carrier concentration within the copper chalcogenide material due to oxygen exposure. X-ray photoelectron spectroscopy was used to relate this increase in free carrier concentration to compositional changes on the viral-templated material surface. 

As science teachers, you observe excitement among your middle school students when they build things, tinker with materials, and work together. The engineering design practices included in the K–12 Framework for Science Education (NRC 2012) are an attempt to harness this excitement and enthusiasm for science and engineering. Integrating engineering design into your laboratory science teaching is an engaging way to support students in learning mathematics and science concepts (Katehi, Pearson, and Feder 2009). This article describes how the three of us (an education professor, a middle school teacher who implements engineering design activities as part of a green STEM curriculum, and an engineering professor) built on student thinking to design a weeklong unit on solar energy that supported mathematics and science learning. The lesson included students designing and redesigning a model solar car and culminated in a model-solar-car race. 

The growth of crystalline copper sulfide using a viral template was investigated using sequential incubation in CuCl2 and Na2S precursors. Non-specific electrostatic attraction between a genetically-modified M13 bacteriophage and copper cations in the CuCl2 precursor caused phage agglomeration and bundle formation. Following the addition of Na2S, polydisperse nanocrystals 2–7 nm in size were found along the length of the viral scaffold. The structure of the copper sulfide material was identified as cubic anti-fluorite type Cu1.8S, space group, Fm3m. Strong interband absorption was observed within the ultraviolet to visible range with an onset near 800 nm. Furthermore, free carrier absorption, associated with the localized surface plasmon resonance of the copper sulfide nanocrystals, was seen in the near infrared with absorbance maxima at 1060 nm and 3000 nm, respectively.