Biomolecule immobilization has attracted the attention of various fields such as fine chemistry and biomedicine for their use in several applications such as wastewater, immunosensors, biofuels, et cetera. The performance of immobilized biomolecules depends on the substrate and the immobilization method utilized. Electrospun nanofibers act as an excellent substrate for immobilization due to their large surface area to volume ratio and interconnectivity. While biomolecules can be immobilized using adsorption and encapsulation, covalent immobilization offers a way to permanently fix the material to the fiber surface resulting in high efficiency, good specificity, and excellent stability. This review aims to highlight the various covalent immobilization techniques being utilized and their benefits and drawbacks. These methods typically fall into two categories: (1) direct immobilization and (2) use of crosslinkers. Direct immobilization techniques are usually simple and utilize the strong electrophilic functional groups on the nanofiber. While crosslinkers are used as an intermediary between the nanofiber substrate and the biomolecule, with some crosslinkers being present in the final product and others simply facilitating the reactions. We aim to provide an explanation of each immobilization technique, biomolecules commonly paired with said technique and the benefit of immobilization over the free biomolecule.

Silver-doped carbon nanofibers (SDCNF) are used as the base material for the selective capture of Escherichia coli in microfluidic systems. Fibers were spun in a glovebox with dry atmosphere maintained by forced dry air pumped through the closed environment. This affected the evaporation rate of the solvent during the electrospinning process and the distribution of silver particles within the fiber. Antibodies are immobilized on the surface of the silver-doped polyacrylonitrile (PAN) based carbon nanofibers via a three-step process. The negatively charged silver particles present on the surface of the nanofibers provide suitable sites for positively charged biotinylated poly-(L)-lysine-graft-poly-ethylene-glycol (PLL-g-PEG biotin) conjugate attachment. Streptavidin and a biotinylated anti-E. coli antibody were then added to create anti-E. coli surface functionalized (AESF) nanofibers. Functionalized fibers were able to immobilize up to 130 times the amount of E. coli on the fiber surface compared to neat silver doped fibers. Confocal images show E. coli remains immobilized on fiber mat surface after extensive rinsing showing the bacteria is not simply a result of non-specific binding. To demonstrate selectivity and functionalization with both gram negative and gram-positive antibodies, anti-Staphylococcus aureus surface functionalized (ASSF) nanofibers were also prepared. Experiments with AESF performed with Staphylococcus aureus (S. aureus) and ASSF with E. coli show negligible binding to the fiber surface showing the selectivity of the functionalized membranes. This surface functionalization can be done with a variety of antibodies for tunable selective pathogen capture.

Bifacial modules with a glass/transparent backsheet (G/CB) structure offer many advantages over their glass/glass (G/G) counterparts. However, compared to traditional opaque backsheets, transparent backsheets can be more susceptible to degradation because UV light can more easily go through the transparent outer layer into the core and inner layers. A better understanding of the degradation mechanism and long-term durability of emerging transparent backsheets is needed. In this study, the G/CB laminated coupons constructed with silica glass, polyolefin elastomer encapsulant (POE) and three types of fluoropolymer-based transparent backsheets were subjected to accelerated weathering under ultraviolet (UV) light at 65 °C and 50% relative humidity (RH) for up to 3600 h with additional 200 thermal cycles. The maximum UV dose (1800 MJ/m2) is equivalent to approximately 45 years of field exposure in Arizona, assuming a 12% albedo. Cross-sectional characterizations of optical, chemical, and mechanical degradation were conducted on the transparent backsheets of the aged and unaged coupons using confocal fluorescence microscopy, microscale infrared spectroscopy, and nanoindentation, respectively. Results showed that a superficial outer layer cracking occurred on coupons constructed with polyvinyl fluoride (PVF)-based backsheet (G/CB1), and local delamination appeared near a corner of polyvinylidene fluoride (PVDF)-based backsheet (G/CB2). However, the coupon containing fluoroethylene vinyl ether (FEVE)/polyethylene terephthalate (PET)/ethylene-vinyl acetate (EVA)-based transparent backsheet (G/CB3) showed the greatest yellowing as well as substantial backsheet cracking. This study suggests that, although the application of transparent backsheet is promising, careful considerations of the long-term UV durability are needed when designing and selecting backsheets for 50-year bifacial modules.

Decarbonatization drives rapid growth of the global bifacial solar market. However, the long-term durability of bifacial technology has not yet been clearly demonstrated. Here, the durability of three types of glass/polyolefin elastomer (POE)/transparent backsheet (G/CB) coupons was investigated under UV/65 °C/50 % RH, followed by thermal cycling. Spatially resolved depth-dependent techniques were used to characterize the degradation of transparent backsheets, POEs, and their interfaces in G/CB coupons. Non-destructive depth profiling of optical and chemical degradation of G/CB was developed by confocal-based Raman microscopy and fluorescence microscopy. Cross-sectional mechanical analyses of transparent backsheets and encapsulants were performed by nanoindentation. The results indicate that aged G/CB coupons show a higher yellowness index than the glass/glass construction, and their values depend on the type of backsheet. Depth-dependent confocal Raman spectra and fluorescence mapping show that the highest emission comes from the POE region closest to the glass, and the yellowness of the glass side-exposed G/CB comes from both encapsulant and backsheet yellowing, which could be related to the migration and interaction of additives in these components. Furthermore, the results from nanoindentation clearly reveal the depth-dependent mechanical changes of individual layers of G/CB coupons after aging.