The COVID-19 pandemic has clearly shown the importance of developments in fabrication of advanced protective equipment. This study investigates the potential of using multifunctional electrospun poly­(methyl methacrylate) (PMMA) nanofibers decorated with ZnO nanorods and Ag nanoparticles (PMMA/ZnO–Ag NFs) in protective mats. Herein, the PMMA/ZnO–Ag NFs with an average diameter of 450 nm were simply prepared on a nonwoven fabric by directly electrospinning from solutions containing PMMA, ZnO nanorods, and Ag nanoparticles. The novel material showed high performance with four functionalities (i) antibacterial agent for killing of Gram-negative and Gram-positive bacteria, (ii) antiviral agent for inhibition of corona and influenza viruses, (iii) photocatalyst for degradation of organic pollutants, enabling a self-cleaning protective mat, and (iv) reusable surface-enhanced Raman scattering substrate for quantitative analysis of trace pollutants on the nanofiber. This multi-functional material has high potential for use in protective clothing applications by providing passive and active protection pathways together with sensing capabilities.

The development of novel physically unclonable functions (PUFs) is of growing interest and fluorescent organic semiconductors (f‐OSCs) offer unique advantages of structural versatility, solution‐processability, ease of processing, and great tuning ability of their physicochemical/optoelectronic/spectroscopic properties. The design and ambient atmosphere facile fabrication of a unique organic light‐emitting physically unclonable function (OLE‐PUF) based on a green‐emissive fluorescent oligo(p‐phenyleneethynylene) molecule is reported. The OLE‐PUFs have been prepared by one‐step, brief (5 min) thermal annealing of spin‐coated nanoscopic films (≈40 nm) at a modest temperature (170 °C), which results in efficient surface dewetting to form randomly positioned/sized hemispherical features with bright fluorescence. The random positioning of molecular domains generated the unclonable surface with excellent uniformity (0.50), uniqueness (0.49), and randomness (p > 0.01); whereas the distinctive photophysical and structural properties of the molecule created the additional security layers (fluorescence profile, excited‐state decay dynamics, Raman mapping/spectrum, and infrared spectrum) for multiplex encoding. The OLE‐PUFs on substrates of varying chemical structures, surface energies and flexibility, and direct deposition on goods via drop‐casting are demonstrated. The OLE‐PUFs immersed in water, exposed to mechanical abrasion, and read‐out repeatedly via fluorescence imaging showed great stability. These findings clearly demonstrate that rationally engineered solution‐processable f‐OSCs have a great potential to become a key player in the development of new‐generation PUFs.

We present a high-throughput and inexpensive fabrication approach that uses self-assembled block copolymer (BCP) films as templates to generate dense nanoscale chemical patterns of polymer brushes for the selective immobilization of Au nanoparticles (NPs). A cross-linked random copolymer mat that contains styrene and methyl methacrylate units serves both as a base layer for perpendicular assembly of nanoscale domains of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) films and as a nonadsorbing background layer that surrounds the chemical patterns. The selective removal of the PMMA block and the underlying mat via oxygen plasma etching generates binding sites which are then functionalized with poly(2-vinylpyridine) (P2VP) brushes. Au NPs with a diameter of 13 nm selectively immobilize on the patterned P2VP brushes. An essential aspect in fabricating high quality chemical patterns is the superior behavior of methyl methacrylate containing cross-linked mats in retaining their chemistry during the grafting of P2VP brushes. The use of BCPs with different molecular weights and volume fractions allows for preparation of chemical patterns with different geometries, sizes, and pitches for generating arrays of single particles that hold great promise for applications that range from molecular sensing to optical devices.

This paper presents electrospin nanolithography (ESPNL) for versatile and low-cost fabrication of nanoscale patterns of polymer brushes to serve as templates for assembly of metallic nanoparticles. Here electrospun nanofibers placed on top of a substrate grafted with polymer brushes serve as masks. The oxygen plasma etching of the substrate followed by removal of the fibers leads to linear patterns of polymer brushes. The line-widths as small as ∼50 nm can be achieved by precise tuning of the diameter of fibers, etching condition, and fiber–substrate interaction. Highly aligned and spatially defined patterns can be fabricated by operating in the near-field electrospinning regime. Patterns of polymer brushes with two different chemistries effectively directed the assembly of gold nanoparticles and silver nanocubes. Nanopatterned brushes imparted strong confinement effects on the assembly of plasmonic nanoparticles and resulted in strong localization of electromagnetic fields leading to intense signals in surface-enhanced Raman spectroscopy. The scalability and simplicity of ESPNL hold great promise in patterning of a broad range of polymer thin films for different applications.

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The ability to encode unclonable information using low-cost materials and processes is of significant interest for anti-counterfeiting and information security applications. In this study, we present a versatile approach based on electrospraying of polymer solutions to generate randomly positioned complex features as a form of physically unclonable function (PUF). The key advantage of this approach is that readily available low-cost bulk polymeric materials can form small and complex features using a simple process. Polymers of varying composition and molecular weight, together with different solvents and electrospraying conditions, are systematically explored to construct the parameter space for PUFs of varying characteristics. Besides the randomness in the spatial positions and sizes of features, the key advantage of the presented approach is the ability to generate complex 3D shapes, which are very difficult, if not impossible to fabricate with the most advanced fabrication techniques. The inclusion of photoluminescent molecules establishes an additional security layer. The additive nature of operation enables multiplexing, i.e., deposition of multiple materials on the same substrate. The fabricated PUFs have an average uniformity of 0.533 and uniqueness of 0.495, which are highly close to an ideal value of 0.5. The authentication is effectively performed using a feature detection algorithm without the need for markers and precisely defined rotation angles, greatly relaxing constraints associated with the imaging. Direct application of PUFs on the label of goods and authentication via a handheld microscope demonstrate the practical utility of the presented approach.

This work reports scalable, low-cost, and simple fabrication of plasmonic heterostructures consisting of gold nanoparticles (NPs) of different sizes to generate intense hot-pots over large areas to serve as substrates for molecular sensing in SERS applications. Our approach involves assembly of massively-available colloidal gold NPs on substrates functionalized with end-grafted poly(ethylene glycol) (PEG) brushes without need for any sophisticated tools and post-modification of the particles and substrates. From real-time monitoring of the adsorption process by using a quartz crystal microbalance, we identified that the cyclic deposition of citrate-stabilized gold NPs on PEG brushes is an effective approach to modulate the kinetics of particle adsorption and greatly improves the surface coverage leading to reduced inter-particle distances. Cyclic deposition of NPs differing in size leads to placement of the small particles in close proximity of the large ones, yielding hot-spots as a consequence of the unique type of interaction between PEG chains and gold NPs. Assembly of heterostructures (60 nm+40 nm and 60 nm+20 nm) at optimized conditions resulted in strong SERS effects with enhancement factors as high as ≈2.0×10 and enabled detection of rhodamine 6G molecules in concentrations as low as 1 nm. The cyclic deposition of NPs also results in increase of the water contact angle without need for any post-modification of the substrate, resulting in ≈30 fold increase in the Raman intensity of aqueous molecules. The insights gained on the adsorption of gold NPs together with the simplicity of the presented approach show great promise for surface assembly of colloidal NPs for a broad range of applications.

Approaches are needed for the tailored assembly of plasmonic building blocks on the surface of substrates to synergistically enhance their properties. Here we demonstrate selective immobilization and assembly of gold nanorods (NRs) on substrates modified and patterned with end-grafted poly(ethylene glycol) (PEG) layers. The ligand exchange from the initial cetyltrimethylammonium bromide to sodium citrate was necessary for the immobilization of gold NRs onto PEG grafted substrates. Linear nanopatterns of PEG were fabricated using electrospun nanofibers as masks in oxygen plasma etching. The selective immobilization of citrate-stabilized gold NRs with a length of ∼50 nm and a width of 20 nm on the nanopatterned PEG layers led to linear and registered arrays of rods. The number of gold NRs per line depended on the width of the patterns and approached 1 when the width of the patterns was comparable to the length of the rods. The confinement of the binding regions led to a ∼3 fold increase in the number of gold NRs immobilized per unit area. The selective and dense immobilization of gold NRs on the nanoscale patterns of PEG resulted in spatially defined and strong surface-enhanced Raman scattering activity enabling detection of molecules at concentrations as low as 1 nM.