Mechanochemical Activation of Silicone for Large-Scale Fabrication of Anti-Biofouling Liquid-like Surfaces.

Large-scale preparation of liquid-like coatings with perfect transparency via solventless and room-temperature processes using low-cost and biocompatible materials is of tremendous interest for a broad range of applications. Here, we present a mechanochemical activation strategy for solventless grafting of poly(dimethylsiloxane) (PDMS) onto glass, silicon wafers, and ceramics. Activation is achieved via ball milling PDMS without using any solvents or additives prior to application. Ball milling results in chain scission and generation of free radicals, allowing room-temperature grafting at durations ≤1 h. The deposition of ball-milled PDMS can be facilitated by brushing or drop-casting, enabling large-scale applications. The resulting surfaces facilitate the sliding of droplets at angles <20° for liquids with surface tension ranging from 22 to 73 mN/m. An important application for public health is generating anti-biofouling coatings on sanitary ware. For example, PDMS-grafted surfaces prepared on a regular-size toilet bowl exhibit a 105-fold decrease in the attachment of bacteria from urine. These findings highlight the significant potential of mechanochemical processes for the practical preparation of liquid-like surfaces.

Disintegration and Machine-Learning-Assisted Identification of Bacteria on Antimicrobial and Plasmonic Ag-CuxO Nanostructures.

Bacteria cause many common infections and are the culprit of many outbreaks throughout history that have led to the loss of millions of lives. Contamination of inanimate surfaces in clinics, the food chain, and the environment poses a significant threat to humanity, with the increase in antimicrobial resistance exacerbating the issue. Two key strategies to address this issue are antibacterial coatings and effective detection of bacterial contamination. In this study, we present the formation of antimicrobial and plasmonic surfaces based on Ag-CuxO nanostructures using green synthesis methods and low-cost paper substrates. The fabricated nanostructured surfaces exhibit excellent bactericidal efficiency and high surface-enhanced Raman scattering (SERS) activity. The CuxO ensures outstanding and rapid antibacterial activity within 30 min, with a rate of >99.99% against typical Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. The plasmonic Ag nanoparticles facilitate the electromagnetic enhancement of Raman scattering and enables rapid, label-free, and sensitive identification of bacteria at a concentration as low as 103 cfu/mL. The detection of different strains at this low concentration is attributed to the leaching of the intracellular components of the bacteria caused by the nanostructures. Additionally, SERS is coupled with machine learning algorithms for the automated identification of bacteria with an accuracy that exceeds 96%. The proposed strategy achieves effective prevention of bacterial contamination and accurate identification of the bacteria on the same material platform by using sustainable and low-cost materials.

Self-Healing of Biocompatible Superhydrophobic Coatings: The Interplay of the Size and Loading of Particles.

The broad application potential of superhydrophobic coatings is limited by the usage of environment-threatening materials and poor durability. The nature-inspired design and fabrication of self-healing coatings is a promising approach for addressing these issues. In this study, we report a fluorine-free and biocompatible superhydrophobic coating that can be thermally healed after abrasion. The coating is composed of silica nanoparticles and carnauba wax, and the self-healing is based on surface enrichment of wax in analogy to the wax secretion in plant leaves. The coating not only exhibits fast self-healing, just in 1 min under moderate heating, but also displays increased water repellency and thermal stability after healing. The rapid self-healing ability of the coating is attributed to the relatively low melting point of carnauba wax and its migration to the surface of the hydrophilic silica nanoparticles. The dependence of self-healing on the size and loading of particles provides insights into the process. Furthermore, the coating exhibits high levels of biocompatibility where the viability of fibroblast L929 cells was ∼90%. The presented approach and insights provide valuable guidelines in the design and fabrication of self-healing superhydrophobic coatings.

One-step Green Fabrication of Antimicrobial Surfaces via In Situ Growth of Copper Oxide Nanoparticles.

Microorganisms such as pathogenic bacteria, fungi, and viruses pose a serious threat to human health and society. Surfaces are one of the major pathways for the transmission of infectious diseases. Therefore, imparting antipathogenic properties to these surfaces is significant. Here, we present a rapid, one-step approach for practical fabrication of antimicrobial and antifungal surfaces using an eco-friendly and low-cost reducing agent, the extract of Cedrus libani. Copper oxide nanoparticles were grown in situ on the surface of print paper and fabric in the presence of the copper salt and extract, without the use of any additional chemicals. The morphology and composition of the grown nanoparticles were characterized using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. The analysis revealed that the grown particles consist of mainly spherical CuO nanoparticles with an average size of ∼14 nm and its clusters with an average size of ∼700 nm. The in situ growth process enables strong bonding of the nanoparticles to the surface, resulting in enhanced durability against wear and tear. Moreover, the fabricated surface shows excellent growth inhibition ability and bactericidal activity against both gram-negative and gram-positive bacteria, Escherichia coli and Staphylococcus aureus, as well as antifungal activity against Candida albicans, a common pathogenic fungus. The ability to grow copper oxide nanoparticles on different surfaces paves the way for a range of applications in wound dressings, masks, and protective medical equipment.

Blood repellent superhydrophobic surfaces constructed from nanoparticle-free and biocompatible materials.

Durable and environment friendly superhydrophobic surfaces are needed for a set of important applications. Biomedical applications, in particular, impose stringent requirements on the biocompatibility of the materials used in the fabrication of superhydrophobic surfaces. In this study, we demonstrate the fabrication of mechanically durable superhydrophobic surfaces via an in-situ structuring strategy starting from natural carnauba wax and biocompatible polydimethylsiloxane (PDMS) materials. The transfer of the structure of the paper to a free-standing PDMS film provided the microscale structure. On top of this structured surface, the wax was spray-coated, initially resulting in a relatively homogeneous film with limited liquid repellence. The key in achieving superhydrophobicity was rubbing the surface for in-situ generation of a finely textured wax coating with a water contact angle of 169° and a sliding angle of 3°. The hierarchically structured surface exhibits mechanical robustness as demonstrated with water impact and linear abrasion tests. We finally demonstrate repellence of the surfaces against a range of blood products including platelet suspension, erythrocyte suspension, fresh plasma, and whole blood.

Chemical Funneling of Colloidal Gold Nanoparticles on Printed Arrays of End-Grafted Polymers for Plasmonic Applications.

Spatially defined assembly of colloidal metallic nanoparticles is necessary for fabrication of plasmonic devices. In this study, we demonstrate high-resolution additive jet printing of end-functional polymers to serve as templates for directed self-assembly of nanoparticles into architectures with substantial plasmonic activity. The intriguing aspect of this work is the ability to form patterns of end-grafted poly(ethylene glycol) through printing on a hydrophobic layer that consists of fluoroalkylsilanes. The simultaneous dewetting of the underlying hydrophobic layer together with grafting of the printed polymer during thermal annealing enables fabrication of spatially defined binding sites for assembly of nanoparticles. The employment of electrohydrodynamic jet printing and aqueous inks together with reduction of the feature size during thermal annealing are critically important in achieving high chemical contrast patterns as small as ∼250 nm. Gold nanospheres of varying diameters selectively bind and assemble into nanostructures with reduced interparticle distances on the hydrophilic patterns of poly(ethylene glycol) surrounded with a hydrophobic background. The resulting plasmonic arrays exhibit intense and pattern-specific signals in surface-enhanced Raman scattering (SERS) spectroscopy. The localized seed-mediated growth of metallic nanostructures over the patterned gold nanospheres presents further routes for expanding the composition of the plasmonic arrays. A representative application in SERS-based surface encoding is demonstrated through large-area patterning of plasmonic structures and multiplex deposition of taggant molecules, all enabled by printing.

Signatures of a quantum diffusion limited hydrogen atom tunneling reaction.

We are studying the details of hydrogen atom (H atom) quantum diffusion in highly enriched parahydrogen (pH2) quantum solids doped with chemical species in an effort to better understand H atom transport and reactivity under these conditions. In this work we present kinetic studies of the 193 nm photo-induced chemistry of methanol (CH3OH) isolated in solid pH2. Short-term irradiation of CH3OH at 1.8 K readily produces CH2O and CO which we detect using FTIR spectroscopy. The in situ photochemistry also produces CH3O and H atoms which we can infer from the post-photolysis reaction kinetics that display significant CH2OH growth. The CH2OH growth kinetics indicate at least three separate tunneling reactions contribute; (i) reactions of photoproduced CH3O with the pH2 host, (ii) H atom reactions with the CH2O photofragment, and (iii) long-range migration of H atoms and reaction with CH3OH. We assign the rapid CH2OH growth to the following CH3O + H2 → CH3OH + H → CH2OH + H2 two-step sequential tunneling mechanism by conducting analogous kinetic measurements using deuterated methanol (CD3OD). By performing photolysis experiments at 1.8 and 4.3 K, we show the post-photolysis reaction kinetics change qualitatively over this small temperature range. We use this qualitative change in the reaction kinetics with temperature to identify reactions that are quantum diffusion limited. While these results are specific to the conditions that exist in pH2 quantum solids, they have direct implications on the analogous low temperature H atom tunneling reactions that occur on metal surfaces and on interstellar grains.

Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen.

Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.8 to 4.3 K temperature range. Upon short-term in situ irradiation the NO readily undergoes photolysis to yield HNO, NOH, NH, NH3, H2O, and H atoms. We map the postphotolysis reactions of mobile H atoms with NO and document first-order growth in HNO and NOH reaction products for up to 5 h after photolysis. We perform three experiments at 4.3 K and one at 1.8 K to permit the temperature dependence of the reaction kinetics to be quantified. We observe Arrhenius-type behavior with a pre-exponential factor of A = 0.036(2) min(-1) and Ea = 2.39(1) cm(-1). This is in sharp contrast to previous H atom reactions we have studied in solid pH2 that display definitively non-Arrhenius behavior. The contrasting temperature dependence measured for the H + NO reaction is likely related to the details of H atom quantum diffusion in solid pH2 and deserves further study.

Fourier transform infrared studies of ammonia photochemistry in solid parahydrogen.

We present 193 nm in situ photochemical studies of NH3 isolated in solid parahydrogen (pH2) at 1.8 K using Fourier Transform Infrared (FTIR) spectroscopy. By recording FTIR spectra during and after irradiation we are able to identify and assign a number of rovibrational transitions to ortho-NH2(X(2)B1) and NH(X(3)Σ(-)). Spectroscopic analysis shows that these two radical species rotate freely in solid pH2 and that effects of the unpaired electron spin remain essentially unchanged from the gas phase. We provide detailed mechanistic studies that show the nascent ortho-NH2 photoproduct is rapidly cooled within the pH2 matrix to the ground vibrational and rotational state before (1) subsequent photodissociation or (2) tunneling-driven reaction (k(tun) = 1.88(17) min(-1)) with the pH2 host to produce ortho-NH3 in a defect site. Once the ortho-NH3 is produced in this defect site it slowly converts (k(conv) = 7.72(51) × 10(-3) min(-1)) back to a single substitution site even at 1.8 K. We demonstrate the in situ photolysis of NH3 can be utilized to generate NH doped pH2 solids that are relatively stable at low temperature. However, the ortho-NH2 + pH2 → ortho-NH3 + H back reaction substantially limits the sequential two-photon conversion of NH3 to NH. These studies also reveal that extended photolysis of the NH3/pH2 system results in the generation of high concentrations of orthohydrogen that must result from repeated cycles of photodissociation and NH2 back reaction within the pH2 host.

Matrix isolation spectroscopy and nuclear spin conversion of NH3 and ND3 in solid parahydrogen.

We present matrix isolation infrared absorption spectra of NH3 and ND3 trapped in solid parahydrogen (pH2) at temperatures around 1.8 K. We used the relatively slow nuclear spin conversion (NSC) of NH3 and ND3 in freshly deposited pH2 samples as a tool to assign the sparse vibration-inversion-rotation (VIR) spectra of NH3 in the regions of the ν2, ν4, 2ν4, ν1, and ν3 bands and ND3 in the regions of the ν2, ν4, ν1, and ν3 fundamentals. Partial assignments are also presented for various combination bands of NH3. Detailed analysis of the ν2 bands of NH3 and ND3 indicates that both isotopomers are nearly free rotors; that the vibrational energy is blue-shifted by 1-2%; and that the rotational constants and inversion tunneling splitting are 91-94% and 67-75%, respectively, of the gas-phase values. The line shapes of the VIR absorptions are narrow (0.2-0.4 cm(-1)) for upper states that cannot rotationally relax and broad (>1 cm(-1)) for upper states that can rotationally relax. We report and assign a number of NH3-induced infrared absorption features of the pH2 host near 4150 cm(-1), along with a cooperative transition that involves simultaneous vibrational excitation of a pH2 molecule and rotation-inversion excitation of NH3. The NSCs of NH3 and ND3 were found to follow first-order kinetics with rate constants at 1.8 K of k = 1.88(16) × 10(-3) s(-1) and k = 1.08(8) × 10(-3) s(-1), respectively. These measured rate constants are compared to previous measurements for NH3 in an Ar matrix and with the rate constants measured for other dopant molecules isolated in solid pH2.

Photodissociation of N-methylformamide isolated in solid parahydrogen.

We report FTIR studies of the 193 nm photodecomposition of N-methylformamide (NMF) isolated in solid parahydrogen (pH(2)) matrices at 1.9 K. By studying the detailed photokinetics we can distinguish between primary and secondary photoproducts. We observe single exponential decay of the NMF precursor upon irradiation and identify three competing primary dissociation channels: HCO + NHCH(3); H + CONHCH(3); and CO + CH(3)NH(2) with branching ratios of 0.46(7):0.032(8):0.51(6), respectively. Two of the primary photoproducts (NHCH(3) and CONHCH(3)) are observed for the first time using IR spectroscopy and assigned via ab initio calculations of the vibrational frequencies and intensities of these radicals. The dominant radical formation channel HCO + NHCH(3) is consistent with efficient C-N peptide bond fission at this wavelength and escape of the nascent radical pair from the pH(2) solvent cage. The significant branching 0.51(6) measured for the molecular channel CO + CH(3)NH(2) is unexpected and raises important questions about the details of the in situ photochemistry. Starting from the NMF precursor, we observe and characterize spectroscopically a wide variety of secondary photoproducts including CH(2)NH, HCN, HNC, HNCO, CH(3)NCO, CH(4), and NH(3).