Three fabrication methods for metal-doped laser-induced graphene (LIG) are compared resulting in stable nanoparticles embedded within LIG. Variable nanoparticle size, distribution, antibacterial and electrochemical properties were observed.
The activity of antimicrobial peptides (AMPs) that contain a large proportion of histidine residues (pK(a) ∼ 6) depends on the physiological pH environment. Advantages of these AMPs include high activity in slightly acidic areas of the human body and relatively low toxicity in other areas. Also, many AMPs are highly active in a multivalent form, but this often increases toxicity. Here we designed pH dependent amphiphilic compounds consisting of multiple ultrashort histidine lipopeptides on a triazacyclophane scaffold, which showed high activity toward Aspergillus fumigatus and Cryptococcus neoformans at acidic pH, yet remained nontoxic. In vivo, treatment with a myristic acid conjugated trivalent histidine-histidine dipeptide resulted in 55% survival of mice (n = 9) in an otherwise lethal murine lung Aspergillus infection model. Fungal burden was assessed and showed completely sterile lungs in 80% of the mice (n = 5). At pH 5.5 and 7.5, differing peptide-membrane interactions and peptide nanostructures were observed. This study underscores the potential of unique AMPs to become the next generation of clinical antimicrobial therapy.
Effective electrode materials are required to eliminate high concentrations of toxic Cr(VI) contaminants from industrial effluents. Kynol activated carbon cloth (CC) is a commercial, high-surface-area, and mechanically stable carbon material that can be used for adsorption and/or electrochemical reduction processes. Here, the mechanisms of Cr(VI) adsorption and reduction by CC in the absence or presence of an applied potential were investigated using X-ray photoelectron spectroscopy, scanning electron microscopy/energy-dispersive spectroscopy, Raman, cyclic voltammetry, and chronocoulometry experiments. The pH change close to the CC electrode during the electrochemical process was monitored using a solution containing Bromo-cresol green as an indicator of the solution pH. The role of surface hydroxyl groups (−OH) on CC in (1) the adsorption of Cr(VI) and (2) the reduction of Cr(VI) to Cr(III) was elucidated. As found, redox reactions between Cr(VI) and surface −OH groups on CC led to the chemical reduction of Cr(VI) to Cr(III). Without an applied potential, the chemical reduction of Cr(VI) to Cr(III) was limited by the number of surface −OH groups on CC. With an applied potential of −0.6 V on CC, the Cr(VI) adsorption/reduction was 2.1 times faster and 1.5 times higher than that without an applied potential after 7 h. With an applied potential, the CC adsorbed Cr(VI) and chemically and electrochemically reduced Cr(VI) to Cr(III). This work indicates that for Kynol CC, the electrochemical reduction process is superior to adsorption when optimizing an electrochemical system to achieve a faster and higher reduction of Cr(VI) to Cr(III).
Laser-induced graphene (LIG) is a platform material for numerous applications. Despite its ease in synthesis, LIG's potential for use in some applications is limited by its robustness on substrates. Here, using a simple infiltration method, we develop LIG composites (LIGCs) with physical properties that are engineered on various substrate materials. The physical properties include surface properties such as superhydrophobicity and antibiofouling; the LIGCs are useful in antibacterial applications and Joule-heating applications and as resistive memory device substrates.
Laser-induced graphene (LIG)-polymer composite materials might be potentially useful in many applications, including water purification technology. For example, water treatment membranes with antibacterial and antibiofouling surfaces that could utilize the electrically conductive property of the surface are envisioned. Polymer composites consisting of LIG fabricated on porous surfaces such as water treatment membranes are mechanically robust, and the solute rejection properties of the membrane can also be tailored. With a goal of assessing the future large-scale fabrication of this membrane configuration, here we established a simple method of coating and cross-linking poly(vinyl alcohol) (PVA) on LIG membrane supports. Ultrafiltration membranes with sizes of ≤20 cm × ≤30 cm were used as substrates to make conductive LIG porous surfaces using a 10.6 μm CO2 pulsed laser, after which 2.5% PVA/glutaraldehyde was coated and immediately cross-linked at 175 °C using a heat gun. The 2.5% LIG-PVA composite membranes showed good surface conductivity, mechanical–thermal stability, and high permeability ranging from 900 to 1300 LMH bar–1. Permeate water with 0.60 NTU was obtained using feedwater containing sludge from a membrane bioreactor, and 10- and 25-fold decreases in COD and BOD, respectively, were observed. An enhanced removal of bacteria was observed at 2.5 V during filtration. This work demonstrates a method to scale up LIG composite membranes, a crucial step that is necessary in determining their commercial potential in water technology applications.
Biofouling on surfaces in contact with sea- or brackish water can severely impact the function of devices like reverse osmosis modules. Single species laboratory assays are frequently used to test new low fouling materials. The choice of bacterial strain is guided by the natural population present in the application of interest and decides on the predictive power of the results. In this work, the analysis of the bacterial community present in brackish water from Mashabei Sadeh, Israel was performed and Rheinheimera sp. was detected as a prominent microorganism. A Rheinheimera strain was selected to establish a short-term accumulation assay to probe initial bacterial attachment as well as biofilm growth to determine the biofilm-inhibiting properties of coatings. Both assays were applied to model coatings, and technically relevant polymers including laser-induced graphene. This strategy might be applied to other water sources to better predict the fouling propensity of new coatings.
Early and reliable detection of an infectious viral disease is critical to accurately monitor outbreaks and to provide individuals and health care professionals the opportunity to treat patients at the early stages of a disease. The accuracy of such information is essential to define appropriate actions to protect the population and to reduce the likelihood of a possible pandemic. Here, we show the fabrication of freestanding laser-induced graphene (FLIG) flakes that are highly sensitive sensors for high-fidelity viral detection. As a case study, we show the detection of SARS-CoV-2 spike proteins. FLIG flakes are nonembedded porous graphene foams ca. 30 μm thick that are generated using laser irradiation of polyimide and can be fabricated in seconds at a low cost. Larger pieces of FLIG were cut forming a cantilever, used as suspended resonators, and characterized for their electromechanics behavior. Thermomechanical analysis showed FLIG stiffness comparable to other porous materials such as boron nitride foam, and electrostatic excitation showed amplification of the vibrations at frequencies in the range of several kilo-hertz. We developed a protocol for aqueous biological sensing by characterizing the wetting dynamic response of the sensor in buffer solution and in water, and devices functionalized with COVID-19 antibodies specifically detected SARS-CoV-2 spike protein binding, while not detecting other viruses such as MS2. The FLIG sensors showed a clear mass-dependent frequency response shift of ∼1 Hz/pg, and low nanomolar concentrations could be detected. Ultimately, the sensors demonstrated an outstanding limit of detection of 2.63 pg, which is equivalent to as few as ∼5000 SARS-CoV-2 viruses. Thus, the FLIG platform technology can be utilized to develop portable and highly accurate sensors, including biological applications where the fast and reliable protein or infectious particle detection is critical.
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