Recent Progress in Stimuli-Responsive Antimicrobial Electrospun Nanofibers.

Electrospun nanofibrous membranes have garnered significant attention in antimicrobial applications, owing to their intricate three-dimensional network that confers an interconnected porous structure, high specific surface area, and tunable physicochemical properties, as well as their notable capacity for loading and sustained release of antimicrobial agents. Tailoring polymer or hybrid-based nanofibrous membranes with stimuli-responsive characteristics further enhances their versatility, enabling them to exhibit broad-spectrum or specific activity against diverse microorganisms. In this review, we elucidate the pivotal advancements achieved in the realm of stimuli-responsive antimicrobial electrospun nanofibers operating by light, temperature, pH, humidity, and electric field, among others. We provide a concise introduction to the strategies employed to design smart electrospun nanofibers with antimicrobial properties. The core section of our review spotlights recent progress in electrospun nanofiber-based systems triggered by single- and multi-stimuli. Within each stimulus category, we explore recent examples of nanofibers based on different polymers and antimicrobial agents. Finally, we delve into the constraints and future directions of stimuli-responsive nanofibrous materials, paving the way for their wider application spectrum and catalyzing progress toward industrial utilization.

Colorimetric Detection of SARS-CoV-2 Using Plasmonic Biosensors and Smartphones.

Low-cost, instrument-free colorimetric tests were developed to detect SARS-CoV-2 using plasmonic biosensors with Au nanoparticles functionalized with polyclonal antibodies (f-AuNPs). Intense color changes were noted with the naked eye owing to plasmon coupling when f-AuNPs form clusters on the virus, with high sensitivity and a detection limit of 0.28 PFU mL-1 (PFU stands for plaque-forming units) in human saliva. Plasmon coupling was corroborated with computer simulations using the finite-difference time-domain (FDTD) method. The strategies based on preparing plasmonic biosensors with f-AuNPs are robust to permit SARS-CoV-2 detection via dynamic light scattering and UV-vis spectroscopy without interference from other viruses, such as influenza and dengue viruses. The diagnosis was made with a smartphone app after processing the images collected from the smartphone camera, measuring the concentration of SARS-CoV-2. Both image processing and machine learning algorithms were found to provide COVID-19 diagnosis with 100% accuracy for saliva samples. In subsidiary experiments, we observed that the biosensor could be used to detect the virus in river waters without pretreatment. With fast responses and requiring small sample amounts (only 20 µL), these colorimetric tests can be deployed in any location within the point-of-care diagnosis paradigm for epidemiological control.

A Review on the Role and Performance of Cellulose Nanomaterials in Sensors.

Sensors and biosensors play a key role as an analytical tool for the rapid, reliable, and early diagnosis of human diseases. Such devices can also be employed for monitoring environmental pollutants in air and water in an expedited way. More recently, nanomaterials have been proposed as an alternative in sensor fabrication to achieve gains in performance in terms of sensitivity, selectivity, and portability. In this direction, the use of cellulose nanomaterials (CNM), such as cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), has experienced rapid growth in the fabrication of varied types of sensors. The advantageous properties are related to the supramolecular structures that form the distinct CNM, their biocompatibility, and highly reactive functional groups that enable surface functionalization. The CNM can be applied as hydrogels and xerogels, thin films, nanopapers and other structures interesting for sensor design. Besides, CNM can be combined with other materials (e.g., nanoparticles, enzymes, carbon nanomaterials, etc.) and varied substrates to advanced sensors and biosensors fabrication. This review explores recent advances on CNM and composites applied in the fabrication of optical, electrical, electrochemical, and piezoelectric sensors for detecting analytes ranging from environmental pollutants to human physiological parameters. Emphasis is given to how cellulose nanomaterials can contribute to enhance the performance of varied sensors as well as expand novel sensing applications, which could not be easily achieved using standard materials. Finally, challenges and future trends on the use of cellulose-based materials in sensors and biosensors are also discussed.

Detection of hydrogen peroxide (H2O2) using a colorimetric sensor based on cellulose nanowhiskers and silver nanoparticles.

Hydrogen peroxide (H2O2) is an important compound for several industrial sectors, but it becomes harmful to human health under high concentrations. Thus, the development of simple, low cost and fast analytical methods capable to detect and monitor H2O2 is fundamentally important. In the present study, we report a simple route for synthesizing silver nanoparticles (AgNPs) in the presence of a nanostructured polysaccharide (cellulose nanowhiskers) to produce a hybrid material, which was employed as a colorimetric probe for H2O2 detection. Our results revealed that AgNPs tend to experience catalytic decomposition when exposed to H2O2, causing a decrease of AgNPs absorption band at 410 nm in accordance with H2O2 concentration. This decrease was linearly dependent on H2O2 concentration (in the ranges 0.01-30 µM and 60-600 µM), yielding limits of detection of 0.014 µM and 112 µM, respectively. The easy-to-interpret H2O2 sensor also proved to be suitable for real samples analysis even in the presence of other interfering substances.

Conductive electrospun nanofibers containing cellulose nanowhiskers and reduced graphene oxide for the electrochemical detection of mercury(II).

Mercury is a heavy metal highly deleterious for the environment being associated to several diseases. Thus, novel and expedite techniques capable of detecting this heavy metal in water, even at trace levels, are highly sought for human and environmental safety purposes. Here we developed a novel electrochemical sensor for detecting mercury(II) using a green hybrid nanoarchitecture composed of reduced graphene oxide (rGO), cellulose nanowhiskers (CNW) and polyamide 6 (PA6) electrospun nanofibers. Scanning transmission electron microscopy (STEM), ultraviolet-visible (UV-VIS) absorption and Fourier transform infrared (FTIR) spectroscopies and termogravimetric analysis (TGA) were employed to elucidate the morphology and composition of CNW:rGO hybrid system. The hybrid composite proved to enhance charge transference properties, which was evaluated by cyclic voltammetry (CV) experiments. Due to the excellent electrical properties of graphene, the nanocomposite (PA6/CNW:rGO) was applied in the electrochemical detection of very low concentrations of mercury in water samples, improving the sensor sensibility. Moreover, the PA6/CNW/rGO electrode demonstrated stability, high selectivity, low detection limit and wide dynamic linear range for the detection of mercury(II).

Cellulose Whiskers Influence the Morphology and Antibacterial Properties of Silver Nanoparticles Composites.

Cellulose, the main component of plant cell walls, is a biopolymer widely used for industrial applications, including, food, paper and textile fabrication. More recently, hybrid materials composed of cellulose nanostructures and metal nanoparticles have been applied in diverse areas such as medical and pharmaceutical applications. In this work, cellulose-silver nanoparticles (AgNPs) hybrid material was synthesized and the influence of cellulose, employed as a stabilizer agent, was investigated. Specifically, cellulose whiskers (CCW) were extracted from commercial cotton fibers by acid hydrolysis route, while the AgNPs were synthesized by reducing silver salt using sodium citrate and/or sodium borohydride in the presence of CCW. The synthesized AgNPs/CCW nanocomposites were characterized in terms of morphology, chemical composition, surface charge and antibacterial properties. The varied synthetic routes generated AgNPs with different morphological characteristics in terms of size, shape and coalescence. The particularity of each sample resulted in distinct behaviors for the tested bacteria. Syntheses employing CCW resulted in AgNPs/CCW nanocomposites with controlled morphology and improved antibacterial effects against E. coli (Gram-negative) and S. aureus (Gram-positive), indicating CCW as a promising compound to be used in the syntheses of silver and other metal nanoparticles with controlled morphology and antibacterial properties.