Surfaces, Volume 5, Issue 1 (March 2022) – 15 articles

Detection of explosives is vital for protection and criminal investigations, and developing novel explosives’ sensors stands at the forefront of the analytical and forensic chemistry endeavors. Due to the presence of terminal nitro groups that can be electrochemically reduced, nitroaromatic compounds (NACs) have been an analytical target for explosives’ electrochemical sensors. Various electrode materials have been used to detect NACs in solution, including glassy carbon electrodes (GCE), platinum (Pt), and gold (Au) electrodes, by tracking the reversible oxidation/reduction properties of the NACs on these electrodes. Here, we show that the reduction of dinitrobenzene (DNB) on oxide-free silicon (Si–H) electrodes is irreversible with two reduction peaks that disappear within the successive voltammetric scanning. AFM imaging showed the formation of a polymeric film whose thickness scales up with the DNB concentration. This suggest that Si–H surfaces can serve as DNB sensors and possibly other explosive substances. Cyclic voltammetry (CV) measurements showed that the limit of detection (LoD) on Si–H is one order of magnitude lower than that obtained on GCE. In addition, EIS measurements showed that the LoD of DNB on Si–H is two orders of magnitude lower than the CV method. The fact that a Si–H surface can be used to track the presence of DNB makes it a suitable surface to be implemented as a sensing platform. To translate this concept into a sensor, however, it would require engineering and fabrication prospect to be compatible with the current semiconductor technologies. Full article

The main goal of this work is to provide a general description of the negative photoconductivity effect observed in Ag/AgO films grown by the spray-pyrolysis technique. X-ray diffractograms display hybrid films with high texturized AgO and metallic Ag phases. Scanning electron microscopy images show small Ag particles on the surface. Due to its surface nature, X-ray photoelectron spectroscopy revealed the predominance of the metallic character of Ag 3d spectra as compared to Ag²⁺. Negative photoconductivity with photoresponse in the order of seconds is observed under several wavelengths of excitation. We found that the amplitude of the negative photoresponse is strongly dependent on the optical absorbance and enhanced by surface plasmon resonance. The low-cost technique employed and the special features regarding negative photoconductivity provide an exciting platform for developing optical-electronic devices with low power consumption. Full article

Silver (Ag) nanoparticles were successfully prepared by using the in-liquid pulsed plasma technique. This method is based on a low voltage, pulsed spark discharge in a dielectric liquid. We explore the effect of the protecting ligands, specifically Cetyl Trimethylammonium Bromide (CTAB), Polyvinylpyrrolidone (PVP), and Sodium n-Dodecyl Sulphate (SDS), used as surfactant materials to prevent nanoparticle aggregation. The X-Ray Diffraction (XRD) patterns of the samples confirm the face-centered cubic crystalline structure of Ag nanoparticles with the presence of Ag₂O skin. Scanning Transmission Electron Microscopy (STEM) reveals that spherically shaped Ag nanoparticles with a diameter of 2.2 ± 0.8 nm were synthesised in aqueous solution with PVP surfactant. Similarly, silver nanoparticles with a peak diameter of 1.9 ± 0.4 nm were obtained with SDS surfactant. A broad size distribution was found in the case of CTAB surfactant. Full article

The severe acute respiratory syndrome originated by the new coronavirus (SARS-CoV-2) that emerged in late 2019, known to be a highly transmissible and pathogenic disease, has caused the COVID-19 global pandemic outbreak. Thus, diagnostic devices that help epidemiological public safety measures to reduce undetected cases and isolation of infected patients, in addition to significantly help to control the population’s immune response to vaccine, are required. To address the negative issues of clinical research, we developed a Diagnostic on a Chip platform based on a disposable electrochemical biosensor containing laser-induced graphene and a protein (SARS-CoV-2 specific antigen) for the detection of SARS-CoV-2 antibodies. The biosensors were produced via direct laser writing using a CO₂ infrared laser cutting machine on commercial polyimide sheets. The presence of specific antibodies reacting with the protein and the K₃[Fe(CN)₆] redox indicator produced characteristic and concentration-dependent electrochemical signals, with mean current values of 9.6757 and 8.1812 µA for reactive and non-reactive samples, respectively, proving the effectiveness of testing in clinical samples of serum from patients. Thus, the platform is being expanded to be measured in a portable microcontrolled potentiostat to be applied as a fast and reliable monitoring and mapping tool, aiming to assess the vaccinal immune response of the population. Full article

Nanoscale surface topographies mediated with biochemical cues influence the differentiation of stem cells into different lineages. This research focuses on the adsorption behavior of bone morphogenetic protein (BMP-2) on nanopatterned gold substrates, which can aid in the differentiation of bone and cartilage tissue constructs. The gold substrates were patterned as flat, pillar, linear grating, and linear-grating deep based, and the BMP-2 conformation in end-on configuration was studied over 20 ns. The linear grating deep substrate pattern had the highest adsorption energy of around 125 kJ/mol and maintained its radius of gyration of 18.5 Å, indicating a stable adsorption behavior. Secondary structures including α-helix and β-sheet displayed no denaturation, and thus, the bioavailability of the BMP-2, for the deep linear-grating pattern. Ramachandran plots for the wrist and knuckle epitopes indicated no steric hindrances and provided binding sites to type I and type II receptors. The deep linear-grating substrate had the highest number of contacts (88 atoms) within 5 Å of the gold substrate, indicating its preferred nanoscale pattern choice among the substrates considered. This research provides new insights into the atomistic adsorption of BMP-2 on nanoscale topographies of a gold substrate, with applications in biomedical implants and regenerative medicine. Full article

Pesticides are unavoidable in agriculture to protect crops from pests and insects. Organophosphates (OPs) are a class of pesticides that are more harmful because of the irreversible inhibition reaction with acetylcholinesterase enzyme, thereby posing serious health hazards in human beings. In the present work, a sensitive and selective immuno-sensing platform is developed using gold inter-digitized electrodes (Au-IDEs) as substrates, integrated with a microfluidic platform having the microfluidic well capacity of 10 µL. Au-IDE having digit width of 10 µm and gap length of 5 µm was used in this study. The surface morphological analysis by field-effect scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) revealed the direct information regarding the modification of Au-IDEs with anti-parathion (Anti-PT) antibodies. In SEM analysis, it was seen that the Au-IDE surface was smooth in contrast to the Anti-PT modified surface, which is supported by the AFM studies showing the surface roughness of ~2.02 nm for Au-IDE surface and ~15.86 nm for Anti-PT modified surface. Further, Fourier transform infra-red (FTIR) spectroscopic analysis confirms the immobilization of Anti-PT by the bond vibrations upon the successive modification of Au-IDE with -OH groups, amine groups after modifying with APTES, and the amide bond formation after incubation in Anti-PT antibody. Electrochemical impedance spectroscopy (EIS) was carried out for the electrochemical characterization and for testing the sensing performances of the fabricated electrode. The developed immuno-sensor provided a linear range of detection from 0.5 pg/L^–1 µg/L, with a limit of detection (LoD) of 0.66 ng/L and sensitivity of 4.1 MΩ/ngL⁻¹/cm². The sensor response was also examined with real samples (pomegranate juice) with good accuracy, exhibiting a shelf life of 25 days. The miniaturized sensing platform, along with its better sensing performance, has huge potential to be integrated into portable electronics, leading to suitable field applications of pesticide screening devices. Full article

Diamond offers great potential for use as a thermal spreader in various applications, including power electronics and radio-frequency (RF) applications. However, to be used as an efficient thermal spreader, the atomically smooth surface of the diamond is critical to be bonded with chips. Herein, a polishing technique for a 2-inch diameter wafer-scale bulk polycrystalline diamond substrate is proposed. In this work, 350 $\mathsf{\mu }$m thick polycrystalline diamond is grown by the microwave plasma-assisted chemical vapor deposition (MPACVD) technique on a Si substrate at a growth rate of 8 µm/h. Thereafter, a three-step polishing process was applied to achieve an atomically smooth surface, consisting of grinding using a diamond slurry with an iron plate, ICP etching using the SF₆ gas, and final mechanical polishing using a resin-bonded diamond wheel. Surface roughness of diamond characterized by atomic force microscopy showed the significantly reduced from 900 nm to 0.3 nm. Hence, this study provide the practical methods for obtaining atomically smooth diamond films suitable for thermal management in various areas including power electronics and RF devices. Full article

Mechanochemistry initiated the reaction of hydrogen-terminated porous silicon (H/por-Si) powder with arginine. Samples were analyzed using Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), zeta potential, scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Arginine, which was physisorbed onto the surface of por-Si, blue-shifted the peak PL intensity from ~630 nm for the H/por-Si to ~565 nm for arginine-coated por-Si. Grinding for 4 h reduced >80% of the initially 2–45 µm particles to <500 nm, but was observed to quench the PL. With appropriate rinsing and centrifugation, particles in the 100 nm range were isolated. Rinsing ground powder with water was required to remove the unreacted arginine. Without rinsing, excess arginine induced the aggregation of passivated particles. However, water reacted with the freshly ground por-Si powder producing H₂. A zeta potential of +42 mV was measured for arginine-terminated por-Si particles dispersed in deionized water. This positive value was consistent with termination such that NH₂ groups extended away from the surface. Furthermore, this result was confirmed by FTIR spectra, which suggested that arginine was bound to silicon through the formation of a covalent Si–O bond. Full article

Here, we discuss the effect of In₂O₃ nanoparticles on the reduced graphene oxide (rGO) gas-sensing potentialities. In₂O₃ nanoparticles were prepared with the polymer precursors method, while the nanocomposites were prepared by mixing an In₂O₃ nanoparticle suspension with an rGO suspension in different proportions. The gas-sensing performance of our materials was tested by exposing our materials to known concentrations of a target toxic gas in a dry airflow. Our results demonstrate that In₂O₃ nanoparticles enhance the rGO sensitivity for strong oxidizing species such as O₃ and NO₂, while a negative effect on its sensitivity for NH₃ sensing is observed. Furthermore, our measurements towards H₂S suggest that the concentration of In₂O₃ nanoparticles can induce an uncommon transition from p-type to n-type semiconductor nature when rGO–In₂O₃ nanocomposites operate at temperatures close to 160 °C. Full article

The corrosion module of COMSOL Multiphysics 5.6® software was employed to simulate the influence of the corrosion products and calcareous deposits on the damage tolerance of a Thermally Sprayed Aluminium coating (TSA) in a simulated marine immersion environment. The capacity of TSA to polarise the steel was evaluated by modelling 5%, 50%, and 90% of the sample uncoated’s area (i.e., substrate exposed). Additionally, the consumption of the sacrificial coating was simulated by Arbitrary Lagrangian-Eulerian (ALE) for the geometry of the experimental system. The parameters used in the model were obtained from polarisation curves and Electrochemical Impedance Spectroscopy (EIS) available in the literature. The results are in good agreement with measurements of Open Circuit Potential (OCP) and Corrosion Rate (CR) from experiments reported in previous studies. The model predicted the sacrificial protection offered by TSA as a function of the exposed steel surfaces, indicating the ability of TSA coating to polarise steel even with up to 90% damage. Furthermore, a 90–70% reduction in the corrosion rate of TSA was calculated with the simultaneous influence of corrosion products and deposits formed after 20 days of exposure to artificial seawater at room temperature. Full article

Background: Cystic echinococcosis (CE) is a highly prevalent parasitic disease resulting from the hydatid cyst of Echinococcus granulosus. It is also described as a zoonotic disease and considered a neglected tropical infection. Aim: This study assessed the antiparasitic activity of silver nanoparticles (AgNPs), against E. granulosus infection in BALB/c mice. Methods: The green synthesis of AgNPs was accomplished using Zizyphus spina-christi leaves. AgNPs were orally administered to BALB/c mice for acute short-term toxicity evaluation, in doses of 50 mg, 100 mg, 200 mg, and 300 mg/kg, and observations for toxic signs were carried out at 24, 48 h, and 14 days, continuously. Moreover, a total of 20 mice divided into two groups were intraperitoneally administered with 1500 viable protoscoleces for secondary hydatidosis infection. Results: The results showed that AgNPs did not induce any adverse effects or signs and no death, in either group of mice. The histopathological findings in the liver, kidneys, and intestine of the mice administered with AgNPs revealed mild histological effects compared with the control ones. The treated-infected mice showed a change in the appearance of the liver hydatid cysts from hyaline to milky cloudy compared with the untreated infected mice. Conclusion: Biosynthesized AgNPs showed anti-hydatic effects and are suggested as anti-echinococcal cyst treatment. Full article

With the growing awareness for the need of sustainable environment, the importance of synthesizing and the application of green nanoparticles has gained special focus. Among various metal nanoparticles, silver nanoparticles (AgNPs) have gain significant attention. AgNPs are synthesized conventionally by physical and chemical methods using chemicals such as reducing agents, which are hazardous to environment due to their toxic properties, provoking a serious concern to create and develop environment friendly methods. Thus, biological alternatives are emerging to fill gaps, such as green syntheses that use biological molecules taken from plant sources in the form of extracts, which have shown to be superior to chemical and physical approaches. These biological molecules derived from plants are assembled in a highly regulated manner to make them suitable for metal nanoparticle synthesis. The current review outlines the wide plant diversity that may be used to prepare a rapid and single-step procedure with a green path over the traditional ones, as well as their antifungal activity. Full article

Plastics are ubiquitous in our society and are used in many industries, such as packaging, electronics, the automotive industry, and medical and health sectors, and plastic waste is among the types of waste of higher environmental concern. The increase in the amount of plastic waste produced daily has increased environmental problems, such as pollution by micro-plastics, contamination of the food chain, biodiversity degradation and economic losses. The selective and efficient conversion of plastic waste for applications in environmental remediation, such as by obtaining composites, is a strategy of the scientific community for the recovery of plastic waste. The development of polymeric supports for efficient, sustainable, and low-cost heterogeneous catalysts for the treatment of organic/inorganic contaminants is highly desirable yet still a great challenge; this will be the main focus of this work. Common commercial polymers, like polystyrene, polypropylene, polyethylene therephthalate, polyethylene and polyvinyl chloride, are addressed herein, as are their main physicochemical properties, such as molecular mass, degree of crystallinity and others. Additionally, we discuss the environmental and health risks of plastic debris and the main recycling technologies as well as their issues and environmental impact. The use of nanomaterials raises concerns about toxicity and reinforces the need to apply supports; this means that the recycling of plastics in this way may tackle two issues. Finally, we dissert about the advances in turning plastic waste into support for nanocatalysts for environmental remediation, mainly metal and metal oxide nanoparticles. Full article

Two-dimensional materials have secured a novel area of research in material science after the emergence of graphene. Now, a new family of 2D material-MXene is gradually growing and making itsmark in this field of study. MXenes since 2011 have been synthesized and experimented on in several ways.The HF treatment although successful poses some serious problems that gradually propelled the ideas of new synthesis methods. This review of the literature covers the major breakthroughs of MXene from the year of its discovery to recent endeavors, highlighting how the synthesis mechanisms have been developed over the years and also the importance of good characterization of data. Results and properties of this class of materials arealso briefly discussed alongwith recent advance in applications. Full article