Two-Dimensional (2D) materials in the detection of SARS-CoV-2.

The SARS-CoV-2 pandemic has resulted in a devastating effect on human health in the last three years. While tremendous effort has been devoted to the development of effective treatment and vaccines against SARS-CoV-2 and controlling the spread of it, collective health challenges have been encountered along with the concurrent serious economic impacts. Since the beginning of the pandemic, various detection methods like PCR-based methods, isothermal nucleic acid amplification-based (INAA) methods, serological methods or antibody tests, and evaluation of X-ray chest results have been exploited to diagnose SARS-CoV-2. PCR-based detection methods in these are considered gold standards in the current stage despite their drawbacks, including being high-cost and time-consuming procedures. Furthermore, the results obtained from the PCR tests are susceptible to sample collection methods and time. When the sample is not collected properly, obtaining a false result may be likely. The use of specialized lab equipment and the need for trained people for the experiments pose additional challenges in PCR-based testing methods. Also, similar problems are observed in other molecular and serological methods. Therefore, biosensor technologies are becoming advantageous with their quick response, high specificity and precision, and low-cost characteristics for SARS-CoV-2 detection. In this paper, we critically review the advances in the development of sensors for the detection of SARS-CoV-2 using two-dimensional (2D) materials. Since 2D materials including graphene and graphene-related materials, transition metal carbides, carbonitrides, and nitrides (MXenes), and transition metal dichalcogenides (TMDs) play key roles in the development of novel and high-performance electrochemical (bio)sensors, this review pushes the sensor technologies against SARS-CoV-2 detection forward and highlights the current trends. First, the basics of SARS-CoV-2 detection are described. Then the structure and the physicochemical properties of the 2D materials are explained, which is followed by the development of SARS-CoV-2 sensors by exploiting the exceptional properties of the 2D materials. This critical review covers most of the published papers in detail from the beginning of the outbreak.

Electrochemical detection of lactate produced by foodborne presumptive lactic acid bacteria.

The detection of lactate is an important indicator of the freshness, stability, and storage stability of products as well as the degree of fermentation in the food industry. In addition, it can be used as a diagnostic tool in patients' healthcare since it is known that the lactate level in blood increases in some pathological conditions. Thus, the determination of lactate level plays an important role in not only the food industry but also in health fields. As a result, biosensor technologies, which are quick, cheap, and easy to use, have become important for lactate detection. In the current study, amperometric lactate biosensors based on lactate oxidase immobilization (with Nafion 5% wt) were designed and the limit of detection, linear range, and sensitivity values were determined to be 31 µM, 50-350 µM, and 0.04 µA µM-1 cm-2, respectively. Then, it was used for the measurement of lactic acid that produced by six different and morphologically identified presumptive lactic acid bacteria (LAB) which are isolated from different naturally fermented cheese samples. The biosensors were then used to successfully perform lactate measurements within 3 min for each sample, even though a few of them were out of the limit of detection. Thus, electrochemical biosensors should be used as an alternative and quick solutions for the measurement of lactate metabolites rather than the traditional methods which require long working hours. This is the first study to use a biosensor to measure lactate produced by foodborne LAB in a real sample.

Ni/NiO/Ni-B/graphene heterostructure-modified electrodes and their electrochemical activities towards acetaminophen.

The surface of graphene was decorated with nickel/nickel oxide/nickel-boron particles to develop high-performance electrochemical sensors. The nanohybrid structures were prepared via a one-step reduction method under an oxygen-rich atmosphere to obtain an oxide phase besides metallic nickel nanoparticles. In addition, the use of NaBH4 as the reducing agent enabled simultaneous formation of Ni-B species on the graphene surface. XRD, XPS, TEM, Raman, and TGA analyses were implemented to characterize the samples. The XRD and XPS results revealed the presence of Ni/NiO/Ni-B on the surface of graphene. The electroanalytical performance of the nanocomposite was investigated against acetaminophen, which is an extensively exploited antipyretic and analgesic drug. The analytical performance results showed that the Ni/NiO/Ni-B/Gr-based sensors had a very wide working window between 10 µM and 2500 µM (y (µA) = 10.706x (mM) + 0.3151 (R2 = 0.9993)). The excellent storage stability, selectivity, and recovery results along with the high analytical performance make the novel Ni/NiO/Ni-B/Gr hybrid systems promising materials for the development of novel sensor platforms.

Synthesis and characterization of Ag+-decorated poly(glycidyl methacrylate) microparticle design for the adsorption of nucleic acids.

In this study, we report on the adsorption of RNA and DNA molecules by exploiting the high binding affinity of these nucleic acids to Ag+ ions anchored on magnetic poly(glycidyl methacrylate) (PGMA) microparticles. PGMA microparticles were synthesized and modified with nicotinamide which enabled to anchor Ag+ ions on the surface. The successful preparation of PGMA was confirmed by the presence of characteristic FTIR peaks. The ESR results showed that the incorporation of FeNi salt to the polymeric structure provided a magnetic property to the microparticles. The amount of nicotinamide and Ag+ ions used to modify the surface of the particles were found to be 1.79 wt% and 52.6 mg Ag/g microparticle, respectively. The high affinity of nucleic acids to Ag+ ions were exploited for the adsorption studies. At the optimum working conditions, the adsorption capacity of microparticles was found to be 40.1 and 11.48 mg nucleic acid/g microparticle for RNA and DNA, respectively. Our study indicated that the use of novel Ag+-decorated magnetic PGMA particles can be successfully employed as adsorbents for fast, easy, and cost-friendly adsorption of nucleic acids with high purity as well as high in quantity.

Aminolated and Thiolated PEG-Covered Gold Nanoparticles with High Stability and Antiaggregation for Lateral Flow Detection of Bisphenol A.

The few lateral flow assays (LFAs) established for detecting the endocrine disrupting chemical bisphenol A (BPA) have employed citrate-stabilized gold nanoparticles (GNPs), which have inevitable limitations and instability issues. To address these limitations, a more stable and more sensitive biosensor is developed by designing strategies for modifying the surfaces of GNPs with polyethylene glycol and then testing their effectiveness and sensitivity toward BPA in an LFA. Without the application of any enhancement strategy, this modified BPA LFA can achieve a naked-eye limit of detection (LOD) of 0.8 ng mL-1 , which is 12.5 times better than the LOD of regular BPA LFAs, and a quantitative LOD of 0.472 ng mL-1 . This modified LFA has the potential to be applied to the detection of various antigens.

Investigation of the Interaction between Nafion Ionomer and Surface Functionalized Carbon Black Using Both Ultrasmall Angle X-ray Scattering and Cryo-TEM.

In making a catalyst ink, the interactions between Nafion ionomer and catalyst support are the key factors that directly affect both ionic conductivity and electronic conductivity of the catalyst layer in a membrane electrode assembly. One of the major aims of this investigation is to understand the behavior of the catalyst support, Vulcan XC-72 (XC-72) aggregates, in the existence of the Nafion ionomer in a catalyst ink to fill the knowledge gap of the interaction of these components. The dispersion of catalyst ink depends not only on the solvent but also on the interaction of Nafion and carbon particles in the ink. The interaction of Nafion ionomer particles and XC-72 catalyst aggregates in liquid media was studied using ultrasmall-angle X-ray scattering and cryogenic TEM techniques. Carbon black (XC-72) and functionalized carbon black systems were introduced to study the interaction behaviors. A multiple curve fitting was used to extract the particle size and size distribution from scattering data. The results suggest that the particle size and size distribution of each system changed significantly in Nafion + XC-72 system, Nafion + NH2-XC72 system, and Nafion + SO3H-XC-72 system, which indicates that an interaction among these components (i.e., ionomer particles and XC-72 aggregates) exists. The cryogenic TEM, which allows for the observation the size of particles in a liquid, was used to validate the scattering results and shows excellent agreement.

Graphene-titanium dioxide nanocomposite based hypoxanthine sensor for assessment of meat freshness.

We report on the fabrication of a graphene/titanium dioxide nanocomposite (TiO2-G) and its use as an effective electrode material in an amperometric hypoxanthine (Hx) sensor for meat freshness evaluation. The nanocomposite was characterized by TEM, XRD, FTIR, XPS, TGA, BET, and CV using the redox couples [Fe(CN)6]-3/-4 and [Ru(NH3)6]+3/+2 respectively. The TiO2/G nanocomposite offered a favorable microenvironment for direct electrochemistry of xanthine oxidase (XOD). The fabricated Nafion/XOD/TiO2-G/GCE sensor exhibited excellent electro catalytic activity towards Hx with linear range of 20µM to 512µM, limit of detection of 9.5µM, and sensitivity of 4.1nA/µM. In addition, the biosensor also demonstrated strong anti-interference properties in the presence of uric acid (UA), ascorbic acid (AA) and glucose. Minimal interference of xanthine (Xn) was observed at ~7%. Moreover, the biosensor showed good repeatability (4.3% RSD) and reproducibility (3.8% RSD). The reported biosensor was tested towards the detection of Hx in pork tenderloins stored at room temperature for seven days. There was a good correlation (r=0.9795) between biosensor response and measurements obtained by a standard enzymatic colorimetric method. The TiO2-G nanocomposite is therefore an effective electrode material to be used in electrochemical biosensors to assess the freshness of meat.

Novel CeO2-CuO-decorated enzymatic lactate biosensors operating in low oxygen environments.

The detection of the lactate level in blood plays a key role in diagnosis of some pathological conditions including cardiogenic or endotoxic shocks, respiratory failure, liver disease, systemic disorders, renal failure, and tissue hypoxia. Here, we described for the first time the use of a novel mixed metal oxide solution system to address the oxygen dependence challenge of first generation amperometric lactate biosensors. The biosensors were constructed using ceria-copper oxide (CeO2-CuO) mixed metal oxide nanoparticles for lactate oxidase immobilization and as electrode material. The oxygen storage capacity (OSC, 492 µmol-O2/g) of these metal oxides has the potential to reduce the oxygen dependency, and thus eliminate false results originated from the fluctuations in the oxygen concentration. In an effort to compare the performance of our novel sensor design, ceria nanoparticle decorated lactate sensors were also constructed. The enzymatic activity of the sensors were tested in oxygen-rich and oxygen-lean solutions. Our results showed that the OSC of the electrode material has a big influence on the activity of the biosensors in oxygen-lean environments. While the CeO2 containing biosensor showed an almost 21% decrease in the sensitivity in a O2-depleted solution, the CeO2-CuO containing electrode, with a higher OSC value, experienced no drop in sensitivity when moving from oxygen-rich to oxygen-lean conditions. The CeO2-CuO decorated sensor showed a high sensitivity (89.3 ± 4 µA mM(-1) cm(-2)), a wide linear range up to 0.6 mM, and a low limit of detection of 3.3 µM. The analytical response of the CeO2-CuO decorated sensors was studied by detecting lactate in human serum with good selectivity and reliability. The results revealed that CeO2-CuO containing sensors are promising candidates for continuous lactate detection.

Graphene based enzymatic bioelectrodes and biofuel cells.

The excellent electrical conductivity and ease of functionalization make graphene a promising material for use in enzymatic bioelectrodes and biofuel cells. Enzyme based biofuel cells have attracted substantial interest due to their potential to harvest energy from organic materials. This review provides an overview of the functional properties and applications of graphene in the construction of biofuel cells as alternative power sources. The review covers the current state-of-the-art research in graphene based nanomaterials (physicochemical properties and surface functionalities), the role of these parameters in enhancing electron transfer, the stability and activity of immobilized enzymes, and how enhanced power density can be achieved. Specific examples of enzyme immobilization methods, enzyme loading, stability and function on graphene, functionalized graphene and graphene based nanocomposite materials are discussed along with their advantages and limitations. Finally, a critical evaluation of the performance of graphene based enzymatic biofuel cells, the current status, challenges and future research needs are provided.