Natural Source-Based Graphene as Sensitising Agents for Air Quality Monitoring

One-Pot Synthesis of Nitrogen-Doped Graphene Quantum Dots and Their Applications in Bioimaging and Detecting Copper Ions in Living Cells

Two natural carbon sources, glutamic acid and tyrosine, were used to fabricate strong green emission nitrogen-doped graphene quantum dots (N-GQDs) with the one-pot pyrolysis method. The morphology of the prepared GQDs has been characterized by high-resolution transmission electron microscopy, showing a well-displayed crystalline structure with a lattice spacing of 0.262 nm. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to analyze the surface functional groups and elemental composition, suggesting that the N-GQDs have active carboxylic and amino functional groups. Meanwhile, photoluminescence and ultraviolet-visible (UV-vis) spectroscopy were used to evaluate the optical properties of GQDs; the prepared N-GQDs show an excitation-dependent fluorescence behavior with a maximum excitation/emission wavelength at 460/522 nm, respectively. N-GQDs showed good photostability and the fluorescence intensity quenched about 10% after irradiating 2800 s in the experiment of time kinetic analysis. The MTT assay was utilized to assess the viability of N-GQDs; good biocompatibility with a relatively high quantum yield of 12% demonstrated the potential for serving as bioimaging agents. Besides, the selectivity study on metal ions indicates that the N-GQDs could be used in Cu2+ detection. The linear range is from 0.1 to 10 μM with a limit of detection of 0.06 μM. Overall, these proposed N-GQDs with one-pot synthesis showed their promising potential in cell imaging and Cu2+ monitoring applications involved in the biological environment.

Carbon Nanostructure Embedded Novel Sensor Implementation for Detection of Aromatic Volatile Organic Compounds: An Organized Review

For field-like environmental gas monitoring and noninvasive illness diagnostics, effective sensing materials with exceptional sensing capabilities of sensitive, quick detection of volatile organic compounds (VOCs) are required. Carbon-based nanomaterials (CNMs), like CNTs, graphene, carbon dots (Cdots), and others, have recently drawn a lot of interest for their future application as an elevated-performance sensor for the detection of VOCs. CNMs have a greater potential for developing selective sensors that target VOCs due to their tunable chemical and surface properties. Additionally, the mechanical versatility of CNMs enables the development of novel gas sensors and places them ahead of other sensing materials for wearable applications. An overview of the latest advancements in the study of CNM-based sensors is given in this comprehensive organized review.

Nanomaterial Gas Sensors for Biosensing Applications: A Review

BACKGROUND

Nanomaterial is one of the most used materials for various gas sensing applications to detect toxic gases, human breath, and other specific gas sensing. One of the most important applications of nanomaterial based gas sensors is biosensing applications. In this review article, the gas sensors for biosensing are discussed on the basis of crystalline structure and different categories of nanomaterial.

METHODS

In this paper, firstly, rigorous efforts have been made to find out research questions by going through a structured and systematic survey of available peer reviewed high quality articles in this field. The papers related to nanomaterial based biosensors are then reviewed qualitatively to provide substantive findings from the recent developments in this field.

RESULTS

In this mini-review article, firstly, classifications of nanomaterial gas sensors have been presented on the basis of the crystalline structure of nanomaterial and different types of nanomaterial available for biosensing applications. Further, the gas sensors based on nanomaterial for biosensing applications are collected and reviewed in terms of their performance parameters such as sensing material used, target gas component, detection ranges (ppm-ppb), response time, operating temperature and method of detection, etc. The different nanomaterials possess slightly different sensing and morphological properties due to their structure; therefore, it can be said that a nanomaterial must be selected carefully for a particular application. The 1D nanomaterials show the best selectivity and sensitivity for gases available in low concentration ranges due to their miniaturised structure compared to 2D and 3D nanomaterials. However, these 2D and 3D nanomaterials also so good sensing properties compared to bulk semiconductor materials. The polymer and nanocomposites which are also discussed in this patent article have opened the door for future research and have great potential for new generation gas sensors for detecting biomolecules.

CONCLUSION

These nanomaterials extend great properties towards sensing the application of different gases for a lower concentration of particular gas particles. Nano polymer and nanocomposites have great potential to be used as gas sensors for the detection of biomolecules.

Recent Progress of Carbon Dots for Air Pollutants Detection and Photocatalytic Removal: Synthesis, Modifications, and Applications

Rapid industrialization has inevitably led to serious air pollution problems, thus it is urgent to develop detection and treatment technologies for qualitative and quantitative analysis and efficient removal of harmful pollutants. Notably, the employment of functional nanomaterials, in sensing and photocatalytic technologies, is promising to achieve efficient in situ detection and removal of gaseous pollutants. Among them, carbon dots (CDs) have shown significant potential due to their superior properties, such as controllable structures, easy surface modification, adjustable energy band, and excellent electron-transfer capacities. Moreover, their environmentally friendly preparation and efficient capture of solar energy provide a green option for sustainably addressing environmental problems. Here, recent advances in the rational design of CDs-based sensors and photocatalysts are highlighted. An overview of their applications in air pollutants detection and photocatalytic removal is presented, especially the diverse sensing and photocatalytic mechanisms of CDs are discussed. Finally, the challenges and perspectives are also provided, emphasizing the importance of synthetic mechanism investigation and rational design of structures.

Acetaldehyde Adsorption Characteristics of Ag/ACF Composite Prepared by Liquid Phase Plasma Method

Ag particles were precipitated on an activated carbon fiber (ACF) surface using a liquid phase plasma (LPP) method to prepare a Ag/ACF composite. The efficiency was examined by applying it as an adsorbent in the acetaldehyde adsorption experiment. Field-emission scanning electron microscopy and energy-dispersive X-ray spectrometry confirmed that Ag particles were distributed uniformly on an ACF surface. X-ray diffraction and X-ray photoelectron spectroscopy confirmed that metallic silver (Ag0) and silver oxide (Ag2O) precipitated simultaneously on the ACF surface. Although the precipitated Ag particles blocked the pores of the ACF, the specific surface area of the Ag/ACF composite material decreased, but the adsorption capacity of acetaldehyde was improved. The AA adsorption of ACF and Ag/ACF composites performed in this study was suitable for the Dose-Response model.

Fluorescent nanoparticles as tools in ecology and physiology

Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecular tracking. However, concerns over toxicity in early types of FNPs, such as cadmium-containing quantum dots (QDs), may have prevented wide adoption. Recent developments, especially in non-Cd-containing FNPs, have alleviated toxicity problems, facilitating the use of FNPs for addressing ecological, physiological and molecule-level processes in biological research. Standardised protocols from synthesis to application and interdisciplinary approaches are critical for establishing FNPs in the biologists' tool kit. Here, we present an introduction to FNPs, summarise their use in biological applications, and discuss technical issues such as data reliability and biocompatibility. We assess whether biological research can benefit from FNPs and suggest ways in which FNPs can be applied to answer questions in biology. We conclude that FNPs have a great potential for studying various biological processes, especially tracking, sensing and imaging in physiology and ecology.

New Bi2MoO6 nano-shapes toward ultrasensitive enzymeless glucose tracing: Synergetic effect of the Bi-Mo association

In a novel approach, an efficient non-enzymatic glucose sensor based on pure phase of aurivillius bismuth molybdate (BM or γ-Bi₂MoO₆) mixed metal oxides is reported. Three BM samples were synthesized, with/without l-cysteine (Cys) and dodecylamine (DDA) as additives, leading to different shapes: bullet (BM-C), confetti (BM-2Cys) and candy (BM-2DDA). The morphology and purity of the structures were confirmed by FE-SEM images and XRD. In order to investigate the sensor application, the samples were integrated on reduced graphene oxide and incorporated into simple and inexpensive glassy carbon electrode (GCE) without using any polyvinylpyrrolidone (PVP) or Nafion. To perform cyclic voltammetry experiments, all three biosensors were measured in PBS solution (pH = 7) in ±1.5 voltage range and 50 mV s^-1 scan rate. Glucose identification by the synthesized composites is an obvious sign of their high efficiency. According to chronoamperomograms, the best sensitivity of 3050 μA L mmol^-1 cm^-2 with linear range of 0.02-0.14 mmol L^-1, low detection limit (LOD) of 0.004 mmol L^-1 and the signal/noise equal to 3 was achieved by BM-2DDA/rGO/GCE biosensor and its speedy amperometric response is less than 5 s. This biosensor showed impressive selectivity, repeatability and reproducibility results besides it maintains its stability considerably in great percentage of 98.5% after eight weeks. Also it showed prolonged stability after 50 min.

Voltamperometric Sensors and Biosensors Based on Carbon Nanomaterials Used for Detecting Caffeic Acid-A Review

Caffeic acid is one of the most important hydroxycinnamic acids found in various foods and plant products. It has multiple beneficial effects in the human body such as antioxidant, antibacterial, anti-inflammatory, and antineoplastic. Since overdoses of caffeic acid may have negative effects, the quality and quantity of this acid in foods, pharmaceuticals, food supplements, etc., needs to be accurately determined. The present paper analyzes the most representative scientific papers published mostly in the last 10 years which describe the development and characterization of voltamperometric sensors or biosensors based on carbon nanomaterials and/or enzyme commonly used for detecting caffeic acid and a series of methods which may improve the performance characteristics of such sensors.

Supramolecular Sensing of a Chemical Warfare Agents Simulant by Functionalized Carbon Nanoparticles

Real-time sensing of chemical warfare agents by optical sensors is today a crucial target to prevent terroristic attacks by chemical weapons. Here the synthesis, characterization and detection properties of a new sensor, based on covalently functionalized carbon nanoparticles, are reported. This nanosensor exploits noncovalent interactions, in particular hydrogen bonds, to detect DMMP, a simulant of nerve agents. The nanostructure of the sensor combined with the supramolecular sensing approach leads to high binding constant affinity, high selectivity and the possibility to reuse the sensor.

Evanescent Wave Optical Trapping and Sensing on Polymer Optical Fibers for Ultra-Trace Detection of Glucose

Graphene sensitization of glucose-imprinted polymer (G-IP)-coated optical fiber has been introduced as a new biosensor for evanescent wave trapping on the polymer optical fiber to detect low-level glucose. The developed sensor operates based on the evanescent wave modulation principle. Full characterization via atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and N₂ adsorption/desorption of as-prepared G-IP-coated optical fibers was experimentally tested. Accordingly, related operational parameters such as roughness and diameter were optimized. Incorporating graphene into the G-IP not only steadily promotes the electron transport between the fiber surface and as-proposed G-IP but also significantly enhances the sensitivity by acting as a carrier for immobilizing G-IP with specific imprinted cavities. The sensor demonstrates a fast response time (5 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (10-100 nM) and a low limit of detection (LOD = 2.54 nM). Experimental results indicate that the developed sensor facilitates online monitoring and remote sensing of glucose in biological liquids and food samples.

Synthesis of Graphene Oxide Using Atmospheric Plasma for Prospective Biological Applications

INTRODUCTION

This paper presents a novel technique for the synthesis of graphene oxide (GO) with various surface features using high-density atmospheric plasma deposition. Furthermore, to investigate the use of hydrophobic, super-hydrophobic, and hydrophilic graphene in biological applications, we synthesized hydrophobic, super-hydrophobic, and hydrophilic graphene oxides by additional heat treatment and argon plasma treatment, respectively. In contrast to conventional fabrication procedures, reduced graphene oxide (rGO) formed under low pressure and high-temperature environment using a new synthesis method-developed and described in this study-offers a convenient deposition method on any kind surface with controlled wettability.

METHODS

High density at atmospheric plasma is used for the synthesis of rGO and GO and its biocompatibility based on various wetting properties was evaluated using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and the viability of cells in response to rGO and GO with various surface features was investigated. Structural integrity was characterized by Raman spectroscopy, FESEM and FE-TEM. Wettability was measured via contact angle method and confirmed with XPS analysis.

RESULTS

We found that GO coating with a hydrophilic feature is more biocompatible than other surfaces as observed in case of fibroblast cells. We have shown that wettability-controlled by GO deposition-influences biocompatibilities and antibacterial effect of biomaterial surfaces.

DISCUSSION

Measuring the contact angle, it is found that contact angle for hydrophobic is increased to 150.590 and reduced to 11.580 by heat and argon plasma treatment, respectively, from 75.880 that was initially in the case of hydrophobic surface. XPS analysis confirmed various oxygen-containing functional groups transforming as deposited hydrophobic surface into superhydrophobic and hydrophilic surface. Thus, we have proposed a new, direct, cost-effective, and highly productive method for the synthesis of rGO and GO-with various surface properties-for biological applications. Similarly, for the dental implant application, the Streptococcus mutans was used as an antibacterial effect and found that S. mutans grows slowly on hydrophilic surface. Thus, antibacterial effect was prominent on GO with hydrophilic surface.

Developed Low-Temperature Anionic 2H-MoS2/Au Sensing Layer Coated Optical Fiber Gas Sensor

Carboxyl-functionalized molybdenum disulfide (COOH-MoS₂) nanosheets were prepared through a facile low-temperature hydrothermal method. The phase transformation of metallic-1T to 2H-semiconductor COOH-MoS₂ nanosheets was conducted through introducing Au thin film on the unclad optical fiber as a sensing layer in a low temperature. The developed structure successfully refined the loss of the semiconducting properties and poor adhesion of COOH-MoS₂ on the unclad polymer optical fiber, which provided limited semiconductor potential as the sensing layers on the optical fiber surfaces. The sensing performance of the as-prepared structure was tested for quantitative detection of three different volatile organic carbons (VOCs) of ethanol, propanol, and methanol gases as well as cross-sensitivity to relative humidity. The operating principle was based on intensity variation of the evanescent wave in the sensing region. The response of the proposed sensing system shows maximum response and better linearity (R² = 0.999) to methanol at room temperature. Finally, the comparative experimental cross-sensitivity to relative humidity and methanol was also studied to evaluate the potential of sensing range.

Quantitative Understanding of Charge-Transfer-Mediated Fe3+ Sensing and Fast Photoresponse by N-Doped Graphene Quantum Dots Decorated on Plasmonic Au Nanoparticles

The formation of a heterostructure with plasmonic nanoparticles drastically alters the optoelectronic properties of graphene quantum dots (GQDs), resulting in exceptional properties. In the present work, we prepare nitrogen-doped GQDs decorated on gold nanoparticles (Au@N-GQDs) by a one-step green reduction method and study its extraordinary fluorescence and photoresponse characteristics. The as-prepared Au@N-GQDs show more than one order of magnitude enhancement in the fluorescence intensity as compared to the bare N-GQDs, which is attributed to hot electron generation and improved absorption in N-GQDs by local field enhancement and the modification of the edge functional groups. Because of the selective coordination to Fe³⁺ ions, the Au@N-GQDs exhibit extraordinary quenching of fluorescence, with ultrahigh sensitivity for the detection of Fe³⁺ (<1 nM). A new model for the charge-transfer dynamics is developed involving the Langmuir's law of adsorption to explain the unusual quenching, which strongly deviates from the known models of static/dynamic quenching. The proposed sensor is successfully implemented for the ultrasensitive detection of Fe³⁺ ions in human serum and Brahmaputra river water samples, representing its high potential applications in clinical as well as environmental diagnosis. Additionally, because of its high absorption in the UV-vis-NIR region and high charge density with long life excitons, the Au@N-GQDs are utilized as photodetectors with ∼10⁴ times faster response than that of bare N-GQDs. The Au@N-GQD-based photodetector possesses a high responsivity of ∼1.36 A/W and a remarkably high external quantum efficiency of ∼292.2%, which is much superior to the GQD-based photodetectors reported till date. The underlying mechanism of ultrafast photoresponse is ascribed to the transfer of hot electrons along with the tunneling of the electrons from Au NPs to N-GQDs as well as the defect reduction of N-GQDs by the incorporation of Au NPs. Without the use of any charge transporting layer, the outstanding performance of N-GQD-based plasmonic photodetector opens up unique opportunities for future high-speed optoelectronic devices.