From diagnosis of life-threatening diseases to detection of biological agents in warfare or terrorist attacks, biosensors are becoming a critical part of modern life. Many recent biosensors have incorporated carbon nanotubes as sensing elements, while a growing body of work has begun to do the same with the emergent nanomaterial graphene, which is effectively an unrolled nanotube. With this widespread use of carbon nanomaterials in biosensors, it is timely to assess how this trend is contributing to the science and applications of biosensors. This Review explores these issues by presenting the latest advances in electrochemical, electrical, and optical biosensors that use carbon nanotubes and graphene, and critically compares the performance of the two carbon allotropes in this application. Ultimately, carbon nanomaterials, although still to meet key challenges in fabrication and handling, have a bright future as biosensors.

Carbon Nanomaterials in Biosensors: Should You Use Nanotubes or Graphene?

Publisher Summary The electroactivity of nucleic acids was discovered several years ago. It was shown that at mercury electrodes, adenine and cytosine were reduced in ssDNA while guanine produced an anodic signal due to the oxidation of guanine reduction product. The DNA signals at mercury electrodes are highly sensitive to changes in DNA structure due to DNA denaturation and renaturation, as well as to minor structural changes resulting from DNA premelting and DNA damage. The changes in DNA structure are reflected not only by the DNA faradaic responses but also by non-faradaic signals due to adsorption/desorption of DNA. Several interesting principles have been used in the development of the DNA sensors—such as amplified electrochemical analysis, investigation of charge transport, and tracing of changes in conformation of DNA. The s ensors for DNA hybridization and DNA damage lead the field of the electrochemistry of nucleic acids. The chapter briefly summarizes some properties of the elimination voltammetry with linear scan (EVLS) method. Oscillographic polarography, at controlled alternating current, was used in the electrochemical analysis of nucleic acids.

Electrochemistry of nucleic acids.

Nanotoxicology and in vitro studies: the need of the hour.

Mass spectrometry (MS) and nuclear magnetic resonance (NMR) have evolved as the most common techniques in metabolomics studies, and each brings its own advantages and limitations. Unlike MS spectrometry, NMR spectroscopy is quantitative and does not require extra steps for sample preparation, such as separation or derivatization. Although the sensitivity of NMR spectroscopy has increased enormously and improvements continue to emerge steadily, this remains a weak point for NMR compared with MS. MS-based metabolomics provides an excellent approach that can offer a combined sensitivity and selectivity platform for metabolomics research. Moreover, different MS approaches such as different ionization techniques and mass analyzer technology can be used in order to increase the number of metabolites that can be detected. In this chapter, the advantages, limitations, strengths, and weaknesses of NMR and MS as tools applicable to metabolomics research are highlighted.

The strengths and weaknesses of NMR spectroscopy and mass spectrometry with particular focus on metabolomics research.

Toxicological studies on silver nanoparticles: challenges and opportunities in assessment, monitoring and imaging

Status of biomolecular recognition using electrochemical techniques.

Quercetin, the most abundant flavonoid in dietary fruits and vegetables, acts as antioxidant or prooxidant depending on the environmental conditions. The antioxidant behavior is believed to involve initial oxidative steps with subsequent changes in the flavonoid skeleton, which ultimately alters the chemical and biological properties of these molecules. Although the mechanism is still unclear, it has been suggested to be strongly influenced by the surrounding media. This paper reports the oxidation of quercetin by air oxygen or autoxidation, bulk electrolysis, mushroom tyrosinase, and azodiisobutyronitrile (AIBN). The central aim of this study is to systematically examine how the similarities and differences of quercetin transformation can be affected by the nature of the oxidation systems. Using a range of molecular and structural characterization techniques (UV−vis, LC-MS, GC-MS, and NMR), the oxidation of quercetin was found to result in the generation of somewhat similar metabolites including depside,...

Comparative Analysis of Quercetin Oxidation by Electrochemical, Enzymatic, Autoxidation, and Free Radical Generation Techniques: A Mechanistic Study

Electrochemical degradation of quercetin: Isolation and structural elucidation of the degradation products

The discovery of fullerenes in 1985 has ushered in an explosive growth in the applications of engineered nanomaterials and consumer products. Nanotechnology and engineered nanomaterials (ENMs) are being incorporated into a range of commercial products such as consumer electronics, cosmetics, imaging and sensors. Nanomaterials offer new possibilities for the development of novel sensing and monitoring technologies. Nanosensors can be classified under two main categories: (i) Nanotechnology-enabled sensors or sensors that are themselves nanoscale or have nanoscale materials or components, and (ii) Nanoproperty-quantifiable sensors or sensors that are used to measure nanoscale properties. The first category can eventually result in lower material cost, reduced weight and energy consumption. The second category can enhance our understanding of the potential toxic effects of emerging pollutants from nanomaterials including fullerenes, dendrimers, and carbon nanotubes. Despite the enormous literatures and reviews on Category I sensors, there are few sensors to measure nanoscale properties or sensors belonging to Category II. This class of nanosensors is an area of critical interest to nanotoxicology, detection and risk assessment, as well as for monitoring of environmental and/or biological exposure. This article discusses emerging fields of nanotoxicology and nanomonitoring including the challenges of characterizing engineered nanomaterials and the potentials of combining existing analytical techniques with conventional cytotoxicity methods. Two case studies are provided for development of Category II nanosensors for fullerene nanoparticles and quantum dots. One highlights the uniqueness of a portable, dissolved oxygen electrochemical sensor arrays capable of detecting the ENMs as well as provide rapid nanotoxicological information. This review has shown that addressing the complex and critical issues surrounding the environmental transformation and toxicity of ENMs must be accompanied by the creation of new approaches or further developments of existing instrumentation.

Sensors as tools for quantitation, nanotoxicity and nanomonitoring assessment of engineered nanomaterials

Quercetin is a naturally occurring flavonoid that is known to form complexes with metals; a process that reduces the environmental availability of toxic metals such as chromium. We hereby report the first evidence of the removal of Cr(VI) from environmental samples using quercetin (QCR) and two synthetic derivatives: namely quercetin pentaphosphate (QPP) and quercetin sulfonic acid (QSA). We successfully synthesized both QPP and QSA using simple procedures while characterizing them with UV-vis spectroscopy, H1-NMR, 13C NMR, 31P-NMR, and LC-MS techniques. The solubility of QPP was found to be 840 mg/mL and aqueous solutions of both QPP and QSA were stable for over a period of 1 year. Quercetin and these derivatives were subsequently utilized for the reduction of Cr(VI) and QCR was found to have a higher reduction efficiency of 99.8% (30 min), followed by QPP/palladium nanoparticles mixture (PdNPs) at 96.5% (60 min), and finally QSA/PdNPs mixtures at 91.7% (60 min). PdNPs catalyst increased the efficiency b...

Ailing Zhou

Papers

Status of biomolecular recognition using electrochemical techniques.

Comparative Analysis of Quercetin Oxidation by Electrochemical, Enzymatic, Autoxidation, and Free Radical Generation Techniques: A Mechanistic Study

Electrochemical degradation of quercetin: Isolation and structural elucidation of the degradation products

Sensors as tools for quantitation, nanotoxicity and nanomonitoring assessment of engineered nanomaterials

Reduction of Hexavalent Chromium Using Naturally-Derived Flavonoids