Molecularly engineered graphene surfaces for sensing applications: A review

Graphene is scientifically and commercially important because of its unique molecular structure which is monoatomic in thickness, rigorously two-dimensional and highly conjugated. Consequently, graphene exhibits exceptional electrical, optical, thermal and mechanical properties. Herein, we critically discuss the surface modification of graphene, the specific advantages that graphene-based materials can provide over other materials in sensor research and their related chemical and electrochemical properties. Furthermore, we describe the latest developments in the use of these materials for sensing technology, including chemical sensors and biosensors and their applications in security, environmental safety and diseases detection and diagnosis.     

Label-free colorimetric aptasensor for sensitive detection of ochratoxin A utilizing hybridization chain reaction

The combination of high selectivity of aptamer with the peroxidase-mimicking property of DNAzyme has presented considerable opportunities for designing colorimetric aptasensor for detection of ochratoxin A (OTA). The activities of both aptamer (as biorecognition element) and DNAzyme (as signal amplification element) are blocked via base pairing in the hairpin structure. Hybridization chain reaction (HCR) between two hairpin DNAs was employed to further improve the sensitivity of this method. The presence of OTA triggers the opening of the hairpin structure and the beginning of HCR, which results in the release of many DNAzyme, and generates enhanced colorimetric signals, which is correlated to the amounts of OTA with linear range between 0.01 to 0.32 nM, and the limit of detection is 0.01 nM under optimal conditions. OTA in yellow rice wine and wheat flour samples was also detected using this method. We demonstrate that a new colorimetric method for the detection of OTA has been established, which is simple, easy to conduct, label-free, sensitive, high throughput, and cost-saving.     

On the DFT Ground State of Crystalline Bromine and Iodine

We report on an erroneous ground state within common density functional theory (DFT) methods for the solid elements bromine and iodine. Phonon computations at the GGA level for both molecular crystals yield imaginary vibrational modes, erroneously indicating dynamic instability—that fact alone could easily pass as a computational artefact, but these imaginary modes lead to energetically more favorable and dynamically stable structures, made up of infinite monoatomic chains. In contrast, meta‐GGA and hybrid functionals yield the correct energetic order for bromine, while for iodine, most global hybrids do not improve the GGA result significantly. The qualitatively correct answer, in both cases, is given by the long‐range corrected hybrid LC‐ωPBE, the Minnesota functionals M06L and M06, and by periodic Hartree–Fock and MP2 theory. This poor performance of economic DFT functionals should be kept in mind, for example, during global structure optimizations of systems with significant contributions from halogen bonds.     

Monomer relative affinity in a copolymer

This paper analyzes data from experiments on simple polymer chains. It measures the extent to which a particular monomer prefers to link with another of the same type. To analyze the data, it derives the likelihood function for a two‐state Markov model in which only the number in each state, but not the order, is observed. This technology is applied to a data set on which experimenters mixed lactic‐glycolic monomers with a known proportion of a contaminant consisting of an extra lactic acid. The resulting copolymers were subjected to matrix‐assisted laser desorption ionization mass spectrometry. This records the number of copolymers at each atomic weight, which can be associated with a given length of copolymer and number of contaminant monomers. Analysis of the data shows that the proportion of contaminant monomers exceeded the proportion of experimentally induced contaminant. Maximum likelihood estimates using the data show that lactic‐glycolic monomers show a positive affinity for the contaminant. Copyright © 2015 John Wiley & Sons, Ltd.     

High Sensitive Electrochemiluminescence Biosensor Based on Ru(phen)32+-loaded Double Strand DNA as Signal Tags use to Detect DNA Methyltransferase Activity

DNA methyltransferase (DNA MTase) can act as biomarker for many diseases and it is important to develop some new methods for sensitive detection of DNA MTase. In this work, a highly efficient electrochemiluminescence (ECL) sensor had been designed for detection of DNA MTase based on Ru(phen)₃²⁺ loaded double strand DNA (dsDNA- Ru(phen)₃²⁺) as signal tags. Ru(phen)₃²⁺ had been efficiently embed in the dsDNA produced through a simple hybridization chain reaction. First, a hairpin probe was designed, which can be specifically recognized by Dam MTase and modified with -SH at one end. It was modified on the surface of gold electrode by -SH as an immobilization probe (IP). This IP will be methylated in the present of Dam MTase and digested by DpnI following. Results in the release of capture probe (CP) which remains on the surface of gold electrode. The CP can hybridize with the single stand part of the dsDNA- Ru(phen)₃²⁺ and make the immobilization of ECL tags on the electrode surface, which results in a strong ECL signals detected. However, without the effect of Dam MTase, the hairpin structure of IP remains stable and cannot capture signal tags, and can only detecte weak ECL signals. The biosensor can detect the activity of Dam MTase in the concentration range of 0.01 U/mL to 20 U/mL with the ECL intensity and the logarithm of the concentration have a linear relationship, and the detection limit is calculated to be 7.6 mU/mL. The developed sensor has the ability to specifically detect Dam MTase, which can be differentiated from other types of DNA MTase. In addition, the designed method has good applicability to detect Dam MTase activity in serum samples and been applied to detect its inhibitor with high efficiency.     

对称季铵碱的烷基链长度对草酸电还原反应的影响

研究了四种不同烷基链长度的对称季铵碱对草酸电还原制备乙醛酸反应的影响。线性扫描测试考察了添加剂对铅电极上阴极反应的影响,结果表明对称季铵碱在电极表面的吸附对析氢反应的抑制程度大于其对草酸电还原反应的抑制程度,且随着对称季铵碱中烷基链长度的增加,添加剂抑制析氢反应效果更明显。计时安培法的结果证明添加剂可影响草酸向电极表面的扩散,随着对称季铵碱中烷基链长度的增加,草酸的扩散系数呈现出先增加后减小的趋势。恒流电解实验结果表明,添加剂能有效提高草酸电还原反应的电流效率,且提高效果随对称季铵碱所含烷基链长度的增加而增强。因此,添加剂的吸附对阴极表面析氢反应的抑制作用是草酸电还原反应电流效率提高的主要原因。本研究表明,四丁基氢氧化铵为添加剂时,草酸还原为乙醛酸的电流效率最高。