Papers by Author: Zhong Cao

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Authors: Ting Deng, Zhong Cao, Guo Li Shen
Abstract: An electrochemical impedance biosensor was proposed for the detection of small molecule biotin based on the plasma-polymerized films (PPF) and the bioaffinity difference between an analyte (biotin) and an analogue compound (HABA) in binding avidin. Avidin formed a metastable complex with 2-[(4-hydroxyphenyl)azo]benzoic acid (HABA) immobilized on the electrode surface. When the sensor contacts a sample solution containing biotin, the avidin was released from the sensor surface to form a more stable complex with biotin in solution. The impedance spectra change recorded is proportional to the desorbed mass of avidin, and there is a clear mathematic relationship between the impedance change and the biotin concentration. The proposed electrochemical impedance bioaffinity sensor has nice response to biotin in the range of 4.8×10-9–5.6×10-4 M. The sensor could be regenerated under very mild conditions simply by reimmersion of the sensor into a biotin solution to desorb the surplus avidin.
Authors: Shu Zhen Tan, Pu Ni Zeng, Zhong Cao, Jiao Yun Xia, Wei Li
Abstract: A novel technique to covalently immobilize indicator dyes with terminal amino groups for preparing optical sensors is investigated. Au nanoparticles are used as bridges and carriers for anchoring indicator dyes on the surface of a quartz glass slide. 1-Aminopyrene (AP) was employed as an example of indicator dyes and covalently immobilized onto the outmost surface of the glass slide. First, the glass slide was functionalized by (3-mercaptopropyl) trimethoxysilane (MPS) to form a thiol-terminated self-assembled monolayer, where Au nanoparticles were strongly anchored via covalent link. Then, 16-mercaptohexadecanoic acid (MHDA) was self-assembled to bring carboxylic groups onto the surfaces of Au nanoparticles. A further activation by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) converted the carboxylic group into succinimide ester. Finally, the active succinimide ester was reacted with 1-aminopyrene (AP). Thus, AP was covalently immobilized to the glass slide and an AP-immobilized sensor was obtained. The resulting sensor was used to determine rutin based on fluorescence quenching. It showed a linear response toward rutin (R) from 5.0 × 10-7 to 6.0 × 10-4 mol L-1 with a detection limit of 2.0× 10-7 mol L-1. This AP-immobilized sensor has very satisfactory reproducibility, reversibility, rapid response and no dye-leaching.
Authors: Yu Cao, Zhong Cao, Jiao Yun Xia, Ju Lan Zeng, Li Xian Sun
Abstract: Four calixarene supramolecular compounds, RCT, PCT, MRCT, and TBCA as active materials, were immobilized on gold substrates of quartz crystal microbalance (QCM) sensors by using L-cysteine self-assembled monolayer (SAM) as a linker. The RCT immobilized QCM sensor possessed the best response characteristics for methanol molecule when the assembling concentration of RCT reached 1.0 mg/mL. The frequency shift response value of the RCT immobilized QCM sensor was in direct proportion to the concentration of methanol vapor with a range of 0 ~ 6000 ppm. Comparing with a gas chromatography, the proposed QCM sensor could be well used for the determination of methanol vapor with a recovery rate of 98.01 ~ 103.9 %, and the two methods showed a well consistent examination result. Also, the sensor possessed good reproducibility and stability, showing that the RCT immobilized QCM sensor can be applied for the detection of the methanol vapor of atmospheric polutants in our living environment.
Authors: Rui Fen Zou, Zhong Cao, Ju Lan Zeng, Yun Lin Dai, Li Xian Sun
Abstract: The adsorption characteristics of four calixarene supramolecular compounds, like RCT, PCT, MRCT, and TBCA, as coating materials of quartz crystal microbalance sensors responding to isopropanol vapor have been investigated in this paper. The results showed that the RCT was the best coating material for isopropanol vapor when the coating mass reached 20.41 μg. The frequency shift of RCT coated QCM and the concentration of isopropanol vapor had a good linear relationship and sensitivity. Comparing with the gas chromatography, the QCM sensor could be well used for the determination of isopropanol vapor with a recovery rate of 95.22~108.1 %, and the two methods showed a well consistent examination result. Also, the sensor possessed good reversibility, reproducibility and stability, indicating that the RCT coated QCM sensor can be applied for the detection of the atmospheric polutant of isopropanol vapor in practice. The mechanism of the calixarene derivative for recognition of the isopropanol molecule has been preliminarily discussed.
Authors: Ji Shan Li, Rong Hua Yang, Shu Long, Ting Zhou, Jing Fang Xiong, Zhong Cao
Abstract: In this paper, a piezoelectric quartz crystal (PQC) sensor has been developed with a coating material of N, N, N’, N’-tetrakis (2-hydroxyethyl) ethylenediamine (THEED). The active compound was selected from fifty-one adsorptive coating materials and was the most efficient one for sensing of carbon dioxide gas. The coated PQC sensor possessed an excellent linear response range of 0.3738 ~ 31.85% with a sensitivity of 53.81 Hz/% to CO2 gas after coating with 91.62 μg of THEED. The detection limit for CO2 gas could reach 100.0 ppm. The sensor also possessed good reproducibility and stability. There were no significant interferences from other gases dissolved in transformer oil such as carbon monoxide, hydrogen, methane, ethane, ethylene, and ethyne. The THEED coated PQC sensor has been successfully applied to the determination of CO2 samples dissolved in transformer oil, showing its promising application for generation set’s safety evaluation in power industry.
Authors: Jing Ling Hu, Ting Zhou, Yun Fei Zhang, Zhe Wang, Dong Mei Luo, Zhong Cao
Abstract: Using four types of calixarene derivatives (RCT, PCT, MRCT, TBCA) as coating materials, quartz crystal microbalance (QCM) sensors have been examined for detection of toxic formaldehyde gas indoors. The results showed that PCT was the most efficient adsorption coating material for host-guest recognition of formaldehyde molecule, when the coating mass was 43.93 μg. The PCT based QCM sensor possessed a linear response range of 109 ~ 2721 ppm formaldehyde gas. In comparison with gas chromatography method, the QCM sensor had a recovery of 97.98~104.59 % with a good reversibility, stability and reproducibility, showing that the PCT based QCM sensor can be well used for the determination of trace formaldehyde in the living environment.
Authors: Zhong Cao, Shu Long, Xiang Shi, Ju Lan Zeng, Li Xian Sun, Rong Hua Yang
Abstract: The electrochemical behaviors and sensing application of 100nm-gold plate electrode based on 6-amino-1-hexanethiol (6-AHT) self-assembled monolayer (SAM) have been investigated in this paper. The 6-AHT assembled nano gold plate electrode exhibited a nice linear potential performance of responding to Hg2+ in the range of 1.0×10-8—1.0×10-6 mol/L with a slope of 42.57 mV/-pC (25°C) in Tris-HCl buffer solution (pH=5.0). No obvious interferences were observed from Na+, K+, Ba2+, Mg2+, Ca2+, and Cr3+. The detection limit can be evaluated to 8.0×10-9 mol/L. In addition, the electrode possessed good stability and reproducibility with a recovery rate of 96.50-103.67%, indicating that it can be used for the determination of Hg2+ content in environmental waste water samples. The sensing mechanism of 6-AHT monolayer has also been discussed by the formation of coordination structure between amino groups of the thiol molecules and the mercury ions.
Authors: Zhong Cao, Zhong Liang Xiao, Yun Lin Dai, Masao Kamahori, Maki Shimoda
Abstract: An extended gate field effect transistor (EGFET) sensing chip has been constructed by using one gold plate electrode for molecule recognition and FET part for signal transduction. By using a 70.7mV DC voltage onto a Ag/AgCl reference electrode, the electrical characteristics of immobilization of the oligonucleotide probe of P1 and hybridization with the target single strand DNA of P2 on the EGFET sensing chip were examined in detail. The electrical signals on the change of a threshold voltage (VT) shift at a constant ID (3000μA) in VG-ID characteristic were obtained, and the VT shift value due to hybridization was calculated to be 12 mV, which may be attributed to the decreased negative charges after hybridization occurred at the gate surface. The surface density of hybridized dsDNA on gold surface of the FET was evaluated to be about 1 × 1012 molecules/cm2, indicating that the EGFET was a promising sensing element for biochip.
Authors: Man Le Zhang, Jing Lin He, Chun Lan Xu, Long Guan Zhu, Yun Fei Zheng, Yi Zhou, Ling Zhang, Dong Mei Luo, Zhong Cao
Abstract: A simple and reliable method for electrochemical determination of nitrite based on Gd doped nano titanium dioxide (Gd-nano-TiO2) modified gold electrode was well developed in this paper. Using cyclic voltammetry, the modified electrode shows electrocatalytic activity for oxidation of nitrite in 0.10 mol×L-1 sulfuric acid solution (pH=0.70). The catalytic peak current was found to be linear with nitrite concentration in the range of 2.0´10-6 ~ 2.0´10-4 mol×L-1, with a detection limit of 1.1´10-6 mol×L-1 (S/N=3). Compared with spectrophotometry, the Gd-nano-TiO2 modified Au electrode could be used for the determination of nitrate in the ham sausage samples with a satisfactory recovery of 95.9 ~ 103.2%, showing its promising application in safety evaluation for food.
Authors: Ling Zhang, Dan Zuo, Su Li Guo, Zhong Cao, Jun Liu, Qiu Jie Meng, Xi Yan Yu
Abstract: A kind of bamboo char with high specific surface area has been studied as the absorption material of the activated carbon electrodes, and the electrosorptive deionization ability of the as-obtained electrodes for elimination of metal ions in tap water has been examined under certain direct voltage. The effects of the distance between the elect rode plates, and the numbers of the electrode plates have been investigated in detail. The results show that the electrodes exhibit the optimal deionization ability over 2 cm of distance between the electrode plates and 4 couples of the elect rode plates. The reverse wash treatment indicates that the activated carbon electrodes can be cycle used. The efficiency order of the electrosorptive deionization of different metal ions on the activated carbon electrode has been summarized as follows: Pb2+>Cu2+>Cr3+>Cd2+.
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