Simultaneous determination of volatile phenol, cyanide, anionic surfactant, and ammonia nitrogen in drinking water by a continuous flow analyzer.

This study developed a method for the simultaneous determination of volatile phenol, cyanide, anionic surfactant, and ammonia nitrogen in drinking water, using a continuous flow analyzer. The samples were first distilled at 145 °C. The phenol in the distillate then subsequently reacted with alkaline ferricyanide and 4-aminoantipyrine to form a red complex that was measured colorimetrically at 505 nm. Cyanide in the distillate subsequently reacted with chloramine T to form cyanogen chloride, which then formed a blue complex with pyridinecarboxylic acid that was measured colorimetrically at 630 nm. The anionic surfactant reacted with basic methylene blue to form a compound that was extracted into chloroform and washed with acidic methylene blue to remove interfering substances. The blue compound in chloroform was determined colorimetrically at 660 nm. Ammonia reacted with salicylate and chlorine from dichloroisocyanuric acid to produce indophenol blue at 37 °C in an alkaline environment that was measured at 660 nm. The relative standard deviations were 0.75-6.10% and 0.36-5.41%, respectively, and the recoveries were 96.2-103.6% and 96.0-102.4% when the mass concentration of volatile phenol and cyanide was in the range of 2-100 µg/L. The linear correlation coefficients were ≥ 0.9999, and the detection limits were1.2 µg/L and 0.9 µg/L, respectively. The relative standard deviations were 0.27-4.86% and 0.33-5.39%, and the recoveries were 93.7-107.0% and 94.4-101.7%. When the mass concentration of anionic surfactant and ammonia nitrogen was 10-1000 µg/L. The linear correlation coefficients were 0.9995 and 0.9999, and the detection limits were 10.7 µg/L and 7.3 µg/L, respectively. When compared to the national standard method, no statistically significant difference was found. This approach saves time and labor, has a lower detection limit, higher precision and accuracy, less contamination, and is more appropriate for the analysis and determination of large-volume samples.

Ultrasensitive electrochemical cocaine biosensor based on reversible DNA nanostructure.

We proposed an ultrasensitive electrochemical cocaine biosensor based on the three-dimensional (3D) DNA structure conversion of nanostructure from Triangular Pyramid Frustum (TPFDNA) to Equilateral Triangle (ETDNA). The presence of cocaine triggered the aptamer-composed DNA nanostructure change from "Close" to "Open", leading to obvious faradaic impedance changes. The unique properties with excellent stability and specific rigid structure of the 3D DNA nanostructure made the biosensing functions stable, sensitive, and regenerable. The Faradaic impedance responses were linearly related to cocaine concentration between 1.0 nM and 2.0 µM with a correlation coefficient of 0.993. The limit of detection was calculated to be 0.21 nM following IUPAC recommendations (3Sb/b). It is expected that the distinctive features of DNA nanostructure would make it potentially advantageous for a broad range of biosensing, bionanoelectronics, and therapeutic applications.

Reversible switches of DNA nanostructures between "Closed" and "Open" states and their biosensing applications.

A novel and versatile biosensing platform based on the structural conversion of 3D DNA nanostructures from ETDNA (Equilateral Triangle) to TPFDNA (Triangular Pyramid Frustum) was proposed for the first time. The inputs of aptamers and their relative targets made the DNA structure change from the "Open" to the "Closed" state, leading to the faradaic impedance changes as the output signals. The specific properties of excellent stability and specific rigid structure of 3D DNA nanostructures made the biosensor function as a regenerable, reusable and intelligent platform. The sensor exhibited excellent selectivity for IFN-γ detection with a wide linear range of 1.0 × 10(-9) to 2.0 × 10(-6) M and a low detection limit of 5.2 × 10(-10) M. The distinctive features of DNA nanostructures make them potentially advantageous for a broad range of biosensing, bionanoelectronics, and therapeutic applications.

Fullerene-nitrogen doped carbon nanotubes for the direct electrochemistry of hemoglobin and its application in biosensing.

The direct electrochemistry of hemoglobin (Hb) immobilized by a fullerene-nitrogen doped carbon nanotubes and chitosan (C60-NCNTs/CHIT) composite matrix is demonstrated. The cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrode. In the deaerated buffer solution, the cyclic voltammogram of the Hb/C60-NCNTs/CHIT composite film modified electrode showed a pair of well-behaved redox peaks with the E°'=-0.335 (± 0.3) V (vs. SCE). The redox peaks are assigned to the redox reaction of Hb(Fe(III)/Fe(II)) and confirm the effective immobilization of Hb on the composite film. The large value of ks = 1.8 (± 0.2)s(-1) suggests that the immobilized Hb achieved a relative fast electron transfer process. The fast electron transfer interaction between protein and electrode surface suggested that the C60-NCNTs/CHIT composite film may mimic some physiological process and further elucidate the relationship between protein structures and biological functions. Moreover, the resulting electrode exhibited excellent electrocatalytic ability towards the reduction of hydrogen peroxide (H2O2) with the linear dynamic range of 2.0-225.0 µM. The linear regression equation was Ip/µA=7.35 (± 0.08)+0.438 (± 0.007)C/µM with the correlation coefficient of 0.9993. The detection limit was estimated at about 1 µM (S/N=3). The sensitivity was 438.0 (± 2.5) µA mM(-1). It is expected that the method presented here can not only be easily extended to other redox enzymes or proteins, but also be used as an electrochemical sensing devices for the determination of H2O2 in cell extracts or urine.

Prussian blue nanospheres synthesized in deep eutectic solvents.

A novel route for controlled synthesis of Prussian blue nanospheres (PB NSs) with different sizes by using deep eutectic solvents (DES) as both solvent and template provider was demonstrated. The size-controlled PB NSs were obtained directly by the coordination of Fe(CN)(6)(4-) ion with Fe(3+) ion in the DES. The probable mechanism of formation of PB NSs was discussed based on the characterization results of UV-visible, X-ray diffraction, X-ray photoelectronic spectrum and transfer electron microscopy. Furthermore, the electrochemical and electrocatalytic properties of the synthesized PB NSs were investigated, and it has demonstrated that the PB NSs exhibited excellent catalytic activity for H(2)O(2) reduction, and then extended this strategy to glucose sensing, by detecting H(2)O(2) formed from the enzymatic reaction of glucose oxidase with its substrate glucose. The linear calibration range for glucose was from 0.9 µM to 0.12 mM, with a correlation coefficient of 0.998. The limit of detection was 0.3 µM and the sensitivity was 61.7 A cm(-2) M(-1). The present study provides a general platform for the controlled synthesis of novel nanomaterials in DES and can be extended to other optical, electronic and magnetic nanocompounds.

Selective determination of cholesterol based on cholesterol oxidase-alkaline phosphatase bienzyme electrode.

A bienzyme electrode for the determination of cholesterol was prepared by the co-immobilization of cholesterol oxidase and alkaline phosphatase (ALP) on the carbon nanotubes modified electrode surface. The parameters influenced the performance of the bienzyme electrode such as the pH of the base solution; the concentration of DPP and the incubation time, were optimized. A linear calibration graph in the 0.05-2.0 mM concentration range with the sensitivity of 4.65 µA mM(-1) was obtained. In addition, this work provides a new interferent-depleted method and universal protocol for the design of multi-enzyme biosensors.

A novel H2O2 sensor based on the enzymatically induced deposition of polyaniline at a horseradish peroxide/aligned single-wall carbon nanotubes modified Au electrode.

A novel H(2)O(2) sensor based on enzymatically induced deposition of electroactive polyaniline (PANI) at a horseradish peroxide (HRP)/aligned single-wall carbon nanotubes (SWCNTs) modified Au electrode is fabricated, and its electrochemical behaviors are investigated. Electrochemical impedance spectroscopy of the sensor confirmed the formation of PANI on SWCNTs through the HRP catalytic reaction. Cyclic voltammograms of PANI/HRP/SWCNTs modified Au electrodes showed a pair of well-defined redox peaks of PANI with reduction peak potentials of 0.211 and oxidation peak potentials of 0.293 V in 0.1 M HOAc-NaOAc (pH 4.3) solution. The oxidation peak current response of PANI is linearly related to H(2)O(2) concentration from 2.5 µM to 50.0 µM with a correlation coefficient of 0.9923 and a sensitivity of 200 µA mM(-1). The detection limit is determined to be 0.9 µM with a signal-to-noise ratio of 3. Thus, the synergistic performance of the enzyme, the highly efficient polymerization of PANI, and the templated deposition of SWCNTs provided an extensive platform for the design of novel electrochemical biosensors.

Enzymatic deposition of Au nanoparticles on the designed electrode surface and its application in glucose detection.

This paper reported the enzymatic deposition of Au nanoparticles (AuNPs) on the designed 3-mercapto-propionic acid/glucose oxidase/chitosan (MPA/GOD/Chit) modified glassy carbon electrode and its application in glucose detection. Chit served as GOD immobilization matrix and interacted with MPA through electrostatic attraction. AuNPs, without nano-seeds presented on the electrode surface, was produced through the glucose oxidase catalyzed oxidation of glucose. The mechanism of production of AuNPs was confirmed to be that enzymatic reaction products H(2)O(2) in the solution reduce gold complex to AuNPs. The characterizations of the electrode modified after each assembly step was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy showed the average particle size of the AuNPs is 40nm with a narrow particle size distribution. The content of AuNPs on the electrode surfaces was measured by differential pulse stripping voltammetry. The electrochemical signals on voltammogram showed a linear increase with the glucose concentration in the range of 0.010-0.12mM with a detection limit of 4µM. This provided a method to the determination of glucose.