Zhanjun Yang

Electrochemical tattoo biosensors for real-time noninvasive lactate monitoring in human perspiration.

The present work describes the first example of real-time noninvasive lactate sensing in human perspiration during exercise events using a flexible printed temporary-transfer tattoo electrochemical biosensor that conforms to the wearers skin. The new skin-worn enzymatic biosensor exhibits chemical selectivity toward lactate with linearity up to 20 mM and demonstrates resiliency against continuous mechanical deformation expected from epidermal wear. The device was applied successfully to human subjects for real-time continuous monitoring of sweat lactate dynamics during prolonged cycling exercise. The resulting temporal lactate profiles reflect changes in the production of sweat lactate upon varying the exercise intensity. Such skin-worn metabolite biosensors could lead to useful insights into physical performance and overall physiological status, hence offering considerable promise for diverse sport, military, and biomedical applications.

Graphene–Au nanoparticles nanocomposite film for selective electrochemical determination of dopamine

A novel graphene–Au nanoparticles (AuNPs) composite film modified glassy carbon electrode (GCE) was proposed for selective detection of dopamine (DA). The resulting electrode was characterized using transmission electron microscopy, cyclic voltammetry and differential pulse voltammetry. Compared to bare and graphene modified electrodes, this nanocomposite modified electrode not only significantly improved the electrochemical peak potential difference between DA and ascorbic acid (AA), but also noticeably enhanced the current response. The constructed DA sensor showed a wide linear range (5–1000 μM) and a low detection limit (1.86 μM). The graphene–AuNPs composite, which was obtained by assembling AuNPs onto the graphene surface, could provide a promising platform to develop excellent electrochemical sensors for detecting DA.

Simultaneous determination of ultratrace lead and cadmium by square wave stripping voltammetry with in situ depositing bismuth at Nafion-medical stone doped disposable electrode.

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth-Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about -0.62 V for Pb(2+) and -0.85 V for Cd(2+), respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 μg L(-1) with detection limit of 0.07 μg L(-1) for lead and 2.0-12.0 μg L(-1) with detection limit of 0.47 μg L(-1) for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method.

A novel photoelectrochemical sensor for the organophosphorus pesticide dichlofenthion based on nanometer-sized titania coupled with a screen-printed electrode.

A novel photoelectrochemical sensor for detection of the organophosphorus pesticide (OP) dichlofenthion using nanometer-sized titania coupled with a screen-printed electrode is presented. Nonelectroactive dichlofenthion can be indirectly determined through the photocatalytical degradation of dichlofenthion with nanometer-sized titania. The electrochemical characterization and anodic stripping voltammetric performance of dichlofenthion were evaluated using cyclic voltammetric (CV) and differential pulse anode stripping voltammetric (DPASV) analysis, respectively. DPASV analysis was used to monitor the amount of dichlofenthion and provide a simple, fast, and facile quantitative method for dichlofenthion. Operational parameters, including the photocatalysis time, pH of buffer solution, deposition potential, and accumulation time have been optimized. The stripping voltammetric response is linear over the 0.02-0.1 and 0.2-1.0 μmol/L ranges with a detection limit of 2.0 nmol/L. The assay result of dichlofenthion in green vegetable with the proposed method was in acceptable agreement with that of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable, and sensitive analysis of OPs in environmental samples.

Carbon nanotubes-nanoflake-like SnS2 nanocomposite for direct electrochemistry of glucose oxidase and glucose sensing.

Multi-walled carbon nanotubes (MWCNTs)-nanoflake-like SnS(2) nanocomposite were designed for immobilization of glucose oxidase (GOx). The direct electrochemistry of GOx and glucose sensing at MWCNTs-SnS(2) modified glassy carbon electrode were studied. Compared with single MWCNTs or SnS(2), the MWCNTs-SnS(2) film has larger surface area and provides a more favorable microenvironment for facilitating the electron transfer between enzyme and electrode surface. The properties of GOx/MWCNTs-SnS(2) were examined by scanning electron microscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry. The immobilized enzyme on MWCNTs-SnS(2) composite film retained its native structure and bioactivity and showed a surface controlled, reversible two-proton and two-electron transfer reaction with a apparent electron transfer rate constant of 3.96 s(-1). The constructed glucose biosensor exhibits wider linear range from 2.0×10(-5) M to 1.95×10(-3) M, much lower detection limit of 4.0×10(-6) M at signal-to-noise of 3 and higher sensitivity of 21.65 mA M(-1) cm(-2) than our previous nanoflake-like SnS(2)-based glucose sensor. The proposed biosensor has excellent selectivity, good reproducibility, and acceptable operational stability and can be successfully applied in the reagentless glucose sensing at -0.43 V. This MWCNTs-SnS(2) composite provides a new avenue for immobilizing proteins and fabricating excellent biosensors.

Nanoflake-like SnS2 matrix for glucose biosensing based on direct electrochemistry of glucose oxidase

A novel biosensor is developed based on immobilization of proteins on nanoflake-like SnS₂ modified glass carbon electrode (GCE). With glucose oxidase (GOD) as a model, direct electrochemistry of the GOD/nanoflake-like SnS₂ is studied. The prepared SnS₂ has large surface area and can offer favorable microenvironment for facilitating the electron transfer between protein and electrode surface. The properties of GOD/SnS₂ are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV), respectively. The immobilized enzyme on nanoflake-like SnS₂ retains its native structure and bioactivity and exhibits a surface-controlled, reversible two-proton and two-electron transfer reaction with the apparent electron transfer rate constant (k(s)) of 3.68 s⁻¹. The proposed biosensor shows fast amperometric response (8s) to glucose with a wide linear range from 2.5 × 10⁻⁵ M to 1.1 × 10⁻³ M, a low detection limit of 1.0 × 10⁻⁵ M at signal-to-noise of 3 and good sensitivity (7.6 ± 0.5 mA M⁻¹ cm⁻²). The resulting biosensor has acceptable operational stability, good reproducibility and excellent selectivity and can be successfully applied in the reagentless glucose sensing at -0.45 V. It should be worthwhile noting that it opens a new avenue for fabricating excellent electrochemical biosensor.

Facile synthesis of tetragonal columnar-shaped TiO2 nanorods for the construction of sensitive electrochemical glucose biosensor.

A tetragonal columnar-shaped TiO2 (TCS-TiO2) nanorods are synthesized via a facile route for the immobilization of glucose oxidase (GOx). A novel electrochemical glucose biosensor is constructed based on the direct electrochemistry of GOx at TCS-TiO2 modified glassy carbon electrode. The fabricated biosensor is characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, electrochemical impedance spectra and cyclic voltammetry. The immobilized enzyme molecules on TCS-TiO2 nanorods retain its native structure and bioactivity and show a surface controlled, quasi-reversible and fast electron transfer process. The TCS-TiO2 nanorods have large surface area and provide a favorable microenvironment for enhancing the electron transfer between enzyme and electrode surface. The constructed glucose biosensor shows wide linear range from 5.0×10(-6) to 1.32×10(-3) M with a high sensitivity of 23.2 mA M(-1) cm(-2). The detection limit is calculated to be 2.0×10(-6) M at signal-to-noise of 3. The proposed glucose biosensor also exhibits excellent selectivity, good reproducibility, and acceptable operational stability. Furthermore, the biosensor can be successfully applied in the detection of glucose in serum sample at the applied potential of -0.50 V. The TCS-TiO2 nanorods provide an efficient and promising platform for the immobilization of proteins and development of excellent biosensors.

A derivative photoelectrochemical sensing platform for 4-nitrophenolate contained organophosphates pesticide based on carboxylated perylene sensitized nano-TiO2.

A novel visible light sensitized photoelectrochemical sensing platform was constructed based on the perylene-3,4,9,10-tetracarboxylic acid/titanium dioxide (PTCA/TiO(2)) heterojunction as the photoelectric beacon. PTCA was synthesized via facile steps of hydrolysis and neutralization reaction, and then the PTCA/TiO(2) heterojunction was easily prepared by coating PTCA on nano-TiO(2) surface. The resulting photoelectric beacon was characterized by transmission electron microscope, scanning electron microscopy, X-ray diffractometry, FTIR spectroscopy, and ultraviolet and visible spectrophotometer. Using parathion-methyl as a model, after a simple hydrolyzation process, p-nitrophenol as the hydrolysate of parathion-methyl could be obtained, the fabricated derivative photoelectrochemical sensor showed good performances with a rapid response, instrument simple and portable, low detection limit (0.08 nmol L(-1)) at a signal-to-noise ratio of 3, and good selectivity against other pesticides and possible interferences. It had been successfully applied to the detection of parathion-methyl in green vegetables and the results agreed well with that by GC-MS. This strategy not only extends the application of PTCA, but also presents a simple, economic and novel methodology for photoelectrochemical sensing.

A subnanomole level photoelectrochemical sensing platform for hexavalent chromium based on its selective inhibition of quercetin oxidation

An indirect photoelectrochemical sensing platform for toxic hexavalent chromium was for the first time constructed based on its redox reaction with quercetin as both the electron donor and photosensitizer on a TiO(2) photoanode, and thus inhibiting the photocurrent quantitatively and selectively. The presence of even 500-fold coexisting Cr(III) does not interfere in the detection of Cr(VI). Under the optimum conditions, the electrode displayed a linear decrease response as the Cr(VI) concentration increased from 1 to 10 nmol L(-1) and from 20 to 140 nmol L(-1) with a detection limit of 0.24 nmol L(-1). Many possible ions in drinking water did not interfere with the detection, and the real sample detection results agreed well with those obtained by GFAAS. This work provide a novel methodology for the simple, low-cost photoelectrochemical detection of Cr(VI) in drinking water.

Platinum nanoparticles functionalized nitrogen doped graphene platform for sensitive electrochemical glucose biosensing

In this work, we reported an efficient platinum nanoparticles functionalized nitrogen doped graphene (PtNPs@NG) nanocomposite for devising novel electrochemical glucose biosensor for the first time. The fabricated PtNPs@NG and biosensor were characterized using transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, static water contact angle, UV-vis spectroscopy, electrochemical impedance spectra and cyclic voltammetry, respectively. PtNPs@NG showed large surface area and excellent biocompatibility, and enhanced the direct electron transfer between enzyme molecules and electrode surface. The glucose oxidase (GOx) immobilized on PtNPs@NG nanocomposite retained its bioactivity, and exhibited a surface controlled, quasi-reversible and fast electron transfer process. The constructed glucose biosensor showed wide linear range from 0.005 to 1.1mM with high sensitivity of 20.31 mA M(-1) cm(-2). The detection limit was calculated to be 0.002 mM at signal-to-noise of 3, which showed 20-fold decrease in comparison with single NG-based electrochemical biosensor for glucose. The proposed glucose biosensor also demonstrated excellent selectivity, good reproducibility, acceptable stability, and could be successfully applied in the detection of glucose in serum samples at the applied potential of -0.33 V. This research provided a promising biosensing platform for the development of excellent electrochemical biosensors.