Zhongping Li

Application of hydrophobic palladium nanoparticles for the development of electrochemical glucose biosensor.

An amperometric glucose biosensor based on an n-alkylamine-stabilized palladium nanoparticles (PdNPs)-glucose oxidase (GOx) modified glassy carbon (GC) electrode has been successfully fabricated. PdNPs were initially synthesized by a biphase mixture of water and toluene method using n-alkylamines (dodecylamine, C₁₂-NH₂ and octadecylamine, C₁₈-NH₂) as stabilizing ligands. The performance of the PdNPs-GOx/GC biosensor was studied by cyclic voltammetry. The optimum working potential for amperometric measurement of glucose in pH 7.0 phosphate buffer solution is -0.02 V (vs. Ag/AgCl). The analytical performance of the biosensor prepared from C₁₈-PdNPs-GOx is better than that of C₁₂-PdNPs-GOx. The C₁₈-PdNPs-GOx/GC biosensor exhibits a fast response time of ca. 3s, a detection limit of 3.0 μM (S/N=3) and a linear range of 3.0 μM-8.0 mM. The linear dependence of current density with glucose concentration is 70.8 μA cm⁻² mM⁻¹. The biosensor shows good stability, repeatability and reproducibility. It has been successfully applied to determine the glucose content in human blood serum samples.

Mode-filtered light methane gas sensor based on cryptophane A.

A mode-filtered light sensor has been developed for methane (CH(4)) gas determination at ambient conditions. The proposed chemosensor consisted of an annular column which was constructed by inserting an optical fiber coated with a thin silicone cladding of cryptophane A into a fused-silica capillary. When CH(4) was introduced to the sensor, selective inclusion of CH(4) into the silicone layer would cause a change in the local refractive index of the cladding, resulting in the change of mode-filtered light that emanated from the fiber. Three detection windows were set alongside the capillary to propagate the light to a charge-coupled device (CCD). The changes of mode-filtered light on exposure to various concentrations of CH(4) were thus simultaneously monitored. The mode-filtered light intensity decreased with the increase in concentration of CH(4). The dynamic concentration range of the sensor for CH(4) was 0.0-16.0% v/v with a detection limit of 0.15% v/v. The highest sensitivity was found at the channel furthest away from the excitation light source. The response time (t(95%)) was about 5min. The reproducibility was good with a relative standard deviation (RSD) of less than 7% from evaluating six cryptophane A-coated fibers. Oxygen, hydrogen and carbon dioxide showed very little interference on detection but interferences from dichloromethane and carbon tetrachloride were observed. The proposed mode-filtered light sensor has been successfully applied to determine CH(4) samples and the accuracy was good. Our work offers a promising approach for CH(4) detection.

Chromatographic separation and mass spectrometric analysis of N-acetyl-L-cysteine-protected palladium nanoparticles

In this study, water-soluble N-acetyl-L-cysteine-protected palladium nanoparticles (NAC-PdNPs) were synthesised. The obtained NAC-PdNPs were well characterised by UV-vis absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The as-synthesised NAC-PdNPs were found to be polydisperse in nature with an average particle size of 2.17 ± 0.20 nm. As such, a reverse-phase high-performance liquid chromatographic (RP-HPLC) methodology coupled with UV-vis absorption detection has been developed for separating and analysing this as-synthesised NAC-PdNPs product. A gradient elution program with mobile phase mixtures of methanol/water containing 50 mM tetrabutylammonium fluoride was successfully applied to separate the as-synthesised NAC-PdNPs sample. The spectral characteristics of each RP-HPLC-separated NAC-PdNPs fractions were captured online using a diode array detector. In addition, most major RP-HPLC fractions were collected and further characterised by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) in order to elucidate their chemical compositions. The mass spectra suggest that the NAC-PdNPs as-synthesised product is indeed a complex mixture of small PdNPs comprising Pd10(NAC)7, Pd11(NAC)7, Pd11(NAC)8, Pd12(NAC)9, Pd13(NAC)6, Pd13(NAC)9, Pd14(NAC)5, Pd14(NAC)9, Pd15(NAC)9, Pd17(NAC)11, and Pd20(NAC)11. The UV-vis spectral characteristics of the separated NAC-PdNPs are closely related to the number of Pd atoms. This study highlights the values of using high-resolution chromatography together with UV-vis absorption spectroscopy and MALDI-TOF MS for revealing the hidden properties of each individual PdNPs species in a PdNPs product.