Investigation of the interactions between silver nanoparticles and Hela cells by scanning electrochemical microscopy.

The interactions between Hela cells and silver nanoparticles (AgNPs) have been studied by scanning electrochemical microscopy (SECM) with both IrCl(6)(2-/3-) and Fe(CN)(6)(3-/4-) as the dual mediators. IrCl(6)(2-), which can be produced in situ and react with AgNPs, is used as the mediator between the AgNPs on the cells and the SECM tip. Another redox couple, Fe(CN)(6)(3-/4-), which has a similar hydrophilicity to IrCl(6)(2-/3-), but cannot react with AgNPs, is also employed for the contrast experiments. The cell array is cultured successfully onto a Petri dish by microcontact printing (muCP) technique, which can provide a basic platform for studying of single cells. The approach curve and line scan are the two methods of SECM employed here to study the Hela cells. The former can provide the information about the interaction between Hela cells and AgNPs whereas the later gives the cell imaging. The permeability of cell membranes and morphology are two main factors which have effects on the feedback mode signals when K(3)Fe(CN)(6) is used as the mediator. The permeability of the cell membranes can be ignored after interaction with high concentration of AgNP solution and the height of the Hela cells is slightly decreased in this process. The kinetic rate constants (k(0)) between IrCl(6)(2-) and Ag on the Hela cell can be evaluated using K(3)IrCl(6) as the mediator, and they are increased with the higher concentrations of the AgNP solutions. The k(0) is changed about 10 times from 0.43 +/- 0.04 x 10(-4) to 1.25 +/- 0.07 x 10(-4) and to 3.93 +/- 1.9 x 10(-4) cm s(-1) corresponding to 0, 1 and 5 mM of AgNO(3) solution. The experimental results demonstrate that the AgNPs can be adsorbed on the cell surface and detected by SECM. Thus, the amount of AgNPs adsorbed on cell membranes and the permeability or morphology changes can be investigated simultaneously using this approach. The dual mediator system and cell array fabricated by muCP technique can provide better reproducibility because they can simplify experiments, and provide a platform for further single cell detection.

Electrochemical DNAzyme sensor for lead based on amplification of DNA-Au bio-bar codes.

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

A chronocoulometric aptamer sensor for adenosine monophosphate.

The selective recognition of adenosine monophosphate by a half-duplex aptamer-modified electrode leads to a simple chronocoulometric aptasensor based on the changes in surface charges.

Comparative study for the analysis of parabens by micellar electrokinetic capillary chromatography with and without large-volume sample stacking technique.

The separation and determination of four parabens (methyl, ethyl, propyl, and butyl p-hydroxybenzoate) which are commonly used as preservatives in cosmetic products, by micellar electrokinetic capillary chromatography (MEKC) with and without large-volume sample stacking (LVSS) technique were compared. As an effective on-line concentration technique, LVSS was successfully combined with MEKC to determine neutral parabens in an acidic media. The effects of some typical parameters such as sample volume, buffer pH, temperature, and concentration of surfactant were examined. The detection limits for this LVSS-MEKC method were found to be 3.0 x 10(-7)M for each of the parabens based on the signal-to-noise ratio of 3, which were around 300 times lower than normal MEKC technique. The curves of peak response versus concentration were linear from 1.0 x 10(-6) to 5.0 x 10(-5)M with regression coefficients of 0.9987, 0.9960, 0.9925 and 0.9864, respectively. A simple and easy-manipulative sample preparation method was developed and validated by analyzing commercially available cosmetic samples. It was found that with current sample preparation process and instrumentation system, 0.5 g of sample is enough for the analysis of parabens preservatives in cosmetic product with satisfactory results.