A new approach based on potential control was firstly used for the immobilization of horseradish peroxidase (HRP) as the model protein. The self-assembly monolayer (SAM) was prepared with 2-aminoethanethiol (AET) on the gold electrode. The charge on HRP was adjusted by means of the acidity of the phosphate buffer solution (PBS) for dissolving the HRP. The in-fluence of electric potential on HRP immobilization was investigated by means of colorimetric immunoassay of enzyme-substrate interaction (CIESI) using an automatic plate reader. The HRP modified electrodes were characterized with X-ray photoelectron spectroscopy (XPS) as well as atomic force microscope (AFM) on template-stripped gold surface. The potential for maximum immobilization of HRP was near the zero charge potential. The result indicates that controlled potential can affect the course of HRP immobilization without the loss of enzymic activity. It is of great significance for the control of biomolecular self-assembly and the intrinsic electric device.

A new activation method has been developed for initiating electroless metal deposition on silicon substrates without SnCl2 sensitization and roughening condition. Silicon wafers are first coated with thiol-terminated self-assembled monolayers (SAMs), and then catalyzed with a stable tin-free Pd(II)-based colloidal solution. Atomic force microscopy (AFM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to characterize the step-by-step surfaces and study the binding mechanism of Pd(Ⅱ) with SAMs onto surfaces. Results show that Pd(II) oligomer particles are chemisorbed on pendant thiol surfaces through S-Pd bonds. This process involves fewer steps than the conventional Sn/Pd combined activation one. Furthermore, the chemical bound initiator possesses longevity and can be stored for a long time before metallization.

Hyper-Rayleigh scattering (HRS) or incoherent second harmonic generation (SHG) technique has been used to investigate the second-order optical nonlinearities of nanoparticles and seems sensitive to nanoparticle surfaces. Here, more direct evidence that shows the importance of surfaces for HRS response of nanoparticles was experimentally obtained. Two CdS nanoparticles of 3 nm average diameter with different surface-capping molecules, CdS/AOT-SO3- (AOT-SO3- is anion of bis (2-ethylhexyl) sulfosuccinate, disodium salt) and CdS/Py/AOT-SO3- (Py represents pyridine molecule), were studied by HRS technique. The "per particle" first-order hyperpolarizability β values were evaluated to be 3.98×10-27 esu for the CdS/AOT-SO3- and 2.63×10-27 esu for the CdS/Py/AOT-SO3- nanoparticles. A reduction in β value is found when AOT-SO3- on CdS nanoparticle surface is replaced by pyridine. Similarly, the reduction of HRS signal intensity of a solution containing the CdS/AOT-SO3- nanoparticles was observed when increasing pyridine concentration in the solution. Furthermore, the dynamic process of the surface-capping molecule exchange was studied by detecting both HRS signal intensity and electroconductivity variations with time. Possible effect mechanism is discussed in terms of a two-level model approximation derived from molecular chromophores, when considering the influence of different surface-capping molecules on the polarity of Cd-S bonds at nanoparticle surfaces.

The assembly of synthetic, controllable molecules is one of the goals in nanotechnology. The primary objective of this contribution is to selectively immobilize DNA on gold via electric potential control. The self-assembly monolayer (SAM) was prepared with 2-aminoethanethiol (AET) on the gold electrode. A new approach based on electric potential was firstly used to control DNA immobilization covalently onto the SAM with the activation of 1-ethyl-3(3-dimethyl-aminopropyl)-carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHS) in low ionic strength solution. The influence of electric potential on DNA immobilization was investigated by means of cyclic voltammogram, A.C. impedance, auger electron spectrometer as well as atomic force microscope (AFM) on template-stripped gold surface. The result proves that controlled potential can affect the course of DNA immobilization. More negative potential can restrain the DNA immobilization, while the more positive potential can accelerate the DNA immobilization. It is of great significance for the control of DNA self-assembly and will find wide application in the fields of DNA-based devices.

The primary object of this contribution is to self-assemble DNA on 2-dimensional array of 1-dodecanethiol-encapsulated colloidal gold (2-DACG). The 2-DACG film was deposited by Langmuir-Blodgell (LB) technique. Through phase transfer of aqueous colloidal gold particles into ethanol solutions containing 1-dodecanethiol, the hydrophobic gold colloidal nanoparticles were accomplished. In the presence of traces of 1-dodecanethiol, the gold nanoparticels were transferred via LB technique to a freshly cleaned gold electrode and 2-DACG of close-packed, ordered monolayer was obtained. The 2-DACG was then used as a substrate for the immobilization of DNA under a controled potential of 0.20V vs. saturated calomel electrode (SCE). The properties of 2-DACG before and after the DNA assembly were investigated by means of transmission electron microscopy (TEM), atomic force microscopy (AFM), cyclic voltaininetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicated that 2-DACG deposited by LB technique was suitable as a substrate for DNA self-assembly.