Electron Work Function–An Effective Parameter for In-situ Reflection of Electron Activities in Various Processes

Abstract

Electron work function (EWF) is the minimum energy required to move electrons at the Fermi level from inside a conducting material to its surface with zero kinetic energy [1,2]. This fundamental parameter largely reflects electron activities and is directly related to chemical, physical, and mechanical properties of materials [2][3][4][5][6][7][8]. Recent studies have shown that EWF can be used as a sensitive parameter to characterize many surface properties of biomaterials. As an example [9], the affinity of medical implant materials for bacteria can be characterized by EWF. Figure 1A illustrates the adhesive forces of nanocrystalline stainless steel samples with different gran sizes. As shown, as the grain size decreases, the adhesion decreases due to the fact that the passive film becomes more protective, blocking the interaction between the steel and surrounding media. Such a trend is consistent with the variations in electron work function, as shown in Figure 1B. A higher surface EWF corresponds to a higher degree of reluctance for interacting with the environment. The decrease in the number of bacteria bound to the surfaces with an increase in EWF provides direct evidence.Another example is the use of EWF in analyzing the photocatalyical activity of TiO2 nanotubes (TNTs). TNTs have been used for different applications such as DNA biosensor [10], detection of bacteria [11] and toxic compounds [12]. TNTs have also been explored for immobilizing proteins and enzymes in biomaterial and biosensor applications [13,14]. Many of the application are related to the photocatalytic activity of TNTs, which is usually evaluated by variations in photocurrent and absorbance under illumination. However, the photocurrent response or absorbance does not provide sufficient information for full understanding of the photocatalytic behaviour of TNAs.Recent studies have demonstrated that the electron work function is a very sensitive parameter for in-situ analysis of photocatalytic activity of TNTs [15]. Figure 2 illustrates variations in the work function of TiO 2 nanotubes with different tube lengths (corresponding to the anodization duration; the larger the anodization duration, the longer the nanotubes). Figures 2A, C, E and G illustrate variations in EWF of the TNAs illuminated successively by lights having wavelengths of 670 nm, 650 nm, 550 nm, 450 nm, 420 nm, 400 nm and 390 nm. As shown, EWF of the TNAs was relatively stable when they were illuminated by lights of 670 nm and 620 nm, indicating that the photonic energies of the lights are not sufficient to excite electrons in the TNAs. While when the wavelength of incident light is in the absorption range of TNAs lower than 550 nm, electrons can be excited accompanied with an apparent decrease in EWF. The observed decrease in EWF with a decrease in the wavelength of incident light is an indication of photoninduced electron-hole separation, which requires photons with their energy above a certain level.The TNAs were also illuminated successively by the lights with different ...

Upgrading of Biomass Monosaccharides by Immobilized Glucose Dehydrogenase and Xylose Dehydrogenase

“…The lower values of specific activity and activity retention noticed for enzymes immobilized onto SBA 15 compared with nanoSiO 2 , might be explained by two factors: (i) lower amount of immobilized biocatalysts and (ii) hindered accessibility of the enzyme active sites for the substrates molecules due to immobilization of enzymes mainly into the pores of the support. Nevertheless, lower activity of immobilized XDH compared with GDH is probably related to the larger conformational changes of 3-D biomolecule structure that occur upon immobilization, as reported earlier by Li et al [19] There is no available literature about efficient immobilization of XDH, and though there are some reports about immobilization of GDH, results presented here go further than previously published data. For example, Baron et al used controlled pore silica with average pore size of 500 Å , as a support for Bacillus megaterium glucose dehydrogenase and immobilized less than 0.5 mg of enzyme per 1 g of the support, [20] whereas here we report a loading capacity of silica nanoparticles of 2.8 mg/g, probably due to higher density of hydroxyl groups on the surface of nanoSiO 2 .…”

High‐Performance Biosensing Systems Based on Various Nanomaterials as Signal Transducers

“…FRET-based FIs have also been investigated for biosensing platforms. [86][87][88][89][90] The FRET effect is a unique and interesting optical phenomenon that occurs between different types of fluorescent materials that possess different bandgap energies for fluorescence irradiation. [91][92][93] In this case, energy transfer takes place from the higher bandgap energy to the lower bandgap energy through dipole-dipole interactions within the range of approximately 10 nm.…”

Ultrasensitive immunoassay for CA125 detection using acid site compound as signal and enhancer

“…And the carbohydrate antigens (CA125, CA724, CA199, etc.) have been reported for many times [8][9][10][11][12][13][14].…”