Laccase-catalyzed cross-linking of BSA mediated by tyrosine

Tyrosine was explored as a cross-linking agent to form cross-linked bovine serum albumin (BSA) using laccase as a catalyst. Liquid chromatography-mass spectrometry (LC-MS) and fluorescence spectra indicated that tyrosine can be mainly oxidized to be dityrosine. Spectra analysis and molecular weight were used to characterize the BSA treated with tyrosine and laccase. Both SDS-PAGE and size exclusion chromatography confirmed the formation of cross-linked BSA, while most of the protein products existed as BSA–tyrosine conjugates. The MALDI-TOF analysis revealed that five tyrosine units were grafted on one BSA monomer, however one cross-linked BSA consists of two BSA monomers and 18 tyrosine. Furthermore, the content of the amino acid of BSA was identified using amino acid analysis, among those the percentage of lysine presented a visible decline from 12.36% to 11.43%, corresponding to 4-5 lysine residues. The pure and modified BSA were hydrolyzed by trypsin and the corresponding peptides were obtained. Different mass of five peptides from LC-MS spectra after hydrolysis indicated that tyrosine could react with Lys-136, Lys-204, Lys-224, Lys-322 and Lys-537 in BSA, promoting the formation of BSA–tyrosine conjugates and cross-linked BSA.This study was supported by Chinese Government Scholarship under China Scholar Council (NO. 201906790043) and “the Fundamental Research Funds for the Central Universities (NO. JUSRP52007A). This study was also supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte

In situ ATR-IR spectroscopy study of adsorbed protein: Visible light denaturation of bovine serum albumin on TiO₂

In this work in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy in a flow-through cell was used to study the effect of visible light irradiation on bovine serum albumin (BSA) adsorbed on porous TiO2 films. The experiments were performed in water at concentrations of 10−6 mol/l at room temperature. The curve fitting method of the second derivative spectra allowed us to explore details of the secondary structure of pure BSA in water and conformation changes upon adsorption as well as during and after illumination by visible light. The results clearly show that visible light influences the conformation of adsorbed BSA. The appearance of a shift of the amide I band, in the original spectra, from 1653 cm−1 to 1648 cm−1, is interpreted by the creation of random coil in the secondary structure of adsorbed BSA. The second derivative analysis of infrared spectra permits direct quantitative analysis of the secondary structural components of BSA, which show that the percentage of α-helix decreases during visible light illumination whereas the percentage of random coil increases

Electron transfer across the germanium–polyelectrolyte–gold nanoparticle interface: convenient detection and applications in sensing

Germanium – polyelectrolyte – gold nanoparticle composites were prepared and characterized using FTIR-ATR spectroscopy and scanning electron microscopy. The germanium (Ge) element served as internal reflection element and the buildup of the layered system was followed in situ. Positively charged polyelectrolyte poly (allylamine hydrochloride) (PAH) adsorbs spontaneously on negatively charged Ge. Citrate-stabilized gold nanoparticles can then be adsorbed onto the PAH layer. Upon illumination of the device with visible light a prominent absorption over the entire mid infrared region is observed which is due to intervalence band transitions in Ge. The strong infrared signals are evidence for holes in the valence band of the Ge semiconductor, which arise due to electron transfer to the gold nanoparticles (GNP). The electron transfer, as evidenced by the holes in Ge, is affected by the nature of the gap between the Ge and the GNP. Increasing the gap by adsorbing polyelectrolyte multilayers hinders the electron transfer. Also heating and vacuum have a pronounced effect. The device is proposed as a sensor, where the sensing event is transduced into an optical signal in the infrared, as demonstrated for a thiol molecule. The thiol has a large affinity for the gold and therefore affects the germanium – gold nanoparticle gap. This reduces the electron transfer and therefore the absorption in the infrared upon illumination with visible light. Removal of the thiol from the solution leads to a recovering of the signal

An IR modulator based on the self-assembly of gold nanoparticles on germanium

By using a polyelectrolyte layer gold nanoparticles have been assembled onto a Ge internal reflection element. Upon illumination with visible and near infrared light a strong infrared absorption has been observed, which can be traced to intervalence band transitions in Ge. This reveals the existence of holes in the Ge near its valence band edge. The switching between bright and dark states is faster than 160 μs and the device acts as an infrared modulator. The effect develops with a peculiar kinetics, which may indicate the development of an interfacial layer between germanium and gold that allows efficient electron transfer upon illumination

Вплив кристалічної об'ємної фракції на електронні властивості гідрогенізованого мікрокристалічного кремнію, дослідженого методом еліпсометрії та моделюванням мікроелектронних і фотонних структур

The main objective of the present work is to study experimentally and by simulation, using the one dimensional analysis of microelectronic and photonic structures program (AMPS-1D), the correlation between the crystalline volume fraction (Fc) and the transport properties of hydrogenated microcrystalline silicon thin films (мc-Si:H). The Fc was determined by spectroscopic ellipsometry (SE) and the electrical conductivity measurements. The мc-Si:H samples were deposited by radio-frequency magnetron sputtering technique of a crystalline silicon target, under an argon (Ar) gas mixture of 70 % of hydrogen (H2) and 30 % of Ar, at three different total pressures (2, 3 and 4 Pa) and changing substrate temperatures (25, 100, 150 and 200 °C). The dark conductivity was measured in a coplanar configuration in an optical cryostat under applied electrical field and controlling current with an electrometer. In the simulation studies of the dark conductivity using the AMPS-1D, we modelled the films as an alternation of amorphous and crystalline regions with different crystalline volume fractions Fc (from 0 to 80 %). The results evidently demonstrated that the conductivity depends on the width of the area separating amorphous and crystalline regions. We found a strong correlation between the c-Si:H films activation energy and the crystalline volume fraction where the grain size-to-thickness ratio plays a crucial role.Метою даної роботи є експериментальне і модельне дослідження кореляції між об'ємною фракцією кристалів і транспортними властивостями тонких плівок гідрогенізованого мікрокристалічного кремнію, використовуючи одновимірний аналіз програми мікроелектронних і фотонних структур (AMPS 1D). Об'ємну фракцію кристалів визначали спектроскопічною еліпсометрією і вимірюваннями елект- ропровідності. Зразки гідрогенізованого мікрокристалічного кремнію осаджували методом радіочастотного магнетронного розпилення кристалічної мішені кремнію у газовій суміші аргону і водню при трьох різних сумарних тисках (2, 3 і 4 Па) та змінюючи температуру підкладки (25, 100, 150 і 200 °С). Темна провідність вимірювалася в копланарній конфігурації в оптичному кріостаті при прикладанні електричного поля і керуючого струму. У дослідженнях темної провідності з використанням AMPS-1D ми моделювали плівки як чергування аморфних і кристалічних областей з різними кристалічними об'ємними фракціями (від 0 до 80 %). Результати показали, що провідність залежить від ширини ділянки, що розділяє аморфні та кристалічні області. Була виявлена сильна кореляція між енергією активації плівок гідрогенізованого мікрокристалічного кремнію і об'ємною часткою кристалічних речовин, де співвідношення розміру зерна до його товщини грає вирішальну роль