Surface organization and photochemistry of free-base porphyrin self-assembled monolayers (SAMs) covalently bonded to the surfaces of tapered optical fibres and reference glass plates were studied. The surface modification was carried out in two steps: (i) surface activation by aminopropyltrimethoxysilane and (ii) porphyrin attachment via activated pentafluorophenyl esters. The measurements of surface activation time and real-time porphyrin adsorption monitoring revealed that each of the two steps required 1 h reaction time. Porphyrin immobilization on fibres was as good as on plane glass substrates. Fluorescence measurements were used to determine the optimum diameter of the coned part of the tapered fibre for sensor applications. For 125 μm fibres with a 10 μm cladding layer, this diameter was found to be 35-48 μm. The mono-and diprotonated forms of free-base porphyrin have distinct fluorescence spectra. This phenomenon was employed to demonstrate a pH sensor application of the SAM-modified tapered fibre, which operates in the pH range of 0.6-3.8.
Room-temperature plasma-enhanced atomic layer deposition (PEALD) of ZnO was studied by depositing the films using diethylzinc and O 2 plasma from inductively-coupled plasma (ICP) and capacitively-coupled plasma (CCP) plasma source configurations. The CCP-PEALD was operated using both remote and direct plasma. It was observed that the films deposited by means of remote ICP and CCP were all highly oxygen rich, independently on plasma operation parameters, but impurity (H, C) contents could be reduced by increasing plasma pulse time and applied power. With the direct CCP-PEALD the film composition was closer to stoichiometric, and film crystallinity was enhanced. The ZnO film growth was observed to be similar on silicon, polycarbonate and poly(methyl methacrylate) substrates, but changes in polymer
Fluorescent proteins have the inherent ability to act as sensing components which function both in vitro and inside living cells. We describe here a novel study on a covalent site-specific bonding of fluorescent proteins to form self-assembled monolayers (SAMs) on the surface of etched optical fibers (EOFs). Deposition of fluorescent proteins on EOFs gives the opportunity to increase the interaction of guided light with deposited molecules relative to plane glass surfaces. The EOF modification is carried out by surface activation using 3-aminopropylthrimethoxysilane (APTMS) and bifunctional crosslinker sulfosuccinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (sulfo-SMCC) which exposes sulfhydryl-reactive maleimide groups followed by covalent site-specific coupling of modified yellow fluorescent protein (YFP). Steady-state and fluorescence lifetime measurements confirm the formation of SAM. The sensor applications of YPF SAMs on EOF are demonstrated by the gradual increase of emission intensity upon addition of Ca(2+) ions in the concentration range from a few tens of micromolars up to a few tens of millimolars. The studies on the effect of pH, divalent cations, denaturing agents, and proteases reveal the stability of YFP on EOFs at normal physiological conditions. However, treatments with 0.5% SDS at pH 8.5 and protease trypsin are found to denaturate or cleave the YFP from fiber surfaces.
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