TY  - JOUR
A1  - Frasca, Stefano
A1  - Rojas, Oscar
A1  - Salewski, Johannes
A1  - Neumann, Bettina
A1  - Stiba, Konstanze
A1  - Weidinger, Inez M.
A1  - Tiersch, Brigitte
A1  - Leimkühler, Silke
A1  - Koetz, Joachim
A1  - Wollenberger, Ursula
T1  - Human sulfite oxidase electrochemistry on gold nanoparticles modified electrode
JF  - Bioelectrochemistry : an international journal devoted to electrochemical aspects of biology and biological aspects of electrochemistry ; official journal of the Bioelectrochemical Society
N2  - The present study reports a facile approach for sulfite biosensing, based on enhanced direct electron transfer of a human sulfite oxidase (hSO) immobilized on a gold nanoparticles modified electrode. The spherical core shell AuNPs were prepared via a new method by reduction of HAuCl4 with branched poly(ethyleneimine) in an ionic liquids resulting particles with a diameter less than 10 nm. These nanoparticles were covalently attached to a mercaptoundecanoic acid modified Au-electrode where then hSO was adsorbed and an enhanced interfacial electron transfer and electrocatalysis was achieved. UV/Vis and resonance Raman spectroscopy, in combination with direct protein voltammetry, are employed for the characterization of the system and reveal no perturbation of the structural integrity of the redox protein. The proposed biosensor exhibited a quick steady-state current response, within 2 s, a linear detection range between 0.5 and 5.4 mu M with a high sensitivity (1.85 nA mu M-1). The investigated system provides remarkable advantages in the possibility to work at low applied potential and at very high ionic strength. Therefore these properties could make the proposed system useful in the development of bioelectronic devices and its application in real samples.
KW  - Direct electron transfer
KW  - Gold nanoparticle
KW  - Human sulfite oxidase
KW  - Ionic liquid
KW  - Sulfite biosensor
Y1  - 2012
U6  - https://doi.org/10.1016/j.bioelechem.2011.11.012
SN  - 1567-5394
VL  - 87
SP  - 33
EP  - 41
PB  - Elsevier
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Rojas, Oscar
A1  - Koetz, Joachim
A1  - Kosmella, Sabine
A1  - Tiersch, Brigitte
A1  - Wacker, Philipp
A1  - Kramer, Markus
T1  - Structural studies of ionic liquid-modified microemulsions
N2  - This work is focused on the influence of an ionic liquid (IL), i.e. ethyl-methylimidazolium hexylsulfate, on the spontaneous formation of microemulsions with ionic surfactants. The influence of the ionic liquid on Structure formation in the optically clear phase region in water/toluene/pentanol mixtures in presence of the cationic surfactant CTAB was studied in more detail. The results show a significant increase of the transparent phase region by adding the ionic liquid. Conductometric investigations demonstrate that adding the ionic liquid can drastically reduce the droplet- droplet interactions in the L-2 phase. H-1 nuclear magnetic resonance (H-1 NMR) diffusion coefficient measurements in combination with dynamic light scattering measurements clearly show that inverse microemulsion droplets still exist, but the droplet size is decreased to 2 nm. A more detailed characterisation of the isotropic phase channel by means of conductivity measurements, dynamic light scattering (DLS), H-1 NMR and cryo-scanning electron microscopy (SEM), allows the identification of a bicontinuous sponge phase between the L-1 and L-2 phase. When the poly(ethyleneimine) is added, the isotropic phase range is reduced drastically, but the inverse microemulsion range still exists.
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/00219797
U6  - https://doi.org/10.1016/j.jcis.2009.02.039
SN  - 0021-9797
ER  - 
TY  - JOUR
A1  - Rojas, Oscar
A1  - Tiersch, Brigitte
A1  - Rabe, Christian
A1  - Stehle, Ralf
A1  - Hoell, Armin
A1  - Arlt, Bastian
A1  - Koetz, Joachim
T1  - Nonaqueous Microemulsions Based on N,N '-Alkylimidazolium Alkylsulfate Ionic Liquids
JF  - Langmuir
N2  - The ternary system composed of the ionic liquid surfactant (IL-S) 1-butyl-3-methylimidazolium dodecylsulfate ([Bmim][DodSO(4)]), the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][EtSO4]), and toluene has been investigated. Three major mechanisms guiding the structure of the isotropic phase were identified by means of conductometric experiments, which have been correlated to the presence of oil-in-IL, bicontinuous, and IL-in-oil microemulsions. IL-S forms micelles in toluene, which swell by adding RTIL as to be shown by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) experiments. Therefore, it is possible to form water free IL-in-oil reverse microemulsions <= 10 nm in size as a new type of nanoreactor.
Y1  - 2013
U6  - https://doi.org/10.1021/la401080q
SN  - 0743-7463
VL  - 29
IS  - 23
SP  - 6833
EP  - 6839
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Dolya, Natalya
A1  - Rojas, Oscar
A1  - Kosmella, Sabine
A1  - Tiersch, Brigitte
A1  - Koetz, Joachim
A1  - Kudaibergenov, Sarkyt
T1  - "One-Pot" in situ frmation of Gold Nanoparticles within Poly(acrylamide) Hydrogels
JF  - Macromolecular chemistry and physics
N2  - This paper focuses on two different strategies to incorporate gold nanoparticles (AuNPs) into the matrix of polyacrylamide (PAAm) hydrogels. Poly(ethyleneimine) (PEI) is used as both reducing and stabilizing agent for the formation of AuNPs. In addition, the influence of an ionic liquid (IL) (i.e., 1-ethyl-3-methylimidazolium ethylsulfate) on the stability of the nanoparticles and their immobilization in the hydrogel is investigated The results show that AuNPs surrounded by a shell containing PEI and IL, synthesized according to the one-pot approach, are much better immobilized within the PAAm hydrogel. Hereby, the IL is responsible for structural changes in the hydrogel as well as the improved stabilization and embedding of the AuNPs into the polymer gel matrix.
KW  - gold nanoparticles
KW  - immobilization
KW  - ionic liquids
KW  - poly(acrylamide) hydrogels
Y1  - 2013
U6  - https://doi.org/10.1002/macp.201200727
SN  - 1022-1352
VL  - 214
IS  - 10
SP  - 1114
EP  - 1121
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Thete, Aniket
A1  - Rojas, Oscar
A1  - Neumeyer, David
A1  - Koetz, Joachim
A1  - Dujardin, Erik
T1  - Ionic liquid-assisted morphosynthesis of gold nanorods using polyethyleneimine-capped seeds
JF  - RSC Advances
N2  - Seed-mediated gold nanorods with tunable lengths are prepared using new polyethyleneimine-capped gold nanoparticles synthesized in ionic liquid. The effect of polyethyleneimine and ionic liquid during nanorod growth is investigated and shows a marked effect on their final aspect ratio.
Y1  - 2013
U6  - https://doi.org/10.1039/c3ra22112a
SN  - 2046-2069
VL  - 3
IS  - 34
SP  - 14294
EP  - 14298
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Thete, Aniket
A1  - Rojas, Oscar
A1  - Neumeyer, David
A1  - Koetz, Joachim
A1  - Dujardin, Erik
T1  - Ionic liquid-assisted morphosynthesis of gold nanorods using polyethyleneimine-capped seeds
N2  - Seed-mediated gold nanorods with tunable lengths are prepared using new polyethyleneimine-capped gold nanoparticles synthesized in ionic liquid. The effect of polyethyleneimine and ionic liquid during nanorod growth is investigated and shows a marked effect on their final aspect ratio.
Y1  - 2013
UR  - http://pubs.rsc.org/en/content/articlepdf/2013/ra/c3ra22112a
U6  - https://doi.org/10.1039/C3RA22112A
ER  -