Electrogeneration of O₂^.− and H₂O₂ Using Polymer‐modified Microelectrodes in the Environment of Living Cells

Abstract

Dedicated to the 60th Birthday of Prof.Dr. Wolfgang Schuhmann 1Introduction Ther eductiono fo xygen in biological systemsd uring oxygen metabolism besides water yields reactiveo xygen species( ROS) [1][2][3].R OS such as H 2 O 2 ,O 2 C À or HOC (hydroxyl radicals) can be released spontaneously by mammalian cells as part of cellular defense mechanismsa nd during metabolic activities [2,[4][5][6].E nzymes and antioxidants exist that regulate the steady-state of in vivo concentrations of ROS.A ni mbalance between ROSp roduction and antioxidant defense mechanisms,e .g. the concentration of antioxidantso rs cavengers,m ay lead to oxidative stress[ 1-3, 7],w hich has been associated to degenerative and neurodegenerative diseases [2,8]. Amperometric detections chemes at positionable microelectrodes (ME) provide spatial and temporal resolutions and can be combined with othert echniques such as fluorescence microscopy as complementary technique [8,9]. ME can detect transient concentrations of short liveds pecies when positioned close to theirs ource, e.g. closet o stimulated cells [1,[10][11][12][13][14][15]. In addition, modifications of the ME surfaces provides electivity. Fori nstance,c ytochromec(cyt c) is used for the detectiono fO 2 C À and H 2 O 2 at different potentials [16,17] and ap olymer prepared from Ni-tetrasulfonate phtalocyanine was usedf or the local detection of NO [12].T he effects of ROSe xposure to cells have been studied as well [18,19].T here have alsob een intensive efforts to deliver NO in situ either by generationa te lectrocatalytic electrodes or by release from specifically optimized polymers [20][21][22].Quinones (Q)s uch as napthoquinones and antraquinones were reported to promote the formation of ROS during aerobic processes which may contribute to their cytotoxic potential [23][24][25][26][27].T hesem olecules form as emiquinoner adical (QC À )a tn eutral pH by ao ne electron reduction, from which O 2 C À is produced by simple chemical reactionsw ith oxygen. O 2 C À is known as ap recursor of other ROS [23][24][25][26][27].Q þ e À ) * QC À ð1ÞAbstract:M icroelectrodes modified with electropolymerized plumbagin (PLG) were used for the generation of superoxide radical( O 2 C À )a nd hydrogen peroxide( H 2 O 2 ) during oxygen reduction reaction( ORR) in an aqueous medium, specifically in serum-free cell culture media. This is enabledb yt he specific design of ap olymer film on the microelectrode.T he generation and diffusion of O 2 C À during electrocatalyticO RR at ap ositionable PLG polymer-modified microelectrode was followed by fluorescence microscopy with the selective dye 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole( NBD-Cl) and by amperomet-ric detection usingacytochrome c-modified electrode at + 0.13 V. H 2 O 2 production, eitherb yd irect oxygen reduction or as product of O 2 C À disproportionation, was monitored by the reaction with AmplexU ltraRed. TheP LG polymer-modified microelectrodes were used to expose mammalian B6-RPE07 retinal cells to definedl ocal fluxes of reactive oxygen spec...

Covalent Modification of Nanoparticle‐Imprinted Matrices for Selective Nanoparticle Recognition

“…[46] This monolayer-covered surface is then used to electropolymerize plumbagin around the template NPs (Figure 1e) yielding a permeable film of defined and adjustable thickness. [46,51] The sample code used for this stage is polyplg/ plg(SiO 2 À NH 2 )/GC. Figure S2c depicts the cyclic voltammogram for polyplumbagin electropolymerization on plumbagin-modified activated GC, suggesting the formation of a permeable film.…”

“…This monolayer‐covered surface is then used to electropolymerize plumbagin around the template NPs (Figure 1e) yielding a permeable film of defined and adjustable thickness [46,51] . The sample code used for this stage is polyplg/plg(SiO 2 −NH 2 )/GC.…”