Browsing by Author "Heikkinen, Joonas J."
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Item Biofouling affects the redox kinetics of outer and inner sphere probes on carbon surfaces drastically differently - implications to biosensing(ROYAL SOC CHEMISTRY, 2020-08-07) Peltola, Emilia; Aarva, Anja; Sainio, Sami; Heikkinen, Joonas J.; Wester, Niklas; Jokinen, Ville; Koskinen, Jari; Laurila, Tomi; Department of Electrical Engineering and Automation; Department of Chemistry and Materials Science; Microsystems Technology; Microfabrication; Physical Characteristics of Surfaces and InterfacesBiofouling imposes a significant threat for sensing probes used in vivo. Antifouling strategies commonly utilize a protective layer on top of the electrode but this may compromise performance of the electrode. Here, we investigated the effect of surface topography and chemistry on fouling without additional protective layers. We have utilized two different carbon materials; tetrahedral amorphous carbon (ta-C) and SU-8 based pyrolytic carbon (PyC) in their typical smooth thin film structure as well as with a nanopillar topography templated from black silicon. The near edge X-ray absorption fine structure (NEXAFS) spectrum revealed striking differences in chemical functionalities of the surfaces. PyC contained equal amounts of ketone, hydroxyl and ether/epoxide groups, while ta-C contained significant amounts of carbonyl groups. Overall, oxygen functionalities were significantly increased on nanograss surfaces compared to the flat counterparts. Neither bovine serum albumin (BSA) or fetal bovine serum (FBS) fouling caused major effects on electron transfer kinetics of outer sphere redox (OSR) probe Ru(NH3)63+ on any of the materials. In contrast, negatively charged OSR probe IrCl62- kinetics were clearly affected by fouling, possibly due to the electrostatic repulsion between redox species and the anionically-charged proteins adsorbed on the electrode and/or stronger interaction of the proteins and positively charged surface. The OSR probe kinetics were less affected by fouling on PyC, probably due to conformational changes of proteins on the surface. Dopamine (DA) was tested as an inner sphere redox (ISR) probe and as expected, the kinetics were heavily dependent on the material; PyC had very fast electron transfer kinetics, while ta-C had sluggish kinetics. DA electron transfer kinetics were heavily affected on all surfaces by fouling (ΔEp increase 30-451%). The effect was stronger on PyC, possibly due to the more strongly adhered protein layer limiting the access of the probe to the inner sphere.Item Fabrication of micro- and nanopillars from pyrolytic carbon and tetrahedral amorphous carbon(Multidisciplinary Digital Publishing Institute (MDPI), 2019-08-01) Heikkinen, Joonas J.; Peltola, Emilia; Wester, Niklas; Koskinen, Jari; Laurila, Tomi; Franssila, Sami; Jokinen, Ville; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Microfabrication; Microsystems Technology; Physical Characteristics of Surfaces and InterfacesPattern formation of pyrolyzed carbon (PyC) and tetrahedral amorphous carbon (ta-C) thin films were investigated at micro- and nanoscale. Micro- and nanopillars were fabricated from both materials, and their biocompatibility was studied with cell viability tests. Carbon materials are known to be very challenging to pattern. Here we demonstrate two approaches to create biocompatible carbon features. The microtopographies were 2 μm or 20 μm pillars (1:1 aspect ratio) with three different pillar layouts (square-grid, hexa-grid, or random-grid orientation). The nanoscale topography consisted of random nanopillars fabricated by maskless anisotropic etching. The PyC structures were fabricated with photolithography and embossing techniques in SU-8 photopolymer which was pyrolyzed in an inert atmosphere. The ta-C is a thin film coating, and the structures for it were fabricated on silicon substrates. Despite different fabrication methods, both materials were formed into comparable micro- and nanostructures. Mouse neural stem cells were cultured on the samples (without any coatings) and their viability was evaluated with colorimetric viability assay. All samples expressed good biocompatibility, but the topography has only a minor effect on viability. Two μm pillars in ta-C shows increased cell count and aggregation compared to planar ta-C reference sample. The presented materials and fabrication techniques are well suited for applications that require carbon chemistry and benefit from large surface area and topography, such as electrophysiological and -chemical sensors for in vivo and in vitro measurements.Item Inkjet-printed flexible silver electrodes on thiol-enes(Elsevier, 2021-06-01) Kuusisto, Eero; Heikkinen, Joonas J.; Järvinen, Päivi; Jokinen, Ville; Department of Chemistry and Materials Science; Microfabrication; Department of Chemistry and Materials Science; University of HelsinkiFlexible and conductive silver electrodes were fabricated by inkjet printing on several different compositions of thiol-ene polymers. Conductive electrodes with resistivity down to 30 µΩcm and good adhesion of the electrodes were obtained by optimizing the printing parameters. The maximum printing resolution was 100 µm lines and 80 µm gaps between the lines. Printing on top of cross-linked off-stoichiometric thiol-ene polymer was tested for compositions ranging from 30 % thiol excess to 5 % allyl (‘ene’) excess. The roughness off the thiol-ene surfaces was shown to greatly improve the quality of the printed electodes: consistently high yield of conductive electrodes was obtained on rough surfaces (roughness ≈ 1 µm), whereas on smooth surfaces the electrodes were often cracked. The lowest resistivity values were obtained on electrodes printed on near stoichiometric thiol-ene substrates. The conductivity of the electrodes was retained after 5 % linear strain and after repeated bending with 1 mm radius of curvature, showing the potential for flexible sensors. The electrodes were also applied to electrical impedance-based monitoring of cell growth on thiol-ene surfaces, which showcased that the electrodes survive stressed cell culture conditions for at least 36 h.Item Novel carbon film induces precocious calcium oscillation to promote neuronal cell maturation(Nature Publishing Group, 2020-10-19) Ludwig, Anastasia; Kesaf, Sebnem; Heikkinen, Joonas J.; Sukhanova, Tatiana; Khakipoor, Shokoufeh; Molinari, Florence; Pellegrino, Christophe; Kim, Sung I.; Han, Jeon G.; Huttunen, Henri J.; Lauri, Sari E.; Franssila, Sami; Jokinen, Ville; Rivera, Claudio; Department of Chemistry and Materials Science; Microfabrication; University of Helsinki; Aix-Marseille Université; Institut national de la santé et de la recherche médicale; Sungkyunkwan UniversityDifferent types of carbon materials are biocompatible with neural cells and can promote maturation. The mechanism of this effect is not clear. Here we have tested the capacity of a carbon material composed of amorphous sp3 carbon backbone, embedded with a percolating network of sp2 carbon domains to sustain neuronal cultures. We found that cortical neurons survive and develop faster on this novel carbon material. After 3 days in culture, there is a precocious increase in the frequency of neuronal activity and in the expression of maturation marker KCC2 on carbon films as compared to a commonly used glass surface. Accelerated development is accompanied by a dramatic increase in neuronal dendrite arborization. The mechanism for the precocious maturation involves the activation of intracellular calcium oscillations by the carbon material already after 1 day in culture. Carbon-induced oscillations are independent of network activity and reflect intrinsic spontaneous activation of developing neurons. Thus, these results reveal a novel mechanism for carbon material-induced neuronal survival and maturation.Item Novel carbon materials and microstructures for electrochemical sensors(Aalto University, 2021) Heikkinen, Joonas J.; Jokinen, Ville, Ph.D., Aalto University, Department of Chemistry and Materials Science, Finland; Kemian ja materiaalitieteen laitos; Department of Chemistry and Materials Science; Materials for electronics; Kemian tekniikan korkeakoulu; School of Chemical Technology; Franssila, Sami, Prof., Aalto University, Department of Chemistry and Materials Science, FinlandCarbon thin films have gained a lot of attention since the discovery of carbon nanotubes in 1991, which ignited widespread research on the many forms of carbon. The most well-known form of carbon is diamond, and its synthetic version has been adopted in applications that require high wear resistance. However, carbonaceous materials have a lot more potential than just that. There is a broad spectrum of carbonaceous materials available which properties can be tailored according to need. In this thesis, three different carbon thin films were studied from the microfabrication and patterning perspective. These selected thin films were especially electrically conductive as their performance was studied as electrode material in multielectrode arrays (MEA). These three materials were nanocarbon (nC), tetrahedral amorphous carbon (ta-C), and pyrolytic carbon (PyC). In microfabrication and thin film technologies, the methods and equipment for carbon thin film patterning are limited. This thesis presents patterning methods for all three studied carbon materials. The nC film was plasma etched, the ta-C film was patterned with lift-off, and PyC was patterned while it was still photoresist before pyrolysis. Most carbon materials are naturally biocompatible without any additional surface coatings. These three materials were used in electrochemical measurements to detect the minor presence of neurotransmitters like dopamine or other biological analytes. From an electrochemistry point of view, carbon is an appealing material as it exhibits a wide potential window that allows the measurement of multiple analytes simultaneously. PyC and ta-C show promising results in dopamine detection from bulk concentrations, but there is still a need for improvement if interfering molecules and impurities are present. These three carbon materials were utilized in multielectrode arrays, which are formed of many microelectrodes close to each other. MEA devices can be used to follow the signaling between neuronal cultures, follow the activity of brain slices, or measure even the minuscule concentration of biological analytes. This thesis presents biological measurements only for nC-MEA (with brain slice). PyC and ta-C materials were successfully implemented in MEAs, but their performance was only tested in preliminary experiments.Item Plasma etched carbon microelectrode arrays for bioelectrical measurements(2018-11-01) Heikkinen, Joonas J.; Kaarela, Tiina; Ludwig, Anastasia; Sukhanova, Tatiana; Khakipoor, Shokoufeh; Kim, Sung Il; Han, Jeon Geon; Huttunen, Henri J.; Rivera, Claudio; Lauri, Sari E.; Taira, Tomi; Jokinen, Ville; Franssila, Sami; Department of Chemistry and Materials Science; Aalto Nanofab; Microfabrication; University of Helsinki; Institut national de la santé et de la recherche médicale; Albert-Ludwigs-Universität Freiburg; Sungkyunkwan UniversityCarbon-based materials have attracted much attention in biological applications like interfacing electrodes with neurons and cell growth platforms due to their natural biocompatibility and tailorable material properties. Here we have fabricated sputtered carbon thin film electrodes for bioelectrical measurements. Reactive ion etching (RIE) recipes were optimized with Taguchi method to etch the close field unbalanced magnetron sputtered carbon thin film (nanocarbon, nC) consisting of nanoscale crystalline sp2-domains in amorphous sp3-bonded backbone. Plasma etching processes used gas mixtures of Ar/O2/SF6/CHF3 for RIE and O2/SF6 for ICP-RIE. The highest achieved etch rate for nanocarbon was ≫389 nm/min and best chromium etch mask selectivity was 135:1. Biocompatibility of the material was tested with rat neuronal cultures. Next, we fabricated multielectrode arrays (MEA) with carbon recording electrodes and metal wiring. Organotypic brain slices grown on the MEAs were viable and showed characteristic spontaneous electrical network activity. The results demonstrate that interactions with nanocarbon substrate support neuronal survival and maturation of functional neuronal networks. Thus the material can have wide applications in biomedical research.Item Platinum Recovery from Industrial Process Solutions by Electrodeposition-Redox Replacement(2018-11-05) Halli, Petteri; Heikkinen, Joonas J.; Elomaa, Heini; Wilson, Benjamin P.; Jokinen, Ville; Yliniemi, Kirsi; Franssila, Sami; Lundström, Mari; Department of Chemical and Metallurgical Engineering; Department of Chemistry and Materials Science; Hydrometallurgy and Corrosion; MicrofabricationIn the current study, platinum - present as a negligible component (below 1 ppb, the detection limit of the HR-ICP-MS at the dilutions used) in real industrial hydrometallurgical process solutions - was recovered by an electrodeposition-redox replacement (EDRR) method on pyrolyzed carbon (PyC) electrode, a method not earlier applied to metal recovery. The recovery parameters of the EDRR process were initially investigated using a synthetic nickel electrolyte solution ([Ni] = 60 g/L, [Ag] = 10 ppm, [Pt] = 20 ppm, [H2SO4] = 10 g/L), and the results demonstrated an extraordinary increase of 3 × 105 in the [Pt]/[Ni] on the electrode surface cf. synthetic solution. EDRR recovery of platinum on PyC was also tested with two real industrial process solutions that contained a complex multimetal solution matrix: Ni as the major component (>140 g/L) and very low contents of Pt, Pd, and Ag (i.e., <1 ppb, 117 and 4 ppb, respectively). The selectivity of Pt recovery by EDRR on the PyC electrode was found to be significant - nanoparticles deposited on the electrode surface comprised on average of 90 wt % platinum and a [Pt]/[Ni] enrichment ratio of 1011 compared to the industrial hydrometallurgical solution. Furthermore, other precious metallic elements like Pd and Ag could also be enriched on the PyC electrode surface using the same methodology. This paper demonstrates a remarkable advancement in the recovery of trace amounts of platinum from real industrial solutions that are not currently considered as a source of Pt metal.
