Browsing by Author "Ras, Robin H. A."

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  • Capillary-driven self-assembly of microchips on oleophilic/oleophobic patterned surface using adhesive droplet in ambient air
    (2011) Chang, Bo; Sariola, Veikko; Aura, Susanna; Ras, Robin H. A.; Klonner, Maria; Lipsanen, Harri; Zhou, Quan
     School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    This letter describes a capillary-driven self-assembly technique using oleophilic/oleophobic patternedsurface and adhesive in ambient air environment. We use a topographical microstructure of porous ormocer functionalized with a fluorinated trichlorosilane for the oleophobic area and goldpatterns for the oleophilic area. The resulted oleophilic/oleophobic patterns show significant wettability contrast for adhesive (Delo 18507), with a contact angle of 119° on oleophobic part and 53° on the oleophilic part. Self-alignment of SU-8 microchips on the oleophilic/oleophobic patterns has been demonstrated. The results provide a promising solution for self-alignment of microparts using commercial adhesives in ambient air environment.
  • Crystalline Cyclophane–Protein Cage Frameworks
    (2018-07-13) Beyeh, Ngong; Nonappa, Nonappa; Liljeström, Ville; Mikkilä, Joona; Korpi, Antti; Bochicchio, Davide; Pavan, Giovanni M.; Ikkala, Olli; Ras, Robin H. A.; Kostiainen, Mauri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Cyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal–organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[5]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane–protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host–guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.
  • Direct Laser Writing of Photostable Fluorescent Silver Nanoclusters in Polymer Films
    (2014-11) Kunwar, Puskal; Hassinen, Jukka; Bautista, Godofredo; Ras, Robin H. A.; Toivonen, Juha
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Metal nanoclusters consist of a few to a few hundred atoms and exhibit attractive molecular properties such as ultrasmall size, discrete energy levels, and strong fluorescence. Although patterning of these clusters down to the micro- or nanoscale could lead to applications such as high-density data storage, it has been reported only for inorganic matrices. Here we present submicron-scale mask-free patterning of fluorescent silver nanoclusters in an organic matrix. The nanoclusters were produced by direct laser writing in poly(methacrylic acid) thin films and exhibit a broadband emission at visible wavelengths with photostability that is superior to that of Rhodamine 6G dye. This fabrication method could open new opportunities for applications in nanophotonics like imaging, labeling, and metal ion sensing. We foresee that this method can be further applied to prepare other metal nanoclusters embedded in compositionally different polymer matrices.
  • Fast capillary waves on an underwater superhydrophobic surface
    (2025-12) Fauconnier, Maxime; Karunakaran, Bhuvaneshwari; Drago-Gonzalez, Alex; Wong, William S. Y.; Ras, Robin H. A.; Nieminen, Heikki J.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The propagation of interfacial waves in free and constrained conditions, such as deep and shallow water, has been broadly studied over centuries. It is a common event that anyone can witness, while contemplating the ocean waves washing ashore. As a complementary configuration, this work introduces waves propagating on an interface restricted by its pinning to the solid microstructures of an underwater superhydrophobic surface. The latter has the ability to stabilize a well-defined microscale gas layer, called a plastron, trapped between the water and the solid phase. The acoustic radiation force produced with focused MHz ultrasound successfully triggers kHz “plastronic waves”, i.e., capillary waves travelling on a plastron’s gas-water interface. The exposed waves possess interesting features, i.e., (i) a high propagation speed up to 45 times faster than conventional deep water capillary waves of comparable wavelength and (ii) a relation of the propagation speed with the geometry of the microstructures. Based on this and on the observed variation of wave speed over time in conditions of gas-undersaturated or -supersaturated water, the usefulness of the plastronic waves for the non-destructive monitoring of the plastron’s stability and the spontaneous air diffusion is eventually demonstrated.
  • Functional Magnetic Microdroplets for Antibody Extraction
    (2022-01-05) Al-Terke, Hedar H.; Latikka, Mika; Timonen, Jaakko V. I.; Vekas, Ladislau; Paananen, Arja; Joensuu, Jussi; Ras, Robin H. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Antibodies play an essential role in modern medicine for diagnostic and therapeutic applications. Even though the production of antibodies is the fastest growing pharmaceutical industry area, the cost of antibodies remains high, which limits access to antibody-based medicine both in developing and developed countries. The bottleneck and major cost factor in the production is purification of the antibody. Here, a proof-of-concept is presented for antibody extraction using ferrofluid microdroplets. An external magnetic field splits oil-based ferrofluid droplets into an array of daughter microdroplets, which serve as a magnetically tunable, hydrophobic, liquid substrate with a relatively large surface area. A fusion protein (HFBI-Protein A), added to the solution surrounding the magnetic droplets, adsorbs strongly at the liquid-liquid interface by the hydrophobin HFBI moiety, creating a bifunctional monolayer that can catch antibody molecules. After adsorption at the liquid-liquid interface, these antibody molecules can be released by decreasing the pH of the solution. The antibody extraction process is investigated using confocal microscopy and gel electrophoresis. In addition, the effect of HFBI on the field-induced ferrofluid droplet splitting is examined. This study provides a proof of concept for utilizing liquid-liquid instead of a solid-liquid system in antibody handling.
  • pH-Responsive Near-Infrared Emitting Gold Nanoclusters
    (2023-12-04) Zhou, Shaochen; Gustavsson, Lotta; Beaune, Grégory; Chandra, Sourov; Niskanen, Jukka; Ruokolainen, Janne; Timonen, Jaakko V. I.; Ikkala, Olli; Peng, Bo; Ras, Robin H. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Near-infrared (NIR) fluorophores with pH-responsive properties suggest merits in biological analyses. This work establishes a general and effective method to obtain pH-responsive NIR emissive gold nanoclusters by introducing aliphatic tertiary amine (TA) groups into the ligands. Computational study suggests that the pH-responsive NIR emission is associated with electronic structure change upon protonation and deprotonation of TA groups. Photo-induced electron transfer between deprotonated TA groups and the surface Au-S motifs of gold nanoclusters can disrupt the radiative transitions and thereby decrease the photoluminescence intensity in basic environments (pH=7–11). By contrast, protonated TA groups curb the electron transfer and restore the photoluminescence intensity in acidic environments (pH=4–7). The pH-responsive NIR-emitting gold nanoclusters serve as a specific and sensitive probe for the lysosomes in the cells, offering non-invasive emissions without interferences from intracellular autofluorescence.
  • Photoconversion of Ag31 to Ag42 Initiated by Solvated Electrons
    (2023-09-12) Jana, Arijit; Dar, Wakeel Ahmed; Jana, Sourav Kanti; Poonia, Ajay Kumar; Yadav, Vivek; Roy, Jayoti; Chandra, Sourov; Adarsh, Kumaran Nair Valsala Devi; Ras, Robin H. A.; Pradeep, Thalappil
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Light-matter interactions, especially in atomically precise nanomaterials, belong to an unexplored realm of research with potential benefits for the synthesis of materials. Here, we present an interesting light-activated expansion process of an Ag31 nanocluster to an Ag42 analogue, both clusters being protected with 6-(dibutylamino)-1,3,5-triazine-2, 4-dithiol (shortly, TRZ-H2) ligands. The conversion process was initially monitored through UV–vis, revealing that the violet-colored Ag31 got converted to greenish Ag42, exhibiting their characteristic absorption features. High-resolution mass spectrometric studies confirmed that the as-synthesized [Ag31(TRZ)10] with coexisting di- and monoanionic charged species in dichloromethane solution got converted to [Ag42(TRZ)13] with a dipositive charge state. Electrochemical studies revealed the photoresponsive nature of Ag31, and light illumination resulted in transient intermediate clusters covered with solvated electrons, which contributed to the core expansion. Ag31 is NIR-emitting, while Ag42 is red-emitting. The ultrafast transient absorption studies reveal that Ag42 has strikingly short excited-state carrier dynamics than Ag31. The stable excited-state carriers for Ag31 upon photoexcitation also underline the unique electronic characteristics responsible for such light-activated structural evolution.
  • Rapid Cationization of Gold Nanoparticles by Two-Step Phase Transfer
    (2015-06-26) Hassinen, Jukka; Liljeström, Ville; Kostiainen, Mauri A.; Ras, Robin H. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Cationic gold nanoparticles offer intriguing opportunities as drug carriers and building blocks for self-assembled systems. Despite major progress on gold nanoparticle research in general, the synthesis of cationic gold particles larger than 5nm remains a major challenge, although these species would give a significantly larger plasmonic response compared to smaller cationic gold nanoparticles. Herein we present the first reported synthesis of cationic gold nanoparticles with tunable sizes between 8-20nm, prepared by a rapid two-step phase-transfer protocol starting from simple citrate-capped particles. These cationic particles form ordered self-assembled structures with negatively charged biological components through electrostatic interactions.
  • Reversible switching between superhydrophobic states on a hierarchically structured surface
    (2012) Verho, Tuukka; Korhonen, Juuso T.; Sainiemi, Lauri; Jokinen, Ville; Bower, Chris; Franze, Kristian; Franssila, Sami; Andrew, Pierce; Ikkala, Olli T.; Ras, Robin H. A.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Nature offers exciting examples for functional wetting properties based on superhydrophobicity, such as the self-cleaning surfaces on plant leaves and trapped air on immersed insect surfaces allowing underwater breathing. They inspire biomimetic approaches in science and technology. Superhydrophobicity relies on the Cassie wetting state where air is trapped within the surface topography. Pressure can trigger an irreversible transition from the Cassie state to the Wenzel state with no trapped air—this transition is usually detrimental for nonwetting functionality and is to be avoided. Here we present a new type of reversible, localized and instantaneous transition between two Cassie wetting states, enabled by two-level (dual-scale) topography of a superhydrophobic surface, that allows writing, erasing, rewriting and storing of optically displayed information in plastrons related to different length scales.
  • Self-erasing and rewritable wettability patterns on ZnO thin films
    (2010) Kekkonen, Ville; Hakola, Antti; Kajava, Timo; Sahramo, Elina; Malm, Jari; Karppinen, Maarit; Ras, Robin H. A.
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Self-erasing patterns allow a substrate to be patterned multiple times or could store temporary information for secret communications, and are mostly based on photochromic molecules to change the color of the pattern. Herein we demonstrate self-erasing patterns of wettability on thin ZnO films made by atomic layer deposition. Hydrophilic patterns are written using UV light and decay spontaneously, i.e. become hydrophobic, or are erased aided by vacuum conditions or heat. We demonstrate that these patterns can be applied for channels to confine flow of water without physical walls.
  • Self-transport and self-alignment of microchips using microscopic rain
    (2015-10-09) Chang, Bo; Shah, Ali; Zhou, Quan; Ras, Robin H. A.; Hjort, Klas
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Alignment of microchips with receptors is an important process step in the construction of integrated micro- and nanosystems for emerging technologies, and facilitating alignment by spontaneous self-assembly processes is highly desired. Previously, capillary self-alignment of microchips driven by surface tension effects on patterned surfaces has been reported, where it was essential for microchips to have sufficient overlap with receptor sites. Here we demonstrate for the first time capillary self-transport and self-alignment of microchips, where microchips are initially placed outside the corresponding receptor sites and can be self-transported by capillary force to the receptor sites followed by self-alignment. The surface consists of hydrophilic silicon receptor sites surrounded by superhydrophobic black silicon. Rain-induced microscopic droplets are used to form the meniscus for the self-transport and self-alignment. The boundary conditions for the self-transport have been explored by modeling and confirmed experimentally. The maximum permitted gap between a microchip and a receptor site is determined by the volume of the liquid and by the wetting contrast between receptor site and substrate. Microscopic rain applied on hydrophilic-superhydrophobic patterned surfaces greatly improves the capability, reliability and error-tolerance of the process, avoiding the need for accurate initial placement of microchips, and thereby greatly simplifying the alignment process.
  • Simple and Efficient Separation of Atomically Precise Noble Metal Clusters
    (2014-12-16) Ghosh, Atanu; Hassinen, Jukka; Pulkkinen, Petri; Tenhu, Heikki; Ras, Robin H. A.; Pradeep, Thalappil
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study of their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au25L18, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au25L18 with different ligands, as well as to a binary mixture of different cluster cores, Au-25 and Au-144, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au-25 clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties.
  • Slippery and magnetically responsive micropillared surfaces for manipulation of droplets and beads
    (2020-08-01) Al-Azawi, Anas; Horenz, Christoph; Tupasela, Topi; Ikkala, Olli; Jokinen, Ville; Franssila, Sami; Ras, Robin H. A.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Stimuli-responsive surfaces are of practical importance for applications ranging from enhanced mixing of reagents in lab-on-a-chip systems until probing cellular traction forces. Non-destructive reversible bending of cilia-inspired magnetic pillars can be used for controlled transportation of non-magnetic objects and bio-inspired sensing. Magnetic actuation of micropillars suspended in liquids allows controlled mixing, propelling, and stirring of fluids as well as droplet manipulation, which are important for various applications including generation of cell spheroids and droplet coalescence in microfluidic systems. In order to expand their practical applications, fabrication processes capable of rapid prototyping have to be developed. Inspired by biological cilia and their functionalities, actuating hairy surfaces are herein fabricated and implemented to manipulate both microbeads and droplets. The artificial cilia are based on microscale magnetic pillar arrays made of flexible polydimethylsiloxane functionalized with magnetic microparticles. The arrays are fabricated by a new method using patterned molds that relies on cryogenic separation to produce transparent cilia-inspired arrays without requiring manual interference to clean the templates during the process. Magnetic actuation of the pillar arrays is demonstrated in isopropanol and silicone oil. Filling with oil yields magnetically responsive slippery lubricated surfaces allowing directional motion of droplets by repetitive bending and recovery of the flexible magnetic pillars. The achieved structures allow manipulation of microbeads and droplets which is uncommon even at the sub-mm scale; directional motion is demonstrated for 250 μm-550 μm sized droplets. Droplet transportation is facilitated by extremely low hysteresis and a high degree of omnidirectional bending of the pillar array.