Poly (N-isopropylacrylamide) Microgel-Based Optical Devices for Sensing and Biosensing

Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group’s efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications

N-isopropylacrylamide-based Photopolymer for Holographic Recording of Thermosensitive Transmission and Reflection Grating

In recent years, functionalized photopolymer systems capable of holographic recording are in great demand due to their potential use in the development of holographic sensors. This work presents a newly developed Nisopropylacrylamide(NIPA)-based photopolymer for holographic recording in reflection and transmission modes. The optimized composition of the material is found to reach refractive index modulation of up to 5 10-3 and 1.6 10-3 after recording in transmission and reflection mode, respectively. In addition to fulfilling the requirements for holographic recording materials, the NIPA-based photopolymer is sensitive to temperature and has lower toxicity than acrylamide-based photopolymers. Possible application of the NIPA-based photopolymer in the development of a holographic temperature sensor is discussed

Waterborne electrospinning of poly(N-isopropylacrylamide) by control of environmental parameters

With increasing toxicity and environmental concerns, electrospinning from water, i.e., waterborne electrospinning, is crucial to further exploit the resulting nanofiber potential. Most water-soluble polymers have the inherent limitation of resulting in water-soluble nanofibers, and a tedious chemical cross-linking step is required to reach stable nanofibers. An interesting alternative route is the use of thermoresponsive polymers, such as poly(N-isopropylacrylamide) (PNIPAM), as they are water-soluble beneath their lower critical solution temperature (LCST) allowing low-temperature electrospinning while the obtained nanofibers are water-stable above the LCST. Moreover, PNIPAM nanofibers show major potential to many application fields, including biomedicine, as they combine the well-known on off switching behavior of PNIPAM, thanks to its LCST, with the unique properties of nanofibers. In the present work, based on dedicated turbidity and rheological measurements, optimal combinations of polymer concentration, environmental temperature, and relative humidity are identified allowing, for the first time, the production of continuous, bead-free PNIPAM nanofibers electrospun from water. More specifically, PNIPAM gelation was found to occur well below its LCST at higher polymer concentrations leading to a temperature regime where the viscosity significantly increases without compromising, the polymer solubility. This opens up the ecological, water-based production of uniform PNIPAM nanofibers that are stable in water at temperatures above PNIPAM's LCST, making them suitable for various applications, including drug delivery and switchable cell culture substrates

The Role of the Initiator System in the Synthesis of Acidic Multifunctional Nanoparticles Designed for Molecular Imprinting of Proteins

Multifunctional nanoparticles have been shown earlier to bind certain proteins with high affinity and the binding affinity could be enhanced by molecular imprinting of the target protein. In this work different initiator systems were used and compared during the synthesis of poly (N-isopropylacrylamide-co-acrylic acid-co-N-tert-butylacrylamide) nanoparticles with respect to their future applicability in molecular imprinting of lysozyme. The decomposition of ammonium persulfate initiator was initiated either thermally at 60 °C or by using redox activators, namely tetramethylethylenediamine or sodium bisulfite at low temperatures. Morphology differences in the resulting nanoparticles have been revealed using scanning electron microscopy and dynamic light scattering. During polymerization the conversion of each monomer was followed in time. Striking differences were demonstrated in the incorporation rate of acrylic acid between the tetramethylethylenediamine catalyzed initiation and the other systems. This led to a completely different nanoparticle microstructure the consequence of which was the distinctly lower lysozyme binding affinity. On the contrary, the use of sodium bisulfite activation resulted in similar nanoparticle structural homogeneity and protein binding affinity as the thermal initiation

Thermosensitive poly(N-acryloyl glycinamide) microgels and their application in catalysis

Poly(N-acryloyl glycinamide) (PNAGA) is a non-ionic polymer possessing an upper critical solution temperature (UCST) in water and saline solutions. This thesis explores the synthesis of stimuli-responsive PNAGA microgels and immobilization of catalytically active species inside these. The synthesis of poly(N-acryloylglycinamide) (PNAGA) microgels was conducted in water by free radical precipitation polymerization below the phase transition temperature of PNAGA in the presence of N,N’-methylenebisacrylamide crosslinker. These water dispersed PNAGA microgels show reversible size changes, swelling upon heating and shrinking upon cooling. Using these PNAGA microgels as host for nanocatalysts was carried out by loading silver nanoparticles (AgNPs) via reduction of AgNO3.The thermosensitive behavior of the PNAGA microgels was retained after loading AgNPs, and the catalytic activity of the metal particles in 4-nitrophenol reduction was tested under different conditions. Furthermore, it was shown that the catalytic activity of the AgNP–PNAGA microgels could be switched on and off by changing the temperature and utilizing the thermosensitivity. To realize biocatalytic microgels, immobilization of an enzyme, β-D-glucosidase, was done by encapsulation of the enzyme during the NAGA precipitation polymerization. Properties of these hybrid microgels were studied varying the enzyme-monomer ratio and the degree of crosslinking. The microgel encapsulated enzymes showed enhanced activity at high pH compared to the native enzymes. Tandem catalysts were then produced by further encapsulation of AgNPs. These were used in cascade reactions involving first enzymatic catalysis followed by AgNP induced reduction. The catalyst loading efficiency as well as the manipulation of the thermoresponsive properties was performed by copolymerizing methacrylic acid (MAA) with NAGA. The volume phase transition behavior and interactions between NAGA and MAA in the poly(N-acryloyl glycinamide-co-methacrylic acid) [P(NAGA−MAA)] copolymer microgels were studied. AgNPs were immobilized inside the P(NAGA−MAA) microgels using both UV light and chemical reduction. The photoreduction resulted in smaller AgNPs and the amount and size of the AgNPs was observed to depend on the content of MAA. The UV-reduced AgNPs show significantly higher catalytic activity than chemically reduced AgNPs in P(NAGA-MAA) microgels.Tämä opinnäytetyö tutkii ärsykkeisiin reagoivien poly(N-akryyliglysinamidin) (PNAGA)-mikrogeelien synteesiä ja niiden käyttöä katalyyttisiin sovelluksiin. Veteen dispergoidut PNAGA-mikrogeelit turpoavat kuumennettaessa ja kutistuvat jäähtyessään. Mikrogeeleihin lisättiin hopeananopartikkeleita pelkistämällä ja niiden katalyyttinen aktiivisuus 4-nitrofenolin pelkistyksessä testattiin eri olosuhteissa. Tutkimuksissa osoitettiin että katalyyttinen aktiivisuus kasvaa lämmitettäessä mikrogeelien turpoamisen aiheuttaman reaktanttien lisääntyneen diffuusion vuoksi ja että katalyyttinen aktiivisuus voidaan kytkeä päälle ja pois päältä muuttamalla lämpötilaa. Biokatalyyttisten mikrogeelien toteuttamiseksi entsyymin, β-D-glukosidaasin, immobilisaatio tehtiin kapseloimalla entsyymi saostuspolymeroinnin aikana. Näiden hybridimikrogeelien ominaisuuksia tutkittiin vaihtelemalla entsyymi-monomeerisuhdetta ja silloittumisastetta. Mikrogeelikapseloidut entsyymit osoittivat parempaa aktiivisuutta korkeassa pH:ssa verrattuna alkuperäisiin entsyymeihin. Näistä tuotettiin edelleen ns. tandem -katalyyttejä lisäämällä hopeananopartikkeleita. Näitä kaksi katalyyttispesiestä omaavia mikrogeelejä käytettiin kaskadireaktioissa. Hopeakatalyytin lataustehokkuutta sekä lämpöresponsiivisten ominaisuuksien muokkausta suoritettiin kopolymeroimalla metakryylihappoa N-akryyliglysinamidin kanssa sekä vertaamalla hopeapartikkelien pelkistämistä UV-valolla kemiallisenn pelkistystä. Happoa sisältävillä ja UV-pelkistetyillä mikrogeeleillä saavutettiin merkittävästi parempi katalyyttinen aktiivisuus

Développement d'un film mince à base de polymère thermo-sensible pour la détection d'analytes cibles

Les polymères stimuli-sensibles ont considérablement attiré l’intérêt scientifique grâce à leur capacité à changer de conformation ou d’état de solvatation sous l’influence d’un stimulus externe tel que la température, le pH, la lumière, les champs électriques et magnétiques ou encore la composition du solvant. Ces polymères peuvent être préparés sous différentes formes (micro-/nanoparticules, films minces, membranes, polymère peigne, micelles …) et sont utilisés dans diverses applications telles que l’ingénierie tissulaire, la vectorisation/libération de médicaments et les (bio)capteurs. Dans le domaine des capteurs, les polymères stimuli-sensibles sont souvent utilisés comme transducteurs entre le milieu à analyser et la plateforme de détection. Le but de cette étude est de développer un film transducteur à base de polymère thermo-sensible pour la détection du fer. La première étape consiste à synthétiser un microgel de poly(N-isopropylacrylamide-co-acide acrylique) (PNIPAM-co-AAc) via une polymérisation radicalaire par précipitation en utilisant un monomère thermo-sensible (NIPAM), un co-monomère (AAc) et l’agent de réticulation N, N’-methylenebis(acrylamide) (BIS). La réaction mène à des microgels dotés d’une température critique inférieure de solubilité (LCST) définie comme la température à laquelle le microgel subit une transition d’un état gonflé à un état replié. Dans le but d’étudier la taille du microgel, la concentration en monomères et la vitesse d’agitation sont variés. Ensuite, les quantités de co-monomère (AAc) et de réticulant (BIS) sont variés afin d’étudier le comportement thermo-sensible. Toutes ces synthèses produisent des microgels dont la LCST se situe autour de 30-32°C avec une excellente réversibilité de la transition de l’état gonflé vers l’état replié. Considérant la nature de l’objet (microgel), la synthèse utilisée dans ce projet est reproductible d’un point de vue taille de microgel et LCST. Afin de prouver le concept de détection, les microgels sont fonctionnalisés avec la dopamine qui contient des groupements catéchol connus pour leur affinité spécifique avec les ions du fer. La LCST des microgels fonctionnalisés est décalée vers les plus hautes températures et la transition de phase est moins brutale. La deuxième étape du projet consiste à déposer le microgel sur un substrat en verre revêtu d’une fine couche d’or fonctionnalisée avec la cystéamine. Différents paramètres (pH, concentration, température, durée de trempage) sont variés afin d’optimiser la déposition du microgel. La microscopie à force atomique (AFM) est utilisée pour observer la surface du microgel déposé et déterminer les conditions optimales de déposition. Suite à cette étape, la spectroscopie par résonance de plasmon de surface (SPR) est utilisée dans le but d’étudier les comportements thermo- et iono-sensibles du film mince de microgel.Stimuli-responsive polymers have attracted considerable scientific interest because of their ability to undergo conformational or solvation state changes under the influence of an external stimulus such as temperature, pH, light, magnetic and electric field or solvent composition. These polymers can be prepared in various architectures (as micro-/nanoparticles, thin films, membranes, polymer brushes, micelles …) and have found application in diverse fields, including tissue engineering, drug delivery and as (bio)sensors. In the field of sensors, stimuliresponsive polymers are often used as transducers between the environment to be analyzed and the detection platform. In this study, we aim to develop a transducer film based on a thermo-responsive polymer for iron detection. The first step is to synthesize a poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-AAc) microgel via free radical precipitation polymerization using a thermo-responsive monomer (NIPAM), a co-monomer (AAc) and a crosslinker (N, N’-methylenebisacrylamide) (BIS). This polymerization yields microgels which exhibit a Lower Critical Solution Temperature (LCST), identified as the temperature at which the microgel undergoes a transition from a swollen state to a collapsed state. In order to study the microgel size, the monomer concentration and the stirring speed were varied. Then, the comonomer (AAc) and crosslinker (BIS) quantities were varied to study the thermo-responsive behaviour. All of these syntheses produce microgels with a LCST around 30-32°C and an excellent reversibility in terms of transition from the swollen state to the collapsed state. Considering the nature of the object (microgel), the synthesis used in this project is reproducible in terms of microgel size and LCST. To demonstrate the detection concept, microgels are functionalized with dopamine that contains catechol groups known for their specific affinity for the iron ions. The LCST of functionalized microgels shifts toward higher temperatures and their phase transition is less sharp. The second step of the project consists of depositing the microgel on a glass substrate coated with a gold thin film functionalized with cysteamine. Different parameters (pH, concentration, temperature, dipping duration) were varied in order to optimize microgel deposition. Atomic Force Microscopy (AFM) was used to observe the surface of the microgel to determine the optimal coating conditions. After this step, Surface Plasmon Resonance (SPR) spectroscopy was used to characterize the thermo- and iono-responsive behaviours of the microgel thin film

Poly (N-isopropylacrylamide) Microgel-Based Optical Devices for Sensing and Biosensing

Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group’s efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications

Poly (N-isopropylacrylamide) Microgel-Based Optical Devices for Sensing and Biosensing

Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group’s efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications