Stimuli-responsive nanomaterials for controlled delivery by light, magnetic and electrical triggers

The use of nanomaterials for biomedical applications is an emerging and important field. This is particularly true of advancements in targeted and controlled drug delivery, which offer several important improvements over traditional drug administration. The clinical efficacy of small-molecule therapeutics is currently limited by many factors, including: poor solubility, inefficient cellular uptake, overly rapid renal clearance and an inability to target only desired locations such as diseased tissues. The use of nanocarriers for drug delivery may greatly improve the efficacy over traditional therapeutics by lowering the total dosage, limiting the exposure to affected areas only, and giving greater temporal control over drug elution. These materials often make use of both organic and inorganic components, exploiting the unique and useful properties of each constituent to achieve novel, synergistic functions. This dissertation presents a study of nanocomposites comprising the three most important materials in this field: titania, iron oxides and polypyrrole. Titania is a strong photocatalyst, iron oxides provide useful responses to applied magnetic fields, and polypyrrole is a polymer with unique electrochemical properties. Studies in this dissertation were aimed at combining these three materials to create a novel structure that is responsive towards light, magnetic fields and electrical stimulation to serve as an enabling platform for the loading and release of biologically interesting compounds. These nanomaterials have been paired with amino acids L-lysine and L-glutamic acid, two organic molecules of interest due to their ability to bind to DNA and proteins, and to form prodrugs that exhibit enhanced performance compared to traditionally administered medicines. Two model compounds have been loaded and released on these carriers: Ketoprofen, an important anti-inflammatory that is traditionally hindered by its limited cellular uptake levels; and fluorescein isothiocyanate, a fluorescent dye molecule that is a common tool used in this field for nanocarrier location and easy visualisation of release-related kinetics. First, an investigation into the effect of pH on the binding of amino acids to titania, iron oxide and polypyrrole is presented with a view towards optimising the functionalised material for subsequent loading and release of the model drugs (in this case, amine-reactive molecules). The release mechanism of photo-activated TiO2 is studied in detail with a particular focus on the competition between the cleavage of bonds versus organic degradation on the catalyst’s surface. Both mechanisms are currently reported in literature and studies were aimed at identifying the more dominant pathway in the system developed alongside understanding the crucial role of reaction time scales on this photochemistry. Then, the pH-tuneable flocculation of the amino acid-functionalised nanoparticles via electrostatic attractions is exploited to create a novel, anisotropic assembly of iron oxides. These filaments display a dynamic and unique response towards a rotating magnetic field by creating local microscale vortices. This motion is used to enhance local delivery rate of molecules through magnetic-field triggered microscale mixing. Finally, this anisotropic iron oxide structure is combined with polypyrrole to create a unique, novel material that possesses directional conductivity, a photothermal response, and magnetic field-triggered release of loaded molecules at enhanced and controllable rates compared with traditional diffusion-limited systems

Advances in Materials and Technologies for Gas Sensing from Environmental and Food Monitoring to Breath Analysis

Gas sensing research experiences a worldwide revival in the last years. From one side, the emergence of novel sensing materials enables unprecedented capacities for improving the device performances. From the other, the increasing opportunities for applications impacting current societal priorities highly motivate further studies. Here, this field is reviewed with special attention to the emerging approaches and the most recent breakthroughs, challenges, and perspectives. In particular, this study focuses on: 1) the sensing layers analyzing recent trends toward nanostructured, low-dimensional and composite materials; and 2) the latest achievements and targets in terms of applications, from environmental monitoring to food aroma identification and quality control up to the healthcare sector with breath analysis and diseases diagnosis

Electrically tunable optical metasurfaces

Optical metasurfaces have emerged as a groundbreaking technology in photonics, offering unparalleled control over light–matter interactions at the subwavelength scale with ultrathin surface nanostructures and thereby giving birth to flat optics. While most reported optical metasurfaces are static, featuring well-defined optical responses determined by their compositions and configurations set during fabrication, dynamic optical metasurfaces with reconfigurable functionalities by applying thermal, electrical, or optical stimuli have become increasingly more in demand and moved to the forefront of research and development. Among various types of dynamically controlled metasurfaces, electrically tunable optical metasurfaces have shown great promise due to their fast response time, low power consumption, and compatibility with existing electronic control systems, offering unique possibilities for dynamic tunability of light–matter interactions via electrical modulation. Here we provide a comprehensive overview of the state-of-the-art design methodologies and technologies explored in this rapidly evolving field. Our work delves into the fundamental principles of electrical modulation, various materials and mechanisms enabling tunability, and representative applications for active light-field manipulation, including optical amplitude and phase modulators, tunable polarization optics and wavelength filters, and dynamic wave-shaping optics, including holograms and displays. The review terminates with our perspectives on the future development of electrically triggered optical metasurfaces

Hydrolysis-directed Vapor-phase Synthesis and Solution Processing of Nanostructured Conducting Polymers

Conducting polymers are a class of organic material that possesses semiconducting properties. Their unique molecular structure facilitates charge transport via delocalized π-electron network in the polymer backbone. Creating nanostructures in a conducting polymer increases its surface area to volume ratio and promotes molecular interaction at the surface of the polymer, resulting in enhanced physical and chemical properties, such as ion transfer, adsorption/desorption efficiency, and electrical conductivity. This dissertation focuses on synthesizing nanostructured conducting polymers and their composites from the vapor phase. The mechanisms in a novel synthetic strategy that utilizes iron corrosion products to initiate polymerization and template nanostructure formation is examined. Vapor-phase synthesis is carried out on both organic and inorganic substrates, and varying reaction conditions, such as temperature, reaction time, or anions in the iron(III) salt, creates a spectrum of morphologies (0D particles, 1D fibers, and amorphous films). This dissertation also presents methods for overcoming challenges in conducting polymer processing. Vapor-phase synthesized conducting polymers are fabricated into electrodes for state-of-art supercapacitors, humidity and temperature sensors, and proof-of-concept functional 3D-printed objects

ADVANCED ANIONIC DOPANTS FOR POLYPYRROLE BASED ELECTROCHEMICAL SUPERCAPACITORS

Electrochemical Supercapacitors (ES), also known as Supercapacitor or Ultracapacitor, has been regarded as an advanced electrical energy storage device for decades. Fabrication of advanced electrode materials is of critical importance for advanced ES. Among various materials used for ES electrode, polypyrrole (PPy) is found to be a promising material due to high specific capacitance, good electrical conductivity, low cost and ease of processing. The use of advanced anionic dopants and addition of multiwall carbon nanotube (MWCNT) have been proved an .effective approach towards advanced PPy based ES with improved electrochemical behaviors. In this research, chemical polymerization of PPy powders and PPy/MWCNT composite materials have been successfully accomplished in presence of advanced anionic dopants, including chromotrope families, amaranth, pyrocatechol violet, eriochrome cyanine R and acid fuchsin. The influence of polyaromatic dopants with different molecular size, charges and charge to mass ratios on the microstructure and electrochemical characteristics has been discussed. PPy coated MWCNT with uniform microstructures was successfully achieved in simple chemical methods. The results showed PPy powders with enhanced microstructures and electrochemical behaviors can be obtained by using such advanced anionic dopants. Multi-charged polyaromatic dopants with larger molecular size benefitted PPy powders with smaller particle size, improved specific capacitance, and enhanced cycling stability, at high electrode mass loadings. Moreover, advanced aromatic dispersant and chemical synthesis was proved a simple and effective method for fabrication of PPy/MWCNT composite materials at different PPy/MWCNT mass ratio, among which the powder with PPy/MWCNT mass ratio of 7:3 showed optimum electrochemical performance. Last but not the least, the use of advanced high porosity current collector (Ni foam) allowed high electrode mass loading and good electric conductivity. As a result, advanced PPy/MWCNT composite materials which allows improved electrochemical behaviors, especially at high mass loading, are promising electrode materials for ES.ThesisMaster of Applied Science (MASc

Conducting Diblock Copolymers as Multifunctional Binders for Lithium-Ion Batteries & Surface-Agnostic Highly Stretchable and Bendable Conductive MXene Multilayers

A conductive block copolymer binder P3HT-b-PEO was studied to form a flexible, tough, carbon-free hybrid battery cathode. Only 5 wt. % polymer was required to triple the flexibility of V₂O₅, and electrodes comprised of 10 wt. % polymer had unusually high toughness (293 kJ/m3) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Addition of P3HT-b-PEO increased lithium-ion diffusion, eliminated cracking during cycling, and enhanced cyclability relative to V₂O₅ alone. We compared the P3HT-b-PEO block copolymer binders with P3HT, PEO, and a P3HT/PEO homopolymer blend in carbon-free V₂O₅. The electrode with P3HT-b-PEO binder showed the highest capacity of 190 mAh/g at a 0.1 C-rate after over 200 cycles, a 2.5-fold improvement of that of pure V₂O₅, whereas P3HT, PEO, and the blend exhibited capacities of 139, 130, and 70 mAh/g. The unique architecture of P3HT-b-PEO, wherein P3HT and PEO blocks are covalently bonded, improved the uniform distribution of the conductive binders within the V₂O₅ structure, whereas the analogous P3HT/PEO blend suffers from phase separation. We presented the strong effects of regioregularity and molecular weight of the P3HT block in P3HT-b-PEO on molecular conformation and electrochemical properties by comparing four different P3HT-b-PEOs of varying P3HT regioregularity (86-97%) and molecular weight (8-19 kDa) while the PEO block was kept the same (7 kDa) to isolate the influence of the P3HT block. Our data show that, as increasing regioregularity, the capacity of P3HT-b-PEO significantly increase and, as increasing molecular weight, the redox potential decreases. The underlying reasons for this finding are revealed by the characterizations of P3HT backbone conformation and chain packing. Also, we studied highly stretchable conductive titanium carbide (MXene) multilayer coatings that can undergo extreme deformation while maintaining their electrical conductivity. The conductive and conformal MXene multilayer coatings that can undergo large-scale mechanical deformation while maintaining a conductivity as high as 2,000 S/m. MXene multilayers were successfully prepared onto flexible polymer sheet, stretchable poly(dimethylsiloxane), nylon fiber, and glass. The coating showed a recoverable resistance response to bending (up to 2.5 mm bending radius) and stretching (up to 40% tensile strain)

Preparation and Properties of Porous Carbon Materials

Porous carbon is indispensable in modern technology applications. It is used for energy storage, gas separation, water purification, catalyst support, and chromatography. The diversity of its applications stems from its unique properties, including high specific surface area, tunable pore volume, and chemical stability. Specifically, the large surface area provides high capacitance for the electric double layer capacitor, and catalytic sites for the chemical reaction and binding substrate for other catalysts in the metal air battery, fuel cell, and water splitting. Tunable pore size holds the same importance as the high surface area. Micropores are always prerequisite for the high surface area, and dramatically affect the solvated ions in the capacitive behavior. Mesopores and macropores are necessary for the mass transfer, which is the most dominant process in drug delivery, gas separation, and ions diffusion in the capacitor and fuel cell. The carbon crystal structure always determines chemical stability. Always, the more graphitic or the more graphenic is, the more chemically stable the carbon is. On the contrary, the structure of amorphous carbon is apt to be damaged under high potentials or in the harsh chemical environments, such as strong acid or base. Porous carbon can be synthesized by inorganic template filling, polymer carbonization or catalytic activation; however, these methods are constrained by high cost, tedious preparation process and low yield, which further limit their practical application. In this thesis, I will introduce a porous graphene preparation by CO₂ activation and magnesiothermic reduction of CO₂. On one side, porous carbon preparation by physical activation, such as H₂O and CO₂, and chemical activation, such as ZnCl₂, H₃PO₄, and KOH, has been used industrially for decades, and plenty studies have been devoted to revealing the pore size or surface area changes during the activation, such as volume of micropores increased by H₃PO₄, lower activation temperature and higher yield by ZnCl₂ and increased surface area and graphitic feature by KOH. However, detailed study of the carbon structure evolution during the activation remains unknown. The reaction mechanism of carbon activated by CO₂ is the simplest due to the single product formation of CO, and the simplicity of this reaction makes possible the elucidation of structural evolution of carbon during CO₂ activation. After analyzing the structural evolution revealed by neutron total scattering, TEM, and other characterizations, we have come to the conclusion that the defective graphenic domains are removed, and turbostratic domains are thinned after the nanoporosity is generated in the initial activation. Furthermore, the tailor-designed porous carbon is synthesized in a short activation time with a high surface area with the guide of the mechanistic insights into the structural evolution of carbon. The synthesis of porous carbon by magnesiothermic reduction of CO₂ holds a very similar design principle as the widely used inorganic template methods. However, the magnesiothermic reduction of CO₂ has the following advantages: (1) the template MgO forms simultaneously with porous carbon, and thus no template preparation is required; (2) MgO template can be easily removed by HCl without using highly corrosive and dangerous HF; (3) carbon source CO₂ is almost free compared to the expensive and tedious polymer synthesis in the inorganic template process. Moreover, some further study widens this novel synthesis method: Zn is added to increase the surface area from ~800 m²/g to 1900 m²/g, Cu is added to increase the graphitic and graphenic features, N2 is added to realize the N-doping. In this thesis, the application of porous carbon includes electric double layer capacitor, Li-O₂ battery, microbial fuel cell, and potassium ion batteries. For the electric double layer capacitor, porous carbon with surface area high up to 1900 m²/g showed a high capacitance of 190 F/g even at the high current density of 10 A/g or high sweep rate of 2000 mV/s. The N-doped porous carbon not only increased the capacity if Li-O₂ battery from 5300 mAh/g to 9600 mAh/g, but also lowered the overpotential in the charging process which led to a more stable cycle life. The increased degree of local crystallinity in porous carbon enabled an improved electrochemical performance in the microbial fuel cell, which has the guiding significance on the catalyst design for the microbial fuel cell. The local curvature of the porous carbon provided the epitaxial template for the growth of polynanocrystalline graphite, which showed an improved cycling life for potassium ion battery compared with graphite

Viologen based electroactive polymers and composites for durable electrochromic systems

Electrochromism, the phenomenon of reversible color change induced by a small electric charge, forms the basis for operation of several devices including mirrors, displays and smart windows. Although, the history of electrochromism dates back to the 19th century, only the last quarter of the 20th century has its considerable scientific and technological impact. The commercial applications of electrochromics (ECs) are rather limited, besides top selling EC anti-glare mirrors by Gentex Corporation and airplane windows by Boeing, which made a huge commercial success and exposed the potential of EC materials for future glass industry. It is evident from their patents that viologens (salts of 4,4ʹ-bipyridilium) were the major active EC component for most of these marketed devices, signifying the motivation of this thesis focusing on EC viologens. Among the family of electrochromes, viologens have been utilized in electrochromic devices (ECDs) for a while, due to its intensely colored radical cation formation induced by applying a small cathodic potential. Viologens can be synthesized as oligomer or in the polymeric form or as functionality to conjugated polymers. In this thesis, polyviologens (PVs) were synthesized starting from cyanopyridinium (CNP) based monomer precursors. Reductive coupling of cross-connected cyano groups yields viologen and polyviologen under successive electropolymerization using for example the cyclic voltammetry (CV) technique. For further development, a polyviologen-graphene composite system was fabricated, focusing at the stability of the PV electrochrome without sacrificing its excellent EC properties. High electrical conductivity, high surface area offered by graphene sheets together with its non-covalent interactions and synergism with PV significantly improved the electrochrome durability in the composite matrix. The work thereby continued in developing a CNP functionalized thiophene derivative and its copolymer for possible utilization of viologen in the copolymer blend. Furthermore, the viologen functionalized thiophene derivative was synthesized and electropolymerized in order to explore enhancement in the EC contrast and overall EC performance. The findings suggest that such electroactive viologen/polyviologen systems and their nanostructured composite films as well as viologen functionalized conjugated polymers, can be potentially applied as an active EC material in future ECDs aiming at durable device performances.Elektrokromismi on ilmiö, jossa pienellä sähköisellä varauksella saadaan aikaan palautuva värinmuutos. Monien laitteiden, kuten peilien, näyttöjen tai älykkäiden ikkunoiden, toiminta perustuu tähän ilmiöön. Historiallisesti elektrokromismi on tunnettu 19. vuosisadalta asti, mutta vasta 20. vuosisadan viimeinen neljännes on osoittanut ilmiön huomattavan tieteellisen ja teknologisen merkityksen. Näiden elektrokromismiin perustuvien tekniikoiden kaupallinen hyödyntäminen on vielä melko vähäistä. Tähän asti myydyimpiä tuotteita ovat olleet häikäisysuojatut peilit (Gentex Corporation) ja lentokoneen ikkunat (Boeing), jotka olivat valtavia kaupallisia menestyksiä osoittaen tekniikan mahdollisuudet tulevaisuuden lasiteollisuudessa. Patenteista selviää, että viologeenit (4,4ʹ-bipyridiniumin suolat) ovat yleisimpiä aktiivisia komponentteja useimmissa markkinoilla olevissa sovelluksissa, minkä perusteella tässä väitöskirjassa keskitytään viologeeneihin. Erilaisista sähköväriaineista viologeenejä on käytetty elektrokromisissa laitteissa jo jonkin aikaa johtuen niiden voimakkaan värisestä radikaalikationista, joka saadaan syntymään pienellä katodisella jännitteellä.Viologeenejä voidaan syntetisoida oligomeerinä tai polymeerinä, sekä toiminnallisena ryhmänä osana konjugoitua polymeeriä. Tässä väitöskirjassa polyviologeenit syntetisoitiin käyttämällä lähtöaineena syanopyridinium-pohjaista monomeeriä. Ristiinkytkettyjen syanoryhmien pelkistävä kytkeytyminen tuottaa viologeeniä ja polyviologeeniä peräkkäisissä sähköpolymerisaatioreaktioissa, mikä voidaan toteuttaa käyttämällä menetelmänä esimerkiksi syklistä voltammetriaa. Systeemiä kehitettiin edelleen siten, että polyviologeenistä ja rafeenista valmistettiin komposiitti, jossa parannettiin polyviologeenin stabiilisuutta, menettämättä sen erinomaisia elektrokromisia ominaisuuksia. Grafeenilevyjen hyvä sähköinen johtavuus ja suuri pinta-ala yhdistettynä ei-kovalenttisiin vuorovaikutuksiin ja synergiaetuihin PV:n kanssa paransi huomattavasti komposiittimatriisin elektrokromista kestävyyttä. Työtä jatkettiin kehittämällä CNP:llä funktionalisoitu tiofeenijohdos ja vastaava polymeeri, mikä mahdollisti viologeenin hyödyntämisen kopolymeeriseoksessa. Lisäksi syntetisoitiin ja sähköpolymeroitiin viologeenillä funktionalisoitu tiofeenijohdos, jonka avulla tutkittiin elektrokromisen kontrastin ja kokonaissuorituskyvyn parantumista. Havainnot osoittavat, että sähköisesti aktiivisia viologeeni/polyviologeenisysteemejä ja niistä valmistettuja nanorakenteisia komposiittikalvoja, sekä myös viologeenillä funktionalisoituja konjugoituja polymeerejä on mahdollista hyödyntää aktiivisena elektrokromisena materiaalina tulevissa suorituskyvyltään kestävissä elektrokromisissa laitteissa.Siirretty Doriast

40th Rocky Mountain Conference on Analytical Chemistry

Final program, abstracts, and information about the 40th annual meeting of the Rocky Mountain Conference on Analytical Chemistry, co-sponsored by the Colorado Section of the American Chemical Society and the Rocky Mountain Section of the Society for Applied Spectroscopy. Held in Denver, Colorado, July 25 - August 1, 1998