Paula M. Mendes

Stimuli-responsive surfaces for bio-applications

The development of surfaces that have switchable properties, also known as smart surfaces, have been actively pursued in the past few years. The recent surge of interest in these switchable systems stems from the widespread number of applications to many areas in science and technology ranging from environmental cleanup to data storage, micro- and nanofluidic devices. Moreover, the ability to modulate biomolecule activity, protein immobilisation, and cell adhesion at the liquid-solid interface is important in a variety of biological and medical applications, including biofouling, chromatography, cell culture, regenerative medicine and tissue engineering. Different materials have been exploited to induce such changes in surface biological properties that are mostly based on self-assembled monolayers or polymer films. This critical review focuses on the recent progress in the preparation of these switchable surfaces, and highlights their applications in biological environments. The review is organized according to the external stimuli used to manipulate the properties of the substrate-chemical/biochemical, thermal, electric and optical stimuli. Current and future challenges in the field of smart biological surfaces are addressed (189 references).

Bio-nanopatterning of Surfaces

Bio-nanopatterning of surfaces is a very active interdisciplinary field of research at the interface between biotechnology and nanotechnology. Precise patterning of biomolecules on surfaces with nanometre resolution has great potential in many medical and biological applications ranging from molecular diagnostics to advanced platforms for fundamental studies of molecular and cell biology. Bio-nanopatterning technology has advanced at a rapid pace in the last few years with a variety of patterning methodologies being developed for immobilising biomolecules such as DNA, peptides, proteins and viruses at the nanoscale on a broad range of substrates. In this review, the status of research and development are described, with particular focus on the recent advances on the use of nanolithographic techniques as tools for biomolecule immobilisation at the nanoscale. Present strengths and weaknesses, as well future challenges on the different nanolithographic bio-nanopatterning approaches are discussed.

Cellular nanotechnology: making biological interfaces smarter

Nanostructured materials can be used as smart interfaces to further understand and control the complex interplay of events and interactions occurring within living cells.

Tailoring 3D Single-Walled Carbon Nanotubes Anchored to Indium Tin Oxide for Natural Cellular Uptake and Intracellular Sensing

The ability to monitor intracellular events in real time is paramount to advancing fundamental biological and clinical science. We present the first demonstration of a direct interface of vertically aligned single-walled carbon nanotubes (VASWCNTs) with eukaryotic cells, RAW 264.7 mouse macrophage cell line. The cells were cultured on indium tin oxide with VASWCNTs. VASWCNTs entered the cells naturally without application of any external force and were shown to sense the intracellular presence of a redox active moiety, methylene blue. The technology developed provides an alluring platform to enable electrochemical study of an intracellular environment.

Discrete Functional Gold Nanoparticles: Hydrogen Bond-Assisted Synthesis, Magnetic Purification, Supramolecular Dimer and Trimer Formation

Amine monofunctional gold nanoparticles (1-AuNPs) were synthesized by employing a solid-supported technique and pH-switchable pseudorotaxane formation. Purification was repeatedly facilitated using crown ether peripherally coated superparamagnetic iron oxide microspheres to yield the monofunctional gold nanoparticles in excellent yield. The product and its related intermediate superstructures were characterized by IR and X-ray photoelectron spectroscopies. Novel supramolecular dimers and trimers were prepared by titrating the 1-AuNPs with bisDB24C8 and trisDB24C8 at different ratios. UV/visible absorption spectroscopic analyses of the supramolecular dimer and trimer solutions, which were formed by mixing their separate components in different ratios, indicated the gradual appearance of two distinct plasmonic resonance bands at 620 and approximately 700 nm. Furthermore, TEM images of the dimers revealed a significant amount of dimer pairs on the surface, while the TEM images of the trimers demonstrated the presence of both dimers and trimers. The trimers appeared as triangular or near-linear shapes.

An Electrically Reversible Switchable Surface to Control and Study Early Bacterial Adhesion Dynamics in Real‐Time

Bacterial adhesion can be controlled by applying electrical potentials to surfaces incorporating well-spaced negatively charged 11-mercaptoundecanoic acids. When combined with electrochemical surface plasmon resonance, these dynamic surfaces become powerful for monitoring and analysing the passage between reversible and non-reversible cell adhesion, opening new opportunities to advance our understanding of cell adhesion processes.

Arp2/3 complex activity in filopodia of spreading cells

BackgroundCells use filopodia to explore their environment and to form new adhesion contacts for motility and spreading. The Arp2/3 complex has been implicated in lamellipodial actin assembly as a major nucleator of new actin filaments in branched networks. The interplay between filopodial and lamellipodial protrusions is an area of much interest as it is thought to be a key determinant of how cells make motility choices.ResultsWe find that Arp2/3 complex localises to dynamic puncta in filopodia as well as lamellipodia of spreading cells. Arp2/3 complex spots do not appear to depend on local adhesion or on microtubules for their localisation but their inclusion in filopodia or lamellipodia depends on the activity of the small GTPase Rac1. Arp2/3 complex spots in filopodia are capable of incorporating monomeric actin, suggesting the presence of available filament barbed ends for polymerisation. Arp2/3 complex in filopodia co-localises with lamellipodial proteins such as capping protein and cortactin. The dynamics of Arp2/3 complex puncta suggests that they are moving bi-directionally along the length of filopodia and that they may be regions of lamellipodial activity within the filopodia.ConclusionWe suggest that filopodia of spreading cells have regions of lamellipodial activity and that this activity affects the morphology and movement of filopodia. Our work has implications for how we understand the interplay between lamellipodia and filopodia and for how actin networks are generated spatially in cells.

A bis-boronic acid modified electrode for the sensitive and selective determination of glucose concentrations

A bis-boronic acid modified electrode for the sensitive and selective determination of glucose concentrations has been developed. The electrochemical characteristics of the sensor with added saccharides were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The bis-boronic acid modified electrode was both sensitive and selective for glucose.

Glucose selective Surface Plasmon Resonance-based bis-boronic acid sensor

Saccharides - a versatile class of biologically important molecules - are involved in a variety of physiological and pathological processes, but their detection and quantification is challenging. Herein, surface plasmon resonance and self-assembled monolayers on gold generated from bis-boronic acid bearing a thioctic acid moiety, whose intramolecular distance between the boronic acid moieties is well defined, are shown to detect d-glucose with high selectivity, demonstrating a higher affinity than other saccharides probed, namely d-galactose, d-fructose and d-mannose.

Nafion®-stabilised Pt/C electrocatalysts with efficient catalyst layer ionomer distribution for proton exchange membrane fuel cells

We report a facile method for the preparation of proton exchange membrane fuel cell (PEMFC) electrocatalysts from Nafion®-stabilised colloidal Pt nanoparticles (Nafion®-Pt/C), offering synthetically-directed formation of the Pt-ionomer interface and providing unprecedented control over the morphology of Pt particles on the carbon support. Electrochemical characterisation of the catalysts in aqueous acidic electrolytes using Rotating Disc Electrode (RDE) techniques revealed that Nafion®-Pt/C catalysts possessed similar specific activity and mass activity towards the oxygen reduction reaction (ORR) as commercial Pt/C catalysts, whilst requiring lower overall ionomer loadings. Combined with the near-100% utilisation measured for the Nafion®-Pt/C catalysts, this implies that Pt nanoparticles synthesised with Nafion® as a stabiliser can be ‘tuned’ to have simultaneous access to the reactant gas, the electron conducting carbon support and the proton conducting polymer electrolyte in the catalyst layer, thereby optimising the triple-phase reaction zone. By taking advantage of this bottom-up approach, which allows nanoscale control of the Nafion®–Pt–carbon interface, new opportunities exist to lower the Pt loading and the cost of the fuel cell.