Nanotechnology with Soft Matter: From Structures to Functions

Guest-Editors of this Special Issue on Nanotechnology with Soft Matter Soft matter science is a multidisciplinary area of chemistry, physics, biology, and materials science. It essentially deals with matter such as functional polymers, amphiphiles, liquid crystals, colloids, and a number of biological molecules, in which the typical energies of interaction are comparable to thermal energies.1 Nanotechnology involves understanding and controlling matter typically on the sub-100-nanometer scale, where unique phenomena enable novel and functional applications.2 The endeavor in nano-technology is to identify the chemical and physical consequences of the miniaturization and to develop nanoscale functional materials and devices, which differ in fundamental properties from the individual molecules or bulk matter.2, 3 When nanotechnology meets soft matter, the first question that arises is how the soft building blocks can be tailored, manipulated, and assembled into nano-structures. This is one of the fundamental focuses in the materials research frontier. This focus has led to the generation of a broad range of soft nanoscale structures such as supramolecular architectures, gels, vesicles, polymer brushes, molecular aggregates, nanofibers, and nanotubes. The goal of such soft nanomaterials is to create new functional materials and devices with novel and valuable properties, which have enormous burgeoning applications, such as nano-electronics, plastic solar cells, medical implants, biosensors and biochips, as well as regenerative medicine. In fact, soft nanomaterials have been part of our lives. For instance, a living cell is the ultimate example of an integrated soft matter system run principally by nanoscale miniaturization, forming the basis for even higher complexity such as organs and living beings.4 We are still at the infant stages of learning how to design and control the soft nanoscale structures with specific properties. Both technical and basic thermodynamic processes have to be understood by learning from nature before higher degrees of complexity and functions such as self-replication can be targeted. Nanotechnology tools, such as scanning probe microscopy, scanning electron microscopy, and optical microscopy, can be used to characterize the soft nanomaterials. They help in answering the fundamental questions in soft matter systems by shedding light on the processes at the nanoscale level. For example, cryogenic transmission electron microscopy (cryo-TEM), a form of TEM where the samples are studied at very low temperatures, has become an important method for determining the structures of bio-macromolecules and for achieving the 3D reconstruction of entire cells. The new developments in optical microscopy with super spatial resolution, such as stimulated emission depletion (STED) micro-scopy5 and stochastic optical reconstruction microscopy (STORM),6 enables one to directly image live cells and organisms far beyond the sub-diffraction-limit image resolution. Beyond imaging, nanoprobe tools can be used to constructively fabricate soft nanostructured materials. For instance, dip pen nanolithography (DPN), a revo-lutionary tool based on atomic force microscopy (AFM), allows one to fabricate nanoscale patterns of biomolecules, such as DNA and proteins, on surfaces by directly transferring molecules from the AFM tip.7 The obtained nano-structured arrays play significant roles in biodiagnostic screening for nucleic acids, proteins, and some biologically relevant small molecules.8 In order to exploit and advance fruitful synergies between soft matter and nanotechnology, we are delighted to organize and present this special issue of Small with the topic of Nanotechnology with Soft Matter. The idea was inspired by the symposium of Nano-technology with Soft Matter at the International Conference on Materials for Advanced Technologies (ICMAT) 2011 in Singapore. This issue brings together contributions from many leading scientists and contains five Review articles, two Concept papers, eight Communications, and eight Full Papers. It covers the following five detailed aspects of nanotechnology with soft matter. 1. Structuring soft-materials at the nanoscale. Normally, two fundamental approaches, Bottom-up and Top-down, are used to synthesize and assemble soft building blocks into higher-order structures. For example, Lu et al. discussed their ability to control the position of proteins in the 3D DNA tetrahedron, and Hu et al. chemically synthesized single-crystalline sharp nanocone arrays of a charge-transfer complex (copper tetracyanoquino-dimethane), which exhibited excellent field-emission properties. Zhang and his collaborators highlighted their recent work on building well-defined nanostructured soft materials by using superamphiphiles. Additionally, Weiss, Andrews, and their co-workers reported their work on using molecular printing methods, such as microcontact insertion printing (μCIP), to fabricate bioactive molecule nanoarrays, which could work as a platform for single-cell-level manipulation and analysis. The substrate or matrix with nanoscale feature can be used as templates to fabricate soft nanostructures with unique optical properties, as demonstrated by Fuchs, Knoll, and their collaborators. Ariga, Chi, Feng, and their collaborators reviewed the converging bottom-up and top-down methods for the formation of organic-thin-film-based nanoarchitectures and conducting polymers patterning, which offer great potential for the development of next-generation devices with electrical, optical, chemical, or biological functions. 2. Fabrication of complex or composite nanomaterials. Understanding and controlling the processes to form complex or composite nanomaterials is an important goal in designing complex functional nanosystems. De Cola and her co-workers described their recent effort in building antenna-like nano-assemblies by coating the dye-loaded zeolite L surface with quantum dots, which showed Förster resonance energy transfer. Alternatively, soft materials (e.g., DNA) can be used as building blocks to induce the assembly of nanoparticles. In this regard, a stepwise thermal and photothermal dissociation of a hierarchical superaggregate of DNA-functionalized gold nanoparticles was demonstrated by Simon et al. This could be of interest in the design of stimuli-responsive materials. Tang, Zhang, Wang, and their collaborators realized composite fluorescent nanoparticles, such as fluorescent silica nanoparticles and luminescent quantum dots coated by amphiphilic polymers, which are benign to living cells and function as fluorescent visualizers for intracellular imaging of HeLa cells due to efficient light emission, excellent colloidal stability, and size tenability. 3. Nanotechnology tools to study the properties of soft nanostructures. As highlighted earlier, nanotechnology tools can be used to characterize the soft nanomaterials by imaging or measuring physical properties to reveal fundamental processes at the nanoscale level. For instance, Vancso et al. probed the collapse dynamics of poly(N-isopropylacrylamide) brushes by in-situ AFM force measurements to reveal the effects of co-nonsolvency and grafting densities. Bazan et al. did a systematic evaluation on nanoscale morphology of a novel conjugated polymer, bearing alkyl side chains on both the donor and acceptor units, to understand the importance of the nanoscale morphology in efficient collection of the photogenerated mobile carriers in plastic solar cells. Spatz and his collaborators revealed the age-dependent changes in cell mechanical properties and in active mechanoresponses by determining the stiffness of human fibroblasts from AFM measurement as well as the cell's reaction to periodic mechanical deformation of the culture substrate. This work is important for understanding the affect of cellular aging on cell mechanical properties and other fundamental physiological cell functions. 4. Nano-bio-interfaces. Nanostructured interfaces are used for studying problems in cell and molecular biology, as well as monitoring and addressing the fundamental aspects related to soft nanotechnology. Venkatraman, Tan, and their co-workers presented how the advancements in micro-/nano-engineering methods allowed researchers to manipulate and engineer a plethora of cellular behaviors, such as spreading and adhesion, induced alignment, as well as stem cell differentiation. The interaction of nanoparticles with soft surfaces of biological systems, such as cells, plays key roles in executing their biomedical functions or toxicity. In this regard, Zhao et al. discussed the cellular uptake ways, as well as location and translocation of nanoparticles, and the cellular responses with potential signaling pathways activated by nanoparticle interactions. 5. Applications of soft nanomaterials. The key impetus for understanding the structure and function of soft nano-materials is to identify suitable applications for them, which constitutes a main research effort in this field. For instance, a new amphiphilic conjugated polythio-phene derivative synthesized by Wang et al. was used for cell imaging and monitoring cellular distribution of cis-platin anticancer drug. This will provide a platform for fluorescent imaging of specific drugs and biological molecules in living cells. The pioneering use of vault nanoparticles (one of the largest known ribonucleoprotein complexes in the sub-100-nanometer range) as vehicles for drug delivery was discussed by Rome et al. Colorimetric detection assays based on Au–biomolecule composite nanoparticles were developed by Liu, Chen, and their collaborators for the detection of HIV-1 ribonuclease H activity and mercuric ion. Such assays showed several superior properties, such as rapid read-out, flexibility, and point-of-care monitoring. It is worthy to note that the progress in this emerging field is impossible without the cross-fertilization between the chemistry, physics, biology, materials science, and engineering communities. We hope that this issue will provide stimulating highlights of the design, fabrication, and exploitation of soft nanomaterials. New soft nanoscale materials and structures, responsive and active soft nanomaterials and devices, functional organic nanoelectronics, integrated nano-bio-interfaces, and energy related issues, will be several key areas to be addressed in this emerging field. In addition, new developments in nano-technology tools and analytical methods, such as microscopes with superhigh spatial and temporal resolution, would be needed to promote and ignite the exploration on soft matter. We are most grateful for the kind support and cooperation from the whole editorial team of Small, in particular Dr. Jos Oliveira and Dr. Lianne Beltran. We would also like to express our gratitude to the colleagues who shared and contributed their research to this exciting and explorative volume of nanotechnology with soft matter. Freddy Yin Chiang Boey received his PhD from the National University of Singapore in 1987. He is currently the Provost and a Professor at Nanyang Technological University (NTU). Prior to his current appointment, he was the Chair of NTU's School of Materials Science and Engineering from 2005 to 2010. His research interests include functional biomaterials for medical devices and nanomaterials for cell regeneration, sensing, and energy storage. Harald Fuchs is Professor of experimental physics at the University of Muenster, Germany, and Scientific Director of the Center of Nanotechnology (CeNTech) in Muenster. His research focuses on nanoscale science and nanotechnology, ranging from scanning probe microscopy to self-organized nanostructure fabrication, and nano-biosystems. He has published more than 350 scientific articles in top journals. He was awarded the Philip Morris Research Prize “Challenge Future” in 1994 and the Münsterland Innovation Prize in 2001. He is currently a member of various scientific organizations and is an elected member of the German National Academy of Science ‘Leopoldina’ and the German Academy of Science and Engineering ‘acatech’. Xiaodong Chen is a Singapore NRF Fellow and Nanyang Assistant Professor at the School of Materials Science and Engineering, Nanyang Technological University (Singapore). He received his B.S. degree (Honors) in Chemistry from Fuzhou University (China) in 1999, M.S. degree (Honors) in Physical Chemistry from the Chinese Academy of Sciences in 2002, and Ph.D. degree (Summa Cum Laude) in Biochemistry from the University of Muenster (Germany) in 2006. After his postdoctoral fellowship at Northwestern University (USA), he started his independent research career at Nanyang Technological University in 2009. His research interests include self-assembly, plasmonics, nanoelectronics, and integrated nano-photo-bio-interfaces.