Bio-Inspired Nanomaterials and Applications

The following sections are included:

• Preface
• List of Contributors
• Contents

Up-conversion nanoparticles (UCNPs), particularly lanthanide-doped nanocrystals, which emit high energy photons under excitation by the near-infrared (NIR) light, have found potential applications in many different fields including biomedicine. Compared with traditional down-conversion fluorescence imaging, the NIR light excited up-conversion luminescence (UCL) imaging, relying on UCNPs, exhibits improved tissue penetration depth, higher photochemical stability and is free of auto-fluorescence background. UCL shows promise in biomedical imaging with high sensitivities. On the other hand, the unique up-conversion (UC) process of UCNPs may be utilized to photosensitive therapeutic agents for applications in cancer treatment. This chapter will focus on the biomedical imaging and cancer therapy applications of UCNPs and their nanocomposites, and discuss recent advances and future prospects in the imaging field.

Polymeric nanoparticles (NPs) have recently emerged as promising candidates for targeted and controlled drug delivery. Theoretically, ideal NPs are capable of possessing high drug loading levels, the ability to deliver drugs to specific pathological sites within the body, and the capacity to rapidly release their drug load at the site of action. However, intracellular barriers such as cellular internalization and endosomal escape have previously hindered drug release in the cytosol or other targeted areas, thereby limiting efficient therapy. Interestingly, intracellular compartments such as the cytosol and nucleus are environments that possess an intrinsically high redox potential. To this end, it is possible to incorporate redox-responsive signals into the polymer architectures of NPs via disulfide linkers or other crosslinking agents. These modifications can thus lead to a more controlled and/or triggered intracellular release of therapeutic agents. Currently, such redox polymeric NPs have been designed and have been based on various nanostructures, including micelles, vesicles, polymersomes, and dendrimers. In this chapter, we highlight several recent and exciting advances in the world of redox-sensitive polymeric NPs that have been designed for intracellular drug delivery, with a focus on their design, drug release performance, and therapeutic benefits.

Polyethylenimine (PEI) is one of the most widely used polymeric gene delivery vectors due to its strong gene binding ability and unique buffering capacity for endosomal escape. However, high transfection ability of PEI is associated with low cytotoxicity. In the past two decades, synthetic methods have been proposed to construct PEI derivatives with improved biocompatibility for safe and potent gene delivery. One method is an integration of PEI with biodegradable polymers such as polyethylene glycol. Another method is the preparation of degradable PEIs, which have chemically hydrolytic linkers. In this chapter, we outline these biocompatible PEIs and their design conception as well as discuss the effects of their physiochemical and gene delivery properties on transfection efficacy and toxicity. It is anticipated that rapid development of biocompatible PEIs will have a great impact on PEI-based gene therapy in the future.

The use of magnetic iron oxide nanoparticles for cancer hyperthermal therapy induced by alternating magnetic field (AMF) is widely accepted. However, AMF applied for clinical therapy requires high currents and voltages. In recent years, a novel strategy of magnetic iron oxide nanoparticle-mediated hyperthermia by near-infrared (NIR) light irradiation has been reported by several research groups. This is a safe, simple and highly efficient strategy for cancer therapy that may be translated into clinical practice. Herein, we discuss the current knowledge on the photothermal therapy (PTT) of the magnetic Fe₃O₄ nanoparticles in vitro and in vivo induced by NIR laser irradiation. The magnetic resonance imaging guided cancer PTT and the limitations of this cancer PTT were also reviewed.

The rapid developments in nanotechnology bring new opportunities to many important fields. Nanomaterial-based novel sensors for environmental safety have attracted great attention. In this chapter, we will review recent progress in nanomaterial-based sensors for detection of environmental pollutants such as heavy metal ions, toxic gases, pesticides and industrial waste water. We will discuss the categories of the three different nanomaterials, namely, metals, carbon materials and semiconductors. Some representative samples will be provided and discussed in brief to illustrate the significant potential of nanomaterial-based sensors in the field of environmental monitoring.

Nanotechnology has great potential in bio-medicine, leading to tremendous efforts in gene transfection, drug delivery, cell targeting and hyperthermia. As researchers gain familiarity with homogeneous nanomaterials, more attention is drawn to Janus nanostructure, an emerging new material with two or more distinct properties. With the uniqueness in asymmetry, Janus nanomaterials offer more possibilities for assembling multifunctional carriers. In this chapter, the synthesis of ternary Janus system of silica, Fe₄O₄ and polystyrene is introduced. A relatively easy method of combining miniemulsion and sol-gel is employed. The reaction mechanism is discussed with controllable morphology obtained. Dual surface functionalities are explored by selectively conjugating targeting group and anti-cancer drug. In vitro drug release profiles indicate a pH-responsive fashion. Cell study proves that the Janus nanocomposites successfully combine targeting and controlled drug release, achieving higher drug efficacy. Future endeavors will focus on structure novelty as well as fabrication simplification and scaling up. With its potential for higher integration, Janus nanostructures can well-serve as a versatile platform for biomedical applications.

Single-molecule detection (SMD) techniques can provide information of the structures, functions, interactions of various molecules at single-molecule level, which can be difficult or impossible to obtain using conventional ensemble averaging techniques. Since traditional single-molecule techniques including scanning probe microscopy methods, organic fluorescent dye assisted optical imaging/spectroscopy methods and electrochemical methods have been well reviewed elsewhere, herein, we will pay special attention to one of the most cutting-edge aspects in recent progress of SMD techniques: nanomaterial-involved optical imaging/spectroscopy singlemolecule detection methods in biomedicine. The related preparing methods of nanomaterial probes, the instruments and analysis methods for SMD and the current application assays in biomedicine will be covered in current chapter.

Carbon nanotubes (CNTs) have many advantages including unique intrinsic physical and chemical properties, have the ability of readily being decorated with various functional materials and biological species and also possess the ability to penetrate into cells, which justifies their worth in being intensively exploited for potential nanobiomedical applications. On the other hand, design and fabrication of multifunctional nanohybrids can significantly improve the early detection and diagnosis of diseases. Thus, it will make great sense in the nanobiomedical area to combine the merits of CNTs and multi-functional nanohybrids together to synthesize CNTs based multi-functional magnetic-fluorescent nanohybrids. In this chapter, we will give an overview on the surface functionalization of CNTs for biomedical applications. Firstly, we will review the water-soluble and biocompatible functionalization of CNTs. Then, we will mainly discuss the combination of CNTs with multi-functional nanohybrids and their applications in multi-modal bioimaging and drug delivery.

RNAi is a sequence-specific post-transcriptional gene silencing (PTGS), which is triggered by double-stranded RNA (dsRNA). Currently, there has been a great interest in the use of small interfering RNA (siRNA) as a research tool to study gene function and drug target validation, and the therapeutic application of siRNAs already draws worldwide attention and appears to show much promise for novel drug discovery. However, RNAi efficiency is largely dependent on the development of many delivery vehicles that can deliver the siRNAs to target cells. This chapter mainly describes intracellular siRNA delivery by various nanoparticle systems, including liposomes, cationic polymers and inorganic nanoparticles. What is more, we introduced our interests on siRNA delivery for cancer therapy which are currently ongoing. At last, the chemical modification of siRNA duplex was also discussed to achieve increased stability and sensitive detection of siRNA.

Semiconducting nanowires have attracted attention as being excellent sensing materials due to their superior physical properties such as high surface-to-volume ratio and tunable electrical properties. Chemical and biological sensors based on nanowire transistors perform extremely well, with ultra-high sensitivity and selectivity. This chapter reviews the application of semiconducting nanowire transistors in chemical and biological sensors, as well as their synthesis and surface functionalization. It also discusses sensor measurements and key parameters for optimum performance, including sensor sensitivity, selectivity and reusability.

The following section is included:

• Index