Nanoparticles are a significant class of nanomaterials. The diameter of nanoparticles can vary from one to a few hundreds of nanometers in size. The enthusiasm for nanoscale materials comes from the way in which their properties change with their size or shape. Nanoparticles can be amorphous or crystalline in nature. The crystalline form of nanoparticles is called nanocrystals. Nanocrystals are also incorporated from metals such as gold, silver, and cobalt. Semiconductors such as sulphide, selenide, cadmium telluride, arsenides, gallium and indium phosphides can also be used to form nanocrystals. Nanocrystals can also be formed from metal oxides. Colloidal nanocrystals are considered to be artificial molecules that essentially constitute a new form of matter. Colloidal metal nanocrystals based positively on gold are most prominent. Colloidal gold has been fabricated to have excellent features in organic and aqueous solutions. They have discrete optical vitality spectra such as molecules that are tunable over a wide scope of wavelengths. Nanocrystals must be crystalline, composed of one domain with a finely distributed size. A specific sample must have a distinctive, unvarying shape of nanocrystal. Nanotechnology has an extensive variety of applicability to different fields including medicine, basic biological research, solar cells, light emitting diodes, biomedical imaging tags, catalysts, and sensors. Biomedicine is a significant area of research. Colloidal nanocrystal synthesis has attracted researchers in the areas of materials science and life science owing to its fascinating features.

The pharmaceutical industry is widely known for its discovery, development, and drug manufacture. The discovery of new, pharmacologically active principles has several challenges. Among these, the poor solubilization capacity of many available drugs is a major challenge of the pharmaceutical industry. This challenge was overcome by the introduction of drug nanocrystals in the field of drug development. In early days, the pharmaceutical industry considered these drug nanocrystals to be highly risky development candidates. However, changes in attitude and continuous research in this field have led to immense success. Drug nanocrystals have a major role in the emerging domain of pharmaceutical nanotechnology. A nanocrystal can be prepared from a hydrophobic compound coated with a thin hydrophilic layer. The biological reactions of the developed nanocrystals strongly depend on the chemical nature of the hydrophilic coating. Abundant nanocrystalline-based drug products are commercially available. Successful scientific research in this field can be seen in the number of patents on drug nanocrystals for various applications. These indicate that the pharmaceutical industry has embraced this universal approach to formulation, which is expected to advance further in the future. In this chapter, we focus on the development, application, and advantages of nanocrystal drugs.

Nanoparticles have unique and interesting physicochemical and biological properties because of their higher surface area to volume ratio compared with bulk materials. Green approaches are essential because of the increasing growth of the population and industry and their influence on the world's natural resources. The eco-friendly synthesis of metal nanoparticles is a bioreduction technique that needs low energy to commence the reaction, which is an alternative to chemical and physical approaches. The one-step green synthesis of metal nanoparticles was used by several biological materials such as bacteria, fungi, algae, and plant extracts. Using plant extracts, synthesis of metal or metal oxide nanoparticles is a simple method for producing wide-ranging preparations compared with bacterial or fungi-mediated ones. These products are referred to as biogenic nanoparticles. Phytochemicals used to synthesize metal or metal oxide nanoparticles can act as both reducing and capping agents. The excellent properties of green synthesized materials include environmental protection and antibacterial, antioxidant, and biodegradable properties. Such nanomaterials are also used in biomedical diagnostics, catalysis, optical imaging, and biolabeling. Green synthesized nanomaterials are widely investigated for applications in electronic devices. To achieve the sustainability of future technologies, these types of green materials must be used to construct the device.

According to the Biopharmaceutical Classification System, the solubility and permeability of a drug are the key drivers of its development. Drugs belonging to Classes II and IV are poorly water soluble and often require their physical form to be manipulated to achieve adequate dissolution. The formation of crystalline nanoparticles or nanocrystals can improve solubility and permeability and ultimately bioavailability owing to the greater surface to volume ratio. Crystalline nanoparticles are a suitable delivery system for all commonly used routes of administration, such as oral, injectable, pulmonary, ocular, and topical applications. In addition, aqueous dispersions of nanoparticles can be processed into tablets, capsules, fast-melts, and lyophilized products for sterile product applications. The pharmacokinetic profiles of nanocrystals may vary from rapidly soluble in the blood to gradual dissolving, after which macrophage uptake and subsequent drug release prolong drug delivery while minimizing the peak height. For certain drug classes, this leads to improved safety, permits higher dosing, and improves efficacy. Nanocrystals can target drug molecules in specific regions through size manipulation and surface modification. This chapter focuses on nanocrystal-based formulations as liquid nanosuspensions and after downstream processing to solid dosage forms, developed as drug delivery systems for various routes of administration. The compilation of material summarizes the therapeutic applications of pharmaceutical nanocrystals, highlighting their universality as a formulation approach to poorly soluble drugs.

Environment and energy are prime issues of the day. CO2 is a greenhouse gas and a major contributor to global warming. With rapid urbanization, its annual production has exceeded the gigaton level. Environment protection policies that plant huge forests to augment natural photosynthesis are not enough to restore the environmental CO2 balance. Therefore, additional techniques of removing CO2 by photo-reduction and electroreduction have been explored. However, research has shown that the reduction of CO2 is a thermodynamically and kinetically unfavorable process. Whereas the thermodynamic barrier is overcome using electrical energy or solar energy, the kinetic problem is solved using suitable catalysts. Cu-based composite catalysts were reported to be most efficient in the electrochemical and photochemical reduction of CO2. These multicomponent composite materials are multifunctional and effective absorbers of CO2. In this chapter, we present important works on the synthesis of some nanocomposite catalysts composed of oxides of Cu and chitosan (a biopolymer) and Cu-oxides and graphene oxide with an emphasis on the applications of these composites in the electroreduction and photoreduction of CO2. The roles of different components of the composite material as documented in the literature are summarized.

Nanoparticles have a significant role in modern life, ranging from materials for catalysis to those for electronics. Owing to their combination of tunable and accessible chemical sites, nanoparticles have remarkable activity in the field of heterogeneous catalysis. This chapter discusses how nanoparticles integrated into the field of catalysis and emerged as green and sustainable materials for a spectrum of industrially important catalytic hydrogenation reactions.

Population growth, the depletion of natural resources, and rising environmental contamination call for the need for up-to-date and efficient methods to solve these issues. Nanotechnology has become the most effective tool that encompasses high economic interest and high efficiency to meet the needs of humanity as well as environmental remediation. The outstanding features of MnO2 at nano-dimensions, such as less toxicity, its catalytic activity, its environmentally benign nature, and its simple preparation strategies make it favorable in nanotechnology. This chapter covers the applications of MnO2 nanostructures that have been addressed in the environmental domains. It offers examples in each field to show the important roles of these valuable materials for addressing environmental concerns.

Several forms of nanocellulose, notably cellulose nanocrystals and nanofibrillated cellulose, exhibit attractive property matrices and are potentially useful for a large number of industrial applications. This chapter provides an overview of synthetic techniques used to prepare colloidal nanocrystals (NCs) of controlled composition, size, shape, and internal structure and the methods for manipulating these materials into ordered NC assemblies (superlattices). Researchers have studied these particles intensely and have developed them for broad applications in the cardboard industry, for use as reinforcing fillers in polymer composites, for low-density foams, as additives in adhesives and paints, as well as for a wide variety of food, hygiene, cosmetic, and medical products. Each NC consists of a crystalline inorganic core coordinated by an organic monolayer. These monodisperse NC samples enable systematic studies of structural, electronic, magnetic, and optical properties of materials as a function of size evolution from molecular species (<100 atoms) to bulk solids (>100,000 atoms). The commercial exploitation of nanocellulose has commenced. This chapter provides a comprehensive and critical review of the state of knowledge of nanocellulose in this format.

Tumors or neoplasms refer to the growth of abnormal tissues resulting in extraneous outgrowth that can easily be differentiated from surrounding tissues. They lead to metastatic cancer, which is the major cause of death worldwide. The incidence rate of cancer is growing at an alarming rate in the world. These tumors develop from a single clone of cells that tend to grow uncontrolled manner and can give rise to benign or malignant tumors. Benign tumors are extra growths that do not metastasize or invade neighboring tissue, whereas malignant tumors invade surrounding healthy tissue. Detecting these tumors at an early stage can be tricky and poses a major problem in diagnosis and therapy. The most common means of tumor imaging are computed tomography, which provides cross-sectional imaging of tumors using X-rays, magnetic resonance imaging, which uses a powerful magnetic field to examine tumors in the head and neck region, and positron emission tomography, which uses a radioactive tracer given to the patient and is detected by scintigraphy. On the other hand, endoscopic examinations are carried out to inspect tumors in the gastrointestinal tract, bronchial tubes, cervix, and prostate regions, whereas in mammography, X-ray images are used to examine tumors in the breast region. These procedures use powerful radiation and strong electron beams, which can hamper the health of patients, causing acute damage to the body. Alternative diagnosis techniques use gold nanocarriers, which can be useful in tumor imaging as well as the targeted delivery of drugs to the tumor site. This dual nature of gold nanocarriers has made them favorable for use in imaging, diagnosis, and therapeutic applications. This chapter deals with the properties, nature, and uses of gold nanocarriers in diagnostic and therapeutic applications, which can be a turning point in the medical field in coming years, ensuring dual benefits to patients.

Carbon quantum dots are a type of colloidal fluorescent semiconducting carbon nanocrystalline material that has attracted considerable interest as a novel member of nanocarbons. They are characterized by easy preparation from a broad spectrum of carbonaceous precursors through the bottom-up or top-down route. Carbon quantum dots, which are small carbon nanoparticles (less than 10nm) with unique optical and electronic properties, have been used in a lot of technological and biological applications. Despite progress in the investigation of quantum dots with better nanocrystalline material performance, there is growing concern that these materials might pose potential risks to human health. Hence, environmentally benign and sustainable fabrication is required. The generation of nanocrystalline materials benefits from biomimetic approaches in which renewable resources such as vitamins, sugars, and plant polyphenols, including agricultural waste residues, can serve as reducing and capping agents. Thus, these strategic approaches address most of the green chemistry principles while producing green functional nanocrystalline materials while minimizing waste. In this chapter, we discuss the most important properties of carbon quantum dots, including their useful structural design and toxicity, and evaluate the foremost studies on green carbon quantum dot synthetic methods associated with the green nanotechnology approach to eco-friendly, nontoxic, clean, safe, and accountable processes to forming biocompatible, photostable, and sustainably sourced carbon quantum dots. The greener and sustainable synthesis of quantum dots has numerous advantages, such as the use of economical and nontoxic raw materials, easy operation, speedy reactions, renewable resources, and uncomplicated postprocessing steps. Advances in biological and technological carbon quantum dot–based applications are also briefly discussed.