Abstract

1  Introduction

Nanotechnology is the understanding, design, and development of new materials with interesting characteristics at the nanometric scale where the e ects of quantum mechanics are noticeable. These nanomaterials have at least one dimension between 1 and 100 nm, and adapt the shape of nanoparticles, nanotubes, or nanosurfaces. On the other side, nanobiotechnology refers to the intersection of nanotechnology and biology, combining the e cacy of biological materials and the rules and tools of basic sciences like physics and chemistry. It is also defined as the science that

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investigates, beyond the molecular level, the design and development of highly ordered structured materials that o er specific responses when exposed to stimuli. The development of these nanomaterials has reached a wide use in numerous scientific and technical fields, including water treatment [1, 2], electrocatalysis [3, 4], catalysis [5–9], materials [10], and biomedical applications from cancer treatment to regenerative medicine [11–13]. In fact, these structures have become increasingly useful in two main areas of biomedicine: (1) nanomedicine, with noteworthy applications in imaging, biosensors, drug delivery systems, and photo thermal therapy; and (2) tissue and implants engineering either as sca old-based nanomaterials or as components of biomedical devices.

These nanocompounds can be subcategorized into four wide groups depending on their composition: carbon-based, inorganic-based, organic-based, and compos- ite-based. Among the carbon-based materials, carbon nanotubes (CNTs)—found by Ijima in 1991—constitute a new allotrope of carbon [14] (Fig. 1) that deserves special interest due to their inherent features (surface, shape, and physical properties) that make them especially suitable for preclinical applications [15].

CNTs are tubular structures made of a layer of graphene rolled up into a cylinder [16]. These NPs are classified according to the number of wall sheets in their structure as single-walled carbon nanotubes (SWCNTs), consisting of a single graphene sheet with diameter that typically varies in the range of 0.4–40 nm, and multi-walled carbon nanotubes (MWCNTs), consisting of multiple sheets forming concentric cylinders with an interlayer distance of 0.35 nm, similar to the basal plane separation in graphite, with diameters from 2 to 100 nm (Fig. 2a). The nanotubes are usually closed at the ends with half-fullerene molecules shape, with pentagonal defects that form the tips. CNTs can be also be categorized into three types, depending on the rolling up of the sheets (Fig. 2b) as armchair, zig-zag, or chiral nanotubes (Fig. 2b) [17].

Fig. 1  Carbon allotropes: diamond, graphite, lonsdaleite, C60-fullerene, graphene, amorphous carbon, C540-fullerite, and single-walled carbon nanotube

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