**1.2 General and basic concepts about nanotechnology, nano-/microrobots (motors), and spintronics**

### *1.2.1 Spintronic*

Spintronic concept raised in the late 1980s refers to the use of spins to information transmission and computational operations [32, 33]. Spintronics is an emergent technology grounded in the information transmission by electronic charge and electron spin [34–39]. Spintronic represents a paradigm break in the field of information to combine charge and magnetism in processing and storage. The beginning of spintronics is marked by the discovery of giant magnetoresistance (GMR) effect, in 1988, which resulted in the award of Nobel Prize in Physics in 2007 to Fert and Grunberg [40, 41]. Firstly, spintronic was associated with inorganic oxides, metals, and semiconductors because of the dependence of spin-orbit coupling (SOC). However, organic molecules have wanted properties such as biocompatibility, flexibility, abundance, the possibility of synthesis, low cost [32, 42], and rapidly gained interest in the spintronic studies. The potential applications for spintronics, particularly for electronic devices, are spin filters, spin diodes, spin transistors, spin field-effect transistors, and spin qubits in semiconductor nanostructures [42]. Spintronic has some emerging and promising subfields that are current-induced torque (CIT), spin Hall effect (SHE), spin caloritronics, silicon spintronics, spintronic aspects of graphene and topological insulators (TIs), and chiral-induced spin selectivity effect [32, 34]. The electron spins are degenerate in energy, but the level of degeneracy is broken inside the helix because the electron velocity generates an effective magnetic field that couples with the chiral potential. In a model of DNA double helix, the spin-down electrons aligned preferentially parallel to their velocity in a right-handed helix, while the same occurred with spin-up electrons in the left-handed helix. In an experimental approach, self-assembled monolayers (SAMs) of 3′ thiolated single- and double-strand DNAs (ssDNA and dsDNA, respectively) were attached on a clean 200 nm-thick polycrystalline gold film that was evaporated on glass slides. Photoelectrons were ejected from the gold film by clockwise and counterclockwise circularly polarized light and transmitted through ssDNA and dsDNA monolayers. A more intense transport of electrons ejected with

**147**

generate the superoxide radicals (O2

*Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro…*

a counterclockwise polarized laser in dsDNA was detected, and no spin selectivity was detected in ssDNA SAMs. Zwang et al. demonstrated that the spin selectivity in DNA is dependent on the supramolecular organization of chiral DNA moieties rather than the chirality of the individual monomers, and thus the spin selectivity can be switched by a conformational change of the molecules [32, 35–39, 43]. The mechanism of CISS effect is believed to be a result of evolution [37], where chiral molecules can increase the conductance of electrons with a spin channel while decreasing the other one [32, 33, 43]. Mishra et al. [44], in recent studies, demonstrated a spin-dependent electron transmission through helical structured bacteriorhodopsin proteins. The study potentially says that the spin degree of freedom may be associated with an important function in electron transport in biological systems. Einati et al. [45] and Roy et al. [46] have shown that the efficiency of electron spin filtering through purple membrane films can be reduced with a green light. So, at potential applications of spin filters, it could modulate the efficiency of the filter.

Nowadays, a new field of study involving nanotechnology is gaining importance: micro-/nanorobotics. Micro-/nanorobots (MNRs) have autonomous motion provided by micro-/nanomotors (MNMs) that are micro-/nanometerscale devices powered with the ability to convert chemical, optical, acoustic, magnetic, and electrical energies into mechanical energy [47]. MNRs can be functionalized to perform complex tasks in a microcosm that constitutes the so-called micro-/nanorobots (MNRs) [48]. MNRs have an extensive range of potential applications such as remediation, nanofabrication, repair of materials, engineering, computing, environment monitoring, and especially in theranostics. Drug delivery systems, cell transport, and DNA and RNA insertions are some of the most numerous studies [49, 50]. The size of MNRs allows their application in minimally invasive diagnosis and treatments [51]. There is a basic classification for nanorobots. They can be biological, artificial, or biohybrid [52]. Also, they are classified according to the type of propulsion: self-propelled or external field-propelled ones. The self-propelled nanorobots convert energy from the environment to kinetic energy for independent movement, and it can be done by self-electrophoresis, self-thermophoresis, self-diffusiophoresis, and tiny bubbles [52]. Among the energy sources that self-propelled MNRs can use, light is highly attractive [47]. Light-powered MNMs can obtain energy from an external source and surrounding chemicals to get efficient propulsion through a photocatalytic process and constitute the photocatalytic micro-/nanomotors (PMNMs). Selfpropelling PMNMs can be controlled in various ways such as chemical concentration or light intensity [47, 48, 53]. Furthermore, these PMNMs can be operated at low levels of optical and chemical energy input, which are highly desired scenarios. An important aspect is that the photocatalytic reactions of PMNMs can

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self-propulsion of the photocatalytic MNMs (**Figure 3**).

environmental remediation, especially in the degradation of organic pollutants. The Janus model can be used to explain the basic principles that respond to the

The external field-propelled MNRs depend on an external force such as electric and magnetic field, light impulses, sonic waves, etc. [52]. The fabrication of MNRs can be direct, indirect, or by self-assembly [51]. The techniques used for the MNR fabrication are the same for the regular nanoparticles: top-down (lithography and scanning probe microscopy) and bottom-up (deposition, a solution with reducing agents). The materials used for MNR fabrication could be super magnetic substances, organic and inorganic compounds, and biological substances [51, 54].

) that give these devices great potential for

*DOI: http://dx.doi.org/10.5772/intechopen.86206*

*1.2.2 Nanorobots*

#### *Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro… DOI: http://dx.doi.org/10.5772/intechopen.86206*

a counterclockwise polarized laser in dsDNA was detected, and no spin selectivity was detected in ssDNA SAMs. Zwang et al. demonstrated that the spin selectivity in DNA is dependent on the supramolecular organization of chiral DNA moieties rather than the chirality of the individual monomers, and thus the spin selectivity can be switched by a conformational change of the molecules [32, 35–39, 43]. The mechanism of CISS effect is believed to be a result of evolution [37], where chiral molecules can increase the conductance of electrons with a spin channel while decreasing the other one [32, 33, 43]. Mishra et al. [44], in recent studies, demonstrated a spin-dependent electron transmission through helical structured bacteriorhodopsin proteins. The study potentially says that the spin degree of freedom may be associated with an important function in electron transport in biological systems. Einati et al. [45] and Roy et al. [46] have shown that the efficiency of electron spin filtering through purple membrane films can be reduced with a green light. So, at potential applications of spin filters, it could modulate the efficiency of the filter.
