# A Brief Review on Challenges in Design and Development of Nanorobots for Medical Applications
## 2 Challenges in the Design and Development of Nanorobots
### Sensors  
The sensing component of a nanorobot and its feedback to a bio-computer or controller is achieved by chemical sensors or bionanosensors [22]. Depending on the task to be performed, the information about the environment is obtained by sensors. Nanorobots depend on nanosensors to obtain information on the status of the position and operation; these sensors are classified as long-distance and short-distance sensors. Navigation of the nanorobot is carried out by the long-distance sensor, while the short-distance sensor aids in locating the unwanted cells [22]. The fabrication of silicon-based chemical sensors and motion sensor arrays has been state-of-the-art in the last decade. These sensors are constructed using a two-level architecture system [6; 7; 8; 9]. It is evident that the usage of nanowires and the costs of energy for circuitry operations and transfer of data are reduced by 60 [9]. The assembly of circuits using nanowires and CMOS integrated sensors demonstrated maximum efficiency in regards to changes in the chemical environment, thereby promoting novel medical applications [10]. Silicon circuits, which are constructed using suspended arrays of nanowires, have reduced self-heating and thermal coupling and increased the operational capacity of CMOS sensors [25]. Nanosensors consume low energy and provide high sensitivity [11]. Processes in the development of nanosensors will use electro fluidic alignment to achieve an integrated CMOS circuit assembly as multi-element systems [26]. Passive and buried electrodes may be used to re-read the signal processing circuitry via cross-section control transistors. The passive and buried aligned electrodes must be electrically isolated so that processed signals are not lost [12]. The drawbacks for improving Bipolar Complementary metal-oxide-semiconductor (BiCMOS), CMOS, and Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) actuators include constructing smaller channel length and lowering the voltage of the circuitry, for which, new materials have been proposed, one of which is a SiGe (Silicon-Germanium) layer. This layer decreases self-heating, which in turn improves performance [6; 7; 8; 9]. [PERSON] et al. [23] used CMOS sensors in their nanorobot device design as a radiofrequency identification device for in vivo positioning and navigation using a well-established protocol for communication [27]. [PERSON] et al. [28] introduced computational nanomechatronics as a pathway for the design, development, and control of nanorobots using the CMOS technology in the design of temperature sensors, mineral detection, and data transmission. Ultrasonic sensors and light sensors can handle nanorobots in the body in conjunction with motion strategy. Biochemical sensors will perceive chemical rates, PH, temperature, and ambient radiation--the bacteria's \"random walk\" concept is the best example of this [22]. Many groups use the mechanical, light, chemical, electrical and biological characteristics to build nanosensors; when PH changes, HSF protein combined with DNA strands causes the resolution colour changes [29]. Apart from this, artificial taxis (also known as microbots) can replicate the ability of an organism to carry out sensing and responsive behaviour to an external signal. These taxis respond to concentration gradients (chemotaxis), surrounding fluid (rheotaxis), magnetic fields (magnetotaxis), or light (phototaxis) [30]. The molecules in the environment are sensed using receptors on the surface of the bacteria. The bacteria can either hold or change the rotational direction of the flagella motors, thereby leading to a reorientation in the body. A movement towards the higher concentration of a chemical attractant thus leads to long straight 'hots' and fewer 'tumbles' of orientation, allowing the cells to find favourable conditions [31]. Bacteria use environmental conditions to perceive variations between the chemical and physical stimuli. The turning action or reorientation of the bacteria is entirely based on the intensity of the stimuli perceived.