**1. Introduction**

Basically, the host-guest non-covalent interaction is the major subtopic of supramolecular chemistry, which succors us to realize the recognition of guest entities, particularly through non-covalent supramolecular interactions [1, 2]. In recent years, the supramolecular host molecules, such as cyclophanes, crown ethers, cryptands, calix[n]arenes, calix[n]pyrroles, cucurbiturils, and cyclodextrins, have drawn an enormous interest of the scientific community worldwide because of their exceptional signatures, particularly molecular recognition and sense of specific analytes, and still much new chemistry with these old macrocycles is to be explored [3–7]. Among the above-mentioned host architectures, the naturally occurring cyclodextrins (CDs) are regarded as most essential by virtue of their selective recognition capability, exceptional biocompatibility, water solubility, non-toxicity, economically inexpensiveness, commercial availability, and easy-functionalization [8]. With the aid of host-guest chemistry, the CDs have found a range of applications in various fields of science and technology *viz.* supramolecular self-assemblies, material sciences, pharmaceutical

chemistry, biochemistry, polymer chemistry, electronics, catalysis, and nanotechnology, besides biotechnological and chemical industries [9–11]. Remarkably, CDs have also been employed as the bricks in building frequent supramolecular structures of particular interest, such as polyrotaxanes, rotaxanes, catenanes, and supramolecular polymeric materials [12].

The CDs are cyclic oligosaccharides-based seminatural products, mostly comprising of 68 units (*α*-, *β*-, & *γ*-cyclodextrins) of glucose connected through *α*-1,4 gycosidic linkages to generate the torus-shaped molecules portrayed by a hydrophilic surface and hydrophobic central cavity (**Figure 1**) [8]. Notably, CDs having glucose units less than six are too much strained for existence, while the CDs containing more than eight glucose units are readily soluble and very difficult to isolate. With an increase in the number of glucopyranose units from six to eight, the inner cavity diameter also increases from 0.44 to 0.83 nm. In particular, the inner cavity diameter of 0.44 nm in *α*-CD is suitable to capture benzene molecule, whereby *β*-CD (0.62 nm) holds an appropriate cavity to encapsulate the naphthalene molecule, and importantly, the *γ*-CD (0.83 nm), can easily occupy the larger guest molecules *viz.* fullerene [13, 14]. The shape of these CDs resembles like a bucket and hence offers a narrow and large entrance on opposite sides. Typically, it has been revealed that there exist primary OH-moieties on the side of narrow cavities and they have got recognition as a primary face. On the front, secondary OH moieties are present on the side of a large cavity and are generally dubbed as the secondary face. It is by virtue of these primary and secondary OH groups that these CDs are selective toward the inclusion of guest entities of particular importance. As a matter of the fact, both primary and secondary OH groups arrange themselves on the outer side of two recognized faces, and the whole inside cavity of these CDs becomes a hydrophobic microenvironment. The hydrophobicity of the inner cavity in turn is responsible for the inclusion of typically hydrophobic guests in aqueous media [8]. Importantly, over the passage of time, selective methods for ease functionalization of CD-scaffold are being proposed

**Figure 1.** *Chemical structures and the 3D-pictorial representation of different CDs.*

constantly in order to enhance the recognition properties of CD-based supramolecular hosts toward analytes [15].

As can be straightforwardly inspected from the scientific publications appearing in the literature, the domain of chemical sensors in general and CD-based sensors in particular are rapidly progressing and strengthening their roots in various aspects of our day-to-day life besides bringing a revolution in diverse arena of science and technology [16]. Keeping these facts in mind and also to expose the importance of sensory materials based on CDs; in this meticulous review chapter, we indented to highlight the recent developments in addition to the conceptual background of CDbased chemical sensors. Hopefully, the readers will enjoy this draft and will for sure be further to explore these old yet new types of macromolecular platforms to an advanced level.
