two structural features are critical for the design

two structural features are critical for the design of colorimetric or fluorometric sensors: functional sites for interaction with analytes, and a chromophore or fluorophore for pairing with the active site. the primary factor is that having numerous classes of strong chemical interactions can be very beneficial, in preference to the van der Waals or physical absorption. based on the kinds of intermolecular interactions which could result in significant colorimetric or fluorometric changes, one can be divided cross-reactive, chemoresponsive dyes into five classes (albeit with a few overlap): (i) acidic dyes or Brønsted base (e. g. , diverse pH markers), (ii) Lewis acid/base dyes (e. g. , metal complexes with open coordination sites or chromogens containing metal ions), (iii) redox dyes, (iv) Dyes with large permanent dipoles (e. g. , zwitterionic vapochromic or solvatochromic dyes) to detect local polarity or hydrogen bonding; further, the preservative matrix of these dyes may be involved in improving their chemical selectivity, both by using modifying the local dye environment or through immobilizing the dye molecules in a sterically confining surroundings (e. g. , molecularly imprinted polymers). Early versions of the colorimetric sensor arrays were made of porphyrins and metalloporphyrins, which were made as sensor components, and mainly used Lewis interactions with metal and Brønsted interactions with free base porphyrins. With the addition of a much wider range of chemical dyes, the variety of sensors has elevated dramatically during the last decade [79]. for example, a lately developed 40-element sensor array that includes an extensive range of chemical dyes has shown promising applications in detecting toxic or explosive vapors [208].