Bromocresol green optical sensor

A dual-transducer approach based on sol-gel optical sensors was recently reported to measure acid and salt concentrations in concentrated aqueous and HC1 solutions57. The acid sensors containing bromocresol purple, neutral red, and bromocresol green indicators were obtained by the immobilization of indicators in sol-gel derived films. The salt-HCl solution was flowed through the sensor cell58. 

The fabrication and characterization of a fiber optic pH sensor based on evanescent wave absorption was presented by Lee63. The unclad portion of a multi-mode optical fibre was coated with the sol-gel doped with pH sensitive dye. The sensitivity of the device increased when the multiple sol-gel coatings were used in the sensing region. The dynamic range and the temporal response of the sensor were investigated for two different dyes -bromocresol purple and bromocresol green. 

Optical pH sensors with linear responses over different pH ranges can be designed by using different groups of indicators. A silica sol-gel glass pH sensor was developed by co-entrapping three indicators (bromocresol green, bromocresol purple, and phenol red)64, which produced a linear response over 3.5 pH units from pH 6.3 to 9.8 with a standard deviation of pH equal to 0.03. 

A large field for optical biosensor modules is their use in analytical flow systems, either with special optical cells within the instrument or with optical fibers for remote measurement. An optoelectronic biosensor , proposed by Lowe and Goldfinch [224], is a flow-through cell mounted in a compact device between a light source and a photodiode, containing enzyme-indicator membranes (eg, with penicillinase and bromocresol green). The linear response of this flow sensor is between O.S and 5 mM substrate. 

For a similar purpose, this type of sensor was prepared with a hypodermic needle containing the optical Hber [29]. The accuracy obtained was 0.013 pH units. Also, Bromocresol Green (BCG) and Bromothymol Blue (BTB) immobilized covalently on a cellulose membrane, with a variation of the signal (1.6-2 V) obtained around pAJ, (7.S for BTB), helped to achieve standard deviations of less than three decimal places [30]. 

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