Sensitivity enhancement of pH indicator and its application in the evaluation of fish freshness

• pH indicator selectivity was improved by regulating pH to its color transition point.
• HSV color model was used to measure the color changes.
• pH regulation of bromophenol blue was realized by adding organic acid or alkali.
• The pH regulated sensors showed high sensitivity in the detection of fish freshness.

The sensitivity of pH indicators is always confined in acidic solvents used during the immobilization because of the large deviation from their color transition points. By regulating the pH of indicators using organic acid or base, the color transition points of indicators could be readily achieved and the sensitivity could be greatly enhanced. In this study, bromophenol blue was selected as an example to interpret this improvement. And Hue, Saturation and Value (HSV) color model was applied to obtain digital color information of pH indicators. In addition, other two kinds of pH indicators were chosen and regulated to their color transition points as well. The resultant indicators together with the original ones were composed to a colorimetric sensor array and utilized to determine fish freshness. Compared with the original indicators, much higher sensitivity in the detection of fish freshness was obtained by the pH regulated indicators.

A novel idea to improve the sensitivity of pH indicators was suggested through adding certain amounts of organic acid or alkali into the indicator solutions to regulate their pH to corresponding color transition points. HSV color model was used as an index to measure the color changes. By comparison between the sensor units composed of original indicators and regulated indicators, we can see that pH regulated sensors showed very high sensitivity in the detection of fish freshness.Figure optionsDownload as PowerPoint slide