Jaume I: Highly sensitive system for detecting citric acid

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The University Jaume I (UJI) in Spain has patented a new fluorescent chemical sensor that is capable of detecting citric acid at low concentrations more rapidly and cheaply than the current optical sensors. The university says the sensor has potential applications in the food and pharmaceutical industries, and in disease diagnostics.

The sensor molecule works as a light indicator, emitting higher or lower intensity fluorescent light, depending on the amount of citric acid present in a sample. The less citric acid present, the less light will be produced.

One of the main advantages of the sensor is its high sensitivity, allowing one molecule of citric acid to be detected among millions of water molecules through fluorescence. Current systems for optically detecting citric acid – the most important being the citrate lyase enzymatic method – are between 100 and 1,000 times less sensitive.

A further advantage of the sensor is its increased fluorescence intensity. “It is possible to achieve gains of up to 1,500 per cent in fluorescence intensity in the presence of citrate. This implies multiplying the signal by a factor of 15, which results in very reliable measurements,” says Francisco Galindo, one of the researchers.

In addition, the sensor reacts immediately with the sample, while with the traditional citrate lyase enzyme method it is necessary to wait up to 30 minutes to obtain the results. “This advantage in the data acquisition speed can be very important when it comes to developing automatic real-time measurement systems, such as those required in food quality control, to detect possible defects in the manufacturing quality of a product, or in urgent medical urine or blood tests, for the rapid diagnosis of diseases associated with the presence of citric acid,” the researchers point out.

Citric acid is an important component of numerous pharmaceutical preparations, foods, drinks and various industrial products. For example, in the food industry it is important to know the amount of citric acid present in products derived from oranges or lemons.

In the pharmaceutical industry, citric acid is used as a stabiliser in various formulations, as a drug component, and as an anticoagulant in blood for transfusions.

In medical diagnostics, the sensor could be used to detect harmful levels of citric acid as a disease indicator. “The relationship between low citric acid concentrations and cancer, such as prostate tumours, is well known. Similarly, there is a relationship between the absence of citric acid in urine and the likelihood of developing kidney stones.