Customization of an efficient and cost-effective optical biosensor for trace cadmium detection in milk samples

Abstract

Conventional techniques for detecting Cd, such as [e.g., atomic absorption spectrometry (AAS), inductively coupled plasma-mass spectrometry (ICP-MS)], often require expensive equipment, extensive sample preparation or specialized expertise. This novel research demonstrates how to customize an effective optical biosensor to detect low Cadmium (Cd) ion levels in milk samples. Compared to the previous report's detection limit of 8.1 μg/L, this unique approach shows a lower limit of 4.8 μg/L. Such fabricated optical biosensor was designed to monitor urease activity to detect Cd ions in milk samples, where calibration was performed using UV–Vis spectroscopy and further validation was done using ICP-MS technology. In this process, the urease enzyme was extracted from the jack bean, which was further immobilized using EDC-NHS coupling for the functionalization, thus optimizing stability and reactivity. An activity assay was performed for immobilized urease at pH 7.5; the optimized enzyme was 67 % stable for up to four weeks of storage at 4 °C due to excellent crosslinking during functionalization and immobilization. The coefficient of determination (R2) was calculated to measure the proportion of biosensor readings with standard readings obtained by the ICP-MS readings. The proposed method obtained a moderate R2 value close to 1, i.e., 0.88674, indicating a moderate agreement between ICMP readings and the proposed biosensor readings. Remarkably, the optical biosensor exhibits great stability and efficiency in detecting Cd ions in milk as low as 4.8 μg/L. FESEM and FTIR spectroscopy were used to examine the morphological and structural properties of the immobilized enzyme. The findings imply that the intended optical biosensor can be employed for on-field detection.

Keywords

• Cadmium
• Immobilization
• Milk
• Optical biosensor
• Urease enzyme
• Spectroscopy