New imaging technique uncovers hidden pesticide contamination on fruits

CHINA – Researchers have developed a cutting-edge imaging method that reveals potential shortcomings in current food safety practices, particularly in detecting pesticide contamination on fruits.

As reported in the American Chemical Society’s Nano Letters, the new method, known as surface-enhanced Raman spectroscopy (SERS), can identify trace levels of pesticides that may go undetected by standard procedures.

Pesticides: A double-edged sword

Pesticides and herbicides play a crucial role in ensuring global food security, protecting crops from pests and diseases. However, these chemicals also pose health risks when ingested, even at low levels.

The challenge lies in developing analytical methods sensitive enough to detect these substances on produce, ensuring consumer safety without compromising the effectiveness of pest control.

The newly developed SERS method, led by researchers Dongdong Ye, Ke Zheng, Shaobo Han, and their colleagues, offers a promising solution. SERS has been gaining popularity as a non-destructive technique for detecting chemical residues from modern farming practices on fruits and vegetables.

The method employs metal nanoparticles or nanosheets to amplify the molecular signals generated when exposed to a Raman laser beam. These amplified signals produce unique molecular signatures, enabling the identification of even small amounts of specific compounds.

Innovative membrane for enhanced detection

To improve the sensitivity of SERS for detecting pesticides, the research team designed a specialized metal-coated membrane. This membrane was created by first stretching a cellulose hydrogel film to form nanoscale wrinkles on its surface.

The film was then coated with silver nanoparticles by immersing it in a silver nitrate solution. The resulting membrane was not only flexible but also nearly transparent under visible light—both essential qualities for effective SERS signal detection.

The researchers tested the membrane’s efficacy by spraying apples with two common pesticides, thiram and carbendazim. After air-drying and washing the fruits to simulate typical household practices, the membrane was laid over the apples.

Remarkably, SERS was able to detect the pesticides on the apples, even at very low concentrations. The technique also distinguished between the two pesticides when both were present and detected contamination through the apple peel and into the outer layer of the pulp.

Implications for food safety

These findings suggest that common practices like washing might be insufficient to completely remove pesticide residues from fruits. In some cases, peeling the fruit may be necessary to eliminate contamination from the skin and outer pulp.

The versatility of the SERS membrane system was further demonstrated when it successfully detected pesticide residues on other foods, including cucumbers, shrimp, chili powder, and rice.

Funded by the National Natural Science Foundation of China, the study highlights the need for more sensitive and comprehensive food safety practices to protect consumers from potential pesticide exposure.