Nano-sensor detects pesti­cides on fruit in minutes

Research­ers at Karol­in­ska Insti­tutet in Sweden have developed a tiny sensor for detect­ing pesti­cides on fruit in just a few minutes. The tech­nique, described as a proof-of-concept in a paper in the journ­al Advanced Sci­ence, uses flame-sprayed nan­o­particles made from sil­ver to increase the sig­nal of chem­ic­als. While still at an early stage, the research­ers hope these nano-sensors could help uncov­er food pesti­cides before consumption.

“Reports show that up to half of all fruits sold in the EU con­tain pesti­cide residues that in lar­ger quant­it­ies have been linked to human health prob­lems,” says Geor­gios Sotiri­ou, prin­cip­al research­er at the Depart­ment of Micro­bi­o­logy, Tumor and Cell Bio­logy, Karol­in­ska Insti­tutet, and the study’s cor­res­pond­ing author. ​“How­ever, cur­rent tech­niques for detect­ing pesti­cides on single products before con­sump­tion are restric­ted in prac­tice by the high cost and cum­ber­some man­u­fac­tur­ing of its sensors. To over­come this, we developed inex­pens­ive and repro­du­cible nano-sensors that could be used to mon­it­or traces of fruit pesti­cides at, for example, the store.”

The new nano-sensors employ a 1970s dis­cov­ery known as sur­face-enhanced Raman scat­ter­ing, or SERS, a power­ful sens­ing tech­nique that can increase the dia­gnost­ic sig­nals of bio­molecules on met­al sur­faces by more than 1 mil­lion times. The tech­no­logy has been used in sev­er­al research fields, includ­ing chem­ic­al and envir­on­ment­al ana­lys­is as well as to detect bio­mark­ers for vari­ous dis­eases. How­ever, high pro­duc­tion costs and lim­ited batch-to-batch repro­du­cib­il­ity have so far hindered wide­spread applic­a­tion in food safety diagnostics.

Flame spray technology

In the cur­rent study, the research­ers cre­ated a SERS nano-sensor by using flame spray – a well-estab­lished and cost-effect­ive tech­nique for depos­it­ing metal­lic coat­ing – to deliv­er small droplets of sil­ver nan­o­particles onto a glass surface.

“The flame spray can be used to quickly pro­duce uni­form SERS films across large areas, remov­ing one of the key bar­ri­ers to scalab­il­ity,” says Haipeng Li, a postdoc­tor­al research­er in Sotiriou’s lab and the study’s first author.

The research­ers then fine­tuned the dis­tance between the indi­vidu­al sil­ver nan­o­particles to enhance their sens­it­iv­ity. To test their sub­stance-detect­ing abil­ity, they applied a thin lay­er of tracer dye on top of the sensors and used a spec­tro­met­er to uncov­er their molecu­lar fin­ger­prints. The sensors reli­ably and uni­formly detec­ted the molecu­lar sig­nals and their per­form­ance remained intact when tested again after 2,5 months, which under­scores their shelf life poten­tial and feas­ib­il­ity for large-scale pro­duc­tion, accord­ing to the researchers.

Detec­ted pesti­cides on apples

To test the sensors’ prac­tic­al applic­a­tion, the research­ers cal­ib­rated them to detect low con­cen­tra­tions of para­thion-ethyl, a tox­ic agri­cul­tur­al insect­icide that is banned or restric­ted in most coun­tries. A small amount of para­thion-ethyl was placed on part of an apple. The residues were later col­lec­ted with a cot­ton swab that was immersed in a solu­tion to dis­solve the pesti­cide molecules. The solu­tion was dropped on the sensor, which con­firmed the pres­ence of pesticides.

“Our sensors can detect pesti­cide residues on apple sur­faces in a short time of five minutes without des­troy­ing the fruit,” Haipeng Li says. ​“While they need to be val­id­ated in lar­ger stud­ies, we offer a proof-of-concept prac­tic­al applic­a­tion for food safety test­ing at scale before consumption.”

Next, the research­ers want to explore if the nano-sensors can be applied to oth­er areas such as dis­cov­er­ing bio­mark­ers for spe­cif­ic dis­eases at the point-of-care in resource-lim­ited settings.