Two-dimensional photonic hydrogel aptasensors for selective detection of pesticide carbendazim

Carbendazim (CBZ), a broad-spectrum benzimidazole fungicide, is widely applied to the management of plant pathogens and the prevention or treatment of fungal diseases in fruits, vegetables, and cereals. However, its excessive and repeated usage can lead to its bioaccumulation in edible crops, posing potential health and environmental risks. Conventional detection methods for CBZ are generally expensive, time-consuming, and unsuitable for on-site analysis. Here we present a portable, low-cost, and selective platform for the trace detection of CBZ residues based on aptamer conformational change and photonic crystal signal. A two-dimensional photonic crystal hydrogel (2DPCH) aptasensor was fabricated by integrating a CBZ-specific DNA aptamer into a poly(acrylamide-co-acrylic acid) hydrogel embedded with an ordered 2D array of polystyrene microspheres. Upon CBZ binding, the aptamer folds into a curled structure, contracting the hydrogel and reducing the interparticle spacing, resulting in a visible increase in the Debye diffraction ring diameter. Under optimized conditions, the sensor exhibited a linear response for CBZ concentrations from 1.0 × 10⁻² μM to 1.0 × 10⁻¹ μM, with a detection limit of 2.8 nM. The aptasensor also demonstrated excellent selectivity, anti-interference and stability, and performed reliably in real-sample analysis of apple skins and soil. This work integrates photonic crystal diffraction and aptamer-based molecular recognition for highly specific and label-free detection of CBZ. The conformational change of aptamer mechanically stresses the polymer network, modulating the interparticle spacing of 2D photonic crystals, and ultimately converting the molecular recognition into an amplified, macroscopic change in the Debye diffraction ring diameter. This strategy can be extended to construct other pesticides aptasensors by simply selecting other pesticides-specific aptamers. The platform enables simple, visual, selective and sensitive detection without the need for complex instrumentation, offering great potential for portable detection of pesticide residues in food and environmental samples.