Graphene quantum dots as cysteine protease nanocarriers against stored grain insect pests

Storing grains remain vulnerable to insect pest attack. The present study developed a biopesticide using biomolecules and their encapsulation in nanoparticles. A 25 kDa cysteine protease extracted from seeds of Albizia procera ( Ap CP) was encapsulated in graphene quantum dots (GQDs). The insecticidal activity of Ap CP, with or without GQDs, against two stored grain insect pests, Tribolium castaneum (Herbst) and Rhyzopertha dominica (Fabricius) was explored. Insects were exposed to three concentrations 7.0, 3.5 and 1.7 mg of Ap CP per a gram of wheat flour and grains. The insecticidal activity of Ap CP encapsulated with GQDs was improved compared to that of Ap CP without GQDs for both insect pests. The number of eggs and larvae of T. castaneum was reduced by 49% and 86%, respectively. Larval mortality was increased to 72%, and adult eclosion of T. castaneum was reduced by 98% at a 7.0 mg/g concentration of Ap CP with GQDs compared to that of Ap CP without GQDs. Exposure to 7.0 mg/g Ap CP with GQDs, the number of R. dominica eggs and larvae was reduced by 72% and 92% respectively, larval mortality was increased by 90%, and eclosion was reduced by 97%. The extraction, purification, characterization, quantification and encapsulation of Ap CP with GQDs were also studied. Cysteine protease nanocarriers have the potential to control stored grain insect pests.