Enzyme Triggered Carriers Based On Cyclodextrin Anchored Hollow Mesoporous Silica For Enhancing Insecticidal Activity Of Chlorantraniliprole And Avermectin Against Plutella Xylostella

In recent years,it is substantial and looked-for to fabricate some surface modifiable hollow carriers in nanoscale with thin shells and ordered meso-channels on the shell surface,besides the high loading capacity.In this study,surface functionalized hollow mesoporous silica(HMS)nanoparticles were synthesized.Then the model pesticides chlorantraniliprole(CLAP)and avermectin(AVM)were loaded into HMS,respectively.?-Cyclodextrin was conducted as the capping agent to seal mesopores of HMS to fabricate controlled release formulation(CRF)which is enzymatically in-vivo uncapped and allow the cargo to be released in insect's midgut.The main results were as follows:A series of enzyme-responsive nano-carriers for the controlled release of avermectin and chlorantraniliprole were prepared.The designed nano-carriers were prepared in three sizes(140 nm,400 nm,and 1500 nm)by condensing tetraethylorthosilicate around polystyrene latex(PSL)templates with varied sizes.The PSL capped with silica was followed by calcination at 873 K to remove the PSL template,forming HMS.After performing HMS surface functionalization with N-phenyl amino propyltrimethoxysilane(Ph AMTES),the pesticides were diffused into the functionalized HMS using solvent evaporation method.The HMS pores were then sealed by ?-CD,which works with the phenyl amine group as stoppers to obtain the CRF.CLAP and AVM were selected as the model pesticides.The morphology and structure of the CRF samples were characterized using a transmission electron microscope(TEM)and scanning electron microscope(SEM),respectively.TEM images of synthesized HMS indicated the presence of hollow structure of silica spheres.SEM images indicated excellent particle symmetry of the synthesized HMS.A fourier transform infrared spectroscopy(FT-IR)was used to observe the chemical grafting processes occurring with the samples.The vibration bands characteristic showed the successful reaction between HMS and Ph AMTES and ?-CD anchoring on the surface.The drug loading efficiency(DLE)was determined by thermogravimetric analysis(TGA).The results showed that the decomposition of ?-CD starts at 518 K and the CLAP decomposition starts at 514 K.Pure HMS had a decrease in total weight due to vapor volatilization(4.96% from the total weight).In contrast,pure ?-CD capped HMS lost 7.91% of the total weight due to the presence of the ?-CD.For CLAP,140 nm,400 nm,and 1500 nm CRF showed significant weight decreases of 50.1%,46.2%,and 41.5%,respectively,which were attributed to the loaded amount of CLAP.For AVM,the weight loss of 140 nm,400 nm and 1500 nm CRF were distinctly diminished by 49.1%,41.2%,and 41.4%,respectively owing to the loaded AVM into the HMS internal sphere.Size distribution was also measured.The results showed that the sizes fluctuated from 118 nm to 190 nm,371 nm to 476 nm,and 1342 nm to 2670 nm for the three HMS samples,with middle sizes of 140 nm,400 nm,and 1500 nm,respectively.The BET model was performed to estimate the specific surface areas.The pore size and pore volume were determined by using BJH method from the adsorption data.The adsorption step ascribed to the mesopores and the pores texture is preserved an appreciable decrease in the N2 volume adsorbed for HMS 140 nm,400 nm,and 1500 nm(BJH mesopore volume = 0.42 cm3 g-1,0.31 cm3 g-1,0.31 cm3 g-1),respectively.The surface area was measured(0.711í103 m2 g-1,0.654í103 m2 g-1,and 0.102 í103 m2 g-1)respectively.The surface area of solid ?-CD capped HMS was reduced about 70% compared to that of blank HMS,due to the external grafting of ?-CD.Analysis of the released CLAP and AVM from CLAP-CRF and AVM-CRF were quantified with highperformance liquid chromatography(HPLC),respectively.Detailed examination revealed that the synthesised CRF has a drastic enzymatic dependence.The release of the trapped pesticides was studied at different temperatures,p H values and in the presence or absence of ?-amylase enzyme.For CLAP,the release behavior in the absence of enzyme was 4.04% to 5.96% from the 4th day to 17 th day,respectively.In contrast,the release behavior in the presence of ?-amylase was 4.05% to 42.47% in the same elapsed time.For AVM,the release behavior without enzyme was 3.98% to 5.88% from the 4th day to 17 th day.On the other hand,the release behavior was 3.93% to 41.6% in the same elapsed time.The release profile validated the theory of selectively unsealing the CRF in the presence of ?-amylase enzyme by the rupture of ?-CD's ?-1,4 bonds between glucose monomers.Thermal and light stability of the CRF were investigated.The decomposition rate of enfolded CLAP in all CRF samples was much lower than that of CLAP technical which revealed more than 98% decomposition after 3 h of UV radiation.Moreover,after 24 h of UV radiation,the decomposition rate of enfolded CLAP in CRF was less than 10%.The obtained data identified that CLAP can be preserved by the CRF shell and represents an outstanding UV-shielding capability for the synthesized CLAP-CRF.For AVM,technical AVM under high temperatures decomposed faster and easier than the entrapped AVM in CRF.For UV photolysis,the technical AVM was much higher photolyzed than the wrapped AVM in all CRF.The technical AVM revealed that more than 98% decomposition after 3 h of UV radiation.On the other hand,after 24 h of UV radiation,less than 9% of AVM in CRF was photolyzed.In addition,the bioassay of CLAP-CRF and AVM-CRF against Plutella xylostella larvae was evaluated by regular cabbage leaf sampling feeding experiment on pesticide treated field-grown Brassica rapa leaves.The CRF biological activity survey showed excellent toxicological properties against Plutella xylostella larvae,which confirms that ?-CD caps could be uncapped enzymatically in vivo and release the pesticides,inducing P.xylostella larval death.For CLAP,at day 14,the mortality for 1.2 mg L-1 of CLAP-CRF was still higher than 90%.In contrast,the mortality of 1.2 mg L-1 of CLAP(Coragen)treated decreased to 66.6%.For AVM,at day 14,the mortality for 0.6 mg L-1 of AVMCRF was still higher than 80% in opposite with AVM-CF 0.6 mg L-1 which decreased to 43.3%,which confirmed that the fabricated CRF has a notable capability to keep the pesticides biologically active until Day 14 with high mortality.In this work,the fabricated CRF can enhance the pesticide-directing capability and extend the pesticides bioavailability with negligible environmental side effects.