aflatoxins ( afs ) are secondary metabolites with toxic and carcinogenic effects , which are produced by species of aspergillus , particularly aspergillus flavus and aspergillus parasiticus ( a. parasiticus ) . the commodities such as peanuts , rice , corn and cottonseed have suitable condition for growth of these fungi , so contamination of these commodities with afs often makes them unfit for consumption . afs are considered the most carcinogenic , mutagenic , and teratogenic compounds found naturally in foods and feeds . aflatoxins b1 ( afb1 ) , b2 ( afb2 ) , g1 ( afg1 ) , and g2 ( afg2 ) are major naturally occurring afs produced by aflatoxigenic fungi . afb1 is the most powerful af ; moreover , afb1 has been classified as a human carcinogen in the group 1 by the international agency for research on cancer ( iarc ) . in addition , afb1 is a hepatocarcinogenic compound that might cause tumors in other organs like colon and kidney . the importance of afb1 led to many researches on the effects of different compounds in order to inhibit its production . nanotechnology for the purpose of manufacturing new materials at nanoscale is considered as rapidly developing field that a large spectrum of research has been focused on its application . different types of nanomaterials like copper , zinc , platinum , titanium , magnesium , gold , alginate and silver have come up , but silver nanoparticles ( agnps ) have proved to be most effective as it has good antimicrobial efficacy against bacteria , viruses and other eukaryotic micro - organisms . for many years , silver has been in use to treat burns and chronic wounds . also silver and its compounds are regarded as a relatively safe antimicrobial metal that has a wide spectrum of activity . recently , due to enhancement of antibiotic - resistant bacteria and limitations of antibiotic usage , silver wound dressings with a variety of silver levels is used again as an alternative treatment . due to new advances of researches about metal nanoparticles , nano - ag has received special attention as a possible antimicrobial agent , which in low concentrations is nontoxic . nanoparticles due to their size have a larger surface area to come in contact with microorganisms than a bigger form of particles . antifungal activities of agnps against different kinds of fungus have not been reported as much as antimicrobial activities of them by researchers . it was reported that agnps could inhibit fungi in low concentrations and those levels had no toxic effect on human cells . in a research by kim et al . , it is indicated that agnps have antifungal activity against trichophyton mentagrophytes , trichosporon beigelii , and candida albicans in comparison with available antifungal agents like amphotericin b and fluconazole . the aim of this study was to investigate the effects of agnps on the growth and afb1 production by a. parasiticus . the a. parasiticus ptcc 5280 , a known producer of afb1 was used throughout the study . potato dextrose broth ( merck , germany ) was the culture medium used for afs production by the fungus . agnps in colloid form with 4,000 ppm were purchased from nanocid company in tehran ( www.nanocid.com ) . a. parasiticus was cultured on potato dextrose broth in 10-well flat - bottom microplates ( iwaki ; well dia . the culture medium was added to microplates in amounts of 1 ml / well and then inoculated with fungal spore suspension ( 110 spores / well ) prepared in sterilized distilled water containing 0.1% tween 80 . different concentrations of the agnps ( 60 , 80 , 100 , 120 , 140 , 160 , 180 and 200 ppb ) prepared in dimethyl sulfoxide ( dmso ) were added to the test wells . ketoconazole and sterile distilled water ( sdw ) were used as positive control and negative control , respectively . growth of mold was observed visually throughout the incubation period . the minimal inhibitory concentration ( mic ) was defined as the concentration of agnps that prevented growth in the media as determined visually . for these experiments 250 l of a suspension containing 110 spores / ml were added to 250 ml erlenmeyer flasks containing 50 ml of broth in the presence of agnps at concentrations lower than the mic ( 75% , 50% , and 25% mic ) . following the addition of each solvent , a 50 ml of potato dextrose broth was mixed with 2.5 g nacl and 100 ml solution of 80% methanol in water for 5 min and then the mixture was filtered on whatman filter paper . the extract was diluted with 25 ml of distilled water and 5 ml pbs with ph 7.4 . finally , 20 ml of this was purified on the immunoaffinity column activated with 20 ml of pbs by gentle syringe pressure at a flow rate of 1 ml / min and then the column was washed with 20 ml of deionized water . the column was dried by blowing air through it for 23 seconds with a syringe . the afs were slowly eluted from the column with 2 ml of hplc grade methanol and then were diluted with 2 ml of deionized water . the a. parasiticus ptcc 5280 , a known producer of afb1 was used throughout the study . potato dextrose broth ( merck , germany ) was the culture medium used for afs production by the fungus . agnps in colloid form with 4,000 ppm were purchased from nanocid company in tehran ( www.nanocid.com ) . a. parasiticus was cultured on potato dextrose broth in 10-well flat - bottom microplates ( iwaki ; well dia . 16 mm ) . the culture medium was added to microplates in amounts of 1 ml / well and then inoculated with fungal spore suspension ( 110 spores / well ) prepared in sterilized distilled water containing 0.1% tween 80 . different concentrations of the agnps ( 60 , 80 , 100 , 120 , 140 , 160 , 180 and 200 ppb ) prepared in dimethyl sulfoxide ( dmso ) were added to the test wells . ketoconazole and sterile distilled water ( sdw ) were used as positive control and negative control , respectively . the minimal inhibitory concentration ( mic ) was defined as the concentration of agnps that prevented growth in the media as determined visually . for these experiments 250 l of a suspension containing 110 spores / ml were added to 250 ml erlenmeyer flasks containing 50 ml of broth in the presence of agnps at concentrations lower than the mic ( 75% , 50% , and 25% mic ) . following the addition of each solvent , a 50 ml of potato dextrose broth was mixed with 2.5 g nacl and 100 ml solution of 80% methanol in water for 5 min and then the mixture was filtered on whatman filter paper . the extract was diluted with 25 ml of distilled water and 5 ml pbs with ph 7.4 . finally , 20 ml of this was purified on the immunoaffinity column activated with 20 ml of pbs by gentle syringe pressure at a flow rate of 1 ml / min and then the column was washed with 20 ml of deionized water . the column was dried by blowing air through it for 23 seconds with a syringe . the afs were slowly eluted from the column with 2 ml of hplc grade methanol and then were diluted with 2 ml of deionized water . initial data showed that agnps was able to inhibit a. parasiticus growth and af production effectively . this inhibition was reported in concentration of 180 g / ml . figure 1 illustrates afb1 production without the effect of agnps , where the determined point was the start time of af production . the hplc results of af production showed that these nanoparticles were able to strongly inhibit afb1 production in a dose dependent manner , also afb1 inhibition was reported at a concentration of 90 g / ml after comparing with non - treated controls ( figure 2 ) . . shows different silver nanoparticles concentrations effect on aflatoxin b1 production , at 90 g / ml ( 50% mic ) agnps , aflatoxin production was inhibited . initial data showed that agnps was able to inhibit a. parasiticus growth and af production effectively . figure 1 illustrates afb1 production without the effect of agnps , where the determined point was the start time of af production . the hplc results of af production showed that these nanoparticles were able to strongly inhibit afb1 production in a dose dependent manner , also afb1 inhibition was reported at a concentration of 90 g / ml after comparing with non - treated controls ( figure 2 ) . . shows different silver nanoparticles concentrations effect on aflatoxin b1 production , at 90 g / ml ( 50% mic ) agnps , aflatoxin production was inhibited . silver is one of the most effective antibiotic substances known and has been used to treat human ailments for over 100 years due to its natural antibacterial and nontoxic properties . since nano - sized silver materials have stronger antifungal activity than bulk silver materials , it has recently attracted great attention . in fact , smaller sized particles possess a larger surface area in contact with the microorganism and have a higher percentage of interaction than bigger particles . although most of the studies are focused on nanoparticle applications , there are limited studies describing the impact of nanoparticles on human health . results of last researches showed that mic of agnps was lower than the cytotoxicity level of tested human cells . therefore , low concentrations of silver nanoparticles could inhibit fungi and those levels had no toxic effect on human cells . panacek et al . have claimed that nano - sized silver has a significant antifungal activity against candida albicans . also , in another study by kim et al . , antifungal effects of agnps on candida albicans were investigated . the mic values of these studies indicated that agnps inhibited growth of candida albicans at low concentrations ( < 4 g / ml ) . in comparison with the last two studies , the present research shows that a. parasiticus growth is inhibited at higher concentration of agnps . this discrepancy can be derived from different species of fungi and agnps used in both works , where agnps were stabilized by surfactants and polymers . in our study , this method was similar to the method performed by nozari et al . , who reported that agnps showed an antifungal effect against candida species isolated from chronic candida vulvovaginitis . many studies have shown the antimicrobial effects of agnps . among the antimicrobial activity of agnps against gram - positive staphylococcus aureus and the mic of agnps against s. aureus and e. coli was 100 - 150 g / ml and in contrast with our study agnps were used in powder form . antifungal effects of agnps on dermatophytes especially trichophyton mentagrophytes , had been studied by kim . some researchers have reported that the activity of antifungal drugs against phoma glomerata , phoma herbarum , fusarium semitectum and trichoderma sp was enhanced in combination with agnps . however , in spite of recent researches , the effects of nano - ag against af producing a. parasiticus and afb1 are mostly unknown . based on previous studies , the main contribution of this study was agnps effect on growth and afb1 production by a. parasiticus . in the present study , we showed agnps inhibiting afb1 production by a. parasiticus in addition to the ability for strong fungal growth inhibition . therefore the mic value of the agnps against a. parasiticus was 180 g / ml and agnps inhibited afb1 production at 50% of the mic ( 90 g / ml ) . when different concentrations of agnps were added to the fungal cultures in media , a remarkable inhibition in aflatoxin synthesis was observed . the inhibition in growth and toxin production was dependent on the concentration of agnps . in this study , since the agnps were used as antifungal drug , antifungal drug of ketoconazole and sterile distilled water ( sdw ) were positive control and negative control , respectively . in a research by gajbhiye et al . , fluconazole , which is antifungal agent , was used as positive control for comparison with ag - nps and kim et al . used amphotericin b as a positive control in their study . to the best of our knowledge , this research was the first study about the effects of agnps on afb1 production by a. parasiticus . due to the important role of af contamination , especially negative effect of afb1 on public health , efforts should be conducted to prevent the contamination , since prevention is the most economical and practical approach . agnps ability indicates that they may be considered as useful candidates to eliminate af contamination in food and feedstuffs . based on the results of the present study , agnps could inhibit growth and afb1 production by a. parasiticus . these nanoparticles must be subjected to further study to determine their effects on other mycotoxins , define toxicity , and evaluate economic feasibility .