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Paper text:
chloroauric acid tetrahydrate ( haucl4 
 4  h2o , 99.9  % ) , silver nitrate ( agno3 , 99.0  % ) , ascorbic acid ( aa , 99.0  % ) , ptoluenesulfonic acid monohydrate ( 98.0  % ) , acetic acid ( 99.7  % ) , tertbutyl nitrite ( 90.0  % ) , 4nitroaniline ( 99  % ) , 4aminobenzoic acid ( 99  % ) , 4aminoaniline ( 99.0  % ) , and diethyl ether ( 99.7  % ) were purchased from sigma  aldrich .
hinton agar ( mha ) was prepared as described by the producer ( oxoid , cm0337 ) and sterilized in an autoclave .
the corresponding arenediazonium tosylates ( 4nitrobenzenediazonium tosylate , 4aminobenzenediazonium tosylate , and 4carboxybenzenediazonium tosylate ) were prepared according to the described procedure.55 
  au multibranched nps ( aums ) were synthesized by a known procedure.44 aqueous haucl4 solution ( 100  l , 10  mm ) was mixed with deionized water ( 3  ml ) , and then aqueous agno3 solution ( 6  l , 10  mm ) was added under magnetic stirring for 30  s. after the solutions had been thoroughly mixed , ascorbic acid ( 2  l , 100  mm ) was  quickly  added , and the solution was stirred vigorously for 10  s at room temperature ( rt ) . when the reducing agent was added , the color of the mixture changed immediately from yellow to dark blue , indicating the formation of aums .
then , the aums were dispersed in water ( 3  ml ) and were purified three times by centrifugation at 5000  rpm for 10  min .
an aqueous solutions of the desired arenediazonium tosylate ( 70  l , 10  mm ; 4nitrobenzenediazonium tosylate , 4aminobenzenediazonium tosylate , or 4carboxybenzenediazonium tosylates ) was added to a freshly prepared suspension of aums ( diazonium salts preparation procedure is describe in previous works).56 , 57 the mixtures were stirred for 5  min .
the nanoparticles were then collected and washed thoroughly by several centrifugations at a speed of 5000  rpm for 10  min by using deionized water ( 1 ) , water / methanol ( 1 , 40:60 ) , and then drying at room temperature .
after the modification process , aums were collected by centrifugation , washed sequentially by using water , a water / methanol mixture , and methanol to remove 4toluenesulfonic acid , unreacted diazonium salt , and its reduction products ( nitrobenzene , aniline , and benzoic acid ) derived from generated aryl radicals ( ptsoh , adts are soluble in water and reduction products are soluble in methanol ) .
this washing procedure needs to be done to ensure that any organic material adsorbed on the surface is removed.58 , 59 
  transmission electron microscopy ( tem ) images of the nanoparticles were obtained with a jeol jem1010 instrument ( jeol ltd . ,
japan ) , with a sis megaview iii digital camera ( soft imaging systems , acceleration voltage 80  kv ) and analysis was performed by using analysis software 2.0 .
scanning electron microscopy ( sem ) ( lyra3 gmu , tescan , cr ) was used for the study of morphology and distribution of the modified aums .
the nanoparticles were deposited on si substrate and the sem images and elemental composition and mapping were performed by using energy dispersive spectroscopy ( eds , analyzer xmaxn , 20  mm sdd detector , oxford instruments ) . the samples were attached by carbon conductive tape to avoid sample charging .
semeds and sem measurements were carried out by using accelerating voltages of 10  kv and 2  kv , respectively .
uv / vis absorption spectra were measured by using a lambda 25 uv / vis / nir spectrometer ( perkinelmer , usa ) in the spectral range 300900  nm at a scanning rate of 240  nm  min and a data collection interval of 1  nm .
the reference spectrum of the solvent ( deionized water ) was subtracted from all spectra .
raman scattering was measured with a dimensionp1 raman spectrometer ( laser power 2.2  mw , integration time 1  s , frames averaged per measurement 250 ) with 785  nm excitation wavelength ( lambda solutions , inc .
the pristine and grafted aums were deposited on si substrate by using the dropdried method .
all spectra were baselinecorrected by subtracting the spectrum of pure substrate followed manual alignment of the background .
the antibacterial activities of pristine and surfacemodified aums were evaluated against two environmental bacterial strains : gramnegative escherichia coli ( e.  coli , dbm 3138 ) and grampositive staphylococcus epidermidis ( s.  epidermidis , dbm 3179 ) . for evaluation of antimicrobial activity in the dark ,
the bacteria were incubated with aums in the dark for 2  h. estimation of the lightinduced antimicrobial effect was performed by the incubation of bacteria with aums for 1  h in the dark , followed by 1  h illumination .
the latter experiments were performed under led irradiation with 780  nm center wavelength . in all cases ,
1  ml of the aums solution was inoculated with 1  ml of the bacterial suspension and after 2  h of action aliquots ( 30  l ) from all samples were subsequently placed on lysogeny broth ( lb ) agar plates .
the growth of e.  coli and s.  epidermidis was evaluated after 24  h of incubation at 37  c and the number of colony founded units ( cfu ) was used as the marker of aums antimicrobial activity .
chloroauric acid tetrahydrate ( haucl4 
 4  h2o , 99.9  % ) , silver nitrate ( agno3 , 99.0  % ) , ascorbic acid ( aa , 99.0  % ) , ptoluenesulfonic acid monohydrate ( 98.0  % ) , acetic acid ( 99.7  % ) , tertbutyl nitrite ( 90.0  % ) , 4nitroaniline ( 99  % ) , 4aminobenzoic acid ( 99  % ) , 4aminoaniline ( 99.0  % ) , and diethyl ether ( 99.7  % ) were purchased from sigma  aldrich .
hinton agar ( mha ) was prepared as described by the producer ( oxoid , cm0337 ) and sterilized in an autoclave .
the corresponding arenediazonium tosylates ( 4nitrobenzenediazonium tosylate , 4aminobenzenediazonium tosylate , and 4carboxybenzenediazonium tosylate ) were prepared according to the described procedure.55 

au multibranched nps ( aums ) were synthesized by a known procedure.44 aqueous haucl4 solution ( 100  l , 10  mm ) was mixed with deionized water ( 3  ml ) , and then aqueous agno3 solution ( 6  l , 10  mm ) was added under magnetic stirring for 30  s. after the solutions had been thoroughly mixed , ascorbic acid ( 2  l , 100  mm ) was  quickly  added , and the solution was stirred vigorously for 10  s at room temperature ( rt ) . when the reducing agent was added , the color of the mixture changed immediately from yellow to dark blue , indicating the formation of aums .
then , the aums were dispersed in water ( 3  ml ) and were purified three times by centrifugation at 5000  rpm for 10  min . for further use
an aqueous solutions of the desired arenediazonium tosylate ( 70  l , 10  mm ; 4nitrobenzenediazonium tosylate , 4aminobenzenediazonium tosylate , or 4carboxybenzenediazonium tosylates ) was added to a freshly prepared suspension of aums ( diazonium salts preparation procedure is describe in previous works).56 , 57 the mixtures were stirred for 5  min .
the nanoparticles were then collected and washed thoroughly by several centrifugations at a speed of 5000  rpm for 10  min by using deionized water ( 1 ) , water / methanol ( 1 , 40:60 ) , and then drying at room temperature .
after the modification process , aums were collected by centrifugation , washed sequentially by using water , a water / methanol mixture , and methanol to remove 4toluenesulfonic acid , unreacted diazonium salt , and its reduction products ( nitrobenzene , aniline , and benzoic acid ) derived from generated aryl radicals ( ptsoh , adts are soluble in water and reduction products are soluble in methanol ) .
this washing procedure needs to be done to ensure that any organic material adsorbed on the surface is removed.58 , 59 

transmission electron microscopy ( tem ) images of the nanoparticles were obtained with a jeol jem1010 instrument ( jeol ltd . ,
japan ) , with a sis megaview iii digital camera ( soft imaging systems , acceleration voltage 80  kv ) and analysis was performed by using analysis software 2.0 .
scanning electron microscopy ( sem ) ( lyra3 gmu , tescan , cr ) was used for the study of morphology and distribution of the modified aums .
the nanoparticles were deposited on si substrate and the sem images and elemental composition and mapping were performed by using energy dispersive spectroscopy ( eds , analyzer xmaxn , 20  mm sdd detector , oxford instruments ) . the samples were attached by carbon conductive tape to avoid sample charging .
semeds and sem measurements were carried out by using accelerating voltages of 10  kv and 2  kv , respectively .
uv / vis absorption spectra were measured by using a lambda 25 uv / vis / nir spectrometer ( perkinelmer , usa ) in the spectral range 300900  nm at a scanning rate of 240  nm  min and a data collection interval of 1  nm .
the reference spectrum of the solvent ( deionized water ) was subtracted from all spectra .
raman scattering was measured with a dimensionp1 raman spectrometer ( laser power 2.2  mw , integration time 1  s , frames averaged per measurement 250 ) with 785  nm excitation wavelength ( lambda solutions , inc .
the pristine and grafted aums were deposited on si substrate by using the dropdried method .
all spectra were baselinecorrected by subtracting the spectrum of pure substrate followed manual alignment of the background .
the antibacterial activities of pristine and surfacemodified aums were evaluated against two environmental bacterial strains : gramnegative escherichia coli ( e.  coli , dbm 3138 ) and grampositive staphylococcus epidermidis ( s.  epidermidis , dbm 3179 ) . for evaluation of antimicrobial activity in the dark ,
the bacteria were incubated with aums in the dark for 2  h. estimation of the lightinduced antimicrobial effect was performed by the incubation of bacteria with aums for 1  h in the dark , followed by 1  h illumination .
the latter experiments were performed under led irradiation with 780  nm center wavelength . in all cases ,
1  ml of the aums solution was inoculated with 1  ml of the bacterial suspension and after 2  h of action aliquots ( 30  l ) from all samples were subsequently placed on lysogeny broth ( lb ) agar plates .
the growth of e.  coli and s.  epidermidis was evaluated after 24  h of incubation at 37  c and the number of colony founded units ( cfu ) was used as the marker of aums antimicrobial activity .
abstractsurfacemodified gold multibranched nanoparticles ( aums ) were prepared by simple chemical reduction of gold chloride aqueous solution followed by in  situ modification by using watersoluble arenediazonium tosylates with different functional organic groups . 
 chemical and morphological structures of the prepared nanoparticles were examined by using transmission electron and scanning electron microscopies . 
 the covalent grafting of organic compounds was confirmed by scanning electron microscopy with energy dispersive xray spectroscopy ( semedx ) and raman spectroscopy techniques . 
 covalent functionalization of nanoparticles significantly expands the range of their potential uses under physiological conditions , compared with traditional noncovalent or thiolbased approaches . 
 the antibacterial effect of the surfacemodified aums was evaluated by using escherichia coli and staphylococcus epidermidis bacteria under ir light illumination and without external triggering . 
 strong plasmon resonance on the aums cups leads to significant reduction of the light power needed kill bacteria under the mild conditions of continuous illumination . 
 the effect of the surfacemodified aums on the lightinduced antibacterial activities was founded to be dependent on the grafted organic functional groups .