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M. Singh et al.
and S. aureus, from 300 s treatment but just 10 s treatment gave 96 and 98% bacterial
reduction for the bacteria, respectively, and that results were maintained even after
ten cycles of washing (Shahidi and Ghoranneviss 2016).
Grafting of textiles has also been used to achieve surface modification for enhancing the antimicrobial efficiency of the fabric. Airoudj et al. reported a solvent-free,
dry-plasma polymerisation method for firmly anchoring silver nanoparticles on cotton fabrics to achieve antibacterial property. Plasma polymer functionalised cotton
was obtained by coating a thin film of maleic anhydride powdered vapours along with
air plasma onto the fabric for 2, 8 and 30 min time interval. The anhydride groups were
then hydrolysed into carboxylic acids by dipping the fabrics in water. These charged
acidic groups were meant to help in better adhesion of silver ions through electrostatic interactions. Then, the maleic acid-plasma polymerised substrate was dipped
in an aqueous solution of silver ions which reduced and coalesced into nanoparticles
in an NaBH 4 solution. The formation and adhesion of nanoparticles were confirmed
by TEM images which showed uniformly distributed spherical-shaped nanoparticles
with an average size of 8 nm. The loading of silver ions was also confirmed by surface
plasmon resonance (SPR) band of AgNPs in the UV–Vis region with a maximum at
415 nm. The UV–Visible absorbance spectra depicted a decrease in optical density
by varying the plasma duty cycle with maximum intensity for 2 min treatment and
minimum for 30 min. Antibacterial activity of treated samples which was evaluated
by two methods, i.e. agar-plate and epifluorescence studies, both reported no or less
growth of bacteria in AgNPs and plasma polymerised samples. The bactericidal effect
was explained as a consequence of the leaching of antibacterial silver ions from the
attached nanoparticles into the plasma polymerised samples. The durability of silver
ions on the plasma polymerised sample was checked by subjecting them to three
washing cycles in a hot water bath. The results depicted no change in colour (yellow
due to the presence of silver ions) of the samples along with no change in UV–Vis
absorbance spectra indicating that silver particles are quite strongly linked to the
fabric (Airoudj et al. 2014). In another study (Haji et al. 2013), researches enhanced
the antimicrobial activity of cotton fabric by using radiofrequency (13.56 MHz)
low-pressure oxygen plasma pretreatment for 5 min along with grafting of acrylic
acid monomer to activate the surface for better attachment of silver particles on the
substrate. The activated cotton fabric samples were immersed in AgNO 3 solution
and after that in NaBH 4 solution to reduce the adsorbed Ag
+ ions into Ag˙ radicals.
A colour change in the fabric from white to brownish yellow indicated synthesis
and attachment of silver nanoparticles which was also confirmed by SEM analysis
as the plasma polymerised and AgNP-loaded surface appeared rough and etched as
compared to untreated. Cotton fabric surface consists of an overall negative charge
due to the presence of carboxyl and hydroxyl group in the polymer chain. Pretreatment with oxygen plasma and acrylic acid helped in enhancing the negative charge
along with increasing the roughness of the surface by plasma etching. The silver ions
carrying a positive charge (Ag
+ ) get incorporated to the surface due to strong electrostatic interactions and gets strongly bonded to the active sites created as a result
of plasma etching and acrylic acid grafting. The absorbed silver ions were converted
to silver atoms and coalesce to generate nanoparticles in the presence of reducing
M. Singh et al.
and S. aureus, from 300 s treatment but just 10 s treatment gave 96 and 98% bacterial
reduction for the bacteria, respectively, and that results were maintained even after
ten cycles of washing (Shahidi and Ghoranneviss 2016).
Grafting of textiles has also been used to achieve surface modification for enhancing the antimicrobial efficiency of the fabric. Airoudj et al. reported a solvent-free,
dry-plasma polymerisation method for firmly anchoring silver nanoparticles on cotton fabrics to achieve antibacterial property. Plasma polymer functionalised cotton
was obtained by coating a thin film of maleic anhydride powdered vapours along with
air plasma onto the fabric for 2, 8 and 30 min time interval. The anhydride groups were
then hydrolysed into carboxylic acids by dipping the fabrics in water. These charged
acidic groups were meant to help in better adhesion of silver ions through electrostatic interactions. Then, the maleic acid-plasma polymerised substrate was dipped
in an aqueous solution of silver ions which reduced and coalesced into nanoparticles
in an NaBH 4 solution. The formation and adhesion of nanoparticles were confirmed
by TEM images which showed uniformly distributed spherical-shaped nanoparticles
with an average size of 8 nm. The loading of silver ions was also confirmed by surface
plasmon resonance (SPR) band of AgNPs in the UV–Vis region with a maximum at
415 nm. The UV–Visible absorbance spectra depicted a decrease in optical density
by varying the plasma duty cycle with maximum intensity for 2 min treatment and
minimum for 30 min. Antibacterial activity of treated samples which was evaluated
by two methods, i.e. agar-plate and epifluorescence studies, both reported no or less
growth of bacteria in AgNPs and plasma polymerised samples. The bactericidal effect
was explained as a consequence of the leaching of antibacterial silver ions from the
attached nanoparticles into the plasma polymerised samples. The durability of silver
ions on the plasma polymerised sample was checked by subjecting them to three
washing cycles in a hot water bath. The results depicted no change in colour (yellow
due to the presence of silver ions) of the samples along with no change in UV–Vis
absorbance spectra indicating that silver particles are quite strongly linked to the
fabric (Airoudj et al. 2014). In another study (Haji et al. 2013), researches enhanced
the antimicrobial activity of cotton fabric by using radiofrequency (13.56 MHz)
low-pressure oxygen plasma pretreatment for 5 min along with grafting of acrylic
acid monomer to activate the surface for better attachment of silver particles on the
substrate. The activated cotton fabric samples were immersed in AgNO 3 solution
and after that in NaBH 4 solution to reduce the adsorbed Ag
+ ions into Ag˙ radicals.
A colour change in the fabric from white to brownish yellow indicated synthesis
and attachment of silver nanoparticles which was also confirmed by SEM analysis
as the plasma polymerised and AgNP-loaded surface appeared rough and etched as
compared to untreated. Cotton fabric surface consists of an overall negative charge
due to the presence of carboxyl and hydroxyl group in the polymer chain. Pretreatment with oxygen plasma and acrylic acid helped in enhancing the negative charge
along with increasing the roughness of the surface by plasma etching. The silver ions
carrying a positive charge (Ag
+ ) get incorporated to the surface due to strong electrostatic interactions and gets strongly bonded to the active sites created as a result
of plasma etching and acrylic acid grafting. The absorbed silver ions were converted
to silver atoms and coalesce to generate nanoparticles in the presence of reducing