Nanotechnologies — Antibacterial silver nanoparticles — Specification of characteristics and measurement methods

This document provides guidance for the specification of characteristics and relevant measurement methods for silver nanoparticles in powder or colloidal forms that are intended for antibacterial applications in nanotechnology. This document is intended to aid the producer in providing the physicochemical characteristics of silver nanoparticles that have an antibacterial effect to the buyer. This document does not cover considerations specific to health and safety issues either during manufacturing or use.

Nanotechnologies — Nanoparticules d'argent antibactériennes — Spécification des caractéristiques et des méthodes de mesure

General Information

Status
Published
Publication Date
02-Jun-2019
Technical Committee
Current Stage
9093 - International Standard confirmed
Completion Date
14-Sep-2022
Ref Project

Buy Standard

Technical specification
ISO/TS 20660:2019 - Nanotechnologies -- Antibacterial silver nanoparticles -- Specification of characteristics and measurement methods
English language
14 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 20660
First edition
2019-06
Nanotechnologies — Antibacterial
silver nanoparticles — Specification
of characteristics and measurement
methods
Nanotechnologies — Nanoparticules d'argent antibactériennes —
Spécification des caractéristiques et des méthodes de mesure
Reference number
ISO/TS 20660:2019(E)
©
ISO 2019

---------------------- Page: 1 ----------------------
ISO/TS 20660:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TS 20660:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 2
5 Characteristics and measurement methods . 3
5.1 General . 3
5.2 Average size and size distribution of primary particles . 4
5.3 Zeta potential . 4
5.4 Specific surface area . 4
5.5 Total silver content . 4
5.6 Hydrodynamic size . 5
5.7 Silver nanoparticle number concentration. 5
6 Sampling . 5
7 Test report . 5
Annex A (informative) Measurement methods for antibacterial silver nanoparticles .6
Annex B (informative) Relationship between silver nanoparticle characteristics and
antibacterial performance . 8
Annex C (informative) Antibacterial performance test.10
Bibliography .11
© ISO 2019 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TS 20660:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 229, Nanotechnologies.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/TS 20660:2019(E)

Introduction
Silver nanoparticles have become one of the most widely utilized nanomaterials in consumer products
for their antibacterial properties. The application of silver nanoparticles is increasingly being adopted
in consumer products to control the growth of microorganisms on the surfaces or interiors of products.
When silver nanoparticles interact with microorganisms silver ions are released, and these ions may
affect and damage microorganisms in different ways. However, the mechanism behind the bactericidal
[1]
effect is not well known . There have been several possible mechanisms proposed in the scientific
literature: 1) silver ions with positive electricity released from silver nanoparticles are able to rapidly
bind to sulfhydryl groups on the surfaces of bacteria, which leads the structures of bacteria to change
and become damaged, 2) the uptake of silver ions or small nanoparticles disrupts adenosine triphosphate
production and DNA replication, and 3) silver nanoparticles and ions generate reactive oxygen species
[2]-[4]
resulting in oxidative damage . Other scientific evidence of the antibacterial performance of silver
nanoparticle is listed in Annex B. The antibacterial properties of silver nanoparticles are related to
their physicochemical characteristics.
Although antibacterial products that utilize silver nanoparticle are widely distributed in the
market, most of these products are sold without providing information on the physicochemical and
corresponding antibacterial characteristics of nanoparticles. Currently, most manufacturers provide
specifications based on their own practices.
This document provides guidance for the specification of characteristics and relevant recommended
measurement methods, referenced from other standards for silver nanoparticles in powder and colloidal
forms that are intended for antibacterial applications in nanotechnology. The major measurement
methods available to industry for the determination of parameters specified in this document are of
course recommended in the specification. This document reviews selected measurement methods that
are commonly used at present, and therefore will require updating on a regular basis.
© ISO 2019 – All rights reserved v

---------------------- Page: 5 ----------------------
TECHNICAL SPECIFICATION ISO/TS 20660:2019(E)
Nanotechnologies — Antibacterial silver nanoparticles —
Specification of characteristics and measurement methods
1 Scope
This document provides guidance for the specification of characteristics and relevant measurement
methods for silver nanoparticles in powder or colloidal forms that are intended for antibacterial
applications in nanotechnology.
This document is intended to aid the producer in providing the physicochemical characteristics of silver
nanoparticles that have an antibacterial effect to the buyer.
This document does not cover considerations specific to health and safety issues either during
manufacturing or use.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the cited edition applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 26824, Particle characterization of particulate systems — Vocabulary
ISO/TS 80004-1, Nanotechnologies — Vocabulary — Part 1: Core terms
ISO/TS 80004-2, Nanotechnologies — Vocabulary — Part 2: Nano-objects
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 26824, ISO/TS 80004-1, ISO/
TS 80004-2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
silver nanoparticle
nanoparticle composed of silver with all three external dimensions in the nanoscale
[SOURCE: modified from ISO/TS 80004-2, 4.1, modified]
3.2
primary particle
Original source particle (3.1) of agglomerates (3.4) or aggregates (3.5) or mixtures of the two
Note 1 to entry: Constituent particles (3.3) of agglomerates or aggregates at a certain actual state may be primary
particles, but often the constituents are aggregates.
Note 2 to entry: Agglomerates and aggregates are also termed secondary particles.
[SOURCE: ISO 26824, 1.4]
© ISO 2019 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/TS 20660:2019(E)

3.3
nanoscale
size range from approximately 1 nm to 100 nm
Note 1 to entry: Properties that are not extrapolations from a larger size are predominantly exhibited in this
length range.
[SOURCE: ISO/TS 80004-1, 2.1]
3.4
agglomerate
collection of weakly or medium strongly bound particles (3.1) where the resulting external surface area
is similar to the sum of the surface areas of the individual components
Note 1 to entry: The forces holding agglomerate together are weak forces, for example van der Waals forces or
simple physical entanglement.
Note 2 to entry: Agglomerates are also termed secondary particles and the original source particles are termed
primary particles (3.2).
[SOURCE: ISO 26824, 1.2]
3.5
aggregate
particle (3.1) comprising strongly bonded or fused particles where the resulting external surface area
is significantly smaller than the sum of surface areas of the individual components
Note 1 to entry: The forces holding an aggregate together are strong forces, for example covalent bonds, or those
resulting from sintering or complex physical entanglement, or otherwise combined former primary particles.
Note 2 to entry: Aggregates are also termed secondary particles and the original source particles are termed
primary particles (3.2).
[SOURCE: ISO 26824, 1.3]
3.6
antibacterial activity
property of substances or phenomena that kills (bactericidal) or slow down (bacteriostatic) the growth
of bacteria
4 Symbols and abbreviations
For the purposes of this document, the following symbols and abbreviations apply:
Abbreviation Meaning
AAS Atomic absorption spectrometry
AgNP Silver nanoparticle
BET Brunauer-Emmett-Teller
DLS Dymanic light scattering
ELS Electrophoretic light scattering
ICP-MS Inductively coupled plasma mass spectrometry
ICP-OES Inductively coupled plasma optical emission spectrometry
NP Nanoparticle
PTA Particle tracking analysis
SAXS Small angle X-ray scattering
2 © ISO 2019 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/TS 20660:2019(E)

SEM Scanning electron microscopy
spICP-MS Single particle inductively coupled plasma mass spectrometry
TEM Tranmission electron microscopy
5 Characteristics and measurement methods
5.1 General
The specification of characteristics and measurement methods for antibacterial silver nanoparticles is
separated into two categories: those that are essential are listed in Table 1 and those that are additional
are listed in Table 2. A producer of antibacterial silver nanoparticles shall measure the characteristics
in Table 1 and should also measure the characteristics in Table 2 and report the results to the buyer of
AgNPs. In Tables 1 and 2, guidance for the measurement methods is listed as information. The listed
ISO standards have been written generically, and measurement methods can be added as technology
advances. Adopting the relevant document be agreed upon by the buyer and producer of AgNPs.
The measurement results for characteristics shall be expressed in the units listed in Tables 1 and 2.
See the informative Annex A describing measurement methods for the individual characteristics
listed in Tables 1 and 2. See the informative Annex B for descriptions of the relationships between
silver nanoparticle characteristics and antibacterial performance. See Annex C for description of the
antibacterial performance test of AgNPs.
Material properties are either intrinsic to the material, or defined by the measurement method. The
values of method-defined properties cannot be directly compared with those obtained using a different
method. In addition, methods for assessing intrinsic properties may be biased, and lead to results that
are different from other methods assessing the same property. Consequently, the results from one
measurement method may not be directly comparable with results from a second measurement method.
Table 1 — Essential characteristics to be measured
Measurement Application form
Characteristics Units Relevant documents
method
SEM Powder or
ISO 16700
1) Average size and
Colloidal
distribution of M
a
TEM Powder or
primary particle
ISO 10797
Colloidal
2) Zeta potential V ELS Colloidal ISO 13099-2
2
3) Specific surface area m /kg BET Powder ISO 9277, ISO 18757
a
ICP-MS Powder or
ISO 17294-1, ISO 17294-2
Colloidal
a
kg/kg or ICP-OES Powder or
4) Total silver content ISO 11885
mol/mol Colloidal
a
AAS Powder or
ISO 26845
Colloidal
a
Powder form has to be dispersed in solvent for measurement. Colloidal form can be directly measured.
© ISO 2019 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO/TS 20660:2019(E)

Table 2 — Additional characteristics to be measured
Measurement Application Relevant docu-
Characteristics Units
method form ments
DLS Collodial ISO 22412
1) Hydrodynamic size m
PTA Colloidal ISO 19430
a
Powder or
spICP-MS ISO/TS 19590
Colloidal
2) Silver nanoparticle number
kg^−1
concentration
Powder or
[17]
SAXS Pauw et. al.
Colloidal
a
Powder form has to be dispersed in solvent for measurement. Colloidal form can be directly measured.
5.2 Average size and size distribution of primary particles
SEM or TEM shall be used to measure the average size of the primary particle. The reference ISO 16700
and ISO 10797 may be useful concerning the measurement of the average size of the primary AgNP.
The primary particles are identified by image processing. Their size may be estimated as an equivalent
spherical diameter or as one or a combination of the Feret diameters of the nanoparticles on SEM and
TEM images. The average primary particle size and its standard deviation shall be calculated from the
distribution of the chosen diameters obtained over the sample.
5.3 Zeta potential
The surface charge of a nanomaterial is one of the key factors determining its stability in a suspension,
[18][19]
and is itself a function of the pH and ionic strength of the AgNP solution . Depending on the
solution’s ionic strength, multiple measurements need to be performed to calculate the zeta potential.
Ideal samples for zeta potential analysis are monodispersed in size, have sufficiently high concentration
to effectively scatter, have low salt concentrations (<1 ms/cm), and are suspended in particulate free
media. The surface charge shall be measured using the electrophoreic method, and the pH value shall be
reported along with the surface charge. Guidance concerning this method can be found in ISO 13099-2.
5.4 Specific surface area
The surface area shall be measured using the gas adsorption method. A technique based on the model
developed by Brunauer, Emmett, and Teller (BET) allows the surface area of a powder to be estimated by
measuring the amount of gas that is adsorbed. The BET analysis is the standard method for determining
the surface area from nitrogen adsorption isotherms, and was originally derived for multilayer gas
[12]
adsorption onto flat surfaces. ISO 9277 applies to the measurement of the specific surface area . This
standard specifies the measurement procedures for the overall specific external and internal surface
areas (diameter > 2 nm) of disperse or porous solids by measuring the amount of physically adsorbed
gas according to the BET method. ISO 18757 provides some useful detailed information concerning
specific materials. Measurement instruments for the BET method are commercially available.
Metrological traceability should be maintained. Reference materials are available for the application of
the BET method to nanoparticles in powder form.
5.5 Total silver content
The total silver content is defined as the ratio of the mass of the total silver content to that of the mass
of the AgNP product. As standard techniques in elemental analysis, ICP-MS, ICP-OES, or AAS have been
utilized to measure the total concentration of dissolved and particulate silver. ICP-MS, ICP-OES, and
AAS offer quantitative capabilities owing to the high degree of ionization for most elements. Guidance
concerning related methods can be found in ISO 17294-1, ISO 17294-2, ISO 11885, and ISO 26845. The
amount and type of acid used to decompose the AgNPs and the conditions of microwave digestion can
be modified if necessary.
4 © ISO 2019 – All rights reserved

---------------------- Page: 9 ----------------------
ISO/TS 20660:2019(E)

5.6 Hydrodynamic size
Unlike NPs in powder form, the hydrodynamic size is the characteristic used to determine the particle
size for NPs in an aqueous solution. The hydrodynamic size is larger than the core diameter in general,
because the hydrodynamic diameter of the particles includes the hydration layer, polymer shells, or
other possible stabilizers. The result for the hydrodynamic size is normally larger than the size result
determined by TEM by an offset that is a function of the capping agent. The hydrodynamic size of
particles shall be measured using DLS or PTA. DLS will give reliable result with a constituent monomer
for a non-agglomerated sample. Guidance concerning this method can be found in ISO 22412 and 19430.
5.7 Silver nanoparticle number concentration
spICP-MS is a technique that is able to generate the number-based particle size distribution of
nanoparticles and quantify the dissolved fraction of the AgNP suspension. Guidance concerning
this method can be found in ISO/TS 19590. SAXS is also applied to measure the AgNP number
[17]
concentration .
6 Sampling
A sample subjected to measurements shall be chosen to be representative of the parent population of
the nanoparticles in powder or suspended form. Sampling and dispersion in liquids of powders should
be carried out in accordance with ISO 14488 and ISO 14887, respectively.
As many nano-objects are reactive, their physical and chemical properties can be affected by the
sampling point and storage environment. Consequently, the producer and end user should agree on the
sampling point and storage of samples for the comparability of results.
7 Test report
The test report shall contain at least the following information:
a) all details generally necessary to identify the product tested (product name, chemical name);
b) a reference to this document;
c) sample description;
d) the relationship between sample applied to the measurements and product tested, to which
characteristics are assigned;
e) the date of test, name of testing laboratory, and statement on the quality system of testing
laboratory;
f) measurement results for the characteristics, with their name and measurement methods as in
Table 1 and, if applicable Table 2;
g) any special information supporting the reliability of measurement results.
Report the results of any antibacterial performance testing with documented test procedure, if it is
available.
© ISO 2019 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO/TS 20660:2019(E)

Annex A
(informative)

Measurement methods for antibacterial silver nanoparticles
Table A.1 gives measurement methods for essential characteristics.
Table A.1 — Measurement methods for essential characteristics
Characteristic Method Guidance
1.1 Average size of TEM Transmission electron microscopy (TEM) is a microscopy
primary particle technique in which a beam of electrons is transmitted
and size through a specimen to form an image. The specimen is most
distribution often an ultrathin section less than 100 nm thick or a
suspension on a grid. An image is formed from the
interaction of the electrons with the sample as the beam is
transmitted through the specimen. The image is then
magnified and focused onto an imaging device, such as a
fluorescent screen, a layer of photographic film, or a sensor
such as a charge-coupled device. Which coupled with EDS
widely used for elemental analysis and chemical analysis.
Guidelines on the application of the method and the sample
preparation process can be found in ISO/TS 10797.
[Source: ISO/TS 12805, modified]
SEM Scanning electron microscope (SEM) is a type of electron
microscope that produces images of a sample by scanning
the surface with a focused beam of electrons. The electrons
interact with atoms in the sample, producing various signals
that contain information about the sample's surface
topography and composition. The electron beam is scanned
in a raster scan pattern, and the beam's position is combined
with the detected signal to produce an image. SEM can
achieve resolution better than 1 nanometre. Specimens can
be observed in high vacuum in conventional SEM, or in low
vacuum or wet conditions in variable pressure or
environmental SEM, and at a wide range of cryogenic or
elevated temperatures with specialized instruments.
Guidelines on the application of the method and the sample
preparation process can be found in ISO 16700 and 10798.
[Source: ISO 16700, modified]
1.2 Zeta potential ELS Zeta potential is the electrostatic potential at the slipping
plane (which marks the region where the liquid molecules
surrounding the particle first begin to move with respect to
the surface) relative to the potential in the bulk solution.
ISO 13099-2 provide methods for measuring electrophoretic
mobility using optical means and for calculating zeta
potential. [Source: ISO/TS 12805, modified]
1.3 Specific surface BET analysis A technique based on the model developed by Brunauer,
area Emmet and Teller that allows the surface area of powders to
be estimated by the amount of gas that is adsorbed.
Typically, nitrogen or carbon dioxide is used, but gases such
as krypton or argon may be used for low surface area
materials because of their sensitivity (mass gain per unit
area). The specific surface area is the ratio of surface area to
mass. Guidance on this method can be found in ISO 9277
and ISO 18757. [Source: ISO/TS 12805, modified]
6 © ISO 2019 – All rights reserved

---------------------- Page: 11 ----------------------
ISO/TS 20660:2019(E)

Table A.1 (continued)
Characteristic Method Guidance
1.4 Total silver ICP-MS ICP-MS uses an inductively coupled plasma source to ionize
content sample materials for analysis by mass spectrometer. ICP-MS
provides accurate and quantitative determinations of
elemental impurities using ICP-MS. Guidance on ultrasonic
spectroscopy methods is available in ISO 17294-1 and
ISO 17294-2.
ICP-OES ICP-OES is an analytical technique used for the detection of
trace metals. It is a type of emission spectroscopy that uses
the inductively coupled plasma to produce excited atoms
and ions that emit electromagnetic radiation at wavelengths
characteristic of a particular element. It is a flame technique
with a flame temperature in a range from 6 000 to 10 000 K.
The intensity of this emission is indicative of the
concentration of the element within the sample. Guidance
on ICP-OES is available in ISO 11885.
[Source: ISO 11885, modified]
AAS Metals in solution may be readily determined by flame
(direct aspiration) atomic absorption
spectrophotometry. Guidance on this method can be found
in ISO 26845.
Table A.2 gives measurement methods for additional characteristics.
Table A.2 — Measurement methods for additional characteristics
Characteristic Method Guidance
2.1 Hydrodynamic DLS This method measures hydrodynamic diameter from
size Brownian motion. It is applicable to the measurement of
particle diameters greater than 3 nm, depending on the test
material. Guidelines on the application of the method can be
found in ISO 22412. [Source: ISO/TS 12805,modified]
PTA PTA is based on measuring the diffusion movement of
particles in a suspension by means of laser illumination,
imaging of scattered light, particle identification and
localization, and individual particle tracking. The
hydrodynamic diameter of the individual particles, droplets
or bubbles is related to Brownian motion parameters via the
Stokes–Einstein equation. Guidelined on the application of
the method can be found in ISO 19430. [Source: ISO 19430]
2.2 Silver nanoparticle spICP-MS spICP-MS is a method capable of detecting single
number nanoparticles at very low concentrations. spICP-MS
concentration determines the size of AgNPs in aqueous suspensions.
Particle number concentrations that can be determined in
aqueous suspensions range from 106 particles/L to
109 particles/L which corresponds to mass concentrations
in the range of approximately 1 ng/l to 1 000 ng/l. Actual
numbers depend on the type of mass spectrometer used and
the type of nanoparticle analysed. In addition to the particle
concentrations, ionic concentrations in the suspension can
also be determined. Guidelined on the application of the
method can be found in ISO/TS 19590.
[Source: ISO/TS 19590, modified]
SAXS SAXS is a method capable of determining NP size
distributions, resolving the size and shape of monodisperse
NP, Silver nanoparticle number concentration can be
determined by SAXS.
© ISO 2019 – All rights reserved 7

---------------------- Page: 12 ----------------------
ISO/TS 20660:2019(E)

Annex B
(informative)

Relationship between silver nanoparticle characteristics and
antibacterial performance
B.1 General
Silver nanoparticles (AgNPs) are well known for their interesting properties and have become one of
the most widely utilized nanomaterials in consumer products to control the growth of microorganisms
[22]
on the surfaces or interiors of products, owing to their antibacterial properties . They are employed
[1]
in catalysis, photonics, medical applications, or even energy storage and conversion . The successful
utilization and manufacture of AgNPs with improved performances have opened up a wo
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.