Analytical Methods for Nanomaterials in Food

1 4TH NANOTECHNOLOGY DIALOGUE, FOODDRINKEUROPE, Brussels, 5th October 2011

Analytical Methods for

Nanomaterials in Food

Hermann Stamm

Institute for Health and Consumer Protection

Joint Research Centre, Ispra

http://www.jrc.ec.europa.eu


Nanomaterials in Food

• Additives

• Ingredients

• Processed Nanostructures

– Conventionally produced

(cheese, milk, mayonnaise, …)

• Naturally occuring

• Food contact materials

Type of Materials Applications

• Manufactured Nanomaterials

– SiO2 TiO2, CaCO3, TiN, Ag …

• Nanoclays

• Nanoencapsulations

– Emulsions

– Micelles, Liposomes

• ……

Diversity of applications and materials


Analytical Methods: Challenges and Needs

• Detection levels

• Release from FCM

• Inorganic/organic NM

• Matrix structure at the nanoscale

• Distinction from background

• Matrix NM interaction

• Detection and quantification of

known/unknown material

• Analytical artefacts

• Availability of standard materials

Background:

Regulatory Issues

Definition

Labeling requests

Safety testing

Consumer information

Consumer behaviour

Validated routine methods


Nanomaterials in Complex Matrices

Detect – Imaging (SEM, TEM, AFM, …)

Quantify – Extraction from matrix

– Separation/fractionation (filtration, centrifugation, chromatography, Field Flow Fractionation,…)

– Elemental analysis (e.g. ICP-MS)

Characterize – Size

– State of dispersion

– Physico-chemical properties

– Surface properties

After Lynch and Dawson,

Nanotoday 2008, (3) 1-2ß


Ensemble analytical techniques Single-particle techniques

NM-Analysis: size and shape, surface

• Scanning Electron Microscopy (SEM)

• Transmission Electron Microscopy (TEM)

• Field emission gun scanning/transmission

Electron Microscopy (FE STEM)

-Energy Dispersive Spectrometry (EDS)

-Electron Energy Loss Spectorscopy

(EELS)

• Atomic Force Microscopy (AFM)

• Dynamic Light Scattering (DLS)

(= Photon Correlation Spectroscopy,

PCS)

• Laser Diffraction/Static Light Scattering

• Low Pressure Impactor (LPI)

Electrical Low Pressure Impactor (ELPI)

• Scanning Mobility Particle Sizer

• Differential Mobility Analyser (DMA)

• Field Flow Fractionation (FFF)

• Centrifugal sedimentation

• Specific Surface Area (BET)

• Time of Flight Mass Spectroscopy

(ToF MS)

Nanoparticle Tracking


Ensemble analytical techniques Single-particle techniques

NM Analysis: Physical and Chemical Properties

• Atomic/chemical structure

-Fourier Transform Infrared Spectroscopy

-Raman Scattering (RS)

-X-ray Absorption Spectroscopy (XAS)

-Extended X-ray Absorption Fine Structure

X-ray absorption Near Edge Structure

-X-ray and neutron diffraction

-Circular Dichroism

• Surface charge

-Zeta Potential

• Surface reactivity

-Comparative microcalorimetry

• Surface Composition

-Electron spectroscopy for Chemical

Analysis ( ESCA) or

X-ray photoelectron spectroscopy (XPS)

-Secondary ion mass spectroscopy

(SIMS)

• Pre-treatment/sample preparation required

• A single method is not sufficient

• Choice of the right combination of methods

• Expert knowledge needed for optimal use


Technique Instrument ScienceDirect Hits* cost

Fourier Transform Infrared SpectroscopyFTIR 239 <20k

Raman Spectroscopy Raman 288(SERS) <50K

X-ray Photoelectron Spectroscopy XPS 340 >500K

Nuclear Magnetic Resonance NMR 152 >500K

Secondary Ion Mass Spectrometry ToF-SIMS 13 >500K

Dynamic Light Scattering DLS 221 (*) <50K

Field-Flow Fractionation XFFF 20 (19 from 2007-2011) <50K

Transmission Electron Microscopy TEM 1222 >500K

Scanning Electron Microscopy SEM 585 >500K

Analytical Ultracentrifuge 6 >100K

Centrifugal Particle Sedimentation CPA 2 <50K

Particle Tracking Analysis PTA 11 <50K

Zeta-potential 264 <50K

BET 116

*Search ScienceDirect for nanoparticle+(technique) in Title/Abstract/Keywords

Chemistry

Size/Shape

Other

Techniques most quoted in literature*


Example

• Known particle type (Au)

• Known size distribution

• Simple matrix

– Imaging

– Separation from matrix


AuNP

5nm

AuNP

15nm

AuNP 45nm

AuNP mix (350:15:1 in numbers)

Basically similar distribution for mixture and pure 45nm NP!!!

NP Mixtures: Dynamic Light Scattering


Imaging (TEM, SEM) - Detection

NRT 1040 – NRT 1043 1:10, 50Kx

Mean Sd Min Max Range Median Kurt N

18.08092 7.8 7.3 84.1 76.8 15.6 17.1 1115

10:1 Mix of monodispersed

Au particles(15nm,30nm

nominal)

50

100

150

200

250

300

Num

be

r of part

icle

s Minor

Feret

Diameter

10 20 30 40 50

50

100

150

200

250

300

First two peaks in a 3 particle fit

P1 diameter 15.29423

P1 dispersion 2.13878

P1 weight 931.8699

P2 diameter 21.60783

P2 dispersion 2.03837

P2 weight 86.12409

Nu

mb

er

of p

art

icle

s

Diameter (nm)

Diameter Fit


Asymmetric Flow Field Flow Fractionation (AF4)


Peak 1 (5nm)

Peak 2 (20nm)

Peak 3 (50nm)

50nm 50nm 50nm

Nanoparticles separation with

Asymmetric Flow Field Flow Fractionation (AF4)

Injection: 20ml of nanoparticle mixture (5, 20, 50nm)


AFFF of SiO2-NP in Cell Culture Medium

Detector: Static Light Scattering 35°

Medium serum free (no proteins)

Medium + proteins

SiO2-NP alone

SiO2-NP + medium serum free

SiO2-NP + medium + proteins


SEM TEM AFFF PTA CPS DLS

Minimum size

Dynamic Range

No. particles

considered in sample

Analysis Time

Ease of Use

Size Data Robust

Mixtures *

In-situ Measurement

Cost

Strengths and weaknesses


SUMMARY

A number of tools –

no best techniques

Detection/Sizing

Physico-

chemical

properties

• Pre-treatment/Sample preparation is key

• All techniques have advantages and drawbacks

• A combination of techniques is needed

• Combination of separation/analysis is particularly promising

• Difficult to make robust analysis without Electron Microscopy

• Non-imaging methods rely on physical models to derive size

• If size is critical do not underestimate the difficulties of size measurement

• Need for standards and reference materials

• No routine methods available


Representative Nanomaterials (NM series) from the European Commission - JRC

TiO2 Carbon Nanotubes

ZnO Silver

SiO2 Nanoclays

CeO2

Repository: Nanomaterials for Testing


2µm

Thank you

for your attention

Acknowledgements

Luigi Calzolai

Douglas Gilliland

Francois Rossi

Analytical Methods for Nanomaterials in Food

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