Instrumentation & Measurement Magazine 24-4 - 3

Using Lock-In Thermography to
Investigate Stimuli-Responsive
Nanoparticles in Complex
Environments
Mathias Bonmarin, Lukas Steinmetz, Fabrizio Spano, and Christoph Geers
T
he use of nanoparticles (NP) has been dramatically
rising in the recent years and NPs can nowadays
be found in various products ranging from food to
composite materials or cosmetics [1], [2]. Currently, the most
frequently employed NP types are titania (TiO2
cal color additive, silica (SiO2
), as a typi),
as anticoagulation agent, and
silver (Ag) NPs, which are added to textiles, due to their antimicrobial
properties. Because of their outstanding physical
and mechanical properties, carbon-containing nanomaterials,
such as graphene and carbon nanotubes, have also experienced
a surge in industrially relevant applications. About 30%
of the NPs are suspended in liquids, ranging from water to
creams and lotions to car lubricants, followed by applications
containing surface-bound (e.g., in textiles) NPs and finally
nanocomposites (e.g., polymer-CNT composites). Together
with biological and physiological fluids, these matrices render
the detection and quantification of NPs fairly complex [3]. The
broad range of chemical and biological compositions of these
environments, including pH and ionic strength, are often detrimental
to the colloidal stability of NPs, potentially causing
aggregation or even dissolution effects and therefore render
NP analysis fairly challenging.
Man-made, so-called 'engineered' NPs can be precisely tailored
with respect to specific and desired properties. These
materials are often stimuli-responsive meaning that they
demonstrate the ability to generate heat upon a stimulus: alternating
magnetic fields (AMF) for magnetic particles like
superparamagnetic iron oxide NPs (SPIONs), and light in the
UV, visible or NIR range for plasmonic NPs like gold spheres
and other photothermal particles. Such a behavior makes them
excellent candidates for active thermal imaging, an investigation
method that is using an infrared camera to record the
transient thermal emission of a sample surface.
In this work we present lock-in thermal imaging (LIT)
[4], an averaging active thermal imaging method that allows
high sensitivity, as a promising investigation tool for NPs
embedded in complex medium. We demonstrate the LIT setups
developed in our laboratory, introduce the algorithms
employed and discuss potential schemes to compensate for
non-steady initial heating, emissivity variations or high absorptive
environments. Finally, we compare LIT with other
methods currently employed to investigate NPs in complex
environments.
Active Thermal Imaging and Lock-in
Thermal Imaging (LIT)
In active or dynamic thermal imaging, the sample is monitored
in the transient state following a thermal stimulation [5].
Active thermal imaging is a well-known technique in engineering,
widely used for the non-destructive testing of materials
(NDT). The source employed to generate the thermal stimulation
depends on the sample under investigation. To localize
water ingress for example, microwaves are particularly suited
[6], [7], whereas eddy currents will be more appropriate to
detect cracks in metallic materials [8]. Our previous work demonstrated
that active thermal imaging is a promising tool for
engineered NPs [9]-[14]. Lock-in thermal imaging (LIT) records
the sample surface temperature during the application of
a harmonic heating stimulus at a defined frequency [15]. Fig. 1
describes the principle of a lock-in thermography setup. The
sample is stimulated at a frequency f0
= 1/T0
called " stimulation
frequency, " while the thermal radiation from the sample surface
is captured by an infrared camera (Fig. 1a). The recorded
infrared images are first converted into temperature maps
or thermograms T(x, y) before being processed according to
the digital lock-in principle which results in an in-quadrature
S90
(x, y) and an in-phase image S0
(x, y) that can be converted into
a phase image ϕ(x, y) and an amplitude image A(x, y).
The phase is a map of the phase angles between the stimulation
signal and the harmonic temperature response of the
sample surface, whereas the amplitude gives the oscillation
amplitude (Fig. 1b).
The primary author of this manuscript was awarded Best in Application Measurement 2019
by the Instrumentation & Measurement Society.
June 2021
IEEE Instrumentation & Measurement Magazine
1094-6969/21/$25.00©2021IEEE
3

Instrumentation & Measurement Magazine 24-4

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 24-4

No label
Instrumentation & Measurement Magazine 24-4 - No label
Instrumentation & Measurement Magazine 24-4 - Cover2
Instrumentation & Measurement Magazine 24-4 - 1
Instrumentation & Measurement Magazine 24-4 - 2
Instrumentation & Measurement Magazine 24-4 - 3
Instrumentation & Measurement Magazine 24-4 - 4
Instrumentation & Measurement Magazine 24-4 - 5
Instrumentation & Measurement Magazine 24-4 - 6
Instrumentation & Measurement Magazine 24-4 - 7
Instrumentation & Measurement Magazine 24-4 - 8
Instrumentation & Measurement Magazine 24-4 - 9
Instrumentation & Measurement Magazine 24-4 - 10
Instrumentation & Measurement Magazine 24-4 - 11
Instrumentation & Measurement Magazine 24-4 - 12
Instrumentation & Measurement Magazine 24-4 - 13
Instrumentation & Measurement Magazine 24-4 - 14
Instrumentation & Measurement Magazine 24-4 - 15
Instrumentation & Measurement Magazine 24-4 - 16
Instrumentation & Measurement Magazine 24-4 - 17
Instrumentation & Measurement Magazine 24-4 - 18
Instrumentation & Measurement Magazine 24-4 - 19
Instrumentation & Measurement Magazine 24-4 - 20
Instrumentation & Measurement Magazine 24-4 - 21
Instrumentation & Measurement Magazine 24-4 - 22
Instrumentation & Measurement Magazine 24-4 - 23
Instrumentation & Measurement Magazine 24-4 - 24
Instrumentation & Measurement Magazine 24-4 - 25
Instrumentation & Measurement Magazine 24-4 - 26
Instrumentation & Measurement Magazine 24-4 - 27
Instrumentation & Measurement Magazine 24-4 - 28
Instrumentation & Measurement Magazine 24-4 - 29
Instrumentation & Measurement Magazine 24-4 - 30
Instrumentation & Measurement Magazine 24-4 - 31
Instrumentation & Measurement Magazine 24-4 - 32
Instrumentation & Measurement Magazine 24-4 - 33
Instrumentation & Measurement Magazine 24-4 - 34
Instrumentation & Measurement Magazine 24-4 - 35
Instrumentation & Measurement Magazine 24-4 - 36
Instrumentation & Measurement Magazine 24-4 - 37
Instrumentation & Measurement Magazine 24-4 - 38
Instrumentation & Measurement Magazine 24-4 - 39
Instrumentation & Measurement Magazine 24-4 - 40
Instrumentation & Measurement Magazine 24-4 - 41
Instrumentation & Measurement Magazine 24-4 - 42
Instrumentation & Measurement Magazine 24-4 - 43
Instrumentation & Measurement Magazine 24-4 - 44
Instrumentation & Measurement Magazine 24-4 - 45
Instrumentation & Measurement Magazine 24-4 - 46
Instrumentation & Measurement Magazine 24-4 - 47
Instrumentation & Measurement Magazine 24-4 - 48
Instrumentation & Measurement Magazine 24-4 - 49
Instrumentation & Measurement Magazine 24-4 - 50
Instrumentation & Measurement Magazine 24-4 - 51
Instrumentation & Measurement Magazine 24-4 - 52
Instrumentation & Measurement Magazine 24-4 - 53
Instrumentation & Measurement Magazine 24-4 - 54
Instrumentation & Measurement Magazine 24-4 - 55
Instrumentation & Measurement Magazine 24-4 - 56
Instrumentation & Measurement Magazine 24-4 - 57
Instrumentation & Measurement Magazine 24-4 - 58
Instrumentation & Measurement Magazine 24-4 - 59
Instrumentation & Measurement Magazine 24-4 - 60
Instrumentation & Measurement Magazine 24-4 - 61
Instrumentation & Measurement Magazine 24-4 - 62
Instrumentation & Measurement Magazine 24-4 - 63
Instrumentation & Measurement Magazine 24-4 - 64
Instrumentation & Measurement Magazine 24-4 - 65
Instrumentation & Measurement Magazine 24-4 - 66
Instrumentation & Measurement Magazine 24-4 - 67
Instrumentation & Measurement Magazine 24-4 - 68
Instrumentation & Measurement Magazine 24-4 - 69
Instrumentation & Measurement Magazine 24-4 - 70
Instrumentation & Measurement Magazine 24-4 - 71
Instrumentation & Measurement Magazine 24-4 - 72
Instrumentation & Measurement Magazine 24-4 - 73
Instrumentation & Measurement Magazine 24-4 - 74
Instrumentation & Measurement Magazine 24-4 - 75
Instrumentation & Measurement Magazine 24-4 - 76
Instrumentation & Measurement Magazine 24-4 - 77
Instrumentation & Measurement Magazine 24-4 - 78
Instrumentation & Measurement Magazine 24-4 - 79
Instrumentation & Measurement Magazine 24-4 - 80
Instrumentation & Measurement Magazine 24-4 - 81
Instrumentation & Measurement Magazine 24-4 - 82
Instrumentation & Measurement Magazine 24-4 - 83
Instrumentation & Measurement Magazine 24-4 - 84
Instrumentation & Measurement Magazine 24-4 - 85
Instrumentation & Measurement Magazine 24-4 - 86
Instrumentation & Measurement Magazine 24-4 - 87
Instrumentation & Measurement Magazine 24-4 - 88
Instrumentation & Measurement Magazine 24-4 - 89
Instrumentation & Measurement Magazine 24-4 - 90
Instrumentation & Measurement Magazine 24-4 - 91
Instrumentation & Measurement Magazine 24-4 - 92
Instrumentation & Measurement Magazine 24-4 - 93
Instrumentation & Measurement Magazine 24-4 - 94
Instrumentation & Measurement Magazine 24-4 - 95
Instrumentation & Measurement Magazine 24-4 - 96
Instrumentation & Measurement Magazine 24-4 - 97
Instrumentation & Measurement Magazine 24-4 - 98
Instrumentation & Measurement Magazine 24-4 - 99
Instrumentation & Measurement Magazine 24-4 - 100
Instrumentation & Measurement Magazine 24-4 - 101
Instrumentation & Measurement Magazine 24-4 - 102
Instrumentation & Measurement Magazine 24-4 - 103
Instrumentation & Measurement Magazine 24-4 - 104
Instrumentation & Measurement Magazine 24-4 - 105
Instrumentation & Measurement Magazine 24-4 - 106
Instrumentation & Measurement Magazine 24-4 - 107
Instrumentation & Measurement Magazine 24-4 - 108
Instrumentation & Measurement Magazine 24-4 - 109
Instrumentation & Measurement Magazine 24-4 - 110
Instrumentation & Measurement Magazine 24-4 - 111
Instrumentation & Measurement Magazine 24-4 - 112
Instrumentation & Measurement Magazine 24-4 - 113
Instrumentation & Measurement Magazine 24-4 - 114
Instrumentation & Measurement Magazine 24-4 - 115
Instrumentation & Measurement Magazine 24-4 - 116
Instrumentation & Measurement Magazine 24-4 - 117
Instrumentation & Measurement Magazine 24-4 - 118
Instrumentation & Measurement Magazine 24-4 - 119
Instrumentation & Measurement Magazine 24-4 - 120
Instrumentation & Measurement Magazine 24-4 - Cover3
Instrumentation & Measurement Magazine 24-4 - Cover4
https://www.nxtbook.com/allen/iamm/24-8
https://www.nxtbook.com/allen/iamm/24-6
https://www.nxtbook.com/allen/iamm/24-5
https://www.nxtbook.com/allen/iamm/24-4
https://www.nxtbook.com/allen/iamm/24-3
https://www.nxtbook.com/allen/iamm/24-2
https://www.nxtbook.com/allen/iamm/24-1
https://www.nxtbook.com/allen/iamm/23-9
https://www.nxtbook.com/allen/iamm/23-8
https://www.nxtbook.com/allen/iamm/23-6
https://www.nxtbook.com/allen/iamm/23-5
https://www.nxtbook.com/allen/iamm/23-2
https://www.nxtbook.com/allen/iamm/23-3
https://www.nxtbook.com/allen/iamm/23-4
https://www.nxtbookmedia.com