SHEDDING LIGHT ON CANCER:
How a mid-infrared transmitting glass could help diagnose early stage cancer
H. Parnell, D. Furniss, Z. Tang, A. Seddon
The chances are we all know someone who has been affected by cancer.
Unfortunately, this comes as little surprise as recent statistics released by Cancer Research UK, now suggest that 1 in 2 of us will develop some form of
cancer within our lifetime. Diagnosing patients whilst they are in the early and most treatable stages of the disease, is vital for their survival. Yet current
diagnostics still rely on a lengthy biopsy procedure.
Current diagnosis
Mid-infrared (MIR) light
Key features of the current Gold standard for
cancer diagnosis:
• Referred to a specialist
following a GP
appointment.
• Tissue is removed from
patient during a biopsy
examination.
• Histopathologist
analyses sample and
provides diagnosis.
• Patient waits for results.
Figure 1: Typical micrograph used by
histopathologist for cancer
diagnosis.
• MIR light is found
beyond the red side of
the rainbow from 3 to
25 µm wavelengths.
• It contains an important
diagnostic tool known
as the ‘molecular
fingerprint’.
• Small changes within
this fingerprint indicate
abnormal changes
within our cells,
signifying the presence
of a cancer.
New diagnosis
Key features of the new MIR technology for
cancer diagnosis:
Figure 2: A typical ‘molecular
fingerprint’ which can be collected
using MIR light.
• Patient attends
appointment lasting 515 minutes.
• The molecular
fingerprints are
collected and analysed
in an MIR image.
• Diagnosis is provided
immediately, with no
need for a biopsy.
Figure 3: MIR micrograph analysed
in-vivo for immediate cancer
diagnosis.
How can we deliver this light?
• CHALCOGENIDE GLASSES are based on one or more chalcogen elements found in Group 16 of the Periodic Table sulfur (S),
selenium (Se) or tellurium (Te). When combined with neighbouring elements, such as germanium (Ge) and antimony (Sb),
MIR light source
the heavy atoms form a ‘low phonon’ glass i.e. the bonds in a chalcogenide glasses vibrate at the same wavelength as MIR
1 MIR light IN
light- this is why they appear opaque to us!
3 MIR fingerprint
• Very few materials are able to transmit MIR light and as glasses,
OUT
chalcogenides have the added benefit of being able to be drawn
Diagnosis
into long lengths of optical fibres.
• Ge-Sb-Se chalcogenide optical fibres are
considered here for use in the endoscopic probe.
2
Tissue – MIR
light interaction
What are the practical challenges?
Crystallisation
Impurities
Glasses are essentially a metastable state. This means they exist at an energy level above their
more stable crystalline form and will therefore, be naturally driven to transform into the lower
energy state if a small amount of energy is given to the system.
High
energy
glass state
+ temp.
Low energy
crystal
state
This energy could come in the form of heat,
which is of course, an integral characteristic in
the production of optical fibres. Therefore,
crystallisation remains a constant problem
when drawing Ge-Sb-Se chalcogenide fibres.
Figure 4: Crystallisation of Ge-Sb-Se chalcogenide glass. The
crystals seen here are that of monoclinic GeSe2.
However, we can tailor the properties of the
Ge-Sb-Se glass by choosing a composition that
has high resistance to crystallisation e.g.
Ge20Sb10Se70 at. %, which has successfully
produced over 100 m of fibre.
For the MIR probe to be as sensitive and selective as possible, we must ensure the
maximum amount of light reaches the patient. Therefore, the Ge-Sb-Se chalcogenide
optical fibres must be made with high purity.
However, our atmosphere is full of impurities
which cause absorptions across the MIR
region e.g. oxides and hydrides. Therefore,
unlike conventional silica glasses,
chalcogenides must be made via a complex
procedure, carried out under vacuum.
Figure 5 shows a typical MIR spectrum for a
Ge-Sb-Se optical fibre which has been initially
purified by a simple sublimation method i.e.
heating the raw elements enough so that
oxides can evaporate off. The dashed red line
signifies the next stage in our research where
the glass will be distilled, eliminating all
impurities.
Figure 5: Unwanted impurity absorptions in Ge-Sb-Se optical
fibres.
Conclusions
•
•
•
MIR light could offer an immediate, in vivo diagnosis for early stage cancer.
Ge-Sb-Se chalcogenide glasses are a promising material for the delivery and
collection of MIR light.
Ge-Sb-Se glasses should be made with high purity and have a good resistance to
crystallisation.
ACKNOWLEDGMENTS: I
would like to thank the
University of Nottingham
for funding my PhD and the
Mid-infrared Photonics
Group for their continual
support throughout my
research.