Instrumentation & Measurement Magazine 24-9 - 73

Fig. 4. Biomedical measurement using SPR optical fiber sensors.
microliter volumes of analytes at low concentrations in medicine,
chemical and environmental monitoring.
Biomedical Applications
The fiber optic biosensor is a label-free sensing device that can
be easily inserted into the media to be sensed. Most biomedical
tests can be performed directly in a liquid environment,
by measuring the refractive index change caused by the interaction
between biomolecules on the optical fiber surface.
A gold-coated TFBG with SPR excitation can significantly enhance
the refractive index sensitivity [6], [7]. By monitoring the
spectral signals of the SPR, including optical wavelength and
intensity, the interaction between biomolecules can be accurately
measured. As shown in Fig. 4, an integrated fiber optic
biosensor can be used to quickly diagnose a small volume of
biological sample. The molecules to be tested in the blood are
first purified, different spectral signals can then be obtained
by using fiber optic biosensors, and finally, the health status of
biological samples can be accurately evaluated by demodulating
these signals.
Living Cell Detection
The cell volume density in the human body is closely related to
the individual's health. Density alteration in non-physiological
cells (DANCE) is a biological change of cells in response to
environmental changes and drugs [8]. DANCE can provide
an important basis for cytopathological feature analysis and
cell resistance research. However, the existing chromogenic
imaging methods require labeling of cells, which can cause irreversible
damage to the cells being studied. In comparison,
due to its label-free detection characteristics, the SPR optical
fiber biosensor can accurately and quantitatively analyze
the microscopic changes of cells caused by drug intervention,
without damaging the cells. Using the difference in optical
transmission spectrum between two orthogonal polarizations
December 2021
for the last guided mode resonance before cut-off (it is located
at the boundary between guided and leaky modes), our
group has realized label-free and high-precision detection of
DANCE [9]. In this study, we successfully realized in-situ discrimination
of leukemia cell lines with different physiological
densities. This study confirms the relationship between the intracellular
density of cells and the corresponding refractive
index, leading to a helpful understanding of drug resistance
of cells, as well as the discovery of new physiological or pathological
cell properties.
Specific Protein Detection
An increase of concentration of aquaporin in urine usually
indicates the presence of kidney disease. Using a plasmonic
TFBG sensing platform on samples of rat urine, Guo et al.
[10] were able to clearly differentiate between healthy samples,
nephropathic samples and samples from individuals
under treatment, by measuring different concentrations of
the protein. Those results show a clear relationship between
protein outflow and refractive index variations as small
as 0.001 RIU of the urine samples, pointing the way to the
evaluation and development of new drugs for treating nephropathy
[10].
Clinical Diagnosis
Recently, the SPR optical fiber sensor has achieved a breakthrough
in clinical diagnosis, by realizing minimally invasive
detection of cancer biomarkers. Relevant studies have shown
that cytokeratins are commonly used for diagnosis in oncology
[11]. Especially in the differential diagnosis of lung
carcinomas, cytokeratin fragments have been shown to be released
from malignant cells and enter the bloodstream. In-situ
detection of cytokeratin in blood can be achieved by a medically
packaged fiber biosensing probe with a limit of detection
as low as 1 pM [12]. This significant recent result demonstrates
IEEE Instrumentation & Measurement Magazine
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Instrumentation & Measurement Magazine 24-9

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