Ultrasensitive SERS immunoassay based on diatom biosilica for detection of interleukins in blood plasma
Ultrasensitive SERS immunoassay based on diatom biosilica for detection of interleukins in blood plasma
Agnieszka Kamińska 0 1 2
Myroslav Sprynskyy 0 1 2
Katarzyna Winkler 0 1 2
Tomasz Szymborski 0 1 2
0 Department of Environmental Chemistry and Bioanalytics, Faculty of Chemistry, Nicolaus Copernicus University , 7 Gagarina Str, 87-100 Toruń , Poland
1 Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44/52, 01-224 Warsaw , Poland
2 Agnieszka Kamińska
An ultrasensitive surface-enhanced Raman scattering (SERS) immunoassay based on diatom biosilica with integrated gold nanoparticles (AuNPs) for the detection of interleukin 8 (IL-8) in blood plasma has been developed. The SERS sensing originates from unique features of the diatom frustules, which are capable of enhancing the localized surface-plasmon resonance of metal nanostructures. The SERS immune tags ware fabricated by functionalizing 70nm Au nanoparticles with DTNB (i.e., 5,5′-dithiobis(2nitrobenzoic acid)), which acted as a Raman reporter molecule, as well as the specific antibodies. These DTNB-labeled immune-AuNPs can form a sandwich structure with IL-8 antigens (infection marker) and the antibodies immobilized on the biosilica material. Our method showed an improved IL-8 detection limit in comparison to standard ELISA methods. The current detection limit for IL-8 using a conventional ELISA test is about 15.6 pg mL−1. The lower detection limit for IL-8 in blood plasma was estimated to be 6.2 pg mL−1. To the best of our knowledge, this is the first report on the recognition of IL-8 in human samples using a SERS-based method. This method clearly possesses high sensitivity to clinically relevant interleukin concentrations in body fluids. The average relative standard deviation of this method is less than 8%, which is sufficient for analytical analysis and comparable to those of classical ELISA methods. This SERS immunoassay also exhibits high biological specificity for the detection of IL-8 antigens. The established SERS immunoassay offers a valuable platform for the ultrasensitive and highly specific detection of immune biomarkers in a clinical setting for medical diagnostics.
Surface-enhanced Raman spectroscopy (SERS); Interleukin 8; Diatom biosilica; Immunoassay
Introduction
Interleukins are secreted proteins that are members of the
cytokine family of immune system molecules that regulate
immune cell activity. Interleukins are produced by immune
system cells such as lymphocytes, macrophages, and monocytes
[
1
]. They modulate inflammation and immunity by regulating
the growth, mobility, and differentiation of lymphoid and
other cells [
2
]. The analysis and quantitation of interleukins in
body fluids is important as it allows us to broaden our
understanding of their immunological functions. Cytokine levels in
body fluids can provide information useful for disease
diagnosis and staging, prognostication, and thus the selection of an
appropriate disease therapy [
3
]. Several analytical procedures
for quantifying interleukins in body fluids and tissue culture
supernatants have been developed. Enzyme-linked
immunosorbent assays (ELISA) are the most popular methods of
quantitating secreted cytokines due to their high specificities
and sensitivities [
4, 5
]. Intracellular staining, the ribonuclease
protection assay (RPA) [
6
], the polymerase chain reaction
(PCR) [
7
], and cytometric assays [
8
] have also been used in
recent decades. However, each of these techniques has at least
one significant limitation. For instance, problems with
cytokine assays, including a lack of accuracy, have been reported;
a number of factors have been shown to affect the validity and
quality of measurements obtained with such assays [
9–12
].
Therefore, there is a need to develop a more sensitive,
selective, stable, and durable method for analyzing these
biomarkers. Recent advances in nanotechnology and
instrumentation development have permitted the
development of a highly sensitive and chemically specific
technique for biomolecular system recognition that uses
surface-enhanced Raman spectroscopy (SERS) [
13
]. The
phenomenon of SERS can be explained as a combination
of an electromagnetic mechanism (EM) and a chemical
mechanism related to charge transfer between a substrate
and an adsorbed molecule [
14
]. Theoretically, the
electromagnetic enhancement can reach factors of 103 to 1011,
whilst chemical enhancement factors of up to 103 have
been calculated [
15, 16
]. This huge enhancement in
Raman scattering—even single molecules can be
observed—ensures that Raman spectroscopy is very
effective for ultrasensitive bioanalysis [17]. Another interesting
characteristic of SERS is the linear dependence of the
SERS intensity on the power of the incident light, despite
the nonlinear signal enhancement that is achieved with
this technique. Thus, SERS could potentially be applied
for the quantitative measurement of analytes with
ultrah (...truncated)