Nanotechnology in allergic
diseases
1. How nanostructures can improve the current in vitro
approaches
Boosting the interactions and response of nanomaterials with the immune
system is essential to design new systems for in vitro/in vivoapplications. Due to the physico-chemical properties, precise control,
and tuneability for designing nanostructured materials, their use can
drive the improvement of in vitrodiagnosis.54,111
Different nanomaterials have been used to develop nanotechnology‐based
diagnostic tests, such as metallic NPs, quantum dots (QDs), SiNPs,
carbon-based nanostructures, dendrimers, and liposomes (Figure
1).54,111 Most of them focus on sIgE determination to
drugs and allergens, whereas only few applications are based on cell
assays.
Approaches involving nanotechnology have been applied in sIgE testing.
Nanomaterials are used either as a solid support to capture antibodies
or allergens, or as a detection tool to enhance the measurement
signal.46,112 Nanofluidics allow to minimise assay
time by enhancing molecular interaction.113 Besides,
in DHRs, dendrimers have been used for emulating carrier proteins and
sIgE recognition after drug haptenation has been
proven.54,111
Based on dendrimer ability for mimicking proteins, Dendrimeric Antigens
(DeAns) have been designed consisting of dendrimers peripherally
decorated with multiple units of the drug (hapten) (Figure 2A,
bottom).114 These DeAns, presenting penicilloyl units
in the periphery, are recognised by sIgE from penicillin-allergic
patients, with increasing recognition extent for higher hapten density
(Table 1).114 Moreover, DeAns are valuable for
understanding interactions between immunoglobulins and haptens: proving
the relevance of antigen tridimensional structure, showing differences
between epitopes of betalactam conformation (Figure 2C,
bottom).53 The inclusion of these two different drugs
on the same DeAn has enabled the detection of sIgE from selective and
cross-reactive patients (Table 1). These findings indicate that
including appropriate bi-epitope-DeAns could represent the basis of a
method for screening a major proportion patients with a single
test.53
Further studies have focused on immobilising these DeAns on different
solid supports for direct diagnosis application through
RadioAllergoSorbent Test (RAST). Using DeAns facilitates controlling
reproducibility, reduces nonspecific interactions, and enhances
accessibility to sIgE in whatever solid supports (Figure 2B,
bottom).54,115
Cellulose materials have been hybridised with penicilloyl DeAns of
different generations, showing the effects of hapten density, and size
scaling on penicillin-sIgE recognition.115 Further
development of hybrid DeAns-cellulose materials, using haloalkanoyl
halides or hydrophilic spacer linkers to anchor DeAns to surfaces, leads
to higher RAST sensitivity.116,117
Recent progress on nanomaterials for biosensors has been reported on the
use of other solid phases such as zeolites,117 and
SiNPs,118 which permits easier handling protocols in
RAST, whereas larger surface area permits efficient functionalisation
and effective quantification of amoxicilloyl-sIgE.118A different approach used dendrimeric gold nanodisks as a solid phase
for quantifying amoxicilloyl-sIgE, showing a good correlation with
ImmunoCAP.119 The nanoplasmonic biosensor device uses
label-free anti-IgE, requiring short analysis time. This represents a
potential new assay for the diagnosis of betalactam
allergy.119
NPs functionalised with allergens have been also used as a solid
supports to capture IgE related to FA.46 For instance,
iron-oxide magnetic NPs coated with peanut extract were used in an
immunoassay in which an external magnetic field shows high sensitivity.
Peanut-sIgE was detected in concentrations close to the minimum
detection range of CAP assay.120 Another approach used
magnetic core-shell NPs coated with alpha-lactalbumin in a microfluidic
assay, detecting low concentrations of sIgE in serum. This is a
potential quick diagnostic tool which still needs more evaluations for
performance.46
Besides, NPs can be chemically modified to allow coupling of detecting
molecules, such as antibodies, aptamer, or enzymes, to amplify the
signal for reaching improved sensitivities.46 AuNPs
coated with oligonucleotide aptamers with high specificity for human IgE
have been used in several systems to measure total IgE level. In a
system relying on surface plasmon resonance (SPR), signal amplification
was clearly achieved by adding IgE aptamer-coated
AuNPs.121 However, such system needs further
evaluations with human blood specimen, as matrix effects may influence
test performances. Recently, to overcome these issues, an antifouling
sensing interface for electrochemical biosensor was fabricated through
the self-assembly of a zwitterionic peptide and the IgE aptamer onto a
macroporous Au substrate. The zwitterionic peptide reduces the
nonspecific adsorption and fouling effect, whereas the high surface area
arising from porous morphology and the high specificity of aptamer
permit it exhibit ultrahigh sensitivity and selectivity towards IgE,
capable of sensitively assaying IgE in biological
samples.122
QDs technology has shown potential for IgE detection but has not been
integrated into functional devices for clinical use
yet.123 For instance, IgE interaction with casein
immobilised onto a sensor chip has been detected using dual polarization
interferometry with signal enhancement using streptavidin-conjugated
QDs. This QDs assay for casein-sIgE had comparable sensitivity to
ImmunoCAP.124
New methods are required for the detection of trace concentrations of
allergens in complex food matrices.125 In this sense,
NPs use for enhancing signal detection in biosensors for applications in
food analysis is a challenging area of growing interest (Figure 2,
top).126,127 A multiplex competitive microimmunoassay
for the simultaneous detection of four food allergens (gliadin, casein,
β-lactoglobulin, and ovalbumin) uses Digital Versatile Discs as sensing
platforms. The immunointeraction is detected using a mixture of specific
gold-labelled antibodies and the signal is amplified with the silver
enhancement method. Limit of detection below the accepted levels of the
international legislations were obtained in real food samples, which
allows promotion of food safety and quality.128
Regarding cellular tests, only few using nanomaterials have been
addressed to allergy diagnosis, mainly to DHRs. Nanoallergens have been
used for detection of platin drug allergies in oncologic
patients.129 These nanoallergens consist of liposomes
as platforms for drug (oxaliplatin and carboplatin) metabolites
displayed in a highly multivalent fashion. These systems trigger
significant degranulation responses from mast cell–like cells
(RBL-SX38) primed with serum IgE from patients with platin allergy.
Interestingly, the nanoallergen concentration that triggered significant
degranulation responses in vitro depended on the clinical
entity.129 In another study, the ability of
penicilloyl DeAns to stimulate basophils was demonstrated in patients
with betalactam allergy (Figure 2D bottom). Those nanoconjugates of
bigger size and displaying higher valency of haptens,
4th generation compared with 2ndgeneration, were more effective in inducing
activation.130 Further studies are needed to evaluate
the potential improvement of BAT with DeAns compared with the test using
the free drug for evaluating penicillin allergy.