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.