Autoimmune diseases (ADs) are a group of various disorders that are characterized by dysregulation of the immune system. This malfunction state leads to an improper activation of immune elements that may consequently attack target molecules, cells, and tissues of the organism, resulting in inflammation and organ damage.
Due to the continuously increasing number of patients with ADs, the severity of ADs’ clinical symptoms, and treatment insufficiency, novel analytical tools enabling early, reliable, and high-throughput disease diagnosis are highly desirable, since such tools may help health systems to confront the burden related to the late diagnosis of ADs and decrease premature mortality. To meet this need, during the last two decades, several immunosensors for detecting AD-related biomarkers have been developed as research prototypes. The AD immunosensors reported to date can be divided into two main categories depending on the biomarker(s) detected, i.e., either various autoantibodies or other protein biomarkers, such as specific inflammation-related cytokines. Most of AD immunosensors are electrochemical, while some optical and a few piezoelectric sensors have also been described in the literature.
Type of Signal Transduction | Immunoassay Principle—Use of Secondary Antibody | Autoantibody-Biomarker | Limit of Detection (LoD)/ Concentration Range |
Autoimmune Disease | Biological Sample | References |
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Electrochemical (Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)) |
Non-competitive, direct-type assay | Anti-oncostatin-M receptor autoantibodies | - |
Type of Signal Transduction | Immunoassay Principle | Protein-Biomarker | LoD/ Concentration Range |
Autoimmune Disease | Biological Sample | References | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Systemic sclerosis (SSc) | Human serum from healthy individuals and SSc patients | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Optical (Multi Area Reflectance Spectroscopy—MARS) |
Non-competitive, sandwich-type assay | Procalcitonin and interleukin-6 (IL-6) | 2.0 ng mL−1 (PCT) and 0.01 ng mL−1 (IL-6)/ up to 100.0 ng mL−1 (PCT) and up to 10.0 ng mL−1 (IL-6) | [ | 41 | ] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Various inflammatory/autoimmune diseases | Human serum | [ | 74 | ] | Electrochemical (Voltammetry) | Non-competitive, direct-type assay | Anti-citrullinated peptide/protein autoantibodies (ACPAs) |
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Electrochemical (Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)) | 15 pg mL | Non-competitive, direct-type assay | −1/ 8–250 pg mL−1 |
Rheumatoid arthritis (RA) | Oncostatin-M receptor (sOSMR) proteinHuman serum (spiked) | 0.42 pg mL−1/ 0.005–500 pg mL−1[18] |
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Systemic sclerosis (SSc) | Serum from healthy individuals and SSc patients | [ | 41 | ] | Electrochemical (EIS) | Non-competitive, direct-type assay | ACPAs | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Amperometry) |
Non-competitive, sandwich-type assay | 0.82 IU ** mL | B cell activation factor (BAFF) and a proliferation-induced ligand (APRIL)−1/ 1–800 IU mL |
0.33 pg mL−1 (BAFF) and 16.4 pg mL−1RA | (APRIL) / Human serum (spiked) |
1.1–100 pg mL−1 (BAFF) and 0.05–20 ng mL−1 (APRIL)[42] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Systemic lupus erythematosus (SLE) | Serum from healthy individuals and SLE patients | [ | 76 | ] | Optical (Spectral correlation interferometry—SCI) |
Non-competitive, direct-type assay; a non-labeled secondary antibody was used | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical | Anti-thyroglobulin (anti-TG) and anti-thyroid peroxidase (anti-TPO) autoantibodies | 6 IU mL | −1 (anti-TG) 1.7 IU mL−1 (anti-TPO)/ 6–400 IU mL−1 (anti-TG) 1.7–860 IU mL−1 (anti-TPO) |
Autoimmune thyroid diseases | Patients’ serum | (Amperometry) | Non-competitive, sandwich-type assay | B cell activation factor (BAFF) and a proliferation-induced ligand (APRIL) | 0.08 ng mL−1 (BAFF) and 0.06 ng mL−1 (APRIL) / 0.24–120 ng mL−1 (BAFF) and 0.19–25 ng mL−1 (APRIL)[ |
SLE46] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Serum from SLE patients | [ | 77 | ] | Piezoelectric quartz-crystal microbalance | Non-competitive, direct-type assay | Anti-phospholipase A2 receptor (anti-PL2R) autoantibodies | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Amperometry) | 0.1 μg mL | −1 | / 0.5–100 μg mL−1 |
Primary membranous nephropathy (pMN) | Patients’ serum | Non-competitive, sandwich-type assay | CCL5 chemokine | 40 pg mL−1/ 0.1–300 ng mL−1[44] |
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Multiple sclerosis (MS) | Serum from healthy individuals and MS patients | [ | 78 | ] | Electrochemical (EIS) | Non-competitive, direct-type assay | Immunoglobulin M—rheumatoid factor (IgM-RF) | 0.22 IU mL−1/ 10–200 IU mL−1 |
RA | Human serum (spiked) |
[47] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Amperometry) |
Non-competitive, sandwich-type assay | IL-6 | 0.42 pg mL−1/ 0.97–250 pg mL−1 |
Rheumatoid arthritis (RA) | Human serum (spiked) | [22] | Electrochemical (Voltammetry) | Non-competitive, direct-type assay; a labeled secondary antibody was used | Anti-tissue transglutaminase (anti-tTG) autoantibodies | 1.8 ng mL−1/ 0.005–1 μg mL−1 |
Celiac disease (CD) | Serum from healthy individuals and CD patients | [50] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Amperometry) |
Non-competitive, sandwich-type assay | CXCL7 chemokine and MMP3 metalloproteinase | 0.8 ng mL−1 (CXCL7) and 1.2 pg mL−1 (MMP3)/ 1–75 ng mL−1 (CXCL7) and 2.0–2000 pg mL−1 (MMP3) |
RA | Serum from healthy individuals and RA patients | [79] | Electrochemical (Impedance spectroscopy and square wave voltammetry) | Non-competitive, direct-type assay | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical | Autoantibodies on red blood cells (RBCs) | (EIS) | Non-competitive, direct-type assay- | Autoimmune hemolytic anemia | Healthy and “sick” RBCs (i.e., RBCs from healthy and affected individuals) | [ | Tumor necrosis factor α (TNFα)52] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
0.085 pg mL | −1 | / | 1–25 pg mL−1 |
Various inflammatory/autoimmune diseases | Serum and tears from healthy individuals; cerebrospinal fluid (CFS) from patients undergone routine lumbar puncture | [80] | Optical (Colorimetry) | Non-competitive, direct-type assay | IgM-RF | 4.15 IU mL−1 | RA | Human plasma (spiked) | [48] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Differential pulse voltammetry (DPV) and EIS) |
Non-competitive, direct-type assay | Myelin Basic Protein (MBP) and Tau proteins | 0.30 nM (MBP) and 0.15 nM (Tau) | MS | CSF and serum from MS patients | [82] | Electrochemical (Electro-chemiluminescence—ECL) | Non-competitive, direct-type assay *; a labeled secondary antibody was used | Anti-myeloperoxidase (anti-MPO) autoantibodies |
15.68 fg mL−1/ 50 fg mL−1–1 ng mL−1 |
Anti-neutrophil cytoplasm antibody-associated vasculitides | Human serum (spiked) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (Voltammetry) | [ | 55 | ] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Non-competitive, direct-type assay | Insulin | 5 pM/ | 5–200 pM |
Diabetes types I and II | Serum from diabetic patients | [83] | Electrochemical (Amperometry) |
Non-competitive, direct-type assay *; a labeled secondary antibody was used | Anti-double-stranded DNA (anti-dsDNA) autoantibodies |
8 μg mL−1 | Systemic lupus erythematosus (SLE) | Patients’ serum | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Electrochemical (EIS) |
Non-competitive, direct-type assay | [ | Interleukin-12 (IL-12) | 56 | ] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
3.5 pg mL | −1 | / | 0.1–500 pg mL−1 |
MS | Fetal bovine serum (FBS) | [84] | Electrochemical (Amperometry) |
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Electrochemical | Non-competitive, direct-type assay; a labeled secondary antibody was used | (Amperometry)Anti-tTG autoantibodies (IgG and IgA) |
Non-competitive, direct-type assay1.4 AU ** mL−1 (IgG) and 3.2 AU mL−1 | Macrophage migration inhibitory factor (MIF) (IgA)/ up to 30 AU mL−1 (IgG and IgA) |
CD | 0.02 ng mL−1/ Patients’ serum
* In the original papers, the immunocomplexes formed (antigen–autoantibody/analyte–secondary antibody) were characterized as “sandwich”. ** U: units; IU: international units; AU: arbitrary/antibody units. 3. AD Immunosensors Detecting Other Protein BiomarkersAlmost all AD immunosensors detecting specific protein biomarkers, other than autoantibodies, are electrochemical, while they are all based on a non-competitive assay principle, of either direct- or sandwich-type. Regarding the most recently reported AD immunosensors (from 2019 to now) of this category, the following can be summarized: An optical immunosensor was developed for the simultaneous determination of procalcitonin (PCT) and IL-6, which are well-known biomarkers of inflammatory diseases, including ADs. Silicon chips with silicon dioxide areas of different thickness were used, each functionalized with either anti-PCT or anti-IL-6 capture antibodies. Moreover, biotinylated detection antibodies were used along with streptavidin and biotinylated bovine serum albumin, to achieve amplification of the optical signal, in a sandwich-type immunoassay setting [74]. Earlier, an electrochemical immunosensor for IL-6 was developed. The sensor was based on a working electrode modified with a hybrid of gold nanoparticles (AuNPs) and graphene. Magnetic beads loaded with capture anti-IL-6 antibodies were also used, on which IL-6 could be bound and subsequently detected through biotinylated anti-IL-6 antibodies (sandwich-type assay setting) and HRP-labeled streptavidin [22]. An electrochemical immunosensor for oncostatin-M receptor, a soluble form of which (sOSMR) had been found at increased levels in sera of patients with systemic sclerosis, was based on a conductive poly-pyrrole layer loaded with gold nanoparticles, on which anti-sOSMR antibodies were immobilized through cysteine chemisorption [41]; this sensor has been already mentioned (i.e., in “2. AD Immunosensors Detecting Autoantibodies”), since, after a slight modification of the assay format/protocol, it may also be applied to the detection of autoantibodies against sOSMR [41]. Another electrochemical immunosensor was developed for simultaneous determination of the cytokines B-cell activation factor (BAFF) and a proliferation-induced ligand (APRIL), both of which have been associated with systemic lupus erythematosus (SLE) [75]. Biotinylated anti-BAFF and anti-APRIL capture antibodies were loaded onto magnetic beads through neutravidin or direct covalent immobilization, respectively, while detection anti-BAFF antibodies along with HRP-labeled secondary antibodies, and detection biotinylated anti-APRIL antibodies along with HRP-labeled streptavidin, were used for assaying BAFF and APRIL, respectively [76]. In another electrochemical immunosensor for simultaneous determination of BAFF and APRIL, biotinylated anti-BAFF and biotinylated anti-APRIL capture antibodies were indirectly immobilized onto the working electrodes, on which neutravidin had been covalently bound. A sandwich-type assay setting was achieved by using anti-BAFF and anti-APRIL detection antibodies along with HRP, all of which were loaded onto nanostructures composed of MoS2/multiwall carbon nanotubes (MoS2/MWCNTs), which enabled signal generation (through the hydroquinone/H2O
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