Advancements in Hydrogel-Functionalized Immunosensing Platforms

Abstract

Explicit antigen-antibody binding has accelerated the development of immunosensors for the detection of various analytes in biomedical and environmental domains. Being a subclass of biosensors, immunosensors have been a significant area of research in attaining high sensitivity and an ultralow sensing limit to detect biological analytes present in trace levels. The highly porous structure, large surface area, and excellent biocompatibility of hydrogels enabling the retainability of the activity and innate framework of the attached biomolecules make them a suitable candidate for immunosensor fabrication. Hydrogels based on polycarboxylate, cellulose, polyaniline, polypyrrole, sodium alginate, chitosan, and agarose are exploited in conjunction with other nanomaterials such as AuNPs, GO, and MWCNTs to augment the electron transfer during the immunosensing mechanism. Surface plasmon resonance, electrochemiluminescence, colorimetric, and electrochemical assays are different strategies utilized for the signal transduction in hydrogel-based immunosensors during the formation of the antigen-antibody complex. These hydrogel-based immunosensors exhibit rapid response, excellent stability, reproducibility, high selectivity and high sensitivity, a broad range of detection, an ultralow limit of detection, and display results similar to those for the ELISA test. This review propounds different hydrogel-functionalized immunosensing platforms classified on the basis of their signal transduction for the detection of disparate cancer biomarkers (tumor necrosis factor, α-fetoprotein, prostate-specific antigen, carbohydrate antigen 24-2, carcinoembryonic antigen, neuron-specific enolase, and cytokeratin antigen 21-1), hormones (cortisol, cortisone, and human chorionic gonadotropin), human IgG, and ractopamine in animal feeds.

Figure 1

Schematic representation of different signal transduction techniques in a hydrogel-based immunosensor.

Figure 2

Diagrammatic representation of the surface plasmon resonance immunoassay. Reprinted with permission from ref (13). Copyright 2006 Elsevier.

Figure 3

Diagrammatic representation of an immunosensor in the sandwich form to detect IgG. Reproduced with permission from ref (7). Copyright 2013, Elsevier.

Figure 4

Electrochemical immunosensor fabrication is represented diagrammatically. Reproduced with permission from ref (20). Copyright 2017, Springer-Verlag Wien.

Figure 5

(a) Electron-transfer mechanism between g-C3N4 and AuNPs. (b) Catalysis of 4-nitrophenol by Au@g-C3N4/MCC leading to color fading. (c) Antibody/antigen interaction with Au@g-C3N4/MCC. (d) Partial color fading after Au@g-C3N4/MCC was incubated with the antigen. (e) Structure and color of 4-nitrophenol (yellow) and 4-AP (colorless). (f) Graph of the natural logarithmic value of 4-nitrophenol absorption [ln(Abs)] at 400 nm over time catalyzed by hydrogels with different MCC and AU compositions. (g) UV–vis absorption spectra of 4-nitrophenol reduced by NaBH₄ for the Au@g-C3N4/MCC hydrogel. Reproduced with permission from ref (22). Copyright 2019 American Chemical Society.

Figure 6

Diagrammatic depiction of the fabrication and working of the electrochemiluminescent immunosensor. Reproduced with permission from ref (24). Copyright 2017, Elsevier.